Understeer all day every day

[markseven]

op says 12, that's not a front bar size ever offered on e30s

Yeah, I got ya ;) but 21mm? Did they make odd number sizes?

[FredK]

Yeah, I got ya ;) but 21mm? Did they make odd number sizes?

Yes. E30 cabrios came with 21 mm front sway bars.

[markseven]

op says 12, that's not a front bar size ever offered on e30s

Yes. E30 cabrios came with 21 mm front sway bars.

Learn something new every day. Thanks!

[ForcedFirebird]

The M42 doesn't make any power and the stock diff hardly locks up at all. The car underteers much less when the diff is working well (rotates better). We're not talking about a 750 hp muscle car with Detroit locker.

We are not talking about breaking the rear loose with power, that's the instantaneous on/off drifters want. The more the lock, the more the car will want to go straight, no matter how much power, until that adhesion limit is reached and a power-induced slide happens.

Why are spools and welded so popular in drag racing/drifting, not so popular in road racing? 100% lock makes a car go straight until power (or roll forces) intervene by loss of grip.

[lcoleman]

25mm front sway with proper endlinks and -3* front camber (Vorshlag camber plates) seemed to make the biggest difference for me.

[Emre]

We are not talking about breaking the rear loose with power, that's the instantaneous on/off drifters want. The more the lock, the more the car will want to go straight, no matter how much power, until that adhesion limit is reached and a power-induced slide happens.

A grossly underpowered car like the 318is doesn't rotate under power...it rotates under braking. An LSD with a decent amount of lockup will help mobilize the rear under brakes.

I've had the experience running a worn-out diff on my own 318is track car one weekend, then running the same car on the same track with a freshly built diff the next weekend. Night and day.

[kronus]

25mm front sway with proper endlinks

that will do the opposite of correcting the op's problem

[econti]

Sway size was a typo. Front is 20

LSD is shimmed supposedly to 40%. It's pretty damn tight. Could be the cause?
I don't actually have another to test with

Yeah it is 205s on an 8 but they're a wide 205 if it makes sense. Not nearly as much stretch as other 205s I've seen

[ForcedFirebird]

Sway size was a typo. Front is 20

LSD is shimmed supposedly to 40%. It's pretty damn tight. Could be the cause?
I don't actually have another to test with

Yeah it is 205s on an 8 but they're a wide 205 if it makes sense. Not nearly as much stretch as other 205s I've seen

Tire stretch is not an issue in this case. We changed from 7 to 8" wheels on the endurance car and saw an improvement in grip, as the tires are less likely to roll (we are required to run 200 tread or higher street tires). I have also ran the SE30 tires (Toyo RR) on 8's, with the same result - the RR's didn't stretch much on the 8's.

IMO you have a few things going on. Your F/R spring ratio is too high, the front bar is too stiff, not enough camber, then adding a 40% diff to the mix isn't helping. Since you have already been driving the car this way, make one change at a time to suit your needs.

A grossly underpowered car like the 318is doesn't rotate under power...it rotates under braking. An LSD with a decent amount of lockup will help mobilize the rear under brakes.

I've had the experience running a worn-out diff on my own 318is track car one weekend, then running the same car on the same track with a freshly built diff the next weekend. Night and day.

All cars rotate under braking, that's why we trail and left foot brake - which is a technique that would help the OP, actually, but it's not something easy for everyone to master, I still have fumble with my left foot and have been racing and doing track days for a good clip.

[berlow94]

I would definitely look at your tire wear as well as fitment.
Your getting almost no slip angle with 205 tires streteched on 8" rims. Im running 235's...
And you also dont need 4.5 degrees of camber if your not running slicks. I have found that there is diminishing returns using anything more than 3.5 degrees of front camber. Just more tire wear.

[ak-]

In my opinion, I think we're taking this too far in terms of setups. Stock, you're car should rotate under braking/weight transfer easily considering it's a 318is.

I think the rates of your coils aren't true or there is a problem with them somewhere.
I suggest getting a brand of coils where you can 100% verify condition and rates, or go tried and true with H&R Race.

[TobyB]

Well, then.

Many of us midmarkers in PRO3 are running springs in the 600f/700r range,
front and rear cambers in the -4 or more range. I've driven 3 of these cars,
not including my own, and none of them stink. (mine stinks. But I digress)

From looking at your numbers, I'd say more relative front camber would help
given your softer spring rates. Radials like camber, and I have yet to see an E30
wear the INSIDE edge off a track tire (unless you take a road race car to an oval track, but I digress again).
One of the things you have to balance on a RWD front strut car is that the front spring
rate is the primary roll stiffener, and you don't have much camber control. So often,
a strut car will respond differently to a spring rate change than the book says.
Yes, if you stiffen the front, it 'should' understeer more- but if your stiffening
massively improves your front contact patch, it might NOT understeer more.
Or it might understeer more on initial turn- in, but then mid- corner grip
goes way UP, and you get a better drive out of the corner. It can be counterintuitive.
Tire temps help a lot here.
Data logging (even just an aim solo) is also really really really really useful. Even that cheesy
G-Tech thingy from all those years ago was a real asset.

At the end of the day (and this post) the one way that's guaranteed to help you to go
faster is to make one change, see what
happens, make another change on the same element, see what happens, repeat. It can
be a pain- but it's how you learn what works on your car at your driving level. I have spent
entire weekends changing springs back, forth, back, forth, farther one way, farther another... You start to learn what does what, and when. And hopefully, how.

But change things.
t

[akorcovelos]

What tire pressures are you running front and rear? Generally your going to run higher than normal pressures on street tires on track. Chalk the sidewalls and see if your scrubbing and up the pressure 2-3psi until your not rolling the tire.

Recording tire temps will also help find the best pressure to run, target a nice even temp across the tread. If your cooking the outside edges your pressure is too low.

[Bullet Ride]

You can be "that guy" all you like, I freely accept I'm not a well trained driver. Decent, but not trained professionally.

Do you know anyone who is a 'well trained driver'? Do you go to the track at all? Do you know any driving instructors who teach at the track?

Ask someone who is well experienced to drive your car and see what they have to say about it.

The only time I've ever seen an E30 understeer excessively was when the person driving it wasn't really sure about what they were doing.

[berlow94]

Do you know anyone who is a 'well trained driver'? Do you go to the track at all? Do you know any driving instructors who teach at the track?

Ask someone who is well experienced to drive your car and see what they have to say about it.

The only time I've ever seen an E30 understeer excessively was when the person driving it wasn't really sure about what they were doing.

^This^