someone please explain the unsprung weight wheel issue
 

ok guys,

i have been doing some research and can't seem to find anyone who has experience tracking their car (especially an RX7) on light wheels vs heavy wheels. is it really as much of a problem as people say it is?

i have been eyeing some enkei RPF1s in 18x9.5 that weigh 17.2lbs. these are great, but cost substantially more that (actually DOUBLE) all of the "ricer" wheels i've found.

all of the 18x9.5 ricer wheels seem to weigh ~25lbs each.

there's the obvious issue of adding almost 32 lbs of weight to the car, but i am wondering how much worse it is that it's 32 extra pounds of UNSPRUNG weight.

i know you all will post "SPEND THE EXTRA MONEY," but i'm wondering why, and if i would even notice a difference in the lighter/better wheels. and will the cheap wheels hold up to track abuse (still not on r-comps)?

Same as with a lightweight flywheel , you are adding mass for the drivetrain and at a big distance as well its not concentrated in the middle its a wheel so its outward weight to spin so it slows everything down . grab a sock put a rock in it and spin it now add a few more rocks and do the same , same concept its not that the rocks are that heavy but when you are trying to spin that extra weight using the car's power it affects acceleration .

Yes u will b able to feel the difference in weight if the wheels and cheaper wheels should b fine for track use. In would get a known brand though. Yea some ppl will say cheaper wheels can break, etc but the likely hood of that happening is very unlikely. Companies are not gonna sell wheels that are gonna break easily. However there are wheel companies that do design to break the wheels at a certain impact but u won't be buying those wheels

Really good analogy. :bigthumb:

I have always had a really hard time spending money on wheels. I have to spend how much? And it's not going to make my car any faster or handle in better and costs the same as some turbo kits or coilovers?

I don't think it's a problem going with a heavier wheel, let me elaborate before some goes nuts on me :). Brian Johns told me a long time ago that until I'm within a few tenths of the leader at an AutoX or a second or two of the leader at a time trial, you'll be ok with mid range stuff(in regards to stuff like wheels and coilovers) from a cost benefit perspective. Is there a performance advantage? Absolutely. Am I going to be able to tell a big difference like upgrading to single turbo or replacing worn out OEM springs and struts for some quality coilovers? no. Not unless you are drop substantial weight off each corner.

For me, I'm the poor track enthusiast trying to get every last bang for my buck so I can get more seat time. Once upon a time, I got some really light wheels and paid a premium for them. I dropped a wheel off at VIR and bent one. I had a really difficult time sourcing a replacement and it was really expensive once it was all said and done. After that, I switched to CCW. They aren't the best looking wheels out there; but they are fairly priced(I normally keep an eye out on the forum for used as well), will hold up on track, and if something happens to one... I'm going to call John(CCW) on Monday morning and order an outer or inner barrel for $125(maybe the price has went up now). I ran 18x10's all around for several years and then decided to put Pettit flares and Ronin front fenders. 315 up front and 335 in the rear. No problem, 4 new outer barrels and I'm now sitting at 18x11 and 18x12.

The RPF1's are a really nice, light wheel for the money though. I have seen some cheap wheels fail while on track, but I think it was a cheap knockoff wheel that some of the Spec E30 guys use to run. I've also seen high end wheels fail while on track. Always a good idea to check your wheels daily. If you get a cheaper knockoff version, I'd probably check them after each session for cracks.

I don't think I really answered your question. Seemed like you were going through the same thought process I do when it comes to wheels though.

Good stuff :nod:

That rock in the sock analogy is awesome :icon_tup:

Rule of thumb is 1 pound unsprung is 2 pounds sprung so saving weight on your upper and lower arms, brakes etc..... pays dividends.

Unsprung rotational weight is 4 to 1 or save 1 pound off your wheel and that's like 4 lbs from the chassis. BUT even more important than the weight saving is how much less your engine has to work to turn those wheels each time you accelerate and that's cheap power.

Like the sock analogy though the longer the sock or the further the weight is from the center the harder that sock is to get swinging so also think about the weight of your tires which is even more important than the weight of your wheels because they are further from the center.

Bottomline is expensive wheels are worth the weight savings :icon_tup:

BUT as Brent mentioned don't break the bank the most important thing any off us can do to lower our lap times is actually getting out there and doing the damn laps and if you're not doing it with the gas pedal all the way down on the floor well you don't need to decrease wheel weight but increase ball weight and that's going to take seat time which cost a lot more than light weight wheels $$$$$$$$ :egrin:

You can find a set of nice used wheels for the price of those heavy ebay wheels. I got my 17x10 CCWs for 1200 bucks after selling my 17x8 and 9 RPF1s for 900 bucks with brand new R1Rs.

Just keep an eye out and be ready to pull the trigger when you see the ones you want.

There's actually been a bit done in open-wheel categories where they've measured sensitivities with unsprung weight variously being added and subtracted. For the most part, with professional drivers the results were negligible and with amateur, unnoticeable.

I think a lot of it dates back to the 60s and 70s where the holy grail was unsprung weight......some of the experiments included, progressive in both winding and wire diameter titanium springs, those weird, bell shaped magnesium wheels, inboard brakes front and rear, etc, now mostly consigned to history.

On the other hand, have seen the cheap nasty wheels break out centres at the track on what I'd consider a minor hit.

Engine Drivetrain Rear Wheels Power Increase - Popular Hot Rodding Magazine

The above link is a cool study

The tiniest bit of speed goes a long way in motorsports and a good driver will absolutely take advantage of ANY weight savings PERIOD.

I got creamed at the last TT I did and he was only 8/10nths faster but trust me that's a fresh set of sticker tires and a good alignment worth of speed on a little over a minute track or 100lbs in weight saving HEHE.

most racers follow these three rules.

1. wheels break when you hit stuff

2. you will hit stuff, or stuff will hit you.

3. we run 2 classes, so we need 2 different sets of wheels and tires. if we run the 25 or something, we'd need 20-28 wheels….

so taking into account we need lots of wheels, and they get broken/damaged here and there, cost is more important than weight.

the number 4 to the list is that sometimes your sponsor makes wheels, so this makes the choice really easy

ok i pulled the trigger and got some RPF1s 18x9.5 +45 from a forum member (the guy with the white FD / 2jz build thread going right now). the wheels also have almost new RE11s on them, so i think this will increase my grip substantially.

Functional good fitment > Hella good fitment.

Good choice! :icon_tup:

Sounds like a great buy good luck , and I'm looking forward to seeing your next track day video .

thanks guys, the 265/35/18 RE11s should be a substantial upgrade from my 225/50/16 RS3s, and should fit pretty well.

Tem, why don't you come to the next event with us? you've got a few months to prepare :)

Id love to , Just gotta get my car running right =) lol , if they make an event for the rotary rally I'd prob try and make it

Noteworthy over here, in one size, fastest slick is 3kg heavier than the lightest equivalent....but will lighten the wallet more to compensate! :lol: I don't see many willingly swapping to improve unsprung and potential acceleration in this case, unless the budget is in the red. As always, there are compromises and more than just one consideration in finding time. If doing straight line stuff, I'd imagine it would bear more pondering.

Jacob what wheels are you running now? I would like to know what you think of the RPFs once you install them compared to your current wheels.

I had a 240sx years ago and switched from stock to kosei K1s. It felt like I picked up some additional tq. via the butt dyno.

Are you still on stock fenders as well?

I agree with the two piece wheel advice. I just got a car with 2 piece wheels. The widths and offsets aren't what I want. The previous owner fixed the sizing with 25mm bolt on spacers. I plan on contacting a company for four new barrels. Should run $750 for the set.

Some pics would be nice too everyone loves pictures lol.

Thanks!

Stanley

I agree you can find time all over the place but if you have the budget short of adding tire size lightening the wheels is a really good place to find easy time.

Road racing is simply drag racing between corners and don't forget it's also easier to slow down a lighter wheel.

stan, i am currently running the stock FD wheels with 225/50/16 hankook RS3s. i just sold these to a forum member (shipped them out TODAY) and i am picking up my RPF1s with 265 RE11s this Saturday. i will definitely post pictures.

i have stock fenders, but they have been rolled, and the quarters rolled and pulled, as the previous owner unfortunately had the car stancebro'd.

RPF1's are on!

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Congratulations on your new setup!

I sadly know the effects of a stanced car. We have one in the group. When we got it you couldn't get on it. There was no suspension flex. It did look sexy as hell.

Please post up any additional feedback on the setup. I think I've settled in getting a 18x10 +50 ccws. I don't think I will out my rx7 on the track but if I do it will be with a setup like yours.