Tyre pressure relief valves
Discussion
jeff666 said:
I was asking for a club racer, (Team Trophy) so a 60 min race, when they come in for the mandatory pit stop (2 mins) we check the pressures and have to reduce them, both guys say the car felt better after the stop.
We start around 24psi cold, and they can be as high as 34 hot, both cars are on ordinary air, not Nitrogen, they are running the Khumos v70's from memory.
I'm not speaking from experience (I do sprints) but knowing the difference between hot and cold would you not be better off under-pressurizing them cold so they reach your targeted pressure when hot? After all, cold only lasts for the first few corners and 60 mins is a long race.We start around 24psi cold, and they can be as high as 34 hot, both cars are on ordinary air, not Nitrogen, they are running the Khumos v70's from memory.
carl_w said:
I'm not speaking from experience (I do sprints) but knowing the difference between hot and cold would you not be better off under-pressurizing them cold so they reach your targeted pressure when hot? After all, cold only lasts for the first few corners and 60 mins is a long race.
I think they are aiming for 30 psi hot, to get that I think the starting pressure would be too low.I agree we are not talking F1 here, but it does make a fair difference to the handling of the car, so I am told anyway.
BertBert said:
yes the issue can be that the cold pressure takes too long to get up to temp so you lose out early on. Or you end up running over-pressure later. That's where running nitrogen could help. I've not experienced how you use it, so no idea how you purge the air out.
Bert
I have been given the name of a tyre co near me, apparently they will get all the old air out 1st before the re-fill, I may get them to do my track day car 1st to see the results.Bert
Must be some sort of vacuum jobbie, I will give them a bell tomorrow, I have a day booked at Coombe next Monday so weather permitting might be a good test.
PS. Track car is running slicks.
There seems to be a little confusion here on a number of subjects, so I'll try to help a bit as I have a reasonable amount of experience in this area.
Firstly, don't use pressure relief valves, ever. They are specifically banned in lots of championships for a very good reason: they're unreliable and can be very dangerous, especially the ones that you have to drill a hole in the wheel to attach. They will not give you a winning edge, but they may cause a flat tyre that sends you into the wall. They are also nowhere near accurate enough.
As for what gas to put in one's tyres, dry air is fine. Nitrogen is clearly a favourite for many, but its advantages over properly dried air are minimal. The moisture content will, absolutely and definitely, affect the pressure increase - I have seen this many times with tyres that teams have fitted themselves with less than optimum quality air and they can end up half a bar too high when hot.
There will always be a pressure increase in a tyre as the temperature increases - you can see this even in a road car. The key is setting your cold pressures correctly so that the pressures stabilise at the correct level. On cross ply race tyres we used to carry out a mid-race bleed because cross plies could fall off the rims at especially low start pressures, but this is less of an issue with radials.
Firstly, don't use pressure relief valves, ever. They are specifically banned in lots of championships for a very good reason: they're unreliable and can be very dangerous, especially the ones that you have to drill a hole in the wheel to attach. They will not give you a winning edge, but they may cause a flat tyre that sends you into the wall. They are also nowhere near accurate enough.
As for what gas to put in one's tyres, dry air is fine. Nitrogen is clearly a favourite for many, but its advantages over properly dried air are minimal. The moisture content will, absolutely and definitely, affect the pressure increase - I have seen this many times with tyres that teams have fitted themselves with less than optimum quality air and they can end up half a bar too high when hot.
There will always be a pressure increase in a tyre as the temperature increases - you can see this even in a road car. The key is setting your cold pressures correctly so that the pressures stabilise at the correct level. On cross ply race tyres we used to carry out a mid-race bleed because cross plies could fall off the rims at especially low start pressures, but this is less of an issue with radials.
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