trail on a swb recumbent

Gary Teale said:

What would be a good amount of trail to have (from what i have read this
is the important bit) on a swb bent. I have checked several bikes
(mountain and hybrid) and they have a couple of inches.

What would be really useful it for you to make the trail adjustable
somehow, and then report back to us on how it handled with different
values.

However, the latest edition of "Bicycling Science" while being
disappointingly un-specific about the effects of trail, shows a table
suggesting 40-55mm for touring, 36-44mm for road racing and 23-36mm for
track racing.

My swb 'bent is definitely twitchy, but I've never established why, the
trail is about 50mm (from memory).

Mike

On Thu, 7 Apr 2005 16:47:50 +0100, "Gary Teale" <[email hidden]>

Quoted message said:

Hi

I am just building a hss 1 swb bent and am thinking about positioning the
head tube. The detailed plans are very good but the dimensions have quite a
margin for error if my main tube bends are not identical (which they
probably aren't) to the drawing.

What would be a good amount of trail to have (from what i have read this is
the important bit) on a swb bent. I have checked several bikes (mountain
and hybrid) and they have a couple of inches.

This is quite a complicated subject, and one of which I don't fully
understand the science of - but there again, the science probably goes
out the window after a while.

After reading as much as I could about the subject, I took what I
thought to be common average readings of: head tube angle 70degrees
and trail of 2". I went on the basis that this would be the starting
point - based on what seemed to 'out there' for swb recumbents.
However, as much as the completed bike rode generally ok, the handling
and stability were a nightmare, and I felt very, very insecure on the
bike. "F***, I've screwed the trail", was my initial reaction, so I
set about getting an opinion from Brol [the really excellent online
recumbent forum]. It was suggested to me that my steering ergonomics
were all over the place, and this proved to be the case. I was
hellbent on having an USS 'lever' style of steeing [like a crane] so
as to avoid handlebar seat interference. I thought about it, designed
it, and built it [albeit crudely] and it worked. It worked
brilliantly, apart from the fact that I was careering all over the
place. Mark Stonich put me right.
http://bikesmithdesign.com/Design/12Steps.html
Cutting a long story short, I ripped out my 'amazing' system and went
for a more conventional USS steering with remote linkage. Same
headtube angle, same trail and it felt like a different bike - really
stable compared to it's former self. So my point is: when you get the
bike on the road, don't always jump to conclusions that handling is
simply a matter of trail, like I did, there's so much more to it than
that.
That said, I am of the blief that more trail gives you stability at
high speeds and twitchy handling at low speeds, and visa vera.
I can say that my SWB handles great at high speeds [say 15mph+] and is
'ok'at slower speeds, but I wonder if less trail would help with the
latter. So, the next one I build [hopefully one made of Carbon fibre],
I'll use a head tube of 70degrees and trail of between 1/2 - 1 inch.
What would be really useful is to rig up some forks that are
adjustable. This would certainly give you some immediate comparisons.

Hope it works out.

Garry

Quoted message said:

I put a post and got a reply saying half an inch but this doesn't seem much.
Is this because there is more weight over the front wheel making the
steering heavy?

Another consideration is that the bike will have full suspension and i
assume that when it is lowered (due to the weight of the rider) the trail
will reduce slightly, if so i could end up with less or even none.

Without the head tube fitted the amount the suspension will settle is just a
guestimate (catch 22) so i would like to go to the maximum without too much.

thanks in advance

Gary

in message <[email hidden]>, garryb59

('[email protected]') said:

That said, I am of the blief that more trail gives you stability at
high speeds and twitchy handling at low speeds, and visa vera.
I can say that my SWB handles great at high speeds [say 15mph+] and is
'ok'at slower speeds, but I wonder if less trail would help with the
latter. So, the next one I build [hopefully one made of Carbon fibre]

H'mmmm...

How much does the assembled multitude think rake and trail should change
as speed increases? I'm working on a bike which doesn't really have to
go round corners at all well, but which does have to accelerate from a
slow-rolling start and which isn't going to have more than a few
degrees of steering movement. The object is to try to achieve 60mph.
I'd been assuming that for prototype #1 I would just work on fairly
conventional steering geometry, but I _really_ don't want to end up
with a bike which goes out of control at speed (c.f. Mango). If it
falls over occasionally before it gets up to dynamically stable speed I
can live with that, but the equivalent of a tank-slapper at 50 would be
No Fun.

--
[email hidden] (Simon Brooke) http://www.jasmine.org.uk/~simon/

;; may contain traces of nuts, bolts or washers.

On Fri, 08 Apr 2005 10:24:17 +0100, Simon Brooke
<[email hidden]> wrote in message
<[email hidden]>:

Quoted message said:

How much does the assembled multitude think rake and trail should change
as speed increases? I'm working on a bike which doesn't really have to
go round corners at all well, but which does have to accelerate from a
slow-rolling start and which isn't going to have more than a few
degrees of steering movement.

Mr Burrows tried that with the Ratracer B. The result was some fairly
fast lap times followed by a very impressive abrasion on his [censored] :-)

Guy
--
http://www.chapmancentral.co.uk

"To every complex problem there is a solution which is
simple, neat and wrong" - HL Mencken

Simon Brooke said:

in message <[email hidden]>, garryb59

('[email protected]') said:

That said, I am of the blief that more trail gives you stability at
high speeds and twitchy handling at low speeds, and visa vera.
I can say that my SWB handles great at high speeds [say 15mph+] and is
'ok'at slower speeds, but I wonder if less trail would help with the
latter. So, the next one I build [hopefully one made of Carbon fibre]

H'mmmm...

How much does the assembled multitude think rake and trail should change
as speed increases? I'm working on a bike which doesn't really have to
go round corners at all well, but which does have to accelerate from a
slow-rolling start and which isn't going to have more than a few
degrees of steering movement. The object is to try to achieve 60mph.
I'd been assuming that for prototype #1 I would just work on fairly
conventional steering geometry, but I _really_ don't want to end up
with a bike which goes out of control at speed (c.f. Mango). If it
falls over occasionally before it gets up to dynamically stable speed I
can live with that, but the equivalent of a tank-slapper at 50 would be
No Fun.

You'll get as many answers as there are people and bikes, at least
this is what I discovered when I embarked on my swb. In the end,
without no other experience to base anything on I took what seemed to
be 'the standard' and went with that [what was the point in doing
anything else?]. And like I said, it's fine, certainly up to 40mph it
is [and I doubt I'll be doing much more than that]. But It's
interesting to note that people with similar bikes, have made changes
to the trail and it has [according to them] made a significant
difference to handling. So I'm curious to find out with mine.
But mine is a swb. Most of the lwb, TE clone bikes have a much
swallower headtube angle and greatly increased rake to get the
required trail, so they offer different dimensions again. And then
others go for negative trail and a steep headtube angle.
Like so many things, 'too much think stinks up the place' and you just
have to draw a line, give it a go and learn with what you've got.
The only thing I regret not doing with #1 is using front forks with
adjustable trail. Ho, ho. Next time, another life.
But it was also a real revelation to me to find out the initial
twichyness of my bike was not down to incorrect steering geometry, but
something very different. We learn from experience - always the best
way.

YMMV

Garry

Mike Causer said:

Gary Teale said:

What would be a good amount of trail to have (from what i have read this
is the important bit) on a swb bent. I have checked several bikes
(mountain and hybrid) and they have a couple of inches.

What would be really useful it for you to make the trail adjustable
somehow, and then report back to us on how it handled with different
values.

http://www.terracycle.com/adj_geom.htm covers the first half of that.

Simon Brooke said:

with a bike which goes out of control at speed (c.f. Mango). If it
falls over occasionally before it gets up to dynamically stable speed I
can live with that, but the equivalent of a tank-slapper at 50 would be
No Fun.

Steering damper? http://www.mtbr.com/spotlight/hopey/