Tire to rim ratio

[redcat]

This is my first contribution to the site.
I'm seem to recall that F1 tyres are high profile so that the maker's name can be clearly read on the sidewall. Of course with a single tyre supplier this no longer appliies.

[RacingManiac]

I am pretty sure thats NOT the reason, but then I can't tell you why they kept the 13inch wheel package for this long...

[modbaraban]

I was just going to ask the same thing but kept forgetting. I'm really curious.

[Jersey Tom]

Has NOTHING to do with having the tire company's name on the side.

13" rim to limit braking.

Tire size is what it is to match with the required load and vehicle performance.

[kilcoo316]

just curious about different racing series' tires and rims. sports cars tend to have larger rims with low-profile tires, but f1 has small rims with very high-profile tires. simple question i suppose, who's got my answer? thanks!

btw im not looking for "because the regs say so"

There was a piece on racetech by Mike Gascoyne on this a few years back.


Unfortunately, the answer is "because the regs say so".


Undoubtedly an F1 car would go faster with lower profile tyres (assuming same tyre diameter), you've better suspension control and a lighter unsprung mass. But, years ago, it was written into the regs how big the bead diameter is (328-332mm) and it has never changed.

[Jersey Tom]

Undoubtedly an F1 car would go faster with lower profile tyres

Not sure I agree with that...

[kilcoo316]

Undoubtedly an F1 car would go faster with lower profile tyres

Not sure I agree with that...

That is not solely my opinion

Gascoyne said it - I'm not going to contradict him.


How much of the relative ride height variation is through the suspension travel, and how much through the tyre sidewall?

Why did Renault build a mass-damper?

[Jersey Tom]

Gascoyne also isn't a tire engineer

There are benefits and drawbacks to short sidewalls, for sure.

[RacingManiac]

just curious about different racing series' tires and rims. sports cars tend to have larger rims with low-profile tires, but f1 has small rims with very high-profile tires. simple question i suppose, who's got my answer? thanks!

btw im not looking for "because the regs say so"

There was a piece on racetech by Mike Gascoyne on this a few years back.


Unfortunately, the answer is "because the regs say so".


Undoubtedly an F1 car would go faster with lower profile tyres (assuming same tyre diameter), you've better suspension control and a lighter unsprung mass. But, years ago, it was written into the regs how big the bead diameter is (328-332mm) and it has never changed.

Not sure about the lighter unsprung mass part....less tire, more rim, bigger uprights, brake package, wheel bearing...more rolling inertia....

[kilcoo316]

Not sure about the lighter unsprung mass part....less tire, more rim, bigger uprights, brake package, wheel bearing...more rolling inertia....

Why not?

The tyre is heavier than the rim! If I recall right (admittedly quite a big if), Michelin's tyres weighed more than 15kg a piece!!


The uprights are defined by the hub, not by the rim. Same with the brake and wheel bearing.

[Jersey Tom]

I highly doubt they're over 15kg a piece, unless they were using steel belts in those tires like they do in other series.

Bridgestones would be a hell of a lot lighter if that was the case.

[RacingManiac]

I don't know how accurate one of those Bridgestone demo car running around at tradeshow and stuff, you get to try F1 tire changes on a Ferrari of some sort, and those are LIGHT....probably lighter than a 13" Formula SAE wheel/tire assembly with alloy wheel(~20-30lb-ish? I don't remember how much a Goodyear FSAE tire weighs, the wheel itself is ~9lb)

Are we talking about though making the tire lower profile, or making the wheels bigger? You would be lighter in the former, definitely heavier in the latter...

[paused]

I highly doubt they're over 15kg a piece, unless they were using steel belts in those tires like they do in other series.

Bridgestones would be a hell of a lot lighter if that was the case.

Definitely not. I was lucky enough to get paddock and pit tour with BMW and we were show how light these were. I can't remember exactly how heavy these were but something around 20 pounds or so (8Kgs). That is tyre and rim together. Of course these were the grooved tyres but I don't think that would make a difference.

[bill shoe]

Tires!!- I love it when we discuss the most important part of the car.

On any typical street car if you upsize the rim diameter and downsize the tire sizewall so the tire OD remains the same then you have increased the assembly weight. On an extreme racecar like a modern F1 I don't know the answer but my guess is the total weight still increases.

Forged aluminum is probably better vs rubber in terms of strength to weight or stiffness to weight. However, the relevant question is forged aluminum vs compressed air contained in a light rubber bladder. Also remember the wheel is (by rule I think) a single simple material while the tire is actually an advanced composite material.

You don't just care about tire/wheel weight, you also care about rotational inertia. When a wheel gets bigger the wheel perimeter moves out to a larger radius and the rotational inertia goes up in proportion to the square or cube of this radius. A larger wheel with a shorter sidewall will definitely have more rotational inertia. In a typical street car the rotational inertia adds around 3% to the effective weight of the car (dim memory here, but it sounds about right). This means the car might weigh 1000 kg, but given that you also have to rotationally accelerate the wheels/tires it's like you are effectively accelerating 1030 kgs. F1 and all other racing categories set minimum limits on the direct weight, but not on the rotational inertia, so if you can reduce the rotational inertia it's like you have cheated the rules and reduced the effective weight anytime you accelerate or brake.

There was some mention in a previous post that larger wheel diameters would lead to heavier uprights, suspensions, etc. I don't think it's that simple. If the wheel diameter increased to 15 inches then teams would still be free to package their uprights and suspensions for a 13 inch wheel and acheive the same suspension weight. They would only increase the upright size, etc. if they thought it somehow resulted in a faster overall car. On the current generation of F1 cars aero is dominant so they all want to move suspension farther from the important aero areas by moving wishbones higher and closer to the fore-aft middle of the car.

After all my techno blabber it comes down to someone's previous observation that anytime wheel diameter is unrestricted by the rules then the competitors use large wheels and short sidewalls. This is clear evidence that this combination offers some advantage. Shorter sidewalls offer higher vertical stiffness and higher natural frequencies that are more conducive to the all-important crushing downforce and rigid/stable ride heights of modern ground-effect racecars. In the absence of these extreme ground-effect and suspension characteristics I think you'd actually see taller sidewalls in other categories such as LeMans prototypes.

[RacingManiac]

There was some mention in a previous post that larger wheel diameters would lead to heavier uprights, suspensions, etc. I don't think it's that simple. If the wheel diameter increased to 15 inches then teams would still be free to package their uprights and suspensions for a 13 inch wheel and acheive the same suspension weight. They would only increase the upright size, etc. if they thought it somehow resulted in a faster overall car. On the current generation of F1 cars aero is dominant so they all want to move suspension farther from the important aero areas by moving wishbones higher and closer to the fore-aft middle of the car.

Was talking more along the line of common sense practice in that you would want to package something with wider installation stiffness by locating various joint as apart as packaging allowed, but obviously F1 car have become so much of a one-trick-pony that they have long ignored that.