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      08-17-2020, 09:08 AM   #1
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stagger for autocross

Running square 255's and I've finally got the understeer/push worked out with the help of -3 up front and an aggressive splitter

throttle out oversteer is considerable and probably my next issue to resolve, how do folks address this without adding understeer back in?!?

vid from saturday event, the ELSD works really well at autocross speeds & elements, it does not work well for me at the track, I'll be adding a M3 rear subframe/LSD at some point

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      08-17-2020, 12:53 PM   #2
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Hey Matt, how'd the afternoon session go? It was cool chatting with you and getting a chance to look over your car. You've got me researching oil pressure gauges and accusump setups now...

I wish their timing system would have worked out, would be cool to see how everyone compared.

Dave
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      08-17-2020, 01:45 PM   #3
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What suspension are you running?

The easiest way to dial out throttle on/exit oversteer is to soften the rear compression. This won't affect oversteer/understeer balance much elsewhere but will help manage throttle induced oversteer.
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      08-17-2020, 02:45 PM   #4
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Quote:
Originally Posted by spidertri View Post
Hey Matt, how'd the afternoon session go? It was cool chatting with you and getting a chance to look over your car. You've got me researching oil pressure gauges and accusump setups now...

I wish their timing system would have worked out, would be cool to see how everyone compared.

Dave
I LOVE this format, its 10 minutes of adrenaline rush, pause 10 and repeat.

I data logged and I have the data in track attack if you have that desktop app send me your @name and I can share it with you.

My best lap was a 43.312, oil pressure was great, never saw any drops and the car is peaking at 1.1 G

lowest psi was right at the peak G in the back sweeper, but only 1700 rpm so I think it's fine


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      08-17-2020, 02:47 PM   #5
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What suspension are you running?

The easiest way to dial out throttle on/exit oversteer is to soften the rear compression. This won't affect oversteer/understeer balance much elsewhere but will help manage throttle induced oversteer.
MeisterR zeta-crd 6k front 12k rear, 2 clicks off full soft front and 2 clicks off full stiff rear

I found understeer worse when I soften the rear

car was also in some kind of limp mode all day, the jb4 would not respond to commands after the first session and would not allow full boost, acted like it was in low boost warmup mode, maybe not even that much

car has jb4 with backend race map flash with some teaks to the throttle tables to remove the buffers
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      08-17-2020, 04:34 PM   #6
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Quote:
Originally Posted by imported_mega View Post
MeisterR zeta-crd 6k front 12k rear, 2 clicks off full soft front and 2 clicks off full stiff rear

I found understeer worse when I soften the rear

car was also in some kind of limp mode all day, the jb4 would not respond to commands after the first session and would not allow full boost, acted like it was in low boost warmup mode, maybe not even that much

car has jb4 with backend race map flash with some teaks to the throttle tables to remove the buffers
If they are one way adjustable, then yes, softening the rear would make it understeer more. This would only work if you have independent compression adjustment.

You could try lowering the rear and/or adding rear toe in to help as well.
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      08-17-2020, 08:57 PM   #7
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Originally Posted by spidertri View Post
Hey Matt, how'd the afternoon session go? It was cool chatting with you and getting a chance to look over your car. You've got me researching oil pressure gauges and accusump setups now...

I wish their timing system would have worked out, would be cool to see how everyone compared.

Dave
they posted times on facebook
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      08-18-2020, 05:55 PM   #8
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Quote:
Originally Posted by imported_mega View Post
throttle out oversteer is considerable and probably my next issue to resolve, how do folks address this without adding understeer back in?!?

vid from saturday event, the ELSD works really well at autocross speeds & elements, it does not work well for me at the track, I'll be adding a M3 rear subframe/LSD at some point
There is no suspension band-aid that is going to fix this - you need a proper mechanical LSD to really achieve a meaningful improvement. I would highly recommend a clutch type - there is a lot of noise about the cheaper priced torsen-style alternatives but frankly there is a reason that virtually any seriously prepared BMW racecar goes clutch type and it is that they simply outperform on the track by a big margin. My diffsonline unit made night and day difference and that was only on a 128 - it would have been even more helpful with more torque from a turbo platform.

-Mark
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      08-18-2020, 06:17 PM   #9
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I disagree, both rear wheels were laying down rubber on corner exit, the elsd was actually working very well

I have two other cars with LSD and if anything more inside wheel grip will make throttle out oversteer even worse
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      08-18-2020, 10:40 PM   #10
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Huh.....

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Originally Posted by imported_mega View Post
ediff on my car must be broken because in tight autocross conditions it's a one wheel wonder
.....did you get a new car?
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      08-19-2020, 06:16 AM   #11
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Quote:
Originally Posted by SKI-R View Post
Huh.....



.....did you get a new car?
HPDE is very different and it does not work well there and definitely needs a LSD for that

I changed my module coding and took out all the nannies and it seems to have helped quite a bit

and yes, new car too, now on coilovers with camber, square tires, better tires, big wing and splitter

that post was probably from my original car years ago on > 200tw tires very different setup
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      08-19-2020, 09:54 AM   #12
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Quote:
Originally Posted by imported_mega View Post
HPDE is very different and it does not work well there and definitely needs a LSD for that
I find this interesting as while I agree that autocross and HPDE have different requirements on the car, the violent transitions at autocross would usually make for more difficulty putting power down and more lean on a good LSD to do its part.

In any event, you are probably going to have to balance the want for a neutral car with enough rear tire to effectively put power down. If you have square 255s right now and go to a 275 on the rear, you are not losing any front end grip, but rather adding to the back - so presumably while the car might FEEL less well balanced, it shouldn't be slower in any part of the course. On the other hand, the extra rubber should allow you to put your foot into the throttle earlier and harder which should improve your times.

In my 128, traction was basically perfect on fresh 255 RE71Rs and I wasn't really hurting for corner exit grip, but could have taken more if I had it available under class rules. For a 135, the extra torque plus the way its delivered, I think a larger rear tire and a mechanical LSD is going to be pretty eye opening as to how much difference it can make.

-Mark
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      08-19-2020, 09:58 AM   #13
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for hpde it sure will be, I have wheel spin at 70mph on the track it's pretty crazy how bad it is

for AX I was getting enough inside wheel assist from elsd to break it loose easily, it was not spinning noticeably instead it kicked the back loose nearly instantly, I need to get my wheelspeed canbus feed working so I can really monitor wheel slip properly
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      08-20-2020, 03:24 PM   #14
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The same shit everyone else does to make these cars not handle like complete garbage:

- LSD
- Solid subframe bushings
- Rear toe arms
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      08-24-2020, 09:00 AM   #15
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what do rear toe arms do for me?
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      08-24-2020, 03:56 PM   #16
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Quote:
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what do rear toe arms do for me?
Allow you to get a correct alignment. As you get lower, you basically can get the correct camber measurement OR the correct toe measurement, but not both with the stock arms. Aftermarket arms will give you the adjustment range you need to optimize both.

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      08-24-2020, 04:07 PM   #17
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ohh ok, no need then I already have the rear aligned I was able to get 0 toe, barely

if I go any lower at all I will have to get the arms, but I have no plans on going lower
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      08-24-2020, 06:22 PM   #18
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ohh ok, no need then I already have the rear aligned I was able to get 0 toe, barely

if I go any lower at all I will have to get the arms, but I have no plans on going lower
0 toe is not very common for the rear of these cars (or actually almost any cars) in a competition setting. Most everybody would run at least some toe in, it will help with putting power down, something your thread suggests can be a challenge.

Generally a rear alignment for these cars in the neighborhood of -2.0 to -2.5 degrees and 1/8 to 1/4 total toe in is a good starting point.

-Mark
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      08-25-2020, 03:05 PM   #19
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i found my printout, my rear is at i'm at -2 rear and total toe in .21 degrees

front is -3.5 and 0 slight toe out, barely measurable. This was too much camber in the front for my setup I was not able to use pyrometer with 10 min between sessions, but there is more inside wear than outside, I would have taken some out on site but with such a small amount of time, we basically came off track and got back in grid
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      08-25-2020, 03:38 PM   #20
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Quote:
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i found my printout, my rear is at i'm at -2 rear and total toe in .21 degrees

front is -3.5 and 0 slight toe out, barely measurable. This was too much camber in the front for my setup I was not able to use pyrometer with 10 min between sessions, but there is more inside wear than outside, I would have taken some out on site but with such a small amount of time, we basically came off track and got back in grid
I wouldn't rush to take camber out in the front - it is generally impossible to get too much camber on an E8X/E9X and across the board many people have found that their times have improved as they have added camber. There have been some people who have said otherwise, but frankly I have never seen any race results from them, but all the people who have actually won in their various disciplines seem to maximize front camber.

I can tell you unequivocally that going from -2.8 degrees (before control arm modifications) to -3.6 degrees (after) made my car WAY faster at autocross. I also did not get any meaningful inside tire wear even doing some highway driving between events - you might want to quickly confirm that your bushings, wheel bearings, etc are all in good shape as slop anywhere in there could contribute to weird tire wear.

I was about the same as you in rear alignment, but I believe a bit more rear camber would make the car faster - I was always shooting for approximately a 1 degree difference between front/rear which necessitated rear toe arms.

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      08-25-2020, 04:51 PM   #21
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everything is brand new, and yes going from -2.8 to -3.5 made the car go from understeer to almost perfect however there is quite a bit of inside wear, it's not rolling over onto the outside. Next event I should be able to use a pyrometer

I am getting inside wear on the rear, due to wheelspin I suspect
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      08-25-2020, 08:10 PM   #22
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How did you set your ride height? I would try lowering the rear in 1/8" increments. There's not a lot of data on ride height from the rocker, but the rear approx 5/8" higher than the front seems to be pretty close.

Last edited by cwlo; 08-25-2020 at 08:37 PM..
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