e46 M3 suspension setup, or how to not downgrade your car with suspension mods

[mrgizmo04]

I would assume that they would quote it for every car based on suspension geometry of every car, i.e. for our cars since they are a "divorced" setup (spring doesnt sit over the shock), they would account for the wheel rate/leverage affect. I think rear rate is about .53 (I might be remembering incorrectly), so I doubt they would stack the washers in the shock to be originally valved for nearly 2x spring rate.

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[timmo]

Don't forget, our rear springs' location means that they provide about 2/3rds their advertised rate, for our cars. So if a shock's limit is 700lbs, you could run 1000lb springs in the car.

The spring is inboard, but the damper connects to wheelhub.

Unless TCK and others are giving that 700lb limit at the control arm and not the damper (which would mean the damper can only control up to about 467lbs, which I doubt is the case).

When I was talking to TCK over the phone, from what I gathered this accounts for the motion ratio due to having the spring inboard. This is also reflected from TCK's website, where in the drop-down menu you can choose rear spring rates from 400# - 700#.

[Obioban]

Tck is saying your can run up to a 700 lb spring, not a 700# wheel rate.

[Tbonem3]

Don't forget, our rear springs' location means that they provide about 2/3rds their advertised rate, for our cars. So if a shock's limit is 700lbs, you could run 1000lb springs in the car.

The spring is inboard, but the damper connects to wheelhub.

Unless TCK and others are giving that 700lb limit at the control arm and not the damper (which would mean the damper can only control up to about 467lbs, which I doubt is the case).

[timmo]

Thanks for that advice. I’ll look into GC. Is there a source that I can reference which shows different spring rate ranges for all the shocks out there?

I wish lol, I called up both GC and TCK because I'm trying to figure out what rates I can run for my kit.

I have a bit of a conundrum on my hands - I bought a GC DA kit used but the rear shocks appear to be the ones from TCK. I managed to get the build sheet from GC and the part numbers don't match.

Build Sheet:



What I actually got:



The thing is, the seller was a very nice and upfront guy, he said nothing was replaced and those were the rear shocks that came with the kit. I do give him the benefit of the doubt, because on the local forum he has a pic from when the kit was new, with the same shocks:



It's just a bit odd how if these rear shocks did truly come with the kit, why it doesn't match the original build sheet. I'm being a bit hopeful that somehow these TCK were revalved to accommodate higher spring rates. On mine, there are these two holes that appear to have been plug welded right above the compression adjusters, and I haven't seen that on any other pics of these shocks, so I'm hoping that is somehow part of the revalve process.



Regardless the pricing was such that even if these rear shocks are original TCK it was still well worth it. But since they can only accommodate 700# that would make it very hard to run flat ride, which would suck - I was hoping to keep the 440# front and bump the rears up to ~900-1000#.

[duracellttu]

TCK says they’re good for 300-700. If they targeted 500, that would be 350-650 with a 30% variance 🤔

TCK did recommend 500# springs to me, but that throws off the whole flat ride attempt I’m making. So what you are stating makes more sense for the range. He says it’s rated to 700# but doesn’t have enough compression that high.

[Obioban]

Isn't there a rule of thumb that most dampers can reasonably accommodate spring rates 20-30 percent above or below what they're valved for?

TCK says they’re good for 300-700. If they targeted 500, that would be 350-650 with a 30% variance 🤔

[IamFODI]

Isn't there a rule of thumb that most dampers can reasonably accommodate spring rates 20-30 percent above or below what they're valved for?

[duracellttu]

Even the TCK DA rear shocks (Koni 8242-1009) only support up to 700#, not more than that.

The GC DA rear (Koni 8042-1134) can support up to ~1100#.

Thanks for that advice. I’ll look into GC. Is there a source that I can reference which shows different spring rate ranges for all the shocks out there?

[timmo]

Any recommendations for replacement rear shocks to support 700# springs? Should I just get TCK DA rears and keep the SA fronts? TIA for the help.

Even the TCK DA rear shocks (Koni 8242-1009) only support up to 700#, not more than that.

The GC DA rear (Koni 8042-1134) can support up to ~1100#.

[Obioban]

I’d try full firm before buying any parts. And I agree with TJ— might as well try full soft, as the effort required is near zero. Useful diagnostic.

[T.J.]

I can try that but doesn’t make much sense. How would that help? (Honest question.)

Mostly just to play around and make sure you’re not missing anything, like jacking down. I would also try full stiff, just to fully understand how everything feels

[duracellttu]

Try the rear on full soft and see what happens

I can try that but doesn’t make much sense. How would that help? (Honest question.)

[T.J.]

Try the rear on full soft and see what happens

[duracellttu]

You should have the fronts on full soft and rears somewhere in the middle of their range, probably. Full soft up front for sure.

maybe more in the rear— 700 is the stiffest spring tck says your can use with their shocks, so it might need to be on the stiffer side to control it.

Just took the car out for another drive after setting the rear shocks to 1/4 turn from full firm. While its much better, its still bouncy. Just doesnt feel planted when going over bumps.

Does this mean I've reached to limitation of my shock? Exchanged a few emails with TC and he said that the SA shock doesnt have enough compression damping control to "be really good", but the DA does

Any recommendations for replacement rear shocks to support 700# springs? Should I just get TCK DA rears and keep the SA fronts? TIA for the help.