E30 M3 suspension

[Yil]

Need dampers for my standard e30 M3. Restoring the car to standard but seem to remember the original spec was a little rolley, although suited the car. What is recomended please?

[benny.c]

The usual suggestion is Bilstein B6 for standard and B8 for lowered. Can’t comment on the B6s but no complaints with the B8s on mine which has an approx 20mm drop.

[E30M3SE]

As above, if you're keeping it all standard then oe shocks were Boge, iirc. If you go for Bilsteins then the front shocks need the bumpstop, which are internal, cutting down to half their size.

[Hoofty]

This is a blast from the past - like a flashback to S14.net circa 20 years ago...

Yep, OE parts were twin-tubes by Boge (who were bought out by ZF Sachs, so should be similar however branded). Problem may be finding any; a quick check of C3/ECP/Autodoc suggests nobody is carrying them any more.

Autodoc list Koni sport twin tubes. No idea what they're like but geometrically they're closes to standard (i.e. you'd use the original bump stops/dust covers).

Bilstein B6/8 mono-tubes still seem widely available. I've run them on mine for years and years, but co-indicidentally have been thinking of looking for standard bits to soften things off a touch. Colour me interested in what you choose!

Nick

[Peter-e2535]

Fit Bilstein B4s and enjoy your car . Leave the B6s / B8s for the ( wannabe) track day warriors.

[stevesingo]

Bilstein B8 are good when the front internal bump stops are cut down by half length. For some inexplicable reason, the standard length bumpstops are so long that when at only 10mm lower, the front suspension only has about 30mm of travel before the bumpstops come the to play this gives a really crash front end.

It takes 30mins to trim them before you fit the shocks.

The bigger issue is springs. H&R don t seem to list any more (they were too soft in the rear anyway), nor Eibach.

I tried H&R and AVO, neither were suitable. I ended up have a custom set wound by Faulkner Springs that were -10mm and +50% stiffer. Rides and handles great.

I have a spreadsheet somewhere with all the research I did

Edited by stevesingo on Wednesday 27th May 19:32

[Jules Sunley]

I recommend having a chat with Kevin Bird at Birds near Iver (BMW, M, and and Alpina suspension guru).


Birds | Ultimate BMW Performance Tuning. BMW Limited slip differentials worldwide. https://share.google/v1dMPFLo3UDvOLzRK

[stevesingo]

stevesingo said:

Bilstein B8 are good when the front internal bump stops are cut down by half length. For some inexplicable reason, the standard length bumpstops are so long that when at only 10mm lower, the front suspension only has about 30mm of travel before the bumpstops come the to play this gives a really crash front end.

It takes 30mins to trim them before you fit the shocks.

The bigger issue is springs. H&R don t seem to list any more (they were too soft in the rear anyway), nor Eibach.

I tried H&R and AVO, neither were suitable. I ended up have a custom set wound by Faulkner Springs that were -10mm and +50% stiffer. Rides and handles great.

I have a spreadsheet somewhere with all the research I did

Edited by stevesingo on Wednesday 27th May 19:32

Done some digging.



Explainer.

Spring rate: just that
WR: The rate at the wheel given the motion ratio (the spring is directly acting on the centre of the wheel)
Freq: https://www.drtuned.com/tech-ramblings/2017/10/2/s...
Ratio: relative stiffness and frequency Fr to Rr. You generally want slightly higher frequency on the rear so the car settles equally after a bump - the front hits the bump first, the rear needs to be faster to settle at the same time.

As you can see, the stock spings are 114/314 lbin with a freq ratio of 1.17, that is the rear is 1.17 x higher frequency.
Eibach pro - mor or less the same but lower.
Eibach race - about 50% stiffer, but 30mm lower. Not good*
All the H&Rs are arse about face. Too soft on the rear. When I tried them you could feel the rear lagging when passing of dips in the road.

As for bilstein dampers, there are various different versions with different lengths and different bump/rebound rates.

https://web1.carparts-cat.com/default.aspx?34=0,10...

I use 34-003350 Front and 24-020275 rear. In conjunction with 155/435 lbin springs from Faulkner Springs, the ride is not too stiff and there is less roll.

• Lowering an E30 is not good for handling on two counts.

Firstly, the front roll centre. Lowering a car reduces its Center of Gravity (CG), which typically reduces weight transfer and improves stability. However, lowering a car alters its suspension geometry, causing the roll center to drop drastically faster than the CG. This increases the "roll moment arm" (the distance between CG and roll center) and creates more body roll, along with potential handling issues like bump steer and loss of grip. So the advantage of stiffer spings is offset by the increase in roll momentum arm.

Secondly, at the rear, the semi trailing arm suspension increases both camber and toe in under compression. Lowering the rear on the spring is effectively doing the same, the wheel sits higher in relation to the suspension arm pick up points. What you get is more rear stability without a corresponding increase at the fron of the car. More corner exit understeer and less throttle adjustability - the nose is less able to pitch toward the apex when entering a corner on a trailing throttle.

[Yil]

Thank you all for the information. Very helpful.

[Yil]

Fuel tank needed - Thoughts on Genuine part or a copy?

[stevesingo]

I recall some have had issues with the fuel pickup pipes on aftermarket tanks. Not sure what brand though.

Also, there a more than one types of tank.

[Yil]

Steering rack need reconditioning, any recomendations please?