Not your normal Tyre Pressure Question

**BigMacca** · 03 Sep 08, 11:23 AM

Hello all,

Sorry if this has been brought up before, I've searched but not found anything.

I'm just wondering whether people allow of ambient temperature changes when setting tyre pressures.

For example, I set my tyre pressures before every ride. So this morning when I set off for work they were at 33f / 37.5r (cold) but it was only about 8 degrees.

When I ride home this afternoon, the temperature is more likely to be something like 18 - 20 degrees and from experience my cold tyre pressures will now be more like 34.5f / 39r.

So should I be setting them a bit lower in the morning to account for the change in ambient temp (anyone know how to calculate the effect temp increase has on pressure?), or just set them and not worry about it?

**Cess pit** · 03 Sep 08, 11:30 AM

Cant say as I worry that much.
Check my pressures once a week religiously plus in addition before a long ride.
Otherwise I dont worry....Im suprised you can feel the difference of 1 or 2 pounds on the road.

**Keninsussex** · 03 Sep 08, 11:39 AM

Nope....everything I've ever seen says tyre pressures should be checked and adjusted when cold for precisely this reason.

**BertAgain** · 03 Sep 08, 12:15 PM

Ambient isn't a big problem unless you live in a desert (with night/day changes of 50+ degrees C) , but I try not to check pressures after riding the bike cos tyres will have heated up ..... racers tend to have different ref pressures as they cant wait for tyres to fully cool....

**SP2 Boy** · 03 Sep 08, 03:31 PM

Quote:

Originally Posted by BertAgain

Ambient isn't a big problem unless you live in a desert (with night/day changes of 50+ degrees C) , but I try not to check pressures after riding the bike cos tyres will have heated up ..... racers tend to have different ref pressures as they cant wait for tyres to fully cool....

I thought they also filled there tyres with a gas, not air so that the pressure was stable at different temperatures. (Perhaps this is only cars.)

**nogaromill999** · 03 Sep 08, 04:00 PM

Set them cold at 31psi front 29psi rear.....

**NedLudd** · 03 Sep 08, 05:05 PM

Quote:

Originally Posted by nogaromill999

Set them cold at 31psi front 29psi rear.....

Dave - I know that trackday regulars run these sorts of temp/s for the extra traction, but isn't there a danger in going too far below the specified pressures on the road? I always fret that if one was running, say 29 rear (which might easily slip down to 27/28 with a little inattention) on a tyre which Pirelli said should be run at 36+, then an accident investigator / insurance assessor might rule that at c.25% under the recommended pressure the tyres were 'under-inflated' or some such. It's a minefield...

**nogaromill999** · 03 Sep 08, 05:11 PM

I dont think so Ned, as the manufacturers themselves say, they are figures for guidance only, and I'd far rather be riding on pressures I am happy with, that give me more grip, than an arbitrary pressure set by someone that doesnt know the road conditions nor the way I ride, nor the temperature that day, nor the bike the tyres will be fitted to,, but its each to his own. I can only speak from my 33 years of experience on road and track.

**NedLudd** · 03 Sep 08, 05:21 PM

Quote:

Originally Posted by nogaromill999

I dont think so Ned, as the manufacturers themselves say, they are figures for guidance only, and I'd far rather be riding on pressures I am happy with, that give me more grip, than an arbitrary pressure set by someone that doesnt know the road conditions nor the way I ride, nor the temperature that day, nor the bike the tyres will be fitted to,, but its each to his own.

Sure. I'm minded to experiment by dropping mine a bit - though caveat emptor of course

.

**Ghost** · 03 Sep 08, 05:44 PM

I never run my 749 with more than 30 in the back, I like a large footprint, the tyre heats up and goes to the recommended pressure or thereabouts.

**nogaromill999** · 03 Sep 08, 06:05 PM

Quote:

Originally Posted by NedLudd

Sure. I'm minded to experiment by dropping mine a bit - though caveat emptor of course

.

Always caveat emptor Ned....however, a certain Ron Haslam told me MANY years ago, before they had tyre warmers, they'd have a lap or so at 12psi, just to get heat into the tyre, then reinflate to running pressures on the line....

**Fastandcorse** · 03 Sep 08, 07:01 PM

Hi everyone. Firstly I think it's a good idea to raise the tyre issues every now and again as technology is continually changing. That said, for road bikes I've tried many combinations in summer and winter and concluded that my bike turns and handles much better on the recommended pressures which I drop by a couple of pounds on the cold damp winter mornings.
I found lowering the pressures was good in theory but had trouble on my normal blasts actually trying to keep them hot enough to raise the pressure due to being stuck in traffic, slowing for roundabouts etc, etc. I have actually travelled in excess of 70mph (in a straight line!) on a completely flat back tyre for a few miles (turning was nigh on impossible) but the chassis coped well and I got home. It's difficult to draw a solid conclusion but my thinking is always that the bike manufacturers must design the bike around the available tyres on the market at that time, so the bike must handle better with the recommended pressures....

**mickchaganis** · 04 Sep 08, 09:33 AM

Maybe for road use we should trust the tyre manufacturers, if Avon says put 34 in your back tyre and Joe Bloggs from down the road says I run mine on 28, I think I will stick to the 34.

**BigMacca** · 05 Sep 08, 11:56 AM

Thanks for the replies guys,

As usual when dealing with tyres everyone has their own opinions

So it looks like people don't bother taking the ambient temp variation during the day into account. I can live with that and I'll continue to set my tyre pressures before every ride without worrying about it.

Cheers

Macca