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Performance and "rolling" weight

2570 Views 17 Replies 11 Participants Last post by  Redman
First off, I am no expert here - so if anyone has better information to add (correct mine) please do.

I was thinking of upgrading my wheels to 20", but got to thinking about the performance impact. As I thought more on it, I think there is room for improvement - but I am not certain it lies in the 20" rim arena. Here are the known factors that weigh heavy on my (or yours also) decission...

[1] Unsprung Weight - This is one of the most critical factors affecting a vehicle's road holding ability. Unsprung weight is that portion of a vehicle that is not supported by the suspension (i.e. wheels, tires and brakes) and therefore most susceptible to road shock and cornering forces. By reducing unsprung weight you, in effect, provide more precise steering input and improved turning characteristics.

[2] Reduced rotation force - Improved acceleration and braking are the major benefits from a reduction in wheel and tire weight. Given 2 wheels of identical circumferences and coefficient of friction - the lighter wheel will provide better overall performance. Reducing the wheel mass, also reduces the gyroscopic effect of the wheel. When a wheel is spinning, it is very difficult to make it change direction, but the lower the mass of the wheel, the easier it is to steer.

The best argument I can think of in favor of a 20" setup is that by reducing the sidewall height, this would reduce the "squishy" feel and provide a stiffer and more stable turn.

I would hink that the 18's are likely the best bet (as I think that I can get the lightest setup this way), but am interested in seeing if there is a good argument in favor of the 20's (I'm deadset against the 22"). If there was a 20" setup that didn't significant penalize a similar 18" setup (or other unconsidered performance benefit) then I'd like to know now before I begin looking to get baby some new shoes!
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I have just installed the MC2ning FZ6 wheel/tire combo with Nitto 420S tires. I did not weigh them personally, but have read they are 7lbs lighter than stock. I could actually verfiy this, but the stockers are now installed on our 02 Explorer. I have 1k+ miles on them since installing - and LOVE them. I would not go back to the 18's on this car.
7lb's x 4 = 28lbs less rotating mass and 14 of that on the driveline.
The 20's are much more responsive, it handles better, and I feel the road through the wheel better. That said - feeling the road is not a bad thing, but if you are used to mushy (stock Conti's) - it's a little odd at first.
And believe it or not, my slight (right) pull is now all but gone!

At $2,300 they are worth the bucks, especially if you sell the stockers.

I can somewhat follow you on angular rotation, but I failed physics....badly. :D

MC2's are forged wheels, not metal. I don't know the difference in weight vs. the stock 18 cladder's without tires - but I do know the stock Conti seals have the black goo in the OUTER edge of the tire - I'll bet making the Conti seals heavier and more of a hinderance on the outer part of the wheel in reference to your angular rotation thing....but like I said, not only did I fail, I don't even remember taking physics!

How can you argue 7lbs of unsprung per wheel being a negative?

Also, I do disagree with your comment of "20's are for bling" - 22's are for bling. :rolleyes:
20's are a performance upgrade with the right wheel/tire combination. If they were a negative, why does the SRT8 have them standard?
It rides much better with 20's IMO. Not harsh at all - steering is tighter, and car is more responsive. I'm glad I chose the 20's over the 22's.
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