2007 Lotus Exige S

[asshanson]

The tender springs are only there to prevent rattling in cornering. The stiff springs don't compress much (way less than the shock travel length), so the inside two wheels might extend past the spring length and rattle around until you put weight on that side of the car and then the perch will set back down on the spring.

I guess you could have shocks that only travel the length of the spring, but the car pushes the springs down less than 1 inch, so that would be virtually no travel at all. When you set the car down on these, the first 2" are completely compressing the tender spring, and then a little on the main spring. So when driving around, the tender is completely flat and doesn't do anything.

I think the ride quality is maintained by the better quality shocks.

[BriK]

^^^ Ding ding ding on comfort/ ride quality being affected by shock tuning, especially the high-speed damping. I'm sure Brandon mentioned the same thing.

Also, it's a bit technical and pedantic, but there's a difference between a helper spring and a tender spring. You describe a helper spring above-- completely compressed at normal ride height, and used to maintain load on the main spring at full travel. Helper springs have practically no spring rate-- maybe 10 lbs/in.

Tender springs have a higher spring rate (150 lbs/ in, for example) and are used to, essentially, create a progressive overall spring rate. The tender spring is not fully compressed at normal load, but will close at a given load so you're only using the main spring. That said, both springs may compress at the same time so it's not like you only use one spring (tender or main) at a time.

As for corner balancing, I believe a few places in the Twin Cities can do it-- not sure how much they'll charge though. I believe Jeff the Alignment Guy does, I'm fairly sure Imola Motorsports (www.ImolaMotorsports.com) does, and I believe Auto Edge (www.auto-edge.com) does as well. To fully take advantage of it though, you should have at least one adjustable swaybar endlink in front and rear so any preload can be removed from the bars. Since changing ride height side-to-side may twist the swaybars, creating pre-load, even just one adjustable endlink will allow you to get the sides of the swaybar parallel again, removing preload.

While you'll have a tougher time determining side-to-side balance and crossweight on your own, you can use ride height to adjust the front-rear weight balance and therefore handling characteristics. As a general rule, lowering the rear ride height will dial out oversteer by shifting more weight onto the rear tires, raising the rear will increase oversteer by removing weight from the rear tires. This obviously takes testing and tuning though.

Finally, the site below has some good calculators to play with but you need to know so many very technical inputs that I've used it more for theory than for actual planning and tuning.
http://www.racingaspirations.com/apps/weight-distribution-calculator

Finally finally, I know you have done events and are not a noob, but I have to continually preach for driver mods.

[asshanson]

Several good points, thanks. And yes I do know driver mod is important, always trying to work on this, I still consider myself a noob.

Mine are tender springs, 150lb and 2" long. I will have to look, but I'm pretty sure the tenders are about completely compressed when the car weight is applied. The main springs in back are 700, so in comparison they will hardly compress at all. The front has less weight and only 550 mains, so they are probably not quite compressed in front. I will get under the car and check this.

I only have a front swaybar, and the endlinks aren't adjustable :( So I can't remove the preload on that. But hopefully left/right are about the same height so there shouldn't be much preload.

As far as front/rear weight, that is not something I can easily adjust. There is not separate adjustment for height and preload, and I need to maintain a 10mm rake front to rear (or so everyone says is necessary on these cars). I think the only thing I can shoot for is even cross weight, and use the shocks/swaybar/camber etc for tuning under/over steer.

Edit: Oh yea, I'm in Iowa, hopefully my friend has time next weekend for a corner balance, or worst case I go to the Lotus shop in KC.

Edit #2: So, in my extremely accurate drunk calculations, I have 400 lbs front and 600 lbs rear on each corner for the car with me in it. Left will be more than right but let's ignore that.

2in * 150 lbs/in for the tender = 300lbs fully compressed (max, because the compressed spring is probably .5" so you only get 1.5" of compression, probably closer to 225-235 lbs total weight absorbed)
Rear spring = 700lb/in. Rear spring would compress .86" without a tender. Wouldn't the tender have to fully compress with 600 lbs on it? There is only 2" of travel with 4 times the weight per inch, and the main spring is compressing less than an inch. Is this ricer math? Or perhaps I need to re-take physics for inline springs and how they interact with each other.

Why isn't there a cool shockwave/flash application on the internet where you can plug in two inline spring rates/lengths and load weight to determine what happens?

[asshanson]

Got supplies from the hardware store to do my own string alignment today. It took awhile but was a good learning experience. I needed 2 pieces of 6 foot long angled aluminum, plus pipe insulation to pad them and protect paint, and then some string. Cost $35. I already had the digital caliper for measuring, but I think I am going to get the ART Dream Stick to make things way quicker in the future.

String box setup:
http://www.dsmstyle.com/photopost/data/675/string_alignment.jpg

Since the car is about 20mm lower all around now, the toe was way off, started at 3mm toe out in front each, and 2.5mm toe in in rear. Final results are .6/.5mm toe out up front, and 1.45/1.55mm toe in in back which is very close to the factory specs.

I also decided to calculate the camber by placing the bar directly over the axle centerline and taping a weight to the bottom, measured -2.5* camber front and -2.75* in rear. I was in the center of my garage so I am guessing there was no left/right tilt. It was sort of cool calculating the distance to string delta in mm, dividing by the total wheel mm, and taking the arcsin to get the angle. (go trig!) /nerd

For my future reference:
Wheel centerline front = 118.6mm
Wheel centerline rear = 96mm
Left tie rod: loosen nut and toe in = DOWN
Right tie rod: loosen nut and toe in = UP
Left toe link: loosen nuts and toe out = UP
Right toe link: loosen nuts and toe out = DOWN

[scheides]

Math = win!

This is pretty sweet man, nice work!

[A//// Guy]

You crazy scientist haha.

[tehehodi]

Nice job! Did Emily think you were crazy or is this not out of the ordinary for you to do? Math wiz. I agree with what Peter said as well.

[Halon]

Science!!

[turbotalon1g]

Nice work.

[Fran05]

Keep in mind, if you floor isn't level - all the work that you did is a waste of time.