E36 M3 5 lug conversion, roll centre?

[alistairolsen]

To answer your specific question, I don’t think the math has been done and clearly communicated quite yet.

You are right that what most people do is try to center the wheel and leave it at that.

It might be fruitful to get in touch in Ground Control; they sell a hybrid e30/e36 strut that has some modifications. I don’t know the specifics, but presumably they’ve put nonzero thought into how the setup should work performance-wise.

Yeah I realised that and gave up on the idea not long after posting this thread, but then someone else brought it back to life. One day someone may compare them, but for now I'd rather spend the money on some wheels that fit correctly than suspension components that probably dont.

[george graves]

I'm not saying or assuming anything of the sort, so please don't put words in my mouth.

That wasn't aimed at you broski. Just in general. Take a chill pill.

[wazzu70]

The GC kit puts the strut housing in the proper angle to match the E30s upper mounting point. If you look at the two suspensions you will see the E30 shock tower mount is further back and the E36 more vertical.

When you put E36 struts in an E30 you have to “tilt them back” so they can mount in the strut bearing.

[kronus]

To answer your specific question, I don’t think the math has been done and clearly communicated quite yet.

You are right that what most people do is try to center the wheel and leave it at that.

It might be fruitful to get in touch in Ground Control; they sell a hybrid e30/e36 strut that has some modifications. I don’t know the specifics, but presumably they’ve put nonzero thought into how the setup should work performance-wise.

[alistairolsen]

I'll interject this jem. Any change you make to suspension setting will have an effect. Good in one way, bad in another. There is no MAGIC suspension that does all, is all, and be all.

You can't say that the placement of 96+ e36 arms "ruins" the suspension. For one, you're assuming the e30 suspension is "the best EVER as stock" and two....What's the goal? You need to clarify that first.

This book is a great starting point. https://www.amazon.com/How-Make-Your.../dp/0912656468 It's super old school, but a great read.

I'm not saying or assuming anything of the sort, so please don't put words in my mouth.

I fully sppreciate that all suspension is a compromise. Mac struts especially so. I read that book a while back, along with:

https://www.amazon.com/Race-Rally-Car-Sourcebook-Competition/dp/1859608469

https://www.amazon.com/Racing-Sports-Car-Chassis-Design/dp/0837602963

https://www.amazon.com/Competition-Car-Suspension-Design-Construction/dp/185960644X

https://www.amazon.com/Chassis-Engineering-Building-Performance-Handling/dp/1557880557

And numerous other papers, articles and builds online when I was building a kit car and modifying my track car, so please dont waltz into a thread with a patronising tone

What I wanted to try to understand when I posted this is whether it is likely to give acceptable motion curves for road use (to offer performance at least as good as the original arrangement). The answer I got basically suggested no one had ever looked into it. Every thread I've seen on the subject says "it's fine" before quantifying that with a picture of the wheel in the middle of the arch. I've yet to even see a static alignment sheet, let alone camber and to in bump and droop, roll centre heights etc.

On that basis, I wasnt prepared to shell out £500 on the parts with no confidence they would offer an improvement to, or even match the existing arrangement.

In an ideal world, both setups need to be measured, modelled and the outcomes compared, however without both setups available this is impossible.

[george graves]

I'll interject this jem. Any change you make to suspension setting will have an effect. Good in one way, bad in another. There is no MAGIC suspension that does all, is all, and be all.

You can't say that the placement of 96+ e36 arms "ruins" the suspension. For one, you're assuming the e30 suspension is "the best EVER as stock" and two....What's the goal? You need to clarify that first.

This book is a great starting point. https://www.amazon.com/How-Make-Your.../dp/0912656468 It's super old school, but a great read.

[alistairolsen]

The fundamental issue is that it's touted on "the internet" as the proper solution, but the measure of that seems to be whether it gives the correct wheel position in the arch/well rather than whether it actually provides proper suspension motions.

Unfortunately it's not cheap to acquire the parts, but it would be good if someone could take some accurate measurements so that the motions could be modelled for the good of the community.

[e30davie]

In general camber impacts your tire contact patch through the range of motion. Castor impacts your high speed stability and ability to return to center.

Castor also gives you more camber as you turn the wheel, so its all connected.

[e30davie]

If you want to get technical there is a piece of software called "optimum k". The free version i belive has all the features you just cant save it. All kinds of nerdy ways to graph suspension things once you input your suspension dimensions in.

http://www.optimumg.com/software/optimumkinematics/

[wazzu70]

In general camber impacts your tire contact patch through the range of motion. Castor impacts your high speed stability and ability to return to center.

[mach schnell]

the tie rod balljoint's pivot point is about an inch lower on an E30 strut than an E36 spindle, which influences bump steer.

the relative position of the virtual axis of rotation of the front wheels is also completely different from stock e30 *and* from how the suspension is mounted in an e36, as are the camber and caster curves, which implies that it doesn't work as engineered.

unclear what the physical effects are.

Interesting. You got my attention. Would like to know more!

[kronus]

the tie rod balljoint's pivot point is about an inch lower on an E30 strut than an E36 spindle, which influences bump steer.

the relative position of the virtual axis of rotation of the front wheels is also completely different from stock e30 *and* from how the suspension is mounted in an e36, as are the camber and caster curves, which implies that it doesn't work as engineered.

unclear what the physical effects are.

[mach schnell]

So what’s the issue with the E36 suspension in an E30?

I understand the geometry is “not proper” - so what’s not proper about it?

Does it result in poor handling? Some weird handling dynamics?

I’m not arguing or disagreeing, just trying to find out more precise info.

[JimmyP]

That was edited to be kind.

[alistairolsen]

I didnt like to say....