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29-07-10, 11:22 AM
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barry cooper
The "C" on a tyre is for commercial as is "LT'" for light truck < its marked with one or the other..
As for the tyre pressure the benefit of running the high pressure is to keep the actual vessel cooler therefore not increasing the internal temperature as much. The friction of the tyre on the road causes the vessel to get hot , the lower the pressure the harder the tyre is working hence the hotter it gets then heats the air inside the tyre. An example, try pushing a carof a car with 10 psi in the tyres then push it with 40 psi in it, neither the pusher or the tyre is working as hard at the higher pressure. 40 psi is fine in the hot weather but if the roads are wet drop them back down 32 or 34psi. I run my 400 with 34psi on 165r16 Avons & find the grip amazing in the wet if a little harsh on the rougher roads My regards Barry. 
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29-07-10, 11:31 AM
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Tyers for a Bristol 407
Thank you Kevin,
in fact the ride is a bit too hard with the tires inflated to 39. I'll try 30psi, as you and Greg suggests, and ride will surely improve. Speaking of tyres and wheels, my 5 wheels (rims) are not looking good, they all are a bit 'warped'. It would be nice to hear from someone who knows where I could find 4-5 wheels in better condition, or if any other Marque used the same pattern as the Bristol. I know that LJKS used Minilites on his 409, but I'm not sure if I like their looks on a classic Bristol. Cheers Stefano
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29-07-10, 11:45 AM
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Tyers for a Bristol 407
Greg,
With vintage tyres the moulds are often no longer owned by the original manufacturer (in this case Vredestein) but by another company who is either retailing or distributing the tyres. They will typically have a run of say 1000 or 2000 tyres produced which may take several years to sell. So they are not really expensive. They may also choose to sell on tyres to other retailers. Is that a bad thing if it keeps the tyres available?
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29-07-10, 11:47 AM
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Stefano,
You could get in touch with the bloke I gave you details of that is breaking a 409. If his wheels are in good condition you could do a deal to swap them so he can still roll it. Or find a scrap yard with Mercedes steel wheels
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29-07-10, 11:57 AM
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cooper_bm
[quote=pasini s;3247]Thank you Kevin,
Stefan A good wheelworks can reroll your steel wheels, buying other used ones may still have the same issue. I had mine rerolled, two of them had to have the centres removed & refitted to ensure correct centreing once this was done they needed minimal weight to rebalance and improved the smooth running noticeable on good roads. My regards Barry
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29-07-10, 12:33 PM
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barry cooper
Actually tyres generate most heat not due to friction but due to a curious
phenomenon called "Hysterysis". The Stress-Strain curve for rubber compounds curiously doesn't follow the same path back when the stress is removed. A quite significant amount of the stored energy (represented by the area between the two curves) is released as heat. By increasing tyre pressure, the tyre sidewall and tread will flex less when rolling, hence lower heat build up. I still wouldn't recommend playing around with the tyre pressures. The big tyre companies continue to spend an awful lot of money on R&D.
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29-07-10, 05:24 PM
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tyres
Quote:
2) On the taxi tyre issue, this is where the Club or new Club should step in, go to Bristol Cars and ask them to issue an official factory statement to the effect that they are acceptable for Bristols that do not exceed 99 mph. Ckaude
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29-07-10, 06:01 PM
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tyres
... Whatever questions you ask, you need to clear it with your insurers, as without their acceptance, If involved in a prang, the vehicle examiner will be checking tyre codes as well as tread depth etc.. I know this from personal experience (I was OK with my tyres, but had a chat about codes, dates of manuf. etc.with him at the time). This is very important when you have a car which does limited miles, & still has plenty of tread. eg signs of cracking in walls?
. ........ Batmanbruce
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29-07-10, 09:15 PM
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Quote:
Quote:
Furthermore, there is Bristol's reputation for rigorously testing components used on their cars. This testing could be done, but it would be expensive to do it properly, having a car of each type in perfect original condition would be a challenge for starters. But why would Bristol do this? I can't see that it would benefit them in any way. Making 15" wheels would be a much more sensible.
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30-07-10, 10:50 AM
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tyres for 407
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.
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30-07-10, 04:30 PM
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Tyers for a Bristol 407
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.
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31-07-10, 09:27 AM
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Tyers for a Bristol 407
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
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24-08-10, 08:19 AM
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Tyres for 407
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
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