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.”

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“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.





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.