How much low trail is good?

[lincoln]

Hi, I have a Soma Speedster conversion.  According to this nifty trail calculator I found with the Pari Motos at 38mm, 73 degree headtube and a 45mm rake fork I am running about 55mm of trail.  I am thinking I would like to try a low trail geometry set up and am thinking of buying the new Soma fork.  At 69mm of rake, the calculator tells me that would be 32mm of trail, probably would notice the difference.  I will not be running much more than a pound or 2 as a front load, maybe if i switch some racks around 3-5, but often unloaded completely.  My interest is to see if slowly climbing the 10 to 15% stuff around here at 4 miles an hour, it would would require less focus to keep the bike from wandering without negatively affecting what are otherwise good handling characteristics of the bike.

My question to those who might know is: Will 32 mm of trail be a bit squirelly unless there is a fair size front load?  From trying to piece together an understanding of the low trail characteristics and benefits by various inputs in this group I am guessing something like 40 to 45 mm of rake might be more what I am looking for without the loaded front end.  Any body have any thoughts?  Anybody know of a 1-1/8 threadless fork with 54-56mm of rake that would work with my 73mm reach calipers?  Preferably with a nice crown.  I believe my fork length is 374mm axle to crown.

At one point I ran a similar question by the group about re-raking forks, that seems to have its own pitfalls. 

Thanks, Mick

[Lee Chae]

Hi Mick. Bicycle Quarterly and Kogswell teamed up to test out a few different low-trail configurations and reported back their thoughts in an article. I think you can peruse the BQ back issues to find out which one contains the article. I know that Kogswell made a PDF available of the findings (I'm not sure if the PDF is exactly the same as the BQ article). Maybe you can find that floating around the Internet somewhere.

From my experience with a 40mm trail Kogswell P/R, I found the steering too light without some type of load up front. Consequently, I'd imagine the 32mm trail setup would be much worse.

My two pennies,
Lee

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[Alex Wetmore]

For me 40mm (+/- a bit) is the sweet spot that handles well unloaded, lightly loaded, and heavily loaded.  

32mm is okay, but will feel quite light unloaded.

Note that a change in axle to crown compared to your current fork will change your head tube angle and adjust trail accordingly.  Is the A-C on the new Soma fork the same as your existing fork?

alex

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From: 65...@googlegroups.com [65...@googlegroups.com] on behalf of Lee Chae [lee...@stanford.edu]
Sent: Friday, June 14, 2013 9:37 AM
To: lincoln
Cc: 650b
Subject: Re: [650B] How much low trail is good?

[Ryan Watson]

I once put 650x32B tires on my 30mm trail Kogswell just out of curiosity.

It was indeed "squirrelly" and I didn't like it. Pretty sure I had my boxy Inijurushi bag on at the time, but that was a few years ago. 

I've ridden the same bike with unloaded  with Hetres and it felt fine.

I've had several low trail 650B bikes and (when equipped with Hetres) all handled very well even without a front load. 

YMMV!

Ryan

[Murray Love]

My experience is close to Alex and Ryan's.  I tried both a 30mm- and 40mm-trail fork with my P/R, and preferred the slightly "heavier" steering feel of the latter.  I wouldn't say lower trail is more squirrelly in the sense that it makes the bike harder to control--since the lighter feel is accompanied by lower sensitivity to handlebar movement--but it does mean the front end feels like it's wandering even when the actual trajectory is pretty straight.  I assume this is corrected with a front load, but I never tried it out.

Murray

Victoria, BC

[Mike Schiller]

Singular cycles in the UK sells a 60mm rake fork that goes with their Osprey bike. But that fork only comes in 1" threaded.

I guess the real question is... if you don't want to carry any front load, why spend the money and time to change something that works?

~mike

[rcnute]

I can see wanting lower trail to keep the front end from wandering while going uphill.

Ryan

[Steve Palincsar]

On Fri, 2013-06-14 at 09:25 -0700, lincoln wrote:
> Will 32 mm of trail be a bit squirelly unless there is a fair size
> front load?

How heavy is "fair size"?

I have a 30mm trail Kogswell P/R and a ~35mm trail M.A.P. Randonneur.
Both feel just fine with nothing more than a large size Berthoud bag
(GB28 or the fancy one, 2882?) a wallet, a pair of glasses, a couple of
tubes and a small tool roll up front. Never weighed it precisely, but
I'm guessing that comes to something like 3-4 lb.

My first ever experience with low trail was with the Kogswell when the
LBS first built it up and nothing on the front at all. That was a real
YOWZA! moment where I noticed something dramatically different with the
feel of the front end, like "What the h*ll is wrong here??" but I'm not
sure "squirrely" is at all appropriate.

Squirrely usually refers to the zigging and zagging motions of a
squirrel, and implies handling that won't track straight. That's not
how it was with the Kogswell. Steering felt unnaturally light, but the
bike held a line. Note that this was with 38mm tires. I have never
used 32mm 650B tires and cannot speak to how the bike would handle with
such narrow tires.

[Mike Schiller]

I just re-read the Blog post on the SOMA conversion fork.  Rake is listed as 65mm on that fork. http://somafab.blogspot.ca/2013/05/low-trail-forks.html

This fork seems more appropriate for your conversion bike that uses caliper brakes. The trail with that fork would be 34 mm. 

The Grand Randonneur comes with a cantilever braked  69 mm rake fork from the new geometry chart.  

~mike

[Brad]

Now that has got me curious.  I have had the same sensation, but what generates it?
Is it because the thing is so ...so... steerable? 

[I think that steerability is related to low flop which concommitant with low trail]

My regular test run after a fix/modification is around the block.  At the corner there is a stop sign which is usually handled with a california stop closely followed by a patched pot hole that has to be steered around or your going over a bad bump at low speed.
After switching to low trail I could get around it with aplomb.  Earlier bikes with 90's geometry- not so much.  With the high trail geometry the corner had to be approached at a higher speed and a more banking turn which usually included the bump.

There are so many sensations on a bike that are different from what is actually going on.  The sensation of speed from a hard narrow tire for example when tests show no advantage.

[Murray Love]

Brad, you might want to search the iBOB Bikelist archives around 2006/07 for a great deal of lively discussion about trail.  

As one of the early experimenters of the new low-trail era, my explanation is that trail is directly proportional to what Jan calls "Flop Factor" [FF = Trail * sin(headangle) * cos(headangle)].  As you turn the handlebars, the front axle drops more on high trail geometries than on low: all else being equal, a 55mm trail will result in 37.5% more vertical axle drop than a 40 mm trail for a given steering input, and the rider has to exert a somewhat greater effort to recover from the axle movement.  I *think* this accounts for the more "twitchy" feel of higher-trail geometries, whether the steering input is intentional or unintentional (e.g. shoulder-checking, reaching for a bottle, hitting a bump, or cross-winds).

I found that lower trail bikes were more forgiving of my carelessness or adverse conditions, at the expense of a slightly more wandery feeling at the bars.  There's less axle drop for a given steering input, and my experience is that you can throw the bars around more without inducing a wild countersteer.  This may explain your experience with potholes, and Jan's observation that you can more easily alter your line in a corner.

Neither of my bikes right now is low trail.  My 1984 Sequoia is 650B converted, riding on 38mm Trimlines, and in that configuration it could really do with about 10mm less trail.  My Vitus 979, on the other hand, must have pretty high trail (40mm fork offset, probably 73° HTA) but it has beautiful, almost telepathic handling on 700x27 tires .  Not sure what's going on there.

Murray

Victoria, BC

[Jan Heine]

At 12:20 PM -0700 6/15/13, Murray Love wrote:
>My Vitus 979, on the other hand, must have
>pretty high trail (40mm fork offset, probably
>73° HTA) but it has beautiful, almost telepathic
>handling on 700x27 tires . Not sure what's
>going on there.

The relationship between trail and
handling/stability is not linear. We've found
that for bikes with moderately wide tires, high
trail and low trail feel very similar, and quite
different from "mid trail."

For example, the Calfee we tested (32 mm tires)
handled beautifully with 61 mm trail. Similar
bikes with 50 mm trail also are great, yet with
55 mm trail, the bike doesn't feel settled and
lack precision.

Clearly, several factors are overlapping here -
trail, flop and perhaps other factors.

Jan Heine
Editor
Bicycle Quarterly
http://www.bikequarterly.com

Follow our blog at http://janheine.wordpress.com/
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