Tyers for a Bristol 407

[Nick Challacombe]

It is safer to run them with tubes, there is no guarantee that after 48
years your wheels are air tight and
as Bristol specified Avon Turbo speeds and Dunlop RS5's the wheels were not
designed for tubless tyres.
Better safe than sorry.

32lbs pressure seems ideal by the way.

Nick 407 6028.

[mickb]

Thanks Nick I thought this would be the case. Have now ordered the relevant tubes.

regards
Mick

[Geoff Kingston]

Bristol cars already offer wider wheels to take advantage of wider modern tyres, If you look in the upgrades section of their site they list these for all models back to and including the 400.

[irienz]

Tyre pressures increase with heat and the heat increases the harder the tyre is worked. On my race car, I look to set pressures cold (before the sun gets on them) and achieve a 5 lb lift in pressure at the end of a track session. If the pressure rise is less, the tyres have not come up to working pressure which means the pressure has been set too high for the conditions - I reduce the pressure to get more heat into the tyre. If the pressure comes up more than 5 lbs, the tyre is under-inflated for the conditions and, somewhat counter-intuitively, the pressure must be increased to stop the tyre overheating.

My race car is an Alfasud, a small front wheel drive saloon, on treaded race tyres (Yokohama A048s). I will commonly start with 26 lbs in the front and 17 lbs in the rear. The rear end sees little weight and does relatively little work so the low pressure is essential to get them up to working temperature. Ordinary road tyres do not have such stiff sidewalls and need more pressure on the track to stiffen them up and stop them overheating.

I run about 30 lbs all round on my 411.


Chris Browne
Auckland, New Zealand
irie@orcon.net.nz
Cellular: +64-21-617007

[Nick Challacombe]

The sole reason for running at 32 lbs per sq in was, that unlike your 411, the 407 has no power steering and the soft side walls of the Michelin X's make low speed parking and maneuvering very hard and puts a great strain on both driver and car. The soft walls also contribute to a far better ride.
I experimented with several tyre pressures for everyday running and found that 32 lbs sq in to be the best compromise.
I am so happy with the tyres after struggling when parking with the Avon Turbo speeds. The lock on the 407 is not good and parking a car 16ft 7inches
long with a turning circle of 39ft, weighing, empty of occupants and fuel, some 32 cwt in old money, was a great strain.
Also the 411 has the engine moved back from the front axle and has an aluminium gearbox.
Just thought I would mention it as the car is used for day to day practical work and not track days or racing. The odd circuit of Le Mans and Silverstone excepted that is!
Happy Bristoling,
Nick 407 6028