The weight of the wheel and its effects on performance

[rick1776]

I was always of the opinion that the lighter the better. If one can reduce the inertia then this is a good thing with respect to performance. Now I am told that this is not necessarily correct. The physics of why this should be the case however escapes me.

From another thread I quote the following:

"Rick, you forget that the gyroscopic effect (again within a certain range) alters the steering considerably. In the Rondeau-Ford test, it was the first thing that the 6 drivers commented after their stint and that could not be immediately understood: after adding 28lbs of unsprung mass (7lbs per wheel center, the outer rims remaining the same) the steering was noticeably lighter, acceleration AND braking were improved as shown on the on-board computer and every driver was lapping an average of 1 second faster than with the lighter wheels. It took a while to figure it out.
The Ligier F1 thing was even weirder. I was involved with a company manufacturing the wheels for both Ligier and Renault F1 teams then. The wheels were about 23-24lbs and they wanted less weight. Ducarouge was the design engineer and we devised a lighter mag center for the 3-piece bolted jobs. We got down to 17lbs per wheel, and the car lost its edge. Both Pironi and Lafitte were complaining of heavy steering and losing speed at various places on the track. A return to the heavier wheels solved the problem instantly.
No one could really come up with a reasonable explanation, Ducarouge claimed that the lighter wheels must have been flexing. Not on our test rig..."

Now I am not disputing the results (I will assume that the person is honest in what he is posting) but the physics of why a heavier wheel should offer better performance escapes me. Is there someone that knows why this is the case?

cheers
rick1776

[cptsideways]

From years of building bicycle wheels, I'd say gyroscopic effects came into play. I think it depends where the weight is on the wheels & this in turn effects feel. Still I'm no physysist but I would like to know more.

I do remember playing with various bike wheels that I'd just built up, spinning them & holding the hub axles you could move them around against the gyro effect & the difference was very noticeable between the wheels of different builds.

[leorest]

rick1776 said:

...7lbs per wheel center, the outer rims remaining the same...

This would obviously be the place to put the weight to make the least difference to the gyroscopic forces. Would have been interesting to progressively add weight to the rims and see how much gave the same results. I'm sure that all this chav/bling sticking big wheels on results in poorer all round handling in 99% of cases.

[victormeldrew]

Maybe it's not the absolute mass of the wheel, it's more the distribution thereof. The Rondeau-Ford test as I read it added mass as the centre, reducing gyroscopic effect and therefore making the wheel easier to turn at speed. I don't see where the advantage is in terms of improvements in acceleration and braking though, I'd have thought unsprung weight was a very minor player in determining how much traction was generated. Maybe for very minor surface irregularities the lighter wheels don't generate enough force to make the suspension work, but the extra unsprung weight makes the forces enough to overcome the "stiction" and inertia in the suspension components and get enough flex to allow the wheel to more accurately follow the surface.

[Mr Whippy]

victormeldrew said:

Maybe it's not the absolute mass of the wheel, it's more the distribution thereof. The Rondeau-Ford test as I read it added mass as the centre, reducing gyroscopic effect and therefore making the wheel easier to turn at speed. I don't see where the advantage is in terms of improvements in acceleration and braking though, I'd have thought unsprung weight was a very minor player in determining how much traction was generated. Maybe for very minor surface irregularities the lighter wheels don't generate enough force to make the suspension work, but the extra unsprung weight makes the forces enough to overcome the "stiction" and inertia in the suspension components and get enough flex to allow the wheel to more accurately follow the surface.

Not sure, but if you take a 5kg wheel, and measure it's gyroscopic procession and rotational inertia, and then ADD weight to the centre only, it's gyroscopic procession (not sure what units that is) but whichever, the inertia WILL be higher, and it's gyroscopic procession will be higher.
Redistributing the mass to the middle would decrease gyroscopic effects, but adding mass to make the relative mass distribution towards the middle won't reduce gyroscopic effect.

Perhaps their lower wheel mass fundamentally altered the suspensions ability to control the wheel due to un-tuned damping, which I'd say was much more significant.
Significantly lighter wheels will need altered damping to make the best of them!

Dave

[rick1776]

Perhaps the answer is in the fact that the suspension was not able to cope with small surface undulations all that well. Poorly sorted?? The higher gyroscopic effect being like a steam roller effect. Surface undulation?? What surface undulation.

The higher acceleration and braking also have me stumped Once again the higher gyro effect would help the wheel from being suddenly displaced by surface undulations.

cheers
rick1776