Tyre pressure survey

MonkeyMonster

thecrofter wrote:

Joelsim wrote:

My LBS put my new tyres on a few weeks ago and I asked what pressure, he said 100psi. Anyway a couple of months later I tested them, one was at 30psi, the other 35psi.

Needless to say they are now back at 100psi!

You only checked a COUPLE OF MONTHS later and you couldn't tell the difference between 35 ish and 100 ish without a gauge? :roll:

+1 that is odd... when mine are at 80 (down from 100) I can very easily tell that its all gone a bit spongey. 30 though?!

waddlie

Run 28s, pumped to 105 psi.

I always wonder, though - you know when the pump/valve does the little pssst thing when disconnecting? Do you not lose a fair few psi out of narrow tyres when that happens?

Pumped up the Mrs's 35s on her touring bike yesterday. They had less than 20psi! :shock:

jds_1981

MonkeyMonster wrote:

thecrofter wrote:

Joelsim wrote:

My LBS put my new tyres on a few weeks ago and I asked what pressure, he said 100psi. Anyway a couple of months later I tested them, one was at 30psi, the other 35psi.

Needless to say they are now back at 100psi!

You only checked a COUPLE OF MONTHS later and you couldn't tell the difference between 35 ish and 100 ish without a gauge? :roll:

+1 that is odd... when mine are at 80 (down from 100) I can very easily tell that its all gone a bit spongey. 30 though?!

The really odd thing is the time travel.

hmbadger

Waddlie wrote:

Run 28s, pumped to 105 psi.

I always wonder, though - you know when the pump/valve does the little pssst thing when disconnecting? Do you not lose a fair few psi out of narrow tyres when that happens?

Pumped up the Mrs's 35s on her touring bike yesterday. They had less than 20psi! :shock:

I've wondered about that. Anyone done any testing to measure?

itboffin

HTFU

http://www.youtube.com/watch?v=6Qm5IYgEdZw

Paul E

mich krylion 25c's 90 front 95-100 back - 12 stone of me on them roll well enough no dramas and they still absorb road buzz

meanredspider

hmbadger wrote:

Waddlie wrote:

Run 28s, pumped to 105 psi.

I always wonder, though - you know when the pump/valve does the little pssst thing when disconnecting? Do you not lose a fair few psi out of narrow tyres when that happens?

Pumped up the Mrs's 35s on her touring bike yesterday. They had less than 20psi! :shock:

I've wondered about that. Anyone done any testing to measure?

I reckon I lose between 5-10psi - lose a little on connecting and lose a little on disconnecting.

Twisterboy

My mountain bike is running 40psi in each tyre.

David

Ride hard

700 x 25 Michelin's running at 105psi each. A very good rolling resistance with a tolerable firm ride.

How the pros ride with tubulars running at 140+ psi is beyond me. It must be like riding a bike with wooden wheels. Sore under carriage anyone :shock:

ride_whenever

meanredspider wrote:

hmbadger wrote:

Waddlie wrote:

Run 28s, pumped to 105 psi.

I always wonder, though - you know when the pump/valve does the little pssst thing when disconnecting? Do you not lose a fair few psi out of narrow tyres when that happens?

Pumped up the Mrs's 35s on her touring bike yesterday. They had less than 20psi! :shock:

I've wondered about that. Anyone done any testing to measure?

I reckon I lose between 5-10psi - lose a little on connecting and lose a little on disconnecting.

You lose virtually nothing on disconnecting, but on re-attaching you tend to lose a fair bit.

I run 25 in the front and 30 on the rear but 2.1" mtb tyres run tubeless. I like the smooth ride of soft tyres and bugger all rolling resistance from the tubeless setup.

meanredspider

ride_whenever wrote:

meanredspider wrote:

I reckon I lose between 5-10psi - lose a little on connecting and lose a little on disconnecting.

You lose virtually nothing on disconnecting, but on re-attaching you tend to lose a fair bit.

I run 25 in the front and 30 on the rear but 2.1" mtb tyres run tubeless. I like the smooth ride of soft tyres and bugger all rolling resistance from the tubeless setup.

Depends on your pump - also depends on the pressure you're running and the volume of the tyre. High pressure in a narrow tyre will lose more pressure than low pressure in a fat tyre.

Escadrille Ecosse

The tyres are supporting the weight (force) applied by the weight of you and your bike. The supporting force is provided by the air pressure in the tyre multiplied by the area of the contact patch. Wider tyres have a larger contact patch so need less pressure to support the same load.

For a road bike increasing the pressure reduces rolling resistance up to a point then all that happens is the ride gets harder. On a mountain bike you are looking for the tyres to deform into the ground to give you grip so you run wider tyres at lower pressure.

Sheldon Brown gives a good description with links for working out "optimum" pressures http://sheldonbrown.com/tires.html

My bikes run
34mm Marathon Racers CX 60psi front 70 psi rear
28mm Conti GP4S 70psi front 100psi rear
2.1" MTB 28psi front 30psi rear (Stans tubeless)

Cars are much the same, my lightweight race car with wide tyres runs 21psi front 17 psi rear (cold). The wife's hatchback is in the mid 30s. The extreme cross country driving guys will run as low as 3 - 5 psi on very soft ground.

rolf_f

I go for a hundred psi on 25 and 23mm tyres. I don't weigh much though!

sketchley

Tyre pressure should be set based on the load over the wheel and the width of the tyre. Follow the sheldon link above, then find the pdf he links to, it has chart showing optimum pressure for given weight and tyre width. Too low means higher rolling resistance so you don't go as fast and two high means bouncy ride so less traction so you don't go as fast.

Me I run 25mm front and back with 110 & 130 respectively. I do weigh a bit. I'm concerned rear needs a bit more so thinking of upping to 28 instead.

As for pressure loss at these psi settings rear needs pumping up every day as drops to 120 in 24 hours, front a little better dropping 10 psi every 3 days.