Ok, I know this has been brought up before, but it seems people just discuss theories and speculate on what SHOULD happen.

Does anyone have first hand experience with switching to heavier wheels? Is there a noticable difference?

All of the 18" wheels I like weight in at 23-26lbs each and the Pirelli tire that fits weighs 19lbs itself. That is about a 10lb increase per corner over stock.

So, if you've changed your wheels to heavier aftermarket ones, please let us know if you can tell a difference in performance and handling.

Thanks!

Jeremy

 

I switched to 16x7's and noticed a difference. I switch back, for winter, and then I REALLY noticed. The car is much quicker with the steelies on there. My milage went up 1mpg on ave (85% highway). I also noticed more lean in the corners..

 

its not all about weight its rotational mass..

more rotational mass needs more force to start/stop movement. forged wheels have less rotational mass due to how they are constructed. therefore some 19's can have less rotational mass than 17;s because of smaller tire + etc.

 

Yeah, I understand that they will have an effect on performance, I guess I'm just trying to figure out how noticable it is. I guess I should have put "heavier and larger" wheels.

If I go from the 34lb. stock tire/wheel combo to a 38lb tire/wheel combo, will I feel the difference?

J

 

Proly not. Just buy your wheels and enjoy cruising your new shoes. It's great when my friends call and scream at me on how hard the car rolls on deep dish wheels. Don't worry so much about it.

 

If you want everybit of movements out of your car, your better off with smaller wheels, I have switched from 16" 205/55 R16 to 18" 225/40 R18 in my eclipse, and have noticed a whole lot less response from my car! Breaking decreased, accelaration decreased, almost like with CAI and without CAI...... And this is a car with 170HP and 145 torque we're talking about!! Considering our 1NZ-FE only has 108HP the effects would be even more significant.... :You want it for the looks, go for it! for performance, better off getting some light 15" or some light weight 16"...

that just my experience with bigger wheels

 

yes there is a very considerable difference between my 17s and my stockers. i took my 17s off about two weeks ago and driving without them feels so much more spirited. its enough of a difference to make me think about selling the 17s a couple of times. if you go bigger make sure you go light weight! i wish i wouldnt have been so cheap and wouldve bought some light weight ones

 

How much do your wheels weigh? See, this is making me crazy! I REALLY don't want to have 15" wheels on my xB! I'd love to have some nice looking 18's, but I don't want to lose a lot of performance or handling. Is it just one of those things where you have to make that sacrifice to have nice wheels? Is there any way to have 18's and not sacrifice performance, braking, handling, etc..?

J

 

ok i have BSA307 17s on nankang 205/40/17 tires. each wheel weighed in at 6 lbs heavier per wheel and tire than stock.

handling greatly improves with the bigger wheels but braking suffered with mine as did acceleration. its a tough choice to make. if u go bigger... then go lightweight. i cant stress that enough

 

I would rather run my 17's all the time. Reason being the sterring response is better, turning is getter and that is what matters to me the most. I just don't want to run expensive wheels in the winters of chicago.

 

Man, I just haven't been able to find many light weight wheels that I think are nice looking. They are either pretty plain or cost an arm and a leg!

J

 

yup, lightweight rims for the most part arent cheap..

 

I found this nice article that sums up about exactly what I wanted to know. Here ya go:

http://www.tirerack.com/wheels/tech/...l_weights.html

 

Read critically, that article had a lot of writing, but no usable data. They completely ignored the fact that they were changing the width and profile of the tire and attributed changes in MPG that were well within the "noise" to wheel weight alone. The article was intended more to sell wheels than to actually study the issue.

Let's do a little theoretical work

If physics frightens you, run away!

Consider a vehicle with mass 1100kg (like an xB) rolling on wheels and tires of mass 15kg. further, let's consider that the mass of the wheel/tire was concentrated at the tread surface at a radius of 0.3m, the most advantageous case for alter the weight of the wheel/tire combination..

At 30 m/s (67MPH) the kinetic energy of the car itself would be:

(1/2)(1100)(30^2)=495,000J

The moment of inertia of a wheel/tire would be:

I=mr^2=15(0.3^2)=1.35kg m^2

At 30m/s road speed, the rate of rotation would be:

omega=(v/(2*pi*r))*2*pi=(30/(2*pi*.3))*2*pi=30/.3=100 rad/s

At the same speed, the rotational KE of the wheels would be:

KE=(1/2)*I*omega^2=1/2*1.35*100^2=6750J

There are four wheels, so the total KE is 4*6750=27000J

So, the total KE of the vehicle would be 495,000+27000=522,000J

Now, let's say that the wheels had a mass of 10kg instead of 15kg. Since the KE is proportinal to the mass, the KE of the lighter wheels would be (10/15)*27000J=18000J.

The total KE of this vehicle would be 495000+18,000=513000J

Now the xB puts out about 100HP of which about 80 is the average power that gets to the wheels. This is equivelent to 80*746=59,680W

The time required to deliver 522000J on the "heavy" vehicle is 522000/59680=8.7s

The time required to deliver 513,000J on the "light" vehicle is 513000/59680=8.6s

That means that, even if we take the most advantageous case for every parameter, reduce wheel weight by a whopping 5kg, and completely ignore the effects of drag, we will achieve a decrease of only 0.1s in the time it takes to accelerate to 30m/s.

If we were to use more realistic numbers for the rotational inertia, wheel weight reduction, and wind resistance the difference would probably drop to half of the calculated value above.

In short, wheel weight doesn't mean much unless you are into racing. For normal street driving, weight won't make any perceivable difference.

If you are still reading at this point, you are a true seeker of knowledge! Congratulations!

George

 

my head hurts.

you cheated and used metric units.

I don't know what .1 secs less to get to 30m/s means in seat of the pants, but my car feels so much better on acceleration with the stocks that it's not funny, and I was running only 16x7's.

 

Assuming constant acceleration:

30/8.7/9.8= 0.352G

30/8.6/9.8=0.356G

So, the "seat of the pants" difference is 0.004G. If anyone can feel that, they truly have a "golden butt!"

I've no doubt that changing wheels can result in noticable differences, but the differences are not due to different weights!

George

 

George,

Thanks for the educated post! I have been wanting to see something like that. Mabybe the "decrease in performance" people are feeling is more due to the size of the wheel more than it is the weight?!?

I have found a set of 18" wheels that I love, but they weigh in at a hefty 25lbs (w/o tire) which will come out to 44lbs with a 215/35/18 Pirelli P-Zero M+S tire (19lbs for you math wizards). Maybe I should just bit the bullet and buy them, slap them on the car as soon as I leave the dealership and then I'll never even know the difference!

J

 

Oh yeah, George... So does increased tire size have a big effect on performance? I know the overall diameter will be the same because of thinner tires, but the bulk of the mass of the wheel will be pushed out to the edge further. Any educated thoughts?

 

Most "plus size" combinations actually end up being slightly larger in diameter than stock, and they can reduce performance because the axle torque is delivered through a longer lever arm.

As my long post showed earlier, the wheels only amount to 5% of the total kinetic energy of the vehicle. You really cannot change the moment of inertia enought to make a difference in "seat of the pants" feel. In fact, my calcs above assumed that the entire mass of the wheel was at the tread surface, a truly "worst case" situation.

George

 

I read your post, and it makes sense,

but I also know for a fact that just going from my friends 17" custom CCW wheels to more fashionable 18" wheels, there's a noticable feel in loss of acceleration. This is also a 400rwhp 300ZX TwinTurbo.

In the Z's case, the 17" wheels were actually wider than the 18" too, and ran stickier tires.
17x9.5 qty4 w/Yoko A032 tires
vs
18x8.5 & 18x9.5 w/Brgstn SO2 tires

So, I'm trying to figure out the missing variable in the equations above. The only thing I can think of is maybe the weight of the tire or rolling resistance of the tires. I've been very suprised at the difference between say a Hoosier race tire and a regular tire, but most people who see differences run street tires on both wheel combos so that might be able to be eliminated... I thought you might have missed the rotation momentum of the added weight of the wheels, but you got that already... Hmmm....

Ok, let's put it this way... Driving w or w/o a passenger, I can easily feel the difference, given a standard 180lb bloke. But the added weight from larger wheels, is MUCH smaller, and shouldn't be noticed, but actually that added weight is multiplied because it's rotational mass too....

Hmm.. something is missing, but I can't put a finger on it... Damb it, your gonna make me brake out my old university physics books... Give me a few days though... It's been a looong time since I've opened them and it'll take some time to find them again!