18 inch tire question....

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GazM3
Posts: 1791
Joined: Wed Oct 26, 2011 12:55 pm
Location: Melbourne, Australia

Re: 18 inch tire question....

Post by GazM3 »

It's a very good point you mention. Some heavy cast 16" or 17" wheels can be heavier than some light 18". If I was to go 18" the BBS RS are reasonably light.
BMW’s
84 E24 M635csi
90 E34 M5 3.6
94 E34 540i/6 SC E85
97 E36 M3 euro SC U/C
97 Z3 2.8 widebody

OTHERS
11 Audi S5 3.0 SC
19 VW Amarok V6
francoid

Re: 18 inch tire question....

Post by francoid »

dwcains wrote:Aesthetics (subjective) aside, the are certainly some performance (objective) negatives to larger wheels and tires that should be mentioned. Heavier wheels and tires increase the unsprung mass of the car
Yes, that's what I explained above...
dwcains wrote:My 635 has Michelin Pilot SX; 205/55-16 and 245/45-16, and while I've never driven it with the original spec wheels and tires, I can say the steering is overly heavy, IMO, and the tramlining is pretty bad - not to mention the tendency to understeer from the staggered setup.
I've heard of that setup but never seen it used. Just does not seem useful...
francoid

Re: 18 inch tire question....

Post by francoid »

GazM3 wrote:It's a very good point you mention. Some heavy cast 16" or 17" wheels can be heavier than some light 18". If I was to go 18" the BBS RS are reasonably light.
Beyond the question of why going 18" which I have already covered and won't belabor further, the point about lighter 18" compared to heavier 16" is questionable. It's not just about unsprung mass, but also about rotational inertia, which is a function of the radius of course; since a lot of the mass is in the rim portion, even lighter wheels of higher diameter will tend to have higher rotational inertia.
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