rear end gets light, how can i fix it?

[daniel]

the car looks hawt on the ring, eric. btw please check your PMs.

[Eric]

Have you had the car corner weighted and the coil overs adjusted for corner balance?

The nervousness of the rear end could be just a weight imbalance or the brake bias could be wrong, or both wrong.

I haven't had it corner balanced yet, just a regular alignment. I want to re-finish my 325 rear subframe with camber/toe adjustments this winter, as well as put a bigger lump of iron in front (S50B30) so i was going to wait until that was done to do the 300 euro alignment, instead of the 50 euro one that was just done

Jim is a better source than I am with car set up...what pressures are you running with the Azenis? Have you tried to set the front sway bar stiffer so that it has a greater tendency to push the front through a corner?

no idea on tire pressure. i had the tires installed on the wheels a few months ago. when i finally got the car on the ground, i was thinking about so many other things than check tire pressure. funny too since i made a million check lists on things to double check before taking it on the track. haha! tires werent flat, so it didnt' stand out.

I'm not sure, but the fact there is 30mm of difference from stock in track width front to rear could cause some issues....Jim, enlighten?

i remember putting 255/40/17 on the front of my old M5 with 235/45/17 on the rear. the turn in was so planted, but the rear did feel like wiggling more. i wonder if the wider track in the front is doing the same thing.

With the stiffness of your swaybars (car in general) and BIG brakes with no ABS you are going to have an oversteer tendency anytime you get on the brakes when the car is not fully settled.

yes, i found this out on my last lap on sunday. comming into Wehrseifen the braking zone is pretty tricky. I'm comming into the corner full power in 4th at about 80ish mph and have to brake to be mid RPM in 2nd. there is a right hand kink right in the middle of the brake zone. I haven't figured out the best way to attack this corner, and i was trying a different approach. A little too much trail braking made for quite a sucked up seat cushin!

What Jim said, and also not having a rear sway can also help "settle" the rear end.

I believe Wider rear track = understeer, wider front = more towards oversteer if the car was neutral.

Do you have true coilovers in the back or is the spring/shock in the stock e30 location?

I'm going to try it out with no rear sway bar. I'm also going to throw a set of 10mm spacers on the rear to bring the track difference in a bit.

I knew that wider tires in the rear would created understear, but track does the same? huh

no true coil overs. they are just E30 M3 H&R coil overs that are non adjustable exept for ride height.

The first thing I'd do is to adjust the coil overs to corner balance the car. If the rear is still nervous, I'd stiffen the front sway to shift weight to the rear tires. If that isn't enough, I'd add weight to the center of the trunk. Somewhere along there the oversteer under power should be conquered. If the rear is still nervous under braking, stiffer springs up front are an option as would be twiddling the front to rear brake bias.

I've been thinking of getting a fuel cell in the spare tire well. I'm thinking the weight in the trunk will help settle the rear, and paying 76 USD cents per liter on base is way better than 1.26 euro per liter at the track

I'm sure my brake bias is off. how do you test/adjust this? I have a bias adjustment knob that i'm going to install some time, i just have no idea how to tune it, so i haven't bothered yet.

that sounds like a LOT of neg camber in the front. Not saying it is a factor on being "loose".

Jim (as always) has good ideas on how to address that.

Yes, i asked him for -3 degree's. i got -1.38 and -2.56. I had to go back and get it re-done. sometimes the translation barior sucks.

and i agree, Jim gives me lots to think about!

what spring rates are you running?

Hi Eric

It seems your rear end is too stiff. Could be the spring rate, the swaybars, the shocks or tires.

Also, a car that has too much front brake can have a twitchy rear end under braking. But also if the rear brakes are too strong. Let me know if you still run the OEM brake pressure valve. Front SL6R/332mm and rear SL4R/310mm is the ideal set-up with stiff suspension and stock pressure valve.

Lee

so if to much rear or too much front bias gives you a twitchy rear, how do you determine which it is? how do you test this? go fast and slam on the brakes. adjust bias knob, and repeat?

right now i have the stock pressure valve still, and i believe those are my disk sizes. I'll have to go measure them again when i have the brakes off.

There's a reason lots of guys run no rear sway bar.

As everyone else has said, Try stiffening up the front sway or loosening up the rear (depending on if you want more or less overall roll stiffness, if the rear is dancing around you might want to give the rear some more compliance).

Car looks fucking awesome by the way.

Right, the rear sway is comming out, and thanks for the compliments;)

So I know nothing about tracking cars and the above responses all seem helpful, but just thought I'd ask about this.

Can I just throw out the idea of a rear spoiler? Or is 100mph not fast enough to give any benefit?

I have a Mtech I spoiler i can put on the car. i don't want to run a megga huge rear wing (one thats actually functional) because i'll still get passed by some local in a stock looking MKII golf. I want the car to look more buisness, and less poser. If my car is falling on it's face over 100mph because it doesn't have enought power, it's going to look silly put-put-putting by the crowds on busy weekends with a 4 foot wide diving board hanging off the back.

Sorry, I dont have much to contribute to this thread. But I'm massively jealous.

If I buy another set of rims do I get a free ride around the ring? :p

Dude, any time! any excuse to go out to the ring, and i use it!

What ride height are you running? Its very possible that you are bottoming on the jounce bumper, which would show itself as nervous/busy on the offending axle.

a friend mentioned ridding the bump stops. how do i check this? will the bump stops be squished?

Make sure that you aren’t bottoming and then work on balancing with spring / bar adjustment.

I think you mentioned that your having trouble with a crest as well, that’s a rear shock issue. The rebound damping isn’t allowing the wheel to drop fast enough, soften up the rebound damping on your rear shocks. This should help with the crest as well as the tendency to OS under braking. The wheel just isn’t dropping.


Have fun at the ring

unfortunetly i can't adjust the shocks.

I don't have anything to contribute about your problem, but do you have any pictures of your bumpsteer spacers? I am interested in how you have that setup.

I have a few pics of them installed... can't find them though, but i'll keep looking.

Mmmmmmmmmmmmm, lack of bumpsteer. :)

unfortunetly i still get bump steer. Lee can i stack you spacers to make a megatron bumpsteer spacer? haha

the car looks hawt on the ring, eric. btw please check your PMs.

thanks daniel, PM replied to.



thanks again for all the ideas guys! i'm going to try a few simple things mentioned in this thread and over at Bf.C. I'm taking my friend up there Wednesday, so well see how she does!

[JeffRR]

Eric,

To check for bottoming, Just crank up the rear spring perches to increase the ride height and run a lap. That's pretty easy and quick and will tell you if your running too low. Make the height adjustment pretty big, maybe an 1" at the wheel, so its noticable, you can always dial it back.

With no adjustment on the shocks, give the brake bias a try like others have mentioned. This isn't going to cure the busy / nervous feel but at least you won't be fighting the brakes as well.

(Lee can comment here since he is Mr. Brake)
With the bias valve installed, start off by doing some limit straight line stops and adjust the bias so that the front and rear lock up about the same time or even with the front locking up 1st. This will at least get you in the ball park, as you get more comfortable with the bias control you can adjust for track, set-up and load conditions.

[2002maniac]

I wouldnt lose the rear bar just yet. Going from a really fat bar to no bar may not be a good idea.

Try throwing the stock rear bar on and stiffening the front bar.

[Eric]

rear bar disconnected

rear end raised about 5mm

bashed the fenders out with Mr sledge for more rear clearence in the rear.

zip tied some loose wires in the cabin

stocked up on oil so i'm not paying 14.95 EURO a quart for the cheep stuff

and i'm off to the ring to see how these changes go...

[Jean]

Great, let us know how it goes and take many pictures at the ring if you can!

I can't even imagine living close enough to the ring arghhhh! :)

[Wh33lhop]

Yep, keep us posted. :)

[Eric]

well Mr hammer worked great since the wheels didn't rub once on the rear fenders (metal part). the rear end felt much better as well, however there are still two corners in the track that feel quite unsettled. One is where there is a crest in a hill right at the apex of the corners, so i understand why it gets light there. the other one is the one i described a few posts up where there is a kink right in the middle of a pretty heavy brake zone.

Now i'm fighting a coolant issue. today was warmer than before, and the temps rose almost into the red. a blown motor means S50 swap so i'm not too too concerned, but it definetly took my concentration away from the track as i was checking the guage often. you can see this in a few spots in the video my friend took.

The car also got pretty greesy a few times under braking. I don't know if it's the azenis getting overheated, or the brakes getting mushy, but doing 3 laps in a row (10 minutes waiting in line each time) the car didn't feel as good.

I also found out that i can't check tire pressure at the local gas station (i have no air) with the turbine covers:hitler:

finally, my buddy took a video on one of the worst laps i've ever done. but it's AVI so i can't get it to play the vid part, just sound. can i upload it to youtube?

[Jean]

I'll have to guess it's probably your tires (unless your pads/fluid is old?), even in Autox when I did back to back runs (fun runs at the end of the day) they get worse and worse as they get HOT quickly.... can you get a tire temp. gauge? The one you point at the tire and read the temperature?

YouTube should accept .avi , try and play it back with VLC on your computer.

[Eric]

So my buddy is a dork at the beginning. I am no way a master, especially with this lap that has to be one of my worst! I also get pretty nervous before each lap, so i'm not in super serious dick mode, just nervous.

From the beginning until about 2 minutes in i'm worried about high coolant temps.

1.42 checking coolant, wrong gear

2.42 worried about smashing into the lotus. the car was really alot closer than it looks in the vid!

3.01 had to slow down a bit for the lotus

3.57 carried too much speed after thinking about my first pass in a braking zone the corner before. this is also where the car got a Little greasy

4.14 real greasy here, i was pretty nervous actually

4.22 this is the corner my rear end gets light under braking. i actually had to counter steer in this vid, but you can't really see it.

4.41 I wasn't sure where this biker was after i passed him so i stayed left. car was still greasy so i got flustered, entered the corner early and went WAY wide. usually i take this corner pretty fast and it's one of my favorite, but i totally butchered this one. after this corner i slowed myself down because i was now unsure about the car and about myself.

7.19 i need more power!

at the end, look at how many cars are backed up. if those cars weren't there, the coolant temps wouldn't rise, and i could have packed a ton more laps in. after every lap we waited about 15 minutes in the traffic jam... sucked.

ok, after all the lame excuses here is my lap

http://www.youtube.com/watch?v=5sCTIiUZsS0

[Massive Lee]

Kuddos to your passenger/friend/slave who was holding the camera. Hopefully he was not looking thru the camera. That's a recipe to be sick within a minute.

Good work (even though I was about to puke on my keyboard, staring at the shaky camera work )

Lee