• Type: Progressive Rate (soft for daily driving, firm for performance).
• Front Rate: 145 lbs/in (soft) to 225 lbs/in (firm).
• Rear Rate: 525 lbs/in (soft) to 820 lbs/in (firm).
• Drop: Lowers the front by ~1.125 inches and the rear by ~1 inch.

CobaltFilly said:

Alright peeps, you know who it is. Cobalt Filly, back at it again with questions.

Currently sitting on Steeda Non-Adj Shocks/Struts, Sport Progressive Lowering Springs, Camber Plates, sway bars...and a ton of other suspension items, but lets just get to the point.

Stepping from 19x11s to 18x11s and going from Michelin 4PS to Hankook RS-4s.

On a car with the goal of NASA TT4/SCCA Time Trials that is significantly lighter than the V8 counterpart, do I really "need" to go full coil-over setup? Or should I just work on getting better shocks/dampers and spring rates? I will be adding LOTS of aero in the coming years...so let's preface with that these suspension changes will be AFTER I have aero, due to the current setup working fantastic on the track and not bottoming me out or riding too "loose". However, the front drops just a tad too much for my liking on hard braking.

Currently, it looks like the Sport Progressive Lowering Springs have the following values, according to the AI search lol:

Steeda progressive lowering springs for a 2015 Mustang offer a dual-rate system: the front springs transition from a mild rate of about 145 lbs/in to a firmer 225 lbs/in, while the rear springs go from around 525 lbs/in to 820 lbs/in, providing great street comfort that firms up for better track performance.
Key Details

• Type: Progressive Rate (soft for daily driving, firm for performance).
• Front Rate: 145 lbs/in (soft) to 225 lbs/in (firm).
• Rear Rate: 525 lbs/in (soft) to 820 lbs/in (firm).
• Drop: Lowers the front by ~1.125 inches and the rear by ~1 inch.

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steveespo said:

The cars need more spring rate than available for stock diameters than are available. You can be very quick on them don't get me wrong, but drivers being equal a proper race coil over with proper spring rates will be the more competitive setup. I tried every level of spring/shock strut combination. Race coil overs are the answer for a dedicated track car. They are not good for street use as the condition of US roads will accelerate wear on them

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CobaltFilly said:

Since my car is lighter I will aim for closer to the 600/800 route.

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CobaltFilly said:

Since my car is lighter I will aim for closer to the 600/800 route.

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steveespo said:

Do you know what it weighs with driver and fuel for session end?

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blacksheep-1 said:

If it's around 3400 pounds you'll want to go lower. This is one of those deals that you are gonna have to experiment with. So you'll be buying several sets of springs unless you just blindly nail the setup

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CobaltFilly said:

A good friend of the forum will be helping me find this out this January. Estimation is 3700 dry tank.

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steveespo said:

That is not light. My race car is 3564 with driver and 4 gallons end of race weight.

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steveespo said:

There is no shame. But always prepare the car for how it will be when it hits the track. Corner balance, even alignments are ideally done with driver weight in the seat, and I prefer mid stint fuel level.

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mavisky said:

FWIW, my car is 3800lbs and I'm on a 700/900 setup, or about 100lbs higher than Steve is on their 400lb lighter car. I wouldn't want to go a whole lot stiffer without moving from a 200tw super to a slick.

Agreed with all of the above though that if timed competition is your focus then there's nothing off the shelf that will provide you with enough rate, and you'll need some good dampers to balance the forces of the springs. Consequences of such large and heavy cars. You could get away with a lot of other solutions back when race cars were all 2400lbs.

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mavisky said:

FWIW, my car is 3800lbs and I'm on a 700/900 setup, or about 100lbs higher than Steve is on their 400lb lighter car. I wouldn't want to go a whole lot stiffer without moving from a 200tw super to a slick.

Agreed with all of the above though that if timed competition is your focus then there's nothing off the shelf that will provide you with enough rate, and you'll need some good dampers to balance the forces of the springs. Consequences of such large and heavy cars. You could get away with a lot of other solutions back when race cars were all 2400lbs.

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Stan Whitney said:

Go with coilovers, to get the spring rate and ride height flexibility. The number of damping adjustments is not as critical initially, even single adjustable will work better than street style struts and shocks. Also if you switch cars later they will swap between s550/650 easily.

I would find a way to budget for better tires, RS-4's are not great and will make for more handling challenges than you want. If you need to stretch wear out over a season, consider the Conti ECF. It is the spec tire we used in WRL and will take a beating lap after lap and be faster. The new set we ran 15hrs at cota still had another 30% or more tread left. You can see the grades below from GRMs tire testing.

View attachment 107174

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CobaltFilly said:

@flyhalf @Fabman talk to me. I can get anything at good prices, what would be the best 200TW to learn on? RS-4 or Conti ECF? I know we have covered this before, but I am a sucker for being preached at.

EDIT: you too, @steveespo

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