What's the difference in the real world?

[CivicSiRacer]

Originally posted by MattyO217
Thanks for your responses.:alien:

My next question is somewhat technical. What would give better traction: 205/50 15 11.5 lb wheel or a 205/40-17 17 lb wheel? It's technical because I'm compairing the decreased weight to the increased contact patch. I don't know if this can be accurately answered. I would think that how much horsepower I plan on making would come into play here. I say that because as you increase hp, traction becomes a bigger issue and I'd think that in straight line acceleration, the increased contact patch would be better. But as for cornering, what would give more grip, all things equal except for wheel weight and tire size? A wheel that's 5.5 lbs lighter with a slightly smaller contact patch or a wheel that's 5.5 lbs heavier with a slightly larger contact patch due to a lower aspect ratio??

Thanks for the help,
M
:smoka:

If you have a 205/50x15" tire and a 205/40x17" tire they are both the same width. So you have the same contact patch. But the 15" wheel is 6lbs lighter and that doesn't take into fact the tire weight difference. Since the tire has a smaller sidewall you need more steel belts (reinforcement) to keep the sidewalls stiffer hence making the tire heavier too.

My 17" wheel and tire package weighed in around 45lbs. My 15" is 32lbs. That's a difference of 13lbs per corner or total of 52lbs your car has to carry.

Plus you would get better response from the 205/50x15" compared to the 205/40x17" cause the 205/50x15" is 1" shorter for better gearing. You would accelerate quicker off the line. The 205/40x17" also will mess up your speedo and odoemeter by about 1-3%.

[MattyO217]

If you have a 205/50x15" tire and a 205/40x17" tire they are both the same width. So you have the same contact patch.

Not entirely true. It is true that both tires measure the same width but this width is NOT the contact patch. The 205 is a measurement of the width of the tire in respect to the sidewall. In other words tire width is from sidewall to sidewall. A tire's sidewall is not perfectly square, it is somewhat rounded, so not all of a tire's width is put on the ground. But as the aspect ratio decreases the sidewall becomes more square, thus putting more of the measured width on the ground. If you compare a 70 series tire to a 40 series tire, this is very apparent. So a lower profile tire increases contact patch area, but not the measured width of the tire (205 mm).

Peace out,
MattyO217

:alien: