anyone with experience autocrossing a muscle car see a difference with lighter rims?

I have read the articles on how the difference in weight doesn't matter with auto cross.  Currently I am using rims and tires that are about 55 pounds each corner.  I'm looking at different rims, but I'm not sure I will be able to shave off enough weight for the cost.  I'm running a super charged 06 mustang gt.

Again, as I said in the title, I was wondering if anyone has experience with a muscle car.  I auto crossed my miata this past weekend, and I was shocked (shocked I say) at how much difference it was with a passenger.  I once had a 300 pound guy in my mustang and I picked up a second!

Thanks for your input.

Doc

https://grassrootsmotorsports.com/articles/are-lighter-wheels-really-better/

They tested at a kart track and with a lighter, less powerful car, but I have to imagine the principles transfer to an autoX course.

thedoc said:

... I once had a 300 pound guy in my mustang and I picked up a second!

Doc

Wait, you added a 300 lb passenger and you went faster?  

p.s. put RFP1's on the Mustang as they are awesome and pretty light.

In reply to thedoc :

Not sure how more weight could make anything "faster"

In reply to Vajingo :

I've actually driven two cars that were faster with a passenger; on one car it changed the balance such that you could then aggressively rotate the car and on the other car it cut down on wheel spin. Obviously changing the set up to fix the underlying issue would be the preferred method. 

Weight matters, and rotating mass and unsprung weight (wheels and tires), is particularly important.

That said, with wheel and tire weight, there's definitely a point of diminishing returns when it comes to comparing cost/benefit. Light wheels are not cheap, and likely there's lower hanging fruit when it comes to weight savings. So when it is time to pull the trigger on lighter wheels, make sure you;re getting the most bang for you buck that you can by maximizing your footprint AND saving weight.

In reply to Tom1200 :

But in that scenario we are talking weight distribution, not power to weight, or unsprung mass. 

Thanks for the  info gents.  On the 300 pound guy, true story.  It is the one time in my life I hesitated to have someone ride with me.  I think the weight balanced my car.  And yes, I was a second faster.  Now the miata is a totally different story!

In reply to Vajingo :

You did ask how more weight could make anything faster. 

As for the original post; in my experience (albeit limited) it takes a significant percentage reduction to matter or at least be noticeable. I currently use a lightish wheel on the Datsun, 13x6 13lbs w/11lb tire, originally I was running 15lb wheel with a 16lb tire and the reduction is noticeable. 

 There are race wheels in the 8-10.5lb range in my size but if you pound the kerbs like I do it's possible to bend them, so in my case I don't find it to be worth the additional weight reduction.  

Not autocrossing, but with the V8 swapped Ranger I saw a dramatic reduction in ET when I swapped from a 15x8 steel wheel to a 15x10 Centerline wheel using the exact same 295/50r15 tire. Fronts went from 15x8 steel and 245/60r15 to 15x6 with a smaller 195/65r15. Obviously the wide tire was not utilizing the contact patch effectively and the mass reduction made a difference.

thedoc said:

I have read the articles on how the difference in weight doesn't matter with auto cross.  Currently I am using rims and tires that are about 55 pounds each corner.  I'm looking at different rims, but I'm not sure I will be able to shave off enough weight for the cost.  I'm running a super charged 06 mustang gt.

Again, as I said in the title, I was wondering if anyone has experience with a muscle car.  I auto crossed my miata this past weekend, and I was shocked (shocked I say) at how much difference it was with a passenger.  I once had a 300 pound guy in my mustang and I picked up a second!

Thanks for your input.

Doc

So, stock size is 235 55 17.  That is a 25 pound tire.  That would mean your wheels weigh almost 30 lbs.

That is ridiculously heavy!

I think anything around 20# or less for a wheel is fairly easy to achieve and should still take some abuse.

Only a lunatic would autocross a supercharged V8 Mustang on 235 width tires. There's no hope for traction or turning there.

QuasiMofo (John Brown) said:

Not autocrossing, but with the V8 swapped Ranger I saw a dramatic reduction in ET when I swapped from a 15x8 steel wheel to a 15x10 Centerline wheel using the exact same 295/50r15 tire. Fronts went from 15x8 steel and 245/60r15 to 15x6 with a smaller 195/65r15. Obviously the wide tire was not utilizing the contact patch effectively and the mass reduction made a difference.

You also removed quite a bit physical and aero drag from the front at the same time. Although I have no doubt that wide of tire was severely pinched on an 8" wheel. 

STM317 said:

Only a lunatic would autocross a supercharged V8 Mustang on 235 width tires. There's no hope for traction or turning there.

oh but doc just may be the lunatic you're looking for

GCrites80s said:

STM317 said:

Only a lunatic would autocross a supercharged V8 Mustang on 235 width tires. There's no hope for traction or turning there.

oh but doc just may be the lunatic you're looking for

Maybe change his handle to "the tiresmoke"?

GCrites80s said:

STM317 said:

Only a lunatic would autocross a supercharged V8 Mustang on 235 width tires. There's no hope for traction or turning there.

oh but doc just may be the lunatic you're looking for

You may be right. He may be crazy.

STM317 said:

GCrites80s said:

STM317 said:

Only a lunatic would autocross a supercharged V8 Mustang on 235 width tires. There's no hope for traction or turning there.

oh but doc just may be the lunatic you're looking for

You may be right. He may be crazy.

I'm crazy, but  not stupid. I was running 275 tires, stupid heavy.  I just found a deal on some enkei rims, really light.  Very excited.  Now I just need that 300 pound guy to ride with me.  

Thanks for your input gents, "tiresmoke" would be a nice handle

I've had the exact same experience in autox with the heavy dude passenger making me faster.  It should tell you something about the difference between manly V8 power and standard Miata power.  When you've got the guts, just worry about grip.  Aim for getting some 315s on that car (with properly sized rims), whatever the cost; you will never go back to lesser tire sizes.  Thank me later.

I've always lost exactly what I should with a passenger aboard. Half a second per 100 lb. on a 60 second course. 944 and IROC-Z.

Vajingo said:

In reply to thedoc :

Not sure how more weight could make anything "faster"

my e30 is always faster at rallycross with a passenger. Not sure if I just drive differently, or if it's because the car is corner-weighed to be best balanced with a co-driver (it's a stage rally car). Without a passenger, it doesn't feel "right" to me. 

of course, the principles of traction are different in rallycross....

I've always been slower with a passenger. Never got light wheels for my mustang.

The one that got me was a performed really really well in my miata one time I wore steel toed boots and therefore didn't have as fine of pedal control.

In a muscle car, I can find about 50 things to optimize before worrying about wheel weights. Sure it may make a difference but there are so many other things that may help more that could be considered first.

In reply to Tom1200 :

Out of curiosity what tires are you running on the Datsun ?

My fastest lap at Summit Point was with a passenger in my Spec E30. She only weighs about 130 lbs though.

Not sure if it was the weight that made the difference or my testosterone-fueled need to show off to the opposite sex.