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?

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The wheel deal.

22 06 2016

Well, I thought I’d share this set of images.

This is the Bontrager Barbegazi, at 20psi, on a Nextie 65mm external rim – 27.5×4.5 (770mm diameter and 115mm casing width, a few more knob to knob).

That’s big.

Compare to a fairly normal 29×2.2 MTN King.

Now, it is next to a Bontrager Chupacabra 29×3 (765mm diameter iirc).

Perhaps most interesting…next to a 26×4.5 Flowbeist (somethign like 745mm diameter – I think! might be 750mm)

As predicted, the Vertigo cycles fatty is a hoot with a 29+ front/27.5+ rear. I actually think it might be bad for my health. Just today alone, I crashed 3 times. Not because I lost traction, more because I was tackling obstacles at a greater speed than I am used to. As a result, I was landing closer to stumps, trees and other immovable objects than I am used to. Sometimes, too close! Interesting.

My curiosity will get the better of me though – I will pull the rear Chronicle in order to mount a Hodag so the bike will be more balanced when I put that Barbegazi on the front.

Oddly, the tape I use (3M 764) failed the first time I mounted the Barbegazi. The tape is 50mm wide so I did one wrap and then dry mounted the tyre, as I usually do, before addign sealant. In this case, the bead seemed to grab the tape on both sides and drag it apart, tearing it down the middle. I re-did it with a little sealant to lube the bead’s passage up the rim into the bead socket and it was golden. Live and learn.





Differential.

12 06 2016

I’ve been messing around with different sized wheels on the Jones for a while now. It has settled on a 27.5×3.8 (nearer 3.5 in reality) front and a 27.×2.8 rear. I like how a slightly bigger front wheel gives good roll over and a smaller rear seems to stay ‘tucked in’ and agile in the tight stuff.

My Vertigo Cycles fat bike has now got a new set of wheels as well. The front is a 29×3 and the rear is a 27.5×3.

The front wheel I have had for a while, shod with a Chupacabra; the rear with a 27.5 Chronicle complements it very well.

The build was as follows: Nextie Junglefox 2, with Sapim D light spokes, DT aluminium nipples and a DT swiss big ride 197 hub.

I followed the advice of Wheel Fanatyk and used beeswax to lube the nipple/rim interface. It worked very well indeed. The nipples are pro lock.

Tensioning was a bit of a mixed bag, it wasn’t quite as smooth as I had hoped and there is more than 10% variation on a couple of the spokes. Perhaps this was because I went with 2 cross due to the extreme bracing angle of the super wide hub and the stiff carbon rim. It seemed to tension very late and suddenly.

In retrospect, I might have gone 3 cross as this would lessen the angle of the nipple at the rim.

That or perhaps I should have used the pro head DT nipples, that are more spherical shaped and thus sit at extreme angles more easily.

I have a couple of hours on it. It seems to be fast, the rear doesn’t particularly feel smaller than the front in terms of roll over, but the bike as a whole is very manoeuvrable. The front is kicked back a touch and feels to have slightly light steering input. It gained a cm in height with the bigger radius over the Flowbeist.

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This wheel change is temporary to further evaluate the mixed wheel size: in time it will be mounted with a 3.8 Hodag rear and 4.5 Barbegazi front, which should be less of a differential.