How much benefit are lighter wheels rotational mass wise

[Campo]

Originally Posted by Sportsguy83

I hate having the same wheels everyone has.... I am looking at TWS T66-F which are even lighter than RPF1s. But, they have two downsides. One more expensive than my current wheels, second, uglier than my current wheels. That's why I'm trying to gauge real actual quantifiable benefit of them.

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Instead of the RPF1, do what I did and go with PF01. Different look, plus (supposedly) the mass is more centralized than the rpf1. the mass centralization part is important to have, but difficult for a lay person to actually measure. 'Visually' the PF01 'looks' more mass-centralized than the RPF1, but I've never driven them back to back for quantifiable measuring.

These in 17x8 with 225/45 are perfect for HPDE on most tracks.


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[CatDaddysBBQ]

Originally Posted by Sportsguy83

I guess you didn't read the whole thread. The question is not "why" or "how", I already knew the answer to both. The questions is quantity. How much of a benefit it really is. If you research, some people say it's negligible others say it's a big improvement so what I am looking for is people with experience on the subject. Someone who has actually changed wheels for same sized wheels but noticeably lighter and their personal opinion of performance improvement.

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I answered earlier with the boot vs running shoe analogy... But yes, I have done a direct swap (exact same size wheel) and found the difference to be VERY noticeable and impressive. Got me addicted to shopping new wheels by weight first, THEN style, which would've seemed crazy to me before I had experience with lightweight wheels. Now, it's CRAZY to buy equal weight wheels, let alone heavier ones.

Honestly though, nobody can tell YOU if it's worth YOUR thousand dollars. But from a perspective of autocross and daily driving, there isn't much by means of "cheap" bolt on upgrades that will change as drastically as a set of light wheels.

In the end, you're going to have to take the plunge and decide for yourself. But yes, it's totally noticeable, and yes a lot of us think it's worth it.

[Pete156]

Huge benefit, though I cannot quantify it. My change was dramatically noticeable because I lightened each wheel by 3 lbs. and lightened the driveshaft by 13 lbs., reducing rotational mass considerably. Significant performance gains accelerating and stopping which is evident to even the novice driver.
I would estimate these changes save me at least 3-5 seconds on a 1 minute autocross run.

[u/Josh]

Originally Posted by Pete156

Huge benefit, though I cannot quantify it. My change was dramatically noticeable because I lightened each wheel by 3 lbs. and lightened the driveshaft by 13 lbs., reducing rotational mass considerably. Significant performance gains accelerating and stopping which is evident to even the novice driver.
I would estimate these changes save me at least 3-5 seconds on a 1 minute autocross run.

There is absolutely no way lighter wheels and driveshaft save you 3 seconds on a 1 minute course. No way...

[stugray]

Originally Posted by u/Josh

There is absolutely no way lighter wheels and driveshaft save you 3 seconds on a 1 minute course. No way...

I was inclined to say the same thing.
Lightening the wheels will make a difference in unsprun weight and polar momentum (quicker response) which would make a good driver faster.

The reduced weight from the 13 lbs reduction in the driveshaft will help with overall car weight, but will do very little to the rotational inertia of the rotating mass.

[kiichiro]

but is it worth a grand?
for me, and you, I bet, yeah

[Hydaral]

I'll give it a shot, for the record, I studied to become a civil and structural engineering draftsperson, but got bored and switched to IT a couple of years in.

I'll use the numbers you quoted and ignore tyres (let's keep it simple). I'll also be using proper units (sorry US, Burma and Liberia).

Gramms:

22lb / 2.2 = 10000g

No diameter specified, so lets assume 17 inch (432mm)

Using this calculator: http://www.botlanta.org/converters/d.../flywheel.html

Assume average speed of 100km/h (wheel RPM of ~800) and even distribution of mass over the radius (disc): 818 Joules (Watt seconds)

Convert to horsepower: 818 / 746 = 1.09 hp seconds per wheel

16 lb wheels:

16lb / 2.2 = 7272g

Still 17 inch (432mm)

Same assumptions: 595 Joules (Watt seconds)

Convert to horsepower: 595 / 746 = 0.79 hp seconds per wheel

So, over 3 seconds of acceleration (say, accelerating out of a corner), the power required to get the wheels up to speed is:

Gramms: (1.09 x 4) / 3 = 1.45 hp
16lb: (0.79 x 4) / 3 = 1.05 hp

But, what if the lighter wheel also has it's mass concentrated towards the centre instead of evenly distributed (smaller moment of inertia)?

We just multiply the disc result by a ratio of the amount of mass that has been moved from the outer edge to the inner edge, lets say the mass is somewhat better distributed and give it a ratio of 80% (0.8).

595 Joules now becomes 595 x 0.8 = 476 Joules (0.64 hp seconds)

So now we have:

Gramms: (1.09 x 4) / 3 = 1.45 hp
16lb: (0.79 x 4) / 3 = 1.05 hp
16lb with better MOI: (0.64 x 4) / 3 = 0.85hp

Braking will obviously be better too, the wheel would slow down faster, so you could brake later.

Most of these numbers are very hand-wavy, without a dyno, they probably cannot be accurately quantified and even then, they may be lost in error margins.

Some dyno tests on a Camaro (heavier wheels and more power, so more measurable): http://www.bimmerpost.com/forums/sho...d.php?t=639783

Oh and as I said before, I'm only a partial engineering draftsperson so if I screwed something up or made a mistake somewhere, please point it out. I'm just calculating using info I have gleaned through my research over the last few weeks.

I went from OEM 16x6.5 inch wheels to Enkei PF01 17x8. By my reckoning I increased mass on each corner by around 1.5-2 kg, but it feels more responsive and quicker, might just be a placebo or the better tyres, but the PF01s seem to have their mass concentrated towards the centre, which would give them a lower moment of inertia.

[Cheeseballs]

Originally Posted by Sportsguy83

I hate having the same wheels everyone has.... I am looking at TWS T66-F which are even lighter than RPF1s. But, they have two downsides. One more expensive than my current wheels, second, uglier than my current wheels. That's why I'm trying to gauge real actual quantifiable benefit of them.

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Ugly? Blasphemy! 15.7 lbs of golden 18x9.5 goodness! I cried once after purchasing but have been nothing but smiles since.

Good luck on your search though.

[FirestormFRS]

I think the advantage is more in the lowering of the unsprung weight. The less weight your suspension has to control the better it can do what it was meant to do. The car should go faster, turn faster, and stop faster. Not sure in seconds what it amount to on a race track. Mikey for CSG should weigh in!

[AyJay]

Welcome to car forums!! Where everyone can be an expert by regurgitating popular opinion/theory but no one can really answer your specific question.

Personally, I've stopped caring about a few pounds of wheel weight and gone the budget friendly route since some of the fastest track guys I've ever seen run **gasp**

20 lb Rotas.

[TylerLieberman]

Lol everybody wants to write a novel about a bunch of information that wasn't asked for.

Question:

Is it worth the $1,000 price in a performance aspect?

Sure.

I mean, $1,000 can just about get you headers and tune which I would imagine would have a more noticeable gain. $1,000 isn't much though for modifying cars; so if you're already considering changing the wheels on your car, I would go for it. Just choose something that would give you what you're looking for style and weight wise.

I have 18" TE37s and am actually going to sell them simply because I'm going back to 17s. Not so much for weight concerns, but for the fact that 18s don't work with the additional steering angle my setup utilizes.

I suppose it just comes down to what you actually want from the car.

[CSG Mike]

Originally Posted by TylerLieberman

Lol everybody wants to write a novel about a bunch of information that wasn't asked for.

Question:

Is it worth the $1,000 price in a performance aspect?

Sure.

I mean, $1,000 can just about get you headers and tune which I would imagine would have a more noticeable gain. $1,000 isn't much though for modifying cars; so if you're already considering changing the wheels on your car, I would go for it. Just choose something that would give you what you're looking for style and weight wise.

I have 18" TE37s and am actually going to sell them simply because I'm going back to 17s. Not so much for weight concerns, but for the fact that 18s don't work with the additional steering angle my setup utilizes.

I suppose it just comes down to what you actually want from the car.

One may be legal where you are, while the other one isn't...

[Hydaral]

Originally Posted by AyJay

Welcome to car forums!! Where everyone can be an expert by regurgitating popular opinion/theory but no one can really answer your specific question.

The question was not specific though, it was: "I want to know how much benefit is it really to go to a 16 lbs or so wheel" and "how much of a difference does it make", how do we quantify that?

I tried to quantify it in power, others have guessed (?) how much time it will cut from track times.

Acceleration before the turbo kicks in was mentioned, the only way to quantify that without a practical test is to determine the extra power used to turn the heavier wheels, with the lighter wheels, this power would then be used to propel the car instead.

[Fizz]

I can only offer my subjective feedback, but when I went from a 20lbs (18") wheel to a 15lbs (17") wheel I was able to immediately feel the difference in acceleration and ride comfort. So yeah...