I remember someone posted a formula before on what the effects are when you reduce the rotational (unsprung) weight on your car, ie: wheels and tires.

I'm getting a set of wheels that are 5.5 pounds lighter on each corner (22 pounds total savings), and was wondering what the quantitative benefits are.

 

The thing to do is to take some baseline of whatever "quantity" it is you're expecting to get better, and measure again after you've installed the new wheels. While there may be a formula for simple non-slipping longitudinal acceleration, it is a lot more complicated and contains a lot more variables than most people like to think about.

Assuming they're the same size, the car will handle better and get faster, especially in the lower gears.

 

I think I know what your talking about mingster, I read it somewhere too, like 100 lbs equal .1 sec off your 1/4 mile or it adds like 10hp, something similar to that.

 

I don't remember for exactly, but I read some where that 1 lb per corner wheel weight is = 1 HP...So you need to know what the weight difference between your old setup with tires to new setup with tires. Assuming the net savings of 22 lbs, it is supposed to have the same affect as 22 flywheel HP.

I have to find that article somewhere...

Terry

 

That 22 lbs is in rotational mass....which is a equivalent to a lot more standing mass....

If i remember correctly, 10 lbs of rotational mass is equivalent to about 60-80 lbs of standing weight..so really you are saving anywhere from 130 to 180 lbs! maybe even more depending....some people have said 10 lbs rotational is equal to 100lbs standing, but that is a little too high of a number.

 

well, from a butt dyno's POV the car's quicker (steering, braking, etc.) and of course it handles better because it's 1 size up (185 -> 195), and I've also used smaller tires for that little extra final gear ratio effect

 

There was a big article full of engineering specs and real world testing in one of the car mags early in the year. I can't remember which one or I would look it up.

I had always heard 1 lb. of weight off the wheels was the equivalent of 5 lbs off the car. I have never heard it equated to hp.

The article "proved" that the 5 lbs formula wasn't always right but was in teh ball park.

It depended upon where the weight was removed. Weight out of a tire was worth more than weight out of the rim because it was further out.

They showed dyno tests to show hp gains, but the main thing I came away with was that the ride and handling definitely improved. Your car was better able to respond to and handle road imperfections which made for definite improvements in mid corner roughness on the track they were using. Lap times went down and car control was easier. Maybe not by huge differences, but it was always a noticeable improvement.

 

No...No...No...No.

I'm the one who posted the formula guys. Please, let this be the last time I ever read where 10-lbs of rotational mass is equivilent to 70-80-lbs of static weight. I'm sure Johnny you have more important things in life to worry about so I'm not knocking you for quoting that oft-quoted, but incorrect
analogy of rotational weight.
The figure is definitely closer to 2-2.5x, so 10-lbs would be equivilent to
25-lbs, not 70 or 80 and no, it's not 5-lbs either. Whichever magazine published that nonsense should be used as bum-wipe.
When I was an MR2-S owner, me and about a half dozen goobers with more degrees than I have Playboys started a thread that lasted for weeks and after it was all said and done and formulas longer than your Johnson were printed, it was generally
agreed that the # I originally posted (2.5x) was the MOST difference rotational weight would make. We linked to articles online that had it as high as 10-15x! bwahahaha Anyways, to top it off, two years of Tazzo runs also support the
2.5x difference so pass on any thoughts of dropping 1/2 second off yer 1/4 with newbie wheels!
Thus Mingster, you're dropping about 55-lbs worth of static weight (9 gallons of gas if you will) from your vehicle, which with all other conditions being equal (the key phrase), you car would be about 5.5hp quicker.
For whatever it's worth fellas, I didn't pull these formulas out of my ass. I spent three years finalizing and working on them. They are pretty darn accurate for vehicles of our weight class. On the street, a fair amount of variables can happen but this is essentially, nothing more than a paper evaluation of what happens when you change your power to weight ratio.

 

 

very,,very,,interesting?