Hollow Wheels in F1?

[ds.raikkonen]

Oh I never thought of that. Really wierd cos there was a combo of BBS+Bridgestone.

BAR Honda used BBS+Michelin combo in 2005.

[modbaraban]

Oh I never thought of that. Really wierd cos there was a combo of BBS+Bridgestone.

BAR Honda used BBS+Michelin combo in 2005.

Toyota (TF103)

But, Toyota too. I think they changed to B'stones to match the newer car, but why not rims

[ginsu]

I think that BMW are using hollow rear wheels on their new car

Last Year


You can see that each of the spokes on the wheels are of I-beam section indicating that the spokes are solid.

This Year


Now, the spokes are of much larger section width and no longer I-beam (I have a much higher res picture to confirm this). This suggests that the spokes are hollow because they are of such large size.

Hollow spokes would probably be open to the inside of the rim surface allowing a much much larger air volume than would otherwise be possible with solid rims. Because of the loss of Traction Control, this should make the tires a lot more forgiving and alter the overall spring rate of the tire as compared to a normal rim.

All in all, if BMW are indeed using hollow wheels to increase the air volume inside the tire it would offer them a large benefit as compared to other competitors.

Q: How does an air spring differ from a coil spring?
A: The visual difference is obvious. The operating principles are different. One produces a spring force by stressing a steel rod, while the other produces the same force by compressing a trapped volume of air. Functionally, there is no difference. The vehicle chassis only interacts with a spring force. It doesn't care whether that force originates from a steel spring or from an air spring. The airspring is different because we can control its properties. We can change its height (and the height of the vehicle) by controlling the pressure within the air spring. We can also change the spring rate in a dual-rate system by altering the volume of air contained inside the spring. To accomplish the same feat with a coil spring requires changing parts: more parts = more time = more money.

[Jersey Tom]

I can't imagine how you'd cast that hollow.. or why.

U-channel rather than I-beam, maybe. Would make a lot more sense.

[ginsu]

You'd cast it hollow, not for structural reasons, but to increase the volume of air in the wheel.

That's why I put that quote, noting that an increase in air volume affects the spring rate of the tire (and probably also the damping). This means that BMW would effectively be running a more compliant, more forgiving tire then all the other teams.

If you don't think there's a benefit to that, then you don't know what makes a car fast.

[mx_tifoso]

That's why I put that quote, noting that an increase in air volume affects the spring rate of the tire (and probably also the damping). This means that BMW would effectively be running a more compliant, more forgiving tire then all the other teams.

Interesting topic going on....

But, BMW's advantage over the other teams is assuming that only BMW has this technology at their disposal. Wouldn't you agree? Because although I don't have any inside knowledge of F1, I don't believe that only BMW has this at the moment.

There are many other wheel manufacturers involved in F1, and I imagine that they too have caught on to this development.

What wheel manufacturer does BMW use?

[ginsu]

As far as teams that run without the wheel fairings, it's easy to determine if the spokes are hollow. But teams like Ferrari and Toyota that are running rear wheel fairings make it difficult. Fortunately, the BMW was running without it's fairings, which is pretty unusual (1 picture out of 40).

I did find out something very interesting that confirms my beliefs about the wheels being hollow.

I have some very high resolution pictures (sorry, don't know how to post them) of the BMW car during testing with the wheel fairings removed and I can confirm that the front wheels still have I-beam section spokes. That means that BMW specifically had a set of wheels created for the rear only that are probably hollow and feature the thick sectioned spoke.

BTW, forging magnesium into a hollow shape is probably an extremely difficult manufacturing job!

[Jersey Tom]

That's why I put that quote, noting that an increase in air volume affects the spring rate of the tire (and probably also the damping). This means that BMW would effectively be running a more compliant, more forgiving tire then all the other teams.

If you don't think there's a benefit to that, then you don't know what makes a car fast.

Why would you do that when its 100x easier to drop the spring rate of the suspension?

Wheel rate is just as much spring rate as it is tire rate. Two springs acting in series.

And more compliance is not always good.

[ginsu]

Well, because the aero loads define the minimum ride height allowable and softening the suspension spring rate will cause the car to bottom out which could lead to a loss of control. I'm pretty sure that the tire's spring rate doesn't have as direct an effect on the ride height (although, it does have some).

They have to run such high spring rates in order to control the aero loads that the spring rate of the tire is actually lower than the spring rate of the suspension, so it's the tire that deflects first.

The spring rate of an air spring is progressive and is non-linear meaning it has an initial linear portion and then the spring rate ramps up really quickly and becomes incredibly stiff. By increasing the air volume of an air spring you move the 'ramp' part of the curve back a little farther delaying the sudden increase in spring rate.

This delay effectively gives the tire a more linear initial spring rate that stays linear for a longer period and under greater deflections than a tire with a smaller air volume. Effectively, this would make the tire more predictable and less sensitive to bump forces (essentially, more compliant) resulting in better traction. Since traction control has been banned, this is one of the few mechanical means to enhance the grip of the rear tires.

There are probably other benefits as well to having a larger air volume, because the tire is visco-elastic it has some damping properties. I'm not sure if the air volume affects this directly, but it's possible.

I tell you one reason why I suspect this is of large benefit is that I've done some back to back comparisons of low-profile tires vs standard tires and there is a significant difference in drivability. Yes, carcass construction does have a part in it, but I think the big difference was in air volume.

Also, I love running big fat tires on my MTB exactly because the increase in air volume really helps out over the bumps.

[DaveKillens]

Additionally, if the spokes are hollow, then there would be more wheel surface in contact with the gas. That would lead to improved cooling of the wheel/tire assembly.

[Jersey Tom]

Well, because the aero loads define the minimum ride height allowable and softening the suspension spring rate will cause the car to bottom out which could lead to a loss of control. I'm pretty sure that the tire's spring rate doesn't have as direct an effect on the ride height (although, it does have some).

Nope. They both have just as much effect. You are correct in the respect that the suspension itself won't bottom out, but if the tire rate goes down it will squash more under load and the car ride height will drop, and the chassis will bottom. Not good!

I tell you one reason why I suspect this is of large benefit is that I've done some back to back comparisons of low-profile tires vs standard tires and there is a significant difference in drivability. Yes, carcass construction does have a part in it, but I think the big difference was in air volume.

Other way around. Commonly accepted that sidewall stiffness is a big link to handling. Low profile = shorter sidewall. Think of it as a beam deflection problem. Shorter length will be effectively stiffer.

Air pressure is going to also have a big effect on how much rubber you have on the road and on steering feel.. but not so much volume.

[CMSMJ1]

Additionally, if the spokes are hollow, then there would be more wheel surface in contact with the gas. That would lead to improved cooling of the wheel/tire assembly.

Agreed..but you would have a problem with fluctuating tyre pressures due to the heat from the rear brakes..

I think this is why you will not see hollow front wheels at all and why all rear wheels might not follow this trend.

You would have an unstablee, unbpredictable car and if there was a safety car your pressures would drop significantly. This as you would run lower pressures when cold to account for the heat transfer from the brakes.

[ginsu]

Nope. They both have just as much effect. You are correct in the respect that the suspension itself won't bottom out, but if the tire rate goes down it will squash more under load and the car ride height will drop, and the chassis will bottom. Not good!

I agree that it will affect ride height, but I don't think it's linear. In my experience, after a certain inflation pressure is reached the tire does not balloon out as much, and so it doesn't affect ride height as directly as it does at lower pressures.

I looked into my only tire book by Paul Haney 'The Racing and High Performance Tire' and it had virtually nothing on air volume. But I think this is because hollow wheels are a relatively new technology and, as such, there is limited information on it's effects. I would note that the original BBS article does mention that the increased air volume enhances ride quality.

Other way around. Commonly accepted that sidewall stiffness is a big link to handling. Low profile = shorter sidewall. Think of it as a beam deflection problem. Shorter length will be effectively stiffer.

Air pressure is going to also have a big effect on how much rubber you have on the road and on steering feel.. but not so much volume.

I agree that sidewall stiffness/carcass construction have large effects on the handling of the tire, but has anybody done any experiments on different air volumes holding the tire size, pressure and construction constant? That would be the only way to know, and unfortunately, I haven't been able to find any conclusive information. Although, tire companies are infamous for hording their data.

I would definitely say that the front tire would not benefit as much from a larger air volume due to needed cornering stiffness, and hence, the front tire spokes look thin, have the I-Beam section and do not look hollow. Although, any development in this area seems to be hidden behind the wheel fairings, which is annoying.

I emailed Scarbs on this subject and he told me he is asking O.Z. racing about the technology. Hopefully we can get some conclusive evidence on the hollow wheels, then the discussion about pros/cons will be a little less speculative.

[humble sabot]

You guys are arguing like the difference in volume is significant.
1-2 hundred mL as compared to the relatively large volume of an F1 tyre in the first place is really not very much. I'd much rather bet on the spokes being stiffer.

[ginsu]

scarbs has told me that 0.Z. said these wheels were specifically developed for BMW, so they are the only team who has them, all the other teams are running I-Beam section wheels and have no problems with them failing, so I don't think they were ever suffering in the stiffness department.

100-200 mL is nothing, I agree, but I was thinking more along the lines of a Liter or so. None of us know how much volume it could make because we have no idea what the wall thickness is on those wheels, it could be significantly thin, or not.

scarbs told me he is now going to contact BMW/Sauber directly.