Tyre Pressures
Discussion
I have recently bought a Griff with 7j 17" rims both ends, the tyres are 205/45/17" Front & 225/45/17" Rear what tyre pressures should I use? as the owners manual stated 22f/24r psi(all be it for a different tyre size), I tried this first - the car was almost impossible to steer and the rear became spongy, I'm currently running them at 27f/29r psi. Also could i get away with increasing the aspect ratio to 50 or 55 on 17" rims as its a bit of a bone shacker at 45?
Hi, and tx for your reply...
The rims are Dare Motorsport X1's, no markings on them so I had to put a tape measure on them to get the width, which measures 8" overall (I guess 7.5" inside the lip).
The tyres are a budget brand "Kumho Ecsta Supra" (I'll be changing them for S03's as soon as I've figured out the best size to go for).
The suspension appears to the std, which has just been overhauled by TVRBodyshop in Nailsea.
Generally is everyone using the std tyre pressures no matter the tyre variation?
The rims are Dare Motorsport X1's, no markings on them so I had to put a tape measure on them to get the width, which measures 8" overall (I guess 7.5" inside the lip).
The tyres are a budget brand "Kumho Ecsta Supra" (I'll be changing them for S03's as soon as I've figured out the best size to go for).
The suspension appears to the std, which has just been overhauled by TVRBodyshop in Nailsea.
Generally is everyone using the std tyre pressures no matter the tyre variation?
swissgriff500 said:
He there,
In fact, I run 2.2bar = approx. 32psi all around (standard Bridgestone tyres Griffith 500) and find it much better...
Cheers, Ozren
That's pretty alarming? Its nearly 50% over the recommended pressure (and IMO the recommended pressure is about right for general use). I wonder whether insurers would use this sort of thing as grounds to invalidate insurance? It certainly seems likely to have a detrimental effect on the car's handling.
My Griff runs Toyo's on 18" Spiders and have 23psi on fronts and 25psi on rears. Of course these pressures were calibrated when the tyres were hot. No complaints..zzIt seems that tyre pressures have not figured as much as tyre sizes have in past thread.
Theoretically different tyre and rim combinations will have differing volumes to inflate, with air being compressable and taking into account differing tread widths and tyre wall strengths, tyre pressures should vary greatly depending on the tyre/wheel/manufacturer combination.
Does any body know what the Griff's weight distribution is?(front/rear). I could then try and get some guidance from the tyre manufacturers for future reference.
Theoretically different tyre and rim combinations will have differing volumes to inflate, with air being compressable and taking into account differing tread widths and tyre wall strengths, tyre pressures should vary greatly depending on the tyre/wheel/manufacturer combination.
Does any body know what the Griff's weight distribution is?(front/rear). I could then try and get some guidance from the tyre manufacturers for future reference.
Hamish Price said:
would that be with or without the drivers weight?
How much fuel in the tank? With or without a passenger? Are you going to reset the pressures when people get in or out or the car? Are you going to get the car corner weighted to check?
The car's suspension is setup with a tyre pressure of around 22-24 lb. With 17 inch wheels and lower profiles the sidewall compliance will be less and the ride will be harsher. So you might find that taking 1 lb or two out will soften it. Using a Toyo which have softer sidewalls is another way round.
So there is no exact pressure and you will find that even a 1 lb or two will make quite a difference. Start with 22/24 and experiment. The important thing is to get an accurate guage and to make sure that the pressures are the same on both sides.
Steve
www.tvrbooks.co.uk
- I mixed up all these different units (plus a gin-tonic too much I guess); I checked my tyres right away this morning and the pressure is spot on the recommended figures indeed Too simplistic I'm afraid unless the car is simply poodled around. You can get some pretty interesting tyre wear simply by driving hard. You can induce more body roll than the camber can cope with and as a result tyres start to wear on the inside edges because the outside edge is actually lifting. You can compensate by increasing the camber but then when the car is not rolling as much, the camber can start to cause wear on the edges because the tyre is leaning in on an edge.
You can get a tyre temp guage and measure the tyre temps and that will help diagnose problems (it identified that the 520 was running with 13mm toe out during some testing earlier this year) but often this is not practical unless you are on a track and get the tyres hot enough.
You can get a tyre temp guage and measure the tyre temps and that will help diagnose problems (it identified that the 520 was running with 13mm toe out during some testing earlier this year) but often this is not practical unless you are on a track and get the tyres hot enough.
Right for what it's worth, running my 17"/18" wheels with Bridgestone SO2pp - When the wheels were fitted I set pressures at 22/24. At my first track day I played with them a bit I found 24/26 to feel the best on that day. Subsequenly on the road I run 24 all-round. I do find it quite sensitive to just a couple of lbs change. Also I found that getting the geometry properly set-up made a HUGE difference, mine was done by Racing Green on their laser alighnment bed and the difference was remarkable. Rich...
I spoke to Toyo this morning...They have a lot of data from their work with TVR and were very helpful.
Due to the car being so light most of the calculation goes out of the window and it comes down to the minimum pressure required for the tyre, as the actual calculation based on weight,camder etc comes out at lower pressure.
For any Toyo Proxes tyre and rim combination the recommend 24 psi front and rear on the Griff.
Bridgestone were not willing to ablige me this info.
Due to the car being so light most of the calculation goes out of the window and it comes down to the minimum pressure required for the tyre, as the actual calculation based on weight,camder etc comes out at lower pressure.
For any Toyo Proxes tyre and rim combination the recommend 24 psi front and rear on the Griff.
Bridgestone were not willing to ablige me this info.
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