I would make a test what aluminium alloy it is , and what kind of heat treatment it has .

I find the discussion on wheels unexpectedly interesting, thank you. I have a couple of questions : How is a good wheel made and why is it good? What is different in the making of a bad wheel and why is a bad wheel bad?

Thank you.
Johan Buchner

I doubt if anyone would race a GP Bugatti with original wheels today. Apart from the age and unknown exploits during days gone by, the Aluminium used by Bugatti would be nowhere near as good as modern alloys.
When the factory made a set of Royale wheels for the Schlumpf Esders recreation in 1965 the material spec on the original drawing was amended from plain "Aluminium", to AS-10 heat treated, Y 23.
Most GP wheels nowadays are in heat treated LM25, but for the Royale I specified
BL 169, which is stronger still.

Regarding alloy wheels.

I believe I have read that PS wheels are heavier than standard Bugatti wheels. If correct this could adversely affect roadholding.

A 35B racing friend who examined a PS wheel was not impressed. He is a university lecturer in mechanical engineering. I understand he has chosen to use some wheels from America using an aircraft industry alloy. This is to a higher specification than the simple "aluminium" required by factory drawings and he is no longer welcome by UK BOC at the Williams Trophy meeting.

Until recently original GP wheels could be seen at places like Angouleme and I saw at least one car being bought back to the paddock with a collapsed wheel.

Referring to Raffaeli's "Memoirs" one sees several pictures of GP alloy wheels with all the spokes smashed off in an accident.

Several competitors at Brooklands chose to replace alloy wheels for wire wheels which were regarded as stronger. This would have necessitated replacement of hub/brake assemblies. Costly and time-consuming.

From the pictures, it seems that the right rear wheel broke first, and probably at speed. The bodywork is damaged at that spot, also the entire brake drum went to pieces, also probably because the car was still at speed.

It seems that as a result of the broken wheel, the car then wint into a slip, with both wheels on the left finding grip when they were at a straight angle to the road, and then broke off as a result of the high sideways force. the car never turned over and must have landed on it's floor pan.

Does anybody know how strong the different makes of replica wheels are? We all know that 80 years old wheels are not safe any more, so every serious driver would be using replica wheels. Which are the best? And; are the Pur Sang wheels any worse than others?

Time for some serious research? At "the office" we have several fatigue machines, in which we can do a series of tests. Looking of course not just at the (fatigue) strength, but also at the post fracture behaviour. In other words: would the wheel remain basically together like the one Lazarus shows, or would it just come off completely, like the one in the accidented Pur Sang?

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normal aluminum is only good for coffee spoons. For this reson it is always an alloy. Former alloys have up to 4% copper. Aluminium with copper get`s destroyed from the inside over the years . After the casting , this alloys harden , but over years lose their stability. Bugattis heat treatments was not the best what several tests did show
The best wheel were milled with a 5 axis machine from a wrought alloy. But this is certainly the most expensiveone. Then came a cast in a preheated metal mold. Still too expensive. So we end up with a sand form. Alloys which are often used do not need head treatment , because it is cheaper.
Every 12 cm a riser is for the foundrys too much work, and good aeronautical aluminum again too expensive. All replica wheels that I have examined so far, are far below the quality standard for new cars.

I believe that it was not the competitors at brooklands who chose to change to wire wheels,but rather that the organisers demanded this modification to wire wheels.The Kay Don T54 being a good example.

The T51 wheel design is very much stronger,The modifications to add ribs to the spokes can be done also to T35 type wheels.

Uh oh, I feel the purists coming already!

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Vive la Marque !!

I'm neither an engineer nor an alloy specialist, but I remember quite well that in the 70's it was usual to use aftermarket foundried wheels instead of e.g. original Mercedes (Fuchs) forged ones. These had been priced abt. 1/3 of the originals. Luckily I always had the Fuchs wheels, some day on the Autobahn at a speed of over 200 kmh the right front tire burst, the car banged down on the rim, and it took me more than 1 km to come to halt (no braking to keep the track). There was nearly any rubber left on the wheel, but testing confirmed that the rim was completely undamaged except some scratches. I doubt that a foundried wheel would have survived that incident.

you can not forge aluminium . people allways talk about forget aluminium wheels and pistons . You can press alu , but not forge .

I am sure many people will find that comment strange as I do.Maybe there is a translation problem here.

Whaddya mean, you cannot forge aluminium?

quite so greg,I seem to remember that spitfire props were forged aluminium.I am sure that there is a translation glitch here.

again , you can press it but not forge it .