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Old 05-06-2019, 11:22 AM   #1
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986 S Build for Unique Series

I race in a unique wheel to wheel road course series that I require some recommendations for.

Rules are as follow:

Any car under 250hp. Exhaust, intake and tuning can push it over that number.

Sponsored by Continental and must run their Extreme Contact Sport Street Tire.

I thought the 986 S would be the best choice of car.

One of the rules caught me off guard. Factory style strut and spring, leaves tire size open.

Threaded coilovers are limiting tires to 235F/245R.

I had purchased JRZ RS pros before knowing about the tire size limitation...

Thoughts on what would be better skinny tires on JRZ?

Wider tire 275F/295R on Strut/Spring combo?

What strut/spring combo would you recommend?

Is it possible to have custom spring rates for stock style mounts?

I am installing an accusump and will be doing a new clutch and IMS soon.

I was previously was racing 170hp Mazda NC MX5 that did very due to weight and handling well but down on power compared to e46 BMWs and 987 base Caymans.

Thanks,

Brad
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Old 05-06-2019, 02:37 PM   #2
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I run 275 35 18 rear and 245 35 18 front with jrz pro rs without any problem. Not sure why you think there will be clearance issues.
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Old 05-06-2019, 03:44 PM   #3
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The clearance is not the issue, its the rules.

If you run a threaded coilover the rules limit you to a 235F/245R, not the actual space.

Tire width is open to whatever fits on stock strut/spring combo.
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Old 05-06-2019, 03:44 PM   #4
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Quote:
Originally Posted by lmnsblu355 View Post
I run 275 35 18 rear and 245 35 18 front with jrz pro rs without any problem. Not sure why you think there will be clearance issues.
The rules limit tire size if you run coil overs.

EDIT - b-raddetail and I posted the same answer at the same minute!
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Old 05-07-2019, 08:08 PM   #5
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Start with camber, then increase tire width, then improve shocks.

What do the rules say about adjustable lower control arms?

I ask because the stock suspension is extremely camber limited - to the extent that if you can't run adj LCA's with the wider tires/stock suspension then the wide tires won't do much good and the narrow tires/coilovers might be the best route. However, if you can run adj LCA's with the wider tires and otherwise stock suspension, then that configuration might be a winner.

If the only way to get adj LCA's is with the narrow tires, then that route is the way to go.
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Old 05-08-2019, 05:23 AM   #6
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Start with camber, then increase tire width, then improve shocks.

What do the rules say about adjustable lower control arms?

I ask because the stock suspension is extremely camber limited - to the extent that if you can't run adj LCA's with the wider tires/stock suspension then the wide tires won't do much good and the narrow tires/coilovers might be the best route. However, if you can run adj LCA's with the wider tires and otherwise stock suspension, then that configuration might be a winner.

If the only way to get adj LCA's is with the narrow tires, then that route is the way to go.
I was thinking same thing. LCA's are critical is you want to be able to effectively use the tires, no matter the width.
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Old 05-15-2019, 03:07 PM   #7
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The GT3 LCA's are allowed and have been purchased.

I Also feel that wider tire and stock style spring strut will be quicker.

My next race is June 2nd and car just got dropped off for a cage yesterday, in the interest of time I decided to do throw in JRZ before going for the cage and we are now allowed 245 square.

If I need more tire/speed I will try the other setup.

Next question,

Where to start with alignment. I cant find and BSR specs online. I know it will need to be fine tuned but need to start somewhere.

Ride height
Camber
Caster
Toe

What do you recommend?
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Old 05-16-2019, 05:24 PM   #8
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Quote:
Originally Posted by b-raddetail View Post
The GT3 LCA's are allowed and have been purchased.
Great, that will certainly help the most.

Quote:
Originally Posted by b-raddetail View Post
I Also feel that wider tire and stock style spring strut will be quicker.
Yes, in general, after camber comes more tire. Not always, but usually, so its a good starting place.


Quote:
Originally Posted by b-raddetail View Post
Where to start with alignment. I cant find and BSR specs online. I know it will need to be fine tuned but need to start somewhere.

Ride height
Camber
Caster
Toe

What do you recommend?
This is a hard question to answer because it really does depend on how you drive and how hard you drive. My setup wouldn't work well for someone else because they drive differently.

The best way to approach this is to be working with a local shop who knows you and your driving style and who can set up the car properly while taking into account a myriad of variables.

However, that doesn't answer the question so I'll throw this out as a general starting point:

Ride height: 90-100mm measured at the bottom of the front crossmember with the rear just slightly higher to provide a bit of front end down rake. Just a little rake to help with whatever aero that might exist.
Camber: Maybe start around -3.0 deg front. About 0.3 to 0.5 deg less in the rear. You might need more, but its really hard to say. Some drivers run more camber in the rear than the front but the safe place to start is with slightly less in the rear. This is your biggest variable and you should monitor tire wear/measure tire temps and adjust accordingly.
Caster: As much as you can get. It's not really adjustable.
Toe: Zero in front to eliminate tire scrub. 1/16" in for the rear will help with stability.

Hope this helps. Your mileage may vary.
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Old 05-21-2019, 02:04 PM   #9
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Thank you for the advice. I will start there and continue to dial in the car.

I have the RSS thrust arm bushings in the GT3 LCA so I believe that provides more adjustment. Is there such a thing as too much caster?
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