The Camaro Club (UK)

A Physics question for you all. Bigger wheels (larger circumference - same width, tread, make etc) quicker or slower accceleration?

I work with loads of engineers and scientists who all say that bigger wheels accelerate slower which I can understand but don't fully. They talk all about power v torque v coefficents and written loads of formula down and talk about big and small cogs on bycyles.

My theory works on the following:-

A Z28 has loads of power and torque (too much sometimes). The quickest acceleration must be the point just before it breaks traction. At this point the wheel nuts are travelling at a certain speed. If I put slightly larger wheels on (say go from 17" to 18"), a Z28 can turn those wheels nuts at that same speed as before (before breaking traction) (in fact I'm sure it can wheel spin those if it wanted too). So at that point the wheel is travelling further due to the larger circumference of the wheel (1 rotation = longer distance) in the same time and therefore accelerating quicker.

So I beleive that whilst your car has enough power to spin the larger wheels it will be accelerating faster with larger wheels (incl Tyre's), it probably then doesn't accelerate as fast as a smaller wheel once traction can't be broken as the wheel "Cog" is larger and takes more power to push round.

So in my summary It will accelerate faster whilst you have the power to break traction but past that point the smaller wheels will then accelerate faster.

What do you think? Or who cares anyway, it comes down to how phat the car looks with bigger wheels.
At the end of the day I know its immaterail but just curious. I am sure the tyre compound, make of tyre and other set ups have a bigger impact and the difference will be immaterial.
To help settle an argument between friends.

im a physicist.

You are and are not correct, its all based upon the used assumptions. Skill of driver and such

1: At the point of slipping, ie with NO SPIN you will accelerate faster with smaller wheels always (assuming the coefficient of friction for the tires is the same)

2: At WOT for example, there will be an optimum tire/wheel size for the vehicle power as to transfer the maximum power/torque to the forwards motion without wheel spin (assuming the coefficient of friction for the tires is the same, as you say the bigger wheels are harder to spin but you still can so they are still not big enough, in this approach)

In 2 there is NO driver skill, plus the wheels would have to be big and there are realistically other factor such as rotating mass, tire wall height, compound. If you were to have a car in situation 2 with a guy who just floors it vs. a situation 1 car with a skilled driver, who can apply throttle such that it doesn't spin tires, then no 1 would win

If you are drag racing, you get smaller wheels, big walled tires, with super sticky compound and then you cant spin them off the line when you stomp it, you just get thrown forwards or bog the engine,but they would be crap for handling in turns etc

I have bigger wheels on mine, 18" with 255/35/18 tires. They are the same rotating radius give or take a few cm, but they are much heavier, have a better tire than stock and can still be spun up. in fact, in certain situations they spin easier cause there is less tire wall give than smaller wheels big tires, so the characteristics change all round, ie handling, straight line, acceleration through corners (aka drifting )

But they look good, so thats all I care about!!

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'99 Z28 A4, 253 LS2 heads, 228R TSP cam, Patriol Dual Springs, Double roller timing chain, LS6 ported oil pump, OBX LTs, 3" True Duals, LS6 intake, 42lb/hr injectors, SLP lid + bellow, EFIlive COS 3 Speed Denisty Tune (self tuned), 3200 Circle D stall, CAI mod, KYB AGXs, Eibach Pro Front Springs, UMI panhard, LCA + Brackets, Strut Brace, Custom Subframe connectors, WS6 axle with 3.42s, 18" American Racing Rebels, US mirrors, 93 tail lights, 3.5 inch custom cowl hood. Mickey T's Street DRs on Vette-ZR1 wheels for the strip !
Best ET: 12.0 @ 116 mph (on a 0-60ft of 1.8 s)

I'm glad you have made it clearer. Its become a heated debate here.

I now believe that up to the point that you have too much power to use it all the bigger wheels will match the acceleration of a smaller wheel but soon as all the power can be applied in full the smaller one will accelerate faster (with equally skilled drivers in a perfect world....). I think my comment re the wheels travelling at the same speed isn't valid as the rubber would be travelling faster at the outer edge (compared to the wheel nuts) and hence if accelerating faster would loose traction. Hence could only match the acceleration. Der.

I've just gone from 275 x 40 x 17 to 275 x 40 x 18 (an extra inch) and the wheels themselves look a lot better so am very pleased. Although the speedo I don't believe is now accurate. I have used it in conjuntion with Tom Tom and believe the speedo is running about 3mph slower than reality. Presumably I can get the garage who has a programmer to change this.

Thanks again for your comments.

what gen camaro have you got?? You've prob said before but cant remember???

generally speedos will run higher than usual with stock wheels for safety reasons, my 4 gen is 4-5 km/h out at 50 km/h for example and mine has been tuned to tires and diff but the dials are actually wrong. My scan tool says the speed is 'blah' which matches the GPS. So all i can do is move the needle itself haha

yeah, the whole tire/wheel thing has so many variables you can argue forever, but if you want better traction, easiest way is drag radials !!!

Glad you like the 18" they are just the right size (for my 4th gen anyway) also next time you get tires check out 'cam skill' they do good prices, i get 255/35/18 as they are cheaper than 255/40/18 i previously had, but all depends on rim width too as they are an odd size, but 275 like yours are more standard, if you get what i mean

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'99 Z28 A4, 253 LS2 heads, 228R TSP cam, Patriol Dual Springs, Double roller timing chain, LS6 ported oil pump, OBX LTs, 3" True Duals, LS6 intake, 42lb/hr injectors, SLP lid + bellow, EFIlive COS 3 Speed Denisty Tune (self tuned), 3200 Circle D stall, CAI mod, KYB AGXs, Eibach Pro Front Springs, UMI panhard, LCA + Brackets, Strut Brace, Custom Subframe connectors, WS6 axle with 3.42s, 18" American Racing Rebels, US mirrors, 93 tail lights, 3.5 inch custom cowl hood. Mickey T's Street DRs on Vette-ZR1 wheels for the strip !
Best ET: 12.0 @ 116 mph (on a 0-60ft of 1.8 s)

I've got 4th Gen 98 Z28 convertable.

I've got 17inch on the front with 18inches on the back (corvette C5 wheels)
The dash board is lighting up all the time though now, as expected, re traction control and ABS. Its turning both of these off itself as it doesn't like the different size wheels. I am more than happy to live with that as the car feels and looks good although I wondered whether this could be changed using the programmer that plugs in under the dash to let the car know what's it wearing. I'm not sure if that will work.

I watched the speed whilst looking at tom tom - not sure how accurate the tom -toms are though re speed reading. I have another GPS device which I can try. Its good to know how accurate your speedo is sometimes...

Thanks for the advice re tyre prices. I get through tyres quite quickly.

I've got a guy hear who used to work for a formula 1 team who has just showed me a mathematical model that shows only some of the variables that effect acceleration and just amazed at how many there are from all the components of a car...

cheers

There tyre prices look very good. thank you

yeah i bet, car torsion, suspension component, diff lock out factor etc etc??

I have EFilive full tuning suite and there is a capability to change wheel and tire sizes but not fo front and rear separatly, usually you get a bit bigger tire on front to compensate, not sure how close to the same size they have to be, i ran stock rims on rear with 18s on back an 255/40 tires and all was ok

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'99 Z28 A4, 253 LS2 heads, 228R TSP cam, Patriol Dual Springs, Double roller timing chain, LS6 ported oil pump, OBX LTs, 3" True Duals, LS6 intake, 42lb/hr injectors, SLP lid + bellow, EFIlive COS 3 Speed Denisty Tune (self tuned), 3200 Circle D stall, CAI mod, KYB AGXs, Eibach Pro Front Springs, UMI panhard, LCA + Brackets, Strut Brace, Custom Subframe connectors, WS6 axle with 3.42s, 18" American Racing Rebels, US mirrors, 93 tail lights, 3.5 inch custom cowl hood. Mickey T's Street DRs on Vette-ZR1 wheels for the strip !
Best ET: 12.0 @ 116 mph (on a 0-60ft of 1.8 s)

Bigger wheel's and tyres (rolling circumference) = slower car in 99.9% of cases...

More show......but less go