Tyre Pressure Calculator?
Discussion
My R1ot weighs 475Kgs and I run Yoko A048's 195's at the rear and 185's at the front. Yoko told me that the lowest they recommend is around 18Psi all around but they have seen similar weighted cars runninng as low as 13Psi all round on a 60 section tyre.
I run them at just below 18Psi all round, a lot of it is experimentation and seeeing what pressure works best with handling vs tyre wear. The lowest I've run is 6 Psi at the front for the SVA to give better self centering on the steering and the car ran fine as it is so light the side walls didn't distort at all. I did pump them back up to 18Psi before I set of home again though.
I run them at just below 18Psi all round, a lot of it is experimentation and seeeing what pressure works best with handling vs tyre wear. The lowest I've run is 6 Psi at the front for the SVA to give better self centering on the steering and the car ran fine as it is so light the side walls didn't distort at all. I did pump them back up to 18Psi before I set of home again though.
One trick - and I should stress that this will NOT give an absolute set of pressures, merely a starting point from which to experiment - is to sit the car on flat, smooth plates (blocks of MDF are fine, so long as they are properly supported)then play around with tyre pressures whilst inserting sheets of carbon paper and photocopy paper under the contact patches.
By using this method, you can judge what pressures give the best shape for the contact footprint. The ideal is a nice, smooth eliptical shape with the major axis running across the tyre and the minor axis (fore and aft) as long as possible.
As others have said, it then gets a bit complicated, as there are many other factors involved... you may want to vary the pressures to give different tyre spring rates, for example, or to adjust oversteer/understeer balance.
By using this method, you can judge what pressures give the best shape for the contact footprint. The ideal is a nice, smooth eliptical shape with the major axis running across the tyre and the minor axis (fore and aft) as long as possible.
As others have said, it then gets a bit complicated, as there are many other factors involved... you may want to vary the pressures to give different tyre spring rates, for example, or to adjust oversteer/understeer balance.
r1ot said:
My R1ot weighs 475Kgs and I run Yoko A048's 195's at the rear and 185's at the front. Yoko told me that the lowest they recommend is around 18Psi all around but they have seen similar weighted cars runninng as low as 13Psi all round on a 60 section tyre.
I run them at just below 18Psi all round, a lot of it is experimentation and seeeing what pressure works best with handling vs tyre wear. The lowest I've run is 6 Psi at the front for the SVA to give better self centering on the steering and the car ran fine as it is so light the side walls didn't distort at all. I did pump them back up to 18Psi before I set of home again though.
I run them at just below 18Psi all round, a lot of it is experimentation and seeeing what pressure works best with handling vs tyre wear. The lowest I've run is 6 Psi at the front for the SVA to give better self centering on the steering and the car ran fine as it is so light the side walls didn't distort at all. I did pump them back up to 18Psi before I set of home again though.
In an unguarded moment a few years ago Ian Gray of Stuart Taylor Motorsport told me he runs about 13psi and it makes the world of difference to his lap times.
He clammed up straight afterwards...
Just as well I wasn't buying a race car off him!
The good sporting trials chaps run at 2-6 psi for maximum grip, but they have the bolts that F1 now use to keep their wheels on and pressure that low can cause the seal with the wheel to go and then you run on a flat.
This is all off road, and I doubt they'd be able to take the car more than a mile on sealed roads
This is all off road, and I doubt they'd be able to take the car more than a mile on sealed roads
Edited by MTv Dave on Wednesday 11th April 10:20
What I've done in the past is to put about 30psi in and then keep letting air out until you just start getting a bulge in the sidewall due to the weight of the car. Seems to give a pretty good starting point. After that it's down to how the car feels and keeping an eye on tread wear for clues as to which way to adjust things.
I've done a bit of experimenting over the last couple of days, starting off with 22 psi front & rear and going up and down a few psi until it felt 'right'. It is hard to describe how I judged the handling but I have now settled on 18 psi front & 25 psi rear. The steering has improved a lot now and is not so over sensitive to potholes and tramlines - generally it is a more relaxing drive.
I will do a temperature check when I get the chance and see if the tread area is evenly heated after a long run.
Graham, My tyres show very little difference in sidewall bulge - they looked the same with 10 psi or 25 psi. I would imagine a higher profile tyre would be easier to set up in this way, but a 35% side wall doesn't give any feedback at all.
Thanks for all the input guys - much appreciated
I will do a temperature check when I get the chance and see if the tread area is evenly heated after a long run.
Graham, My tyres show very little difference in sidewall bulge - they looked the same with 10 psi or 25 psi. I would imagine a higher profile tyre would be easier to set up in this way, but a 35% side wall doesn't give any feedback at all.
Thanks for all the input guys - much appreciated
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