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  1. #1
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    Caution;  Merge;  Workers Ahead! Warning (29er geek talk): what happens to tires during corner lean?

    Please no “Just get out and ride” or “use the search” or “this has been discussed to death” etc.

    Gathering information across the interwebs and here on MTBR has partially answered the question, but I’m hoping to crowd source facts from riders here who have much more knowledge about the physical properties of different tire designs, compounds, and the dynamics of the physics involved.

    My personal goal is to find a tire that stays predictable in terms of handling while the angle of the bike relative to the ground decreases. Frame geo, bb height, fork type, etc all play a role. However, I’m talking specifically about the dynamics of tire shape while turning. Due to the high number of variables involved, let us limit the discussion to rim width/design, tire pressures, tire design, and tire tread life.

    The obvious:
    Sticky compounds grip better, but have a short tread life. Harder compounds grip less, but last longer. (Think auto tires or climbing shoes.)
    Rims with bead lock, e.g., Stan’s et al. can hold a tire to the wheel at a lower PSI compared to a tube setup.
    Larger knobs designed to dig in and grip the riding surface provide increased traction in loose conditions, the expense of weight and rolling resistance.
    Smoother tread design will grip less, weigh less, but provide better rolling resistance.

    The murky:
    For a given tire that is designed to balance tradeoffs of grip with rolling resistance, being ridden across a mix of surface types;
    In tire compound design, vulcanization prevents the polymer chains from moving independently. As a result, when stress is applied the vulcanized rubber deforms, but upon release of the stress, the tire reverts to its original shape.

    The level of deformation in shape due to compound design is difficult (for me) to conceptualize and isolate, from tire pressure and rim widths, all other factors being equal. Any good explanation on this? Links? What about tread life and durability?


    Predictability in corning is what I’m after.

    For example: Descending a moderate grade with relatively wide flat surface into a open type turn (say fireroad with a bit of loose over hardpack) no berm, coming in hot. Leaning forward to keep the front weighted, initiating early, weight on the outside foot, no breaking.

    What is happening to the contact patch and the shape of the casing? How much of the patch is loss due to the angle of lean of the entire bike? >10%? <10%? More lean= less patch?

    Would a higher PSI make a given tire more rounded on a standard rim width of 24.4mm (Arch)?

    Would the same higher PSI on a 28mm (Flow) rim result in the same tire having more contact with the surface? Better grip?

    Is the key tradeoff just/only tire pressure? More PSI= more rounded shape, more rolling resistance, less contact patch while corning? Less PSI = less rounded shape, less rolling resistance, more contact patch while corning?

    The ideal tire for me would very durable, predictable while leaning, high volume, and low rolling resistance, lightweight, and inexpensive. I know “pick any two”. I chose predictability and low rolling resistance as 1 and 2, durability as 3.

    Suggestions? Thoughts? Error of logic or omissions? Other considerations? Links? Thanks.

    PS- Tire shopping next week, as I will have lots of time to ride, due to the probable government shutdown.

  2. #2
    Nouveau Retrogrouch SuperModerator
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    Quote Originally Posted by swill'n
    Please no “Just get out and ride” or “use the search” or “this has been discussed to death” etc.

    Gathering information across the interwebs and here on MTBR has partially answered the question, but I’m hoping to crowd source facts from riders here who have much more knowledge about the physical properties of different tire designs, compounds, and the dynamics of the physics involved.

    My personal goal is to find a tire that stays predictable in terms of handling while the angle of the bike relative to the ground decreases. Frame geo, bb height, fork type, etc all play a role. However, I’m talking specifically about the dynamics of tire shape while turning. Due to the high number of variables involved, let us limit the discussion to rim width/design, tire pressures, tire design, and tire tread life.

    The obvious:
    Sticky compounds grip better, but have a short tread life. Harder compounds grip less, but last longer. (Think auto tires or climbing shoes.)
    Rims with bead lock, e.g., Stan’s et al. can hold a tire to the wheel at a lower PSI compared to a tube setup.
    Larger knobs designed to dig in and grip the riding surface provide increased traction in loose conditions, the expense of weight and rolling resistance.
    Smoother tread design will grip less, weigh less, but provide better rolling resistance.

    The murky:
    For a given tire that is designed to balance tradeoffs of grip with rolling resistance, being ridden across a mix of surface types;
    In tire compound design, vulcanization prevents the polymer chains from moving independently. As a result, when stress is applied the vulcanized rubber deforms, but upon release of the stress, the tire reverts to its original shape.

    The level of deformation in shape due to compound design is difficult (for me) to conceptualize and isolate, from tire pressure and rim widths, all other factors being equal. Any good explanation on this? Links? What about tread life and durability?


    Predictability in corning is what I’m after.

    For example: Descending a moderate grade with relatively wide flat surface into a open type turn (say fireroad with a bit of loose over hardpack) no berm, coming in hot. Leaning forward to keep the front weighted, initiating early, weight on the outside foot, no breaking.

    What is happening to the contact patch and the shape of the casing? How much of the patch is loss due to the angle of lean of the entire bike? >10%? <10%? More lean= less patch?

    Would a higher PSI make a given tire more rounded on a standard rim width of 24.4mm (Arch)?

    Would the same higher PSI on a 28mm (Flow) rim result in the same tire having more contact with the surface? Better grip?

    Is the key tradeoff just/only tire pressure? More PSI= more rounded shape, more rolling resistance, less contact patch while corning? Less PSI = less rounded shape, less rolling resistance, more contact patch while corning?

    The ideal tire for me would very durable, predictable while leaning, high volume, and low rolling resistance, lightweight, and inexpensive. I know “pick any two”. I chose predictability and low rolling resistance as 1 and 2, durability as 3.

    Suggestions? Thoughts? Error of logic or omissions? Other considerations? Links? Thanks.

    PS- Tire shopping next week, as I will have lots of time to ride, due to the probable government shutdown.
    The contact patch area is entirely dependent on the inflation pressure and load. That does not change significantly with tire design. Deformation is affected by the casing construction, inflation pressure, rubber compound, tread shape, rim width, and load applied (at least).

    How the tire performs depends on the tread design, terrain/surface, and riding style. One one tire can work everywhere for every rider.

    Different tires work better for different conditions, but even on the same trail two riders can have the same tire perform very differently.

    The rim width has more affect on the tire profile than pressure. You use pressure to adjust grip and stability. I usually want my tires to be as soft as possible without feeling squirmy in hard cornering.

    Some tread designs and tires work better, or worse, on different rim widths. I find the wider Kenda Nevegals to track and corner poorly on rims narrower than ~27mm. But the similar Panaracer Rampage does fine on narrow or wide rims.

    Then you need to pick the tread design that works for your conditions and riding style. If you like to progressively lean the bike into the turn, a tread with good transition/intermediate blocks will give the consistent feel you want.
    The "gap tooth" tires (open groove between center and edge knobs) will feel like you are falling off a ledge as you lean. They are designed to be thrown into the corners.

    The ideal tire does not exist, especially because there are so many variables in mtbing. But look at the "my new favorite tire" thread on this board.
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  3. #3
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    Knob design and tread pattern will have a big effect. Knobs that are too tall and/or not supported well enough will squirm under pressure and make the tire feel vague or even move around under you. Plus, if the tread pattern just isn't right for the terrain the other parts won't matter too much.

    I've really enjoyed the Specialized Purgatory 2.4 as a front tire in Bidwell. Big volume, rounded profile, chunky tread with big cornering knobs that don't squirm, tubeless-ready bead, tough casing, not too heavy, rolls surprisingly fast for a chunky 2.4" tire.

    I recently picked up a Wolverine 2.2 and it has worked well for cornering grip as a rear tire. It's a tall 2.2 with lots of volume but not nearly as chunky as the Purg 2.4. The large number of cornering blocks way out at the edge have held pretty well on fast off-camber hardpack, as as the redone section going out after the Toilet Bowl

    I see you've been using Ardents front and rear. What sizes? I liked my 2.25 Ardent ok up front, but the short and sparse transition knobs meant it had little grip in the turns unless you made sure to lean the bike well. It didn't feel that tough either; more like a racing tire with a bit more grip.

    Those are my preferences and my feelings at least. YMMV

    I totally understand your quest for solid cornering. Too often I used to feel unsure in fast turns but with my current setup I'm getting much more than just some baseless feeling of confidence from having more tire than I need. I can definitely feel the difference when I throw my bike into a turn that now it plants its feet like a big NBA center and wants me to dig in and push against the ground. Me likey

  4. #4
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    @boomn We ride the same trials so I appreciate the info. I've been riding Purgatory 2.4 front, Captain 2.2 rear. The captain felt fine at first but now it's worn down and feeling unsafe only after 200 or miles and I'm not a hard breaker, if fact I rarely skid at all. I try to keep the trails nice for everyone else too. The main issue is with the lava cap, I think it kills rear tires really fast just from climbing. May try the Wolverine 2.2 to replace the Captain and see if I get better mileage out of it.

    I too have been enjoying the Purgatory 2.4 as a front for the same reason you discussed. It's got another month of riding life left. Once it expires I think I want try the 2.2 version to see if I can speed things up a bit, but then the corning could suffer, and I would have to lower the PSI, resulting in a moot point. Trial and error I guess.

    @shiggy "a tread with good transition/intermediate blocks will give the consistent feel you want." Yes. This is what I need to look for. I think a rear tire that incorporates these design features would fit the bill perfectly. I may try the Rampage as a solution. Off to re-read the New Favorite Tire Thread. Thanks.

  5. #5
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    Glad to help. I must have been looking at an old pic because I didn't realize you had switched tires. Good to know I'm not crazy for loving that Purgatory.

    As for the Rampage, I used the 29er version for a while and the 26" version before that. Lots of miles on those in Bidwell. It's a nice all-around tire that will have predictable grip in most trails conditions and when it did lose grip it was never without warning and often salvageable too, but the grip won't blow your mind and it's actually a somewhat slow tire. My Ardent 2.25 felt like a rocket compared to the Rampage.

    That Panaracer CG XC in the thread Shiggy is referring to does look like an awesome rear tire for our kind of trails. I'm very curious to try one

  6. #6
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    Quote Originally Posted by boomn
    Glad to help. I must have been looking at an old pic because I didn't realize you had switched tires. Good to know I'm not crazy for loving that Purgatory.

    As for the Rampage, I used the 29er version for a while and the 26" version before that. Lots of miles on those in Bidwell. It's a nice all-around tire that will have predictable grip in most trails conditions and when it did lose grip it was never without warning and often salvageable too, but the grip won't blow your mind and it's actually a somewhat slow tire. My Ardent 2.25 felt like a rocket compared to the Rampage.

    That Panaracer CG XC in the thread Shiggy is referring to does look like an awesome rear tire for our kind of trails. I'm very curious to try one
    Remember that feeling fast does not mean you are really moving fast. I have had tires that felt very fast, but the data graphs showed the opposite. They were "exciting" and on the edge of control, but the lack of grip did not let me reach the speed of other tires that did not slide around. Some of those "fast" tires would just rocket me straight off the outside of corners.


    The CG XC is more than just a rear tire.
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  7. #7
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    Quote Originally Posted by shiggy
    The CG XC is more than just a rear tire.
    I know, I was just saying that based on our shared enjoyment of the bigger Purgatory up front on our trails and his desire for a new rear tire. I'm not looking to replace my front tire any time soon, but I guess swill'n did mention looking for something lighter down the road. The side knobs look a little sparse but I guess that's no reason it couldn't still work really well, especially if the compound is really that good

    As for the speed of the Rampage I was just referring to rolling resistance on the straights. It cornered well enough here to certainly be considered a "fast" tire in that regards, whereas I was less confident with the quicker rolling Ardent and was often slower on certain fast, tricky trail sections because of that

  8. #8
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    Quote Originally Posted by boomn
    I know, I was just saying that based on our shared enjoyment of the bigger Purgatory up front on our trails and his desire for a new rear tire. I'm not looking to replace my front tire any time soon, but I guess swill'n did mention looking for something lighter down the road. The side knobs look a little sparse but I guess that's no reason it couldn't still work really well, especially if the compound is really that good

    As for the speed of the Rampage I was just referring to rolling resistance on the straights. It cornered well enough here to certainly be considered a "fast" tire in that regards, whereas I was less confident with the quicker rolling Ardent and was often slower on certain fast, tricky trail sections because of that
    I think I just need to get more variety. Purgatory 2.2 front and Captain 2.0 rear for general fire road and smooth singletrack riding. Purgatory 2.4 front and GC XC 2.25 rear for AM stuff. Going to see if it's in QBP yet, meanwhile I'll ride the Captain until it's toast. Moving to SoCal this summer, so having options in my quiver may help with the adjustment to the different conditions. Thanks for the help guys.

  9. #9
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    Let me reinforce a couple points and then add a few points.

    The tool tall knobs, like boomn stated, can be squirmy on harder surfaces. This also seems to apply to a tire design that is more square in cross-section than round. It kinda has an "edge". I don't like this type of tire because it seems to hold really well until it lets go all at once. boo. The old Panaracer Smoke is like that. boo. Round-section tires seem more forgiving that way.

    Transition knobs - I think everyone may have seen the Pinkbike video of some expert cornering perfectly. I am pretty sure he had Maxxis High Rollers (no transition knobs). I have tried that tire (FS 26er). It seems to work if you make hard, edgy turns. But if you're on a long sweeper the transition is right where the tire rides. boo. I couldn't make them work for my cornering style. In GA, where the trails are fairly wide and fast, I looped right out of a turn (like upside down). The tire just drifted right up and over what little berm there was. Granted, it was wet Georgia red clay, but I've done better with other tires.

    The tread design also plays a large role. Take an Exi-Wolf tire as an example. The angled tread near the edge of the tire only works in one direction. For my purposes it only works on the rear. I have tried it reversed on the rear and it only worked in a straight line. Uphill switchbacks were nearly impossible due to those little slivers of tread transmitting very little rearward traction (they point in the direction of your traction force like a point instead of across it like a bar). On the front I couldn't get it to do anything except stop in a straight line. Running it in the rear, in the "correct" orientation seems to do OK.
    Ignitors kick a55.
    And wayyyyy back when Tioga made the Farmer John, that tire provided the most predictable traction ever. I could pedal out of turns, drift, slide, and knew exactly what that tire would do no matter what the conditions. I don't know what made it so.

    Tire deformation - this is often affected by how much traction you can get. A tire that will not stick will not deform any further than what your weight causes. If you get a floppy (that is unstable, due either to low pressure, super-thin side walls, or whatever) tire, it will need constant attention and steering correction if you are traversing varying conditions of traction, esp. at higher speeds. They are also problematic on off-camber terrain. They are also more likely to roll sideways off the rim if you suddenly find excellent traction in a turn or if you need to make a desperate steering input.

    And lastly, if I'm not running Ignitors, I try to make sure I have more traction on the front tire than the rear. A washed out front end is tough to recover from, but a drifting rear tire is almost comfortable for me. Right now I have a RR2.4/Exi 2.3 (F/R), or the Ignitors. The RR2.4 would probably respond better if I had wider than a 23mm rim up front (hence I always have the Ignitors at the ready - I really want an Ignitor 2.3...along with a unicorn ). I def. want to try Ardent and Ikon but I'm cheap and seldom swap tires before they're worn out (unless they're just terrible). I don't often use soft compound tires either since I traverse a good bit a pavement to get to certain trails - I look for dual-compound tires (harder in the center), or slightly harder like the Ignitors.

    Hopefully you got something out of that.

    -F

  10. #10
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    Yep, options are always good. Among other tire options, I have a Dissent in the garage for the occasional time that I just really feel like getting stupid on Guardian

    Then again, having a second bike takes away some of the need to find a perfect set of tires that is somehow both XC and AM. You know you want to

  11. #11
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    Quote Originally Posted by boomn
    Yep, options are always good. Among other tire options, I have a Dissent in the garage for the occasional time that I just really feel like getting stupid on Guardian

    Then again, having a second bike takes away some of the need to find a perfect set of tires that is somehow both XC and AM. You know you want to
    What? Only two bikes each with just one set of tires?
    NEVER!
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  12. #12
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    Quote Originally Posted by boomn
    Yep, options are always good. Among other tire options, I have a Dissent in the garage for the occasional time that I just really feel like getting stupid on Guardian

    Then again, having a second bike takes away some of the need to find a perfect set of tires that is somehow both XC and AM. You know you want to
    Oh golly! Cats out of the bag! If and only if I've got a spare 2k plus. RIP, WFO, 429 territory. To do it right, I should get some flows too. I could potentially switch with the Arch's tires mounted. For now, I'm working with what I've got and saving up.

    Great tire wisdom so far. Appreciate the advice.

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