tyre pressures?

welshkev

i've had about 7-8 punctures in about my last 12 - 15 rides, 2 of which were at afan on saturday!!!!

i run my tyres at between 35-40 psi, i got speaking to some guys whilst changing one of the punctures and they said they run theirs at about 25 psi. am i just running my tyre pressure too high?

i'm about 14 stone, i ride a felt compulsion 2 with the rear shock running about 160 psi

they're all pinch puncture/snake bite types by the way. :?

pyro_maniac

snakebites i would have thought not enough pressure in them
i run 50ish psi and i am 19 stone,lol
never had a snakebite though
(bet i get them all the time now...............)

nicklouse

http://www.bikeradar.com/forum/viewtopi ... e+pressure
http://www.bikeradar.com/forum/viewtopi ... e+pressure

welshkev

pyro_maniac wrote:

(bet i get them all the time now...............)

LOL

RealMan

If you get a snake bite every other ride while running 35-40 psi I think you may want to start looking at your riding style.

Try not slamming the bike down so hard, riding into rocks etc.


Else, the harder you pump them the less pinch punctures you will get. But of course it makes the bike ride horribly, huge rolling resistance, and low grip.


Tubeless is the answer..

welshkev

cheers nick,

i know you must see multiple posts about the same thing, thanks for pointing me in the right direction

welshkev

RealMan wrote:

If you get a snake bite every other ride while running 35-40 psi I think you may want to start looking at your riding style.

Try not slamming the bike down so hard, riding into rocks etc.


Else, the harder you pump them the less pinch punctures you will get. But of course it makes the bike ride horribly, huge rolling resistance, and low grip.


Tubeless is the answer..

cheers dude, yeah, i am a bit harsh i think, i need to try and be more fluid.

i think i'll definately look t tubeless aswell

Anonymous

i find i get less rolling resistance with hard tyres but my wheels bounce around a bit more and i have less grip.

i accidentally ran my tyres at about 27psi t'other day and found the bike superb, i had oodls of grip even when climbing on slippy rocks.

i only noticed the "mistake" when i got back and prepped my bike for the next ride and pumped the back tyre upto my usual 40psi. when i went for the following ide i found my rear wheel was spining out on the same terain. i let some air out and it made everything well behaved again.

i found what i lost by increased rolling resistance i made up for in grip both up and down.

i run tubeless by the way and it is the business.

furby

I just pump them up to 'just a slight squish' psi and not had any problems.

grumsta

What tyres are you using and how old/knackered are they?

I used to get loads of pinches with old-ish worn High Rollers. Got some new tyres and barely had a puncture since.

Also started running tubeless which means I can get away with 25 PSI, which is superb for grip - hate running really hard tyres.

Daz555

RealMan wrote:

Else, the harder you pump them the less pinch punctures you will get. But of course it makes the bike ride horribly, huge rolling resistance, and low grip.

Rolling resistance does not go up with increased tyre pressure. If anything it goes down. However, we'd be hard pressed to notice either way, as long as they are not stupidly soft.

Anyway I run about 40psi on the back and a bit less on the front.

rhyko7

welshkev wrote:

i've had about 7-8 punctures in about my last 12 - 15 rides, 2 of which were at afan on saturday!!!!

i run my tyres at between 35-40 psi, i got speaking to some guys whilst changing one of the punctures and they said they run theirs at about 25 psi. am i just running my tyre pressure too high?

i'm about 14 stone, i ride a felt compulsion 2 with the rear shock running about 160 psi

they're all pinch puncture/snake bite types by the way. :?

it sounds like you need to run taller tyres to me, i am guessing you are running small tyres 2.1's?

when i pump my rear tyre up i give it what i call the thumb bite test-i put my thumb under my opposite hand on top of the tyre then aggressively put all my weight on it, if i can push it ionto the rim i keep putting more pressure in until i cant push it in to the rim.

but if you run taller tyres you can run them at lower pressures without biting. i find a maxxis adantage 2.25 excellent at Afan on the rear cos its so tall.

Hercule Q

i run about 20-25 psi in maxxis 2.35s i'm 12 stone and this works perfect oodles of grip and when it lets go its really progressive

yoohoo999

i love the grip of low pressures, but i must have low pressure related OCD because I always think I have a flat!

welshkev

i run maxxis ignitors which are only 8 months old (came new with bike) the side walls aren't knackered as i've checked, i think they're 2.3's.

i think tubeless is the answer, i know they'll be another thread here somewhere but does anyone know a ball park figure for changing to tubeless?

RealMan

Daz555 wrote:

RealMan wrote:

Else, the harder you pump them the less pinch punctures you will get. But of course it makes the bike ride horribly, huge rolling resistance, and low grip.

Rolling resistance does not go up with increased tyre pressure. If anything it goes down. However, we'd be hard pressed to notice either way, as long as they are not stupidly soft.

Common misconception. Even met people who work in bike shops who still believe that.


As your tyre moves along the trail, it encounters obstacles - stones, sticks, bumps, etc.

If you have a lower psi, the tyre deforms better to these obstacles, and keeps on rolling forward.

If you have a higher psi, the tyre doesnt deform as well, and instead the whole bike is lifted up as it passes over the obstacle. This turns your forward momentum into upwards momentum, which isnt what you want, because it slows you down.

welshkev wrote:

i think tubeless is the answer, i know they'll be another thread here somewhere but does anyone know a ball park figure for changing to tubeless?

If you go ghetto, you can do it for about £20 probably. If you already have tubeless wheels, then less. If you want proper tubeless kit, then £60 ish. If you want tubeless tyres as well, then £60-70 for a pair of those as well.

Northwind

It's not that simple though, depends on the tyres and the surfaces you're riding on. And also on the bike to some extent.

BoardinBob

14 stone
Kevlar Fire XC Pros
25psi front and back
No punctures

RealMan

Northwind wrote:

It's not that simple though, depends on the tyres and the surfaces you're riding on. And also on the bike to some extent.

Obviously, but for 99% of rides I do on a mountain bike, lower psi = lower rolling resistance. I only ever pump them up hard for urban xc races. And then I only go to about 50psi, as any harder makes stairs feel pretty harsh.


Of course, if youre riding on road all the time, higher psi will help. So will a road bike.

BoardinBob

Northwind wrote:

It's not that simple though, depends on the tyres and the surfaces you're riding on. And also on the bike to some extent.

+1

Rolling resistance is best considered on a flat smooth surface. A low pressure tyre will have more tyre in contact with the road/ trail which results in more friction which increases rolling resistance.

A high pressure tyre has less contact with the road/ trail hence less friction and a reduction in rolling resistance.

Obviously on a real life trail it will vary throughout.

BoardinBob

http://en.wikipedia.org/wiki/Rolling_resistance

Rolling resistance, sometimes called rolling friction or rolling drag, is the resistance that occurs when a round object such as a ball or tire rolls on a flat surface

RealMan

BoardinBob wrote:

Rolling resistance is best considered on a flat smooth surface.

If youre riding on a lot of flat smooth surfaces, then youre on the wrong bike.

BoardinBob wrote:

A low pressure tyre will have more tyre in contact with the road/ trail which results in more friction which increases rolling resistance.

A high pressure tyre has less contact with the road/ trail hence less friction and a reduction in rolling resistance..

For the road part, you are correct. For the trail part, you are incorrect.

BoardinBob

RealMan wrote:

BoardinBob wrote:

Rolling resistance is best considered on a flat smooth surface.

If youre riding on a lot of flat smooth surfaces, then youre on the wrong bike.

BoardinBob wrote:

A low pressure tyre will have more tyre in contact with the road/ trail which results in more friction which increases rolling resistance.

A high pressure tyre has less contact with the road/ trail hence less friction and a reduction in rolling resistance..

For the road part, you are correct. For the trail part, you are incorrect.

Which is why I said

Obviously on a real life trail it will vary throughout.

But on a basic level, to equalise everything, rolling resistance should be considered on a flat surface in the first instance.

yoohoo999

^ no that's not a correct starting point.

rolling resistance is completely subjective

it's like using Fort Bill DH as a starting point for measuring the rolling resistance of some slicks on a road bike.

BoardinBob

Actually it's not subjective at all. A particular preference is subjective but the basic physics of rolling resistance and friction aren't open to debate!

RealMan

BoardinBob wrote:

But on a basic level, to equalise everything, rolling resistance should be considered on a flat surface in the first instance.

Well no, because thats a different type of rolling resistance to the one you encounter while mountain biking.

Some rolling resistance is to do with the rotational weight of the wheel & tyre. But this is a constant in all situations, so we will ignore it.

Rolling resistance on a flat surface is about the bonding of the tyre to the surface, and how much force is needed to break that bond. Think about when you put your hand on something, then take it away, you can feel your skin sticking to it slightly. So of course, the less rubber on the surface, the less force needed to keep rolling. Which is why you pump road bike tyres up hard.

Rolling resistance on a trail is about how much forward momentum is wasted going over obstacles. Which is why lower psi gives you less rolling resistance. Of course, some of the bonding between the trail and tyre does occur, but this is such a minimal amount compared to the loss of forward momentum over obstacles, that it is ignored.

yoohoo999

BoardinBob wrote:

Actually it's not subjective at all. A particular preference is subjective but the basic physics of rolling resistance and friction aren't open to debate!

my point is that it's utterly useless to calculate the comparative rolling resistance of different tyres by inflating them all to the same pressure and rolling them along a road.

what does that achive? what does it tell the commuter? what does it tell the trail blazer? what does it tell the DH racer? what does it tell the hucker? what does it tell the enduro racer?

it's pointless and provides no information that can be accurately translated by the people wanting to use the tyres - therefore it should be subjectively analysed.

incidentally, if you own the test bike and ride on the exact same test road with your tyres at the exact same test pressure and ride in the exact same style as the test rider/machine............then yes, your test is a great starting point

rhyko7

the difference in rolling resistance between xc tyres is no negligible that I barely notice it, sometimes a lower pressure tyre may absorb and roll over a bump as apposed to riding into it, hard tyres roll quicker on smooth ground, but I rather have less grip that snake bite every ride (tall tyres are the answer and way forward)
However the weight of the tyre has a much greater impact on how fast you can ride, this is much more noticeable between tyres.

RealMan

rhyko7 wrote:

snake bite every ride (tall tyres are the answer and way forward)

when you say tall tyres, you mean tubeless, right?

el loco pollo

Welshkev I used to have the same problem, it's a real pisser. After trying tubeless, it was ok but hassle, I now run thick DH tubes and my tyres at 25psi, no punctures for the last 2 years!

So you pay a bit in weight, but are you racing ?

stevieboy

I run 29 F and 32 R with tubes for racing, used to run 35 F and 40 R but felt like I was pinging off everything.

Wouldn't dream of running them any higher now, it's much faster overall.