Bimmerfest - BMW Forums - View Single Post - All of these "doesn't handle well enough" comments need some perspective
View Single Post
Old 01-04-2013, 06:52 PM
Jamesonsviggen Jamesonsviggen is offline
Officially Welcomed to the 'Fest
Location: Michigan
Join Date: Jun 2007
Posts: 3,259
Mein Auto: '98 M E36/7:'06 Saab 9-5
Originally Posted by bmw_or_audi View Post
When it comes to larger wheels, the penalty is not simply the extra weight, but also the increased moment of inertia (AKA rotational inertia). Even with identical weight, the 19" will have higher moment of inertia than 18", which will affect acceleration. Moment of inertia for a small mass m scales with m * r^2, where r is the radius about the axis of rotation. Note how it is a squared term. The big heavy rim of the wheel will be one inch further out from the axle, increasing moment of inertia by about 11% (for the rim alone). I would have to make a back of the envelope calculation to know to what extent this affects acceleration, but in the hair splitting regime it may make a very real difference.

But I have never put a larger wheel on a car without the wheels being lighter than the oem setup.

Plenty of people go only by looks and throw on 30lb wheels and alter the braking, handling and acceleration. Not my MO.

E36/7: Dinan/RMS stage 2+ blower@11-16lbs of BOOST! 18" BBS LM's, too much more to list
F30: 6mt, SOLD

'06 Saab 9-5 wagon 5mt LSD, clipped turbo, 19psi, 400ft lbs of tq
Reply With Quote