Cross-weighting results

[SoundGuyDave]

I just finished a short tour leg, and left my car with my sponsor, Elmhurst Auto Care (elmhurstautocare.com), and while I was away, he had the opportunity to corner-weight the car... Interesting results!

I'd been running a 62lb cross-weight differential, which equates to 1.7%, and now that he's done, that dropped to a total of 7lbs, or 0.195%. It'll be interesting to see if my car balances out better on track after that! Prior to this, I'd noticed a trend where I could turn left at a reasonably higher g-load than I could turn right, so I'm hoping that this will help to even out the trend.

Basic setup was with the swaybars disconnected (duh!), 165lbs dummy load in the driver's seat (to simulate me, race suit, helmet, Defender, shoes, etc.), and a full fuel load. I ran a full load to eliminate fuel slosh as a factor in the weighting process... Assuming that I keep a 4gal reserve in the car, that equates to 84lbs of excess fuel, but at least it's not randomly distributed. Backing out the fuel load, that would drop "competition weight" (as coming off the track at end of session) to right at 3500lbs, so the last round of weight reduction pulled nearly 100lbs out of the car. That ALSO makes me ever-so-happy, since my last scaled weight coming off track was 3605. Still fat, but getting slimmer! I can go as low as 3450 before I get into trouble with points, so in essence, I cut my overweight margin by 66%.

Baseline:
RF 1022 RR 928
LF 833 LR 801

LF-RR 1761, RF-LR 1823, total 3584*

Final:
RF 1006 RR 946
LF 851 LR 784

LF-RR 1797, RF-LR 1790, total 3587*

*(Honestly not sure where the extra 3lbs came from, but I figure that's still close enough!)

Weight reduction mods, for those of you that are interested:
Steeda competition cowl hood
Steeda tubular radiator crossmember
Braile 11.5lb race battery (stock location, stock tray removed)
no brake backing plates
passenger seat delete
front seatbelt delete
center console delete
Ultrashield aluminum driver's seat with Simpson 5-point harness
rear seat delete
rear seatbelt delete
trunk trim delete
rear axle weight delete
5zigen FN01R-C wheels (18x9.5) with 275-35/18 Dunlop rubber
Full exhaust swap: ARH long-tubes, catted midipipe (trying to get past emissions!), FR500S mufflers
Full suspension swap: AST coilovers, Stranoparts bars and competition links, Maximum Motorsports LCAs and PHB,

Weight additions:
FRPP power steering cooler
Setrab oil cooler, remote filter mount (FL1A), thermostat
GT500 front brakes
Steeda front control arm bushing kit (hard inserts)
Autopower roll bar
fabricated rollbar mount reinforcements
front tow hook
SLP resonators after the midpipe
Hidden Hitch tow hitch (tire trailer)

So now I just have to get some track time in to see how the balance has changed... As you can see, most of the weight came out of the middle and rear of the car, which actually pushed my F/R balance the wrong way, to 51.8% and 48.2%. Still much, much better than a Fox or SN95 chassis, but I think I need to concentrate on front-end reduction for those last 50lbs or so. Or just gut and cage the car and start over on the weight!

 

[Red06GT]

Great info! I'm bookmarking this for sure. Did you decide to lose the Accusump? I didn't see it in your list of weight adders.

 

[SoundGuyDave]

Yes I did, for the moment. Somehow, I developed a leak on the air-charge side, so the unit needs to be rebuilt. Just been too busy to send it in, so I've been running without it for most of the season. No effect on oil temps, but very noticeable on pressures both on track and after-session. I'm running a half-quart over full, and that seems to do enough for now. Since I'm running TT format, with shorter runs (lower oil temps), the end-of-session sag doesn't appear to be that much of an issue. For safety's sake, though, I will re-install once I get it rebuilt, most likely over the winter. Not a lot of $$ to rebuild it, but I honestly just don't have the time, now that touring season is in full swing.

 

[gbrown]

Maybe I'm having a dumbass moment here but something about your numbers doesn't seem right. I have corner weighed a lot of cars and have never seen a production based car that was heavy on the right (passenger) side.

Are you sure you don't have those numbers mixed up?

 

[SoundGuyDave]

Maybe I'm having a dumbass moment here but something about your numbers doesn't seem right. I have corner weighed a lot of cars and have never seen a production based car that was heavy on the right (passenger) side.

Are you sure you don't have those numbers mixed up?

Hell, man, anything is possible! I wasn't there, but I did get a copy of his notes, and that seems to be the way it shook out. It looks like I'll find out in a couple of weeks at Autobahn... I still haven't completely mentally digested the whole thing, and now that you bring it up, yeah, it's possible that I input the numbers into the post wrong. Unfortunately, I'm about 2200 miles from the car (and the notes) right now, but I'll check when I get back on Friday. Even if the left and right numbers were transposed, the cross-weights will still be valid, though, so at least there's that!

 

[gbrown]

I'm just guessing here and it will be interesting to see the notes but I'll bet the numbers should read like this:

LF 1006 RF 946
LR 851 RR 784

Those numbers would make a LOT more sense. I have only worked on one production car where a rear tire was heavier than the front and it had a lot of ballast and other work done to move weight to the rear.
If I'm right all of your calculations will need to be redone and you won't be near as happy as you are now.

For your sake I hope you are right.

 

[SoundGuyDave]

Assuming you're correct, which you probably are, the cross-weight (7lbs) and % (0.195%) still stay the same, which was the main purpose of the exercise, but yeah, the F/R balance took a hit in comparison to my earlier numbers... 54.4%/45.6% vice 52%/48%. Just goes to show that yes, I need to drop that last 50lbs off the NOSE of the car. Honestly, I already knew that, but the numbers are showing up a little more of a glaring difference.

I'll have to check once I get home, but I'm 99% sure that I have to say: "GOOD CATCH, GREG!!"

PS: STILL happy with the cross-weight numbers. If I can get the right turns going as good as the lefts, that's probably worth a half to a full second a lap on the club tracks...