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Date: 20 May 2005 20:35:01
From: geepeetee
Subject: recumbent trail question
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Hi
I am just in the process of building a SWB recumbent and have got to the
critical part of positioning the head tube on the frame.
I have done some calculations using formulae found on the internet and am
probably gonna end up with about 20mm, with a head tube angle of just under
70 degrees. I was going to give a bit of tolerance and go for 40mm (ish)
but this gives a head tube angle of 65 degrees which looks too low.
Rake of the forks is 65mm and radius of the wheel (with tyre fitted) is
250mm
I was thinking that the lowering of the bike when the rider sits on would
lessen the trail, but assuming the bike lowers equally front and rear (thus
not altering the head tube angle, i have to make some assumptions) this wont
alter any of the equation [trail = (radius of wheel x cos of head tube) -
Rake / sin of the head tube] so it will remain the same.
The only part of the equation that could alter is the radius of the wheel
due to compression of the tyre but this is negligible.
Any comments appreciated
Gary
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Date: 20 May 2005 22:12:49
From: geepeetee
Subject: Re: recumbent trail question
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Hi
Thanks for reply, would 65 degrees be ok, i know ,most bikes seem to aim for
70degrees.
One guy said i should go for 15mm trail but i thought this was too little,
thought i was going on the safe side with 40 (ish)
thanks for your replies
Gary
"geepeetee" <geepeetee@gazeta.pl > wrote in message
news:d6le59$rte$1@inews.gazeta.pl...
> Hi
>
> I am just in the process of building a SWB recumbent and have got to the
> critical part of positioning the head tube on the frame.
>
> I have done some calculations using formulae found on the internet and am
> probably gonna end up with about 20mm, with a head tube angle of just
> under 70 degrees. I was going to give a bit of tolerance and go for 40mm
> (ish) but this gives a head tube angle of 65 degrees which looks too low.
>
> Rake of the forks is 65mm and radius of the wheel (with tyre fitted) is
> 250mm
>
> I was thinking that the lowering of the bike when the rider sits on would
> lessen the trail, but assuming the bike lowers equally front and rear
> (thus not altering the head tube angle, i have to make some assumptions)
> this wont alter any of the equation [trail = (radius of wheel x cos of
> head tube) - Rake / sin of the head tube] so it will remain the same.
>
> The only part of the equation that could alter is the radius of the wheel
> due to compression of the tyre but this is negligible.
>
> Any comments appreciated
>
> Gary
>
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Date: 20 May 2005 19:43:38
From: Bill Patterson
Subject: Re: recumbent trail question
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It all depends on the height of your seat and the angle of the seat
back. Among others. 60 mm trail would be more to your liking. The best
idea is to build a "boiler plate" fork with a slot going backward. ride
the bike and move the front wheel back in the slot until you are happy.
Then build a real fork.
Bill "still don't understand why it is bad to 'top post'" Patterson
geepeetee wrote:
> Hi
>
> I am just in the process of building a SWB recumbent and have got to the
> critical part of positioning the head tube on the frame.
>
> I have done some calculations using formulae found on the internet and am
> probably gonna end up with about 20mm, with a head tube angle of just under
> 70 degrees. I was going to give a bit of tolerance and go for 40mm (ish)
> but this gives a head tube angle of 65 degrees which looks too low.
>
> Rake of the forks is 65mm and radius of the wheel (with tyre fitted) is
> 250mm
>
> I was thinking that the lowering of the bike when the rider sits on would
> lessen the trail, but assuming the bike lowers equally front and rear (thus
> not altering the head tube angle, i have to make some assumptions) this wont
> alter any of the equation [trail = (radius of wheel x cos of head tube) -
> Rake / sin of the head tube] so it will remain the same.
>
> The only part of the equation that could alter is the radius of the wheel
> due to compression of the tyre but this is negligible.
>
> Any comments appreciated
>
> Gary
>
>
--
Don’t be a 0 to 60 sheep, be a 60 mpg wolf. Yes Miles Per Gallon.
See some Bikes At:
http://home.earthlink.net/~wm.patterson/index.html
Class and Helicopter
http://www.calpoly.edu/~wpatters/
The Pony Express
http://www.geocities.com/Pentagon/Base/6850/PonySong.html
Reply to wm.patterson@earthlink.net
wpatters@calpoly.edu
william.patterson@1962.usna.com
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Date: 20 May 2005 12:43:32
From:
Subject: Re: recumbent trail question
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You might want to check here:-
http://bikesmithdesign.com/Design/12Steps.html
Hope this helps.
Lewis.
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