Tyre & tyre pressure survey

[iain.hamlton]

I this is a well trodden subject but if you have moment please let me know about your tyres and pressures.

Here are mine:
Old: Firestone 560 165 x 13; 24 psi front; 28 psi back. not much roadholding but neutral.
New: Firestone 590 165 x 13; 24 psi front; 28 psi back. MUCH better roadholding, a bit understeery.


What do you think would be the ideal pressures for roadholding and handling?

best regards, iain

[msd1107]

Original - Dunlop SP 155-13. 18/23 originally (per manual) then 28/33 (better feel and handling)

First replacement Dunlop SP 165-13 on 5.5" rims. Again at 28/33. A step up in responsiveness and handling.

Next replacement (Dunlop not available) Phoenix Stahflex 185/70-13, again at 28/33. Had to work on spring towers and wheel arches, but tires were excellent. Unfortunately, they went out of production.

Next replacement Yokohama 185/60-13 AVS intermediate, again with 28/33. I didn't have my spreadsheets around then, so didn't realize how much smaller these tires were than the 185/70-13 before. Complained to my mechanic that the tach was reading high. These tires are even wider than the 185/70-13, so went to small spring diameter and carved even more away inside the wheel wells.

The car has been laid up recovering from being hit by a wrong way driver and lack of capable mechanic, so I don't know exactly what tires will go on next. I am not excited by anything available in 13" size, and am thinking of making the difficult conversion to 15" forged aluminum wheels (to keep the weight the same as the 13" wheels) and 185/55-15 tires, of which a few high performance examples are available. The 185/55-15 have virtually the same rev/mile figure as the 155-13 or 165-13 or 185/70-13 tires, so the car will be rolling on standard diameter tires again.

Traditionalists, load your weapons! But Chapman probably would have gone this way also.

David
1968 36/7988

[bill308]

Ian,

If you want to reduce understeer and given your current pressures, I've always found increasing the front tire pressure a couple of pounds at a time will gradually dial it in nicely. Alternatively, you could reduce the rear tire pressures to decrease understeer.

Bill

[thor]

Hm.
I've got the Firestone 165/80 - 590 tyres, and not happy with current 24/26, will try the 28/33 theory tonight.

Just the small problem of a snapped handbrake wire and handbrake locked ON to sort out first. have replies to my post that it's probably the snapped wire wrapping itself around the prop or driveshaft causing the rear brakes to have locked, which sounds slightly weird ... But I'm jacking it up in an hours time to see...

[greg.harvey]

I had Goodyears.
Now on Uniroyals, as recommended by Paul Matty Sportscars in the UK. I think I have R680s, as discussed here:
http://steveww.org/index.php?id=83

Tend to set the pressure at 30 psi all round, but I know the fronts should probably be a little softer.

As an aside, I have to pump up the tyres every time I use the car anyway (see this thread), as the garage that fitted them had a tough time with the Plus 2 alloys and didn't do a very good job - a common problem, I'm told. To quote Barry Ely: "I don't mind them because I know what I'm doing, but most garages only do new tyres on Plus 2 alloys once!" Apparently it's a pig of a job.

[thor]

true, I have a slight occasional leak on the right hand front..

VERY pleased with the results of the 28/33 pressure change! lovely delicate steering feel.

[b-havers]

true, I have a slight occasional leak on the right hand front..

VERY pleased with the results of the 28/33 pressure change! lovely delicate steering feel.

Obviously car is not sold yet, Thor??
Mine neither; I'm in for the engine recon now - then I'll keep the car. It's too fun driving