Author Topic: 318is suspension compared to E30 M3? (Read 10011 times)

Frankie · « **on:** January 07, 2007, 04:13:56 AM »

I read from the Purcell's website that the suspension of 318is is quite similar to E30 M3? Is this true and how similar they actually are? How rigid is the chassis of 318is, does it need reinforcement i.e welding some material to it?

romkasponka · « **Reply #1 on:** January 07, 2007, 04:38:26 AM »

It depends what you want and what you have. It is better to check what is done on M3 group A and DTM cars. If you have roll cage alredy fitted basicly you have to reinforce suspension and subframe mounting points after you replace all bushings with spechrical bearings. E30 frame is stif enough for amateur racing, exccept rear shock/damper upper mounting point.

cecotto · « **Reply #2 on:** March 18, 2007, 06:45:15 AM »

Quote from: Frankie;17019

I read from the Purcell's website that the suspension of 318is is quite similar to E30 M3? Is this true and how similar they actually are? How rigid is the chassis of 318is, does it need reinforcement i.e welding some material to it?

The suspension on the two are different

The front:
* Different struts
* Different dampers
* Different springs
* Differet brakes
* Different geometry.
* Diferent track width.
* Different rack and pinion with fewer turns lock to lock
* Different swaybars + mountig points

The rear:
* Same geometry
* Different springs
* Different dampers
* Different brakes
* Different track width
* Different swaybars (Same mounting points)

D. Clay · « **Reply #3 on:** March 18, 2007, 04:56:13 PM »

The M3 windshield is urethaned in adding rigidity to the unibody structure. The rear suspension crossmember mounts the trailing arms on a 12 degree angle instead of 15 like the regular E30. This results in less bump steer and camber change in roll. A stiffer suspension allowing for less body roll is necessary to take advantage of this change. The front sway bars are a lot stiffer in roll due to a change in the mounting point on the car (strut versus control arm).

cecotto · « **Reply #4 on:** March 18, 2007, 05:42:15 PM »

Quote from: D. Clay;21578

The M3 windshield is urethaned in adding rigidity to the unibody structure. The rear suspension crossmember mounts the trailing arms on a 12 degree angle instead of 15 like the regular E30. This results in less bump steer and camber change in roll. A stiffer suspension allowing for less body roll is necessary to take advantage of this change. The front sway bars are a lot stiffer in roll due to a change in the mounting point on the car (strut versus control arm).

You're correct about the front and rear windshields being bonded to the frame.

But the rear crossmember have the same geometry as the rest of the series, only difference being the exhaust mounting point.. This is the reason for the difference in partnumbers between them. The trailing arms are exactly the same as the series, it's just got a 5 lug flange installed instead.

However you're onto something, in motorsport the rear axle was available in the angles you quote, however you had to pair the crossmember and trailingarms. 15 degree crossmember had to have 15 drgree trailingarms. And vice versa.

Jtuner · « **Reply #5 on:** March 18, 2007, 07:38:22 PM »

I would like to add to that question,, what m3 suspension components bolt directly on to our 318is's? and what advantages might they have?

e9nine · « **Reply #6 on:** March 18, 2007, 08:15:39 PM »

Quote from: Jtuner;21590

I would like to add to that question,, what m3 suspension components bolt directly on to our 318is's? and what advantages might they have?

You can do a plug and play swap of the entire suspension and differential.

Advantages - bigger brakes, bigger wheel bearings in front and last but not least - cool looking :cool:

As to bigger brakes, there's options for 4 lug brakes which can be put together for less than the cost of a 5 lug swap. Most however just want bigger brakes for "the look."

b318isp · « **Reply #7 on:** March 21, 2007, 07:35:25 AM »

Quote from: cecotto;21544

The suspension on the two are different

The front:
* Different struts
* Different dampers
* Different springs
* Differet brakes
* Different geometry.
* Diferent track width.
* Different rack and pinion with fewer turns lock to lock
* Different swaybars + mountig points

The rear:
* Same geometry
* Different springs
* Different dampers
* Different brakes
* Different track width
* Different swaybars (Same mounting points)

As far as I know, the front ARB is the same diameter, but due to the pickup on the strut, the leverage is less on the M3 (so stiffer). Front springs on the earlier M3s were exactly the same as the 318is. Geometry differences were dictated by the control arm bush, adding a little extra castor.

For the rear, the ARB was the same. The trailing arms were 12 degree instead of 10 degree (or was it the other way around?). I think this was done to have slightly better toe/camber control.

Regarding track width - was this done by offsetting the wheels? I don't think the suspension pickups were widened. If so, the extra leverage would counteract the increase stiffness of the suspension somewhat.

Gunni · « **Reply #8 on:** March 21, 2007, 09:28:40 AM »

Trailing arms have the same part number in the ETK so they can�t be diffrent.
all 91mm trailing arms. Thats from 09/86
Before that E30�s had 88mm fitted to first facelift 316, 318i M10 and 320i
all other E30�s have the later 91mm trailing arms

b318isp · « **Reply #9 on:** March 21, 2007, 11:14:25 AM »

Quote from: Gunni;21896

Trailing arms have the same part number in the ETK so they can�t be diffrent.
all 91mm trailing arms. Thats from 09/86
Before that E30�s had 88mm fitted to first facelift 316, 318i M10 and 320i
all other E30�s have the later 91mm trailing arms

Maybe it was their angle when mounted in the subframe?

D. Clay · « **Reply #10 on:** March 21, 2007, 11:38:54 AM »

The 1990 M3 has a 19mm front bar and a 12 mm (or 14 mm) rear. The E30 has a 20 mm front and 14 mm rear bar. The front sway bar arm geometry results in a significantly stiffer front bar on the M3. When I went to M3 links attached to the struts the difference was immediate. The car is almost flat in the corners with 165# front springs. The main difference in the M3 and E30 from a handling standpoint is that the M3 is significantly stiffer in roll in the front only. An initial observation would be that this would result in understeer, not a reported problem with the M3.
This is interesting in that a lot of E30 owners feel that stiffer springs (3-4 times stiffer) are the way to control body roll. BMW's approach on the M3 was to use 140# springs and a much stiffer bar.

cecotto · « **Reply #11 on:** March 21, 2007, 12:36:45 PM »

Quote from: Jtuner;21590

I would like to add to that question,, what m3 suspension components bolt directly on to our 318is's? and what advantages might they have?

As said you can bolt on the entire suspension no problem.

However i think you're asking if theres any select parts taht could be used instead without any major problems. I'd say you could use the dampers, provided you have the 51mm struts. (Which as i remember all 318is has, but you should measure them as a precaution). Also the excentric front controlarm bushings will bolt on directly. And increace your castor slightly.

When you increase the caster you among other things get more camber gain during turning. This is helpfull for increased tyre contact during heavy cornering, while still having acceptable camber for cruising. Also directional stability are supposed to be better too... There might be other benefits...

cecotto · « **Reply #12 on:** March 21, 2007, 12:54:39 PM »

Quote from: b318isp;21885

As far as I know, the front ARB is the same diameter, but due to the pickup on the strut, the leverage is less on the M3 (so stiffer). Front springs on the earlier M3s were exactly the same as the 318is. Geometry differences were dictated by the control arm bush, adding a little extra castor.

When the M3 were introduced it had concentric controlarm bushings. And the tech-spec. Said the M3 had 3-times the castor as the the series cars. The excentric bushings were introduced from 9/1987 onwards increasing the castor slightly again. Have you seen the M3 struts?, they are of a completely different design(Well still mac pherson:-) So the different geometry is built into the strut. The conrol arms are the same as the series, so are the top shock mount.

Quote from: b318isp;21885

For the rear, the ARB was the same. The trailing arms were 12 degree instead of 10 degree (or was it the other way around?). I think this was done to have slightly better toe/camber control.

As said the partnumber on the trailing arms are the same as the new disc brake version on all the E30's.

Quote from: b318isp;21885

Regarding track width - was this done by offsetting the wheels? I don't think the suspension pickups were widened. If so, the extra leverage would counteract the increase stiffness of the suspension somewhat.

I havent measured it but the flanges are different, the extra track width could be built into those..

mikko · « **Reply #13 on:** March 22, 2007, 06:53:16 AM »

Quote from: Gunni;21896

Trailing arms have the same part number in the ETK so they can�t be diffrent.
all 91mm trailing arms. Thats from 09/86
Before that E30�s had 88mm fitted to first facelift 316, 318i M10 and 320i
all other E30�s have the later 91mm trailing arms

i think its same geometry, size is for wheelbearing, difference is brakes, drum->disc

b318isp · « **Reply #14 on:** March 22, 2007, 08:03:39 AM »

Quote from: D. Clay;21907

When I went to M3 links attached to the struts the difference was immediate. The car is almost flat in the corners with 165# front springs. The main difference in the M3 and E30 from a handling standpoint is that the M3 is significantly stiffer in roll in the front only. An initial observation would be that this would result in understeer, not a reported problem with the M3.
This is interesting in that a lot of E30 owners feel that stiffer springs (3-4 times stiffer) are the way to control body roll. BMW's approach on the M3 was to use 140# springs and a much stiffer bar.

Also interesting that most aftermarket kits have a significant upgrade to front spring rate (and a simultaneous lowering of the front centre of roll) and not the rear.

Many modern cars seem to be set up with relatively strong ARBs too, may be our fixation with springs is unfounded! Personally, I've always steered away (pun!) from upgrading ARBs too much as they reduced the independancy of the suspension.