Teach me lightweight wheels :)

So I was reading up on un-sprung weight and it all makes perfect sense to me in theory. Lighter wheels are make the car more nimble and ride better. What I’m curious about is the degree in the improvements and if I can quantitatively justify buying light weight wheels.

For my fun set of wheels, I was going to just source a set of Stock 19” Genesis Coupe Track Trim Rims with some decent sticky tires. A used set here is like 200 USD. The alternative is to get a set of 18” Enkei RPF1s with some sticky tires. I’ve done the math and the weight different between the two set ups is about 15 lbs per corner. The cost differences in rims alone is about 1,060 USD.

I think with the car’s current setup, I’m happy with most of it. One thing that always erked me was the ride comfort. Will dropping 15 lbs per corner drastically help ride comfort?

As some of you might have read in my other post, the wife is preggers. I’m buying this as a welcome to fatherhood present, I’m just wondering if it’s a best a reasonable buy that’ll net me the results I want.

Thanks Guys!!!

Normally I'd say no, but a fifteen pounds per corner saving is good, and I would say if you don't notice a difference in acceleration, you'll definitely notice it in the nose when you transition.

What's the current weight per corner? The change in performance and comfort that you feel is going to be more proportional to the percentage of weight lost of the total unsprung weight rather than to an absolute number. That being said, 15 lbs is a solid amount, and I'd be surprised if that didn't acceleration in the lower gears feel more sprightly as well as noticeably helping ride quality. That extra sidewall will help too.

These are the weights of the R-Spec 19" Wheels with 100% Thread.

Front 55.0 lbs Rear 57.4 lbs

Rims alone, the Enkies will be around 18 lbs, whereas the stock wheels will be 28-29 lbs.

For track use you really want the smallest dia wheel you can find, since it will be lighter, and tires will be cheaper. If 15s or 16s will clear the brakes, that's where you should start.

I shopped for a while and managed to find forged 18" Konig wheels for $240 in absolutely perfect condition for the GS on Craigslist. Save a search and start looking! It was well worth it for the savings. you might not find exactly what you want but you can comfort yourself with a stack of cash.

The only caveat really is that stiffness is also important, as if the wheel's flexing more during cornering, your dynamic alignment will be changing that much more. This will require more static camber for proper tire temps and wear during hard use, which compromises braking and acceleration, leading to slower times. I've seen tests where heavier wheels are faster, but it'll also be dependent on the surface, car, track, etc, with rougher surfaces favoring the lighter setup.

Never EVER go light AND cheap.

^RPF1s are thoroughly well proven wheels that have been around a long time.

RX8driver wrote: The only caveat really is that stiffness is also important, as if the wheel's flexing more during cornering, your dynamic alignment will be changing that much more. This will require more static camber for proper tire temps and wear during hard use, which compromises braking and acceleration, leading to slower times. I've seen tests where heavier wheels are faster, but it'll also be dependent on the surface, car, track, etc, with rougher surfaces favoring the lighter setup.

Link please.

Dietcoke wrote: For track use you really want the smallest dia wheel you can find, since it will be lighter, and tires will be cheaper. If 15s or 16s will clear the brakes, that's where you should start.

16"s have almost no tire selection. I'd avoid those.

I'd pick wheel size based on what has a good selection of tires that are a reasonable overall size for the car. Pay attention to tire weights, as I've seen plenty of cases where going an inch bigger on the wheels doesn't increase the total weight of the combo at all.

Dietcoke wrote: For track use you really want the smallest dia wheel you can find, since it will be lighter, and tires will be cheaper. If 15s or 16s will clear the brakes, that's where you should start.

z31maniac wrote:

RX8driver wrote: The only caveat really is that stiffness is also important, as if the wheel's flexing more during cornering, your dynamic alignment will be changing that much more. This will require more static camber for proper tire temps and wear during hard use, which compromises braking and acceleration, leading to slower times. I've seen tests where heavier wheels are faster, but it'll also be dependent on the surface, car, track, etc, with rougher surfaces favoring the lighter setup.

Link please.

Haven't multiple GRM tests shown that the smallest and/or lightest setup isn't necessarily the fastest?

.

Lof8 wrote: 16"s have almost no tire selection. I'd avoid those.

High performance tire selection 16" wheels is really not that different than high performance tire selection for 15" wheels...In fact, if the size you need is one of the few remaining popular sizes for either, the 16's actually have better overall availability of summer tires. So it depends on what you're comparing them to. That being said, 17" tire selection does blow both out of the water.

Just realized I have 15mm and 20mm spacers on the car. That can't be helping with the unsprung weight.

Found this article on tirerack.

Ah crap...

15 lbs per wheel is huge.

More tire choice in the 18 diameter.

The impact of wheel weight loss is also much more drastic on lighweight/low power cars. On a 500HP Mustang, losing 15lbs per corner is probably an imperceptible difference. On a Miata you would immediately notice the change.

Imagine how goofy a Genesis would look with fifteens...

the advantage of wheel and tire weight and diameter reduction are easily underestimated.

-you get the normal advantages of weight savings in straight line acceleration and car rotation

-you get the advantage of reduced rotational inertia.
I=mr(squared) This is where the reduced diameter really helps. Not only are the smaller diameter wheels and tires normally lighter but the distance from the axle is squared. So going from 19 to 17" without any weight savings will reduce your inertia four times!

-and you get reduced inertia of your unsprung weight allowing your suspension to react much quicker to inputs.

so lighter wheels and tires help you in three different ways and are likely the most advantageous place to save weight.

pointofdeparture wrote: The impact of wheel weight loss is also much more drastic on lighweight/low power cars. On a 500HP Mustang, losing 15lbs per corner is probably an imperceptible difference. On a Miata you would immediately notice the change.

Ive noticed as little as a 3-5lb change on small low powered cars.

pointofdeparture wrote: The impact of wheel weight loss is also much more drastic on lighweight/low power cars. On a 500HP Mustang, losing 15lbs per corner is probably an imperceptible difference. On a Miata you would immediately notice the change.

I agree with this. I have RPF1 wheels and also a set of other brand that were heavier. My car weights about 2300 lbs at it's lightest (Without driver) I saw over a 50 lb drop in total car weight when I went with the RPF1s. Plus the unsprung weight and the rotational weight savings were noticeable!

Be careful about going too far out on the ice. That is, you can get really light wheels that are made only for racing - and they aren't kidding. Like, hit a couple curbs or a pothole and it'll bend them. A tire shop bent all four of my race wheels because they had no idea how delicate they were. Also, real race wheels are consumables due to metal fatigue.

The mag and Tire Rack did another test with lightweight wheels, and didn't find a huge performance increase. Plus, that article isn't a true apples to apples comparison since the tires were different on the stock wheels vs. the lighweight wheels. I think that the best route is to just get a performance set of 18" wheels and use the extra few hundred bucks on a softer compound tire,sway bars, or whatever is the Genesis Coupe's weak link.

Driven5 wrote: Haven't multiple GRM tests shown that the smallest and/or lightest setup isn't necessarily the fastest?

I seem to remember this. Lots of people are saying what lighter wheels should do, but I haven't seen anyone post any quantitative data on what lighter wheels have actually been shown to do.

This should be definitively tested in a coming issue in a way that has quantifiable results. The fact that in a community like ours, this is up for debate is silly. A weight and how much difference it makes article could be a great ongoing feature. First unsprung, then sprung (high vs low?), then driveline, on and on.

sesto elemento wrote: This should be definitively tested in a coming issue in a way that has quantifiable results. The fact that in a community like ours, this is up for debate is silly. A weight and how much difference it makes article could be a great ongoing feature. First unsprung, then sprung (high vs low?), then driveline, on and on.

Oh La La