SCCA CAM-C Thread

[mavisky]

Are you doing 700 or 750 rear then? Ive been a bit torn on 650 or 700. I think with the Steeda bar on the way doing 142-197% of stock and the drilled OEM is ~135% will work with the slightly stiffer rear rate.

Currently 700F and non-divorced 900R

Looking at something along the lines of a 650F/750R non-divorced in the rear. Not a major change, but I think this will suit our bumpier courses a little better. Front may be going down to 600 as well.

Currently on the Steeda competition bars with the front set to the softest it can be set without interfering with the ride height sensor mounting (still haven't moved those) and the rear is on full soft as well.

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[Dallas J]

Just thinking about the spring ratio balance (which obviously isnt the only balance effect, but to stay consistent..), If you liked the balance you had with 700/900, doing 650/750 would push the balance forward a fair bit.

(Lower number is more rearward)
450/550 = 0.82 (Balance would be good, though I would like a little more front bar)
550/700 = 0.79 (A bit more rear bias in spring to be balanced with more front bar)

Your rates,
700/900 = 0.78 (Similar to what Im planning)
650/750 = 0.87 (Bias pushed forward a fair bit)

Dont know how your car handles, just food for thought.

 

[NightmareMoon]

My car is 650 front, and steeda DR rear which is up to 1200 divorced.

so thats like 650/600 non-divorced? Its very neutral with the bars and alignment I have.

personally I feel 600 would be ideal for the front for many situations. If its very bumpy, maybe 550. Tried 550 once and went back to 650 for faster courses on concrete.

 

[Dallas J]

The numbers I have for motion ratios are,

Divorced : 0.48
Shock/Coilover: 0.75

(Confirm if possible, differ if known otherwise)

So a coilover would compare to a divorced rate by 0.48^2/0.75^2 = 0.41

1200 * 0.41 = 492 effective coilover rate.

 

[mavisky]

Just thinking about the spring ratio balance (which obviously isnt the only balance effect, but to stay consistent..), If you liked the balance you had with 700/900, doing 650/750 would push the balance forward a fair bit.

(Lower number is more rearward)
450/550 = 0.82 (Balance would be good, though I would like a little more front bar)
550/700 = 0.79 (A bit more rear bias in spring to be balanced with more front bar)

Your rates,
700/900 = 0.78 (Similar to what Im planning)
650/750 = 0.87 (Bias pushed forward a fair bit)

Dont know how your car handles, just food for thought.

Car turns in like a monster, but you have to be really delicate in power application on corner exit. I have to get new tires first, but really targeting the 600F, but not wanting to soften the rear too much which is why I have been delaying the rear spring purchase.

 

[NightmareMoon]

The numbers I have for motion ratios are,

Divorced : 0.48
Shock/Coilover: 0.75

(Confirm if possible, differ if known otherwise)

So a coilover would compare to a divorced rate by 0.48^2/0.75^2 = 0.41

1200 * 0.41 = 492 effective coilover rate.

I'll leave it to the experts, but IDK why those values are squared.

 

[WItoTX]

I just went 400/800, and drove the car. My biggest problem is my lack of driving skill

 

[mavisky]

I dont understand the math, was basing myself off of thr way my car feels and the published spring rates out there for other non-divorced setups.

Surprisingly the Vorschlag GTS rates are almost exactly what im targeting. The Nitron street setup may be good as well and may put a little more grip in the rear thay could be dialed in via bars, but may get you off the line quicker in a pro-solo style scenario.

• Vorshlag's GT Spring Package is 450 #/in Front / 550 #/in Rear
• Vorshlag's GTS Spring Package is 600 #/in Front / 750 #/in Rear
• Vorshlag's GTR Spring Package is 800 #/in Front / 1100 #/in Rear
• MRR street enthusiast 400F/600R
• MRR gt4 spec 700F 900R
• MRR gt4 optional 750F 1000R
• ISC Coilovers 504F 784R
• Nitron road 628F 658R
• Nitron track 799F 1028R

 

[Dallas J]

I'll leave it to the experts, but IDK why those values are squared.

Lol, all good. Its a funky thing to wrap your head around the first time. Short is that the lever arm effect both travel directly and force inversely. So you end up with MR^2 to relate spring rate to wheel rate.

I dont understand the math, was basing myself off of thr way my car feels and the published spring rates out there for other non-divorced setups.

Surprisingly the Vorschlag GTS rates are almost exactly what im targeting. The Nitron street setup may be good as well and may put a little more grip in the rear thay could be dialed in via bars, but may get you off the line quicker in a pro-solo style scenario.

• Vorshlag's GT Spring Package is 450 #/in Front / 550 #/in Rear = 0.82
• Vorshlag's GTS Spring Package is 600 #/in Front / 750 #/in Rear = 0.80
• Vorshlag's GTR Spring Package is 800 #/in Front / 1100 #/in Rear = 0.73
• MRR street enthusiast 400F/600R = 0.67
• MRR gt4 spec 700F 900R = 0.78
• MRR gt4 optional 750F 1000R = 0.75
• ISC Coilovers 504F 784R = 0.64
• Nitron road 628F 658R = 0.95
• Nitron track 799F 1028R = 0.78

Added ratio to each. I know its just numbers on a page, but for me it helps to compare spring balance.

Seems something around 0.75-0.80 is a good average range with shifting balance with bars.

 

[NightmareMoon]

Lol, all good. Its a funky thing to wrap your head around the first time. Short is that the lever arm effect both travel directly and force inversely. So you end up with MR^2 to relate spring rate to wheel rate.



Added ratio to each. I know its just numbers on a page, but for me it helps to compare spring balance.

Seems something around 0.75-0.80 is a good average range with shifting balance with bars.

So if my stock location rears at ~1200 are an effective x0.41, then the 650 fronts mean ~0.7569?

Anyway, I know the car is balanced well enough as-is for my driving style, but its fun to play with numbers.

 

[Dallas J]

So if my stock location rears at ~1200 are an effective x0.41, then the 650 fronts mean ~0.7569?

Anyway, I know the car is balanced well enough as-is for my driving style, but its fun to play with numbers.

The rear is the denominator is the "scheme" laid out above.

So in your case, its 650/(1200*0.41) = 1.32. So you have a huge forward bias on spring rate.

To get to an effective 0.80 coilover ratio, youd need ~1980 lb/in rear divorced springs. Thats the power of MR^2.

Im sure that number is probably a bit shocking but I think the mustang works better than most with low rear rates because it has a big effect on corner exit and putting power down. But I would say you'd gain more front grip dropping front spring rate or increasing rear.

 

[NightmareMoon]

The rear is the denominator is the "scheme" laid out above.

So in your case, its 650/(1200*0.41) = 1.32. So you have a huge forward bias on spring rate.

To get to an effective 0.80 coilover ratio, youd need ~1980 lb/in rear divorced springs. Thats the power of MR^2.

Im sure that number is probably a bit shocking but I think the mustang works better than most with low rear rates because it has a big effect on corner exit and putting power down. But I would say you'd gain more front grip dropping front spring rate or increasing rear.

My car has definitely got a lot of front spring, and you think that would make it understeer everywhere. I don't even use all that much rear swaybar. I also have a very large and effective dual element rear wing. I DO have more front splitter than most of the guys here (Camaros aside).

...and yet on track and at autocross, my car is neutral (within the range of my swaybar tunings), it throttle steers, rotates well in corners and big sweepers, etc. I can't explain that from the numbers you're comparing. Kinda seems like it should be broken AF, but the car won CAMC at Nats in 22, and everyone who drives it finds it super easy to wheel, as long as they some basic throttle discipline. For track events I drop the wing down a notch for a bit less aero effect at speed, and that's it.

The coilover package I have was originally for a guy named J Paulson, who used to be active here and was a very analytical guy, and I've basically been running those rates for a while.

I did try a softer front spring (500), but I didn't like how it gave up so much transition speed. The big front spring is there to give support to the heavy nose on corner entry under dive, and to help it change direction quickly for slaloms. Softer springs gave even more front grip in some elements but they were too slow to pickup and change directions.

Maybe I need more rear spring, I'll allow that as possibility, but I was always fighting to get as much rear grip as possible on exit (and changing rears is a pain) so I never bothered.

 

[Dallas J]

The coilover package I have was originally for a guy named J Paulson, who used to be active here and was a very analytical guy, and I've basically been running those rates for a while.

Ahh cool, James and I are part of the same region and been running together close to 20years. IIRC, he had Megan externals with ProParts custom internals. He changed to a SS 1LE and back to FS for a while and now in a CS MX5 (boooo )

I def felt the softness and slow response trying to run mild springs up front. I know lots will say you dont need to be super stiff but I much rather have a flatter and more responsive car than the "flop-then-turn".

My Evo runs 800lb/in front springs with 125lbs less front corner weight.

 

[Dallas J]

Got some of the changes knocked out over the last week.

• Rear lower control arm - forward spherical
• Rear Upright - Toe Arm FP spherical
• BMR rear cradle lockout
• Swapped from 450/550 to 550/700
• Waiting for Steeda 35mm front bar that got lost and returned :(

Forgot how much changing bushings is a pain in the arse. Spent way too much time trying to press them out. In the end drilling around the rubber to push out the core then a hacksaw to break the shell was the most effective approach.

 

[Dana Pants]

The easiest way to deal with bushings seems to be a push-pull kit, not a press or ball joint tool.

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