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  1. #1
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    Back to Basics: What width tire?

    Sorry for such a basic question, but after ten minutes searching this forum, I feel more confused rather than more educated! Im riding a 26er full rigid SS. Im not a weight weenie, but I definitely like the feel of a lighter bike when manualling over bumps or hopping around a switch-back. Im focusing on fairly quick XC riding over technical-ish trails. I do ride a fair number of stunts and sometimes I need to bail off them from a few feet up. No true AM or DH.

    I weigh 190lbs if that matters, and as this is a SS, I often need to mightily mash up hills.

    Im looking for a new pair of tires, probably Rocket Rons. Ive been riding Kenda Slant Sixes and Small Block 8s in 2.1 width, but honestly I never stopped to think about whether larger or smaller tires would be better.

    Should I consider a wider tire up front? Both tires wider?

    Thanks in advance...

  2. #2
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    Personally I don't think you should go any smaller than a 2.1", I've ridden many of the same trails that you have and on 1.9" tires it's not fun. Sure the smaller tire is a bit lighter but it doesn't feel any faster and the compromise in traction, flat resistance, and ride quality isn't worth it at all. I am significantly slower on my local loop using my set of 1.9" Specialized Team Control/Master than a 2.1" set of Ritchey Z-Max tires from the same era, both were XC race tires.

    I'd say stick with a 2.1 or go to something in the 2.2 - 2.25 range for both tires, you probably won't notice the weight and I doubt it'll slow you down, but it'll give you a bit more room to experiment with tire pressure to gain some additional comfort & traction.

  3. #3
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    For your information, it is fairly well established that all being the same (tire type, pressure etc.), a wider tire has better rolling resistance and better traction. Here is an explanation from Schwalbe.

    I therefore generally use the widest tire I can fit into my frame without interference. The only negative is more weight but I don't really notice a few ounces.
    The trouble with having an open mind is that people will insist on trying to put things in it.

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    Quote Originally Posted by Ronnie View Post
    For your information, it is fairly well established that all being the same (tire type, pressure etc.), a wider tire has better rolling resistance and better traction.
    A wider tire at the same pressure will have lower rolling resistance but there's no reason to believe it will have more traction. The contact patch size is the same and it's of identical design, as per your example.

  5. #5
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    Quote Originally Posted by craigsj View Post
    A wider tire at the same pressure will have lower rolling resistance but there's no reason to believe it will have more traction. The contact patch size is the same and it's of identical design, as per your example.
    Yes, you are technically correct but the wider tire affords the flexibility to reduce pressure and increase traction. You can substantially reduce the pressure before reaching the rolling resistance of the narrower tire. According to Schwalbe:

    "Rolling resistance:
    At 2 bar a 60mm wide tire rolls as well as a 37 mm tire at 4 bar."

    The trouble with having an open mind is that people will insist on trying to put things in it.

  6. #6
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    Quote Originally Posted by Ronnie View Post
    Yes, you are technically correct but the wider tire affords the flexibility to reduce pressure and increase traction.
    But you didn't say at reduced pressure, you said at the same pressure. To your credit, your conditions were specific. It wasn't a technicality.

    Once you reduce pressure, it's hard to make such simple generalizations. One of the greatest values of a wider tire is in using reduced pressure, which isn't the same as saying it works better when you don't.

    There are multiple things that contribute to rolling resistance. Some are improved with lower pressure, others are improved with higher pressure. Optimizing is more complex than people want to believe it is.

    Schwalbe's marketing pseudo-science isn't going to help the conversation any. Taking their word as gospel contributes to poor understanding. Their goal is to get people to use big tires and low pressures. That's good advice for many but not for all circumstances.

  7. #7
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    So are you folks suggesting, "Wider tires and lower pressure?"

  8. #8
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    Quote Originally Posted by raganwald View Post
    So are you folks suggesting, "Wider tires and lower pressure?"
    Yes

    Exceptions might be if you are very light or ride relatively smooth trails, neither of which seem true for you. Sometimes the fastest XC racing tires aren't the widest.

  9. #9
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    Quote Originally Posted by craigsj View Post
    But you didn't say at reduced pressure, you said at the same pressure. To your credit, your conditions were specific. It wasn't a technicality.

    Once you reduce pressure, it's hard to make such simple generalizations. One of the greatest values of a wider tire is in using reduced pressure, which isn't the same as saying it works better when you don't.

    There are multiple things that contribute to rolling resistance. Some are improved with lower pressure, others are improved with higher pressure. Optimizing is more complex than people want to believe it is.

    Schwalbe's marketing pseudo-science isn't going to help the conversation any. Taking their word as gospel contributes to poor understanding. Their goal is to get people to use big tires and low pressures. That's good advice for many but not for all circumstances.
    I'm not going to get into a protracted argument but I'd like to know if you have any non-pseudo-scientific rationale that contradicts what they say. I do know and have read in German magazines articles that they in fact do dynamometer testing to back up the claim. Why would their goal be to get people to use big tires and low pressure? There is after all only about $5 difference in the retail price of say a 2.1 Racing Ralph compared to a 2.35. Also, I definitely don't see their interest in getting you to use lower pressure as marketing hype. We are after all talking about mountain bike tires used off road. I see no disadvantage (ever) to using a pressure low enough to allow the tire to form to obstacles instead of bouncing off. Obviously that "lower" pressure is personal, dependent on rider weight, speed and tire width.
    The trouble with having an open mind is that people will insist on trying to put things in it.

  10. #10
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    Quote Originally Posted by Ronnie View Post
    I'm not going to get into a protracted argument but I'd like to know if you have any non-pseudo-scientific rationale that contradicts what they say. I do know and have read in German magazines articles that they in fact do dynamometer testing to back up the claim.
    I do and have posted it here on MTBR before. The problem isn't that the overall idea isn't good, it's that their data is poorly done and doesn't support their assertions. Mostly it's that they present an anecdote as scientific evidence.

    Quote Originally Posted by Ronnie View Post
    Why would their goal be to get people to use big tires and low pressure? There is after all only about $5 difference in the retail price of say a 2.1 Racing Ralph compared to a 2.35. Also, I definitely don't see their interest in getting you to use lower pressure as marketing hype.
    Because it's what they believe. Also, using lower pressure isn't their marketing hype, claiming they have tests that prove it is. I believe in their conclusions generally, just not universally, and the problem is that they over-simplify.

    Quote Originally Posted by Ronnie View Post
    We are after all talking about mountain bike tires used off road. I see no disadvantage (ever) to using a pressure low enough to allow the tire to form to obstacles instead of bouncing off. Obviously that "lower" pressure is personal, dependent on rider weight, speed and tire width.
    Right, but that's much different than the "lower pressure is always faster off road" dogma that's repeated here often with inevitable links to the Schwalbe paper as proof. What you just said is excellent advice.

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    There is so much voodoo in tire pressure and width, that I'm not sure anyone really knows what's going on with it these days.

    For a road bike, I think everyone can agree that skinnier tires mean more aerodynamics, and as a result, better rolling resistance AT HIGHER speeds. Contact patch area, as many will state, is the same for skinny and fat tires at the same pressure. For pressure, on a smooth surface, higher pressures are more favorable, until the pressure stops providing vibration dampening, at which it gets actually worse than underinflation. So for a road bike, the moral of the story is a skinny tire for drag resistance, and middle-of-the-road tire inflation. 80~110 depending on rider weight. Most cite the optimal pressure @ 15% sag study, though some refute this claim.

    On the mountain bike, I don't even really understand the benefit of a fat vs. skinny tire anymore. Wide tires have less rolling resistance at a lower pressure, but more weight. So, what's the performance ratio of rolling resistance to weight? Is the rolling resistance on a low pressure fat tire outweigh the weight loss?

    I'd like to see someone do a scientific test with controls where rolling down a rooty decent from a stop, with skinny vs fat tires, to see which setup rolls farther.

    It seems like the only tangible benefit I can qualify to the classic fat front/skinny back setup is that the rear will breakway first in the corner (due to being more rounded profile), giving a more predictable feel.

    The physics of all of this sure makes my head hurt.
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  12. #12
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    On sharply uneven surfaces, conformance is vey important, so personally I want softer tires on rougher terrain such as roots and rock gardens. Even though contact patches have the same surface area on flat surfaces, I wonder if the softer tire wraps round the root more than the harder tire?

    If so, bigger sounds better for rough, technical trails.

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    Quote Originally Posted by raganwald View Post
    On sharply uneven surfaces, conformance is vey important, so personally I want softer tires on rougher terrain such as roots and rock gardens. Even though contact patches have the same surface area on flat surfaces, I wonder if the softer tire wraps round the root more than the harder tire?

    If so, bigger sounds better for rough, technical trails.
    But then is there even any disadvantage on hardpack with a big tire, other than straight up weight? And if the lower pressure of the wide tire gives you less rolling resistance, does it make up for the weight gain? (i.e. is there really a tangible benefit to skinnier tires on a mtb, when aerodynamics are no longer a concern?)
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  14. #14
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    on my HT i liked the feel of a big (2.35) tire on the back to soften the ride a bit, helps take out some of the chatter. (my personal experience).
    I also like to add I just switched from a 2.3 tire that weighed 900g to a 2.4 that weighs 565g. So you dont always have to add weight with a wider tire, I have lost some traction but it is definately faster rolling.
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  15. #15
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    Quote Originally Posted by raganwald View Post
    On sharply uneven surfaces, conformance is vey important, ..............
    If so, bigger sounds better for rough, technical trails.
    YES!

    My 2:
    For a hardtail, I always go with the biggest rear tire that will fit in the frame.
    And the smallest knobs your terrain will allow.

    Bigger tire = lower pressure / better traction / softer ride

  16. #16
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    Quote Originally Posted by raganwald View Post
    Sorry for such a basic question, but after ten minutes searching this forum, I feel more confused rather than more educated! Im riding a 26er full rigid SS. Im not a weight weenie, but I definitely like the feel of a lighter bike when manualling over bumps or hopping around a switch-back. Im focusing on fairly quick XC riding over technical-ish trails. I do ride a fair number of stunts and sometimes I need to bail off them from a few feet up. No true AM or DH.

    I weigh 190lbs if that matters, and as this is a SS, I often need to mightily mash up hills.

    Im looking for a new pair of tires, probably Rocket Rons. Ive been riding Kenda Slant Sixes and Small Block 8s in 2.1 width, but honestly I never stopped to think about whether larger or smaller tires would be better.

    Should I consider a wider tire up front? Both tires wider?

    Thanks in advance...
    Personally, were I in your situation, I would find the extra weight of a big tire (up to 2.4 for sure, if they will fit) to be completely worth it. Lower pressure, better traction, more stable in the rough. On my rigid 29er, I went with a 2.25 in the rear (biggest that it would fit well) and 2.4 up front.
    15mm is a second-best solution to a problem that was already solved.

  17. #17
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    Quote Originally Posted by kapusta View Post
    Personally, were I in your situation, I would find the extra weight of a big tire (up to 2.4 for sure, if they will fit) to be completely worth it. Lower pressure, better traction, more stable in the rough. On my rigid 29er, I went with a 2.25 in the rear (biggest that it would fit well) and 2.4 up front.
    Update: I purchased a 2.4 and 2.25 Rocket Rons (one each), EVO and TL-Ready. They were 40% off at chain reaction with free shipping to Canada. The 2.1s came off and I put the 2.4 on the front. Its a MASSIVE tire. Honestly, I think I see a wider rim in my future for this tire alone.

    The 2.5 is also substantially higher volume than the 2.1 it replaces on the back. But it seems dwarfed by the 2.4. I have renamed my bike bigfoot. Both tires were installed tubeless. It took a fair bit of swooshing sealant around to get a seal. Since I had the sealant and tape out, I installed one of the 2.1s on my GFs bike. Shes now running a 2.1 Kenda Slant Six on the front and the 2.1 RoRo on the rear, both tubeless. The Slant Six looks bigger than the RoRo.

    Ive had two rides on local trails since then. The first was on dry-ish clay, somewhat loose. The difference in traction was startling. Most notably, I climbed a number of nasty switchbacks that had defeated me in the past. The bike is 2oz heavier overall, including the switch from tubes to tubeless.

    The second ride was on much wetter clay, and while there were some frustrating moments, overall the performance was amazing. One thing I noticed was that on descending switchbacks, I was taking the turns at the same speed, but I could do a lot more of my braking on the rear wheel, letting the front roll better. Felt good.

    Thanks, everyone!

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