E30 M52-swapped Trackday Car

[stevesingo]

B'stard Child said:

motorhole said:

What am I doing in 2020

So I've figured that the limiting factor for the car is understeer in medium-high speed bends. I'm going to try and dial that out. Tyres show bluing on the outer edge suggesting more camber is required and I suspect I'm getting toe-in with suspension compression. I intend to add more camber, measure the bump steer and correct if necessary and drop the whole car by 10 mm or so, then see what difference that makes. And I would like to get more than 4 trackdays in!

It's been a while since I was looking at E30's suspension information but in the back of my mind I remember seeing some references to very strange consequences with rear end geometry when lowered too much.......

It was something to do with the trailing arm pick up points being not in alignment and getting worse with lowering but I might be wrong.

The semi-trailing arm set up adds camber and toe exponentially on compression. As the car rolls, the outer wheel toes in and adds camber, increasing stability. If you lower the car on springs alone, the increased toe and camber won't help with understeer. You can weld in some plates on the sub frame to add the provision for toe and camber adjustment. But, this will only correct in the static state and the lower you go, the greater the toe/camber gain for a given compression is. The DTM M3s were lowered by raising the trailing arm pick up points, thus keeping the rate of change more constant.

Lowering on springs alone also changes the roll centres, in effect causing greater leverage for roll.

On my M3, I elected to keep broadly the same ride height and added roll stiffness through firmer springs. As it is primarily a road car I went with 50% firmer front and 45% rear. Stock E30 M3 springs are 100lb/in front and 300lb/in rear. This seems mismatched, but this is due to the motion ratio differences front to rear. The rate at the wheels (WR) are 87/123, giving a ratio of 0.71. My springs are 150/435, WR 135/176 with a ratio of 0.77.

This is counter to most after market E30 springs. In almost many cases the springs supplied are proportionally stiffer at the front.

H&R 26663-188/285-WR:163/116-Ratio 1.4
H&R 26664-205/285-WR:178/116-Ratio 1.53
H&R Race-314/570-WR:272/233-Ratio 1.17 as examples.

Rates for coil overs on the rear need to be much lower due to the change in motion ratio (0.64 vs 1.04).

My thinking is that the stiffer you do, the closer to a ratio of 1.00 on the wheel rates you will need to be as you still want some roll and pitch to take advantage of the geo changes under load.

My advice would be not to lower but try a firmer rear spring. I would also avoid going too stiff unless the car has a welded in cage as the chassis is not torsionally rigid enough. On the track, I would go for wheel rates of 250lb/in front and 300lb/in rear.

What springs are you currently running?

[motorhole]

stevesingo said:

B'stard Child said:

motorhole said:

What am I doing in 2020

So I've figured that the limiting factor for the car is understeer in medium-high speed bends. I'm going to try and dial that out. Tyres show bluing on the outer edge suggesting more camber is required and I suspect I'm getting toe-in with suspension compression. I intend to add more camber, measure the bump steer and correct if necessary and drop the whole car by 10 mm or so, then see what difference that makes. And I would like to get more than 4 trackdays in!

It's been a while since I was looking at E30's suspension information but in the back of my mind I remember seeing some references to very strange consequences with rear end geometry when lowered too much.......

It was something to do with the trailing arm pick up points being not in alignment and getting worse with lowering but I might be wrong.

The semi-trailing arm set up adds camber and toe exponentially on compression. As the car rolls, the outer wheel toes in and adds camber, increasing stability. If you lower the car on springs alone, the increased toe and camber won't help with understeer. You can weld in some plates on the sub frame to add the provision for toe and camber adjustment. But, this will only correct in the static state and the lower you go, the greater the toe/camber gain for a given compression is. The DTM M3s were lowered by raising the trailing arm pick up points, thus keeping the rate of change more constant.

Lowering on springs alone also changes the roll centres, in effect causing greater leverage for roll.

On my M3, I elected to keep broadly the same ride height and added roll stiffness through firmer springs. As it is primarily a road car I went with 50% firmer front and 45% rear. Stock E30 M3 springs are 100lb/in front and 300lb/in rear. This seems mismatched, but this is due to the motion ratio differences front to rear. The rate at the wheels (WR) are 87/123, giving a ratio of 0.71. My springs are 150/435, WR 135/176 with a ratio of 0.77.

This is counter to most after market E30 springs. In almost many cases the springs supplied are proportionally stiffer at the front.

H&R 26663-188/285-WR:163/116-Ratio 1.4
H&R 26664-205/285-WR:178/116-Ratio 1.53
H&R Race-314/570-WR:272/233-Ratio 1.17 as examples.

Rates for coil overs on the rear need to be much lower due to the change in motion ratio (0.64 vs 1.04).

My thinking is that the stiffer you do, the closer to a ratio of 1.00 on the wheel rates you will need to be as you still want some roll and pitch to take advantage of the geo changes under load.

My advice would be not to lower but try a firmer rear spring. I would also avoid going too stiff unless the car has a welded in cage as the chassis is not torsionally rigid enough. On the track, I would go for wheel rates of 250lb/in front and 300lb/in rear.

What springs are you currently running?

Thanks for your input guys!

The car has a welded in cage and the inner wings are stitch welded throughout. It's easily rigid enough to get 3 wheels in the air by jacking just one corner.

Car sits higher than a lot of the E30 race cars I've driven alongside, namely because it is still road legal and once you go so low, you start risking sump and exhaust etc on the road. But there is still leeway to drop it a little more. Spring rates are already pretty stiff. It's on KW Clubsports which are 2-way adjustable for compression and rebound. Front springs are 680lb and rear (inboard springs) are progressive, 400lb - 700lb. Rear also has an adjustable rear beam so I can dial out toe and camber/adjust to suit if required as part of alignment & corner weighting. It is actually lifting an inside front wheel on the way out of some corners - so I do have a set of shorter, linear 700lb rear springs available but I'm going to try dropping it a further 5-10 mm first - its an easy, reversible change and I'll quickly be able to tell if it helps or not.

Whilst the car looks fairly standard-ish from the outside, it's actually very far from it

[stevesingo]

motorhole said:

Thanks for your input guys!

The car has a welded in cage and the inner wings are stitch welded throughout. It's easily rigid enough to get 3 wheels in the air by jacking just one corner.

Car sits higher than a lot of the E30 race cars I've driven alongside, namely because it is still road legal and once you go so low, you start risking sump and exhaust etc on the road. But there is still leeway to drop it a little more. Spring rates are already pretty stiff. It's on KW Clubsports which are 2-way adjustable for compression and rebound. Front springs are 680lb and rear (inboard springs) are progressive, 400lb - 700lb. Rear also has an adjustable rear beam so I can dial out toe and camber/adjust to suit if required as part of alignment & corner weighting. It is actually lifting an inside front wheel on the way out of some corners - so I do have a set of shorter, linear 700lb rear springs available but I'm going to try dropping it a further 5-10 mm first - its an easy, reversible change and I'll quickly be able to tell if it helps or not.

Whilst the car looks fairly standard-ish from the outside, it's actually very far from it

Before I went to custom wound springs, I was using H&R and my car also lifted the inside front coming out of tight corners (Knickerbrook at Oulton and Hawthorn and the hairpin at Croft), as seen at on this vid following me https://youtu.be/CEFwHsU1Bzk?t=8m30s

When I changed to my current spring rates, no such issues.

Although it is difficult to say what the installed rate of the progressive spring would be, I would swap to the 700lb/in linear springs, this would give wheel rates of 591fr/757rr, a ratio of 0.78.

[motorhole]

stevesingo said:

Before I went to custom wound springs, I was using H&R and my car also lifted the inside front coming out of tight corners (Knickerbrook at Oulton and Hawthorn and the hairpin at Croft), as seen at on this vid following me https://youtu.be/CEFwHsU1Bzk?t=8m30s

When I changed to my current spring rates, no such issues.

Although it is difficult to say what the installed rate of the progressive spring would be, I would swap to the 700lb/in linear springs, this would give wheel rates of 591fr/757rr, a ratio of 0.78.

Thanks again Steve - I think I was on that trackday as a spectator Was that the one where Sam's supercharged S54 M3 was there?

I've measured the rear spring rate when compressed at the current ride height using a known amount of weight and the known ratio of spring rate/wheel rate at the rear. Comes out about 590lb iirc. I think you have that ratio the wrong way round? 700lb rear should give a wheel rate of 448lb for the rear. I concur with the 0.64 btw, that's what I got too when measuring the rear trailing arms.

So 680 * 1.04 gives 707 fr and 700 * 0.64 gives 448 rr. 707/448 gives a ratio of 1.57 with the 700lb springs. Does seem pretty high, compared to off the shelf kits suggesting even stiffer rear springs required. But I guess an E30 prepped as a track car loses a lot more weight from the rear than the front. Rear roll can also be addressed with a stiffer ARB if required.

Anyway, in the spirit of changing just one or two things at a time so I know what I get a benefit from and what I don't, I'll do the lowering and front camber change first - then next in line is the stiffer rear springs. At the moment, it's hard to unsettle the rear unless you intend to - and I don't want to upset that too much in one fell swoop and not be able to figure out what the root cause is

Edited by motorhole on Wednesday 8th January 17:47

[stevesingo]

motorhole said:

stevesingo said:

Before I went to custom wound springs, I was using H&R and my car also lifted the inside front coming out of tight corners (Knickerbrook at Oulton and Hawthorn and the hairpin at Croft), as seen at on this vid following me https://youtu.be/CEFwHsU1Bzk?t=8m30s

When I changed to my current spring rates, no such issues.

Although it is difficult to say what the installed rate of the progressive spring would be, I would swap to the 700lb/in linear springs, this would give wheel rates of 591fr/757rr, a ratio of 0.78.

Thanks again Steve - I think I was on that trackday as a spectator Was that the one where Sam's supercharged S54 M3 was there?

I've measured the rear spring rate when compressed at the current ride height using a known amount of weight and the known ratio of spring rate/wheel rate at the rear. Comes out about 590lb iirc. I think you have that ratio the wrong way round? 700lb rear should give a wheel rate of 448lb for the rear. I concur with the 0.64 btw, that's what I got too when measuring the rear trailing arms.

So 680 * 1.04 gives 707 fr and 700 * 0.64 gives 448 rr. 707/448 gives a ratio of 1.57 with the 700lb springs. Does seem pretty high, compared to off the shelf kits suggesting even stiffer rear springs required. But I guess an E30 prepped as a track car loses a lot more weight from the rear than the front. Rear roll can also be addressed with a stiffer ARB if required.

Anyway, in the spirit of changing just one or two things at a time so I know what I get a benefit from and what I don't, I'll do the lowering and front camber change first - then next in line is the stiffer rear springs. At the moment, it's hard to unsettle the rear unless you intend to - and I don't want to upset that too much in one fell swoop and not be able to figure out what the root cause is

Ah, I thought you were using rear coilovers. The calculation should be Wheel Rate = Spring Rate * (Motion Ratio * Motion Ratio)

The motion ratios for E30 M3 are front 0.9326, rear 0.64, rear with coilover 1.04.

So you have, as installed;

Front 680*(0.9326*0.9326)=591lb/in Rear 590*(0.64*0.64)=241lb/in in the standard location: Ratio=2.45!!

If the rears are coilovers, that would be 591 and 638 respectively-Ratio 0.93.

If you are using the stock rear spring location, you are way off on spring rate. FYI, E30 M3 Gp N springs are 680 front 1085 rear (in stock location).

[motorhole]

Ah I, I got you. On another note why is x square of the motion rate and not just the motion rate?

I wonder why KW package their kit with such soft rears with respect to fronts. Perhaps they are designed to be used with a thick anti roll bar? Nevertheless, lifting a front wheel and the unstickable rear end make sense

[stevesingo]

motorhole said:

Ah I, I got you. On another note why is x square of the motion rate and not just the motion rate?

I wonder why KW package their kit with such soft rears with respect to fronts. Perhaps they are designed to be used with a thick anti roll bar? Nevertheless, lifting a front wheel and the unstickable rear end make sense

As you might guess, I'm not a mathematician

All the sources I have used state this formula as a basic, the full formula includes the angle of the spring in relation to the axis of wheel travel. http://performancetrends.com/Definitions/Wheel-Rat... for example. AS our springs are more or less vertical, I don't bother with the full formula.

There are a lot of spring kits which are proportionally stiffer on the front than rear. My guess is for two reasons. Firstly, the roll centres front to rear are likely to be different. As one of the things we are trying to achieve with stiffer springs is increased roll stiffness, a fixed percent increase in roll stiffness front/rear may require a different percent increase in spring rate. Secondly, as you and I have found out, a soft rear makes for a stable car. Selling spring kits which decrease stability my have a negative reaction from customers.

[stevesingo]

I've been doing some revised reading to refresh the research I had done a few years ago.

It would seem that the higher the performance that is required from the suspension, the higher the frequency of the suspension is needed. With this higher frequency the perceived ride quality deteriorates. It is generally accepted that frequencies in the region of 1-1.5hz are typical in road cars, the higher the performance the higher the frequency. Track cars without downforce can be expected in the region of 1.5-2.5hz.

It would also seem that for a car to have good ride qualities there needs to be a suspension frequency mismatch front to rear with the rear having a frequency some 20% higher than the front. This is to ensure both ends of the car settles at the same time and with the rear passing the bump after the front, it needs to settle faster.

This leads to a compromise where the front may have a lower frequency than is ideal for the required performance.

Looking at the E30 M3 (as I have the data for that to hand), and some commonly available aftermarket spring rates we have the following spring rates (SR), wheel rates(WR) (lb/in) and frequencies along with your set up.

Parameter	Stock	H&R26664	H&R Race	H&R CoilOver	Eibach Pro	Eibach Race	BMW Grp N	E30 M52 Weapon
SR Fr	100	205	314	342	114	160	680	680
SR Rr	300	285	570	405	325	445	1040	590
WR Fr	87	178	273	297	99	139	591	591
WR Rr	123	117	233	438	133	192	424	242
freq Fr	1.22	1.75	2.17	2.26	1.31	1.55	3.19	3.19
freq Rr	1.49	1.45	2.15	2.81	1.55	1.81	2.77	2.09
Freq Ratio	1.22	0.83	0.95	1.24	1.19	1.17	0.87	0.65

The Stock and Eibach springs tends to fit in with my reading and also from anecdotal comments the Eibachs ride quite well.

The H&R26664 is an anomaly IMO as the same springs are sold for 325s, which has a heavier engine. Probably why my front ride height was higher than expected when fitted.

The BMW Gp N springs seem to shift the frequency rearward, possibly to increase stability by allowing some roll induced camber change.

As you can see, your set up is a big outlier in the table WRT frequency ratio. You could go for a set of Gp N rear springs and see how it goes.

There is much more to it than this in relation to body stiffness also, but let's not go there for now.

Edited by stevesingo on Thursday 9th January 13:26 for spelling

Edited by stevesingo on Thursday 9th January 13:37

[motorhole]

Ah, thanks for the link, that's really helpful. I think I understand why its the square of the motion ratio now, when I have some time I'll derive it myself to be sure

So I'd been thinking of the moment about the suspension pivot point being the motion ratio, but there's a little more to it there. Also, as I'm running a 5-stud swapped car (ti rear & E36 M3 Evo front), the wheel offset and rear track are a bit different to a standard E30 so the motion ratio may be slightly different from a standard car. I'll need to do some measuring and redo the numbers. But I suspect you're right; the rear is very soft with respect to the front.

I'm currently running a 325i touring rear bar on shortened drop links, but I have a set of H&R bars in the garage I've not fitted yet. That's another change to add incrementally along the line somewhere!

[Kev_Mk3]

I am about half way through reading this thread. WOW

This isn't helping my need / want for a E30 cant wait to read the rest - When I am not meant to be working lol

[motorhole]

Thanks Kev, hope you enjoy! I certainly enjoyed the 2nd half of the project more than the 1st half

To illustrate my point about lifting a front wheel, here's a capture from Blyton in September. Funnily enough, despite the front wheel lift, body roll seems to be kept nicely in check

[motorhole]

I was looking forward to getting more track time this year than I have in previous years. As it happens, events have panned out to prevent that from happening. Regardless of what 1st world problems I have to complain about, a lot of people are losing friends and relatives, jobs and income and perhaps even family homes, it's truly horrendous. I can only hope lessons are learnt, both with respect to handling such situations but also about the vulnerability of the world economy and how it operates. Probably not, but I digress...back on topic.

So yes, wanted more track time. Doesn't look like it's going to happen, not early in the year anyway. But I did manage to get out to Blyton Park just before all trackdays were cancelled and we went into lockdown. This gave me the opportunity to test out some minor tweaks I'd made over the winter.

I'd fitted some adjustable front drop links in order to set up the front ARB properly. I also fitted shorter rear drop links from a Z3 as the rear ARB was at an angle that meant it probably wasn't doing a great deal. Coupled with about an 8 mm drop all round, I was ready to rock.

The car went great at Blyton. Literally drive up, adjust tire pressures, overtake everything, drive home. Upon inspecting the data when I got home, it showed I'd dropped into the 1:13s and looking at sector times etc, the car has a 1:12 in it without a doubt. I'm led to believe that's a pretty good time for a car on road legal rubber around Blyton.

On-throttle understeer was significantly improved. The car changed direction beautifully and GPS speed was hitting up to 107 mph before the wiggler, so straight line performance was on point.

Video and photos:
https://www.youtube.com/watch?v=ixv5x_cNR2k









So, what next? I can't work on the car currently as getting to my lockup during lockdown is problematic. But I don't think it needs much. It does need wheel alignment sorting and I have an oil separator and catch tank to go on it. That's probably all Ill do before next time out. I still have stiffer springs to go on the back too, but I'll try that after next time out.

[Matter88]

^^^ Lovely calm & neat driving, bravo.

Car looks a treat

[motorhole]

So, lockdown rules are slowly being loosened, which means I've been able to get to my lockup and access the car over the past couple of weeks. So I've taken the opportunity to spend a bit of time doing a few odd jobs.

First was my routine post-trackday checks. Torque test key nuts and bolts on suspension and brakes. Look for things falling off. Run the engine, listen for noises, run a diagnostic and so on. Delightfully, this once more revealed very little wrong. Except that one of the rear ant-roll bar drop links had 'walked' off the end of the bar. On E30s, Z3s and E36 Compacts, these drop links are a push-on design and this is apparently a common issue.

No problem - I have a set of H&R bars in the garage (a bolt-through design), so I decided to finally fit the rear bar. Haunted by torrid memories of trying to thread the previous bar through the suspension, exhaust and over the differential, I wasn't looking forward to this job - but I'd obviously retained some of that experience and getting the old bar out and the new bar in and set up on the softest setting wasn't hard at all.

The wiring in the passenger footwell was something else I wanted to address. I'd relocated the fusebox and re-wired a lot of the car during the refresh but I'd kind of just left everything hanging there once I had it working. It looked untidy and I was concerned about a passenger catching something with their feet. I ended up making a brace out of ABS plastic that bolted across the bulkhead to some of the factory studs and this gave me a nice solid mounting to which I could secure the cabling. With a bit of unplugging, re-routing and re-plugging I ended up getting it all pretty solid, immovable, neat looking and out of harm's way.

The car also got a much needed wash!

So, Donington on 4th July next. And maybe the 15th too. We'll see how it goes. I can't wait to get back to Oulton though - my 'local'. That might have to wait until August or beyond however looking at the bookings...

Edited by motorhole on Friday 19th June 21:05

[motorhole]

So the lockdown track time drought has finally ended. Got to Donington as planned on the 4th of July.

The weather was forecast to be changeable there and for the drive to/from Warrington, it was downright awful in places. So I elected to stick with the treads for the day. But as it turns out, apart from it throwing it down when I left at 6.30am, I could probably have gotten away with the R888rs. Ah well...

Turned out to be a good day nevertheless. Was great to meet some new faces, including the infamous W00sher and his Pinderwagon

I did have to call it early as my nearside front was barely legal for the way home - these tyres have done 6 or 7 trackdays now, so that's fair enough. Couple of learning points though...

1) Traffic. Every time I go to Donington, I struggle to string together more than 1 clean lap at any point. I'm always moving over for quicker cars or having to make my way past slower ones. I don't seem to have the same issue at other tracks, is it just a Donington thing? Anyway, by the afternoon most of the paddock had cleared out. So next time do less laps early and more laps later!

2) Oil starvation seems to be occurring under hard braking. Only under braking and not under cornering. And again, not really been an issue anywhere else. I think the downhill approaches to Redgate and Goddards exacerbate it. Biggest drop I saw was down to about 13 psi. So next time out, I'll be dropping in half a litre over with a view to getting a sump baffle in there over winter - along with the Achilles Motorsport oil pump nut/sprocket upgrade.

3) Not to stay out so long I run my tank down to nearly empty. Self explanatory that one really, but I'm not always paying attention to my fuel gauge on track.

4) Gearbox has started spitting a bit of oil out the breather when it's hot. I understand this is fairly common on the ZF 5-speed, but something to keep an eye on nevertheless.

Despite all the above, the car was great again. I did feel quite restrained due to the tyres, you just can't lean on them like you can semi-slicks. It sometimes felt like an age before I could get on the power! The addition of the H&R rear bar does seem to have helped with inside front wheel lift though and the car feels nice and pointy on corner entry.

So back to Donington on 15th July. I'll be there with sf_manta in his E46 Touring this time.

[1602Mark]

Looks great. I can't wait to get my 02 out on track.

[shalmaneser]

This looks ace on track. Can you log oil pressure in some way? I'd be a bit nervous about flogging the car hard if you think you might be having pressure drop. Baffled sump sounds a wise buy, maybe check the bearings while you're there?

[motorhole]

shalmaneser said:

This looks ace on track. Can you log oil pressure in some way? I'd be a bit nervous about flogging the car hard if you think you might be having pressure drop. Baffled sump sounds a wise buy, maybe check the bearings while you're there?

Thanks!

I have an SPA dual temp/pressure gauge that falls nicely within view of my GoPro! That's how I've spotted it. Biggest drop I've seen was to 13 psi; bearing in mind the gauge has a 0.1s refresh rate and displays the 0.4s average at any time. Oil pressure light comes on at 6 psi and that's never flickered. It is only happening under braking, so falling rpm & big longitudinal g - when the engine isn't under load. Thankfully never seen it caused by lateral g, when you're more likely to be on throttle.

Hopefully an overfill by half-litre will improve matters. Seems to be consensus in E36 circles with the M52 engine. Otherwise I'll need to brake less hard downhill until I get a baffle fitted

[stevesingo]

This can also be an issue on the S14 engine, where under braking the oil moves forward and up the timing case. The BMW Motorsport recommendation in the Grp A manual is to over fill be 0.5lt. You should be fine with that.

[motorhole]

1602Mark said:

Looks great. I can't wait to get my 02 out on track.

Me too - to see the pics & videos. Love an '02! Beautiful little things.

stevesingo said:

This can also be an issue on the S14 engine, where under braking the oil moves forward and up the timing case. The BMW Motorsport recommendation in the Grp A manual is to over fill be 0.5lt. You should be fine with that.

Thanks Steve! Once more, your input proves super helpful