Tire size mixing okay?

[Steve Sloan]

I have a bike I'd like to mix tire sizes on. I can't imagine why this would cause any problem at
all. Here's what I want to do:

I commute about 22 miles a day into downtown San Jose, CA. The transit agency, streets and traffic,
sewer, power and telecom folks seem to be competing with each other trying to see who can tear up
the streets the most! There are potholes and patches on patches. I cross six railroad tracks. I
carry a computer, books in my panniers plus my weight (total about 250 lbs) over this, the roughest
ride I do.

I have broken 2 frames, so far, please see:

http://homepage.mac.com/s_sloan/Show7/12.htm

A couple of weeks ago I hit a pothole and bent a rim (and it was a stout rim!) The rim was a Mavic
T220 with 36 14 straight gauge spokes and Top Touring 700x32 tires.

I replaced the bent rim with a bigger Mavic 520 with 36 14 straight gauge spokes. I am thinking
maybe if I increase the rear to 700 x 37 it will give me more of a cushion of air to protect my rim
and frame and support the weight better. My front tire/rim are in fine shape and have less of a
load. Is there a problem if I run a700 x 32 on the front with the bigger tire in the back?

--Steve Sloan [email protected]

 

[Sheldon Brown]

Steve Sloan wrote:

> I have a bike I'd like to mix tire sizes on. I can't imagine why this would cause any problem at
> all. Here's what I want to do:
>
> I commute about 22 miles a day into downtown San Jose, CA. The transit agency, streets and
> traffic, sewer, power and telecom folks seem to be competing with each other trying to see who can
> tear up the streets the most! There are potholes and patches on patches. I cross six railroad
> tracks. I carry a computer, books in my panniers plus my weight (total about 250 lbs) over this,
> the roughest ride I do.
>
> A couple of weeks ago I hit a pothole and bent a rim (and it was a stout rim!) The rim was a Mavic
> T220 with 36 14 straight gauge spokes and Top Touring 700x32 tires.
>
> I replaced the bent rim with a bigger Mavic 520 with 36 14 straight gauge spokes.

It was a false economy to use the cheap spokes. You would have been better to spring for butted
spokes--they're not that much more expensive, and result in a sturdier wheel.

> I am thinking maybe if I increase the rear to 700 x 37 it will give me more of a cushion of air to
> protect my rim and frame and support the weight better.

That sounds like a good idea.

> My front tire/rim are in fine shape and have less of a load. Is there a problem if I run a700 x 32
> on the front with the bigger tire in the back?

Nope. Theoretically it will raise the rear end of the bike by 2.5 mm, but that's insignificant.

I address the issue of mixing tires on one of my Websites, see:

http://sheldonbrown.com/tires.html#mixing

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| Asimov |
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Massachusetts Phone 617-244-9772 FAX 617-244-1041 http://harriscyclery.com Hard-to-find parts
shipped Worldwide http://captainbike.com http://sheldonbrown.com

 

[Paul Kopit]

On Thu, 20 Feb 2003 10:56:19 -0800, "Steve Sloan" <[email protected]> wrote:

>I replaced the bent rim with a bigger Mavic 520 with 36 14 straight gauge spokes. I am thinking
>maybe if I increase the rear to 700 x 37 it will give me more of a cushion of air to protect my rim
>and frame and support the weight better. My front tire/rim are in fine shape and have less of a
>load. Is there a problem if I run a700 x 32 on the front with the bigger tire in the back?

I don't think you'll have any problem unless the tire doesn't clear brakes or chainstays. I do it on
the tandem all the time and frequently on singles.

What's marked on the tires frequently doesn't mean much. My Panaracer Pasela 700x35 measures
700x31. My 700x28 Specialized measures 700x32.

If I were breaking stuff as much as you have, I'd consider a more rugged bicycle like a MTB with
some suspension.

 

[David Ornee]

"Paul Kopit" <[email protected]> wrote in message
news:[email protected]...
> On Thu, 20 Feb 2003 10:56:19 -0800, "Steve Sloan" <[email protected]> wrote:
>
> >I replaced the bent rim with a bigger Mavic 520 with 36 14 straight gauge spokes. I am thinking
> >maybe if I increase the rear to 700 x 37 it will
give
> >me more of a cushion of air to protect my rim and frame and support the weight better. My front
> >tire/rim are in fine shape and have less of a
load.
> >Is there a problem if I run a700 x 32 on the front with the bigger tire
in
> >the back?
>
> I don't think you'll have any problem unless the tire doesn't clear brakes or chainstays. I do it
> on the tandem all the time and frequently on singles.
>
> What's marked on the tires frequently doesn't mean much. My Panaracer Pasela 700x35 measures
> 700x31. My 700x28 Specialized measures 700x32.
>
> If I were breaking stuff as much as you have, I'd consider a more rugged bicycle like a MTB with
> some suspension.

I agree with both Sheldon and Paul. I would add that a quality suspension seatpost and front rack
with front low riding bags can help balance the load.

David Ornee, Western Springs, IL (riding with potholes, RR tracks, and other road hazards)

 

[Jim Adney]

On Thu, 20 Feb 2003 14:42:29 -0500 Sheldon Brown <[email protected]> wrote:

>Steve Sloan wrote:

>> My front tire/rim are in fine shape and have less of a load. Is there a problem if I run a700 x
>> 32 on the front with the bigger tire in the back?
>
>Nope. Theoretically it will raise the rear end of the bike by 2.5 mm, but that's insignificant.

Don't forget that the extra weight in the rear will remove at least some of this. He's actually more
likely to come out level this way. Not that it matters at all....

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Jim Adney [email protected] Madison, WI 53711 USA
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