Darth Lefty 

My nerd eye has turned upon suspension forks lately, mostly with a focus on mountain bikes. What I've learned does not square with the Bike Forums conventional wisdom, which seems to have been inherited frozen in amber from Usenet in the mid-90's and has a contrarian bent. Only some of it squares with experience, design, or features of actual forks for sale on bikes right now, so I thought I'd lay out some thoughts on the topic. I've got an outline in mind. The next post will be about the benefits and disadvantages of a suspension fork, in general. The second will run through some details of what a fork does. The third will be about inexpensive Suntour forks (XCT, NCX, and so on). The fourth will be about the less-expensive Rockshox forks (35, Recon, Judy, et al). Then I'll circle back for discussion. They're not all coming in a sudden heap, so stay tuned. At least it will give us something to do in the commuting forum while we wait out the crisis.

Darth Lefty 

Suspension forks absorb impacts to the front wheel, instead of sending them through the handlebars into your body.

Do you need this? There are pros and cons. On the pro side, this improves stability and control of the bike, and as a benefit of that, improves comfort. In the process some forward motion is lost and turned into heat, but ideally the energy lost is balanced by the improved performance of the rider who is not absorbing these impacts with his body. GCN, for a stunt back in 2017, did the Carrefour de l'Arbre on a road bike, a cyclocross bike, and a cross-country MTB, all high zoot racing bikes with power meters, and the mountain bike had the best time with the least power. But they point out at the end, there's only 50 km of cobbles out of the 250 km of Paris-Roubaix. If you are talking about e-bikes, they are faster and heavy enough that suspension is usually a given. What I observe in this forum in practice, is that people who have long commutes every day eventually settle on some flavor of road bike, while short-haulers like myself use a much wider variety of bikes, that are more likely to have suspension forks.

You may wish to have a suspension fork on your bike because it is in dual service as your commuter bike and your mountain bike. Suspension forks very often have a lockout, or you can crank down the low speed compression damping, and the bike behaves much as if it would with a rigid fork. This may not be all that important. I leave my own suspension fork unlocked and find it does not move much at cruise, seated level pedaling. Since it doesn't bother me, I leave it open. Otherwise I tend to forget to open it back up for the trail.

As for weight, yes it adds weight. It might not be as much as you think. As with all bike stuff it's definitely a price for lightness. The heaviest suspension forks weigh nearly six pounds but the most premium are less than three, and a rigid chromoly fork of the same size still weighs nearly three pounds.

Enve carbon road fork 370 grams
Salsa Waxwing fork (carbon gravel bike) 520 g
Surly Cross Check fork 1050 g
Salsa firestarter fork (heavy duty chromoly) 1200 g
RS SID SL (premium XC fork): 1326 g
RS Reba (nice XC fork): 1586-1662
RS Judy Gold (inexpensive but ok): 2009 g
RS Judy TK (steel stanchions, coil spring) 2545 g
Suntour NEX (coil spring, hydraulic lockout): 2550 g

There's a case to be made for bigger tires. They do improve the ride comfort. Still, this acts like an air mattress compared to a real mattress. There's damping but it's not enough. There seems to be a reasonable limit of about 2 inches for balloon tires, which gives maybe another half an inch of deflection vs a regular commuter tire, while a suspension fork can make a lot more. There are a few fat tires built like roadie tires that can be run very soft. Although Rene Herse tires performed poorly at the Bicycle Rolling Resistance site, adherents argue that they result in an overall more efficient ride - much like the argument for the fork, you may notice.

Someone might chime in to say a suspension fork is bad because it has elastomers that might be worn out. This was something tried out in the 1990's. The spring and damping were both provided by dense foam rubber - multicellular urethane, or MCU. By the early 2000's they were all gone from the market, and rightly so. Not only did they wear out quickly, they also tended to turn to goo in the presence of any lubricants. You are only likely to find one of these on a 1990's mountain bike and if you do, feel free to run the other way. Forks made today have rubber bump stops, but not anything like this.

Suspension forks use oil and grease and seals, and so they do ask for occasional maintenance. At the level we are discussing, they are not complicated, using mostly mechanic tools. Rebuild kits and spare parts are available, and instructions for the service can be found in PDF or video form.

mtbikerinpa

I will very much attest to using what was a mountain/rando style bike initially for a basis of a commuter. Evolving parts spec to tune in relevance has yeilded a very satisfactory result for multi-surface commuting. I use a 20" 1994 Giant Sedona cromoly frame with discs added(custom tab). Hollowtech crank with 48T biopace(yes) double rings. Rear cassette 11-40 9spd. XTR mountain derailleurs and rapidfire rear control. Barcon front control. That was due to the odd trimming tendencies of the biopace rings. The fork is a 2004 Rock shox sid with platform and lockout. The nice thing of the Sid fork is when it is locked it can still 'blow' if you hit a large pothole. Open it up if you get to a construction zone or gravel road/path. Recent enhancement was to add Sun-Ringle Helix 27.5" rims and Clement MSO 42mm tires. The total package and fit is such that it all clicks in and just feels like a resounding yes.
Part of starting with that base chassis is that I have the full XTR level XC 26 x 2.3" wheel mtb that I do races with and it fits like a glove. Drop barring the commuter version was a logical extension of it, particularly since my commute involves a gravel stretch, potholes and other such wilderness liabilites. I commute on either one and the XC version is not bad in itself but the peak speed is definitely improved on the drop bar version. In the steep climb territory its a bit grayer since the XC is 3 ring mtb gearing. Ive had both on 50 mile runs, but 35 is more the typical due to time.
The beauty of the Rock Shox forks like Judy or Sid is they are truly quality pieces for what you get, but nowdays are very affordable. I have gotten a Sid at a swap meet for $80 because it needed a oil change. Long way from 800 new, lol.

base2 

Not necessarily a commuter because I'm now retired, but we did do nearly 40 gravel miles in the forest yesterday & 13 miles of flow-y single track cross country with a few 2-3 foot drop offs, a couple or 3-4 foot drops (with suitable transitions) & bunches miscellaneous tiny jumps, earlier in the week.



I found that my "gravel bike" with Gravelking 700x38's just wasn't up to the gravel riding I was doing. A broken fork & disintigrating tire casings seemed to indicate as much. So, I sought out to outfit a more capable bike. I have not had luck with Panaracers of any variety, so make of that what you will.

I usually run the RockShox Recon with the lockout open & accounted for the suspension sag when setting the bar height. I do hit the lockout if I intend to stand on the pedals at all as the bike does tend to absorb a lot of effort when standing.

To get a similar fit to my road bikes, I started with a zero-offset seatpost, found road handlebars whose width was the same as the OEM straightbar grips measured center-to-center, 42cm. After that is was a matter of finding a stem that was the right combination of rise/run to put the hoods in the right place when actively riding & buying Gevenalle shifters with short pull for canti/road brakes & Dynasys/mountain 11 speed shifting. Around $250 for the drop bar conversion all told...mostly on shifters.

I don't do centuries on it but that is more on account of the supremely knobby 559x 52 tire choice & the riding (or absence thereof) I have been doing lately than anything else. I don't see any reason why not, though. The fit is comparable to my century bikes & it's only been configured as such for the last few months. I weigh 190 pounds & usually set the fork air pressure at 130psi for road/gravel use. On Gravel I find I use around 80mm of suspension travel & when mountain biking I bottom out regularly.

You may take notice of the Schlumpf Speed-drive. Mated to the 11-46 cassette the combination yields 700% range.

In the picture is also an Adventure Hydration 1 gallon/4 liter water tank. It performs exactly as you would expect.

I think the biggest drawback about using a suspension fork on a commuter would be the maintenance requirement to replace worn seals just from the shear number of accumulated hours & the constant friction wear in a very narrow range on the stanchions. Any full-on suspension fork in commuter duty would not be a lifetime purchase. In this regard, I think Lauf might be on the right track. High frequency damping, short travel, no real moving parts subject to wear by friction, little to no & or very simple maintenance.

The capabilities of an honest to goodness mountain biking suspension fork in commuter duty are probably so much more than is necessary, it would only add trouble & complication where none is necessary.

Darth Lefty 

Mountain bike suspension forks come in a lot of sizes and brands but they have some fairly universal characteristics. They have a one-piece lower fork leg assembly forged in alloy, with sliders for the an upper assembly. The uppers have stanchions (tubes) that slide into the lowers, and a crown that attaches the stanchions to the steerer tube. The springs and dampers are both located inside the upper tubes and are operated by a piston shaft from the end of the lowers. The external seals you see between the lowers and the stanchions are dust wipers and sometimes oil seals, but hold no pressure.

There's a lot of press, yearly updates, and aftermarket modifications for premium forks like the Rockshox Yari and Pike and Sid. But those are premium mountain bike racing products. Stuff in our price range is simpler and the marketers don't pretend it's better every year. Still it's nice to know how it works.

The least expensive forks, usually from SR Suntour, have steel stanchions, and steerer, and a coil spring. They may have a cartridge that provides lockout or damping, but then again they might not. (There is a rubber part called a damper in their diagrams, but it seems to be a silencer to keep the spring from rattling.) There are a few smaller brands seldom seen in this price range like RST and Zoom. Upgrades from here are mostly about weight (air spring, aluminum parts), and adding damping with adjustments. In top end commuter bikes or midgrade mountain bikes, most likely a buyer will find Rock Shox, and there are some better Suntour forks that show up too.



Coil springs perform really well. Specifically, for this application, they do not pressurize any seals, so they have almost no running friction. But they are a big piece of steel, so for weight savings most nicer forks use air springs. Air springs usually have at least two chambers, positive and negative, on either side of the piston. In this price range they have a mechanism to equalize the negative chamber to the positive at top-out, so they can be pumped from the positive side alone. Air forks are tuned with pressure to suit the rider's weight and preference, just like tires, which is a benefit over coils, which need to be swapped if they are incorrect strength.



Damping, if present, is achieved by running oil through small orifices. Compression damping (when the fork moves up on impact) and rebound damping (when the fork springs back out) are usually done with separate "circuits" where the oil is metered for the desired force in one direction and WFO in the other. It seems intuitive that both would be on the piston, but in Rockshox and most other forks they are separated. The rebound circuit is on the piston, freely moving up and metered going down. The compression circuit is in the top end of the stanchion and meters the oil displaced up by the incoming piston shaft. Most forks with damping come with rebound adjustment at a minimum. Rebound is the most important adjustment, because it needs to be matched to the spring rate and that keeps the chassis under control. However, because it's the second thing that happens, it has less influence on the feel of the fork, which is why there is a lot more attention paid to engineering and marketing the compression damping.

If the fork has a lockout function, it usually closes the compression damper down or off. (The Suntour HLO damper cartridge also blocks an oil path but does not provide any useful damping.) The lockout function may have a cable operated remote on the handlebar.

Air forks, and rear shocks too, are pressurized with a shock pump. This has a Schrader valve with a screw-on chuck that seals before it pushes the valve, to prevent leakage, so the pressure is correct. It has a small piston to achieve high pressure with precision. It could potentially be used on a tube but it would take a lot of pumping.

Darth Lefty 

SR Suntour is the corporate successor to a couple of Japanese companies that were popular during the 1970's bike boom. Now they make a lot of piston-cylinder parts, not just forks but also shocks and a suspension seat post. Their inexpensive forks are endemic to sub-$1000 mountain and commuter bikes. Suntour makes a complete range of forks and their expensive ones are just as nice and as anything by the big two manufacturers, but the ones on commuter bikes are... okay.

Models like the XCT are not much beloved. The biggest dig on them is that most of them, as sold, provide no damping. This is a recipe much like a wish sandwich. The other is that they are heavy. In their defense they are inexpensive (most under $200, some under $100, the Suntour US website will feed you a 20% off coupon), sturdy, reliable (there's little to break and nothing to leak), can sometimes be upgraded to have damping or at least a lockout, and if you are not convinced by any of that, they use standard interfaces so they are easily replaced. These inexpensive forks generally have steel stanchions and steerer and a steel coil spring, explaining their weight, which is five to six pounds.

For lockout and damping, they use cartridges that are simple to install and swap with mechanic tools, like the one shown in the right leg in the last post's diagram. If the fork has a lockout feature the cartridge may also provide damping. If it does not have a damper you can sometimes add one, depending on the model. The coil spring can be replaced with one that is stiffer or softer.

The problem here is that in the Suntour food chain, we are usually getting the plankton, at the low/right end of the following chart. Forks like the NEX and XCT have a pretty low ceiling for upgrades. Mostly they are coming with no cartridge at all, or the HLO cartridge which only provides lockout. They have no compression damping. If they have rebound damping it's not adjustable, which suits the single rate coil spring that you could, but are probably not going to change out.



There is a notable option not shown here. Specialized has a proprietary damping cartridge for Suntour forks called MCD, and Suntour US will sell it to you. It will go in the XCT, NEX, and a few others.

Another matter of note: Suntour will sell you a replacement fork at a discount. They used to describe this as a "trade in" but they just sell you the better one. They will help you make sure your upgrade still fits your bike. At the moment they only show mountain, not hybrid forks.

So why don't we see many of the better forks in the US market? I am really not sure. There are a few. The current Trek Dual Sport 4 has an NRX RL. At the price point where the OEM's add rebound adjustment, they typically switch over to Rock Shox on mountain bikes, and the hybrids with suspension don't go that expensive.

gsa103

My one comment on suspension forks is that coil forks are not particularly useful, and probably not worth the added weight. Air forks are excellent, and I could definitely see wanting one, but the cost is significantly higher.
The biggest problem with coil forks, is that the spring stiffness is set at the factory, and it's usually a stiff spring, so that larger riders don't blow through the travel. When I had a mountain bike with a coil fork, it was effectively locked out, because I didn't weigh (160 lbs) enough to move it. A typical mountain bike ride would use at most 20mm of travel.
Once I switched to a bike with an air fork, it was a night and day difference, the ride was much smoother because I set the spring rate to match my weight. The drawback is that the air fork alone cost twice what the entire previous bike did.
Suntour does make some lower end decent forks like the XCR32-Air that would be good on a commuter bike if you have a rough section of road. It's $200 to upgrade to something like a Raidon through Suntour.

Darth Lefty 

Rockshox started in 1989 and was an instant hit, bringing scaled-down motorcycle forks to mountain bikes. In 2002 they had hit hard times and were eaten by SRAM, along with a few other legacy companies like Sachs and Avid. SRAM has kept Rockshox as its own line, unlike Avid, Huret, or Sachs, for instance, which were fully metabolized. Rockshox pretty much has two categories of forks. One line is the fully-serviceable, upgradeable line where all the premium stuff lives. These bottom out about $500 with the Reba and Revelation.

We are going to be talking about the cheaper stuff, from <$200 to $450, which currently includes...
28mm stanchions: Paragon Gold
30mm: 30 Silver, Judy, Judy Silver TK, Judy Gold RL
32mm: Recon RL, Silver TK, Silver RL, Gold RL
35mm: 35 Silver and 35 Gold

These forks appear mostly on mountain bikes, up to a pretty high spec (here's a $3200 Salsa that has a 2020 Sektor which for reasons unknown is same as a 2021 Recon Gold... but it deserves a Reba, same performance but the Reba could upgrade) and on a few nicer hybrids. Some of them are OEM-only, you can't buy them all at retail. These are different sizes, and provide a few different options for the travel, brake, and steerer. But for this discussion, they all work the same way. The 35 models are the newest in this family and present a heavy duty option for e-MTB's.

The naming conventions are not entirely consistent. But generally...

• The Gold versions all have aluminum stanchions, while the Silver and no-metal-name have steel.
• Some of the Silver or no-metal-name models have a coil or air option, while the Golds are air spring.
• The TK, no-metal, and Silver models have the Turn Key compression damper with no adjustment, just open and locked
• The RL and Gold versions have the Motion Control compression damper which gives a range of adjustment from open to locked.
• Rock Shox used to call all of the cheap air fork springs Solo Air, but lately they have started using the Debonair name too.
• Unlike the better forks, these have no part numbers in the catalog for the uppers and lowers. Chassis damage like a dent or a really bad scratch in the stanchions is therefore a new fork..

The air spring seems easy to understand but hides some fun complexity. The distinction between Solo Air and Debonair is not clear, because at first glance they did not change the upper piston design. They all use a valve in the piston that opens at top-out to equalize the positive and negative chambers. This allows the fork to reach zero force at top-out instead of slamming into a bump stop. But it seems like the Debonair versions have provisions for volume tokens, and have a seal in the bottom plate of the air spring rather than a floating piston. Either way, they all have one air valve. Travel spacers go in the negative chamber between the seals. In some of these forks you can add tokens - pieces of rubber that press onto the air valve and take up volume in the positive chamber, so the volume ramps up faster, acting like a higher spring rate in spite of starting at the same or lower pressure.

The rebound damper is in the right piston. It's a check valve. Going up, it's wide open and provides no resistance. Going down, the check valve closes and oil passes through the small holes. The rebound is adjustable on all of these forks, so far as I know. That's important given that adding pressure changes the spring rate, and the rebound must change to match.

The compression damper is an assembly threaded into the top of the right stanchion and it uses the oil displaced by the incoming piston shaft. Again, it's a check valve, directed through small holes going up and wide open running out. These forks all have Turnkey or Motion Control. The big difference between them is that Turnkey has two settings, open or locked, while MoCo has a range of low speed compression adjustment from open to locked. There were once fancier versions of these dampers, but in recent years they have been replaced in premium forks by the Charger cartridge damper, and simplified for these cheaper ones. There's a small volume of air above the compression damper to take up the volume of oil displaced.

Because of the variety of sizes needed for the different travel and stanchion diameters and thicknesses, the internal plastic parts are not usually interchangeable between forks, even though they are doing pretty much the same thing in all of them.

There are a few major things that separate these from the more expensive Rock Shox forks and other brands - but that also likely don't matter for commuting. Probably the biggest is that better forks have dampers that use a stack of spring steel shims that deflect under oil pressure, so that the force vs shaft speed can be designed and adjusted with more control. More expensive forks also commonly provide more knobs to turn, especially high speed compression. The air spring in the nicer Rock Shox forks uses a dimple in the stanchion where the piston tops out to equalize. This is better because it makes a consistent negative volume shared by every fork. It's also simpler and probably cheaper to make, but it's definitely lighter, so $$$. Travel change requires a different air shaft instead of spacers. Some other fork brands use three air chambers, allowing tuning of every point in the spring curve. Rock Shox does not, but there are aftermarket parts that do it. And of course the more expensive forks have all the usual bike part tricks applied to add lightness - stronger alloys, butted tubes, in a few places carbon fiber. Finally, there are very long travel options, and some really heavy-duty forks for downhill, like the Rockshox Boxxer and Fox 40.

Germany_chris

Suspension is only as good as it's tune..

My Jeep has $1000 in shocks and $800 worth of tuning, When I was a "real" mountain biker I sent my fork and rear shock to get tuned to my weight, rear suspension geometry, and riding style. In the end I'm not looking to maximize every watt heading to work and back, I just want to clear my head and de-stress a bit.

Darth Lefty 

Honorable mention goes to the Specialized Future Shock, a suspension steerer. This cropped up first in 2018 Roubaix models and has since appeared on the Diverge gravel bike, Sirrus hybrid, and Turbo Vado SL and Turbo Creo e-bikes, all models that have a pretty high odds of getting used for commuting. I can't tell if it will last in the market but it seems pretty successful right now. Their launch marketing had a lot of head scratching assertions why they did it this way, while it seems pretty obvious - they wanted it to be small. But the thing surely works. Funny enough, the first generation didn't have damping and came with a few sentences of ad copy how it didn't need it... and the second generation got damping. It's only on Specialized, only a few years old, and I don't know where it will go from here. It could proliferate or die. But for today, it's an option. It only has 20mm of travel in its current form, but that's about doubling what you get from the tires on those bikes. Tuning is very limited. Past suspension products have always gotten longer but the stack limits the size. It's sort of reminiscent of the Cannondale HeadShok, though that was on the fork side and not the stem side. Like that, it's in the steerer and it's proprietary.




There is also a suspension stem available right now, Redshift Shock Stop, using... elastomers! Remember those from the first post? It has a single hinge instead of a parallel linkage like the old Girvin Flex Stem, so the bar rotates away from you when it moves.

Darth Lefty 

So what kind of bike takes a suspension fork? The answer is, they usually come with it. That seems glib but it's true. In the mass market there are several kinds of bikes aimed at commuting, and the ones sold as "rugged" or the ones sold as "comfortable" often do. So do a lot of e-bikes.

Rugged: here is a Trek Dual Sport 4 with a nicer than usual Suntour fork. The sales pitch is pretty much the same as it is for an SUV.



Comfortable: here is a Raleigh Venture. Note also the spring seat and sprng seat post. No damping in any of them! A bike like this can be very comfortable for occasional short jaunts, and its natural habitat is on the back of an RV. In daily commuting use it might come up short in a lot of ways.



It's probably not a good idea to put a suspension fork on a bike not designed for it. They have more stack for the added height under the headset. Mountain bikes also have reinforcements for the head tube, though I couldn't say about that Raleigh. When a bike is designed to have a suspension fork it is referred to as "suspension corrected" and a rigid fork for that bike will be extra long. A good example of this is the Surly Karate Monkey, especially if compared to a Bridge Club, which is not. You can see that the KM fork is extra long to provide tire clearance and its head tube is extra short to keep the stack under control. There are other differences here too - the BC has a narrower head tube that will only allow a 1-1/8 steerer while the KM has a wider head tube for a 1-1/2 tapered steerer. The BC will get you a little more room in a frame triangle bag. Surly began a few years ago differentiating their bikes into "trail" with suspension correction and big head tubes, and "touring" which are not.



Generally drop bar bikes are not rated for suspension forks, but that is not to say you can't have a drop bar. As in the example above from @mtbikerinpa, you can find a way to put drop bars on a mountain bike. There are also bikes designed specifically to have both, Probably the best known of that type is the Salsa Fargo, which held the category for a while, and has lately been joined by the Cutthroat, a carbon fiber adventure racing version. These are both able to take 29er forks with 100mm travel.

There are also a few forks specifically designed for road gravel bikes. The Lauf Grit and Fox AX forks might void your warranty but they are not going to upset your bike too much. The AX is a short travel variant of the most premium Fox 32 XC racing fork. An older 26er or 27.5 XC racing fork with the travel reduced might also be a good bet. The Grit is an odd design with carbon fiber leaf springs.

squirtdad

I think you may be missing a big point here for many. there is a huge difference between quality shocks and cheap ones.

IMHO if you are talking about a 300 to 500 dollar bike (or anything from big box stores) suspension should be avoided.

Darth Lefty 

So should all the other parts, probably.

I definitely want to convey that Suntour forks, especially, are not a dire mess. Yes they are heavy and yes they lack features. But they are sturdy, require essentially no maintenance, and there are ways to make them work better that are not expensive, not hard to buy, and easy to install. Damping cartridges are fifty bucks and different strength springs are twenty, and you install them with sockets and allen wrenches that you probably have already.

Darth Lefty 

This is fun. I just took the Judy Silver (inexpensive trail fork, air spring and chrome steel stanchions) off my hard tail and replaced it with a clapped-out DVO Diamond (premium heavy duty trail / enduro fork with cartridge damper and a air positive / coil negative spring).

The Judy tops out my little kitchen scale at 2300 grams. The Diamond rings up 2218. It might be a little unfair; the Diamond's steerer is about half an inch shorter

The swap required 2, 4, 5, and 6mm Allen wrenches. 2 for the brake hose guide, 4 for the stem pinch bolts, 5 for the top cap and caliper, 6 for the axle. That's it. Oh, and a screwdriver for the crown race.

Darth Lefty 

Let's talk a bit about maintenance.

Suspension forks have oil and grease and o-rings, so they do benefit from maintenance. If they go too long without it, they will break down the lubricants and lose some performance. There are recommended service intervals that will keep you well under that threshold. I suppose some people follow them. Eventually they will wear out their seals and lose grease and start to scratch themselves up. Definitely don't let them go that long, and if it's been sitting a few years, don't start it up without doing some work first.

Suntour forks of the type we are dealing with here don't have an oil bath, except in the sealed cartridge. All you really need to do is clean the old grease out and smear new grease in. If the wipers (part 2c in the post #6 diagram) are frayed, you can swap them. If the slider bushings (2b) wear out and the fork gets play, you can replace those too. Both of those come in the rebuild kit, which also has grease, replacement locknuts, and the little plastic wrench for the top caps. If you have a cartridge damper that leaks, you replace the cartridge. All the parts are available direct from Suntour US. I can't find a service guide like Rockshox provides, but they have a bunch of videos and each model has an exploded view. If you're just cleaning it out they sell the little wrench for three bucks, but I found a 12 point socket in my tools that fit close enough.

Forks like Rockshox with air springs and oil dampers rely on their air and oil seals so they benefit more from maintenance and stop working correctly if they leak. Maintenance is easy. No, really! You do need to take it off the bike, but that's only undoing some small bolts, as one post earlier. It's easier than a few other normal bike operations that require knuckle busting torques (like crank pullers or cassettes). The rebuild kit is just a bag full of o-rings, and the wipers. The rebuild is taking it apart, cleaning it, replacing the o-rings, and putting it back together with fresh oil and grease. It might seem intimidating at first because when you look at the service manual for the Judy (for instance) you will see that it runs to 89 pages. However a second glance will show they have made a manual for twelve different fork model combinations, given you plenty of pictures for each step, and added a lot of lawyerly gloves-and-goggles stuff. You do need a few tools and goops to do it yourself. The Judy needs grease and two weights of oil, one for the lower leg bath and one for the damper bath. Mostly it uses mechanic tools, but there might be a few you don't have. You definitely need snap ring pliers. In some cases you can make do with a compromise. No manual will ever tell you to use a crescent wrench but you probably have one, and you probably do not have a 24mm socket (unless you are already the kind of person who does everything yourself on your car). Same goes for the torque wrench. It's important to get the oil level right. The lowers need hardly any, barely more than a teaspoon. The manual shows a syringe to measure it. The damper oil is around four ounces but must be measured out precisely since too little will have the compression damper sucking air and too much will cause hydrolock. The manual shows a graduated cylinder but a big baster syringe could work too.

Gresp15C

Something that's occurred to me is that pavement is the new gravel in regions where the powers-that-be have decided to let the roads deteriorate. Such as, Wisconsin. Maybe this is why gravel bikes are suddenly so popular.

There are some counties in northern Wisconsin where the roads are worn out, and there is no funding to re-pave them, so the only cost effective option is to grind up the pavement and turn it into a gravel road. Elsewhere, the paved portion of the road is getting narrower as pieces chip off the edges. Man, I don't like riding on those roads.

A decade ago, had you suggested suspension for pavement commuting, I would have looked at you funny. Today, hmmm... Fortunately my county is still capable of maintaining its roads, but who knows how long that will last.

Darth Lefty 

One of the fondly repeated digs on suspension forks is that they are lossy.

The mountain bike industry and the internet community have done a ton of work in the last twenty years on the losses incurred by rear suspension. It all concentrates on isolating and preventing the input to the rear end caused by pedaling, and it's been really successful. However, I went looking for something about front suspension, and found little about measured power losses from suspension, either from rear or from forks. Most of the work done on forks is instead about how the longest travel forks feel when they handle the worst obstacles.

Here's a pretty old literature review (2004) on the topic. Most of the studies quoted in it are from the 90's and predate or don't use power meters. However in general all the studies come down in favor. The couple-percent losses seen are worth the benefit.

What I did turn up was everyone's favorite Jan Heine and his tire tests. While not going into the tire stuff for the sake of this thread, I wanted to note that he also tested:

• a Rockshox Ruby SL fork from the 90's, already old even at the time, that had elastomers (here's an article about it)
• a springy light steel fork (Reynolds 531 SL blades) from his custom Alex Singer
• a heavy duty stiff steel fork (from a "Trek hybrid" most likely a 7 series Multi Track

The Trek fork took by far the most power. It was somewhat improved by excessive padding on the handlebars. The springy forks were way better and nearly equivalent, whether the spring was in a tube or not. The same trends were found both on the rumble strips and the fresh pavement. He shows they saved thirty-ish watts on the level, 203-213 vs. 242. That's about 15%! This is probably fully metabolized by the roadies, they are all riding around on carbon forks well known for having suspension properties. What it really shows is that a very rigid fork... sucks.

Heine is fond of saying that steel drum tests of his tires don't measure everything. It would not seem impossible to put the fork, and some kind of spring to be the human, into one of those steel drum tests and see what happens.

He wrote,
But in fact the Rockshox actually shows only about half a percent difference at high power on the rough rumble strips and 10W less power lost on level ground. Gotta wonder what he'd find with a coil or air spring and oil damped fork.

The tests were in BQ in 2009 and reblogged in 2012 and 2018:
https://www.renehersecycles.com/suspension-losses/
https://www.renehersecycles.com/myth...des-dont-flex/ (this one has the power numbers)

Darth Lefty 

The above gave me a little pause. One of the familiar digs on disc brakes as applied to road bikes is that they require a stiffer fork due to the torque incurred. (But flexible forks are compliant and springy, don't call it suspension or the C&V will evict you!). Gravel bikes, the most popular cultivar of new road bikes for sale right now, have disc brakes, and they have a lot of cargo capacity on the fork, so it's a doozy. They also have fat tires, for handling the dirt roads they might one day travel. But with that fork, do they need those fat tires to be a good ride at all? Shoppers often say they will (but may not actually) buy another wheel set with skinny roadie tires. Is that really a good idea?

Notso_fastLane

My recumbent road bike has front and rear suspension. After riding a similar bike without suspension a couple times, I don't know if I would want one without. On a bent, I can't stand to avoid the bad bumps. I don't think the suspension adds more than a 1.5 lbs, and that's mostly the shock in the rear.

Also, being able to put air in or take a little air out when I know I'll be going on a specific route is a nice feature of the air shocks specifically.

My velo has spring shocks on the front wheels (not easily adjustable) and an air shock on the rear.

Darth Lefty 

Notso_fastLane I had the same experience with my heart-surgery-recovery tadpole last year. It was helped tremendously by a fatter rear tire and I can easily see why there are a lot of them with suspension. I do remember wondering if trike makers have the rear suspension kinematics as well figured out as the mountain bike makers do. There are some simplifying factors, like the single chain line created by the chain tube or idler and not influenced by the front shift, which gives a result kind of like the 1x improvement in mountain bikes (no weird anti squat changes and wider pivot bearings). But I sold out when I was able to ride normally again and didn't follow up.

rhm

Reading this thread with interest. Count me as a hater, if you will forgive me. I have had suspension forks on several bikes, and it just never seemed worth the compromises. Still, the subject interests me....

Oh, I think plenty of C&V people are well aware of the fork as a suspension device, especially the Bates "diadrant" forks of the 30's-40's. In pre- and post-war era GB the best fork blades were Accles & Pollock "kromo" chrome-moly tubing. I have a bike with that fork, and it is the lightest steel fork I've weighed. When riding, you can see it deflecting at bumps. Almost alarming! But it works, and at 70-80 years it's not showing signs of aging.

The problem with putting a disc brake on a springy fork is that the brake is on one side of the hub. So when the brake activates, it torques the left fork blade, but not the right. This effectively twists the whole fork, making steering erratic. In normal braking that's no big deal, but in an emergency, when you hit the brake hard and things are happening fast and you can't pay attention to everything all at once, that's not a good time for the bike to veer suddenly to the left. To counteract this the builder has to make the whole fork beefy, eliminating all of its springiness.

Rim brakes vs disc brakes is a separate but not quite separate subject. On older bikes the fork is straight down to a certain point, at which it bends forward. This makes the fork springy. Nowadays forks are straight, offset at an angle from the head tube. There is no vertical flex at all. That's fine for disc brakes, but it completely negates the benefits of rim brakes.

Oh, sorry, I shoulda mentioned, I'm not just a suspension fork hater, I'm also pretty much anti-disc brake. Or I was, until I got a bike with disc brakes. I've toned down my anti-disc rhetoric lately. My disc brake bike, with 48 mm tires, is just about equal in comfort to my bike with a light springy fork and 53 mm tires. With tires that fat, the springiness of the fork is buried in the mix.

No doubt there are places where real suspension is needed, but I never ride there. I ride the roughest roads imaginable, but they are always roads. Fat tires are an absolute necessity. But suspension? Sorry, I'm not there yet.

grolby

I think Heine dislikes the drum tests because his tires consistently fail to impress in those comparisons. He’s not wrong about them being incomplete, but his preferred testing methods have their own problems with precision, replicability and independence. Rolling resistance and power loss measurement is pretty complicated! Similarly, I think he’s unlikely to test with a modern suspension fork for fear of getting results he wouldn’t like. I don’t think he’s dishonest, in that I don’t believe he’s deliberately lying, but that all his experiments consistently confirm that his particular aesthetic preferences also have the best performance should engender a bit more skepticism.

Anyway, I do a fair bit of mountain biking, including riding on the roads between my house and the trail. I do usually lock the fork out on the road, but it really only matters when you get out of the saddle to sprint through a light or jam up a hill. You feel in those situations that a lot of the power you’re putting into the system with your upper body is just being used to move the front end up and down, and that’s probably true. But otherwise, riding around seated, I would be surprised if the front suspension had any losses worth measuring, except for getting the increased mass up to speed from a stop. Those with a spirited riding style would find a suspension fork frustrating on the road. I know I would. If your style is to just cruise, front suspension losses are probably much lower. Keeping in mind that my mountain bike has a modern oil-damped air spring fork.

This is one of those topics where I think theory runs up against reality, most of the time. In theory, yes, a rim brake fork can be more springy and comfortable. In practice, most people are already riding on very stiff forks that don’t contribute much comfort to the riding experience, for a couple reasons. For one, lots of people are riding relatively low-cost frames built to hit a price point and satisfy safety requirements while keeping QA costs down. And so those forks will be stiff and overbuilt. Surly can claim in their ad copy that their steel forks are springy and comfortable until the cows come home, but that doesn’t make it true (and I assure you: it isn’t true). On the other hand, you have people on high-end, speedy performance-oriented bikes. And the trend in high-end, speedy performance-oriented bikes for the last decade and half has been a heavy emphasis on front-end stiffness, to enhance handling precision, and reduce the chances of speed wobble and brake chatter - even rim brakes are a lot more powerful these days than they were 25 years ago. This is especially true for bikes that used to come with cantilever brakes, i.e. cyclocross bikes and touring bikes. The price of a soft and comfortable fork on your cantilever cyclocross bike is much greater tendency toward brake squeal and chatter. So a lot of people would be giving up a lot less comfort than they think, because they’re riding on very stiff forks already.

Darth Lefty 

rhm

Good to have you along! Thank you for humoring me.

There are a couple of things I see enabled by the suspension forks.

The most important is that they nearly always have a travel of at least two inches for the city/trekking/hybrid versions, and usually 4-5 for a trail hardtail mountain bike. That's on top of what you get from the tire. The second is that they can have damping, and it can be designed for the purpose, not relying on your jiggling corpus or whatever you get from the tires.

The brake stuff is interrelated, obvs. But I think it's an effect and not a cause. You could not have fork blades that flexed two inches and still use a rim brake. I think that's the main reason the MTB side ditched cantis so hard in the mid 90s for V brakes, even before discs got popular. The cable goes right to the caliper and the caliper is on the element that stays with the wheel and no extra stop is needed on the frame in the way of the suspension movement.

Darth Lefty 

I've left alone the topic of rear suspension in this thread, even though I think it has merit enough for discussion, mostly because that's not what's marketed to commuters. The other styles (hybrid, fitness, comfort, gravel, hardtail) are all cross-marketed for commuting, but four-bar full suspension bikes for Mountain Biking are not. Their prices start in the $2000's, they limit cargo options to a backpack, and nearly all of them have 4in travel or more.

Flexy frames for road and gravel bikes are now very popular at the high end. I'm not sure whether to include that here. Roadies certainly commute on their carbon bikes but I still tend to think of them as just road bikes - exercise and racing machines.

noglider 

Now high end bikes have squooshy things in the stem. It may make more sense than an oil filled cylinder.