Faster time from .. lightweight wheels .. or suspension ?

[vijen6]

The car is a 2001 Box S and currently have 19" ebay "Miro" brand wheels on it. Not sure how much they weight but since it came "stock" to me with OEM 18" chrome, maybe not much more than "stock". My best guestimate is in the 25# range not including tires. Suspension is completely stock.

The car is technically my streetcar but will mostly be used for AX. I have a bike so I only drive maybe 2500 miles / year on the high end. This basically translate to "I don't mind going a bit stiff with the new suspension".

My question is:

If you guys had about 3-4k to do either of those mods, which would be a better mod to improve AX time?

If I go for wheels, it will be TE-37s ( yeah JDM on Boxster .. LOL ) 8.5" in front, and 10.5" in the rear .. similar to what I have on now with the MiRo wheels .. should be about $3.5k after tires are added in.

Not sure yet about coilovers.

[vijen6]

Whoops .. didn't realize I posted in Show + Tell .. doH!

Can an admin help me move this to the appropriate section ? Thanks!

[Topless]

Check the rule book for the organization you want to AX with and see what your options are. With some clubs, coilovers put you in a modified class with Vettes and Vipers. Not a good plan if you want to compete to win. Usually tires are the first and most important choice to make, and tire choice will determine suspension needs. The more tire grip and lateral Gs you develop, the more "tied down" and precise your suspension needs to be.

If these are your wheels they are downright portly and switching to a stock 17" would probably shave 2 seconds off your lap.

"The weights of ALT-MiRo Type 368 or Type 366 wheels are:
19"x 8.5": 36 lb.
19"x10.0": 39 lb..
This information was supplied to my by ALT-Miro wheels."

[vijen6]

They're not, its the type 371 .. however seeing those weight numbers was shocking. I thought they were heavy so I said 25# range but .. jeeze !

Correct me if I'm wrong but ..

1. Conventional wisdom says 1# rotational / unsprung weight = 7# sprung weight.
2. Conventional wisdom also says every 6 lb lost is similar to gaining 1 HP.

TE-37 in 18x8.5 is just under 17.5# and the 18x10.5 is just under 19.5#. Assuming 30# for my current wheels .. that's rough about 10# rotational mass X 4. A total of 40lbs rotational mass total difference.

Applying conventional wisdom rule 1 would mean the new wheel will feel like driving a 280# lighter car.

Applying conventional wisdom rule 2 would mean the new wheel will feel like the car has 46.6 more HP !?!

Definitely sounds like I'm going with wheels first.

[Atomicblue99]

If you haven't yet done it, spend a little money on the Evolution Autocross School http://evoschool.com/. It will drop your lap times more than any modification you can make to your car. Something about "tightening the nut behind the wheel"

[Topless]

Originally Posted by vijen6

They're not, its the type 371 .. however seeing those weight numbers was shocking. I thought they were heavy so I said 25# range but .. jeeze !

Correct me if I'm wrong but ..

1. Conventional wisdom says 1# rotational / unsprung weight = 7# sprung weight.
2. Conventional wisdom also says every 6 lb lost is similar to gaining 1 HP.

TE-37 in 18x8.5 is just under 17.5# and the 18x10.5 is just under 19.5#. Assuming 30# for my current wheels .. that's rough about 10# rotational mass X 4. A total of 40lbs rotational mass total difference.

Applying conventional wisdom rule 1 would mean the new wheel will feel like driving a 280# lighter car.

Applying conventional wisdom rule 2 would mean the new wheel will feel like the car has 46.6 more HP !?!

Definitely sounds like I'm going with wheels first.

It is possible to overthink the wheels a bit. Smaller wheels will be faster. Again, choose tires first, and then match wheels to the tires. a 10.5 rear sounds too wide for a podium AX car. Top drivers are running 245/265 or 255 square. 8" and 10" should be plenty of wheel.

[Johnny Danger]

Originally Posted by vijen6

They're not, its the type 371 .. however seeing those weight numbers was shocking. I thought they were heavy so I said 25# range but .. jeeze !

Correct me if I'm wrong but ..

1. Conventional wisdom says 1# rotational / unsprung weight = 7# sprung weight.
2. Conventional wisdom also says every 6 lb lost is similar to gaining 1 HP.

TE-37 in 18x8.5 is just under 17.5# and the 18x10.5 is just under 19.5#. Assuming 30# for my current wheels .. that's rough about 10# rotational mass X 4. A total of 40lbs rotational mass total difference.

Applying conventional wisdom rule 1 would mean the new wheel will feel like driving a 280# lighter car.

Applying conventional wisdom rule 2 would mean the new wheel will feel like the car has 46.6 more HP !?!

Definitely sounds like I'm going with wheels first.

What is the offset on the Volk rear wheels ? At 10.5 you'll have a very difficult time trying to clear the perch on adjustable coilovers if you ever go that route.

[vijen6]

I believe its 41mm.

[Perfectlap]

Originally Posted by Atomicblue99

If you haven't yet done it, spend a little money on the Evolution Autocross School The Evolution Performance Driving School - Building Champions since 1993 - Autocross, Driver School, HPDE, License. It will drop your lap times more than any modification you can make to your car. Something about "tightening the nut behind the wheel"

I took the beginner and advanced courses with EVO. The advanced was in the most insane monsoon of rain I have ever driven in. I drove out to the venue almost sure that it would be canceled. Nope. They said to me "We're driving in this stuff so brake accordingly"
Wipers were going full speed as was the car! then in the post-lunch session the sun came out full force. I don't think I would have ever have had the oppourtunity to drive like that in wet conditions if not for the event. It was a unexpected blessing. The thing I learned is that the Boxster should be driven CONSERVATIVELY in the rain. First, it doesn't take too harsh a spin on the road to cause massive damage to the suspension/wheels should you lose the car and find it slamming into curbs or dividers. You can easily total the car with damage that doesn't seem that great from afar. Afterall these are sports cars that are fragile, they aren't SUV's.

For $4K I would get the Forgestar F14 wheel which is ~20 lb. wheel that has sold for about $1,500. Depending on the size, I'd get a solid tire like the RE-11A, MPSS (probably the best for cars driven to the AX), Dunlop Z2, BFG Rival, Hankook RS3.
replace the battery with an Optima, and pick up a GT3 seat (direct bolt in). You'd have a few bucks to spare for the EVO school. Going with PSS9 or some other coil over will almost surely bump you up into a bigger engine class in most AX clubs. Tinkering with the suspension will eat up most of your budget so better to spend that on tires/wheels first.

scroll down for 18" wheel weights. Some of these are availble in Porsche fit.
http://www.bimmerboost.com/showthread.php?7867-Wheel-weight-comparison-Weights-of-various-popular-18-20-inch-rims

[Topless]

If it was my car (and it isn't) and I wanted to be competitive in AX up to a state championship level, I would do what top AX drivers do:

Find a nice set of OEM takeoff 17" or 18" wheels for $400-$500 per set, mount some fast tires, and really learn how to drive the car at the top of my class. Find an event every weekend and get in the right seat with lots of different top AX drivers. Then get them in my right seat and do exactly what they tell me to do. Spending a bunch of Benjamins on super-lightweight wheels at this point will likely have a low return on investment. Stock wheels are 18-23 lbs.

[vijen6]

Originally Posted by Perfectlap

I took the beginner and advanced courses with EVO. The advanced was in the most insane monsoon of rain I have ever driven in. I drove out to the venue almost sure that it would be canceled. Nope. They said to me "We're driving in this stuff so brake accordingly"
Wipers were going full speed as was the car! then in the post-lunch session the sun came out full force. I don't think I would have ever have had the oppourtunity to drive like that in wet conditions if not for the event. It was a unexpected blessing. The thing I learned is that the Boxster should be driven CONSERVATIVELY in the rain. First, it doesn't take too harsh a spin on the road to cause massive damage to the suspension/wheels should you lose the car and find it slamming into curbs or dividers. You can easily total the car with damage that doesn't seem that great from afar. Afterall these are sports cars that are fragile, they aren't SUV's.

Yeah I had looked into taking Evo school in the past but for the past few years, the site they used was notorious for unmaintained surface shredding tires. I didn't have the budget to get a new set of tire after the school, so never signed up. It seems they have now changed location. Hurrah for that.

Originally Posted by Perfectlap

For $4K I would get the Forgestar F14 wheel which is ~20 lb. wheel that has sold for about $1,500. Depending on the size, I'd get a solid tire like the RE-11A, MPSS (probably the best for cars driven to the AX), Dunlop Z2, BFG Rival, Hankook RS3.
replace the battery with an Optima, and pick up a GT3 seat (direct bolt in). You'd have a few bucks to spare for the EVO school. Going with PSS9 or some other coil over will almost surely bump you up into a bigger engine class in most AX clubs. Tinkering with the suspension will eat up most of your budget so better to spend that on tires/wheels first.

Yep, for the price, the F14 seems unbeatable value. Though there's a few horror stories from people buying through mod-bargain.

Originally Posted by Perfectlap

scroll down for 18" wheel weights. Some of these are availble in Porsche fit.
Wheel weight comparison - Weights of various popular 18-20 inch rims

Nice link! I didn't know that there was that much of a difference between the TE37 and the SuperLaps. Those Advan RZ-DF are quite sexy too.