tyre pressures

[Huw Peplow]

Did a 150 mile round trip with only a few rattles last night and the only obvious fault was too much tyre pressure and possibly suspension set to hard .

using 17 inch wheels and 275 and 225 tyres respectivley any one chosen a suitable pressure yet that seems ideal for road use

the new rf any recomendations

[Ross Nicol]

Huw the Ford GT tyre pressures could be a starting point. Contact J Clarkson he will most likely remember them. Only joking.You wouldn't be too far out with pressures from a car of similar weight and tyres.I honestly think there are too many variables for anyone to say any pressure will be perfect. It's quite often ride quality versus performance with tyre pressures on the road.I'd pump them up a bit when you go for a spirited drive though.
Ross

[40 Bud]

There is no perfect answer. Try dead cold pressures of 22lbs. front and 24lbs. rear, raise 2 to 3 lbs. for more spirited driving. This is for general road use, not track driving.

[Jerry]

Hi Huw,

I run the tyres at 32psi front and rear, as advised by the old Roaring Forties, and found them to be about right. No harshness when driving and gives good grip. Never used for track work though.
Jerry

[Cliff Beer]

Huw, agree with everyone else here - there's no one universally applicable correct pressure, even for a specific tire dimension. However, there will be a pressure which is correct for your particular car and suspension settings - one setting for the street and likely a different setting for track time.

A key indicator of what's right for your car is tire wear - keep a close eye on the wear pattern on your car's tires. If there is more wear on the outsides of the contact patch than in the middle then you might consider raising the pressure (converse is also true). Of course, if you have greater wear on inside v. outside then you might have camber or toe issues but this can sometimes be moderated slightly with tire pressure adjustments but start with the basic approach above.

[Chris Simpson]

Hi Huw

Just to complicate things further, shock absorber settings will also have an effect on general handling and ride comfort. I think that our RF's are the only ones with Protech adjustable shocks so we are on our own there - I would start with them in the middle of their range and play around with them from that point.

The tyre pressures recommended in this thread so far have quite a range, 22 - 32 psi. We have 17 inch wheels which will have different pressures from 15 inch wheels with the same tyre width. I believe Gerry has 16 inch wheels. It is all very confusing!

Chris

[Jerry]

Hi,
Yes mine are 16" rims.

[Howard Jones]

Here is my notes/data at two track days.

#1 Hot day, air temp mid 90sF, full sun, Afternoon, still air, Started session with 21F 23R, 10 laps/ 30 mins 24-25F 29-31R This track has a very fast long banked L and the higher pressure was in the RR. I didn't like the feel and will run 1-2 PSI less in the RR next time there.

#2 Cold day, air temp low 60's F, overcast, morning 30-35 MPH wind, Started session 23F 25R, 9 laps, 25 min, 25F, 27R.

Tires were SP8000 Dunlops 225.45.17 and 285.35.17 in both sessions above. I have since changed tires to 245.40.17 and 315.35.17 Sumotomos and used the same starting pressures. Have had similar results, about a 2-3 PSI gain to 25-26F 26-28R

Old rule of thumb divide the total vehicle weight by 100 and run that pressure in the tires all the way around as a starting pressure. Example, 2500 pound car / 100 = 25PSI. This isn't the BEST setup but it will be a safe starting point.

For a Sunday run down the highway at legal speeds/moderate temp day I would put 25-27 PSI in them and have a look at pressures in a couple of hours. Expect a gain of a pound or two. Much more that 30 PSI will result in a harsh ride and it's not necessary.

This is of course my car with my shock setting and spring rates and the way it feels to me. The fun of owning these cars is the learning. Try some stuff and get a feel for how things effect performance.