Shocks and ride height type 65 Coupe

[neilkuy]

I am working with a Type 65 coupe gen 3 and am looking for some help on understanding what the ride height looks like with the different mounting holes for the front LCAs (and steering rack). The upper holes are intended for track and the lowers for street application. I intend to use the lower holes but I am curious to see what it looks like as a final product and what ground clearance you end up with. Also curious to know what springs you have and how much a preload you are putting on the springs to adjust ride height.

So, I have two questions.
1. Please comment the length of your springs (front and rear) when loaded by the vehicle. Also are you using the stock 500lb/in front and 400lb/in rear springs. might be important to note what engine is in the vehicle for a weight reference.
2. What ground clearance and tire to wheel well clearance do you have - I realize tire selection will play here too. I plan to use 275/40/17(front) and 315/35/17(rear); however I haven't confirmed this yet.

Thanks

[edwardb]

It's a process. Don't overthink it during the build. First, for street use, only the lower holes. The chassis is quite low even when built that way. I would use the upper holes for a track only build. For mine, I used the kit provided shocks and springs which for most will be fine. Start with those and unless you have some specific reason down the road, I doubt you'll change them. When you assemble the coilovers per the instructions, rotate the adjusters until they are just touching the bottom of the springs and keeping them from moving. That's your starting place. Install them into the chassis per the instructions. Later in the build, when you've got everything together and on the ground, then you can start measuring ride height. With the springs adjusted as I described, it will probably be a little high. But that's OK. You'll back them off as needed always adjusting the front pair and the rear pair exactly the same number of turns. Some will do corner weighting, which is fine. It's even more precise but I've found for a street driven build and if you're careful, what I described works. I had access to corner weights for my 20th anniversary Roadster so measured it after I had set it up. It was within a few pounds all around. We didn't change a thing.

My Coupe ride height ended up at front 3-1/4 inches and rear 3-3/4 inches. That puts the chassis as low as I'm comfortable with on the street. I have 18" wheels, but your 17's will be fine. The overall tire diameters are nearly the same.

[Namrups]

I did exactly as Paul just described on my coupe. Dropped it off jack stands and without moving it I thought I'd check the ride height. Without adjusting anything DR front was 4". PS front was 4 1/8". Rear both sides was 4 1/4".After I get it registered and have driven it a little I will decide what height to set everything at but until then I will leave it as is.

[GT_Rich]

Hey Paul, 3.25" front is race ride height. Do you have any bump steer issues with that height using the street mounting holes (designed for 4.5" ride height)?

Also, general note, if your springs are loose in the coilover assembly at full droop, keeper springs and couplers are an easy addition to the assembly and something I would recommend.

https://www.summitracing.com/parts/hyc-cs100

https://www.summitracing.com/parts/e...BoCarEQAvD_BwE

[neilkuy]

Thanks for the insight. To add some clarity. I would like to keep the full stroke of the shock in play. Here is an article that describes this well.
https://www.motortrend.com/how-to/10...t-spring-rate/
It suggests that there is a proper spring rate for each shock length/spring length combo. It is a combination of spring rate + spring and shock length to get the desired ride height while maintaining optimum performance.

Using the formula they show it would be interesting to understand the loaded spring height to see how close the factory spring rate are to ideal according to this article. The unloaded spring length is 8", the shock stroke is 3.5". I need the loaded spring length to complete the math shown.
Ideal spring rate = (F-L)R/(Ra*S)
F = Spring Length Free
L = Spring Length Loaded
R = Spring Rate
Ra = Ratio (Compression/Rebound)
S = Shock travel (full length - compressed length)

EdwardB, Namrups. Can you guys share what your loaded spring length is as well?

[Erik W. Treves]

Hey Paul, 3.25" front is race ride height. Do you have any bump steer issues with that height using the street mounting holes (designed for 4.5" ride height)?

Also, general note, if your springs are loose in the coilover assembly at full droop, keeper springs and couplers are an easy addition to the assembly and something I would recommend.

https://www.summitracing.com/parts/hyc-cs100

https://www.summitracing.com/parts/e...BoCarEQAvD_BwE

I run mine the same way - no issues in this area anyway - approaching 10,000 miles

[edwardb]

Hey Paul, 3.25" front is race ride height. Do you have any bump steer issues with that height using the street mounting holes (designed for 4.5" ride height)?

Also, general note, if your springs are loose in the coilover assembly at full droop, keeper springs and couplers are an easy addition to the assembly and something I would recommend.

https://www.summitracing.com/parts/hyc-cs100

https://www.summitracing.com/parts/e...BoCarEQAvD_BwE

No bump steer issues. Alignment was done at that ride height. With the ride height at the kit recommended dimension (4.5") and the street mounting holes, the wheel well openings are too far above the tire/wheels. Not a good look. I adjusted the ride height as low as I thought I could get away with and look decent. Pictured in post #2 above. Yes, at full droop (e.g. on the lift) the springs are loose. Same as the Roadster BTW. That's why they have you put the tie wraps around the top hat to keep them seated. I'm aware of helper springs and I know guys who've installed them. But I've never encountered any issues with the setup as is, let alone experienced a full suspension droop while driving. That I know of.

[David Williamson]

Well on my Coupe the front spring compressed length is about 6 3/4 inches. This is a standard Koni coilover and a Dart 363 TKO 600 drive train. Not easy to get at the backs right now. I run my ride height about the same as edwardb, maybe slightly higher. Mine is an IRS car and the ride/handing is great but these are not a normal street car so the ride a way tighter.
David W

[GT_Rich]

JB2_5948 - Copy.JPG

I've only had my car together a month and have done two track days. Full droop can be found while in motion. For folks that plan to track the car I would recommend the helper spring setup. Cheap insurance.

[Namrups]

Thanks for the insight. To add some clarity. I would like to keep the full stroke of the shock in play. Here is an article that describes this well.
https://www.motortrend.com/how-to/10...t-spring-rate/
It suggests that there is a proper spring rate for each shock length/spring length combo. It is a combination of spring rate + spring and shock length to get the desired ride height while maintaining optimum performance.

Using the formula they show it would be interesting to understand the loaded spring height to see how close the factory spring rate are to ideal according to this article. The unloaded spring length is 8", the shock stroke is 3.5". I need the loaded spring length to complete the math shown.
Ideal spring rate = (F-L)R/(Ra*S)
F = Spring Length Free
L = Spring Length Loaded
R = Spring Rate
Ra = Ratio (Compression/Rebound)
S = Shock travel (full length - compressed length)

EdwardB, Namrups. Can you guys share what your loaded spring length is as well?

MY front are 6 3/8" and rears are 5 7/8". They are the Koni DA's.

Scott

[LateApex]

I have not lowered my car to track height [yet], despite how much better the fit between wheel well and wheel is (thx for the photos Paul!), in part because I have speed bumps, or speed humps, or Sleeping Policemen (depending on your locale), and I am not inclined to creep about. A couple of observations:

• After the first 1000 miles, I noted the rear end had sagged a bit (~ 1/4" to 3/8"). A tad unusual, but things are settling in as I run the coupe through its paces. I corrected it to 4.5" all around
• With the 3-link suspension, the rear adjustments are 1:1. So if you adjust the coil overs 3/8" (three turns) the ride height in the rear adjusts 3/8". The front is different, as there is a swing arm involved, and given the coil-over mounting point is in-board from the wheel about 40% of the distance to the swing arm pivot point, one needs only apply ~ 1/2 of the number of turns as one would apply to the rear to adjust the ride height. I think ... Likely different with the IRS.
• I added helper springs. They may not be needed in practice, but I didn't like the thought of the "slap" that would result from unloading the rear suspension fully for whatever reason. I would recommend helper springs - they are cheap insurance Note that zip ties will degrade over time - they are plastic after all.

I will at some point lower my ride, maybe to 3.5", or maybe to just 4". This is easy to do with wheels on. It is a function of when I do this, not if, and whether I stick with it. What I really need to do before I muck with my set up is take The Coupe for a hard ride on one of my well traveled canyon roads, and check my smile after same :-)

When I wander out to High Plains Raceway for an Open Track Day, all of this is up in the air. Lots of things involved with prep for that :-) Like trailer, eliminating anti-freeze, maybe tire change, wearing a helmet and/or suit. The whole enchilada :-) On this note, I think it is a good idea to think about what you really want to do with your build. "Occasional track use" is probably the hardest design point!