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  1. #1
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    tire width/tire diameter/rim width questions

    On my 2018 Fuel EX 9.8 27.5 + bike I am running 2.8 Nobby Nic tires on Bontrager Pro Line 40 mm carbon wheels.

    I recently upgraded to a carbon crank in a 170mm length vs. the stock 175 mm. I was looking for more pedal to ground height.

    I am thinking of going to a 2.6 wide version of this tire. I am looking for the following information.

    1. Is a 40 mm wide rim too wide for a 2.6 tire?
    2. What is the tire diameter differnce between the 2.6 and 2.8 sizes? One soure of information shows a 5.08 mm diameter or 2.54 mm radius. With the shorter crank width, this would still gain me 2.46mm more clearence for my pedals.

    Anyone have any facts, opinions or real world observations.

    I emailed Schwalbe with these questions, no answer yet.
    2018 Trek Fuel EX 9.8 27.5 plus
    2012 Trek Madone 4.7

  2. #2
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    Static diameter gets to be not useful because tires squish down. Over a bump, you can easily hit your rim depending on pressure. If you do, your effective diameter is the rim diameter, regardless of your tires size unweighed.

    If you want tons more clearance, ditch any debonair type can for a standard can.

  3. #3
    NedwannaB
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    I'd say no wider than 35 internal for a 2.6 or you'll expose too much sidewall I would think.
    Wait whuuut, who did he tell you that!?!?....

  4. #4
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    Swap that bike over to 29 x 2.6 you will have plenty of pedal clearance

  5. #5
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    Quote Originally Posted by JMac47 View Post
    I'd say no wider than 35 internal for a 2.6 or you'll expose too much sidewall I would think.
    This is my recommendation too. 40mm internal is borderline too wide for 2.8 tires, IMO
    2008 BMC Fourstroke 19-559 ISO (RIP in peace)
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  6. #6
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    Where's eb1888 to tell us about his 1.5 bonty tires on 50mm rims??

  7. #7
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    Quote Originally Posted by One Pivot View Post
    Static diameter gets to be not useful because tires squish down. Over a bump, you can easily hit your rim depending on pressure. If you do, your effective diameter is the rim diameter, regardless of your tires size unweighed.

    If you want tons more clearance, ditch any debonair type can for a standard can.
    When you mention the effective rim diameter, do you mean the 27.5" rim diameter?

    What static diameter are you referring to?

    I think the concern is the rim width vs. tire width, not wheel diameter.




    Also, I have a 2.8" tire on 40mm rims (factory setup. The same 40mm rim is used for a 3.0 tire.Without personal experience I think dropping to a 2.6 would be a bit of a narrow tire for the 30mm rim width. It seems like a poor pairing combo but again, I don't know that I've read any reports of others having tried it.

  8. #8
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    It sounds like the OP is concerned about pedal clearance, so total overall wheel and tire diameter.

    Static as in unweighed on the bike just sitting there, inflated. A 1.95 tire is significantly shorter than a 3.0 tire. The diameter is easily an inch shorter... but if you run them both low enough to get a rim strike, they both strike in the exact same place and your pedal-to-ground distance is then identical.

    So sure, a 27.5 plus wheel is basically the same size as a normal sized 29er unweighed, on the trail is really not. For the OP, his choice of downsizing is technically going to be a shorter tire, but on the trail? Eh, Id call it a wash and focus solely on everything else, like how it handles on that rim. In the chunk, you could easily be losing that extra height hitting rocks and compressing both tires.

  9. #9
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    Thanks for the feedback guys.

    I agree that static tire/wheel height might seem irrelevant on the trail, but as a point of reference, it is relevant. What I mean by that is for my current setup, the amount of pedal strikes is reasonable. My recent change to a 170mm length crank, gained me 5 mm static BB clearance. According to Schwalbe, the 2.6 tire is 10mm on the diameter smaller than the 2.8. So, this 5 mm shorter on the radius would offset the shorter crank arm, still speaking of static conditions. So, from a static standpoint by effective BB height would be the same as stock and I am ok with that. The big unknown remains the amount of deflection difference between the 2 tires sizes in real world application on the trail.

    As far as tire size to rim width, Schwalbe sent me information that shows a recommended rim internal width of 30- 40 mm for a 2.6 wide tire. Also, since I just purchased a set on Bontrager Pro Line 40 carbon wheels, going to a different width or diameter isn't an option.

    Based on the above, I may try a set of either Bontrager or Schwalbe 2.6 tires.
    2018 Trek Fuel EX 9.8 27.5 plus
    2012 Trek Madone 4.7

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