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02-16-2004, 05:17 PM

Tony wrote:

> Hello, have a question that is puzzling me and I hope someone can
> help.
>
> I have a 99 Specialized StumpJumper Comp. I commute to work in
> Michigan, about 2.75 miles each way. It is cold out but the sidewalks
> are usually clear, maybe ride a little ice and packed snow at
> intersections.
>
> My question is my rear tires are getting these weird diagonal lines on
> the sidewalls where the tire just seems to be thinning out. This
> first happened on a Hutchinson Alligator. I only noticed it when a
> few of these wearing out bands got so bad that the tube was actually
> bulging out. So, I switched it out for a Specialized Dirt Master comp
> which is on a different rim. Now I am noticing the same wear pattern
> on this second tire.
>
> It is multiple diagonal lines that run almost the entire sidewall.
> They are spaced less than an inch apart and it just looks like it is
> wearing out. I thought at first it must be rubbing but I can't see
> anywhere that the tire doesn't clear the frame and the brake pads
> aren't far enough out to cause it. It is not abrasion from rocks or
> whatever because I am riding only on the sidewalks and roads, and only
> very occasionaly these aren't cleared of snow. Is it the cold?
> Haven't had any problems with the front tire though, still has the
> Hutchinson on it and no problems.

That is a fairly common failure mode for a modern nylon
casing bias tire. With use, notably with wide tires at low
pressures, the fabric simply comes apart. Notice how your
tire bulges out at the bottom? A wide tire without enough
pressure does that to a much greater degree. Casing flex,
taken to an extreme, pulls the layers of nylon thread from
each other and more quickly when the latex has dried and
flaked from the sidewalls.

As always, replace when the casing first gets lumpy, that
is, before the fabric actually rends. And you'll get much
better cornering and control with higher (normal, as written
on the sidewall) pressures anyway, on any hard surface such
as a street.

It's true that you get a wider footprint in loose material,
sometimes to very good effect in snow or wet mud, but we'd
consider that a temporary condition for most bikes.

--
Andrew Muzi
www.yellowjersey.org
Open every day since 1 April, 1971

02-16-2004, 05:17 PM	#18 (permalink)
A Muzi Guest Posts: n/a	Re: Bizzare Tire Wear Tony wrote: > Hello, have a question that is puzzling me and I hope someone can > help. > > I have a 99 Specialized StumpJumper Comp. I commute to work in > Michigan, about 2.75 miles each way. It is cold out but the sidewalks > are usually clear, maybe ride a little ice and packed snow at > intersections. > > My question is my rear tires are getting these weird diagonal lines on > the sidewalls where the tire just seems to be thinning out. This > first happened on a Hutchinson Alligator. I only noticed it when a > few of these wearing out bands got so bad that the tube was actually > bulging out. So, I switched it out for a Specialized Dirt Master comp > which is on a different rim. Now I am noticing the same wear pattern > on this second tire. > > It is multiple diagonal lines that run almost the entire sidewall. > They are spaced less than an inch apart and it just looks like it is > wearing out. I thought at first it must be rubbing but I can't see > anywhere that the tire doesn't clear the frame and the brake pads > aren't far enough out to cause it. It is not abrasion from rocks or > whatever because I am riding only on the sidewalks and roads, and only > very occasionaly these aren't cleared of snow. Is it the cold? > Haven't had any problems with the front tire though, still has the > Hutchinson on it and no problems. That is a fairly common failure mode for a modern nylon casing bias tire. With use, notably with wide tires at low pressures, the fabric simply comes apart. Notice how your tire bulges out at the bottom? A wide tire without enough pressure does that to a much greater degree. Casing flex, taken to an extreme, pulls the layers of nylon thread from each other and more quickly when the latex has dried and flaked from the sidewalls. As always, replace when the casing first gets lumpy, that is, before the fabric actually rends. And you'll get much better cornering and control with higher (normal, as written on the sidewall) pressures anyway, on any hard surface such as a street. It's true that you get a wider footprint in loose material, sometimes to very good effect in snow or wet mud, but we'd consider that a temporary condition for most bikes. -- Andrew Muzi www.yellowjersey.org Open every day since 1 April, 1971