Camera's 818C

[mcamera]

Added helper springs and rebalanced my front shocks. Here's my final corner balance. Slight improvements all around compared to last year, but with a more appropriate rear spring rate and properly sized dampers (twice the travel and in the middle of it's travel at ride height). Still waiting on hardware to bolt down the 25lb brick of lead under my passenger seat. I also torqued down all my suspension bushings at ride height which is something I didn't do properly when assembling the car. I had used a jack to raise the wheel some, but not exactly at ride height.

IMG_5290.JPEG

I'm excited to take a test drive and start adjusting my dampers, but it's been too cold here. Recommended to not put weight on 200 tires below 20F or the compound irreversibly cracks. And if they do get below 20F, you have to get them above 40F for at least 24 hours before using them. I've been careful all winter to keep the car on stands. Should get a chance to drive within a couple weeks as things are warming up. The tires don't stick below 60F so it's not like I could push the car anyways, but it would be good to find any issues now. Points races start 4/13!

[driveslikejehu]

Can you remind me where you ended up with spring rates? Did you start with 350F, 275R?
Also, I think you’re using driver weight when you corner balance?
Our weights are similar; 2325# for my R with me in it, tho I’m about 20# heavier than you. I thought the coupe might be heavier but I guess the R is similar with all the steel in it.

I found a forum post from Jim at FFR recommending the setup for a non-aero R as similar to the S but “probably 50# stiffer.” So I built my R with 400F/300R.

The S spring plan never really made sense to me though I respect that FFR did the right analysis and testing. My Cayman, and other mid-engined cars I researched, have heavier rear springs. So partway thru track season last year I swapped front and rear springs (300F/ 400R) and I have a splitter. Got a good corner balance as before and feels about the same on the track.

Now I’ve added a rear wing so may go to 500# rears as in the planned R setup.

Thanks for sharing your development work. I don’t know if I could tell the difference in damping rates, but maybe as I get more used to the car.

[Hobby Racer]

As another data point. I run 500# fronts and 700# rears on my R. I have quite a bit of down force and run on smooth high speed tracks mostly. I've been tracking the car since about 2018 so I have a lot of seat time in it.

[mcamera]

I started with the FFR 350 front / 275 rear. Added 25lbs of lead under my passenger seat to get to 2330lbs (minimum weight for my autocross class). Corner balanced with me in the car (165lbs). My springs are now 350 front / 500 rear.

I read through a lot of posts from FFR and members (thank you everybody that's shared) regarding spring rates and here's what I concluded.

- The FFR springs were chosen as a compromise for the street (350 Front / 275 Rear). This is not a hardcore, optimized for racing setup.
- It's softer in the back (275lb) because the shock mounts further out on the arm (less leverage) than the front shocks which mount further in on the arm (more leverage means you need a stronger spring for the same effect).
- If you're building a track car or adding aero, you can swap the springs (275 front / 350 rear) because you need a stronger spring in the back to help with the added downforce
- Wayne ran 500 front / 600 rear on slicks w/ full aero. A member tried this and said it was too much for a car on street tires, so he backed off to 425 front / 500 rear.
- Bob eliminated his body roll by only upgrading the rears to 500lbs. No change to the front.
- Sixstar had good results with 350 front / 550 rear

To bring it all together, I used a dynamics calculator to find the appropriate spring rates based on my suspension geometry and it came out just under 350lbs for the front and 500lbs for the rear. Stiffer isn't always better. There's a sweet spot where your wheels react quickly to bumps but softly enough that your tire stays pressed into the ground. If your car hops over every bump you're taking weight off the tires and losing grip. Here's the calculator I used. This site also has a lot of great info.

https://farnorthracing.com/autocross_secrets16.html

My own speculation after upgrading my dampers/springs this winter is that there's a cost/design portion to this equation also. The rear suspension has a longer travel than the front. When you combine the yellow Koni's which have a short travel and a softer 275lb spring which compresses quite a bit at ride height, you can use the whole range of travel. If you put a 500lb spring on the koni, it doesn't compress much at ride height so the spring can unseat when you hit a dip in the road (you need a helper spring). If you upgrade to a damper with longer travel, once again the spring can unseat (you need a helper spring). I think FFR used a shorter damper + a softer spring, so the package was simpler, cheaper, and kept the spring safely seated. Even though it comes with lots of other compromises.

[driveslikejehu]

Thanks for the info...
I can't remember if you mentioned "vsusp.com". Another site to calc suspension geometry, etc.
My first calcs didn't show dramatically different front and rear wheel rates; maybe 1.5:1 rear and 1.7:1 front, but I haven't confirmed these.
A little warmer today here in Chicago, so only 2 months till track time, lol.

[mcamera]

Lol I feel ya. I finally drove my car for the first time Sunday. Getting some days in the 60's now down in Kentucky. I haven't used vsusp but I've heard it mentioned.

Been playing with my damper settings but I need more seat time to figure it out. Pretty fun to play with but I'm going to drive myself crazy looking for perfection haha. My dampers have 18 settings for compression and 18 settings for rebound. 0 is soft, 18 is hard.

0C/0R - very comfortable, floaty ride

8C/0R - firmer over bumps, but bouncy

12C/6R - close to a good firmness, slow bouncing turns into smaller/quicker bounces, kind of like driving on a brick road

10C/10C - best so far, caught myself going 15mph over on the highway because the car felt so well planted. Not sure if good for street driving will mean good for autocross but this would be a nice starting point.


Rebound is interesting. At 0, the wheels rebound the fastest so it makes the car feel bouncy because the damper extends too quickly/strongly. Turning that up to 10 (should have gone to 11 for Spinal Tap) slows down how quickly the damper extends, which let's the car "fall" over bumps more firmly. Makes the car feel more confident in what it's doing even though you're slowing down the wheels' reaction time.

[driveslikejehu]

As always, sharing your development is appreciated; interesting and informative
The only time I've messed with damping adjustments was on motorcycles back in the day. Too much rebound and we'd see what we called "jacking it down." Couldn't rebound fast enough before the next bump, so you ended up compressed almost onto the bump stop.
Next time I pass thru on the way to NCM MSP I'll ping you...

[mcamera]

As always, sharing your development is appreciated; interesting and informative
The only time I've messed with damping adjustments was on motorcycles back in the day. Too much rebound and we'd see what we called "jacking it down." Couldn't rebound fast enough before the next bump, so you ended up compressed almost onto the bump stop.
Next time I pass thru on the way to NCM MSP I'll ping you...

I read about jacking down. Hopefully I realize it's happening if I go too far on rebound. Yeah let me know if you're passing by. I'm down in Lexington