Apples to apples, or a frank discussion of low-trail bike handling from someone with direct experience!

Just found this in the bikelist.org archives of the 650B list...WOW! I am copying it here because it is a great practical description of how a low-trail bike handles differently vs. a high-trail model...

Archive-URL: http://search.bikelist.org/getmsg.asp?Filename=650b.10604.0046.eml
Subject: Re: Was [650B] [Fwd: [KOG] Subjective P/R Observations] - ref. 40mm
From: mlove(AT)questertangent.com
Date: Thu, 27 Apr 2006 09:00:00 -0700

Mark wrote on 27-04-2006 07:28:28 AM:

> For those of us who would not understand the implications of a 40mm vs
> 64mm trail fork for a Bleriot (me included), what does the lower trail
> do to the handling of the bike. I have a Bleriot on order and the idea
> of having a fork option is intriguing yet it is not obvious to me why I
> would want the option.
>
> Apologies in advance if I am asking something that is obvious.
>
> Cheers,
>
> Mark
>

It's not obvious at all, Mark. In fact, the whole trail thing is a bit of
a conceptual can of worms. Simply put, increasing trail (by decreasing the
head angle and/or reducing the fork offset) increases the front wheel's
tendency to resist changes in direction and to recenter itself after a
steering deviation, so high-trail bikes have more straight-line stability,
in theory.

But that's not all there is to it. Increasing trail also increases the
"wheel flop factor" -- the amount by which the front end of the bike lowers
under steering. If you put a bike in a workstand with the wheels just
touching the ground and turn the handlebars, you can see the front wheel
lift off the ground. The higher the trail, the higher the wheel will lift
for a given steering angle. This means that when you steer while riding
the bike, a higher-trail bike will drop more at the front, and this will
begin to initiate a turn. So, in this sense, high-trail bikes are LESS
stable, since it takes a smaller steering input to initiate a turn.

How do these factors combine in practice? I have some first-hand
experience with this. A few months ago, Matthew sent me a spare fork for
my Kogswell P62, and I had a local framebuilder increase its offset from
45mm to 55mm. Compared to the original fork, the extra offset reduced the
P's trail from ~59mm to ~48mm, which is lower than virtually all modern
production bikes. (It also caused the head angle to increase by ~0.5° to
73.5°, which is a confounding factor, but the main effect of that change
will be to reduce the bike's turn radius for any given steering angle.)

Compared to the original configuration, I've noticed the following effects
of changing to a lower-trail geometry:

- Lighter-feeling handling. There's noticeably less effort required to
turn the bars. You might think that would make the low-trail bike twitchy,
but that's not the case at all, since there's also less responsiveness to
steering inputs.

- Less tendency to veer. With higher trail, the bike would tend to veer
under careless or accidental steering inputs (shoulder-checking, reaching
for a water bottle, hitting an unseen bump, ...), since the high-trail
geometry is eager to initiate turns.

- Easier to change line in a turn. Some people like this, others prefer
the high-trail tendency to stick to a single line throughout. Since I'm
not a great cornerer, I welcome the opportunity to change my mind in the
middle.

- More precise steering. Because the lower-trail bike doesn't want to
initiate a turn with each nudge of the handlebars, I find it easier to pick
my way through and around roadside debris.

In more general terms, the lower-trail geometry gives up nothing in
stability or confidence, while providing several advantages. I do like it
a lot better.

You may also be interested in some results of testing the Kogswell P/R
prototype with three different fork offsets.
http://kogswell.com/testPR.pdf

Hope this helps,

Murray


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