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Old 04-15-2004, 05:08 PM   #1
Flexx999
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Default Question about heavier wheels

I have been reading about heavier wheels and loosing hp and such. Anyone know the deal on this.

I weighed my stock rims and winter tires (same size as stock so the weight should be pretty damn close) they came out to 40lbs.
I weighed my summer rubber 17 x 7.5 rims with 235/45/17 tires and they came out to 50lbs.

So I added 40lbs to the weight of my car........not a big deal but then everyone is talking about rotating wheel mass and such and when you add weight on the tires your actually adding more then just the scale weight............whats the deal with it....all the posts I read just confise the hell outta me and everyone has a different opinion.

I knew my wheels would be heavier so I put on the perrin lightened crank pulley and it is supposed to be like removing 100lbs. from your car. So this should take care of the added weight from the wheels...correct?
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Old 04-15-2004, 06:31 PM   #2
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Its called "Rotational Momentum" and the amount of momentum is a function of the rotational speed (rpm's), acceration (torque), and mass on the wheel. The larger the mass, the more force you need to move it (or in this case rotate it).

A couple years ago, Dave Coleman (Mech Eng.) from Sport Compact Car did an analysis of the effect a flywheel has on the acceleration of a car. A set of wheels has the same effect, its just working on the other end. of the drivetrain.

To make a very complicated and long story short, the general effect is that heavier wheels have a larger impact on acceleration at lower speed's, than they do at higher speeds.

If you're looking for some definative "numbers", I suggest you talk with a couple of the MechE's on the board (Zuffy) to see if they can quantify the number for you, but even then, they'd need to know a ton of info about your wheels as how the weight of the wheel is spread out over its profile/diameter is as important as the mass itself. Keep in mind, that a hefty chunk of that weight could also come from your tires and not just your wheels. This is very likely the case with you as you went from 205/55/R16's to 235/45/R17's.

Most definately a topic that is WAY LONG and requires significant knowledge to quantify accurately.
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Old 04-15-2004, 07:12 PM   #3
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Short version

For every inch you increase your wheel diameter (assuming the wheels weigh the same) is like adding 200lbs to you cars weight.

Adding width to your wheels/tires is good because the contact patch is bigger(upto a point of course).

Going very large diameter wheels on a WRX like 18" spells tranny problems if you drag, plus its slower and your clutch is toast (isn't it Sean)

BYE
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Old 04-15-2004, 07:18 PM   #4
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The diameter of my aftermarket tires are very close to the diameter of the stock ones. My aftermarket ones are maybe an inch bigger on the diameter, (1/2" on the radius) So the only difference is the weight.

I don't need exact numbers or anything just a guess on how that weight affects performance.

One thing, I had my summer rubber on yesterday and my winters on today and the ol butt dyno didnt feel any difference in acceleration
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Old 04-16-2004, 12:49 AM   #5
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Ok, Flex999 and Markus you have tweaked my interest in this and I did some calculations and made up an Excel spreadsheet to calculate the moment of inertia for wheel and tire combinations. If anyone is interested in seeing the effects of changing their wheels and tires and the changes to the moment of inertia I can email them a copy. It's kinda interesting (maybe to eggheads only, what effect of heavy tires and big wheels have compared to stock wheels.) I haven't had time to double check the calculations in the spreadsheet so don't take this as gospel.

Anyways, GRM magazine did up a test in their June 2003 issue on the effect of heavy wheels. What they found on a 2000lbs car, that by removing 8lbs/wheel (total of 32lbs) and at the same time added 32lbs to the chassis, so the effective static weight was the same, the 1/4 mile time was faster by just over 5 hundredths of a second. I don't think any butt dyno will be able to percieve that, but they also said that for wheels, reducing their mass is 70% more effective than losing "sprung weight." I've obsessed over heavy wheels and tires and it took me a year to decide on the wheels and tires.

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Old 04-16-2004, 10:12 AM   #6
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So basically if they are saying by removing 8lbs per wheel they where able to gain 0.05 of a second in the 1/4, so if I added 10 lbs per wheel I might have lost at the most 0.1 of a second in the 1/4. Plus I put on the lightened crank pulley thats supposed to be like removing 100lbs. from the car.

So in a nut shell it affects the performance but your really only gonna notice it if you race or put on really heavy wheels.


I can live with that for the bling bling..........

ps: I find it funny that some guys on (not in the canadian forum) here are so worried about adding heavier wheels yet they will throw like 200lbs of stereo equipment in their cars...........
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Old 04-16-2004, 02:15 PM   #7
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Quote:
Originally posted by Flexx999
I find it funny that some guys on (not in the canadian forum) here are so worried about adding heavier wheels yet they will throw like 200lbs of stereo equipment in their cars...........


That's one of the reasons why I don't post on the main suspension forums. Kiddy litter
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Old 04-16-2004, 03:47 PM   #8
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This maybe worthless input. And has zero science behind it, but with my 16 stockers and pzero tires 13.5X best time in the 1.4

15 inch steelies with winter Nokians... 13.4X best time

now where did i put hose 13's??

on the street you will notice ZERO difference.. I"VE HAd as high as 18s and i noticed nothing but more pretty girls looking at ..... my wheels...
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Old 04-16-2004, 04:32 PM   #9
Flexx999
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Quote:
Originally posted by HOK
on the street you will notice ZERO difference.. I"VE HAd as high as 18s and i noticed nothing but more pretty girls looking at ..... my wheels...

Now theres the answer I was after..................
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Old 04-16-2004, 05:50 PM   #10
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its the only answer that matters hahah
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Old 04-16-2004, 06:24 PM   #11
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Quote:
This maybe worthless input. And has zero science behind it, but with my 16 stockers and pzero tires 13.5X best time in the 1.4
Actually that makes lots of sense. Heavy rims will not have as much of an effect on the total moment of inertia of the rim and tire combo, as large diameter, heavy tires. Tires are always are much heavier then the rims, and are the largest distance from the hub (axis of rotation,) so both these factors will have the largest impact on moment of inertia. My spreadsheet gives results that agrees with your 1/4 mile times.

I assume that traction on launching down the 1/4 mile wasn't a problem so I think your higher profile, but lighter tires gave you the edge to have a better time then your 16" rim/tires.
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Old 04-16-2004, 06:29 PM   #12
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Quote:
Originally posted by Zuffy


Anyways, GRM magazine did up a test in their June 2003 issue on the effect of heavy wheels. What they found on a 2000lbs car, that by removing 8lbs/wheel (total of 32lbs) and at the same time added 32lbs to the chassis, so the effective static weight was the same, the 1/4 mile time was faster by just over 5 hundredths of a second.
Interesting. So they assumed that the guy who drove it did it with such precision that they concluded 5 hundredth of a second difference came from the added effective inertia, huh. Speaking of voodoo science.
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Old 04-16-2004, 06:44 PM   #13
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sweet.... can you email me that spreadsheet? does it do dead weight?

pmd you
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Old 04-16-2004, 08:01 PM   #14
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Quote:
Originally posted by Len
Interesting. So they assumed that the guy who drove it did it with such precision that they concluded 5 hundredth of a second difference came from the added effective inertia, huh. Speaking of voodoo science.
I agree with you that experimental error, repeatablility, the temperature of the run, driver error, etc... will affect the results of their tests. If you read the article they do things as scientifically as possible, but there is nothing voodoo about physics. Making anything heavier is gonna make it more resistant to forces and you can't argue that.

Unless you still believe the world is flat.
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Old 04-16-2004, 08:31 PM   #15
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haha I do love to drag race and thats my background but prodrive recomends the 18's for road racing... thats why I ordered my volks in that size.... as for my 18" rotas I just plain got them cheap and i'm not after performance in the winter.
they look good though!!
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Old 04-16-2004, 09:36 PM   #16
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Quote:
Originally posted by Zuffy
I agree with you that experimental error, repeatablility, the temperature of the run, driver error, etc... will affect the results of their tests. If you read the article they do things as scientifically as possible, but there is nothing voodoo about physics. Making anything heavier is gonna make it more resistant to forces and you can't argue that.

Unless you still believe the world is flat.
Well, first of all I don't think we disagree on this subject. Having that said, I do major physics (though a lowly grad student) and I didn't mean it in any way to deny the validity of science. (well, me no native speaker) My point was that, no matter how hard they tried to be scientific, there was no way they could control the variables so well and reduce the margin of error so much to yield any valid conclusion on that result. We are talking about 0.05 sec out of 15 sec, after launching, manual shifting, tire burning etc... No way.

I totally agree that lighter is better. But the question is how much better, and I do feel that the effect of the dreaded "rotational inertia" tend to get blown out of proportion from time to time. If you actually do the calculation you'll find out it's not THAT big of a deal for a few lbs difference per corner.

Oops, what am I doing in canadian forum anyway.
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Old 04-16-2004, 10:58 PM   #17
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Quote:
If you actually do the calculation you'll find out it's not THAT big of a deal for a few lbs difference per corner.
Yep, I totally agree. The tests and butt dyno arguements make for interesting car chat, but I just can't help but get some numbers down on paper to satisfy the engineer geek in me, no matter how insignifigant the difference might be.
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