Wheel swP

[Kevin.payne.15]

Guys. I've changed the wheels on the GT6 to the 5.5 inch versions. Does anyone know the correct tyre pressure that should be used. Mines a non rotoflex version.

 

Thanks

 

Kevin

[Clive]

I would try 24psi all round, and see how it feels.Or try the std "book" tyre pressures. Wheel size doesn't have a big effect.

 

Is this a late swing-spring GT6, or a mk1? IIRC the late car had odd front/rear tyre pressures?

And what size tyres are you using?

[Pete Lewis]

Modern tyres seem to need a few lbs more than the older book pressures but as you have not changed the area = load x presure unless you change the load whatever tyre you fit will keep the same foot print area for the same pressure

 

so keep the front /rear balance and as clive says play to suit the tyres play a big part of the suspension

on old cars less so with moderns with silly profiles

 

you, need enough pressure to give side wall control but not hard to wreck any ride quality.

[dougbgt6]

Haynes says 20 on the front, 24 on the rear, which is too soft for modern tyres. I maintain the 4lbs difference and have 24 & 28.

[Colin Lindsay]

My local tyre fitter of many years experience claims that modern tyres need higher pressures than the original handbook would have recommended. He puts my GT6 to 30 / 32 all round everytime he changes a tyre (mostly due to sidewall cracking from sitting in the garage, rather than from road-use wear)

[Clive]

Interesting about the higher pressures.

I tried 30psi in the spit on track, but found it made the car a bit skittish. Much better at 26. 

 

The bes way was suggested by JohnD. Take teh car for a run, and use a (cheap at £2) IR thermometer and take the temps across the tyres. If set up correctly, it should be even. Makes sense, as the whole tyre is doing the work.

 

Another thought, I am using Goodyear Efficientgrip Performance tyres. These have quite soft sidewalls, which may allow the lower pressures?? Some modern tyres have stiff sidewalls, and could mean the tyre will run on the edges unless a bit harder? Just a thought. (a russian tyre that was fitted to the wheels when purchased was almost rock solid at zero psi! Not old either, plenty of tread if anybody wants it!)

 

Re book pressures, I think there is an oddity with late swing spring pressures?? again, just a thought that is worth considering.

[Kevin.payne.15]

Mine is a late swing spring version and I've fitted 175/70 uniroyals and they looked pretty decent and were considerably cheaper than dunlops

 

 

 

I'll try the 24/28 and see how it goes. It seems strange to have the higher pressure on the rear when all weight is on the front wheels or am I the only one who believes this?

 

The previous owner of the wheels was running them on a tyre from 1985 which was pretty firm !

 

Thanks

 

Kevin

[Pete Lewis]

Yes cornering puts a lot of weight at the back

 

if you reverse the balance you may find roundabouts exciting

 

pete

[dougbgt6]

Tyres from 1985 would be no longer rubber and extremely dangerous, modern wisdom is tyres should be replaced after 7 years, worn out or not.