Ok, what's the real conversion.

Every 1 pound on the wheels = 4 in the car, or is it 8.

I'm going to a wheel that weighs 12.9 lbs in 17x7.5

How much will this help me over my current wheels ~18-19 lbs.

 

maybe 0.2 sec less for 0-60 timing...
I'm thinking of getting lighter rims too...

 

i hear it's 1lb of unsprung IE wheel weight equal 10 lbs of dead weight in the car.

 

what wheels are you getting?

 

I'd guess he's getting SSR Competitions, but they're 12.7lbs for 17x7.5.

Stereodude

 

My wheels weighed in at 13.6 lbs. The good part is that it definitely improves acceleration. The bad part is that you will get MAD wheelspin .
-Cyrus

 

nice wheels

bling bling

 

It works out to be roughly 8 lbs per 1 lb removed from rotational unsprung weight. However, keep in mind that you are running 17s vs the stock 15/16 which means the weight will be further outside on the rim therefore making it harder for the motor to accelerate the wheel. Also, 17" low profile tires are usually 3-4lbs heavier due to MUCH thicker sidewalls and added belts. A typical 17" 215/50-235/45 will weigh in around 25-27lbs. Yeah, tires are heavy. And again, the added weight of the tires increases the rotational weight. Low profile tires aren't good for off the line acceleration because the contact is wide and thin. Wide and thin is good for lateral g's, but not straightline. Taller and narrower tires have narrow and long contact patches which get good traction off the line, but suffer in the turns.

With all things considered, your 17" package should perform as good or slightly better than a stock 15/16" package.


Dave

 

So that means if I take a 2002 SE and shave 10lbs off each wheel for a total of 40lbs off the unsprung mass (wheels) the cars will accelerate like a car that weighs 320lbs less?

What's that do to the 1/4 mile time and speed then? A 320lb weight reduction would be huge I would think.

Stereodude

 

Yes they are SSR Competitions, and I've driven 50 miles so far. On the freeway the car seems faster than ever before, or right around as fast as it always us, but the only difference is, I'm still lugging 200+lbs of wheels in my backseat. I'm about to go for a spin with an empty car.

 

Can you explain this a lil better? Would that be per wheel or all four as well?

 

So every 1lb you take off each wheel, its like taking out 8lbs of dead weight in the car? Well damn, im sure glad i bought these 300zx rims to replace my chrome rims.

Anyone thinkg 225 is too wide for dragging?

 

Sounds like from what Dave B. said it's 1 lb of unsprung rotating mass equals 8lbs of sprung mass. If you can shave 1lb from each wheel you save 32lbs total. 10lbs per wheel and you save 320lbs. That's how I understand it anyhow.

Stereodude

 

I was under the impression that wide = good for dragging. Most wide tires are low profile which may hurt draggin' I was planning on putting 245/45-17's on 17x8 SSR Competitions on my 2k2 (if the dealer ever decides to get the car).

Stereodude

 

You don't factor in the rear wheels into the equation because they aren't connected to the drivetrain. If you had AWD, then yes, you do factor in all 4 wheels.

For my car, I added 15lb 16" Kosei K1s along with 215/55 Avid V4s. The total weight is 38lbs. The stock setup weighs 40lbs (15s with 215/60 RSAs). Techically I removed 32lbs from my car, but the fact that I pushed the weight further out on the rim most likely negated what I shed in weight.

Wide SLICKS are what give you traction. You never see low profile slicks. They are fairly wide and usually a tall 65+ series tire. Low profile tires have wide and thin contact patches. Wide and thin is good for laterla g's, not staightline.


Dave

 

Those would look great on my Max Phouong. But why did you buy me 4 lug rims?

 

It's strange how every one use to think my old 17' Chrome epic rims were heavy. They weighed 42 lb's with 235/45/17 Sumitimo's. I guess they were pretty light the.

 

You also want more sidewall to allow for flexing once the weight/energy is transferred. More flex allows for a wider contact patch and less chance of wheel hop.

 

Not too wide. For every day driving I use 225/50/17's at 35 psi, for straight line speed I use shaved 225/55/16's at 18 psi on the front. My best times so far were with my wife's 225/50/16's, but that was more of a gearing thing. The 2k2 6spd shifts at 89-90mph with those tires which helps 1/4 times (for me at least).

 

Ahhh so that is where low psi front tires come into play as well?

 

yup lower is better

 

one of the better threads i've read all week..

 

yes. lower tire pressure allows for flex in the sidewall but it also makes the tire leave a larger contact patch (this is why with low tire pressure tires wear on the outer sidewall). When tire pressure is high, it bunches in the center (causing center of tire to wear quicker) and makes a smaller contact patch area.

 

WRONG, dude. It doesn't matter if it is FWD, RWD, AWD, one wheel drive, etc. What matters is that ALL the wheels have to rotate. Technically, the rear wheels ARE part of the drivetrain on any car. On an AWD car, they are connected by the driveshaft and diff. On a FWD car they are connected to the drivetrain by the moving asphalt underneath them. Either way, they need to rotate, and something has to make them rotate.

I know this sounds strange, but think about it. What matters is that the wheels and tires have to spin. The power from the engine has to move the car AND roll the wheels. It doesn't matter if the power goes to only 1 wheel or all 4 wheels through the drivetrain. The engine has to overcome the rotational inertia of the wheels to move the car, all 4 wheels. Whether the engine accomplishes this by a driveshaft driving all 4 wheels or only 2 wheels doesn't matter. What matters is that the wheels need to be rolling, and they all roll at the same speed. In other words, the power to move the car and spin the wheels remains the same amount of power no matter if the engine drives one wheel, 2, 3, or all 4 wheels.

The only time this would NOT apply is during a burnout, when the wheels are spinning and the car is not moving as fast as the spinning wheels. THEN it would matter, because the engine only is spinning whatever is directly attached to the drivetrain.

 

This is also what I was thinking. The engine might not be directly connected to all the wheels, but it does have to rotate all of them to move the car forward.

Stereodude

 

You are correct, sa!

DaveB usually gives good info, and no offense towards him, he just really screwed the pooch on this one.

 

I don't agree.

It really doesn't make much sense to me because the drivetrain doesn't have that extra weight mounted on to it therefore it's not creating the driveline drag. Sure, more weight is on the rear wheels and tires, but the drivetrain itself is only pulling that weight. There is more rotational weight, but it's not the same thing as the drivetrain rotational weight. The extra rotating weight on the rear is closer to extra static weight than true rotational unsprung weight. I've never heard anyone factor in all 4 wheels when they are talking about removing rotational weight unless they were talking about AWD.


Dave

 

ya for once i'm gonna agree with you kinda. it's prolly a little worse then having static weight but not as bad as more weight on the front two wheels. get lightter rotors. or take them off to race and use the e-brake

 

Sorry, but this is incorrect. The force you are trying to overcome is the TOTAL rolling inertia of all those parts (wheels, tires, rotors). Simple physics. I know it sounds weird and doesn't seem to make sense, but this is how it works.

Again, the only time it wouldn't matter is when the wheels are rolling at different speeds - as in a burnout, or donuts, or off-road racing, hanging it out in turns, etc. As long as all the wheels are rotating at about the same speeds, the power could be coming from a jet engine off the back of the car - it doesn't matter where it comes from. All you are trying to do is push 3000 pounds of car forward and get 4 wheels to rotate faster than they already are. Whether you do it by a drivetrain rotating those wheels, or a propeller off the back of the car doesn't matter. The AMOUNT of power needed to do it is the same. The only wheel that doesn't matter is one that's not rotating - the spare.