The largest of my three unis is a 28" Sem (not the XL - it’s the one with the
two-piece frame with the bolt through the seatpost). I am unable to figure out
why I am constantly twisting to one side. What happens as I ride it is that my
right arm crosses in front of me, my left arm reaches back, my upper body leans
to the right, and I am constantly FIGHTING to keep the thing going in a
straight line. I can keep my arms down only if I bend my body to the right
(leaning the wheel to the left). The twist is always to that same side. I can’t
find anything wrong with the uni. I have eyeballed the seat, the frame, the
wheel, the cranks, everything, but can’t find anything that’s out of line. I’ve
tried bracing the wheel with my feet and brutally turning the seat to twist the
whole frame a bit to one side or the other (the seatpost itself can not turn
because of the bolt), and it doesn’t seem to help much either way. I hold onto
a lamppost and get myself all set, to be sure that my feet are evenly placed
and everything, and push off, and it doesn’t help. It came with an airseat
conversion; I replaced this with a Viscount to see whether the mushy saddle was
the problem, but no. On my 24" I can ride along nonchalantly with my arms
dangling at my sides for hours at a time; on the 28" I ride several blocks and
am completely exhausted from constantly twisting and hauling the wheel back
into the direction I want to go. Can anyone think of any reason for this, that
would be caused by something not visibly misaligned, or something that I
haven’t thought of looking at? It’s driving me crazy.
Tires with a center ridge or an uneven tread pattern can/will cause the problems that you describe. Do you have a picture of the tire tread and tire profile?
>this is a shot in the dark but to get things rolling i will ask.
>
>Is it possible that one of your crank arms is 10mm longer than the
>other?
>
>
>–
>jagur - Random Member
>What tire do you have on the 28?
>
>Tires with a center ridge or an uneven tread pattern can/will cause the
>problems that you describe. Do you have a picture of the tire tread and
>tire profile?
>
>john_childs
Both cranks are 5" from hub to pedal base.
The tire came with the uni and is marked:
Schwalbe 47 - 622 (28x1.75) HS159
I’ve been having problems with AOL’s file space for most of the month, so this
picture may or may not be available…
If the image won’t show, the tire has what I can describe as a center ridge
with triangularish knobs in a zigzag pattern on either side of it. It looks
pretty symmetrical, but I will try replacing it today and see what happens.
Another shot in the dark …
If you are travelling further on your 28 you may be more likely to be travelling on the roadway.
Roadways have a camber that pulls you to one side in a similar manner to the way you describe.
The Semcycle frame is flexible (especially the 28) so you might be overcompensating and setting up a resonant swerve!
Try experimenting with your tyre pressure too high = twitchy, too low = squishy and hard to steer.
It looks like the tire has a bit of a “V” profile. The “V” profile combined with the center ridge could be causing the problems. Try finding a tire with a more round profile with no center ridge and with an even tread pattern.
Anyone know of a good 28" tire that would fit Joe’s rim?
>The AOL link isn’t working, but I found a pic of the Schwalbe tire at
><http://www.schwalbetires.com/Cat3Schwalbe159.html>
>
>It looks like the tire has a bit of a “V” profile. The “V” profile
>combined with the center ridge could be causing the problems. Try
>finding a tire with a more round profile with no center ridge and with
>an even tread pattern.
>
>Anyone know of a good 28" tire that would fit Joe’s rim?
>
>
>–
>john_childs
I got another tire today, branded “Serfas VIDA,” marked:
35-622 (700x38C)
This one is a bit more rounded I think. It doesn’t actually say 28" (I couldn’t
figure out a good way to put that in quotes) anywhere on it, but seems to fit
perfectly. I switched the tires at the bike shop and rode a few miles. I now
feel no tendency to lean in either direction more than the other. So it appears
that the tire was indeed the problem! Thank you MUCH!
The tire pictured at the Schwalbe site has the same tread pattern as my old one
but apparently takes higher pressure than mine (I think mine takes 45 psi; I
don’t remember now and the tire is down in my car and I don’t feel like running
down to look at it). Now of course I have other things to adapt to, like
suddenly riding on about 70 psi, which makes for a much more, ah, lively ride.
Being able to track a straight line is sheer bliss though, compared to before.
I’ll look around for a lower-pressure tire with a proper tread. I may just get
used to this one though. It has Kevlar! Ooooo!
I am able to view my images now. They may not work for you. Anyway here is the
new tire:
>I got another tire today, branded “Serfas VIDA,” marked:
>35-622 (700x38C)
Just this weekend someone explained the system behind the first two
numbers to me. In case anyone’s interested: it is the so-called
“European” system, called to life in an attempt to end the multitude
of tyre size systems. Paradoxically but it seems to work as it is
gaining wider recognition. Anywhy, the first number is the tyre width,
the second number is the diameter of the heel thread. Both numbers are
actual dimensions in millimeters, not nominal values.
>It doesn’t actually say 28" (I couldn’t
>figure out a good way to put that in quotes)
You could try “28 inch”. Now put THAT in quotes
>I got another tire today, branded “Serfas VIDA,” marked:
>35-622 (700x38C)
Just this weekend someone explained the system behind the first two
numbers to me. In case anyone’s interested: it is the so-called
“European” system, called to life in an attempt to end the multitude
of tyre size systems. Paradoxically but it seems to work as it is
gaining wider recognition. Anywhy, the first number is the tyre width,
the second number is the diameter of the heel thread. Both numbers are
actual dimensions in millimeters, not nominal values.
>It doesn’t actually say 28" (I couldn’t
>figure out a good way to put that in quotes)
You could try “28 inch”. Now put THAT in quotes
Good deal!
The problem with tires with a center ridge is that you never end up riding directly on the ridge. You are either riding on one side of the ridge or the other which causes a constant lean and a constant tendency to turn to the side.
Looks like your new tire is a good tread design for a unicycle.
