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8 & 10 cyl Bristol cars Type 407 onwards - restoration, repair, maintenance etc

411s5 tyres

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Old 18-03-12, 12:32 AM
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Default 411s5 tyres

Gentlemen! I have an embarrasing question.
I am running my 411 on Pirellis, 215/70 zr 15 tyres.

Which tyre pressure should I hafe Front / back?

I have now about 35 PSI on all 4.
Thanks
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Old 18-03-12, 12:50 AM
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Hi,

30 PSi all around is recommended and seems to strike the right balance.

As a side note I switched from Avon ZV3 tyres to Michelin Primacy and the transformation on grip and ride was quite something. I really can through the 412 around with a lot of confidence, certainly more than you would expect with a big old unit like a Bristol.

Does anyone else have experience of changes between makes. If we compared everyones experience we night be able to work out which tyres give the best overall performance with a little bit of boolean algebra.

P
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Old 18-03-12, 03:52 AM
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I had 30 psi on them, but the tures "scrubbed" the tarmac on roundabouts, specially the front.
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Old 18-03-12, 11:39 AM
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Quote:
Originally Posted by Janne View Post
I had 30 psi on them, but the tures "scrubbed" the tarmac on roundabouts, specially the front.
What do you mean but this?

There's nothing actually wrong with running 35 psi, but it may make for a harder ride.

Brian Marelli once told me to experiment with pressures between 28-32 psi.

What rims are you running on - the Avons of the Bristol steel rims?

My personal view is that 215 tyres are a bit too wide for the steel rims, but I think plenty of people use them. The Avon rims are wider.
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Old 18-03-12, 02:29 PM
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I have tha Avons on it.
Here on Islafnd, the roundabouts have a camber that slopes out. Sound crazy, it is craxy, but done so the water runs off during the trop. rains.
When I had 30 PSI on them, when I went arond thr roundabouts, the car understeered hugely. It fnelt almost like when you have a flat.
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Old 18-03-12, 05:58 PM
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Quote:
Originally Posted by Janne View Post
I have tha Avons on it.
Here on Islafnd, the roundabouts have a camber that slopes out. Sound crazy, it is craxy, but done so the water runs off during the trop. rains.
When I had 30 PSI on them, when I went arond thr roundabouts, the car understeered hugely. It fnelt almost like when you have a flat.
That doesn't sound right at all, I wonder if the front geometry needs reseting? I recall driving a 409 that had been refurbished by the owner, who was particularly pleased with the money he saved rebuilding the front suspension himself. It had more understeer than a piano.

That said I would imagine that a severe adverse camber would cause understeer, particularly on soft settings.

I have accidentally run lower pressures before and the softer settings do improve comfort a little but don't help cornering

P
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Old 18-03-12, 08:36 PM
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Default Radial Tire Pressures

Most every manufacturer specifies 32 to 35 PSI, and the members are correct in that a pressure below 32 PSI is not recommended. The tire is engineered to do it's best at 32 PSI with no compromise in performance or tread wear. Many manufacturers used to recommend raising the pressure for high speed or high performance driving, and I recall the Dunlop people and Jaguar suggesting higher pressures. But that was yesterday, and tire technology has made quantum leaps since then. If you have handling or braking problems, it is likely that it is not the fault of qualitiy tires, but suspension settings.
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Old 19-03-12, 12:28 AM
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Originally Posted by Ronald G. Stephenson View Post
and the members are correct in that a pressure below 32 PSI is not recommended. The tire is engineered to do it's best at 32 PSI with no compromise in performance or tread wear.
Not recommended by whom?

A simple internet search will find innumerable examples of modern cars with manufacturer-recommended pressures of less than 32 psi (and it's ridiculous to suggest that 32 psi is some magic ideal pressure for every vehicle, tyre and situation).
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Old 19-03-12, 01:03 AM
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Originally Posted by Philip View Post
Not recommended by whom?

A simple internet search will find innumerable examples of modern cars with manufacturer-recommended pressures of less than 32 psi (and it's ridiculous to suggest that 32 psi is some magic ideal pressure for every vehicle, tyre and situation).
Bristol Cars recommended 30psi all around to me mine. I did a quick check on the Michelen site and they used 28 and 29 psi respectively to illustrate top performance for braking and cornering, as compared to 15psi (pretty poor) and 7PSI (dangerous). I shouldn't have thought a couple of psi either way would have any effect on real world performance.

That said every car is different, and things like sidewall stiffness and curvature have their effect too.
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Old 19-03-12, 06:28 AM
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Quote:
Originally Posted by Ronald G. Stephenson View Post
Most every manufacturer specifies 32 to 35 PSI,
While I don't agree with/believe this generalisation, I did note that last time I changed the tyres on our Merc ML430 the tyre fitters (a large national chain in Australia) inflated the tyres to about 38 PSI, they said the tyres would last longer. However the ride was too hard so I deflated them to about 30 psi. Mercedes recommend 29 psi, but that is for the tyres that were fitted to the car when it was new.

Back to camber on the 411. The 411 was originally set up with zero camber and generally speaking it is not adjustable. At least not without disassembly of the front suspension and drilling new holes for the fulcrum brackets, which are bolted to the front crossmember and govern the camber. Castor is 1 degree and "toe in" one eight of an inch.

Janne, I suggest you get the front suspension geometry checked. Tyre fitters should have the equipment to do it.

If the camber is wrong, it's possible that some of the suspension bushes are badly worn, or perhaps the front suspension has been dismantled previously and the wishbone arms have been swapped around (that is assuming the wishbone arms are not exactly the same). The latter is a bit of a long shot, but when I disassembled mine Brian Marelli advised me to mark all the components so that all the wishbone arms etc were put back in exactly the same position.

Unfortunately it's difficult to determine the condition of the front suspension bushes without dismantling the suspension!
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Old 19-03-12, 04:26 PM
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Default Tire Pressures are very much like opinions....

Having gotten this old, and having owned all manner of cars numbering around 200 to date, I seldom question the need for correct pressure in tires, and this experience in sports cars, luxury cars of all makes and especially my beloved big Chryslers and Imperials that go back to the time of belted tires, I have found that most radial tires need the 30 to 32 pounds of pressure. Below that amount, the handling changes for the worse, not to mention the poor treadwear. I have owned cars with pressure recommendations posted on the door openings, with rediculous settings like 26 pounds to provide the smooth ride. This is dangerous, and the recall of so many Ford Explorer SUVs in the 90's and 2000's pointed this out. Dangerous practice.
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Old 19-03-12, 05:33 PM
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Default Thanks

Thank you all for your help. I need to take it in for a tune up ( it has been standing for a year) of the engine, and I will ask them to check the supention.
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