28 replies to this topic

[Paul McLucas]

Many race cars have large diameter wheels where the tyre looks like a thin black band around the wheel.

However Formula 1 wheels look very small in diameter to me. I seem to remember that they are only 13". As a result the tyres seem to have a very high profile compared to other race cars. But I always thought that a lower profile was better as it made the side wall stiffer.

Does anyone know why F1 tyres made like this?

[Oho]

Originally posted by Paul McLucas
Many race cars have large diameter wheels where the tyre looks like a thin black band around the wheel.

However Formula 1 wheels look very small in diameter to me. I seem to remember that they are only 13". As a result the tyres seem to have a very high profile compared to other race cars. But I always thought that a lower profile was better as it made the side wall stiffer.

Does anyone know why F1 tyres made like this?

Ave !!

The reason is simpply the big difference in the maximum allowed (or is it mandated*) rim diamater and the maximum allowed wheel (*) diameter. Anyway even if they could run lower profile tyres with 13 inch rims they would not do it as they definately want to maximize the size of the contact patch and perhaps to minimize the rpm of the wheels.

- Oho -

[Schummy]

The question would be WHY that big difference between allowed rim and tyres sizes. If there is some tech reason why no other series uses it?

[mp4]

There is a rule on the books that says a tire's overall diameter cannot exceed 26". There's nothing to say a rim can't be bigger than 13".
Many years ago, Williams tried a rim with a 15" diameter but it didn't seem to go anywhere.
I have a theory. Because the suspensions are so stiff, these days, the teams like a 13" tire because it can help absorb some of the load experienced during the course of a lap.
There is NO reason they couldn't race with 18 or even 19 inch rims. I'm guessing it's easier to fluctuate tire pressures than it is to redesign a suspension system...

[naes]

With such stiff suspensions in F1 now the tyre is indeed used as part of the suspension and this is where a lot of the research goes into.

séan

[ray b]

I thought the rim dia is by rule as are all the other tyre dimenions
small rim limits brake size tooo

[desmo]

12.4 Wheel Dimensions:

12.4.1 Complete wheel width must lie between 305 and 355 mm when fitted to the front of the car and between 365 and 380 mm when fitted to the rear.

12.4.2 Complete wheel diameter must not exceed 660 mm when fitted with dry-weather tyres or 670 mm when fitted with wet-weather tyres.

12.4.3 Complete wheel width and diameter will be measured horizontally at axle height when fitted with new tyres inflated to 1.4 bar.

12.4.4 Wheel bead diameter must lie between 328 and 332 mm.

[Paul McLucas]

Desmo, thank you for that.

I see now that the rules force the rims and tyres to be the way they are, particularly the 13" rim size (Rule 12.4.4). The question now is WHY the restriction?

The only things I can think are either

1. Cost saving. F1 has used 13" wheels for a long time and the FIA are stopping the manufacturers experimenting with other sizes

2. Limit the Brake size.

Can anyone clarify this for me?

Thanks

Paul

[Ben]

Tradition.

Ben

[PAD]

I read somewhere recently (can't remember where) but it said that because at 200mph the downforce has increase the effective weight of the car so much that the tyres need to have the large air volumes to compensate for this.

However I can't understand this myself as I would have thought that it was to do with the pressure of the air in the tyre rather than the volume. Can anyone explain further/destroy this theory

[AndreasNystrom]

I think limiting the brakes size is supposed to limit the speeds they can drive with. No idea to drive 500km/h if you cant brake before the hairpin =)

[Oho]

Originally posted by AndreasNystrom
I think limiting the brakes size is supposed to limit the speeds they can drive with. No idea to drive 500km/h if you cant brake before the hairpin =)

Ave !!

Increasing the brake size, I doubt, would much increase the availbale brake force as the tyre traction (friction force between the tyre and tarmac) to my understanding is already the limiting factor at any speed. Then again I do not know the friction force the tyres would generate at 500 kmh and whether that force would exceed the maximum available braking force. Increasing the brake size would however increase the available braking (power) or effect as in ability to do work, by increasing their ability to dissipate heat. After all brakes are thermodynamic machines that convert kinetic energy into heat.

I am not an automotive engineer but I really doubt any race car designer perfers a non dampped springs (air in the tyre) over a dampped spring, thus I belive the tyre compliance is something they have to live with, not something the desire.

- Oho -

[GrooveJet]

I have a theory. Because the suspensions are so stiff, these days, the teams like a 13" tire because it can help absorb some of the load experienced during the course of a lap.

I think the opposite is true, it would be better to eliminate tyre flex altogether and to control all movement with the suspension. Part of the reason that suspension is so stiff is because there is also unwanted flex in the tyre.

[Schummy]

Reading all what was said in this thread I assume rim size is limited just for tradition and to maintain a certain "look" in F1 cars. Is it right? I'd like to see lower profile tyres, but it's just a personal opinion.

[Joost]

Puzzling this is. Teams obviously wan't to maximise rim size and maximise tire height.
In F1 the rim size is set to 13'', but in touring cars the rim size is increased up to 21'' whatsoever. I think to fit in maximum size brake dics. In order to fit to wheel under the car, they use low section tires.

But why do F1 teams use tires up to 660mm, while the rim size is only 330mm?

I can see advantages
- Lower wheel RPM (less friction)
- Relatively less rubber deformation (=better car control)
- Better temperature control
- Increased contact patch area (is this true actually and what's the difference?)

But also disadvantages
- Aerodynamic penalty of large wheels. Not unimportant I guess
- Increasing weight, especially because it's rotating mass effectively counting twice!
- Increased unsprung mass
- Less responsive tire
- Less stiff tire (sidewall)


Please help

And if the rim size wouldn't be set to 13'' would they then use 23'' wheels with low section tires?

[Yelnats]

Perhaps there's a saftey issue involved. The enregy of Tire to tire contact between cars would be better absorbed with a thicker tire profile. Not to mention absorbing the violent forces generated by the curb hopping habits of F1 drivers.

[desmo]

Safety Warning! On the other hand a low profile tired wheel mightn't bounce as far from the scene as a current F1 type wheel in the event of its becoming detatched. Just a thought!

[Group B]

Is anyone here a clever bunny with graphics so we can see what it would look like on one of the current cars?

[Top Fuel F1]

Originally posted by Paul McLucas
Many race cars have large diameter wheels where the tyre looks like a thin black band around the wheel.

You don't want low profile tires on F1 race cars where they continually go over those very bumpy curbs. Even passenger cars, with low profile tires, are well known for getting into trouble (bursting tires) when they hit a curbs or a irregular object.

[Paul McLucas]

You don't want low profile tires on F1 race cars where they continually go over those very bumpy curbs. Even passenger cars, with low profile tires, are well known for getting into trouble (bursting tires) when they hit a curbs or a irregular object.

But don't lots of much heavier race cars such as ALMS and touring cars, hit the same curbs with much lower profile tyres without problems?

Paul

[MrAerodynamicist]

Originally posted by Group B
Is anyone here a clever bunny with graphics so we can see what it would look like on one of the current cars?

This is a topic thats seems to pop up repeatly. Technical issues aside, I just don't find low profile as aesthetically pleasing. I guess I've just exposed to f1 tyres for too long. Plus the phase "low profile tyres" makes me think of Rice!

[Top Fuel F1]

Originally posted by Paul McLucas


But don't lots of much heavier race cars such as ALMS and touring cars, hit the same curbs with much lower profile tyres without problems?

Paul

The originator of the Thread was talking about a really low profile:

Originally posted by Paul McLucas
Many race cars have large diameter wheels where the tyre looks like a thin black band around the wheel.

I was looking at a Race Tech. magazine special issue on Le Mans Sports cars and although the side wall dimensions appear to be less than F1 they also appear to be nothing near the dimensions of the extreme low profile tires. Now there is some finite tire dimension ratio that delineates "Low Profile" from Non. I don't know if the LM's tires under that would fall into the LP category or not. Some of the exterme LP tires have such stiff side walls that they are termed "Run Flat", which under conditions of losing pressure can still run some distance until you can change them.

[Wolf]

Here's a thought- I've heard that tyres account for almost 30% of the 'suspension' (I take it it's not travel, but absorbed energy). But if suspension was to do the whole work it would have to have more travel than the current tyre/suspension combo and that would need either bigger ride height or stiffer springs, plus I think it would be quite difficult to obtain so good a geometry over greater suspension range.

Either way it seems to be a loss in downforce and grip, or grip and driveability... Maybe, if regs didn't specify 13" rims, manufacturers would've found better compromise (say, 14 or 15"); but somehow I don't think we'd be seeing 25% profiles, like on some regular cars I've seen.

[DEVO]

I always thought that the reason behind the 13" rims is to control the size of the brakes that the teams can use. It's already to the point that you can't outbrake other cars... imagine if bigger brakes were allowed.

[Yelnats]

The large proportion of suspension movement accomodated by the higher profile F1 tire would effectivly reduce the deflection of the much heavier suspension and wheel rim. This would result in a reduction of the unsprung weight of these elements due to the lower velocities when compared to the much stiffer compliance of a lower profile tire and the greater movements of the rim resulting.

The higher profile tire seems to have several advantages and one wonders if the lower profile designs are used in full fendered classes like the LeMans prototypes because of the shrouding effect of the fenders on the brakes and the need for an increased air movement through the wheel rims. Note that CART and IRL also use the higher profile tires as do many other open wheeled racers.

[CdnF1Fan]

Consider also for a moment that when you do the math, you'll find the tire profiles on an F1 car to be approx. 50 (series or profile) at the front, and just under 45 (series) at the rear (using the widest allowable tread sizes at either end).

They certainly could achieve far greater handling (and of course much better times) by reducing the tire profile (while at the same time increasing the max allowable rim diameter). Whether this is the logic that the FIA is using by maintaining the small rim dia (13"), or if they are also limiting the maximum brake rotor size is anyone's guess.

CFF

[Yelnats]

Reducing the ratio of height to width is not going to give the expected gains in handling if the width is constrained by regulations. Road cars have benifited from radical aspect ratios as low as 35 because this increase is acheived by widening the tire. This of course is not the case in F1 so I fail to see how these dramatic hanling improvements will be acheived by reducing the height of rubber without increasing the width.

Of course there may be some increases in responsivness due to less tire deflection but I think F1 cars are already regarded as super responsive and perhaps would become unmanagable with lower profile tire. As mentioned in my previous post I am unaware of any top open wheel racing series that has used low profile tires and I am presuming that this has something more to do with handling than regulations.

[Sundar_v]

Oho is correct about brake size being not an issue. I work with aircraft brakes, which uses same material as F1. I would say the limiting factor is the torque generated by the friction of tyre to the surface. Increasing the brake size would increase the friction capability. However, it would be of no use if there is not enough friction between tyre and surface.

Also, if the teams wanted more friction force, they could always play around the contact surface between pads and disks, etc. I have not really seen a brake design drawing of F1 car in depth. But if anyone has any drawings, I would appreciate it.


Sundar

[desmo]

These are all of the Brembo CCR brakes fitted to the Ferrari F12000, other than the cooling scheme these are similar to current practice. Note that the rears had a very much current style "can" shroud at the time although no one seemed to realize it's significance at the time, probably because it was largely out of view.