I was a bit unbalanced, but I'm much better now

Sunday, May 9, 2010 at 10:20
I had the opportunity yesterday to do a corner-weighting session on my car and a few others. For those that don't know, corner-weighting is done for race cars to even out as much as possible the amount of weight borne on each tire of the car by making adjustments to the suspension. Even weight distribution = better handling. The process is done using a special set of scales with a weight pad under each tire and a central readout.

While I don't have a set of those scales, I was fortunate to be able to borrow a set from a friend. I decided to make the most of the opportunity and got together with a few others from the Wild Rose Miata Club. We chose to do the work at Doug's Garage of Awesomeness and Car Parts Emporium. The Garage of Awesomeness has a lift, at least one (and usually two) of every useful tool known to man and enough spare parts inventory to build at least 1.5 complete cars from the leftover bits. As proof, see the photo at left. I mean really, who has that many 1/2in ratchet extensions? Show off.

So we started off the morning as any any great day starts: With hot coffee and Timbits. Then it was time to get down to business.

We started by lowering my ride height about 1 inch all around. This year I'm running some smaller diameter racing wheels (13in vs 15in) and it made sense to drop it down a bit more as I have an extra inch of fender clearance. I'm probably around 2-2.25 inches lower than stock now. I've got fairly stiff springs in the car, so bottoming out isn't much of an issue. I'm running at 12 in F, 12.5 in R, height measured from bottom of fender to center of hub.

Next up, the scales of truth. Good news! My Miata weighs quite a bit less than I thought it did. Weight without the driver and with 1/2 a tank of gas is 2075 lbs. That's encouraging as I haven't really done anything specific to add lightness to it. My racing seat is about 10lbs lighter than stock, but that's about it. I thought that the stock weight was around 2300lb but this is a good bit less than that.

Next step is to put the driver (that's me!) in the car and start adjusting the spring perches up/down as needed to balance out the weight. The target is for 50% crossweight and 50% F/R weight. Crossweight is defined as

(Right Front / Left Rear) / Total car weight

Adjustments are made at opposite corners of the car - RF/LR and LF/RR are adjusted in pairs to adjust the corner weights. It took us (and by "us" I mean "not me", because I was sitting in the car up on the lift) a couple rounds of adjustment, but the final setup was very close to the optimum.

With two of the cars (Doug's and Alvin's), we really lucked out because they needed no setup adjustment at all. They were already about as close as you'd need to be without making any new adjustments.

Doug's Car:

Admittedly, we forgot to put Doug in his car, but this was a pretty good result and he insisted we just leave it alone and move on to the next car. Not fixing something that isn't broken just doesn't seem right somehow and at this time I started to question Doug's sanity, but he was also wielding a large torque wrench and so I opted not to argue about it.

 Alvin's Car (without driver)

Alvin's Car (with driver)

Steven's Car (before adjustment, without driver)

Steven's Car (after adjustment, with driver)

Since we were already at the best shop in town, Steven took the opportunity to diagnose and fix a fuel leak at the fuel pressure regulator. In doing so, we discovered the custom bracket that holds the throttle cable to the intake was bent and almost broken off. No problem! After all the weighting was done, Doug fabbed up an even better stronger one from some angled aluminum. Nice work!


jimwhitelaw.com | Powered by Blogger | Entries (RSS) | Comments (RSS) | Designed by MB Web Design | XML Coded By Cahayabiru.com