18 replies to this topic

[Luke Macahan]

Hi,

I'm sure people have asked this before, but I am still ignorant: why are open wheel race cars fitted with high profile tires? Supposedly fast road cars are usually fitted with low profile tires.

Please enlighten me!

Martin

[Chevy II Nova]

The Formula rules surrounding tyres require that makers use a minimum sidewall height, among other things.

[BRIAN GLOVER]

The low profile can be structured to take higher loads with lower tire pressures without foot print distortion and is more compliant to limitations of camber gain in typical f1 suspensions with little movement. There might be damping considerations that I am not aware off. There are some suspension whiz kids here, so I am surprised you havent got many responses.

Originally posted by Luke Macahan
Hi,

I'm sure people have asked this before, but I am still ignorant: why are open wheel race cars fitted with high profile tires? Supposedly fast road cars are usually fitted with low profile tires.

Please enlighten me!

Martin

[RJL]

F1 rules require a 13" rim.

[Greg Locock]

In road tyres, at least, there is an 'optimum' aspect ratio, for dry weather tyres, at around 50-60%. If you go any lower profile than that then you have to start weakening the sidewall such that you don't really get any further benefit from the shorter sidewall.

Super low profile tyres on street cars are put there by stylists/packaging, not ride and handling engineers.

Stringing together ideas in the previous notes, for F1 you want maximum contact patch area for max lat acc and traction for a given life. You want to minimise the tyre size to reduce drag. You have 13 inch rims. The compromise between those sets your tyre size.

I, personally, would not be surprised to see some experimenting with smaller tyres, if that is allowed.

[Rainer Nyberg]

Originally posted by Greg Locock
Super low profile tyres on street cars are put there by stylists/packaging, not ride and handling engineers.

I am sure if the regulations would allow it, all F1 cars would use as large wheels as possible (and therefore super low profiles).

Compare with sportscars which in some cases are basically built as single seaters with their wheels covered. They all typically use 18" or 19" diameter wheels.

However the F1 designers does also use the springing effect of the balloon tyres.

http://www.racingspo...0-09-30-077.jpg

[Wuzak]

Originally posted by Greg Locock
I, personally, would not be surprised to see some experimenting with smaller tyres, if that is allowed.

The maximum is regulated.

The dry tyres must be 660mm (I think) in diameter when new and presurised at 1.4bar, and wet tyres 670mm under the same conditions.

So there is no reason why someone couldn't make small tyres if they so wished.

[Luke Macahan]

Alright... Thanks for replying!

Martin

[powertrain]

Originally posted by Luke Macahan
Hi,

I'm sure people have asked this before, but I am still ignorant: why are open wheel race cars fitted with high profile tires? Supposedly fast road cars are usually fitted with low profile tires.

Please enlighten me!

Martin

For one thing, fat tires absorb shocks better than running almost on the wheel rim...

[RDV]

As stated before F1 rules establish size of tire. This came about during the Goodyear years; while tires were still cross-ply, very low profile tires make for difficult cord orientation and keeping the flat surface required.

Remember we were using tires with 20" wide tread; the cords were acting like a catenary and when not inflated tread was actually concave. Due to tread width tyres were actually lower ratio than today, especially the rears.

During that period we actually did a lot of testing with 10" dia rear rims to help that problem. When radials came to F1 with Michelin (first time around) rims had been fixed at 13" by rules, but O.D. was still free. During transition period while Goodyear was competing with Bridgestone sizes (width and then O.D.) got frozen.

Michelin, already running 18" dia rims and then 19" dia in sport cars, LMPs and touring cars requested bigger sizes on re-entry to F1 but Bridgestone did not agree, due to very different carcass design philosophy.

So despite the better suitability of bigger rim dia, especially on lateral spring rate to vertical spring rate ratio (common ratio on LMP tires are @ 1.1, whilst F1’as are @ 0.85 +/- 8% depending on manufacturer, with Michelin tending to be stiffer rate vertically and laterally) sizes continue to be a retrograde choice by the FIA.

The tire carcass concept skirmish was highlighted at Hungaroring slanging match.

[RDV]

In road tyres, at least, there is an 'optimum' aspect ratio, for dry weather tyres, at around 50-60%. If you go any lower profile than that then you have to start weakening the sidewall such that you don't really get any further benefit from the shorter sidewall.

This is mainly for ride reasons; a stiff carcass is not acceptable on road cars for comfort. Ride harshness not really a concern in racing, contrary to production cars, smaller OD will mandate a stiffer compound also as rubber will flex more and generate more heat, also giving belt to tread attachment problems...

Tire manufacturers in F1 will always go to biggest contact patch available, and increase diameter as much as possible to accommodate load. Remember that in the 70's it was not unusual to see F3 (with @ 120 bhp) using 11" wide fronts and 14" wide rears, almost as wide as today's F1 tires.

[turbolimac]

Also, very large rims are used because you can fit big brakes underneath....

In F1 rim size is mandated by the rules....

[Luke Macahan]

Again: Thank you for your replies! It seems there are some great sources of knowledge on this forum!

Martin

[Felix]

I have spoken to Technical Directors from teams running either of the tyre brands presently in F1 (and two who have run both brands in succession) and all agree that low profiles are the way forward. (One actually said he found it ridiculous that F1 trucks have lower profiles than the cars they carry!)

But, right now neither tyre company actually wants to change - Bridgestone has 13"/65 aspect data going back to '97, and Michelin is now facing its fourth season under its present visit to F1, so the chances of either wanting to change for the sake of change are basically zero.

(Don't forget, here, that Michelin has its Optimum Camber Patch patents which theoretically give them an advantage over Bridgestone, and all Michelin's F1 exposure with OCP has been on 13" rims.)

But, there are numerous semi-bright lights on the horizon: steel brakes, retained (or stored) energy and spring rates. If the FIA wishes to go steel brakes, it will need to increase disc size to maintain present braking rates for safety, and that needs bigger rims. Bigger rims and present rolling radius mean lower aspects.

Second, the FIA has commenced study into the amount of stored energy in a tyre, and the lower the sidewalls, the lower the elasticity and therefore 'bounce' potential of flying tyres. Think back on the number of flying wheels, tethers notwithstanding, and the two marshals killed in the last three years...

Finally, Technical Directors wish to have control over spring rates, and with tyre sidewalls providing greater springing than the springs (torsion bars themselves) they are lobbying for lower aspects to reduce thye amount of 'outside' springing.

Will these points lead to lower sidewalls more in keeping with what we see on high-performance road cars and Le Mans racers? My opinion is NO- simply because higher sidewalls give more advertising space for the tyre manufacturers to stick their names on...

[Wuzak]

Originally posted by Felix
Will these points lead to lower sidewalls more in keeping with what we see on high-performance road cars and Le Mans racers? My opinion is NO- simply because higher sidewalls give more advertising space for the tyre manufacturers to stick their names on...

Couldn't they mandate those floating wheel covers that stay in the same position as the wheel rotate? Planty or room for the manufacturer's name on them!

Or that special system that Toyota had on one of the Newman/Haas cars a year or two back?

[RDV]

Second, the FIA has commenced study into the amount of stored energy in a tire, and the lower the sidewalls, the lower the elasticity and therefore 'bounce' potential of flying tires. Think back on the number of flying wheels, tethers notwithstanding, and the two marshals killed in the last three years...

Tut, tut, flawed reasoning... not unless you change the material.... what is important is the tire spring rate, for a given tire the deflection might change as a function of energy dissipated into it, but if we have similar rates although the deflection will be different, discounting carcass hysteresis, it will bounce just as much..... if you use steel tires it might change.... or if you change the vertical spring rate to stiffer.

The logo size has less to do with it than current economic situation, Bridgestone has had a hemorrhage of funds with the Firestone/SUV tire saga in the US and related legal costs plus recalls, and has had a production problem as one of their major factories in Japan, thus not very keen on spending a lot of money on development, over and above what they are committed to.

[Felix]

And do away with Max Mosley's (or Ferrari's) beloved pit stops, as the covers do not allow tyre changes in a hurry? Not likely!

I know the CART type covers, but, frankly, they were almsot illegible, and CART (on ovals, where Toyota used the covers) hardly ever changed tyres, and certainly not due to wet weather.

[Felix]

I can assure you that marketing people from both tyre companies advised me that the sidewall height is an EXTREMELY important marketing consideration. Also, Bridgestone's fire has little or no impact on its overall revenue steams as the disruption, whilst seemingly large in production numbers, is minute when expressed as a percentage of total annula output. Plus, the losses are/were covered by insurance...

As for sidewall elasticity, a higher sidewall from a given formulation has greater elasticity ('bounce') than a lower aspect of the same formulation. I don't say so, physics does... Plus, this elasticity also comes into pl;ay when wheels/tyres interlock - the greater the sidewall, the greater the catapult effect.

[McGuire]

Personally, I am not a fan of low-profile tires and large-diameter wheels for road use, and I won't buy a car on which they are the only combination available. Their all-weather capabilities are comically poor -- in snow they can render a car nearly undriveable. Also, the wheel, hub, and suspension loadings are far greater with these rubber bands. If you find a curb or pothole it can be incredibly costly. At the least you will be buying a very expensive wheel and quite possibly some front end parts.

And maybe I am getting old... but to me, the sacrifice in ride quality with these radically low profiles is just not worth the slightly better grip and turn-in. Not being a maniac, I don't need the marginally better performance 99% of the time. I'll stay with the donuts as long as I can. Just my subjective preference.