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LSD causing understeer


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I recently put a rear LSD (friction type) in my 88 wagon. :banana: I was having problems before with both inside wheels spinning on tight and fast corners; however the handling was still pretty neutral.

 

With the LSD installed the spinning is gone, however I have a pretty good understeer going on when I apply power on corner exit. I guess this makes sense as both rear wheels are trying to drive the car straight.

 

Anyone else notice this? My 88 came stock with rear anti sway. What can I do to get it neutral again, go with an XT6 rear sway? Those things are like hen's teeth...

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I recently put a rear LSD (friction type) in my 88 wagon. :banana: I was having problems before with both inside wheels spinning on tight and fast corners; however the handling was still pretty neutral.

 

With the LSD installed the spinning is gone, however I have a pretty good understeer going on when I apply power on corner exit. I guess this makes sense as both rear wheels are trying to drive the car straight.

 

Anyone else notice this? My 88 came stock with rear anti sway. What can I do to get it neutral again, go with an XT6 rear sway? Those things are like hen's teeth...

You figured it out and yes the LSD will cause significant understeer compared to an open diff. I had the same issues with my Brat that I used for rallycross years ago. I did add a rear sway bar to my Brat but found that reducing speed before going into a turn and using less throttle in the turn works also. I would imagine a stiffer rear swaybar would help the situation. If you can't find an XT6 swaybar, check the Whiteline website and find a US re-seller (Rallitek in Portland is my suggestion). The Whiteline swaybar is a bit pricey but it's one of the best.
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You figured it out and yes the LSD will cause significant understeer compared to an open diff. I had the same issues with my Brat that I used for rallycross years ago. I did add a rear sway bar to my Brat but found that reducing speed before going into a turn and using less throttle in the turn works also. I would imagine a stiffer rear swaybar would help the situation. If you can't find an XT6 swaybar, check the Whiteline website and find a US re-seller (Rallitek in Portland is my suggestion). The Whiteline swaybar is a bit pricey but it's one of the best.

 

Thanks! I've been trying your suggestion about not using as much throttle and it seems to be working. It's funny, 'cause normally more power = more oversteer. Also, I find that when the traction is not as good (wet vs dry pavement) it doesn't push as much.

 

I'm a little concerned about slapping on a rear sway cause I don't want it to be too tail happy when off the throttle. Like if I do something dumb like lift the throttle in a turn and spin out like a 911...

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Boy, I can't say for sure whether the rear swaybar I installed on my Brat made it "tail-happy." I don't rallycross it anymore; it's become my "work" Brat. But in normal driving, there's no tendency for the rear to come around. The Brat is very well behaved.

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  • 3 weeks later...

A few days ago I installed XT6 front & rear bars, both 20mm; thanks John. The old bars were 19mm front, 18mm rear. The new bars reduced roll considerably. They also reduced the understeer, now it only pushes just a little bit. :banana: It's good now, I'm happy with it. I suppose I could put the 19mm back on the front but I'm going to try like it is for a while.

 

The difference in bar diameter might seem small but the stiffness is the 4th power of the diameter. My rear is (20/18)^4 = 152% and front (20/19)^4 = 123%.

 

Thanks for your input edrach!

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A few days ago I installed XT6 front & rear bars, both 20mm; thanks John. The old bars were 19mm front, 18mm rear. The new bars reduced roll considerably. They also reduced the understeer, now it only pushes just a little bit. :banana: It's good now, I'm happy with it. I suppose I could put the 19mm back on the front but I'm going to try like it is for a while.

 

The difference in bar diameter might seem small but the stiffness is the 4th power of the diameter. My rear is (20/18)^4 = 152% and front (20/19)^4 = 123%.

 

Thanks for your input edrach!

Your welcome. It's such a pleasure to see some closure in a thread. So often someone starts a thread, gets suggestions and you never hear what, if anything, worked out.
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do you notice a difference at all while driving normal...like commuting, rather than maxed out tearing it up? just curious, that is crazy that little bar was that noticeable.

 

Well the rear is much stiffer (152%) than the old one, and the front is not a bad improvement either. I did notice an immediate difference. The car feels much tighter around town, the steering input has a more immediate response. However on the bumpy back roads the car now tends to get bumped side to side when going over uneven roads; before the new bars the suspension would allow the car to track flat rather than the car following the side-to-side undulations of the road like it does now.

 

In terms of overall speed I think I did not gain that much. I could go almost as fast before but I did not feel like I was in as much control, especially during transitions in S-curves.

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  • 2 weeks later...

The XT6 front bar was rubbing on the lower control arm; the bends are a bit different. I put back on the 19mm original front, still 20mm XT6 on the rear. It seems great so far, a hint of understeer perhaps, but it seems "ideal" now.

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