Equipoise.

7 12 2016

Fast and furious. The development of new* tyre sizes that is, not so much the covering of ground!

It probably goes without saying that I have enjoyed several years of messing with 29+, 27.5+ (or B+), 26 fat, 26 fatter, 27.5 fat (B fat) and even 27.5 (B) fatter. There have even been some options appearing with the 27.5 fat, not that my love for the Bontrager Hodag is in any way diminished.

I have also spent some time messing with mixed wheel sizes. Typically a bigger rim diameter on the front than the rear or a bigger tyre volume on the front than the rear.

Is it time for any conclusions?

Perhaps.

27.5×4.5 (the Bontrager Barbegazi – and recently released Gnarwhal) is the undisputed best in super soft conditions. The huge diameter and massive paw print is quite frankly remarkable. However, it is a HUGE wheel – over 770mm in diameter. This is bigger than 29+.

26 fat does an admirable job of not being too big, hefty or cumbersome but offering good floatation.

B fat (as I have become accustomed to calling the Hodag and the new Maxxis Minion DHF 27.5×3.8) makes an outstanding front tyre in combination with a 2.8 or full 3″ rear 27.5 tyre. These tyres both have insane traction, in crappy or dry conditions, but don’t add too much rolling resistance when paired with a faster rolling b+ rear tyre.

B fat as a rear tyre is tricky: both options are very knobbly tyres and as such, rolling resistance is relatively high. If this is not an issue, or indeed a bonus, fire away, with the same up front or even a Barbegazi.

29+ is the king of roll. The effect is more pronounced on the front than the rear, but there is no doubting a bigger diameter, relatively fast tread will cover (moderately rough) ground like nothing else. Special mention here must go to the Bontrager Chupacabra for being both light and seemingly durable. Not the most aggressive, but adequate.

29+ front 27.5+ rear appears (to me at least) to keep a lot of the benefits of the roll over of a f+r 29+ but – for an indefinable and physics-defying reason – feels a little more playful. about the only factor that can really make much of a difference given that some of my bikes will have the same stay length regardless of which diameter is in use, is the radius and therefore how the bike behaves over different amplitudes of hits. The bigger radius might also potentially change lean angle in cornering.

The more I read about this, the more confused I become. For starters, within the parameters of a bike, the weight of the rider far exceeds the bike and thus acceleration differences are likely to be negligible. Wheel stiffness and response are probably very, very small effects also.

The difference in gyroscopic force and moment of inertia between the sizes would seem to be too small to be detectable at the speeds we ride at (with the wheel weights we use) and the same would go for the difference in effect of acceleration with the torque that can be applied (see here for a nice, plain explanation of applying torque to a wheel and then consider the force a human can produce and the difference in wheel diameter/weight).

I have also always wondered if the gyroscopic force of a wheel *not* in line with the direction of travel affects how a bike feels (consider sitting in a rotating chair and holding a spinning wheel then twist this and you will spin around on the chair. Surely, when we tweak that move in mid air, the two wheels rotating affects your position in the air? and would a bigger wheel exert more force noticeably?

And what of B fat front? Can the added weight and girth be detrimental? particularly with the Hodag – which weighs little more than a robust 29er tyre – I believe not. The combo of low psi and ~745mm diameter (the same as a good size 29er) mean you get the low pressure smearing grip, the lack of knocks from impact and good roll over obstacles, too.

It makes normal 29ers feel like a ‘cross bike.

No doubt as more sizes become available, (I’m looking at you, 27.5×2.6) and more tread patterns are brought to market, I will refine my thoughts.

At present, B fat front/B+ rear or 29+ front/B+ rear is the best performing wheel combo for my riding.

*it all stems from the Gazzaloddi, right?

Advertisements

Actions

Information

5 responses

7 12 2016
Alec

Excellent. Doing the work for a few of us there. Really liking B fat front Hodag on the Farley, aiming for a 29+ wheel option for summer/ longer hauls.

8 12 2016
Chris

Great review & bang up to date information…..im running 29+ Chupacabra front & B+ Chupacabra rear on the Jones, really like the combination, fast & reasonable all-round grip. Though they have a squirmy feel if the pressures are too low, would like to try a tougher sidewall/lower pressure B+ on the front for rockier rides. Keep exploring – Chris

15 12 2016
Bryan

Thanks for that Jon. Just setting up a Jones right now and have gone for b+ front and rear and 29x 38mm front and rear but I guess there’s more decisions and options to work through. B.

18 09 2017
Gregorio

Hi, thanks for the info. What about barbegazi 27.5 front and 29 plus on the rear. I own a trek stache 5 (rigid fork). I´m looking for more comfy ride in the front. I ride rocky sections in my local trail. Dry conditions always. Your opinion advice please! Thank you.

18 09 2017
velopest

i have not run that combo myself, but dont see why it wouldnt work. when i have used 27.5+ rear, fat front (26×4) it worked pretty good….i imagine 29+ rear and b-fat front would be even better! hope it works for you!

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s




%d bloggers like this: