ML <
[email protected]> writes:
> Benjamin Lewis wrote:
>> [email protected] wrote:
>>
>>>Benjamin Lewis wrote:
>>>
>>>>No. My criticism is that Forester is claiming bicycles with long
>>>>trail have more sensitive steering, when exactly the opposite is
>>>>true.
>>>
>>> Only if you take the party line at face value.
>>
>> I wasn't aware there was a "party line".
There is a "party line" only to the people who want to appear like
they have superior and arcane knowledge. The rest of us are just
trying to separate myth and lore from reality, and are usually happy
to get real facts.
> The "party line" is the commonly accepted facts without
> consideration of other possibilities. Benjamin Lewis obviously
> believes the party line but I have my doubts if he's really
> considered the other possibilities
Which might just be why he's asking the questions and trying to get
reliable information.
>>>Longer trail will help a bike track better but if you get inputs to
>>>the steering outside of your control (wind, holes, bumps, ...)
>>>longer trail will actually make your bike more sensitive. It's a
>>>longer lever arm.
>
>> This is contrary to my experience, at least with regard to holes
>> and bumps. Do you have any citations to support this? If steering
>> does indeed have to do directly with length of the lever arm, it
>> seems to me that a bump will result in a fixed lateral
>> displacement, which for a longer lever arm will result in a smaller
>> change in steering angle.
>
> No citations just experience & thought experiments.
Your post is at least as inaccurate, but Benjamin at least has the
wits to be asking for information whereas you are just pontificating.
> Let's consider what happens when you push on the head tube of a
> bike, holding the bars fixed. With zero trail there will be no
> twisting of the head tube around the head tube axis because the
> tire/road contact point is directly on the axis.
This only works as you claim when the steering axis is normal to the
ground- e.g., a vertical head tube.
> As you increase the trail & the actual contact point moves away
> from the 0-trail contact point, the twisting forces increase. Now
> how do you twist this in real life? A strong wind puts a sideways
> force on the bike. This force doesn't affect the rear (fixed) but
> the front of the bike can get pushed sideways.
********. The entire bike- including the rear wheel- can get leaned
over by the wind while the bike is being ridden. The front wheel can
get leaned over with the rest of the bike; there is one more degree of
freedom, of course, which is the turning of the fork along the
steering axis. That can happen on a bike with 100 mm of trail or 0 mm
of trail, so long as the steering axis is not vertical. Your
description also neglects the effects of gravity and the rider's
weight, and also the self-centering action caused by the angle o the
steering axis.
> If there was zero trail, the front wheel would act fixed like the
> rear and the front wheel would still be tracking the direction of
> travel.
Again, this is utter malarkey.
> As trail increases, any rotation of the fork translates into a
> larger offset of the contact point and affects the direction of
> travel of the bike.
You mean the bike steers? Yet the bike becomes more stable as trail
increases, not less stable. Your description makes it sound as though
increased trail results in less stability. I think you're confusing
trail and fork offset (also called rake) which have an inverse
relationship with each other.
> The more flexible the front triangle the more affect this has on the
> bike. As far as holes, cracks, etc my belief is that the shorter
> the trail the easier it is for the rider to resist the change caused
> by the outside influence. Again consider the differences from zero
> trail to something larger.
My experience is that the effects of trail on road anomalies are
minimal and easily countered, whether riding a track bike with a large
amount of trail or a touring bike with less trail. There is a
difference in feel, and IME bikes with less trail are less affected by
lean angles when cornering.
Much is made about trail, and yet the practical differences are few
and easily compensated by rider skill. The design parameters of a
bicycle are such that variations in trail are really quite small,
compared to the URB experiments which used utterly huge differences in
trail- including one bike with so much trail that it could balance
alone, without a rider, and was not perturbed by local anomalies in
the road surface (exactly the opposite of your claim). You can read
about it in Whitt and Wilson (and possibly Popadopoulus and Wilson).
There's also an interesting article in the Rivendell Reader #31, pp
30-33, which compared bikes with different forks, one resulting in
trail of 105 mm and the other in trail of 37 mm. The "standard" trail
for a road bike is about 60 mm.
