The Bigger, The Worse?

[heavyD]

http://www.youtube.com/watch?v=-_NYWyVHcl0&feature=related

So the bigger rims cause the R8 to be slower than it is with smaller rims. (Well, not really smaller, they're still massive 20" ones.)

Th host says the bigger rims can't put all the power down. Any ideas on this? I though lower profile tyres was supposed to be better at handling and all.

[Ripper]

low profile tyres are better for cornering since the lower profile allows very little sideways movements as opposed to a tyre that has more rubber between the tarmac and the steel.

What's happening with larger wheels is that it takes more effort by the engine to make it turn. Simple physics

certain amount of power will be sacrificed just to make the larger wheel turn

The trick is to find the perfect balance where the wheels are big enough but not too big of a burden for the motor to handle and also perform at it's optimum

[heavyD]

low profile tyres are better for cornering since the lower profile allows very little sideways movements as opposed to a tyre that has more rubber between the tarmac and the steel.

What's happening with larger wheels is that it takes more effort by the engine to make it turn. Simple physics

certain amount of power will be sacrificed just to make the larger wheel turn

The trick is to find the perfect balance where the wheels are big enough but not too big of a burden for the motor to handle and also perform at it's optimum

Never liked Physics...

Didn't think that an engine with that much power would have a problem with the rims being a bit bigger. Three seconds off the lap time is a huge difference.

[Sifaan]

Never liked Physics...

Didn't think that an engine with that much power would have a problem with the rims being a bit bigger. Three seconds off the lap time is a huge difference.

I had never thought about how much difference it could make, but the issue is not so much that the bigger rims are heavier, but that the additional weight is far away from the axis of rotation (read the overview section here http://en.wikipedia.org/wiki/Moment_of_inertia) so even a small increase in mass can result in a much bigger increase in the moment of inertia.

[heavyD]

I had never thought about how much difference it could make, but the issue is not so much that the bigger rims are heavier, but that the additional weight is far away from the axis of rotation (read the overview section here http://en.wikipedia.org/wiki/Moment_of_inertia) so even a small increase in mass can result in a much bigger increase in the moment of inertia.

That explains it a bit.

So it's safe to assume that, what's stopping manufacturers from putting tyres with bigger sidewalls on their cars is the decrease in handling and style?

[The Stig]

That explains it a bit.

So it's safe to assume that, what's stopping manufacturers from putting tyres with bigger sidewalls on their cars is the decrease in handling and style?

Yep and since lower profile tires have small side walls they tend to be stiff so when cornering at high speeds they dont sway to sides like normal tires, but sacrifices a little ride comfort.

Also bigger rims means that manufacturers can fit in brakes with bigger diameter disks as well.

[Sifaan]

That explains it a bit.

So it's safe to assume that, what's stopping manufacturers from putting tyres with bigger sidewalls on their cars is the decrease in handling and style?

I think manufacturers select rim size, tyre width and profile to give the best balance of handling, comfort, fuel economy, tyre life, and style for the target audience (city car vs. family car vs. off road vs. sports car etc).

so perhaps just like it is possible to upsize, there might be space to downsize as well

as for limiting factors, apart from space for brake discs, there might also be other problems with really high profile (90? 110?) tyres. trying to figure that out may require more physics than you are willing to suffer

[jerryda]

http://www.apa.ca/template.asp?DocID=94