pressure

bails_89

Hello all,
I am running conti gravity’s front and back. I know they arnt the best tyre but they will do for now. I am running the back at about 18 psi and the front around 15.i went out with some m8s the other day and their tyres felt so hard. I weigh about 11 and a half stone if that makes any difference.

My question is,are my tyres to soft? And what do you guys run yours at?

Iv had no problems running them at this pressure but it just made me think.
thanks cb

supersonic

Yes, that is far too soft! You risk the tyres rolling of the rim, and rim and tyre damage.

You want a minimum of 25psi really. Experiment from there.

At 12 stone, and similar tyres, on my XC bike I run 35-40psi on hard ground, sometimes 30 psi.

sniper68

I weigh 13.5 stone and run 36R,30F.in summer i up it to 42R,36F

bails_89

ok sweet guys,thanks for the help.

il crack them up 2 30psi and have a little play around with from there:)

SiPaton

Bails89,

Always run your front tyre 3-5psi lower than your rear.
This will give you better grip on the front as more tyre is in contact with the ground.
The rear 95% of the time follows the front thus you can get away with a higher pressure. This will reduce the chance of pinch punctures and will accelerate fast!

Cheers.

Si..

Chevie

Well am a total beginner an i pump mine up to 55psi, i got FAST TRAK LK on my new rockhopper am weighin in at 17st an a bit more, are mine whacked way to hard then?

I just thought harder the better being a big lad

mudsucker

i weigh 13ish stone and i usually run about 35-40 psi. A lower pressure will give you more grip with more tread on the ground but more rolling resistance. A higher pressure will give you less grip in the mud but also less rolling resistance. Also, if you run them too soft you will get loads of pinch flats (or snakebites) where the tube gets trapped between the rim and tyre when hitting the ground. Best thing to do is have a play and find a happy medium.

Maximoos

mudsucker wrote:

A higher pressure will give you less rolling resistance

Not quite true, only applies for roads.

Check out these facts and stats here, they were produced by physicists for a very well known tyre manufacture Schwalbe, really interesting recommend you all reed in.

http://www.bicicletta.co.za/Downloadable%20Docs/Rolling%20Resistance%20Eng%20illustrated.pdf

Max

sniper68

Chevie wrote:

Well am a total beginner an i pump mine up to 55psi, i got FAST TRAK LK on my new rockhopper am weighin in at 17st an a bit more, are mine whacked way to hard then?

I just thought harder the better being a big lad

A riding mate weighs about the same as you,he runs his below 30.

supersonic

Maximoos wrote:

mudsucker wrote:

A higher pressure will give you less rolling resistance

Not quite true, only applies for roads.

Check out these facts and stats here, they were produced by physicists for a very well known tyre manufacture Schwalbe, really interesting recommend you all reed in.

http://www.bicicletta.co.za/Downloadable%20Docs/Rolling%20Resistance%20Eng%20illustrated.pdf

Max

It does depend on the tyre design. The results have varied with other brands. What we can say is that a tyre will have the least rolling resistance with a specific pressure (and rider weight) on certain surfaces.

Bigger tyres also weigh more, and have higher air resistance. This is why XC racers still use narrow, higher pressure tyres for weight and total resistance savings.

jadamson

on my kendas they say from 40-65 psi! surely 30 would be way under?!?

supersonic

Not neccessarily. The manufacturers like to play it safe with the ranges - not too little to cause pinch flats, or risk them rolling off the rim, not too high for them to explode.

Experiment see what works best for you.

Vivid

supersonic wrote:

Not neccessarily. The manufacturers like to play it safe with the ranges - not too little to cause pinch flats, or risk them rolling off the rim, not too high for them to explode.

Experiment see what works best for you.

+1

They should be used as guidelines only. My current tyres suggest 35-80 psi. For road use i usually aim around the highest psi 80, however for trails atm with the wet and slippery conditions i am running 30 rear and 25 front. Experiment and see what suits your style of riding.

bellys

i ride with 30front and 35back im 15stone.

Mattbot2

7 stone. 65 rear. 60 front.

Mmm.

I let them down to about 45 / 40 when i'm going off road though. Had them at 35 / 30 in the snow.

smackmypitchupǃ

15 stone.

At least 50psi both ends.

MeddlE

Something I've had to get used to coming from BMX is the lower tyre pressures. I run 100 - 120 psi on my BMX for skatepark use so initially pumped my tyres up to their max psi on the Kona. That was a mistake.

Anyway, Maxxis High Rollers, 26", 40-45psi front and rear. Plenty of grip and still good rolling.

smackmypitchupǃ

ibbo68 wrote:

Chevie wrote:

Well am a total beginner an i pump mine up to 55psi, i got FAST TRAK LK on my new rockhopper am weighin in at 17st an a bit more, are mine whacked way to hard then?

I just thought harder the better being a big lad

A riding mate weighs about the same as you,he runs his below 30.

which sounds silly IMO.. his rear wheel must look flat when he's on it. I'm 15st and could never run my rear that low without risk to the rim and even on the front I'd be wary.

Northwind

It depends on the tyres too, stiffer sided tyres need less air for the same support since the tyre itself will do some of the work- the horible wire bead Factory XCs that came on my bike are pretty stiff, when I got it I rode it before checking the pressures and afterwards it turned out it was at 20psi :shock: It felt soft, but not softer than say my folding carcass nevegals at 35, which is my usual.

SiPaton

Talking XC routes then building on what I said above about the front tyre being at least 2-3psi softer than the rear and taking into account your all running single ply xc tyres:

Your average 12st guy should ride:
Front - 30-40psi
Rear - 35-50psi

Lighter or heavier then go down or up on the pressures stated.
(For DH you would take 10psi off the above figures)

On a damp wet day for extra grip you can always let a bit more out, will meanmore tyres is on the ground for maximum grip though will offer noticeably more drag.

Out on a dry hard trail then wack up those pressures, fast rolling and less grip but it's dry so you should still be able to corner on a dime!

Just remember the less tyre pressure the more grip and the more chance to pinch puncture! Running dual ply (thick side walled tryes) allows you to run lower pressures and thus more grip and the reduced chance of pinch puncturing.

If your ever at a DH race in 2009 then pop over and i'll explain all in person!

Cheers.

Si..

Stephen-Hawking

Fantastic thread guys, I'd always assumed a direct trade off between rollong resistance (effort on my part!) and grip - on all surfaces, clearly not. Time to let out some gas :oops:

Banned!

I run my tires at 40psi for getting there and down to 30f 35r once Im there.

I will sometimes run them as low as 30, but only when im riding with 2 tires each wheel. this gives a much wider gripping surface and less chance of pinches. it does make then heavier, but the upshot of this is a bigger mass and rolling weight so a little more speed without much loss of control.

mtbikerboy

i'v never heard of two tyres being run on 1 wheel. is this something that people do commonly or is it just you? (unless you didnt mean at the same time)

Banned!

no, I often run two tires on the same rim.

cut a 1/4 inch off the sidewall (each side) of a worn or slick/semi slick tyre and put it inside your proper tire. it can take a bit of welly to get them onto the rims if theyre narrow, but once theyre on pinch flats are a thing of the past. you might need to cut a little off the tires circumference too to make it fit snugly, but do this a very little at a time. theres no use running 2 tires if theres a big gap at one point on the rolling surface.

this does make them a bit heavy but you can run them at a lower pressure and not have to worry about punctures so much. the downside is that if you do get a puncture its a hassle fixing it, but anything that will win you a flat will probably take the rim out too.