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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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.





Time to ride.

23 01 2016

Sloppy, slimy and slick. Thick mud and treacherous rocks. Teflon coated roots. It is winter, after all.

The hodag needed very little time to find it’s way to my heart. It rides lighter than it would seem. Feels kinda sporty-like. It replaced a chupacabra on a nextie 50mm rim so the weight gain is in the region of 360g or so. I never felt like I was struggling with the girth though. And the grip…oh the grip!

Those sipes and spaced out blocky tread make for a very secure front tyre. Granted, with a 45mm internal rim, the profile is round, but at 9psi I had bite everywhere I needed it.

The diameter is 20 mm or so less than the chupa. It *was* noticeable. The roll over a 29+ has is a boon. I missed it in some places. But the chupa struggles in mud…not so much on slick surfaces: the compound is great and offers security.

The hodag clears well and keeps coming back for more. It did not fold under and I suspect I will end up lowering the pressure a touch just to see how it feels, though it absorbed chatter and square edges with aplomb.

Yeah, like it.





No pressure.

25 09 2015

A recent mtbr thread (I know, I know…) got me thinking…

Here is my input on a thread about ‘plus’ tyres…

“So I got to thinking about this a bit more. I dont know too much about the physics, but I do know I like the combination of a higher volume tyre at lower pressure for my relatively low speed, reasonable tech riding on a hardtail or rigid bike.

Why is that?

Considerations for tyres (and/or wheels):

Comfort
Control/traction
Rolling resistance
Puncture resistance
Rim durability
Weight

My thoughts:

a) Lower pressure = more comfort given the same casing construction

b) A bigger volume tyre feels similar to a small volume tyre at less pressure (pounds per square inch…I guess it is self explanatory) given similar casing

c) Less aggressive tread gives less rolling resistance given the same casing construction and size (I don’t know how true, but for rolling resistance of pick up truck tyres, 60-70% is often associated with the tread design)

d) Increased hysteresis can lead to increased rolling resistance (‘tacky’ DH tyres anyone?)

e) Increased hysteresis gives more traction (‘tacky’ DH tyres anyone?)

f) Less tyre pressure is unlikely to make you slower (increase rolling reistance) given the range that is realistic for bikes. It is also, probably, unlikely to make you faster if considered in isolation

g) Bigger volume tyres create a bigger foot print in general, though pressure and casing design affects this

h) Bigger foot print is associated with more traction

i) Lower pressure tyres can lead to pinch flats with tubes, and rim strikes

j) Casing design can be beefed up (specifically on the sidewall) to mitigate this, but then the tyre becomes less supple – see hysteresis

k) Casing design can reduce or promote sidewall wear and piercing type puncture risk

So: a bigger tyre volume, with a lower pressure, and less aggressive tread might provide similar or better traction than a smaller, narrower tyre.

It might roll at the same speed (or perhaps faster if the tread allows) and it might be more comfortable.

If it is made well – with good quality casing – it might not wear fast or be at risk from punctures and it might not be too heavy.

Given the whole light strong cheap triumvirate, it is unlikely to be inexpensive.

Depending on how you load the tyre this may be a *good thing*. If it is more likely to flop around on the rim (too narrow a rim, or just high bulbosity) and is used in a high speed/direction changing terrain, it might feel more vague. This is probably why enduro racers/DHers are using no more than 2.5” tyres I suspect.

I guess that, in a nutshell, is why I like ’em?

Now – I am no expert – this was purely typed as a vague self assessment. I’d love to hear if anyone else has any thoughts on all this.”





Fire and ice.

1 02 2015

What a beautiful day! Arctic winds have kept the temperature very low since the last snow fell, so everything is crunchy with very little standing water. After a grim but brief cold, I was feeling pretty human today. Out the window, the sun was glinting off the ice covered trails and so I took off to mess around in the woods.

Recently, I have been trying to ride the singlespeed as much as possible – as a strength building exercise. I used to ride singlespeed exclusively, so I notice the lack of torque I can produce since dabbling with shifters again. Today, on account of being a snotty mess so recently, I reached for T.N.T with it’s super low ratios.

It was interesting to ride a full 29+ bike after spending the majority of the last few weeks aboard a 27.5+/fat or 29+ hybrid. I am sure in time I will come to more concrete conclusions on the whole thing. I used the opportunity to scope out some newish lines in the woods and I also took along my fire steel and knife with a view to a mid-ride fire to warm the cockles.

It escapes me if I have mentioned this previously or not, but over the last few months I have been practicing making fire with a fire steel and natural, found tinder. The purpose originally was simply to acquire a potentially useful ‘backcountry’ skill. Lighting a fire with natural tinder is pretty easy when everything is dried out, but considerably more difficult when all I can scavenge is sopping wet kindling, old man’s beard or bark. Unfortunately, this is likely to be the case when I might be most in need of a fire

Practice, practice, practice though, eh? I forget – is it 10,000 hours it takes to become an expert? Ray Mears has a unique style of presenting, but you cannot fault his ability to raise some flames when needed. I have tried and failed several times on account of wet silver birch bark and not using a stone under the tinder to stop it drawing up moisture from the ground. Toady, it lit with the 3rd strike of the fire steel and due to diligent prep with my Mora, I had plenty of kindling to keep the bugger going. warmth was welcome, today, indeed.