Hard tail vs. rear suspension - how important?

[JefferyB]

I'm looking at the Challenge Seiran, a HiRacer with USS for riding around town and daytrips.

This bike has 26/26 wheels. Anyone have experience with or without rear suspension in a similar bent?

Thanks!
-Jeff

[keith-pam]

Rear suspensionon on a bike wastes energy. It also adds unnecsasary complications with incresed unreliability. Did you pump it up today and how long before the seals start to leak in the ultra high pressure shock.Necessay flex can best be obtained through the frame or if you want comfort put on fat tires and a cushioned seat. Rans stoped makeing it's shocked bikes several years ago for good reason.

[Mars]

Rear suspensionon on a bike wastes energy. It also adds unnecsasary complications with incresed unreliability. Did you pump it up today and how long before the seals start to leak in the ultra high pressure shock.Necessay flex can best be obtained through the frame or if you want comfort put on fat tires and a cushioned seat. Rans stoped makeing it's shocked bikes several years ago for good reason.

I'm not so sure about that. Suspension has been around long enough on bikes that it is pretty proven technology. If you ride nice, smooth roads all the time, I guess that you don't need it. However, the flex provided by a well designed system is not just about comfort. the suspension makes your bike more stable when you hit harsh bumps at speed. On my roadie, I would nearly lose control if I wasn't focusing on the road in front of me and hit a pothole. On my HP Velotechnik SpeedMachine, which has front and rear suspension, the bike is much more stable in poor road conditions.

[zoridog]

My bent has 1.5" tires that go to 100 lbs pressure. I find that if I lower the pressure a little I get a nice cushy ride. I do the same with my mountain bike. It takes trial and error to get it just right. The only time I max tire pressure is with the road bike because I am the suspension.

I've never owned a bike with suspension so take this for what it's worth.

[World Tour]

I notice on my daughter's dual-susp. MTB that a lot of added motion comes from my pedaling, so I agree that susp. wastes your energy. Unless you're climbing a mountain on your "mountain" bike who needs susp.?

[jeff-o]

How is the road where you plan to ride? Is it well maintained, or are there lots of bumps? Rear suspension will definitely help smooth out your ride; how much work it has to do depends on the road. ;)

The rear suspension on a recumbent won't rob your energy like it does on a mountain bike. On a traditional-style bike, you push down on the pedals, which causes the entire rear suspension to flex. However, on a recumbent, you are pedalling forwards rather than downwards, so you don't lose energy to the suspension.

[BlazingPedals]

If I rode cobblestone I'd definitely want suspension, but for my roads I just don't need it. YMMV. As far as energy lost, I've ridden behind a SpeedMachine. It bobbed up and down like the owner was on a pogo stick. The owner liked the cushy ride but couldn't figure out why the bike was such a dog. Even on a recumbent, there IS a price to be paid for suspension.

[jeff-o]

If I rode cobblestone I'd definitely want suspension, but for my roads I just don't need it. YMMV. As far as energy lost, I've ridden behind a SpeedMachine. It bobbed up and down like the owner was on a pogo stick. The owner liked the cushy ride but couldn't figure out why the bike was such a dog. Even on a recumbent, there IS a price to be paid for suspension.

I suppose it depends then, on whether the BB is above or below seat level. A Speedmachine's BB is a few inches above the seat, and the shock assembly is nearly parallel with the road. It makes total sense that in this case, pushing on the pedals would push your back into the seat, thus compressing the rear suspension.

Looking at the Challenge Seiran, I would *suspect* that you will get some pogo effect going on, just like the Speedmachine. There will probably be less pogo on the Mistral, Wizard and Hurricane.

This bike, from ActionBent (http://www.actionbent.com/ASSEMBLY_MANUAL/ABRRSusUSS.htm), has the BB lower than the seat, so there probably be much less pogo effect than any of the above bikes.

[bentrox!]

The rear suspension on a recumbent won't rob your energy like it does on a mountain bike. On a traditional-style bike, you push down on the pedals, which causes the entire rear suspension to flex. However, on a recumbent, you are pedalling forwards rather than downwards, so you don't lose energy to the suspension.

Suspension design will have a lot to do with how much energy you may lose through your pedal stroke. On some steep or long climbs where I push hard into the rigid seat on my Lynx I've definitely felt some energy-robbing "pogoing" from the rear spring shock. Funny - I thought that pogoing is all but eliminated on the HP Speedmachine, a similar SWB design but with the shock oriented horizontally instead of vertically as it is on the Lynx. Maybe the shock needs adjustment? The near-horizontal shock orientation on my Specialized MTB, a 4-bar Horst-link design which the Speedmachine suspension resembles, mitigates most pogoing on my off-road rides.

In contrast, my Baron has no suspension but the long length of frame tempers the rides, which are not on rough road conditions in my case anyway.

Neither Lynx nor Baron have front suspension where the 20-inch wheels transmit the greatest shock. The larger 26-inch front wheel on a Seiran will blunt these impacts, especially with lower tire pressure.

[PuttPutt]

"Pogo-ing" is usually eliminated when the chainline dissects the control arm pivot axis (laden).

[bentrox!]

"Pogo-ing" is usually eliminated when the chainline dissects the control arm pivot axis (laden).

Huh?

[PuttPutt]

The photo below shows the ActionBent Road Runner rear suspension. Because the chain is in tension, and below the control arm pivot axis (shown in red) it tries to pull the axle end of the control arm DOWN (effectively elevating the rear of the bike at each pedal thrust). This downward force, is what initiates pogo-ing. IMHO, it's a poor design.
http://i20.photobucket.com/albums/b238/Keugene/RearSection01.jpg
The lower the gear, and/or the greater the distance between the (drive side)chain and the control arm pivot axis (shown in red) , the more intense the pogo-ing.

[Dr.Deltron]

"Pogo-ing" is usually eliminated when the chainline dissects the control arm pivot axis (laden).

PuttPutt,

Thank you for explaining in plain english why my Hurricane has no pogo-ing that I can recall. The drive side of the chain does go right across the pivot point, especially in the larger cogs.
I always appreciate knowing more about what I'm riding.

ZoomZoom,

Dr.D

[bentrox!]

And to think I always thought dissecting is what happens to frogs in biology lab class and that pogo simply meant an up-and-down movement, which a vertically-oriented shock will produce if the seat above it is pressing down on it in the rythmic motion of pedaling. Now I know I can blame it on chain tension instead.

[squeaker]

"Pogo-ing" is usually eliminated when the chainline dissects the control arm pivot axis (laden). Thanks PuttPutt, saved me the bother of explaining the chain line effect :)

There is, however, another excitation on DF bikes; that of the rider jumping up and down when pedalling. The current crop of 'platform' shocks (and forks) try to put a stop to this using various strategies - cheapskates (?) just sit and spin smoothly and keep decent suspension action. Not usually a problem on a bent though ;).

Finally, even with an ideal chain line, you can get pogoing at the front fork if you're pedalling style is not smooth due to rear wheel torque fluctuation trying to 'wheelie' the bike. A platform fork (expensive, and not available in 20" ?) would stop this, but again a smooth spinning style is your best (cheapest) option.

[jeff-o]

The photo below shows the ActionBent Road Runner rear suspension. Because the chain is in tension, and below the control arm pivot axis (shown in red) it tries to pull the axle end of the control arm DOWN (effectively elevating the rear of the bike at each pedal thrust). This downward force, is what initiates pogo-ing. IMHO, it's a poor design.
http://i20.photobucket.com/albums/b238/Keugene/RearSection01.jpg
The lower the gear, and/or the greater the distance between the (drive side)chain and the control arm pivot axis (shown in red) , the more intense the pogo-ing.

Ah, but even if the tensioned chain is trying to pull the swingarm down, the rear shock is still close to its maximum extension already. The pogo effect would be far worse if the tensioned chain were placed above the pivot axis, which would cause the shock to compress, rather than decompress.

[PuttPutt]

Ah, but even if the tensioned chain is trying to pull the swingarm down, the rear shock is still close to its maximum extension already.On the Road Runner, I dunno, maybe... but on a properly designed suspension, the "travel" should be at about half-mast... laden.


The pogo effect would be far worse if the tensioned chain were placed above the pivot axis, which would cause the shock to compress, rather than decompress.On some bikes, yes... on others, no. Do you know why?

[jeff-o]

It would seem that there is a lot going into the pogo effect:

- the height of the BB compared to the seat
- whether the tensioned half of the chain is above or below the suspension axis
- whether the rear shock is horizontally or vertically mounted
- where the suspension axis is, relative to the seat bottom

If you can visualize it, imagine the forces pushing on various part of the bike when you pedal. Imagine the chain pulling on the rear derailleur. Imagine the hips pushing into the seat. Imagine the shoulders pushing on the seat back. Imagine the arms, pulling on the handles. All of these factors will push, pull, or have no effect on the suspension. It all depends on the bike'd geometry.

[Mars]

As far as energy lost, I've ridden behind a SpeedMachine. It bobbed up and down like the owner was on a pogo stick. The owner liked the cushy ride but couldn't figure out why the bike was such a dog.

Really? That's an eye opener. I have observed the pogoing effect on mtb, but not on my SpeedMachine. Did the owner of the bike you are talking about feel the bike bobbing or did it only reveal itself through your observation?

[PuttPutt]

It would seem that there is a lot going into the pogo effect:Probably seems that way, but it's really quite simple. Of course, I'm refering to the torque induced pogo-ing (the most common type), caused by a poorly designed suspension system - as indicated by maligned chain line in the illustrated example.



- the height of the BB compared to the seat
- whether the tensioned half of the chain is above or below the suspension axis
- whether the rear shock is horizontally or vertically mounted
- where the suspension axis is, relative to the seat bottomIMO, the only one of your four examples that has any direct relevance to the torque induced pogo-ing on recumbents, is your second statement: "whether the tensioned half of the chain is above or below the suspension axis". (which was indicated in my first post)

[jeff-o]

Again, you must take into account not only the torque-induced pogoing, but also the effects of pushing on the pedals (and thus, pushing against the seat).

I also forgot to add:

- the pressure in the rear shock

Obviously, if the pressure is too low, the pogo effect will be worse.

[PuttPutt]

Again, you must take into account not only the torque-induced pogoing, but also the effects of pushing on the pedals (and thus, pushing against the seat).Not really. The "effects" you speak off, are isolated within the sprung mass. The "tensioned" side of the chain however, is what transfers the energy from the "sprung mass" to the unsprung mass. Any mechanical misalignment between the two, and energy gets diverted.


I also forgot to add:

- the pressure in the rear shock

Obviously, if the pressure is too low, the pogo effect will be worse.The shock can ONLY modulate the pogo-ing, not eliminate it - Seems foolish to design a system which requires the shock to dampen design flaws... instead of using it to dampen road irregularities

[jeff-o]

That's not what I meant... if the rear shock is set to a "softer" setting, ie. compresses more easily, then it will be easier for the tensioned chain (or other forces) to compress the shock. More compression equals more pogo.

An idler, placed in such a location that the tensioned chain is made to pass directly over the axis of the suspension arm, would eliminate any pogo effect from the chain.

[bentrox!]

PuttPutt has spoken...
It's all about the chain.
Nothing else matters.

[jeff-o]

Well in any case, if you spin instead of mash, you can also reduce the pogo effect. That will work on any bike, no matter how the geometry is set up.

[JefferyB]

Thanks to all for a very informative analysis of suspension and suspension gone awry.

The reason for the question: Hard tail vs. Rear suspension

-- I've always ridden a DF bike, for the most part commuted on a hard-tail mountain bike because I wanted comfort (riding position) and durability. I found that my legs offer plenty of suspension - one can see a bump or curb coming and by just standing up on my pistons (legs), with knees bent, I'm fine, so why waste energy, weight and expense dragging around suspension systems...

-- On the other hand, a recumbent does not offer one the ability to stand momentarily to take on the bumps that one encounters comfortably and safely, and my concern is that the rider's body (lumbar and cervical discs?) ends up providing the suspension...

Recently I converted to a DF cyclocross (more efficient than my MB, but still durable). I love the Cyclocross, but want to experience the recumbent, so I'm about to invest in one. I chose the Challenge Seiran (SL or E), because Challenge seems to offer a combo of quality, unique design, cost effectiveness, and gorgeous lines in their bikes and because the high racer will allow me to sit up at a level where the cars are most likely to see me during commuting.

I never like suspension on a DF, because my legs work wonderfully, so unless you're doing serious downhill mountain bike riding, the weight, lost efficiency, etc aren't worth the trade off (kind of like a 4 wheel drive auto driven only on city/hwy streets -- a waste of fuel and technology)

Seat suspension on a bent will not be as reliable nor robust as standing on ones legs with knees bent, but it seems like it would be worth investing in a quality little piston, nonetheless (after making sure the tensioned chain crosses the suspension axis, of course ;) ) On the other hand, I have an opportunity to get a great deal on a new Seiran SL (no suspension :eek: ), so I may have to just take the bumps, after all. :o

Thanks!
Jeffery

[keith-pam]

The bumps will not hurt so much when they are spread across a much larger surface area that the recumbent provides. On a DF you are always adding pain on top of soreness because of the little touture divice you are seting on. I went to look at the Seiran SL--what a sweet machine. Riding that bike could be better than sex .