Different tire size front and rear.?

[Bernard Duhon]

 

 

Gang,

In my quest for fitting the largest tires my frames will take, I have put a larger tire on the front 38 mm of my 700 C and 35mm  in the rear.

 

On my 650 B conversion of a 700 C bike I have a 42 mm in the front and a 38 mm in the rear.

 

The larger tire is 3.5 mm taller than the smaller tire on an unweighted bike  

I suspect the lower tire pressures would result in an even smaller difference when I ride  the bike.

 

In any event I have noticed little difference.

 

Am I missing something here?

 

Bernard

 

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[daxo potato]

because of a bulging sidewall i had to put my spare on the rear during a ride. it's a 38, replacing a 42. I was surprised at how slight the size difference was from the front which is a 42. this does drop the back end slightly, resulting in a slightly different head tube angle and trail. i am not particularly sensitive to trail and can't say i notice the difference. i am, however, sensitive to the top tube no longer being perfectly level. this actually bothers me a great deal, and i shake my head and vow to do something about it some day, and i go back to riding.

so: a perfectly level top tube is what I'm missing. your mileage may vary.

Dave "level top tube" in NY

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[Tim Tetrault]

I've been wondering about this myself, with the Schwalbe Marathon being taken over by the "Green" Marathon- it looks like a 35mm tire is no longer offered, only a 37mm. I have a pretty slack headtube (Sam Hillborne from Rivendell) so I'm just going to run it. 

Tim in Seattle

[njh...@gmail.com]

Several decades ago I had a touring bike with 27" wheels. About 20 years after I acquired it, I managed to bend the front rim, and by that time none of the local bike shops were still carrying that size of rim - everything had switched to 700c - so I put in a spare 700c wheel I had and lowered the brake blocks a few mm. I rode it around like that for quite a while, and can't recall that I noticed any difference in the handling.

The 700c and 27" tyres were much the same width, so with the smaller front wheel the front end was a few mm lower than previously.

Nick Payne

[Harry Travis]

Can we do the math? 38 vs 42mm tire.

4mm / 1000mm wheelbase.

That is, by my measurement, the difference in slope of fore vs aft location of the rear axle in a slanted rear dropout. (Somebody please explain those to have only known  thru-axles) haha.

(Yes, I am ignoring great non-linearity in the effect of the load at the end of the 410-440 mm chain stays. )

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Harry P Travis

17.4.1

On Apr 1, 2024, at 12:56 PM, njh...@gmail.com <njh...@gmail.com> wrote:



Several decades ago I had a touring bike with 27" wheels. About 20 years after I acquired it, I managed to bend the front rim, and by that time none of the local bike shops were still carrying that size of rim - everything had switched to 700c - so I put in a spare 700c wheel I had and lowered the brake blocks a few mm. I rode it around like that for quite a while, and can't recall that I noticed any difference in the handling.

The 700c and 27" tyres were much the same width, so with the smaller front wheel the front end was a few mm lower than previously.

Nick Payne

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[lena...@gmail.com]

On Monday, April 1, 2024 at 1:35:00 PM UTC-7 travis...@gmail.com wrote:

Can we do the math? 38 vs 42mm tire.

4mm / 1000mm wheelbase.

You asked for it ;-)

arcsin(4/1000)=0.23... 

That is roughly a quarter of a degree of change in the pitch of the bike or a quarter of a percent in terms of gradient.

[JSO]

What Sheldon has to say - a number of years ago, I wanted wider tires (35 or 38 at the time) on one of my bikes for a tour that involved some badly paved roads. It turned out that the front clearance was fine, but not the rear. So I looked up what Sheldon had to say and happily used a wider tire on the front, noticing nothing.

Mixing/Matching Tires

Most bikes come with identical tires front and rear. This is all right for general use, but if you want to optimize your bike, you should consider using different tires front and rear. The front and rear tires have different loadings and different requirements.

• Narrower Front, Wider Rear

  If lightness is the primary goal, tire width/weight is limited by the risk of pinch cut flats, a.k.a. "snake bites." Since there is more weight carried on the rear tire, you can get away with a slightly narrower tire in front than you can in back.

• Wider Front, Narrower Rear

  A wider front tire makes sense in many applications, however, when handling and ride comfort are considered. A wider tire will generally provide better cornering traction than a narrower one, assuming appropriate inflation pressure.

  A wider tire also provides superior shock absorbency. I personally prefer a slightly wider tire in front, since I suffer from some wrist discomfort on occasion.

• Off-Road Issues

  Bicycles that are used some of the time on loose surfaces often benefit from a wider front tire, with a fairly aggressive tread, coupled with a somewhat narrower, smoother rear tire.

  The wide, knobby front tire will provide the all-important front-wheel traction. Front-wheel skidding almost always leads to a crash. For riding on soft surfaces, such as sand or mud, a wide front tire is essential. If the front tire sinks in and gets bogged down, you're stuck. If the front tire rolls through a soft patch OK, you can generally power the rear through to follow it.

  The narrower, smoother rear tire will have lower rolling resistance. Since most of the weight is carried by the rear tire, rolling resistance is more important on the rear than the front. If the rear tire slips, in most cases the worst that will happen is that you'll have to get off and walk.

  This is a great idea that developed out of BMX racing.

  Some mountain-bike tires come in matched sets, with different tread front/rear. The front tires tend to have the knobs set up more or less parallel to the direction of travel, for improved lateral grip and better steering control. The rears tend to have transverse knobs for driving/braking traction.

Joan O.

Arlington, VA

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