So you want to know if rear wheel weight makes a difference....

*I30tMikeD* · 10-14-2003, 04:09 PM

For me it didn't. Reduced rear wheel weight by 40lbs when I was at tje tracl and saw no difference in ET. Many runs were done before and after. Just thought you all should know.

*Quicksilver* · 10-14-2003, 04:12 PM

Quote:

Originally Posted by I30tMikeD

For me it didn't. Reduced rear wheel weight by 40lbs when I was at tje tracl and saw no difference in ET. Many runs were done before and after. Just thought you all should know.

Weight may not make much of a difference, but going to a thinner width wheel/tire combo does...

*I30tMikeD* · 10-14-2003, 04:49 PM

Quote:

Originally Posted by Quicksilver

Weight may not make much of a difference, but going to a thinner width wheel/tire combo does...

I was going to swap out my 53lbs 235/45 17 wheel tire combo with 205/65 15 32lbs combo, but the millenia wheels won't fit on the rear. I used Neal's 17" 33lb ssr comps with 235/40's.

Isn't Jime using millenia rims on the rear?? They would not fit for me.

*Jime* · 10-14-2003, 05:17 PM

Quote:

Originally Posted by I30tMikeD

Isn't Jime using millenia rims on the rear?? They would not fit for me.

Ya I use them on the rear, I think Neal uses them on the front too but I couldn't get the slicks to seal on them.

They do fit on the front too though because I sold them to Jer with my D/R's on them and he ran them a couple of weeks ago when I was at the track so don't know why they wouldn't fit on yours.

*I30tMikeD* · 10-14-2003, 07:43 PM

Quote:

Originally Posted by Jime

Ya I use them on the rear, I think Neal uses them on the front too but I couldn't get the slicks to seal on them.

They do fit on the front too though because I sold them to Jer with my D/R's on them and he ran them a couple of weeks ago when I was at the track so don't know why they wouldn't fit on yours.

I use them on the front all the time, but this time I tried to use Neals on the back (the ones with street tires). The wheel would not fit over the metal cap coming out of the hub. The rear does not have the pin going through it like the front axel does. Got me???

Anyhow, the point was that rear wheel rotational mass will not effect acceleration. I have done this same test with the front millenia wheels and gained .25 1/4 mile by shedding 40lbs of wheels and tire weight.

*BEJAY1* · 10-14-2003, 08:02 PM

You've got hard evidence backing up that rear wheel weight and I can't debate that. I'm gonna run it by my auto-x and roadrace buddies though to see what they think.

http://www.sportcompactcarweb.com/ed..._technobabble/

*I30tMikeD* · 10-14-2003, 08:34 PM

Quote:

Originally Posted by BEJAY1

You've got hard evidence backing up that rear wheel weight and I can't debate that. I'm gonna run it by my auto-x and roadrace buddies though to see what they think.

http://www.sportcompactcarweb.com/ed..._technobabble/

I have heard conflicting things, but it's hard to not believe it when taking 40lbs of the rear wheels did nothing.

*mad-max98* · 10-15-2003, 12:42 AM

in the rear weel case the engine doesn't have to rotate them so they don't have any effect on the power of the engine , but u can consider partialy dead weight 100lbs =.1 sec but the wheels are rolling so they are not completely dead weight maybe halfway dead weight so 100lbs =.05 sec so if u shave 40lbs off the weight that's about .02 sec , peace

*Jime* · 10-15-2003, 05:18 AM

Quote:

Originally Posted by I30tMikeD

I use them on the front all the time, but this time I tried to use Neals on the back (the ones with street tires). The wheel would not fit over the metal cap coming out of the hub. The rear does not have the pin going through it like the front axel does. Got me???

Anyhow, the point was that rear wheel rotational mass will not effect acceleration. I have done this same test with the front millenia wheels and gained .25 1/4 mile by shedding 40lbs of wheels and tire weight.

Yes you are correct, I had to do a little corrective surgery with the dremel, I did it a long time ago so almost forgot.

I sure can't disagree with your numbers but the best time I got with my 97 was 15.4. I put the same engine and trans from the 97 into the 95 and did some more lightening, including the sound deadening, crash support etc, plus the wheels, not real extensive but enough. No other performance mods though and the time N/A on the 95 was 14.6 so it had to be weight, how much was the wheels, who knows but weight was the only difference between the two cars because I used the same mods off of the 97.

Sounds a little disheartening when you hear the experts claim that a 1 lb of unsprung weight is equivalent to 8 lbs of sprung weight. By that calculation you should have lost the equivalent of 40 x 8 or 320 lbs.

*I30tMikeD* · 10-15-2003, 05:53 AM

Here are my times. Sorry I could not scan the slips, but Nealoc187 and bejay1 can vouch for me.

full interior and 53lb 17's on the back

60' 2.337
330' 6.251
1/8 9.484
mph 76.61
1000 12.324
1/4 14.706
mph 95.15

Removed passanger seat and 33lb 17's on the back

60' 2.233
330 6.193
1/8 9.430
mph 76.11
1000 12.273
1/4 14.659
mph 94.99

And while I have your attention. I am a bit baffled how my 1/8 mph was at 76mph all day long, which is up from a normal 73 or 74 mph but I did not see any faster times??? We did have a strong headwind, but.....

HondaV6 · 10-15-2003, 09:39 AM

I would assume you have a 2002+ I30. What mods do you have? Good times by the way!

*I30tMikeD* · 10-15-2003, 10:32 AM

Quote:

Originally Posted by HondaV6

I would assume you have a 2002+ I30. What mods do you have? Good times by the way!

96 I30 5-speed. Performance mods are in my sig.

Kanaka · 10-15-2003, 11:19 AM

Quote:

Originally Posted by mad-max98

in the rear weel case the engine doesn't have to rotate them so they don't have any effect on the power of the engine , but u can consider partialy dead weight 100lbs =.1 sec but the wheels are rolling so they are not completely dead weight maybe halfway dead weight so 100lbs =.05 sec so if u shave 40lbs off the weight that's about .02 sec , peace

actually the engine does have to rotate the rear tires. it's actually like a pulley system. to rotate the rear tires, the car has to move forward. to move forward the front tires need to rotate, so actually the rear tires are linked to the front tires through the motion of the car. imagine putting a big a rope across both tires like tank tracks. the front tires drive the rear tires as well as the front tires. so not only do you lose weight by going to a smaller rear wheel, you lose rotational mass too, which is why reducing wheel weight is very benneficial.

As far as your runs, there are so many factors that could have come into play. most notably traction. looking at your time slips, it seemed like you did hook up a little better on your second run, that's why your et was quicker and top speed was lower. also, it's hard to tell from only 2 runs.

Personally, I have noticed a difference of about .1 seconds by putting my steelies (~36lbs) instead of my 255/40/17's (~66lbs) on the rear. granted this was on different nights, so again, other factors come into play like temperature, wind, etc, but on average, I can consistently get 14.7 with the steelies, but only 14.8 with the rims. one other thing i noticed is that with my car at least, it hooks up a bit faster w/steelies so my usualy R.T.'s of .5-.7 often turn into redlights. gotta adjust for the (seemingly) quicker pick up.

*I30tMikeD* · 10-15-2003, 02:52 PM

Quote:

Originally Posted by Kanaka

actually the engine does have to rotate the rear tires. it's actually like a pulley system. to rotate the rear tires, the car has to move forward. to move forward the front tires need to rotate, so actually the rear tires are linked to the front tires through the motion of the car. imagine putting a big a rope across both tires like tank tracks. the front tires drive the rear tires as well as the front tires. so not only do you lose weight by going to a smaller rear wheel, you lose rotational mass too, which is why reducing wheel weight is very benneficial.

As far as your runs, there are so many factors that could have come into play. most notably traction. looking at your time slips, it seemed like you did hook up a little better on your second run, that's why your et was quicker and top speed was lower. also, it's hard to tell from only 2 runs.

Personally, I have noticed a difference of about .1 seconds by putting my steelies (~36lbs) instead of my 255/40/17's (~66lbs) on the rear. granted this was on different nights, so again, other factors come into play like temperature, wind, etc, but on average, I can consistently get 14.7 with the steelies, but only 14.8 with the rims. one other thing i noticed is that with my car at least, it hooks up a bit faster w/steelies so my usualy R.T.'s of .5-.7 often turn into redlights. gotta adjust for the (seemingly) quicker pick up.

Those were just two runs for an example. I had 3 or 4 runs with the heavy wheels and tires and 4 or 5 without them. Same track, same day so I don't see how you could do a better comparison than that.

There difference you got with your steelies is probably do to the reduced friction. 255 is a wide tire, and I doubt your stockers are more than a 215. Different nights is not a good comparison.

You can't get any better comparison that what I did.

**Nealoc187** · 10-15-2003, 09:57 PM

Quote:

Originally Posted by Kanaka

looking at your time slips, it seemed like you did hook up a little better on your second run, that's why your et was quicker and top speed was lower. also, it's hard to tell from only 2 runs.

He made many more than 2 runs. I don't believe that "better 60' means a slower trap speed" stuff either. I think that theory is a crock personally.

*I30tMikeD* · 10-15-2003, 10:36 PM

Summary of my experiment:

reduced front wheel weight by 40lbs = .25 lower 1/4 mile

reduced rear wheel weight by 40lbs = negateable difference

*mad-max98* · 10-21-2003, 05:41 AM

Quote:

Originally Posted by I30tMikeD

Summary of my experiment:

reduced front wheel weight by 40lbs = .25 lower 1/4 mile

reduced rear wheel weight by 40lbs = negateable difference

amen brotha that's what i ve been trying to say

*SteVTEC* · 10-21-2003, 06:40 AM

hmmmmm.... So that would be at least two people now that have done this experiment with no significant difference. But at the same time, saying that the rear wheel weight doesn't matter is impossible because that defies the laws of physics. Big/heavy rims and tires still require more energy to spin up to a certain speed than smaller/lighter rims.

I'll have to think about this some more. There is an explanation for everything.

*SteVTEC* · 10-21-2003, 08:14 AM

I think I know what's going on.

Just need some time to test out the theory.

**deezo** · 10-21-2003, 09:00 AM

Quote:

Originally Posted by I30tMikeD

Summary of my experiment:

reduced front wheel weight by 40lbs = .25 lower 1/4 mile

reduced rear wheel weight by 40lbs = negateable difference

I know you might not want to do this but pull out the back seat to reduce weight. Don't look at it as "cheating". You just have to find your cars combination that's going to work.

*sleepermaxima* · 10-21-2003, 11:38 AM

Quote:

Originally Posted by SteVTEC

hmmmmm.... So that would be at least two people now that have done this experiment with no significant difference. But at the same time, saying that the rear wheel weight doesn't matter is impossible because that defies the laws of physics. Big/heavy rims and tires still require more energy to spin up to a certain speed than smaller/lighter rims.

Exactly.

Very interesting evidence though. Kinda makes me feel better about not getting lighter wheels yet.

D

*SteVTEC* · 10-21-2003, 06:39 PM

Quote:

Originally Posted by SteVTEC

I think I know what's going on.

Just need some time to test out the theory.

bleh...gonna be all tied up this week for awhile so no time to test theory in cartest.

Here's what I think is going on....

The other half of the Inertia equation that is conveniently omitted is the part about acceleration. It's actually I=mr^2 x A where A is the rate of acceleration. What this says is that the moment of inertia on the wheels is dependent on the rate of acceleration. So the moment of inertia is zero at steady state cruising speeds, but the harder you accelerate, the more they'll resist and hold you back. Same with braking. With big blingin wheels those suckers won't want to stop and will load up the brakes a lot more.

So in the scope of a 1/4 mile race, is the rate of acceleration of the wheels they same. They are not! In a FWD car when you launch you get the front wheels spinning (higher rate of acceleration) whereas the back ones are just along for the ride and not really moving yet. So because the moment of inertia on the front is higher due to the higher acceleration, this would mean that extra weight on the front would hurt you more and heavier rims at the back would hurt you less. Once you have full traction the rate of acceleration between all 4 wheels is equal and all of them are hurting you equally.

It's more or less established that every pound you add per corner will have the effect of about 8 pounds due to the moment of inertia. But that assumes equalized acceleration rates at all four wheels.

So on a 1/4 mile launch...

- Acceleration on Front is > Acceleration on Rear.
- Therefore, moment of inertia is much higher on Front than rear.

Front: 12:1 ratio (maybe) for inertia
Rear: 4:1 ratio (maybe) for inertia

Just pulling numbers out of my arse without having tested it, but this is what is happening and that's how you could model it and think of it. And this would also explain why Mike and Dave got much better results by dropping the weight on the front but did not see any significant differences by dropping the weight on the rears also. Weight on the rear still matters, but just not as much in the scope of a 1/4 mile drag race. A 4:1 ratio on the back is probably a small enough difference that you could almost ignore it. But the 12:1 ratio up front is very big so that's why there are such big difference just by switching the front tires. From a roll acceleration rates are always equal though so it would go back to the 8/8 idea instead of 12/4.

*BEJAY1* · 10-21-2003, 08:29 PM

Nice theory or is it fact?

Just so happens my auto-x buddies were discussing wheel/tire weights related to solo courses. Much of it applies to the dragstrip.
Here's links for those who can use...

SCC magazine regarding flywheel interia

Dan Cyr's calcuations (SCCA '03 cart champ)

Kevin Steven's response to my direct acceleration question - like the previous post stated

Andy Welter's inertia spreadsheet taking Steve's formula the next step

*SteVTEC* · 10-21-2003, 09:55 PM

bleh, you have to be a member of the discussion groups (which i'm not) to get to those links.

Could you cut and past?

The spreadsheet link works though and is pretty sweet! I was thinking that there HAD to be somebody out there that actually went through all of the calculations to figure this out. I'll have to dig through it a bit later.

*I30tMikeD* · 10-22-2003, 12:42 AM

Quote:

Originally Posted by deezo

I know you might not want to do this but pull out the back seat to reduce weight. Don't look at it as "cheating". You just have to find your cars combination that's going to work.

I already do