E36 M3 5 lug conversion, roll centre?

[JimmyP]

Plenty of people are running this conversion but it all seems to be a bit "suck it and see" without much actual research.

"I've fitted it and havent crashed yet" seems to be good enough!

I think you may be overestimating the base a bit.
I would bet 90% of the guys who swapped E36 parts onto their E30s have no idea what Roll Centre is, or care, or wouldn't know what to do if they knew it was good, bad or ugly.
They did it to get access to a wide variety of 5x120 wheels to show off at Cars and Coffee.

If you look around this site (and others) 60-70% of the cars wheels don't even fit even remotely right let alone has anyone thought about Roll Centre. You have cars with fucked camber setting to get the wheels to fit, grossly wrong offsets, ride heights set by eye so they look good, etc.

[alistairolsen]

Indeed, there is clearly no ideal solution (apart from E30 M3 parts) which certainly in the UK are simply impossible to find.

I'd love to see all the plots for the E30, E30 M3, E30 with E36 M3 retrofit etc for comparison.

[wazzu70]

Agreed. I have the stock geometry modeled, but dont have the other parts so Ive never modeled them. Im curious to know how big the change really is.

[alistairolsen]

I understand how to do the calcs, I just dont have the parts. Plenty of people are running this conversion but it all seems to be a bit "suck it and see" without much actual research.

"I've fitted it and havent crashed yet" seems to be good enough!

Before deciding which of about 6 options to take, it would be handy to know what the outcome would be but it seems that unless I take all of them in turn, no one has any useful data

[wazzu70]

I think everyone knows (or should know) the E36 swap does not give you proper geometry.

Front geometry is not that hard to model. You can use a protractor with magnetic base to get the angles.

I dont think the RC would be worse with the e36 stuff. The castor is most likely the most messed up.

[alistairolsen]

Yeah I just can't believe that for all the conversions that have been done and the sheer number of recommendations for it, no one has actually checked it works properly.

[cocofunk]

You need to be an engineer to graph all the angles of the suspension and get an imagery of the theoretical roll center. Then there are so many applications (all 96+ components; 95 CA with offset CAB and 96+ spindle, non-M components, etc). So many different variations out there. Good question, but I have a hard time believing that someone drew out the geometry and all the angles to gather a roll center answer to this swap.

[alistairolsen]

Has anyone ever seriously looked at the various suspension motions when using this conversion?

I've seen plenty of guides which imply it bolts together, and even some with alignment sheets and pictures of the wheel in the arch to show that the static alignment is acceptble, but has anyone ever really looked at:

• Bump steer
• Camber change
• Roll centre height

Given the price of the parts, I'd like to know the answer before settling on it, which means modelling the whole suspension. In the name of 'standing on the shoulders of giants' and all that, has anyone started or finished a similar exercise and happy to share their findings?


Thanks


Al