Larger wheel diameter - slower acceleration

[Forg]

But ... as I said above, the V8 Supercar wheel size isn’t necessarily chosen because it’s optimal; it’s a fixed size, in fact I think they may even only be allowed to use one brand+model of tyre, it could even have been chosen because it’s more affordable and a bit of a challenge for drivers ...

 

[vc commodore]

But ... as I said above, the V8 Supercar wheel size isn’t necessarily chosen because it’s optimal; it’s a fixed size, in fact I think they may even only be allowed to use one brand+model of tyre, it could even have been chosen because it’s more affordable and a bit of a challenge for drivers ...

Depends on which V8 supercar class you are referring to.

The main teer and 2nd teer super cars run the Dunlop control tyre.....About 4 years ago, they changed from a 17" rim and tyre to an 18" rim and tyre, to cater for larger front brakes.....You also have the Kumho V8 supercar series....Shouldn't be hard for you to work out the tyre supplier....They actually run both the 17" and 18" tyres.....Now that's where the challenge lies, in which size rim to run

 

[VFBlack]

Depending on the wheel design itself, it may be significantly heavier. And the mass is concentrated further from the centre of the wheel than before - don't forget that rotational acceleration & momentum relate to mass with the square of the radius, so the extra effort involved in spinning-up larger wheels with mass further from the centre of a wheel is squared with the moving of that mass further from the centre.

I gut-feel used to struggle with being able to see any difference at all, how can an extra kg of mass that's distributed an extra 2" from the centre require that much extra juice to spin-up? But people have tested it, it does make an appreciable difference. Probably more so if you've also changed the effective gearing, which you have.

If it's a problem, fit a numerically-larger diff … simples!

I was under the impression that since wheel size has remain unchanged that the effective drive ratios are the same. Could you elaborate more if I've misunderstood this completely

 

[Forg]

I was under the impression that since wheel size has remain unchanged that the effective drive ratios are the same. Could you elaborate more if I've misunderstood this completely

The original poster said the overall tyre diameter was larger than before the wheels were changed.

If you’re wanting an elaboration on the physics of rotating the mass that’s further from the centre ... dunno if this post on the previous page might help explain?

 

[VFBlack]

I can't recall any quantifications, sorry … just that it's noticeable. What I'm talking about is not to do with unsprung weight, that affects handling but will hardly affect acceleration (unless it contributes to something like axle-tramp or other loss of traction); I'm talking about the change in ability to accelerate the wheels due to the mass being further from the centre.

OK try this if you're sitting in a chair that spins (at work or in a home office). Consider how little your hands/arms weigh compared to the rest of you. Spin the chair around with your arms held out, at a (safe) decent rate … then pull your arms in. You rotate faster, and noticeably faster. You've not changed the total mass involved, just pulled it in closer to the centre, and without any energy input the rate of rotation increased.
To accelerate your car, the diff has to increase the rate at which those wheels are turning; the further from the centre the mass is, the more energy it takes to increase the wheel's rate of rotation (and without spinning the wheels faster the car can't go faster).

There's enough variation from day to day & track to track that you'd need to set out to test back-to-back to tell, I suspect.
Unless you got someone who'd put in a few years' worth of experience driving one with the Forg'd wheels and then fitted the cast ones.

I could be wrong, but I do believe handling is affected more by wheel weight than acceleration is.​

I was under the impression that aftermarket wheels on average are lighter than stock despite being bigger?

ps running niche rims

At the moment it seems like there may be a different cause - assuming aftermarket rims should be lighter or about the same and that wheel size the same

Anyone have advice moving forward diagnosing the issue? Taking it down to mechanic?

 

[Forg]

I was under the impression that aftermarket wheels on average are lighter than stock despite being bigger?

The aftermarket will tell you this I guess; reality is that the expensive wheels are indeed lighter but the average Tempe Tyres spec wheels are heavy. Factory forged alloys will be lighter than factory cast ones in the same size (eg. -MY14 Redline alloys are forged & are lighter than MY15+ ones), but I'd bet most higher quality aftermarket alloys are still lighter than factory forged ones.

However - I was talking about the location of the mass not the total of the mass, ie. how far it is from the centre of rotation. A lighter yet larger rim has all that rim mass further from the axle than a heavier smaller rim; and that lighter larger rim (+tyre) can easily take more power to spin-up than the heavier smaller (+tyre) one.

At the moment it seems like there may be a different cause - assuming aftermarket rims should be lighter or about the same and that wheel size the same.

No his overall rolling diameter is more now, and as I said it's not necessarily the weight that matters but how for from the axle the mass is.

 

[Anthony121]

The aftermarket will tell you this I guess; reality is that the expensive wheels are indeed lighter but the average Tempe Tyres spec wheels are heavy. Factory forged alloys will be lighter than factory cast ones in the same size (eg. -MY14 Redline alloys are forged & are lighter than MY15+ ones), but I'd bet most higher quality aftermarket alloys are still lighter than factory forged ones.

However - I was talking about the location of the mass not the total of the mass, ie. how far it is from the centre of rotation. A lighter yet larger rim has all that rim mass further from the axle than a heavier smaller rim; and that lighter larger rim (+tyre) can easily take more power to spin-up than the heavier smaller (+tyre) one.

No his overall rolling diameter is more now, and as I said it's not necessarily the weight that matters but how for from the axle the mass is.

MY14 and MY15 wheels were forged. The MY16 wheels were not even tho the MY15 and MY16 wheels look the same they are slightly different.

 

[Skylarking]

^ is there any markings on the rim that state they are drop forged ?

 

[Forg]

MY14 and MY15 wheels were forged. The MY16 wheels were not even tho the MY15 and MY16 wheels look the same they are slightly different.

Woah, woah … are you sure about that? It's the first I've read of it, and in fact I'm fairly sure there were people on here stating that the MY15 wheels weren't forged before the VF2 was released (ie. before there was any possibility of confusion between MY15 wheels & VF2 wheels).
I'm gonna have to compare our MY15 wheels to some VF2 ones …

*edit*
Well for Chev SS, it's definitely correct. MY15 were forged according to this, and MY16 changed to cast according to this.
I guess it's possible that Oz got the cast ones from MY15 (because US got the best of everything we didn't) ...

 

[Anthony121]

Woah, woah … are you sure about that? It's the first I've read of it, and in fact I'm fairly sure there were people on here stating that the MY15 wheels weren't forged before the VF2 was released (ie. before there was any possibility of confusion between MY15 wheels & VF2 wheels).
I'm gonna have to compare our MY15 wheels to some VF2 ones …

*edit*
Well for Chev SS, it's definitely correct. MY15 were forged according to this, and MY16 changed to cast according to this.
I guess it's possible that Oz got the cast ones from MY15 (because US got the best of everything we didn't) ...

I have a set of 19 inch MY15 redline wheels in a box made in USA compare to the ones on my car which are made in Thailand.