mdilthey

Hi All,

Still not solid on the concept of "Low Trail." I know the result is a bike that prefers a front load, but I'm not sure how to achieve it.

My frame is a Soma Double Cross Disc. I am currently using a Salsa Vaya fork, which has a 405mm axle-to-crown length and a 50mm offset (not sure how to interpret those numbers in terms of "trail."

I want a fork that works better for a front load bias. Currently, the bike hates a front rack and basket, and the steering gets very wobbly, especially at speed.

Can anyone suggest a steel disc fork with mid-blade eyelets that will convert my bike to "low trail," or show me how to interpret the offset and axle-to-crown measurements so I can find one myself? I'm looking at the Surly LHT disc fork, the Cross-Check fork, the Straggler fork, and the original fork that comes with the Soma DCD.

Thank you!

Salamandrine 

Neither am I. I think the idea is that it improves the handling at low speeds, which is an issue when you're climbing with loaded touring bikes on rough roads in low gears. More trail is usually conducive to more stable handling at speed.

Anyhow, you can google trail calculator and there are several IIRC. You need the head tube angle, fork rake (offset), and wheel size. Basically a fork with more rake will be lower trail.

50mm is 6mm than the stock forks - just looked it up. You've got 58mm trail now, which pretty normal for a road bike, but 6mm less than what the bike was designed with.

Bicycle Trail Calculator | yojimg.net

fietsbob

as you offset the bend in the fork blades More You reduce the trail, because the plumb line thru the hub
is behind the head tube angle at the ground. so bending more gets the axle line closer to the HTA line.


A smaller wheel results in a shorter trail if your head tube angle and fork offset remain the same

Vs Larger wheel, as it's closer to the point where those 2 lines cross , above the ground.

mdilthey

Thanks, Salamandrine.

I guess the synthesis of my question is, "which fork do I buy if I want stability when loaded like this:"





Thanks Stefan for the inspiration.

fietsbob

Hire one Made for your bike, Custom, to get the trail numbers you choose .
and the braze ons in the places You want them .

I Have front panniers on My Bike Friday. pocket Llama ..
they, BF, Have sold tens of thousands of those Travel Bikes world wide ..



Read data, Brompton has a 72,4 degree HTA and supposedly a 35mm trail.

It works well with the big head tube mounted touring Bag..

robow

Have you spoken to soma or are you certain that they will only recommend their fork?

Tim_Iowa

I've read a lot of information and testimonials on how a low trail fork makes a bike handle a front load better. However, I haven't tried one yet myself.

As far as I know, there are no regular-production low trail forks with disc brake tabs. None of the forks you listed have enough rake to be low trail.

The Soma Champs-Elysee fork is low-trail and has mid-fork eyelets, but is for rim brakes.
Jeff Lyon will make you a custom fork for a reasonable price, but again he only builds for rim brakes. Several people on the Rivendell, BOB, and 650b google groups have contracted custom forks from Jeff Lyon.
Glen Copus of Elephant bikes makes a model with low-trail and disc-brake tabs, the National Forest Explorer. They may do a similar fork for you as a custom order.

mstateglfr 

I have accepted that trail is like elves. Some may argue it cant be seen(determined), but you see the result in the shoes those little elves make for the shoemaker.
Ive read about trail a lot only to come out more confused each time when applying it to my bikes(which all seem to have different trail).

Shimagnolo

Calculator: Bicycle Trail Calculator | yojimg.net

less trail = less stable, quicker turning
more trail = more stable, slower to turn

fietsbob

Soma is a Retail outlet and Brand for Merry Sales Imports .. Taiwan does the actual Making and exports to them.


I read Thorn SJS wont sell a raked fork with a disc Mount , though they do sell disc Brake forks but the blade is straight

You can understand that when you put on the disc brake the force is trying to Un Bend the fork rake ?

79pmooney

I looked up the Soma Double Cross. Rake of 44, HTA of 72. That's a trail of ~65. A lot! A graph I put together put that outside the range of acceptable. Your fork with 50 mm offset gives you about 59 mm trail. My Raleigh Competition, an old school geometry, has an offset of 65 and a trail of 45. Sweet handling. I haven't tried it loaded, especially with a handlebar bag (which I have steered well clear of for the past 40 years for exactly what you describe) but I suspect it would do well as long as I stay within the limits of the skinny tubes of that frame (both fork and stays).

Your handlebar bag would make me very nervous going down that hill in your photo. Lowriders? No sweat!

Ben

79pmooney

Head tube angle is completely tied in with trail, twice. First, it (and fork and wheel dimensions) determines the trail, Second, handling is not determined just by trail but by the combination of that trail and that head angle. Two bikes of different head angles will NOT handle the same with the same trails. Very roughly, increasing your head tube angle one degree will require lowering your trail by 5 mm to get roughly the same "feel".

Ben

Salamandrine 

The current wisdom is that lower trail (more offset) works better with front loads.

The old wisdom is that higher trail (less offset) makes the bike more stable at higher speeds.

Since your problem is wobble at high speed with a heavy front load, the solution to your problem is a contradiction - I have no idea. You may need to try a couple extremes and see what works best for you. I've never ridden a bike loaded like that.

fietsbob

People have used long slot dropouts like on the rear, in a fork and allowing the axle to have a variety of places to be,
to test by Riding.

nickw

I can offer up my opinion for what its worth. I had a Soma DC that I used for touring and decided to go with a more forward packing strategy. Bought the Soma Champs Elysees fork, used it with some high rider Panniers and a small rear load in a basket. I don't have much to compare with from a loaded touring standpoint besides my LHT from years past, which is obviously not a apples to apples comparison. I wasn't better or worse, it was just different.

When loaded down it rode fine, completely unrideable with no hands though, it was really squirrely and once it got off line you couldn't correct without grabbing the bars. Had a couple sketchy moments trying to remove my jacket. Overall though it was a nice pleasant ride. May have been different with low rider racks since I know that a high trail setup with higher rider panniers can be a bit sketchy too. With weight it steered more naturally and felt a bit better at low speeds than other bikes. The front hand a tendency to wash out in gravel more than I would have expected.

Unloaded I have a better comparison. Even unloaded though it was really difficult to ride no hands and it had some shimmy if I tried. I just put a carbon CX fork on it and I think it handles IMMENSELY better. Easy to ride no hands, rails corners and just tracks a lot more effortlessly.

Not that my 'experiment' is the full picture of what low-trail geo means for handling. I think if a bike was designed around a low trail fork things may of been different. Slapping a low trail fork on (essentially) a CX Race bike is probably not the best way to debunk or validate if it works.

I have done/did a lot of reading about low trail and you get opinions ALL over the map. Easier to ride no handed, harder to ride no handed, better handling, worse handling...and everything in between. I think part of it is due to what you are used too and have ridden for years and how well the frame/fork/tires/rack work together as a SYSTEM.

Here is my setup:

arctos

Max:
Do the same handling problems exist without the handlebar bag weight forward of the steering axis and front axle? My experience is that such high and forward weight degrades handling at slow speeds and can cause shimmy at higher speeds.

My solution was no handlebar bag or only a small one and placing the panniers higher but still partially behind the steering axis. (I use a Bruce Gordon High Mountain Front Rack.) No scientific method or formula used just trial and error until I found what worked for me. I am very happy with the on and off pavement handling with a full self sufficient touring load.

Chris Pringle

Hi Max,

It is quite possible that your shimmy (i.e., wobble) is not a result of your fork. Unless your front bags are attached somewhat loose, you should not experience wobble with the additional front weight. Quite the opposite - it should actually make the bike more stable and grounded.

I have the suspicion that your frame itself (designed for to absorb the impact of cyclocross at lower speeds and no heavy weights) might be flexing too much under the additional weight intensified at higher speeds. The result is shimmy. A stiffer frame designed for the kind of touring you enjoy might be in order.

Dave Moulton has written several articles on shimmy. Here is one.

Tourist in MSN

What happened to the bikepacking gear? Why the switch to front panniers?

mdilthey

No reason. Three bikes, lots of potential, just playing around. I will be touring this summer with Kelley, and I might bring more stuff than usual to make the trip memorable, if it feels like something we want to do.

As for the rest of the thread, yeah, seems HTA and Trail are business partners, which complicates things. Lots of respect for framebuilders. The weight of my previous basket setup was very high; I will try mounting panniers lower and see how that feels.

Only notice the shimmy when I take my hands off the handlebars, as others have mentioned. We will see!

Tourist in MSN

I suspect that all the bike manufacturers attempt to make their bikes handle like their competitors bikes because if people like a certain bike for handling and the word gets out, everyone will copy that geometry for their bikes too. If that suspicion is correct, you probably are not going to find any new forks that significantly change your trail from what you have.

I recently build up a rando bike, the manufacturer specifically called the geometry mid-trail at 56mm (it is a 700c bike), I would have suspected low trail from the way it handles. My touring bikes, if I take my eyes off the road for a few seconds and then look back, I am still going in a straight line. But this new build I find that I can't take my eyes off the road very long at all or I find I am going in a different direction. I suspect that is another characteristic of the shorter trail.

If I recall correctly, you used a RackTime TopIt rack on the front with panniers. That is pretty high. I am just guessing here, but I think if you try shifting the weight back as far as possible on that rack to get it as close as possible to the steering axis (the head tube), that could reduce wheel flop. But, maybe you already did that.

But shimmy, I have no clue how to help on that. I had a bad shimmy on my LHT, the only way I got rid of it was to get rid of the LHT.

If I was starting over for gear, I would consider the Salsa Anything Cages or the similar Blackburn ones instead of a front rack, then use lightweight dry bags.

niknak

As perhaps the only person in this thread with a low-trail bike (40mm trail) that I use for touring, here are my thoughts:

- If you're having shimmy issues now, adding a fork with more offset is not going to help the problem. You're simply packing incorrectly for your bike, probably too much weight in the wrong spots.

- A bike with lower trail will be very stable at cruising speeds and slower. It'll ride on rails. This is great for touring and long distance riding as speeds are fairly low.

- A bike with lower trail will become more lively at descending speeds. If you're a skilled descender with a light touch, a lively bike at high speeds allows you to easily change course mid turn, say to avoid a patch of gravel. If you're confident and loose, descending on a low-trail bike is wicked fun. If you're not a skilled descender, you'll hate low-trail handling at high speeds. For example, if I'm descending a mountain straightaway at 40mph approaching a turn and I don't scrub enough speed before the turn and enter the turn too fast for my comfort, my body will tense up and I'll grip the bars tighter as I attempt to brake while turning. The tighter my grip the more the bike shimmies. For this reason alone I'm willing to bet it's why 99% of bikes in the market don't have lower trail than around 56mm.

- The only way to get a high offset fork with disc mounts is to go custom or buy a bike with that fork included. The NFE Elephant and the new Rawland bikes may be the only production options available.

nickw

Per my post, I've tried a "low-trail" fork on my bike and didn't care for the handling at any speed, it was fine and not obnoxious, but not as great as I was expecting. High speed, say 25+, with no hands was super sketchy, lower speeds was manageable but still poor IMO, at least on my bike, YMMV...sounds like Tourist MSN had a similar experience.

My hunch was actually the very opposite of yours, I think somebody with little to no experience would jive with the handling more than somebody experienced with traditional geo's with the ingrained muscle memory of how they ride. After switching to my std carbon fork, it felt weird for 2 minutes but was instantly more comfortable and felt much more at home.

But again, without taking ALL geo into account you can't really say for sure if it works or not. All the varying opinions online I think allude to this, none of which account for "experience" levels.

Tourist in MSN

For an unladen bike for exercise rides, I like the handling of my "mid-trail" bike with 56mm trail. I would not say poor handling. But it did not have that characteristic of a long trail touring bike that wants to go in a straight line, instead it will easily go wherever I want it to go. Sort of like comparing the handling of my old F250 pickup truck that would go in a straight line just great, compared to the handling of my MGBGT sports car that would corner effortlessly at speed.

My comments above are for unladen handling, I do not anticipate putting a touring load on this "mid-trail" bike, it is more for exercise and distance riding. And I have a big handlebar bag on it that is not exactly light, so there is an up high load forward of the steering axis.

For touring I want a longer trail that will hold direction better with a load so I can take my eyes off the road to look at the map or GPS for longer periods of time while maintaining speed.

I don't try to ride no-handed, so I have no clue if any of my bikes are good for that or not.

Salamandrine 

The decades old wisdom would be that if your bike is shimmying at speed, you need more trail not less, and/or a stiffer frame.

The value of low-trail seems to be more than somewhat inflated by it's current trendiness. I'm a skilled descender, but I prefer conventional tour geometry for touring bikes.

This is definitely a case of find what works for you.

niknak

I agree that low trail is a trend right now that will never catch on. I happen to enjoy the handling most of the time but I admit it's far more picky than a bike with higher trail. Most people will probably prefer higher trail because it feels rock solid at higher speeds. It doesn't matter if you weave around a bit more when climbing as long as when you're descending you feel like you're on rails. That's why almost all production bikes are built this way.

The ideal use of a low trail bike is for randonneuring and ultralight or credit card touring, where your loads are relatively light. Putting a load up front has very little impact on handling because of the low flop factor. You also don't get the wagging the tail effect when riding out of the saddle, as is common with heavy rear loads or with bikes that aren't super stiff.

My advice to the OP is to just move weight to the rear of the bike where it's designed to go. If it still shimmies, you'll have to reduce weight or get a stiffer bike. But if you're determined to load your bike at the front, you'll have to get a bike designed for that purpose.