Tyre Pressure question

[daxtojeiro]

Hi all,
I wonder if anyone can help me, I have a Dax Cobra replica and Im concerned the tyre pressures are set far too low, Dax recommend 20psi, that to me seems far too low, Ive been driving it like it for 3 years but as Ive now set the suspension up Id like to set the tyre pressures. So I thought that theres a good chance the TVR's would have a siliar weight and tyre size to the cobra so may be I should start with the settings they use,
Phil

[tvrbob]

A lot depends on the tyres. The 'tyre' contribution to your cars suspension is a combination of tyre wall rigidity/height and tyre pressure. Therefore if you have very low profile tyres and/or high wall rigidity, you will need to compensate by having low tyre pressure. 20psi is at the low end of pressures for cars like these but it's probably OK. You will need to increase this pressure by as much as 10psi for track work but that doesn't relate to the road. The only concern I would have is that the combination of high torque and low tyre pressure can cause the drive tyres to slip around the rim. This is dangerous because tyre pressure is easily lost when it happens. Do a test, put a little mark on the tyre adjacent to the valve, then go for some hard launches. If they stay in line then I would say Dax probably know best and 20psi will be OK.

>> Edited by tvrbob on Monday 14th March 20:01

[daxtojeiro]

Hi ,
thanks for the advise, I forgot to mention the tyres are 255/17/45 rear and 235/17/45 front, I will try the chalk test, I hadnt thought of that, I do know of one that derimmed 2 front tyres on cornering at 20pis, he was told by the tyre manufactourers that 20psi was far too low, they recommended 32, Ive been told the same by several people now, hence why I thought Id see what you were all running,
Phil

[19560]

daxtojeiro said:

20psi was far too low, they recommended 32, Ive been told the same by several people now, hence why I thought Id see what you were all running, Phil

20 is fairly low but low profiles on low weight cars need to be. TVRs usually run 22 to 24. 32 is high for this type of car.

[tvrbob]

32psi sounds way too high. If your looking for a range to try I would suggest 20 - 26 psi. Rules of thumb:

The bigger the rim the lower the pressure
The lower the profile the lower the pressure
The harder the sidewall the lower the pressure
The lighter the car the lower the pressure

Your tyres rate on three if not four of these factors so low pressure is required. 32psi is shopping car territory.

[deeen]

I run 22 all round on the road, 30 on trackdays, on Bridgestones, stiff sidewalls.