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Discussion Starter #1
Hi everyone... I want to take the lightweight route regarding wheels/tires, so I'm looking at 7 or 7.5x18" options, and I'm planning to stay on 215s tire wise. My idea is to drop at least 8-9 pounds per corner in rotating unsprung weight, pretty easy in these sizes.

I've read everything and then some about the topic and it's hard to come to any conclusions. The physics do say that there are a few advantages of lighter wheels, which I don't intend to discuss here in depth. I know they are there, but regarding how noticeable they can be... It gets complicated.

I also know that the rules of thumb you cand find everywhere online are mostly BS or plain wishful thinking. There are just too many factors in the mix, from the weight of the car itself to the exact shape and weight distribution in the alloys, to tire weights. So, for anyone out there who has dropped significant weight in wheel+tire combo in this car:

1) Has acceleration improved?
2) If so, is it more noticeable from a standing start or, say, flooring it at 3500 rpm in 3d gear?
3) Does the car generally feel nippier, with some more torque?


I have a european 2.0, so yes, I'm looking for a bolt-on performance gain hehe... And no, I don't do track days and I don't care much about tenths and hundredths, I mostly want the car to feel a little quicker and better for overtaking. I know lighter wheels are expensive but it's the only thing I want to do to the car for the moment, cos it won't void my warranty (you can't imagine what a pain in the ass, legally speaking, it is to try and mod a car here in Spain).

Sorry about the rant, thanks everyone!
 

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I can definitely notice quicker acceleration with my volk setup on my gen 2 skyactiv. Wheels are 18x7.5 and weigh a smidge under 15 lbs. With a light tire like a dw or dws, 225/40 in my case, it is a 34.7 lb per corner setup. Let my friend who rocks the ms3 gen 2 wheels, so identical 18x7.5 wheel at close to 25 lbs try them, and the difference was immense. I would say that your butt dyno will feel differences in the 6-7 lb or more per corner range.
 

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Achtung!
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I'm at just under 40lbs a corner, but I did go up considerably in sizing (19x8.5 and 235/35/19 Yokos.)

My 18" factories are 26.7lbs a corner, and 52lbs per with the all season 215/45s wrapping them.
My 16" factories are just a hair heavier than my 19" setup currently. Like within a pound or two.

-12 lbs per corner, I could have gone lighter by going with 17x9 rpf1s (and still might later on) - but I'm quite happy.


Noticeably better steering response, car grips for days, gas mileage is negligible, but I didn't lose any due to upsizing.
 

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1) Has acceleration improved?
2) If so, is it more noticeable from a standing start or, say, flooring it at 3500 rpm in 3d gear?
3) Does the car generally feel nippier, with some more torque?
1. Yes
2. Bigger difference at lower speeds
3. Yes, but your butt dyno will readjust in 1-2 weeks.

Vice versa if you install larger brake rotors and/or really wide wheel and tires that have more inertia
 

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Discussion Starter #7
Thanks joey.lisano, how much weight did you save per corner?

Tastic, do you think the effect is more noticeable in more powerful cars, or the other way round? The 2.0, for those of you who haven't driven it, is pretty underpowered, even in the european higher compression/hp version. So I'm hoping to alleviate the lack of torque, mostly (I used to have a turbodiesel, so I'm a little spoiled torque-wise haha!)

For those physics-literate: I think not only the OEM 18"s are very heavy, but they also must have a pretty nasty weight distribution, just look at how fat the spokes are at their outer ends. Apparently, the shape of the wheels has a huge influence on the whole thing, too, doesn't it?
 

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Tastic, do you think the effect is more noticeable in more powerful cars, or the other way round?

Other way around. The identical wheel swap would be less of a noticeable difference on the speed3 with all the extra torque. To illustrate the reverse, the guy I bought the volk setup from was selling them because they were too light for his modded Acura. He was just spinning them most of the time.
 

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Achtung!
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-12 lbs per corner is quite the reduction... Butt-dyno feeling better throttle response?
Not personally, but I also don't have a commute conducive to testing out throttle response...

You're also forgetting the advantages that lighter wheels have for your suspension. The lower unsprung rate will translate into less linear momentum in the y-plane, and thus allow your suspension to respond much quicker.

What this translates into is a much better steering feel, suspension handling and 'ride.'

Unsprung weight is a great debate, but there is no debate that unsprung weight will have a markedly better effect on the handling of the vehicle. Does it have a noticeable effect on mileage or performance? Not really - as rolling mass and inertia don't take the 3000lbs of the vehicle surrounding the rotating assembly.
 
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...The lower unsprung rate will translate into less linear momentum in the y-plane, and thus allow your suspension to respond much quicker.

What this translates into is a much better steering feel, suspension handling and 'ride.'

... Does it have a noticeable effect on mileage or performance? Not really - as rolling mass and inertia don't take the 3000lbs of the vehicle surrounding the rotating assembly.
Yes and yes. I went down 10lbs per corner and can definitely tell the difference in the ride ... much smoother over road imperfections. As for the other stuff ...

1. I think so ... my butt (or my brain) says so ... a little
2. Not sure
3. Yes, but I forked over some big bucks to lose 10lbs per corner and so maybe I just NEED to believe! :)

Mileage is about the same ... I have logged my best commute since on the new setup (41 mpg vs 39) but that could've been an extra light traffic day. Still it FEELS faster.
 

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I went from the OEM 16" steels to 18x7.5 RPF1s, so significant weight loss (~10 lbs per corner min).

1. I'd say it has improved a little, but I havent been mashing on it a ton to say that with a lot of confidence.

2. Most experience I've had is from standing launch or from a rolling second gear push and it does feel a little more responsive. Nothing extraordinary.

3. The handling feels more improved than the acceleration. After autocrossing once with the steels and once with the RPF1s i can safely say that the car feels more responsive to steering input at different moderate cornering speeds (25-50mph) (i'm on similar hardness all-season tires at 10mm wider)
 

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Discussion Starter #12
Not personally, but I also don't have a commute conducive to testing out throttle response...

You're also forgetting the advantages that lighter wheels have for your suspension. The lower unsprung rate will translate into less linear momentum in the y-plane, and thus allow your suspension to respond much quicker.

What this translates into is a much better steering feel, suspension handling and 'ride.'
I guess your case is a little particular since you went from 215s to 235s, so it could stand to reason that this extra rubber partially killed the possible gains in acceleration, but not all of the other benefits of lighter wheels (I've also considered these other benefits and they are very welcome too!)
 

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I went from the OEM 16" steels to 18x7.5 RPF1s, so significant weight loss (~10 lbs per corner min).


3. The handling feels more improved than the acceleration. (i'm on similar hardness all-season tires at 10mm wider)
Might I ask what spacers you're using and whether you extended your studs? Thx in advance!
 

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Definitely an improvement!

Any time you can knock weight off a vehicle it is improvement. And taking 10+ lbs. of un-sprung weight off of each corner should result in a marked improvement in suspension response, turn-in, steering wheel "feel", and, to a lesser degree acceleration.

And don't forget that every 8 lbs. of weight reduction is equivalent to 1 HP, so a 40 lb. reduction is akin to having 5 more HP - w00t!!

As Colin Chapman, of Lotus fame, once said: "Simplify, then add lightness...."

-CD-
 

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Any time you can knock weight off a vehicle it is improvement. And taking 10+ lbs. of un-sprung weight off of each corner should result in a marked improvement in suspension response, turn-in, steering wheel "feel", and, to a lesser degree acceleration.

And don't forget that every 8 lbs. of weight reduction is equivalent to 1 HP, so a 40 lb. reduction is akin to having 5 more HP - w00t!!

As Colin Chapman, of Lotus fame, once said: "Simplify, then add lightness...."

-CD-

That "x lbs = 1 hp" is dependent of the power to weight ratio of the vehicle, sprung or unsprung weight, and isn't a flat number.

example:

Car weighs 3000lbs and has 400hp
Power to weight ratio; 400/3000 X 2240 = 298.7 hp/tonne
If you get rid of 12lbs off your car then 400/2988 X 2240 = 299.9 hp/tnne
So if you stick the new power to weight ratio back into the formula using your original weight:
"X" /3000 X 2240 = 299.9
"X" = 401.65 hp
So your 12lb reduction is the equivalent to adding 1.65hp to the base 3000lb car.
Your 100lbs on the 3000lb/400hp car would be worth 13.8hp
 
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Yes, I realize what you are saying, but you must admit that my 1HP per 8 lbs. works out pretty darn close to what you did with a bunch of math [smile]. In fact, my method is a bit more conservative because you come up with 1.65 HP per 12 lbs. and my method yields 1.5 HP for the same 12 lbs.

No matter, if he shaves 40 lbs. off his car, he will be seeing the equivalent of a 5 - 5.5 HP gain in addition to the improved handling characteristics. Sounds like a win-win to me....

-CD-
 

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Yes, I realize what you are saying, but you must admit that my 1HP per 8 lbs. works out pretty darn close to what you did with a bunch of math [smile]. In fact, my method is a bit more conservative because you come up with 1.65 HP per 12 lbs. and my method yields 1.5 HP for the same 12 lbs.

No matter, if he shaves 40 lbs. off his car, he will be seeing the equivalent of a 5 - 5.5 HP gain in addition to the improved handling characteristics. Sounds like a win-win to me....

-CD-
I did the estimate on a much more powerful machine in the same weight class as our chassis (a Porsche) - the numbers would be entirely different as a 155hp entry into the 3000lb class, like our Mazda 3s in 2.0l fashion.

In fact - here ya go.

155/2840(My car as it sits) x 2240 = 122.25
155/2800(deducting 40lbs) x 2240 = 124.
?/2840 x 2240 = 124
157.25/2840 x 2240 = 124.03

So, your 40 lb drop netted just north of 2.25hp (nothing else adjusted), not 5 or 5.5hp.


More powerful cars have more advantage in the power/weight sliding scale, because they have a shorter adjustment scale.
 
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Loud3, I'm crying "uncle" right now, you're killing me with facts!! [very big smile] Anyway, less weight is a good thing - I think we can all agree on that.....

-CD-
 

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Loud3, I'm crying "uncle" right now, you're killing me with facts!! [very big smile] Anyway, less weight is a good thing - I think we can all agree on that.....

-CD-


No worries! I wasn't trying to run anyone into the ground. And yes, anytime the weight goes down, the performance goes up!

:thumbup1 1:
 
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