MCS spring length

[MR RIZK]

M3SQRD The gas pressure adds a force that needs to be overcome before the piston actually moves, in a sense a preload as you have mentioned. The gas pressure to some degree can increase feeling of running a higher rate spring. The spring rate does not change, the rate is the rate however higher gas pressure will provide some additional support.

Everyone’s use case is different, mine is dual duty and I found that that higher gas pressures led to the tire not tracking the road as the gas force was preventing the damper from actually working. To be clear this is for roads that have consistent irregularities in the surface, easiest way to explain is like there is high frequency chatter. What would happen is the car would skip over these bumps vs tracking them and ultimately unsettling the car. Reducing the spring rate did not help the situation, and reducing bump was getting to the point where I was sacrificing performance for compliance. Reducing gas pressure went a long way to stabilising the car for me, provided mechanical grip while adding back some compliance.

I run a flat ride setup on my M2 (higher rear hz) and front sway bar to bring back some roll stiffness ie not a traditional track pitch setup. Gas pressure is set at 110psi and I still have sufficient damper adjustment for my chosen spring rates and track work.

All I’m saying is that in my opinion you would feel the affects of altering gas pressure more than adjusting the preload. Additionally the gas pressure would form part of the equation on what spring rate to initially go with.

Well that is what my ass tells me.

[M3SQRD]

MR RIZK

Correct. As I said, the gas pressure force acts like a fictitious preloaded compressive spring that acts in parallel (not series) with the main spring. The main spring may or may not be preloaded and depends primarily on spring length, spring rate and ride height. The combined gas pressure force + main spring compressive preload have to be exceeded before the damper piston rod starts to move. No piston rod relative motion (velocity) = no damping. Undamped applied forces = impact on ride quality due to lack of piston rod relative movement. This is where a twin-tube damper outperforms a monotube damper. So to address this you need to run the monotube gas pressure force high enough to prevent cavitation yet low enough to avoid a “locked” compressive piston rod due to low applied undamped force from track undulations (e.g., small uniform track surface irregularities in a 200 ft section of a braking zone). Main spring preload and gas pressure force have the same effect on low force undamped applied forces - 50 lbf of gas pressure force and 50 lbf of main spring preload means a 100 lbf applied load is required before the piston rod starts moving into the damper body whereas a 99 lbf applied load would be insufficient to start moving the piston rod into the damper body. Spring rate and damping coefficient/force are not affected by the magnitude of the gas pressure force.

Flat ride is a good approach to suspension tuning. For people not familiar with the concept of flat ride, it’s an approach that has the rear sprung mass frequency set slightly higher than the front sprung mass frequency so that the rear oscillations can “catch up” with the front oscillations which started first because it encountered the disturbance first. The rear “catches up” because of its higher frequency and once caught up the front and rear oscillations are damped out together, hence, the name flat ride.

Unfortunately, it sounds like you’ve become an expert at fine tuning damper performance and street ride quality under variable reservoir gas pressures and a specific type of road irregularities. Your lower gas pressure + flat ride frequency setup must have good street manners. I’ve come across a large group of people over the years who have experienced the low compressive applied force-high reservoir gas pressure condition and blame it on the high-end dampers because they’ve never experienced it on their other suspension setups (usually a low pressure twin tube damper setup). They can’t understand the explanation so they sell their high end damper setup and go back to their twin tube setup. From then on, all they do is spread misinformation on high pressure remote reservoir monotube dampers. BTW, I’m running 125 psi reservoir pressure in MCS 2WR damper setups on my e92 M3, f82 M4 and f22 240ix.

[sly1types]

I run 5" 800lbs front and 700bs 6" rear with helpers. I used to run 700/600, with 6' front, but it was too soft especially on slicks and i wanted to run wider fronts.

I need to go with 7" rears as the 6" collar is maxed out and i'm tucking tire. Its been this way for a few years. I need to move to a 7" rear to raise the rear up .5".

[M3SQRD]

Originally Posted by sly1types

I run 5" 800lbs front and 700bs 6" rear with helpers. I used to run 700/600, with 6' front, but it was too soft especially on slicks and i wanted to run wider fronts.

I need to go with 7" rears as the 6" collar is maxed out and i'm tucking tire. Its been this way for a few years. I need to move to a 7" rear to raise the rear up .5".

Looks great. It’s nice seeing a car, albeit a track car, with an appropriate amount of take. I’m tired of seeing F8x and G8x with an absurd amount of forward rake to get the front wheel gap to match the rear wheel gap. It’s so bad on the G8x that Eibach offers a front only lowering spring kit! Why? I don’t get. Thanks again for a functional looking setup.

Here’s are pics of my Moonstone/Opal White F82, F22 240ix and e92 M3 all with MCS 2WR setups:

[Gossypiboma]

Are helper springs needed both front and rear with 5 inch front and 7 inch rear springs?

I definitely feel like a helper spring may not be needed in the rear with a 7inch main spring.