LucasEV

I am considering swapping my stock 17" rims for some lighter 18" rims like the Enkei GTC01 which weigh 18 lbs (I believe the stock are around 23lbs). I want the 18" for looks and the weight for performance. I know increasing the radius of an object increases its moment of inertia (making in harder to accelerate) and lightning it decreases its moment of inertia. I am wondering if anyone noticed a performance difference going from stock TSX wheels to 1" larger diameter but lighter rims. Or if anyone knows the moment of inertia for the two rims lol!

curls

If you get larger wheels, you usually get thinner tires, so the overall diameter is nearly identical. So that's a moot point. The weight of a 17" wheel and tire combo vs. an 18" wheel and tire combo is entirely dependant on the specific combos you are looking at. I know Tirerack.com lists weight of tires by size, so you can compare there if you want.

Frankly if you aren't racing professionally I don't think this should be a make/break feature of wheels or tires though. That being said, you'll never see me with heavy-ass chrome-dipped wheels, thanks.

Itchytoe

If you have any significant weight reduction, that reduction will probably have a larger impact than the increased diameter. You see a decrease in performance when going to larger wheels because those larger wheels are generally much heavier. Going from stockies (23 pounds?) to a 17 pound 18 inch wheel will get you some improvement in the performance category. It'll also get you a rougher ride.

PACman

It's been a long time since I've changed out my stockies for 18"s. My 18 tire/wheel combo is definitely lighter to lift by hand compare to stock, so I'm assuming it's easier for the engine to propel.

amadeus303

iTrader: (2)

Lucas, you're correct in your assumptions. I've never tested it, but my butt dyno tells me I'm slower off the line in my 18" *lighter* wheel setup w/ UHP tires than my 17" stock setup w/ performance winter rubber. A lot of blokes think lighter=quicker, but since you're pushing more of the unsprung weight away from the center of the wheel, it makes it harder to turn the wheels. With that said, as someone already noted, if you're not tracking, I don't think it's significant enough to be concerned.

LucasEV

Thanks guys for the replies. I didn't really think about the thinner profile tire making the ride rougher. How noticeable is the change in ride quality. amadeus303 that makes sense because I would expect most of the weight of a tire would be towards the outer edge of the tire, therefore having a larger effect if the diameter is increased.

gdcwatt

On the ride issue, different tires of the same size tire give different ride qualities, likely a sidewall stiffness issue. There's a lot of good (and some bad) info at tirerack.com, but their own testing looks well thought out, and is probably more objective that what they get from the public.

If it's that important, check the manufacture's websites (or send them an email if they don't post the info) with what you might find at tirerack.com. [For example, TR has the weight of Continental's new 225/50-17 Extreme Contact DWS at 22lbs, but Continental's website lists that tire's weight at 24.6lbs. Of course, they could both be wrong.]

A couple of years ago I had some email correspondence with tirerack.com about errors in some of their tire specifications, in particular tire weight and overall diameter. Some of the numbers for different sizes of the same model tire from the same supplier were obviously wrong (ie a 195/50-16 would have a larger OD than a 205/50-16). They said their numbers were based on the electronic file information they get from suppliers, and they just dumped that into their online charts. Still, tirerack.com seems to be the most convenient best source of wheel and tire weight information out there.

DiaBando

iTrader: (3)

Aside from the aesthetics; My Centerline 18s (17lbs ea.) with the Hankooks V12s (sidewall 3.7" vs. 4.2 stock) produce a better ride quality than the oem Michelin, or, my Falken 912s on the oem rims. And, general overall handling has greatly improved. Newark, NJ's poorly patched n' potholed streets are not nearly as jarring. Off the line go is at best, a non-issue. I thought hard about ditching the Aspec suspension, but, with my summer tires and lighter wheels; it a good set up, for the present. It will be hard to go back to the oem rims and Falkens for the winter.

kanonen

wait a minute...are you guys saying that decreasing the wheel's weight by 5 pounds each (and decreasing their moment of inertia) on a 3000 pounds car will be felt by the driver on a street car (from an acceleration point of view) !!!!!!

curls

Assuming moment of inertia (distance of weight from the centre/axis) for the old and the new wheel/tire combos are similar, then yes, the reduction in rotational mass would probably be noticeable to some degree.

The general rule of thumb is that each pound of rotational mass lost provides an equivalent performance gain as a 10 pound reduction in vehicle weight. For example: A reduction in the weight of the rim/tire assembly of 5lbs x 4 (all around the car) is equivalent to a 200lb weight reduction in vehicle weight.

200lb is pretty significant if you ask me! Have you ever noticed a difference with some luggage in the trunk, or another 200# pasenger in the car? I have -- driving dynamics change considerably when loaded with a few hundred pounds of weight in the car!

kanonen

Assuming your formula is correct, sure a 200 pounds is noticeable. What's the basis of your formula?

RogerPodacter

This is a great physics/engineering question. I absolutely notice a difference with just 1 passenger in the car vs just me driving solo.

Heavier rims is harder to get moving. But once the car is moving the inertia when you take your foot off the gas and coast is greater. So this could give better gas mileage because the higher inertia keeps the car moving on average while driving around town.

However having lighter rims logically makes the engine have to perform less work to get the car moving and accelerating.

So what is the optimal rim size diameter and weight paired with our tsx engine? Its a great physics question.

curls

Honestly? Some seemingly-very-knowledgeable tech article on . I forgot to link to it, sorry.

carmagnut

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I heard it was 14" gold daytons and tires with white sidewalls... J/K This is a good thread. Interesting.