[davewilkins]

Hi,
I am running 225/50/16 on my GTR R32. I wasn't sure what pressure to run the tyres at and put them to either 32 or 34 psi and the car felt unsteady down the lanes tonight (driven hard). Also it is wheel spinning when it did not used to (in 1st).
Anyone (Mr Scott?) got any advice on what pressure to run to save me finding out from trial and error?
Dave

 

[Scott]

Under Pressure ?


Dave,

Just read your note and then talked to a friend who races cars. Ok he only races MG Maestro's but they aren't allowed to have any mods other than to suspension and brakes. The cars are all blue printed and the whole field is covered by 5 bhp. This make very close racing as I have witnessed, and very little discrepancy between settings tell lap after lap.

Talking we reckoned that even on the track he could only perceive 2-3 psi variation!! On the road 5 psi. There are too many other variables to put lack of traction down to just 2 psi in your tyre. It may of been more humid, took a very slightly different line, more or less fuel, tyre tempreture etc. etc.

I personally use 2.3 bar as the sticker on my door jamb suggests. But even getting the pressures spot on an the garage air pump still gives 4 psi variation according to my pressure monitor. I guess as long as they are with in 5 psi (Obviously closer between front pair and rear pair), You shouldn't really notice it unless you are really on the edge, dialled in 100%. What is the chance of doing that safely on our crappy roads. If you run them all at the the lower end of the scale, contact patch will go up, and as we have already read in another thread this will be more affective at gaining grip than fitting wider rims. Also the lower pressure will give the handling greater complacency, which makes thing safer, (as long as their not too low of coures).

Now my question is, now I have 17 inch rims with 245/40/17, what pressure would people recommend?
What does the book say for R33's, due to them running these lower profile wider rims, (albeit 45 not 40's)?

 

[davewilkins]

2 much pressure

Thanks Scott. What is 2.3 bar in psi as I guessed it and my electronic pressure gauge is in psi?

 

[SteveC]

psi-bar

1Bar = roughly 15 psi (it is 15. something.)

thats what I use when I am diving in imperial measurement countries.

Steve

 

[davewilkins]

2.4 bar in psi

Well that is about 34 psi then which is what I put in the tyres. Still depends on conditions I suppose.
Dave

 

[Joss]

To be more exact

1 bar = 14.5 psi ( or for pedants: 14.503773773)

I think the 15 psi number (which I remember from school) comes from rounding up 1 Atmosphere = 14.7 psi.

So it's 33 psi, but what's 1 psi

oh and 1 kg/cm² = 14.22 psi, as lots of people think their boost guage is in bar when older displays are in kg/cm²

- I have a killer HP 48G calculator with all this stuff built into it

 

[SteveC]

sounds logical....

I'd go along with that Joss, things in Diving are usually rounded up to increase the safety margin.


I asked Jeeves

To convert from bar to lbf/in² multiply by: 14.503774
Conversion result: 1 bar equals 14.503774 lbf/in²

should have looked there first ...DOH

/Steve

 

[davewilkins]

psi......

cheers chaps.
Any replys to scotts question?????

 

[SteveC]

I'll have a lookat lunch time.....

/Steve