Performance and "rolling" weight

2572 Views 17 Replies 11 Participants Last post by Redman, May 4, 2005

jhelmuth

Discussion Starter · May 2, 2005

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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Northern Rider

· #2 · May 2, 2005

I'm running all of your arguments myself, looking for a good performance wheel / tire combo.

It appears possible to get a 20" set up with less weight than OEM. The problem is we don't have real good tire options at the moment. Most tires in our spec range are truck/suv and not designed for performance.

jhelmuth

Discussion Starter · #3 · May 4, 2005

an interesting combination...

20x8.5 EVO Penza 5 SL Chrome Plated (26.5 lbs.)

245/45YR20 Goodyear Eagle F1 Supercar (? - need to find the weight on these)

Might be alot like the SRT8 (with only 5 spokes - not 9).

Northern Rider

· #4 · May 4, 2005

jhelmuth said:
an interesting combination...

20x8.5 EVO Penza 5 SL Chrome Plated (26.5 lbs.)

245/45YR20 Goodyear Eagle F1 Supercar (? - need to find the weight on these)

Might be alot like the SRT8 (with only 5 spokes - not 9).

Jim, that looks like a very good combo. The weight on the F1's should keep the total package under 55 lbs per wheel. And would compare well with the SRT-8.

I wonder what the wear rate is on the F1's?

jhelmuth

Discussion Starter · #5 · May 4, 2005

Northern Rider said:
Jim, that looks like a very good combo. The weight on the F1's should keep the total package under 55 lbs per wheel. And would compare well with the SRT-8.

I wonder what the wear rate is on the F1's?

It's not good... and they didn't get a great rating (other than performance).

5point7

· #6 · May 4, 2005

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.

Northern Rider

· #7 · May 4, 2005

5point7 said:
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've heard good things about the MC2's from others and it seems to be a DCX approved dealer option. Not surprised about the right wander - my winter Pirellis ran dead straight until I wanted to turn - my summer contis really wander ant low and moderate speeds.

Vanillapimp300c

· #8 · May 4, 2005

bfg kdw 2

these tires are awesome and bearly even spin you guys should look into them i will get you pics next week of mine 255/55/18 i paid $136 ea
if you want to see them go to

http://www.tirerack.com/tires/tires...lse&partnum=555VR8GFTAKDW2RF&fromCompare1=yes

Dutch

· #9 · May 4, 2005

Even if your 20s weigh the same or less than the 18s, you're still making the angular rotation problem worse by moving more weight (metal wheel) to the outer part of the tire/wheel assembly. Weight farther from the center of the wheel will have more inertia.

I think the only real reason to get 20s is for bling, which the Chrysler 300 already has in spades. They're a negative for almost everything else.

5point7

· #10 · May 4, 2005

Dutch,

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

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.

20's are a performance upgrade with the right wheel/tire combination. If they were a negative, why does the SRT8 have them standard?

Dutch

· #11 · May 4, 2005

I didn't see your post about saving 7 lbs. That definately outweighs what I mentioned. The SRT has different springs, shocks, and brakes to go along with the 20s. All of those components would be taxed by adding unsprung weight, but I guess if you save weight they wouldn't.

How does a 300 on 20s ride? Isn't it really harsh?

5point7

· #12 · May 4, 2005

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.

marlinspike

· #13 · May 4, 2005

I think part of the reason this car handles well on 20's is that the overall diameter is so huge. I mean, how many other cars take a 45-profile on a 20-inch wheel? The kinda stock luxo size is 225/55 - 16 or some variant of that, and 245/45-20 is a good 3.5inches bigger diameter, which is huge. The closest size to 225/55-16 in 20 inch would be 245/30-20, which is a 1/3 less sidewall, and would probably be very jittery and handle poorly. Basically, what I'm getting at, is I think 20's work on this car because the car is so friggin huge (which is the same reason the 14's I have don't work on my 20 year old car of equal size).

Mr.DJ

· #14 · May 4, 2005 (Edited)

You can always try my latest set-up:

Mopar 'SRT-8' OEM 20x9 forged polished aluminum wheels with Goodyear 'Eagle F1 Supercar' 45 series Z-rated tires ~ 245s up front & 255s on the rear.

Each tire weighs 34lbs and maximum air pressure is rated at 51psi...according to recent info supplied by 'The Tire Rack'.

Specs:

http://www.tirerack.com/tires/Spec.jsp?make=Goodyear&model=Eagle+F1+Supercar

Ratings:

http://www.tirerack.com/tires/tires...reModel=Eagle+F1+Supercar&sidewall=Blackwall&

It should be noted, however, that ultra high performance tires are not known for long tread-life, but more for their superb performance/handling characteristics.

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Model 57

· #15 · May 4, 2005

The comment earlier by 5point7 'why does the SRT8 come with 20's?' At least part of the reason for it was to make room for the big Brembo brakes that they put on it. That comes from the press info that DCX put out early on about the SRT8.

vvv90

· #16 · May 4, 2005

Beginners guide to Rotational Mass

http://physics.unr.edu/faculty/phaneuf/classinfo/P100wk5.ppt

HEMEEE

· #17 · May 4, 2005

vvv90 said:
Beginners guide to Rotational Mass

http://physics.unr.edu/faculty/phaneuf/classinfo/P100wk5.ppt

cool link!

Redman

· #18 · May 4, 2005

Take diameter, divide by 12, then 3X inertia weight of...

HEMEEE said:
cool link!

Yes, but my head is still spinnin....

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