3

Both sets of tires are from different reputable manufactures but the details are the same. ie Clinchers folding etc.

I recently changed my tires on a road bike, the clearance on top section of the rear seat stay was always very small with OEM wheels and tires. I would guess about 3-4mm.

I got new tires with the same specs from different manufacture and at the recommended psi the clearance from the top of the seat stay is about 1mm and I never noticed it while riding about 3k miles. But once i took it apart i noticed that the tire has been rubbing on the seat stay. I can see the paint has rubbed of slightly.

Update: picture below - hard to see because of brakes but the top of the seatstay is marked with red line and the top of the tire is marked with green line. enter image description here

Wheels are true!

8
  • What pressure is in the tyre? Do you have headroom to add a little more air? I wouldn't worry about some witness marks, as the tyre wears down there'll be a bit more room. However you don't have room for any larger tyres. (fyi this would be in the class of "fag paper clearances" if you're ever stuck for conversation !)
    – Criggie
    Aug 3 '16 at 20:27
  • 1
    Around 110psi for the rear.
    – nolawi
    Aug 3 '16 at 21:24
  • With that little clearance, I'd go with a smaller tire.
    – Batman
    Aug 4 '16 at 1:18
  • 2
    A 2mm difference in tire dimension between tires of different manufacturers and with different treads and specs is not at all unexpected. Aug 4 '16 at 1:27
  • 1
    Could also be your rims are a bit narrow for this size of tyre, so its fractionally taller than it would be on a wider rim. What's the frame made of? If it was steel I wouldn't care, carbon I'd definitely worry. If its aluminum... not sure.
    – Criggie
    Aug 4 '16 at 6:59
4

I'd check if the wheel was in properly and is in good condition (true) along with the tire being mounted properly on the rim.

There is some variation in tires true sizes despite being marked the same size, though half a cm would be a lot larger variation than one could reasonably expect, especially with older tires. Features like studs, knobs can also affect this. If you have reasonable clearance for a given size of tire, one should reasonably expect a similar tire from another manufacturer to also give reasonable clearance, though this is not always the case.

2
  • So are you saying the tire height could be different - around 1/4 a cm or 2-3mm?
    – nolawi
    Aug 3 '16 at 19:00
  • 1
    yes, unfortunately the tire sizing can change from manufacturer to manufacturer even though they are both 700 x 25. Although is should be very little, 2-3mm falls within that range.
    – Nate W
    Aug 3 '16 at 20:58
1

Yes, it is possible that the tires are sized differently. Tire manufacturers have become much more consistent in their sizing, but there are still small variations.

Part of the issue lies in the fact that tire profile changes slightly depending on the rim it is affixed to. Essentially, a narrower rim will result in a larger outer diameter and a narrower profile while a wider rim will result in the tire having a smaller diameter and wider profile. But since there is no standard rim size in the bike industry, upon which rim size do you base your measurements? Different tire manufacturers have settled on what they believe to be the 'best' or 'most true', but with no consensus, there's bound to be some inconsistency.

But that's not all. There's also a historical precedent (admittedly much diminished in the past couple of decades) of tire manufacturers intentionally LYING about their tire sizing. Why would this occur? Because having the lightest tire is a sales point. But what if your tire isn't actually the lightest one out there? Well, maybe your 23 is lighter than the lightest 25, and no one's going to pull out the calipers to actually CHECK. So, just change the number on the sidewall and happily claim to be the lightest "x25" tire in the world.

Interesting historical oddity: Why do we call tires that fit on 622mm rims "700c" (actual outer diameter ~660mm) and tires that fit on 571mm rims "650c" (actual outer diameter ~610mm)? Answers: http://www.sheldonbrown.com/tire-sizing.html#french

0

Short answer: Not necessarily.

Longer answer: Time ago wheels started to have more standard sizes (650b,700c) and at some point manufacturers made tires with a slightly lower size but labeled as standard, which still happens nowadays.

Judging by the picture, the tires you used are some Continental Grand Prix 4000 S II which are slightly bigger due to the ticker tire compound, and if you were to try some Continental Gator Skin from the "Same" size they would simply not fit (Since the ticker shell for extra puncture protection make them bigger than measured in most cases).

Still, that amount of clearance is pretty low and I have seen it only on aerodynamic frames which try to keep the turbulence at minimum by eliminating any gaps between components. If this is not your case, you may want to go with smaller tires in order to have some clearance (To avoid scratching or damaging the components due to any debris stuck in between).

-2

Car tires are specified with wheel size and aspect ratio ("height" of the tire). Bike tires are not, specifying only the wheel size.

Never heard this to be a problem in bike land though...

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