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):

Rolling resistance
Puncture resistance
Rim durability

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.”




11 responses

25 09 2015
dave macdonald (@davechopoptions)

Was just talking to a bike dealer about this. I think it suits two camps.
The passenger camp who also benefit from FS bikes for the same reasons – 1) comfort and 2) traction.
2nd camp is those that like low speed tech where the 1)traction and 2) comfort are beneficial. FS bikes don’t help here as the dynamic geometry alters too much, and the smaller higher pressure tyres don’t offer the same deformation/traction as 3″ tyres.
For fast aggressive riders, the tyres would need more supportive sidewalls and more pronounced shoulders which would take them into 1.3kg tyre territory, which rules them out.

25 09 2015

Yup! Good points! I’m looking forward to trying the 800g Rekon though… 800g seems too good to be true- makes me wonder if some sort of new molding or casing material is being used?

25 09 2015

I’m with you on some of this. I’m sold on Plus for hardtails. My hardtail of choice is now a Solaris running 275 Plus on 2.8’s. More comfort/traction/monster truck effect for little or no increased weight or rolling resistance with the right tyre choice (currently Trailblazers, but looking forward to WTB’s slightly more aggressive tyres for the front) .

However, I’ve been doing a bit of work recently running 275 Plus on the FS and I definitely don’t like it as much, and is even more sensitive to tyre pressure combined with shock setup. Hand waving now, but I ‘think’ that on the FS I’m going that much quicker and the suspension allows me to load the tyres that much harder than the hardtail that the tyres are more liable to squirm and move due to their high volume, so you have to look at heavier, draggier constructions which brings the downsides to the fore (the Bridger 3.0 is WAAAAY slower and heavier than a Trailblazer, and despite the extra grip I’m not sure it’s worth the downsides on the rolling and weight), or run higher pressures which nullifies the potential advantages. I think particularly with longer travel suspension I found the impact on the comfort much less marked than on the hardtail (obvs really) and the additional grip offset by the slightly odd interaction between tyre and suspension meaning I didn’t have enough feel in what the bike was doing to commit to corners. Trying to even vaguely get my head around the physics of modelling the tyre and suspension together to tune them as a system (the way they do on cars) makes my head hurt a lot. Straightline monster trucking and slow speed rocking crawling is awesome, but as you say, anything involved high lateral loads doesn’t seem to be ideal. More work to be done……..

30 09 2015

good thoughts cy!

29 09 2015

I think that much of your love for the Plus thing comes from your die-hard hardtailness. The comfort factor is less important on a susser as you have shocks for that, same for some traction too, so why add an extra inch of inpredictable, undamped tyre to the equation? For a hardtail, I get it, though. But hey, who rides those these days? 😉 (About 50% of our readers it seems…)

30 09 2015

defo chipps. i would struggle to see how a plus tyre would be a good thing on a good sus bike. maybe they will work on the tyres and get layups sorted, but i would be surprised if it really takes hold….adam was right on the money, i suspect?

30 09 2015

I totally agree with the break down of the + tyres when using a rigid or Hardtail bike but throw trail conditions into the equation and almost the opposite applies.
Suddenly that soft fat tyre becomes a big balloon when trying to ride wet greasy trails, surely a slightly harder narrower tyre would become the ultimate compromise?
Or is tyre choice always going to be one big compromise?

30 09 2015

do you mean that a lower profile tread is more likely to slip on greasy trails despite the footprint? you could be right….there is definitely compromises on these things. I love a low profile tyre for the speed they give but i also crave the grip my MAxxis DHF 2.5’s give!

1 10 2015

Only had 2 crashes this year, both my front Surly Bud sliding out from under me trying to ride straight line over a waterlogged mud hole. In some slippy clay like mud even an aggressive fat tyre will fail where a skinny (2″) mud tyre will cut through and grip fine. Ive gone off the idea of +tyres on a FS bike, sticking with a hard-tail for Fat/+.

1 10 2015

I think similar experiences are where my comment stems from and strangely enough with the same tyre
Looking at swapping out for a Dirty Wizard when I can finally find one but also now dabbling with a 650b wheelset as there seems to be a wide range of knobble/width combinations to go at
Maybe time to move somewhere dry and dusty and avoid the constant dilemma 🙂

11 10 2015

For hard tail wider is better – gone slowly over the years from 1.9 to now where I have a hans damp 2.35 on my lynskey HT. For bikepacking I tried a fat bike (but so slow for 96%of the time despite the fun of never picking a line or floating over mush) but now going to build up rigid 27.5 Genesis with 2.8 tyres. On full suspension rigs you don’t need the width as initial compression bumps are dealt with in shock.

Leave a Reply

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

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

Google+ photo

You are commenting using your Google+ 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 )


Connecting to %s

%d bloggers like this: