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      03-16-2016, 03:11 PM   #23
M6-Coupe
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Quote:
Originally Posted by Acexxon View Post
One question regarding going 21" on the M6.

A local shop has told me that his lap time is actually quicker with the 20" wheels as compare to the 21". Does this hold any truth? I mean surely 21" would definitely look better on the car, but in terms of performance?

Any suggestions or opinions?

Thanks!
Basic physic says it should be truth!
The acceleration is the product of Force and weight where "a=F/m" so more Force (on wheels) or less weight cause higher acceleration or "quicker"
The Force by itself is the product of torque so basically:
F = [TQ (at crank) * gear ratio * axle ratio * (1-drivetrain loss)]/R
and R is the radius of your wheel; so the less radius means higher torque (on wheel) causing higher acceleration.
Now lets go back to your question. if you are using 20" wheel with 296/30/20 tires, the total radius of your wheel is ~13.5" .... (20 + 2 *30% * 295/25.4)/2
If you are using 21" with 295/25/20 tire, the total radius is 13.4" ... you will gain 0.7% acceleration... BUT in case of our cars you will have less traction and in fact you will have more traction issue... so as C5driver says don't confuse them with performance
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      03-16-2016, 09:08 PM   #24
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Originally Posted by EL MEJOR View Post
Thanks Jason! Absolutely love the wheels. Dropped her off today at the dealer to get all the interior mods. And have appointment on 4/1 for all the exterior mods install. Will have pics a few days after that.
What Mod's you doin?
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      03-16-2016, 09:40 PM   #25
EL MEJOR
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Quote:
Originally Posted by terrainx
Quote:
Originally Posted by EL MEJOR View Post
Thanks Jason! Absolutely love the wheels. Dropped her off today at the dealer to get all the interior mods. And have appointment on 4/1 for all the exterior mods install. Will have pics a few days after that.
What Mod's you doin?
Vorsteiner CB Rear Diffuser
Vorsteiner CB Trunk deck Spoiler
Vorsteiner CB GTS-V Front lip Spoiler

BMW Performance CB Alcantara steering wheel
BMW Performance CB mirror caps
BMW Performance CB shift knob
Interior white LED lighting

KW HAS suspension

After all this is complete I will be looking into getting it tuned and track ready with exhaust, CCB
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      03-16-2016, 11:25 PM   #26
brad850csi
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Also 21" wheels are heavier and tyres are about the same weight normally, so more rotating mass which equals harder to turn.
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      03-18-2016, 03:08 AM   #27
Acexxon
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Quote:
Originally Posted by M6-Coupe View Post
Basic physic says it should be truth!
The acceleration is the product of Force and weight where "a=F/m" so more Force (on wheels) or less weight cause higher acceleration or "quicker"
The Force by itself is the product of torque so basically:
F = [TQ (at crank) * gear ratio * axle ratio * (1-drivetrain loss)]/R
and R is the radius of your wheel; so the less radius means higher torque (on wheel) causing higher acceleration.
Now lets go back to your question. if you are using 20" wheel with 296/30/20 tires, the total radius of your wheel is ~13.5" .... (20 + 2 *30% * 295/25.4)/2
If you are using 21" with 295/25/20 tire, the total radius is 13.4" ... you will gain 0.7% acceleration... BUT in case of our cars you will have less traction and in fact you will have more traction issue... so as C5driver says don't confuse them with performance
Thank you for the thorough explanation! I guess 21" to make the car look stunning, but sticking to the 20" makes it easier to drive
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