Spring rate differences

[Bjr888]

Hello all. I have some suspension questions I could use some help with. I recently purchased a set of TC Kline SA coilovers with some additional swift springs. I sent this to TCKline but never heard back, but hopefully you can help me! Hello. I recently purchased a set of your SA suspension kits for my car. It came supplied with 400# springs installed in front and 672 for the rear. I noticed you recommend 350/600 on your site. Could you explain the differences I might notice between the two setups? They are not installed yet and I want to make sure I put the right setup for me in the first time. The car is my daily but I do plan on doing a few autox days and a track day or two. The only other suspension mods at this time will be m3 control and tension arms for the front, adjustable end Links, your camber plates, and new strut mounts in the rear . Thanks in advance for your help.

[John_01]

You could also run 350 Front / 672 Rear and it would probably ride slightly better on the street.

I'm guessing that maybe the 400 / 672 are intended to be used with the stock sway bars. That's the sort of question you could ask to TC Kline.

[Bjr888]

I did ask TCK, but they did not reply. I do plan on using the stock sway bars at this time. The set up is not installed on the car yet. The 400 lb springs are installed on the front coil overs and I did not receive 350's. I have both 600 TCK's and 672 Swift's for the rear. My question is what's the difference between the 350 and 400's up front for mostly daily driving. Will I be dissappointed not having the recommended 350's? If I stick with the 400's up front which ones should I put on the rear? Thanks!

[HP Autosport]

50 lb isn't much of a difference, but if you plan to run stock front bar go with the 400 lb front springs. For the rear 600 will be better for antuocrss and 672 for a road course. If you are worried about ride quality at all, go with the lower rates front and rear.

[John_01]

I think it will be a pretty subtle difference. Its more a question of what you use it for and what your preference is. If you change either front or rear sway bars you will shift the balance again, so the spring rate will depend on everything else. If you really think its going to be too uncomfortable on the street you might like to swap the front 400 for 350. Then you can add a M3 front sway bar to restore the front roll stiffness as needed.

[Bjr888]

Thanks for the help guys. I think I'll try the 400's in the front with the 600's in the rear per Howard's recommendation. Can you recommend some alignment specs for me to shoot for?

[HP Autosport]

Originally Posted by Bjr888

Thanks for the help guys. I think I'll try the 400's in the front with the 600's in the rear per Howard's recommendation. Can you recommend some alignment specs for me to shoot for?

For street or track?

[Bjr888]

street

[tracer bullet]

Originally Posted by HP Autosport

For the rear 600 will be better for antuocrss and 672 for a road course.

I'd have guessed the opposite, seems like people tend to shoot higher spring rates for autocross turning and lower for road course stability. You have 100x more experience so I trust the suggestion, just wondering.

[Bjr888]

And to be clear, Howard, you're saying the majority of the difference between the lower and higher spring rates for street driving would be comfort level and ride quality where lower spring rates mean better comfort and ride...is that correct?

[HP Autosport]

Originally Posted by tracer bullet

I'd have guessed the opposite, seems like people tend to shoot higher spring rates for autocross turning and lower for road course stability. You have 100x more experience so I trust the suggestion, just wondering.

That was just a suggestion, but if more rotation is needed the 700 lb rear spring may be the ticket.

[HP Autosport]

Originally Posted by Bjr888

And to be clear, Howard, you're saying the majority of the difference between the lower and higher spring rates for street driving would be comfort level and ride quality where lower spring rates mean better comfort and ride...is that correct?

Lower rate springs equal better ride and more mechanical grip.

[Bjr888]

Harold, is it possible to make some recommendations on the alignment settings for the street so that I can provide them to my installer? Thanks for the help!

[HP Autosport]

Originally Posted by Bjr888

Harold, is it possible to make some recommendations on the alignment settings for the street so that I can provide them to my installer? Thanks for the help!

Shoot for zero to 1/16" of toe in up front with no more than -2 of camber. For the rear -1.8 to -2 of camber with 1/8" of toe.

[Bjr888]

Thanks so much for the help!

[Ginger_Extract]

For what it's worth, I'm running the TCK S/A with 400/700 springs. Moving down to a Swift 336 lb/in front spring. Too much front spring rate relative to the rear, balance of the car isn't right with that setup and leaves much to be desired with road driving comfort/NVH when I drive the car to/from the track.

Take vendor recommendations with a BIG grain of salt. I'm not bashing, but I've seen HPA recommend the same spring rates to 135i, 335i and even the new F8x chassis M3/M4 people. There's a solid 500lb weight disparity between those cars, and their suspension requirements are definitely not one size fits all, as I've learned the hard way.

[bNks334]

Originally Posted by Ginger_Extract

For what it's worth, I'm running the TCK S/A with 400/700 springs. Moving down to a Swift 336 lb/in front spring. Too much front spring rate relative to the rear, balance of the car isn't right with that setup and leaves much to be desired with road driving comfort/NVH when I drive the car to/from the track.

Take vendor recommendations with a BIG grain of salt. I'm not bashing, but I've seen HPA recommend the same spring rates to 135i, 335i and even the new F8x chassis M3/M4 people. There's a solid 500lb weight disparity between those cars, and their suspension requirements are definitely not one size fits all, as I've learned the hard way.

I've seen you talk about under-steer. I HIGHLY suggest you give deleting your front sway a try. The spring rates vendors recommend for this platform are heavily understeer biased. I cant believe people have ran BC racings recommended spring rates of 9k/9k without noticing their car rides like shit. Even if damping would be able to control the bounce on the street you'd be sacrificing a ton of grip by running the rear damping overly stiff to keep it from bouncing.

336/700 (6k/12k) is still going to understeer pretty heavily even with the front sway deleted.

I am currently running 6k/16k with NO FRONT SWAY and the car handles well. Tire wear is still right at the wear bar even with the tires at a fairly low psi of 34F/32R. 2.2* camber. Slight understeer still but that's expected as the front has a higher effective spring rate under cornering loads even with the sway deleted.

[ShocknAwe]

Originally Posted by bNks334

I've seen you talk about under-steer. I HIGHLY suggest you give deleting your front sway a try. The spring rates vendors recommend for this platform are heavily understeer biased. I cant believe people have ran BC racings recommended spring rates of 9k/9k without noticing their car rides like shit. Even if damping would be able to control the bounce on the street you'd be sacrificing a ton of grip by running the rear damping overly stiff to keep it from bouncing.

336/700 (6k/12k) is still going to understeer pretty heavily even with the front sway deleted.

I am currently running 6k/16k with NO FRONT SWAY and the car handles well. Tire wear is still right at the wear bar even with the tires at a fairly low psi of 34F/32R. 2.2* camber. Slight understeer still but that's expected as the front has a higher effective spring rate under cornering loads even with the sway deleted.

This is interesting. Glad you brought it up. I have a set of 7k/12k swift springs getting ready to go on my TCKs this weekend and was considering removing my 27mm H&R front sway when I did this. Was also considering pulling the rear sway out. Had cars in the past with higher spring rates and removed the sways for great results. But, not an engineer or any kind of expert so been holding off tinkering with the actual structure of this setup.

[bNks334]

Originally Posted by ShocknAwe

This is interesting. Glad you brought it up. I have a set of 7k/12k swift springs getting ready to go on my TCKs this weekend and was considering removing my 27mm H&R front sway when I did this. Was also considering pulling the rear sway out. Had cars in the past with higher spring rates and removed the sways for great results. But, not an engineer or any kind of expert so been holding off tinkering with the actual structure of this setup.

7K/12K is heavily understeer biased. Leave the rear bar alone and try deleting the front bar. The rear bar contributes very little to the rear effective spring rate. Removing it is a lot of work that will only contribute more to understeer...

Removing the H&R sway has the added benefit of allowing for a more independent front suspension (hitting potholes/curbing on track will be less unsettling) and weight reduction (that 27mm solid bar is HEAVY).

[ShocknAwe]

Originally Posted by bNks334

7K/12K is heavily understeer biased. Leave the rear bar alone and try deleting the front bar. The rear bar contributes very little to the rear effective spring rate. Removing it is a lot of work that will only contribute more to understeer...

Removing the H&R sway has the added benefit of allowing for a more independent front suspension (hitting potholes/curbing on track will be less unsettling) and weight reduction (that 27mm solid bar is HEAVY).

Should be fun! I'll try it with the bar removed. Yes, the bar is heavy, one of the reasons I was thinking about pulling it out. If I can control the body with springs alone, that's a more elegant solution unless the bar contributes some necessary function that can't be achieved with coil rates.

[bNks334]

Originally Posted by ShocknAwe

Should be fun! I'll try it with the bar removed. Yes, the bar is heavy, one of the reasons I was thinking about pulling it out. If I can control the body with springs alone, that's a more elegant solution unless the bar contributes some necessary function that can't be achieved with coil rates.

Sway bar is there to increase roll resistance for handling purposes while leaving the spring rates alone to allow for a comfortable daily drive. Problem is the stock spring rates are entirely too soft for performance driving and the car squats/dives excessivly under braking/accelerating. This can be solved by moving to stiffer springs. There is no reason to stiffen both the spring rate AND the sway bar... that is unless you have some sort of specific goal in mind... They both accomplish the same thing, but in a different way. The other problem is the rear sway can't be changed easily so most people only change the front sway causing MORE understeer since the rear hasnt been increased as well... I ran 4k/16k for a while and the 27mm front bar made for a well handling ride, but the 4k spring didn't allow me to increase my ride height enough for my liking forcing me up to a 6K spring. I then had to remove the front sway because 6k/16k and a 27mm bar understeered like crazy again.

To answer your PM, I have no background in cars (I do Internal Audit work). I have just used knowledge posted here by Fel1x and others, and my own trial and error, to test various suspension setups. From my experience, the math checks out and a lot of the recommendations you find here are misguided. People just don't seem to take the time to ever figure out WHY they are doing things. Like Ginger, I've learned the hard way that much of it is bad advice.

E8x/E9x is a fairly well balanced car as is. Keep the spring setup neutral (roughly 1:3 depening on sprung weight) and dial out understeer that BMW dialed in off the factory floor. They accomplished this through a staggered tire setup, a stiff front sway, and adding a "negative" rake to the ride height. There is no need to make the front of the car more stiffly sprung than the rear, unless you like understeer of course...

Take the time to visit other forums. Miata, WRX, EVO, BRZ... they all have sections discussing this kind of technical suspenion tuning. None of those communities take vendor information at face value. For whatever reason BMW forums completely lack this kind of tuning knowledge. While Fel1x posted some very technical and informative information, he stopped short of interpreting it and making recommendations (something he openly disclosed he wasnt going to do). If you follow his posts in his threads he has moved to a 1000lb spring out back (18k)! Wheel rates and spring frequencies are touched on almost everywhere to some degree. Without taking the suspensions geometry into consideration you can't have any possible way of knowing how the changes you're making will effect the ride...

Here is the spreadheet I've been able to put together:https://drive.google.com/open?id=1VR...8UvX7BwusPj5yw

It's not much, but it will at least give you an idea of how the changes you're making will effect your car and it's balance... I've posted it elsewhere previously as well...

[ShocknAwe]

Originally Posted by Ginger_Extract

recommend the same spring rates to 135i, 335i and even the new F8x chassis M3/M4 people. There's a solid 500lb weight disparity between those cars, and their suspension requirements are definitely not one size fits all, as I've learned the hard way.

Not to drag anyone into the dirt, but they're not the only ones. Same front spring rate recommended for a E82 128i as a F80M3, not just 128i vs 135i or even 335i. Makes me question which one is correct.