29er grip on loose surfaces

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  • 29er grip on loose surfaces
  • Premier Icon johnnystorm
    Subscriber

    Been scooting up stuff like that here in France on my Fargo. You’d have to redo the same trail on the same tyres but on a 26″ to really compare. I just find that my 29er gets up stuff better than my 26″ did in all situations.

    Premier Icon roverpig
    Subscriber

    Yes, I’ve been doing back to back comparisons; riding the same trails on a FF29 and a 26″ Trance. Both shod with Nobby Nic Evo tyres running tubeless at the same pressure. The 26″ bike has 2.35″ tyres and the 29er 2.2″.

    Obviously there is a lot more difference between those bikes than the wheels and the 29er does indeed climb better, but it’s going down where it seems to be worse. On fast loose surfaces it just feels more likely to wash out. Actually it’s more than just a feel and has had me on the ground a few times. I’m trying t work out whether that is down to the geometry of the bike (combined with technique of course) or whether this is just an area where the 29ers don’t actually have any more grip.

    Careful with those kind of comments roverpig,you’ll end up facing the inquisitors on a charge for heresey.

    AlasdairMc
    Member

    So you’re comparing a hard tail with narrow tyres to a full sus with wider tyres? No wonder they ride differently.

    I’ve had no problems with grip on my El Mariachi, even with the rigid forks. It just seems to fly up everything as well.

    bikebouy
    Member

    Tyre pressures??

    I have a couple of fire roads on one of my trails and yes my back end scoots around a bit, but I’m 40psi on the rear.

    Premier Icon roverpig
    Subscriber

    Well I guess that’s my point really. The 29er HT feels less secure when going fast down loose rock/gravel surfaces than the 26″ full suss, but is that actually anything to do with the wheels.

    It’s often stated that the contact patch is longer and thinner on a 29er, but why is that. If me and the bike weigh the same and the pressure in the tyres is the same then obviously the contact patch area is the same. But why isn’t it just circular in both cases? Is it just that people tend to run narrower tyres on 29ers? Also, is a narrow contact patch actually what you want on fast loose surfaces?

    Premier Icon roverpig
    Subscriber

    So, 29ers should have more grip right? OK, I think I’m feeling that with my Kinesis FF29 on normal trails, but not on loose rock, where it seems to have less grip than a 26″ bike. I’m talking about trails where you are just riding on a carpet of small loose rocks (not gravel, but no more than fist size).

    Is this just a situation where a long thin contact patch is worse than a short fat one (more chance of being knocked sideways by one rock)?

    TooTall
    Member

    Wow – overthinkiing. You are trying to look at the difference in wheel size as the only reason why two totally different bikes don’t handle exactly the same, then project that across every bike with the same wheel size.
    Too many other differences – suspension being one (geometry being another etc etc)

    Premier Icon roverpig
    Subscriber

    No, I guess I’m no explaining this very well. I’m trying to find out whether this much quoted extra grip that you get with a 29er holds on all surfaces. My experience is that it doesn’t as I seem to get extra grip on most trails, but less on loose surfaces. I’m well aware that there are more differences between the two bikes than just the wheels, but they are the only data points I have access to. So, I thought I’d see whether other people (with different bikes) also experienced the same thing or not. Simple as that really.

    ojom
    Member

    You’ve fallen for the myths.

    You can’t say that all 29rs will have better grip. It’s a blanket statement which holds no weight as there are far too many other variables not just technically. The lump on top of the bike has the mot effect.

    Premier Icon jameso
    Subscriber

    I suspect what you may be feeling is shorter trail on the 29er, or the same trail on a larger wheel which can feel the same as less trail on a 26 when it comes to loose ground stability. Tricky to explain well tho. Try a slacker 29er to compare.

    Premier Icon roverpig
    Subscriber

    I suspect what you may be feeling is shorter trail on the 29er, or the same trail on a larger wheel which can feel the same as less trail on a 26 when it comes to loose ground stability.

    That’s interesting. I think trail is about the same (steeper HA on the 29er, but a bigger wheel). But why would it feel different with a bigger wheel and particularly on a loose surface? Is this something to do with the gyroscopic effect i.e. the way that, if you try to turn a spinning wheel about one axis it wants to try and move about a perpendicular one too?

    Mbnut
    Member

    You are saying that at speed on rough, loose ground your steep HA’d, rock hard rear ended, light weight, shorter wheelbased, smaller tyred bike has less grip than your less steeply HA’d, 125mm rear travel, heavier, longer wheel based, bigger tyred bike.

    All of the above will probably out weigh the wheel size.

    I have a 130mm travel 29er set up for trail abuse and it has grip aplenty but I would love a touch off the HA as on very steep, slippery terrain it can tuck under in corners, it is a size down from my usual size mind, so I have just one offset bush coming to tweak 1/2 degree off and drop 4mm off the BB….

    Compromise and tweaking are words that will forever be linked to mountain biking I reckon.

    Compromise and tweaking are words that will forever be linked to mountain biking I reckon.

    Really ? I’m quite happy that my mtb is set up exactly how I want it for the type of riding I do.I don’t tweak it,and it doesn’t feel compromised in any situation.

    I ride it, clean it, maintain it – repeat.

    xanboy
    Member

    When I changed from 26 to 29 the biggest thing I noticed was that I could run lower pressures in the 29er tyres. I dropped between 5-10 psi depending on the tyres. On my Rubber Queens I was running 25 psi on 29er and 30 psi on 26.

    TimCotic
    Member

    Roverpig, you can’t say that because your 29er hardtail is less secure downhill than your 26inch susser – that it’s the wheels size that’s responsible. I was hoping my El-Mariachi Ti would totally replace my DW Flux but it just can’t. When the speed gets high and the surface bumpy enough the El-Mar just can’t stay calm and in control like the Flux. Wheel size can only go so far in replacing suspension. In most situations the 29er hartail does a great job but it’s not a miracle worker.

    Tracker1972
    Member

    You have been doing back to back tests on totally different bikes, where the only thing in common is the tyre tread, and are trying to draw conclusions about the wheel size? For a start shouldn’t the larger volume 29″ tyres be at a (slightly) lower pressure? Bit like far bikes having much lower pressures, with much larger volumes? But that ignores the fact that it is a hardtail I guess…

    Remind me to reinforce fair testing in my next science lesson though!

    Premier Icon mikewsmith
    Subscriber

    Well I guess that’s my point really. The 29er HT feels less secure when going fast down loose rock/gravel surfaces than the 26″ full suss, but is that actually anything to do with the wheels.

    Well one has more suspension that the other. If I put 29″ wheels on a BSO would it be better than a nice 26″ bike?

    pjm84
    Member

    Desktop overthinking!

    Now if you said an issue with understeer on a 29er and didn’t compare it with a 26er I would have agreed.

    Both my Cannondale 29ers are / were plagued with understeer. A part of Swinley was horrendous and I think the general consensus was my body positioning. I thought it tyre, my mate, bars and stem. I’ve now cured this by running a HD 2.35 on the front. Same tyre as my mate. Amazed how much grip I now have compared to an RR of NN. XC hasn’t been this much fun.

    My AM 29er is fitted with Crest rims and an HD. XC is fine. Run down a steep run with cut backs and berms and its not right (I’m 16.5stone). It wants to run wide. I’m happy with the tyre so believe this to be a flex issue with the rim.

    Both have Lefties so it could be a possible attribute of the design?

    steve_b77
    Member

    One of them is a full suss, the other is a stiff alloy ht, the former will generate more grip regardless on loose rocky trails over the latter.

    Much in the way that my Anthem 29’er gets a boat load of traction on techy climbs, but my FF29 was (before I sold it) faster on smooth climbs.

    Premier Icon roverpig
    Subscriber

    Blimey, this is proving harder than I expected 🙂 Probably my own fault; I should have just asked the simple question “has anybody else found a 29er to have less grip than a 26er on fast loose surfaces?” and left it at that.

    I’m encouraged by everybody’s support for rigorous scientific testing. I wish some of our magazine editors shared this devotion to the scientific method. However, I’m not, as some people seem to be assuming, jumping to any conclusion based on a flawed test. Quite the opposite; if I’d formed a conclusion I wouldn’t need to start a thread.

    I’ve made an observation (one of my bikes feels less stable on fast loose surfaces than the other). I’ve formed a hypothesis (it could be due to the wheels). I don’t have the resources to test this hypothesis and don’t fancy my chances of getting a grant to do so. However, I can check to see whether other people have noticed the same phenomenon.

    Of course I could have started a thread about how my HT feels less stable than my full suss and no doubt everybody would have leapt to point out that my test was flawed because the wheels were a different size 🙂

    crosshair
    Member

    It’s because you’re carrying so much extra speed on the 29er 😉

    Bit like saying ‘4X4’s are better in the snow’ well yes, in places that’s true but they don’t stop any better down an icy hill.

    Premier Icon mattjg
    Subscriber

    Mr Pig, I fully understand we all enjoy our bikes in different ways, and I’m not unknown to a bit of detail obsession myself, but I’m with the chappies up there “thou doth think too hard”.

    Premier Icon mattjg
    Subscriber

    And FWIW I never noticed the fabled extra grip on my 29ers when I switched from 26. (But boy do I notice how well they roll. Or preserve momentum, in science speak, I suspect).

    yunki
    Member

    I,m freaking out because the grip on my 26″ hardtail is a bit less on loose turns than my 29″ FS.. This thread has blown my **** mind.. I,m going to take up lawn bowls

    Premier Icon ads678
    Subscriber

    Flat or crown green?

    steve_b77
    Member

    Indoor ftw

    Toasty
    Member

    I found they had more grip in a straight line, but have slipped out a few times unexpectedly leaning around corners. Both of these could just be due to the longer wheelbase I guess.

    Premier Icon mikewsmith
    Subscriber

    Just to freak you all out I have ridden 26 bikes that have different grip characteristics.

    Premier Icon roverpig
    Subscriber

    Thanks Toasty. I’ve also had a couple of front wheel washouts on the 28er and can’t recall any on the 26.

    Premier Icon paul4stones
    Subscriber

    28er? Blimey.

    Premier Icon mikewsmith
    Subscriber

    Andy Welch wrote:

    Thanks Toasty. I’ve also had a couple of front wheel washouts on the 28er and can’t recall any on the 26.

    28″ Is that when the 29 goes flat? That would explain it.

    In all seriousness not all bikes are equal, wheel size does not mean it has all the special characteristics listed in the press release. When I hear people sending 29″ bikes out for demo and when selling them here they are keen to point out that you need to ride them differently, especially when turning. Accept they are different and try and change the variable you can control (it’s located between the saddle and the bars)

    Premier Icon mboy
    Subscriber

    5″ of suspension travel both ends and slacker angles on the 26″ bike have a lot more to do with your confidence and grip going downhill than wheel size.

    29ers aren’t suddenly supposed to instill an amount of indestructibility in the rider, or make them descend like a god. 29ers are arguably quicker against the clock though, they’re marginally quicker most places and its usually evidenced by the clock.

    JCL
    Member

    26 V’s 29″ Stumpy Evo’s. 2.3 Ground Control Rear/Butcher Control front both bikes. Float 34’s and RP23’s on both bikes. Same bar with and very similar reach/stack. Approx 3-5psi less in the 29″ tires. Same trails and dry/loose conditions.

    Yeah the 29″ has more grip but more importantly is the way it breaks away. Much more feedback and predictability on the limit. But I do attribute the longer rear centre on the 29″ to be half of the reason fo the improvement. Bottom line is geometry has at least as much as an effect on performance as wheel size.

    Premier Icon jameso
    Subscriber

    That’s interesting. I think trail is about the same (steeper HA on the 29er, but a bigger wheel). But why would it feel different with a bigger wheel and particularly on a loose surface? Is this something to do with the gyroscopic effect i.e. the way that, if you try to turn a spinning wheel about one axis it wants to try and move about a perpendicular one too?

    Sorry, I made a simple and not too clear comment on something that’s not simple at all. I was getting at the relationship between tyre contact patch and trail on loose surfaces, it’s a bit like that tuck-under sketch I posted on your other thread. Your 29er is a HT so I expect it rides with a steeper front in those situations than the 26″ FS. you may have more weight over the front too. All that can make the front feel less secure on loose ground, particularly as the tyre sinks in a bit.
    Overthinking maybe, but trying to understand how bikes react and why isn’t easy.

    Premier Icon roverpig
    Subscriber

    Thanks jameso. I think you are on to something with the tuck-under and the way the HA steepens on the hardtail. I’ll give it some more thought.

    Overthinking maybe, but trying to understand how bikes react and why isn’t easy.

    What is this crap about overthinking? I can’t say I’ve ever looked at the world and thought “you know what the problem is here? too much thinking”. Of course it’s complicated, but that’s no reason not to try and understand it a bit better if you want to. Fair enough if you’d rather leave the theory to somebody else and just ride your bike, but I wish people would stop trying to tell other people how to enjoy themselves. Some of us enjoy thinking about stuff. It’s not (yet) a crime.

    Premier Icon roverpig
    Subscriber

    Yeah the 29″ has more grip but more importantly is the way it breaks away. Much more feedback and predictability on the limit. But I do attribute the longer rear centre on the 29″ to be half of the reason fo the improvement.

    Thanks JC. It’s always going to be hard to attribute the difference in feel to any one thing. A few people have mentioned wheelbase. The wheelbase on my 29er (FF29) is actually 25mm shorter than my 26″ (Trance). The chainstays are 10mm longer though (so presumably front centres are 35mm less on the FF29).

    Premier Icon jameso
    Subscriber

    What is this crap about overthinking?

    Yup. Often good to switch off but for some of us it’s interesting stuff to figure out.

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