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post #1 of 6 (permalink) Old 02-28-2017, 05:18 PM Thread Starter
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Track Spring Rates

So this weekend I decided that my 500/700 spring rates just aren't enough to keep the platform stable through the COTA Esses. I also kinda mangled my brand new home made diffuser!

I saw there was a TT2 elise there with 1000 lb springs in the rear but I didn't get to talk to him a ton as we were both having a series of mechanical issues. So I don't know what his fronts were.

I am a pretty good driver, driving the car near the limit, sliding through high speed corners, but I don't want to get into a situation where only an expert could drive the car fast, so my question.

Is 700/1000 the right spring rate for me? Should I go maybe just one step below this to 650/900? That might be a little safer too as the car will still push slightly. I am using Penske DA shocks and Fred said they are fine with 1000 lb springs.

I have a carbon 2011 rear wing and dual canards + splitter in the front. Not sure what my down force is in lbs, but it is certainly non zero.

2007 Exige S with almost every track mod...
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post #2 of 6 (permalink) Old 02-28-2017, 05:35 PM
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Kevin,

Try to catch up with Phil at BOE. The 2011 rear wing does not create enough downforce to warrant 1000# rear springs. I would suggest maybe moving up to 800# or 850# springs in the year. Talk with Fred also about matching the front spring rate to the rear. You need to be careful because you are slowly turning the car into a go-cart chassis. The only compliance that you will have will be in the tires. If you start taking curbing with that stiff of a spring, the car is going to start launching itself instead of being compliant.

Later,
Eldon
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post #3 of 6 (permalink) Old 02-28-2017, 05:49 PM Thread Starter
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Quote:
Originally Posted by eldonz View Post
Kevin,

Try to catch up with Phil at BOE. The 2011 rear wing does not create enough downforce to warrant 1000# rear springs. I would suggest maybe moving up to 800# or 850# springs in the year. Talk with Fred also about matching the front spring rate to the rear. You need to be careful because you are slowly turning the car into a go-cart chassis. The only compliance that you will have will be in the tires. If you start taking curbing with that stiff of a spring, the car is going to start launching itself instead of being compliant.

Later,
Eldon
Do you have data on the downforce of the 2011 carbon wing on the lowest setting? The car I am referring to was getting 120-180 Lbs of downforce at 100 MPH based on APR's data (i think he had the elise APR wing).

I plan on maintaining the ratios I have now as the car is nicely balanced. I may want to go with slightly stiffer in the front if I am between sizes to keep the car slightly pushy. I know the car will be less compliant after, but I am losing a TON of time for example between 4-5 and 6-7 where you have the high speed transitions. Plus I want to not wreck my splitter in one weekend. Need to go at least a bit stiffer.

I emailed phil about the same question, I hope he responds as I am sure he will know.

FYI I did a 2:28.1 this weekend and there is still lots more to be had. Only had one session where everything in the shiffter and clutch worked

2007 Exige S with almost every track mod...
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post #4 of 6 (permalink) Old 02-28-2017, 06:03 PM
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Kevin,

When you are referring to the "Carbon Wing", are you referring to the HKFever's wing?

Also, getting a rear diffuser that is efficient creates downforce without creating drag. There are little tricks to do to the rear diffuser and if you had looked closely at mine, you would have seen this.

And just so you know that I am around aero all day long, check out this website: Windshear, Inc. Wind Tunnel - 180-MPH Rolling-Road Wind Tunnel.

Later,
Eldon
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post #5 of 6 (permalink) Old 02-28-2017, 06:19 PM Thread Starter
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Eldon, Yeah the same wing that I believe that you have. I know you work there so I assumed that you had that data

I saw your difuser. I may go that way one day myself, but my metal fabricating skills are not top notch so it is a project for another day. I currently have a difflow diffuser and I will change to the difflow track diffuser soon. I know it made a ton of difference when I got this one. The suspension block of plates also made a big difference.

2007 Exige S with almost every track mod...
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post #6 of 6 (permalink) Old 02-28-2017, 06:30 PM
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Kevin,

I don't have any hard numbers but I did some aero track testing with that wing and it is not very efficient. Do not tilt the wing up because it really starts creating more drag than downforce.

The cost of getting into the tunnel is $4k per hour, min of 10 hours and $500K liability insurance. If you want to share the cost, let me know. ;-)

I tried adding a wicker bill to the wing and that did not help much either. Having driven an Exige that had APR aero pieces, I was really impressed at how much downforce the car created over mine. I have been trying to get one of the aero-engineers interested in building a wing but the last person I talked to went to F1. I have a few more contacts but without quantity, it is hard to justify the mold cost.

Have you added the 90 degree pieces to the outsides of the diffuser? This helps keep the air from interfering with the efficiency of the diffuser. I have not tried the Difflow's racing diffuser since I still drive my car on the street.

Later,
Eldon
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