MCS spring length

[Gossypiboma]

After doing a lot of research on the correct spring lengths for MCS dampers with true rear coilover I'm still confused. It seems a lot of the information available is from a few years ago before Bimmerworld came out with their revised GTmore sway bar kit.

If I plan to run 295/30/18 front tires will I need to run a 5 inch front spring or will a 6-in front spring clear?

And for the rear. Do I need to run a 6 in or 7-in rear spring for a true rear coilover setup? Does the spring in the rear need to somewhat match the front? As in if I have to run a 5 inch front spring do I need to run a 6 in rear spring with helper spring? Or will a 7-in rear spring without a helper spring be fine with a 5 in front spring?

One issue I'm concerned about is if I have to run a 5 inch front spring and use a 7-in rear spring is the amount of preload I will have to induce on the rear spring to match the front ride height. Or is this not a concern?

[M3SQRD]

Front and rear spring lengths are selected independently. Are you running a divorced or coilover rear setup? What are your spring rates? Assuming a divorced setup, a longer rear spring is fine and is required in most cases (running an extremely high rear spring rate might have a similar length to the front but at that point you should be running a rear coilover setup). The length of the rear spring really depends on the spring rate you’re running. A 6” rear spring would be for a very high spring rate. Also, you have to be careful with a 5” front spring because if you’re running a 500-700 lbf/in front spring rate, a 5” spring might coil bind and limit full travel. Rear spring preload level is fine for 6-9” springs with appropriate spring rate. I’m running a divorced setup with a 6” 700 lbf/in front spring and an 7” 1100 lbf/in rear spring. I have all of the parts to convert to a coilover rear but have been too lazy to do the swap. Switching to an 800/800 lbf/in setup when I do the conversion.

[Gossypiboma]

Originally Posted by M3SQRD

Front and rear spring lengths are selected independently. Are you running a divorced or coilover rear setup? What are your spring rates? Assuming a divorced setup, a longer rear spring is fine and is required in most cases (running an extremely high rear spring rate might have a similar length to the front but at that point you should be running a rear coilover setup). The length of the rear spring really depends on the spring rate you’re running. A 6” rear spring would be for a very high spring rate. Also, you have to be careful with a 5” front spring because if you’re running a 500-700 lbf/in front spring rate, a 5” spring might coil bind and limit full travel. Rear spring preload level is fine for 6-9” springs with appropriate spring rate. I’m running a divorced setup with a 6” 700 lbf/in front spring and an 7” 1100 lbf/in rear spring. I have all of the parts to convert to a coilover rear but have been too lazy to do the swap. Switching to an 800/800 lbf/in setup when I do the conversion.

This for for MCS 2WR with rear coilover. 800F and 700 rear spring rates.

So, can I not use a 6 in front spring with 295/30/18 front tires? Or do I have to use a 5 in spring?

Bimmerworld sold me 5in front and 7in rear springs with helper springs, but after researching it I'm concerned this may not be optimal.

I thought there would be a cookie cutter go to setup considering this platform is quite old at this point, but the info is hard to come by.

[M3SQRD]

Originally Posted by Gossypiboma

This for for MCS 2WR rear coilover. 800F and 700 rear spring rates.

So, can I not use a 6 in front spring with 295/30/18 front tires? Or do I have to use a 5 in spring?

sold me 7in rear springs with helper springs, but after researching it I think this may be incorrect.

I thought there would be a cookie cutter go to setup considering this platform is quite old at this point, but the info is hard to come by.

The 18” wheel setup thread in the track forum has a lot of info on spring lengths but it’s scattered throughout the thread. Definitely hard to find the info easily.

2.25”-dia or 60 mm-dia spring on the front? 5” 2.25-dia springs will clear because it moves the adjuster up above the tire sidewall. A 6” front spring typically has clearance issues with tire sidewall but it’s worse for some 295s that are closer to a 305 in width. Also, clearance is worse for tires with a side bead protector. I run a staggered 285/305 setup so I’m not an expert on fitting 295s on front. I’d refer you to the 18” wheel thread or get SYT_Shadow to chime in.

Yeah, a 7” rear spring sounds long but perhaps it’s due to the 700 lbf/in rate. I have a 6” 800 lbf/in so 800 to 700 could be the rate change that requires a longer spring? Mistakes happen so just confirm with BW that a 7” 700 lbf/in spring is the correct length for a rear coilover setup. Rear coilover setups have become more popular over the past few years.

Edit: here’s a link from the 18” wheel thread showing a 295 with a 6” MCS front spring setup:
https://f80.bimmerpost.com/forums/sh...&postcount=170

[RugbyBro]

I run a 6in front and 7in rear (700/600TC). I found there is very little height adjustability with a 6in rear spring in TC configuration, you’ll basically be at max height and still be pretty slammed. I also am able to fit 295/35/R18s up front with a 25mm spacer and -3.5 camber. You would have no problem with a 30 profile.

A 5in front would be nice for easier fitment purposes but BW has told me they only rec that for 850 or above.

[jfritz27]

Originally Posted by Gossypiboma

This for for MCS 2WR with rear coilover. 800F and 700 rear spring rates.

So, can I not use a 6 in front spring with 295/30/18 front tires? Or do I have to use a 5 in spring?

Bimmerworld sold me 5in front and 7in rear springs with helper springs, but after researching it I'm concerned this may not be optimal.

I thought there would be a cookie cutter go to setup considering this platform is quite old at this point, but the info is hard to come by.

I have same setup in terms of MCS and the spring rates you list in true coilover rear.

If you want to ensure maximum clearance for a 295 tire up front, you want the 5" spring, particularly considering the newer tire offerings which are quite meaty. I asked same question to BW about coil bind -- sounds like you might get a slightly different answer depending on who you talk to there, but they were OK with an 800# front spring. I don't believe I've experienced it.

As RugbyBro said, a 6" spring in the rear does make for a tucked look on the 20" stock wheels/tires on my CS with collars at max height, but it's not horrible by any stretch. And you'll still have forward rake, even with the fronts set comfortably for street clearance (as indicated by ground to rocker distance -- don't get tricked by the illusion of the fender gaps). And, when my 18" 295 square track set goes on (shifting balance away from understeer), I actually felt the need to lower the rear a few mm to keep the back feeling more settled under braking (which helped).

After playing with the dampers a bit (with some helpful advice from an SCDA instructor when I was at VIR), this setup on 295 RE71RS feels fantastic on the track. On the street, well, not exactly, but whatever ....

[D_SheerDrivingPleasure]

I run 295 square with 5' front spring on MCS suspension. No issues. Clearance is tight with certain tires as others have noted. BW TAR wheels 10.5 ET36 fit nicely well with a 15mm spacer. The ET40 Apex wheels are popular too but require a 20mm spacer.

[markw10702]

Originally Posted by Gossypiboma

After doing a lot of research on the correct spring lengths for MCS dampers with true rear coilover I'm still confused. It seems a lot of the information available is from a few years ago before Bimmerworld came out with their revised GTmore sway bar kit.

If I plan to run 295/30/18 front tires will I need to run a 5 inch front spring or will a 6-in front spring clear?

And for the rear. Do I need to run a 6 in or 7-in rear spring for a true rear coilover setup? Does the spring in the rear need to somewhat match the front? As in if I have to run a 5 inch front spring do I need to run a 6 in rear spring with helper spring? Or will a 7-in rear spring without a helper spring be fine with a 5 in front spring?

One issue I'm concerned about is if I have to run a 5 inch front spring and use a 7-in rear spring is the amount of preload I will have to induce on the rear spring to match the front ride height. Or is this not a concern?

Have you contacted Phil at Bimmerworld? He should be able to fix you up with the correct spring configuration. This is right in his wheelhouse.

phil@bimmerworld.com

As an alternative you should contact Wyatt Gilbert at MCS for spring configurations.

wyatt@motioncontrolsuspension.com

After reading through all the replies to your post, nobody is giving you the answers that are correct for your setup. Go contact the experts who do this for a living. You will thank yourself later (so will your wallet).

[jfritz27]

Originally Posted by markw10702

Have you contacted Phil at Bimmerworld? He should be able to fix you up with the correct spring configuration. This is right in his wheelhouse.

phil@bimmerworld.com

As an alternative you should contact Wyatt Gilbert at MCS for spring configurations.

wyatt@motioncontrolsuspension.com

After reading through all the replies to your post, nobody is giving you the answers that are correct for your setup. Go contact the experts who do this for a living. You will thank yourself later (so will your wallet).

Based on the collective experience here, I would say the combo of a front, 5" (2.25 diameter), 800# front spring, with a rear, 6" (2.25 diameter), 700# spring in c/o config, on MCS shocks with stock aero, is fairly "standard", and is in fact what has been recommended fairly consistently by BW. (And should say many people run helpers front and rear, I have them). You may get differences of 50-100# on the spring rate recommendation, but this comes down to comfort tolerance on the street. When running the rears inverted there has been (I think) issues with OEM swaybar clearance that I believe is addressed by the GTMore bar (someone else correct me if I'm wrong).

Regarding preload, while I'm not an expert, when one is dealing with linear springs as we are here, I'm not sure that preload in and of itself is or should be an independent concern. The spring length will obviously influence static ride height (so use of a longer spring may dictate that more of the spring is compressed at a given static height), but the dynamic behavior of the spring shouldn't be any different regardless of its preload (assuming there is no coil bind, which is not an issue in the rear with either a 6" or 7" spring). Again, someone correct me if I'm wrong here.

[M3SQRD]

Originally Posted by jfritz27

Based on the collective experience here, I would say the combo of a front, 5" (2.25 diameter), 800# front spring, with a rear, 6" (2.25 diameter), 700# spring in c/o config, on MCS shocks with stock aero, is fairly "standard", and is in fact what has been recommended fairly consistently by BW. (And should say many people run helpers front and rear, I have them). You may get differences of 50-100# on the spring rate recommendation, but this comes down to comfort tolerance on the street. When running the rears inverted there has been (I think) issues with OEM swaybar clearance that I believe is addressed by the GTMore bar (someone else correct me if I'm wrong).

Regarding preload, while I'm not an expert, when one is dealing with linear springs as we are here, I'm not sure that preload in and of itself is or should be an independent concern. The spring length will obviously influence static ride height (so use of a longer spring may dictate that more of the spring is compressed at a given static height), but the dynamic behavior of the spring shouldn't be any different regardless of its preload (assuming there is no coil bind, which is not an issue in the rear with either a 6" or 7" spring). Again, someone correct me if I'm wrong here.

Preload does affect handling because the applied load has to exceed the spring preload before the piston rod starts to move. So spring rate + spring length + ride height do have an effect on preload when the height adjuster is the lower spring seat on the damper. The Ohlins R&T height adjuster (see below) is on the upper damper mount for the rear, and on the front strut its height adjuster is at the bottom of the strut (see below; Ohlins TTX front strut is similar except it uses shims at the strut interface with the knuckle), which changes the length of the damper, not the length of the spring and, therefore, doesn’t affect preload.

[jfritz27]

Originally Posted by M3SQRD

Preload does affect handling because the applied load has to exceed the spring preload before the piston rod starts to move. So spring rate + spring length + ride height do have an effect on preload when the height adjuster is the lower spring seat on the damper. The Ohlins R&T height adjuster (see below) is on the upper damper mount for the rear, and on the front strut its height adjuster is at the bottom of the strut (see below; Ohlins TTX front strut is similar except it uses shims at the strut interface with the knuckle), which changes the length of the damper, not the length of the spring and, therefore, doesn’t affect preload.

Ah, ok, interesting... need to think about this more, but trust you are correct

[Gossypiboma]

I really appreciate all the reaponses though this thread highlights my confusion. It still isn't 100% clear weather I should use a 6 in or 7 in rear spring.

A 5 in front spring will 100% work, but I may buy an extra set of 6 in springs to test fit before I get an alignment. Currently I'm using 18x10.5 +22 in front with a 295/30 tire and would love to be able to use a 6 in spring to remove any chance of coil bind.

[M3SQRD]

Posts 5 and 6 answer your question. A 6” rear spring will be used with the height adjuster at or near its maxed out position and still be at a lower ride height. 7” spring gives you more max height and the ability to run lower, if needed. Your rear spring rate is 100 lbf/in stiffer so it’ll compress 15% less so you’ll have an even higher max ride height than a 6” 600 lbf/in spring. 7” is correct unless you want to run a lower ride height and be limited in being able to raise the ride height. With the 7” 700 lbf/in spring you’ll gain ~0.75-85” in max ride height compared to a 6” 600 lbf/in spring.

[Gossypiboma]

Originally Posted by M3SQRD

Posts 5 and 6 answer your question. A 6” rear spring will be used with the height adjuster at or near its maxed out position and still be at a lower ride height. 7” spring gives you more max height and the ability to run lower, if needed. Your rear spring rate is 100 lbf/in stiffer so it’ll compress 15% less so you’ll have an even higher max ride height than a 6” 600 lbf/in spring. 7” is correct unless you want to run a lower ride height and be limited in being able to raise the ride height. With the 7” 700 lbf/in spring you’ll gain ~0.75-85” in max ride height compared to a 6” 600 lbf/in spring.

It doesn't answer my initial question of will using a 7 in rear spring induce a lot of unnecessary spring preload when lowering the rear to match a front 5 in spring. This is a real concern. I'm sure it will work, but I see a lot of guys using 6 in springs in the rear. Are they using 6 in rear springs because that's just what was sold to them, they want a lower ride height, or is it because they're also using a front 5 in spring.

[M3SQRD]

Ah…I missed the preload part of your question. How high relative to stock rear ride height do you plan on running? From what I’ve seen a 6” spring on the rear damper doesn’t fully compress the helper spring even at max ride height so zero spring preload for a 6” spring. I’d estimate there’s still 3/4” of helper spring travel remaining before it’s fully compressed. So for a 7” spring it would have either zero or minimal preload at max height. Lower preload level as you lower the car. Max spring preload should not be an issue with a 7” 700 lbf/in rear spring with a helper spring.

[RugbyBro]

Just for clarity, here’s how the rear sits on 7in springs nearly at max height. 1+2 are on 285/30R20 Cup 2s and 3 is on 285/35R18 RS4s.

[Gossypiboma]

Originally Posted by RugbyBro

Just for clarity, here’s how the rear sits on 7in springs nearly at max height. 1+2 are on 285/30R20 Cup 2s and 3 is on 285/35R18 RS4s.

My car is also a LRG F80 CS.

That's about the ride height I would want. Definitely no lower, but you're using a 6 in front spring and I imagine a 5 in front spring is going to sit lower.

[MR RIZK]

For me I would be more concerned about gas pressure vs preload.

FWIW on my M2C I run 6” fronts and 7” rears on MCS 3 Ways with C/O rears. I initially ran 6/6” however since I run a softer rear spring than most I would experience some coil bind so I increased the length but retained the rate so I would gain some additional useable spring travel.

Don’t use me as an example as I’m on a M2 and don’t run as wide tires as you.

Just sharing my experience with gas pressure and spring lengths etc.

[RugbyBro]

Originally Posted by Gossypiboma

My car is also a LRG F80 CS.

That's about the ride height I would want. Definitely no lower, but you're using a 6 in front spring and I imagine a 5 in front spring is going to sit lower.

You could get the same front height by running the collar higher up the damper - here’s a pic of where my fronts sit. This is also the clearance I have running a 295/35R18 in front with a 25mm spacer.

[Gossypiboma]

Originally Posted by RugbyBro

You could get the same front height by running the collar higher up the damper - here’s a pic of where my fronts sit. This is also the clearance I have running a 295/35R18 in front with a 25mm spacer.

That pic makes it seem like a 295/30 tire would almost certainly clear a 6 in front spring.

Sounds like I need to buy a set of 6 in springs to try out.

[M3SQRD]

Originally Posted by MR RIZK

For me I would be more concerned about gas pressure vs preload.

FWIW on my M2C I run 6” fronts and 7” rears on MCS 3 Ways with C/O rears. I initially ran 6/6” however since I run a softer rear spring than most I would experience some coil bind so I increased the length but retained the rate so I would gain some additional useable spring travel.

Don’t use me as an example as I’m on a M2 and don’t run as wide tires as you.

Just sharing my experience with gas pressure and spring lengths etc.

What nitrogen pressure do you run? The gas pressure lifting “spring” is in parallel to the main spring and any load carried by the gas lifting pressure reduces load on the main spring. Damping force is not affected by gas pressure force. Gas pressure force acts just like a precompressed main spring so spring preload and gas pressure force have the same effect. Are you suggesting the gas pressure force is considerably higher than spring preload and, therefore, main spring preload is negligible?

[RugbyBro]

Originally Posted by Gossypiboma

That pic makes it seem like a 295/30 tire would almost certainly clear a 6 in front spring.

Sounds like I need to buy a set of 6 in springs to try out.

Yah a 30 profile will definitely fit but here are the caveats: you’ll still need to use a 25mm spacer and 34-36 offset wheel to clear the perch and run -3.5 or more camber to clear the fender.

The primary benefit to the 5in spring is that you could use less spacer and therefore less camber. This will also allow you to use a wider range of offset wheels such as Apex’s et40 offerings. However you need to run a short 295+ tire (30 profile), if you run a taller tire you likely are back to square one and practically would have to do the same things as a 6in spring.

I’m running 700lbs in front so that is too soft for a 5in spring per BW’s recommendations. If I were running 850+ I’d probably use a 5in spring just for extra clearance.