25mm tires. Faster than 23's for 100 KG rider?

Discussion in 'Cycling Equipment' started by PeterF, Jan 24, 2009.

  1. PeterF

    PeterF New Member

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    I have been using 26mm tires for the winter since the cold weather in the Northeast US has opened up some pretty big holes and cracks in the roads. I like the extra cushion to smooth out the roads. Apart from the smoother ride, I'm not entirely sure if they are slower. In fact they may be faster for me. I am a larger cyclist at 100-103 kg. The 26mm tires I'm using are not a race tire, but yet they seem to corner well and roll nicely. I'm considering using these in the summer and rotating out my 23's for 25's. Thoughts?
     
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  2. kdelong

    kdelong Well-Known Member

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    The common theory is that because the 26mm tire usually has a larger contact patch than a 23mm or a 25mm tire, it will also have more rolling resistance. When you start talking about specific tires, this theory goes right out the window. There are a lot of variables that effect the size of the contact patch and rolling resistance. Contact patches and rolling resistance of the same size tires varies from tire to tire, depending upon the design of the tire. Without getting too long winded here and venturing into subjects that I am not qualified to comment on, I'll just say that you should ride whatever feels best to you. Just remember, it is not the tire, or any part of the bike that makes you faster. It is YOU that makes you faster. You're doing the right thing though, riding through the winter!
     
  3. frenchyge

    frenchyge New Member

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  4. artemidorus

    artemidorus New Member

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    For track or very good quality roads, a smaller tyre at higher pressure will be faster. On rough roads, where you will bump around a lot at a tyre pressure high enough to prevent pinch flats at your weight, you would probably be faster with the 25mm tyres at a lower pressure.
     
  5. Phill P

    Phill P New Member

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    This is a very interesting point, and I agree with KDELONG. Ride what works for you.

    Look at Roubaix, they ride 25-28mm tires because they believe it makes them faster. Not only do they not fatigue as quickly and corner better, but the tires will roll over the rough roads faster. Same with MTBs. They went through a phase of narrow higher pressure (6kpa) racing tyres, then went tubeless and bigger with low pressure was better.

    Rough roads makes a different equation, I don't know if weigh makes that much difference, air pressure would account for weight changes.
     
  6. oldbobcat

    oldbobcat Well-Known Member

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    I think the theory for heavier riders going faster on fatter tires has to do with the pressure at the contact patch. The fatter tire, with a larger contact patch, exerts less pressure and hence less friction and less rolling resistance over the road. This seems plausible but I've never seen the numbers or done A-B testing.
     
  7. HandMeDownRider

    HandMeDownRider New Member

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    This slowtwitch article makes very good points.
    Does adding a kevlar insert change the "construction" of the tire and therefore the contact patch size? I would guess no, but it would affect other factors? Has anyone tried these and like to comment? I did have some in my touring bike and didn't have a puncture for a few thousand miles. I never compared to the ride without them though.
     
  8. oldbobcat

    oldbobcat Well-Known Member

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    It will certainly change the way the tire complies with surface textures and bumps in the road. Whether it changes it enough to compel you to stop using them is your decision.

    Our choices are driven by compromises. I prefer 23 mm Continental GP4000s; there are faster tires, but I like the longer wear, the stronger casings, the flat protection, and that they're a little fatter than most everyone else's 23.
     
  9. alienator

    alienator Well-Known Member

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    Adding kevlar to the carcass certainly does change the construction and thus the rolling resistance. Whether that's a substantive change or a change important to you is another matter. Does it change contact patch size? Technically, yes. Theoretically contact patch size is function of tire pressure and weight suspended by the tire. When you dig deeper, however, you see that weight is also suspended, a bit, by the tire carcass. However, the weight suspended by the carcass isn't generally considered because it is so small compared to the weight suspended by the air in the tire. You can however feel the effect of a stiffer carcass in its slightly less compliant ride at a given pressure compared to the ride of a more flexible carcass at that same pressure. Tires with higher thread counts tend to have more flexible carcasses and also lower rolling resistance. A tire with a thread count of 60 tpi (threads per inch) can be noticeably stiffer than a tire with 120 tpi. As oldbobcat indicated you need to determine what comprises you are willing to accept. Not having a robust anti-puncture layer will give a tire with less rolling resistance and better compliance at a given pressure, but that same tire will have reduced puncture and possibly cut resistance compared to a tougher tire. IMHO, the sweetest compromise is the Conti GP 4 Seasons tire.
     
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