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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Tyre Armageddon.

24 04 2016

At the end of the world, I wonder if the new Maxxis Minion 29+ will stand alone on the field of battle?

This picture, lifted from Vitalmtb, will serve as evidence to back my conjecture.

max_DSC4123

On the right, as you look at it, is a 27.5×2.4 Minion. Not a small tyre, by any normal standards. The other tyre is a 29×3 Minion.

Now *thats* what I’m talking about.





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.”





“The wide World is all about you…”

11 07 2015

Over the last few years, wide rims for bikes (road and mtb) have become more common. Back in the day, wide rims were the norm until a certain Mr Bontrager came along and re-rolled Mavic MA-2 rims from 700c to 26″ wheel size. Why? quality and weight: the aluminium rims were much lighter and easily as durable as the poor quality offerings available at the time specifically for mtbs. With wheels, there is always a balance point between tyre performance, weight and durability.

This re-rolled rim heralded a general move to sub 25mm external width rims. Tyres at the time were relatively narrow for the most part and with inner tubes, you were running 25psi+ in order to avoid (frequent) punctures.

Fast forward to Surly releasing the Pugsley with the ridiculous Endomorph tyre. Yes, DH bikes had arrived and wider rims and tyres were not unheard of, but they were too heavy for XC use for the most part. The Endomorph was designed for truly questionable terrain: snow and sand. Even with the 50-60mm trials or the Surly rims of the day, sub 10psi was a *maximum*.

My first experience of a Pugsley was riding hot laps on Shaggy‘s Pugsley at Bristol Bike Fest. The race course is baked dry, usually, in the summer and was very rooty with low amplitude rocks and rough trail in places. On the Pugsley, you could charge into the roots, overtake other racers in the rough next to the smooth line and bomb the descents with abandon.

There was definitely something to this.

In the proceeding years, I experimented with light tyres and lighter tubes as I moved to 29″ wheels. It was’t unusual for me to ride 600g tyres with 100g tubes. I flirted briefly with tubeless systems, but struggled to get my tyres of choice (Continental) to seal well. The sidewalls were very porous and the interface with the rim bead seat was loose.

In the end, I began to use a small amount of sealant inside very light tubes, but I’ll admit I was plagued with punctures.

Many years ago, I had procured a 50mm wide Uma ‘snow’ 29er rim. This was heavy, singlewall and of questionable strength, but it changed the tyre profile out of all recognition and if the interface had been better, I would have relished the low pressures I was able to run with minimal risk of pinching.

I stopped using this set up because the angle of the spokes combined with the relatively noodly rim made me suspicious it would fold in use. That, or the tyre would roll off the rim. Still, it was interesting.

Wider hubs, or at least flange spacing, make all the difference.

When Surly, again, led where others follow and produced the Krampus I knew I wanted to try the new, 29+ wheel size out. The raison d’etre for this frameset was fitting the, frankly, ridiculous Knard 29 ‘plus’ tyre. 700c but 3″ wide. Huge. Having messed around with Endomorphs and then Nate tyres on the front of my bikes for a few years and the brief spell with a wide rim and standard 29er tyre, the likelihood was that it would work well.

It was a game changer.

The full-on fat bike tyres of the time were heavy 1300-1800g. The Knard offered a lot of floatation, shock absorption and did so with a relatively small weight penalty over a normal 29er tyre: they weigh 1000g or so.

Yes, the sidewalls were thin and the tread pattern minimal, but in fairly short order there was reasonable choice on the market and with the Chronicle from Maxxis, EXO sidewall protection. 9psi and 35-50mm rims is a magic carpet ride for a rigid bike.

Syntace offered a simple exlpanation for the benefit of wide rims, which I would recommend reading, here. There is more discussion of value on the Open Cycles blog.

I started using carbon fiber rims a number of years ago as it is a fantastic material to make a light, strong, stiff rim from and this pays dividends particularly as the rims become wider. Indeed, it allows the whole ‘plus’ tyre thing to be fully realised. One of the main detriments of plus bikes is the added weight of the wheel at the outer edge. With the development of improved tyre-rim interfaces and tyre construction, tubeless is a snap. Light, wide rims paired with wide tyres make for a superb system for covering rough ground.

Lately, for 29ers, I have been looking seriously at Kappius’ offering, the 46mm external/40mm internal, cross country orientated KR-XCW-29, with a weight of 435g +/-15g and a good looking profile to facilitate tubeless set up. I have appended some links regarding the Kappius offering at the end of the post.

Things were turned round again with the arrival of the WTB Trailblazer, a 27.5+ tyre – in essence a 650b bead size, with a 2.8 to 3″ tyre, designed to retro-fit in 29er frames, but offer much of the benefit of the 29+ Knard. In the words of Bob Poor: “the idea was hatched in a seine skiff while catching 20,000 lbs of salmon every hour in the remote waters of SE AK”.

I am very glad Mark Slate at WTB took the idea on and had the tyre mould made. The 29+ is amazing, but in some instances the huge diameter is a slight hinderance. I’m going to come back to this; I have been having some interesting conversations with bike designers on the matter that do not feel concluded and I am also in the embryonic stages of working with Sean at Vertigo Cycles on a 27.5+ bike, perhaps like this one.

As much as you hear complaints that there are too many wheel sizes available at the moment, choice is a good thing to have.

“The wide world is all about you: you can fence yourselves in, but you cannot for ever fence it out.”

― J.R.R. Tolkien, The Fellowship of the Ring

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Kappius on facebook.

Kappius in Mountain Flyer.

Kappius on Fat-Bike.

Kappius on empty beer.

Kappius on Pinkbike.

Kappius on Vital mtb.

Kappius on Singletrack World.

Kappius on Cycling Dirt.

Kappius review on MarathonMTB.

Kappius on bikerumor.





Facts & figures.

9 07 2015

Spent 10 minutes measuring various wheel/tyre combos. Maxxis Chronicle 29×3″ on Nextie junglefox 50mm is 766mm at my riding pressure (9psi). A WTB Trailblazer on a Nextie 650bx50mm rim is 727mm and a Maxxis DHF 2.5 on a 30mm Enve rim is 742mm. The Nate on a HED BigDeal rim is 737mm at 18psi, which is higher than riding pressure. So it may drop a mm or two?

Why the measurements?

Fox announced a 27.5plus 34 fork recently and Rock Shox announced the Lyrik and Yari in a 27.5plus/29er casting as well.

The Fox is *likely* to have an a-c of ~532.8mm in a 120mm travel setting. This is an extrapolated figure as I could not find an actual a-c. for this fork. The 34 29er version from 2013 had an a-c of 542.8 for the 130mm travel model. Take 10mm for the reduced travel and you get the 532.8mm.

Now, add sag of 25mm, leaving an actual a-c of 507.8mm – but lets call it 508mm.

If I used a WTB Bridger or 27.5×3 Chronicle when they become available, the diameter is likley to be around 737mm or so – bit less than a good sized 29er – with me? so the radius is 368.5. Along with a 508mm a-c height this takes the total to 876.5mm.

The 29plus tyre diamter is 767mm so radius is 383.5mm. 876.5 minus 383.5 = 493mm. The a-c of some readily available carbon rigid forks, more or less.

A frame designed around this ride height could use a suspension fork with a 275×3″ front wheel or by swapping to a 29+ wheel, a rigid fork, with no real change in geometry.

Interesting, eh?

Oh, btw, the vinyl tape dropped 10psi in 24 hours without sealant, with sealant, no drop in 24 hours. Pretty stoked.

Edit: Fox tech specs are here. As you can see, the 120mm fork is 525.5mm a-c. This would put the equivalent rigid fork length at 485.5mm. Not bad at all. Oh, and the Fox 27.5+ fork fits 29+ it seems.





Semi-fat ?

16 02 2015

Plus? semi-fat? I’m not entirely clear what the nomenclature ought to be, but the ‘plus’ sized wheels are definitely here to stay.

As such, the range of useful components to build a plus wheel set is growing – rims and tyres.

After a fair amount of lurking around on forums, I decided to order up a set of Nextie hookless, semi-fat rims: 29″ front and 27.5″ rear. Both are 50mm wide and 34mm deep (if memory serves). They seem reasonably well made (more on this later) and are light for the sheer volume of the things. just above and below the 500g mark respectively.

I built them up today and mounted tyres. The weight saving was a mind boggling 300g for the front (1.3kg wheel to a 1kg wheel) and 150g (1.15kg to 1kg) for the rear. With an additional 200g for a tube on the front (albeit with 100g or so of sealant back in at both ends) the weight saving is 450g. This is at the rotating edge of the tyre so is keenly felt.

In addition to the weight loss the rear tyre ballooned. the casing on the 50mm rim is 73mm wide at 30psi and the tread sits at 61.5mm. obviously I expect the casing to shrink a little when the pressure is dropped to 10psi or so, but probably not much. Huge.

So, more on the build soon.