Rear coilover conversion

[DirtKurt]

I wandered over from the non m section in search of more involved discussions on suspension setup. The 335 guys are generally more interested in hwy racing or stance then track performance.

I have been looking into full coil over setups and have narrowed down to either nitron or mcs. The car will be mainly used for autocross but will most likely end up seeing some road course time as well.
My main concern is running true rear coilovers on the stock shock towers. I have found a few people saying that they are plenty strong and a few saying the car needs to be caged and towers gusseted. Anyone with experience who could offer insight would be greatly appreciated.

[tlrid3r]

Originally Posted by DirtKurt

I wandered over from the non m section in search of more involved discussions on suspension setup. The 335 guys are generally more interested in hwy racing or stance then track performance.

I have been looking into full coil over setups and have narrowed down to either nitron or mcs. The car will be mainly used for autocross but will most likely end up seeing some road course time as well.
My main concern is running true rear coilovers on the stock shock towers. I have found a few people saying that they are plenty strong and a few saying the car needs to be caged and towers gusseted. Anyone with experience who could offer insight would be greatly appreciated.

I run a PSI raceline ttx36 ohlins kit and its offered as regular and true coilover kit but they recommend reinforcement for true coilover. That said I don't see the down fall of a regular setup kit. works really well.

[italyix]

I run Nitron rear true coilover and have had zero issues thus far. One thing I absolutely must recommend is if you buy Nitron, specify from the beginning that the rear will be true coilover, I originally bought divorced for the rear and had to go through multiple iteration of parts from a distributor to get the right ones. The rear springs are much thinner than the fronts and the hardware holding the spring to the shock is different than the front. Also, make absolutely sure you calculate your spring rates based on car's corner weight. I chose 450 front and 550 rear after lots of math and the car feels amazing and it's still supple on the street. I can post pics later, since I'm writing from the iPad and my pics are on the iPhone. Feel free to message me with any other questions on Nitron. VAC is the only distributor in the US for BMW and they are super slow to respond. I ended up using Sector111 in Los Angels and those guys are amazing with their customer service and response times, although their expertise is Lotus.

On the topic of chassis reinforcements, I spoke to multiple shops and I heard both ends of the spectrum, I need and I don't need to reinforce. Does not matter at this point since the car is getting a 4 point cage next year and is not my daily anymore. Long run I would reinforce, short run you don't need it.

Btw, the car got completely transformed by running rear true coils. I am finally able to match the front springs to the tears and have a balanced setup, vs running a stupidly heavy spring in the rear and still overall being softer than the front (motion ratio related).

[italyix]

The yellow helper spring is KW, since the Nitron ones did not fit well. Again, multiple iterations of hardware and I was done at this point. Works flawlessly.

[OM VT3]

Originally Posted by italyix

I run Nitron rear true coilover and have had zero issues thus far. One thing I absolutely must recommend is if you buy Nitron, specify from the beginning that the rear will be true coilover, I originally bought divorced for the rear and had to go through multiple iteration of parts from a distributor to get the right ones. The rear springs are much thinner than the fronts and the hardware holding the spring to the shock is different than the front. Also, make absolutely sure you calculate your spring rates based on car's corner weight. I chose 450 front and 550 rear after lots of math and the car feels amazing and it's still supple on the street. I can post pics later, since I'm writing from the iPad and my pics are on the iPhone. Feel free to message me with any other questions on Nitron. VAC is the only distributor in the US for BMW and they are super slow to respond. I ended up using Sector111 in Los Angels and those guys are amazing with their customer service and response times, although their expertise is Lotus.

On the topic of chassis reinforcements, I spoke to multiple shops and I heard both ends of the spectrum, I need and I don't need to reinforce. Does not matter at this point since the car is getting a 4 point cage next year and is not my daily anymore. Long run I would reinforce, short run you don't need it.

Btw, the car got completely transformed by running rear true coils. I am finally able to match the front springs to the tears and have a balanced setup, vs running a stupidly heavy spring in the rear and still overall being softer than the front (motion ratio related).

Did you have kw's before these I've been looking at getting these for a while but not sure if I need to reinforce the rear and if full coilover would make a big difference

[DirtKurt]

Originally Posted by italyix

I run Nitron rear true coilover and have had zero issues thus far. One thing I absolutely must recommend is if you buy Nitron, specify from the beginning that the rear will be true coilover, I originally bought divorced for the rear and had to go through multiple iteration of parts from a distributor to get the right ones. The rear springs are much thinner than the fronts and the hardware holding the spring to the shock is different than the front. Also, make absolutely sure you calculate your spring rates based on car's corner weight. I chose 450 front and 550 rear after lots of math and the car feels amazing and it's still supple on the street. I can post pics later, since I'm writing from the iPad and my pics are on the iPhone. Feel free to message me with any other questions on Nitron. VAC is the only distributor in the US for BMW and they are super slow to respond. I ended up using Sector111 in Los Angels and those guys are amazing with their customer service and response times, although their expertise is Lotus.

On the topic of chassis reinforcements, I spoke to multiple shops and I heard both ends of the spectrum, I need and I don't need to reinforce. Does not matter at this point since the car is getting a 4 point cage next year and is not my daily anymore. Long run I would reinforce, short run you don't need it.

Btw, the car got completely transformed by running rear true coils. I am finally able to match the front springs to the tears and have a balanced setup, vs running a stupidly heavy spring in the rear and still overall being softer than the front (motion ratio related).

This is what i was looking for! Thanks for taking time to respond. How long have/many miles have you been running this setup? Also can't quite tell from the photo did you go with the remote res or standard version? Love to see any other pictures you have.

[DirtKurt]

Originally Posted by tlrid3r

I run a PSI raceline ttx36 ohlins kit and its offered as regular and true coilover kit but they recommend reinforcement for true coilover. That said I don't see the down fall of a regular setup kit. works really well.

My logical side keeps telling me just to stick with the standard setup, but ever since I came across the coilover conversion and reading up on it I cant make up my mind.

[tlrid3r]

Originally Posted by DirtKurt

My logical side keeps telling me just to stick with the standard setup, but ever since I came across the coilover conversion and reading up on it I cant make up my mind.

An easy way to look at it is: the structure frame of the car was not designed to hold all the weight on the rear shock tower and the rear m3 spring control arm (camber arm) is really beefy for a reason. The benefit of a true coilover may come on destruction of the unibody. Just like e46 cracking the body.

[italyix]

OM VT3 - I did not have KWs before, my friend happened to have an extra set of helper springs from his 135.

The rear piggy backs are located in the trunk.

DirtKurt - I have put roughly 10k miles on the conversion so far and it seems to be holding. Mind you I live in the woods, roads are not smooth.
Also, the benefit of running a true coil over in the rear is the ability to use a softer spring:
1. OEM setup uses a motion ratio of roughly .5, meaning the actual spring rate will be half of what you put in. An 800 spring will act like a 400lb spring in the rear. Switching to true coilover, that same 800lb spring now is closer to 600lb...a 200lb delta.
2. By having the ability to now match the rear spring rate to the front, the car will act balanced and will not be soft in the rear. In addition, running softer springs allows for a supple ride. What we need to remember is most of the suspension tuning comes from the valving of the shock, having a stiff spring does not allow the shock to do its job.

From my own experience I can truly say the difference can be felt, albeit I am also running solid subframe bushings, solid diff bushings and full spherical conversion in the rear, so all of the parts come together to form one solid piece with no flex. Also the new 1.5 way diff is amazing

Please note I did extensive research on this topic, I did not randomly convert and slap spring rates. I bought the Nitron R3 NTR knowing I wanted to do this, although I shied away from it in the beginning because of the internet fear of cracking the subframe.

[OM VT3]

Originally Posted by italyix

OM VT3 - I did not have KWs before, my friend happened to have an extra set of helper springs from his 135.

The rear piggy backs are located in the trunk.

DirtKurt - I have put roughly 10k miles on the conversion so far and it seems to be holding. Mind you I live in the woods, roads are not smooth.
Also, the benefit of running a true coil over in the rear is the ability to use a softer spring:
1. OEM setup uses a motion ratio of roughly .5, meaning the actual spring rate will be half of what you put in. An 800 spring will act like a 400lb spring in the rear. Switching to true coilover, that same 800lb spring now is closer to 600lb...a 200lb delta.
2. By having the ability to now match the rear spring rate to the front, the car will act balanced and will not be soft in the rear. In addition, running softer springs allows for a supple ride. What we need to remember is most of the suspension tuning comes from the valving of the shock, having a stiff spring does not allow the shock to do its job.

From my own experience I can truly say the difference can be felt, albeit I am also running solid subframe bushings, solid diff bushings and full spherical conversion in the rear, so all of the parts come together to form one solid piece with no flex. Also the new 1.5 way diff is amazing

Please note I did extensive research on this topic, I did not randomly convert and slap spring rates. I bought the Nitron R3 NTR knowing I wanted to do this, although I shied away from it in the beginning because of the internet fear of cracking the subframe.

If I went with these do you think I'd need to reinforce the strut Tower?

[italyix]

Originally Posted by OM VT3

If I went with these do you think I'd need to reinforce the strut Tower?

I would down the road, but short term you should be fine.

[warp10]

Just went through this with my MCS setup. MCS and Bimmerworld both suggested to stay with the standard set up over the true coil over. One was the chance of damage to unibody. Other was possible clearance issues. Because my cage plan does not incorporate a reinforcement for the rear shock towers and the fact that many Race org don't allow it made me stay with the OEM design on my MCS 2 ways.

[italyix]

Originally Posted by warp10

Just went through this with my MCS setup. MCS and Bimmerworld both suggested to stay with the standard set up over the true coil over. One was the chance of damage to unibody. Other was possible clearance issues. Because my cage plan does not incorporate a reinforcement for the rear shock towers and the fact that many Race org don't allow it made me stay with the OEM design on my MCS 2 ways.

That's the downside of this, not being able to enter certain races

[OM VT3]

Originally Posted by italyix

The yellow helper spring is KW, since the Nitron ones did not fit well. Again, multiple iterations of hardware and I was done at this point. Works flawlessly.

If I do this will I need to get the kW helper Spring?

[italyix]

Originally Posted by OM VT3

If I do this will I need to get the kW helper Spring?

Not necessarily. I didn't want to wait for Nitron to send me correct helper springs, so I chose KW since I had them handy. Had I ordered the Nitrons as a non-divorced rear, the kit would have been complete