Lsd Swap, Understeer, And Rear Toe Angle
05-21-2004, 12:03 AM
#1
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Thread Starter
Join Date: Dec 2003
Location: Corvallis, Oregon
Posts: 419
I finally got around to swapping in an LSD in my 87 base FC. Its other mods were streetport, ported intake manifold, ram/cold air intake, five lug swap, springs and struts, 300zx wheels and 225/50/60 summer tires, a GXL rear anti-sway bar, rear steer eliminator bushings, front camber adjustment slots, aluminum hood swap and about 200 pounds of crap removed from the chassis.
I had the suspension dialed to be pretty neutral before the swap. Some light trail braking could be used to counter the natural turn-in understeer on turn entry, and then all braking could be released to allow the car to glide tightly through a turn at around .8-.9G. But power could _never_ be put down early in a turn, unless I wanted to spin out into a ditch or just spin the inside rear wheel.
So I put a GXL LSD in the other day and it had 15 foot-pounds of static friction between the output shafts, measured with my torque wrench. It had about 110k miles on it and was probably half worn-out, but I wasn't complaining. The open diff had less than one foot pound of friction between the shafts, so it was an improvement.
After installation, the rear felt MUCH more stable, like I put a rudder on the car or something. Power could be put down right away, almost before the apex of a turn, and if traction broke, the car would just go sideways slightly but not spin the inside wheel like before. But the LSD caused some understeer to come back. The car wouldn't glide as hard through a turn like before.
The fix: adding a tad more rear toe-in using the adjustment cams on the front of the rear trailing arms. This increased the slip angle of the outside rear tire in a turn, reducing understeer. The car is great now and just like before, but with that stable feeling that it never had. I can drive it pretty damn hard now and wring it out like the sports car it should be.
So anyways, if anyone cares, when you swap in an LSD to your base model FC, you can get rid of some of the understeer it causes by dialing in some toe-in to the rear wheels.
I had the suspension dialed to be pretty neutral before the swap. Some light trail braking could be used to counter the natural turn-in understeer on turn entry, and then all braking could be released to allow the car to glide tightly through a turn at around .8-.9G. But power could _never_ be put down early in a turn, unless I wanted to spin out into a ditch or just spin the inside rear wheel.
So I put a GXL LSD in the other day and it had 15 foot-pounds of static friction between the output shafts, measured with my torque wrench. It had about 110k miles on it and was probably half worn-out, but I wasn't complaining. The open diff had less than one foot pound of friction between the shafts, so it was an improvement.
After installation, the rear felt MUCH more stable, like I put a rudder on the car or something. Power could be put down right away, almost before the apex of a turn, and if traction broke, the car would just go sideways slightly but not spin the inside wheel like before. But the LSD caused some understeer to come back. The car wouldn't glide as hard through a turn like before.
The fix: adding a tad more rear toe-in using the adjustment cams on the front of the rear trailing arms. This increased the slip angle of the outside rear tire in a turn, reducing understeer. The car is great now and just like before, but with that stable feeling that it never had. I can drive it pretty damn hard now and wring it out like the sports car it should be.
So anyways, if anyone cares, when you swap in an LSD to your base model FC, you can get rid of some of the understeer it causes by dialing in some toe-in to the rear wheels.
05-21-2004, 01:36 AM
#2
Senior Member
Join Date: Nov 2003
Location: Woodstock, Georgia
Posts: 583
How about on an '88 T2? I've heard all this stuff about there being this toe thing in the rear end that'll turn the tires inward or some crap, similar to the all-wheel steering of a Mitsu 3000GT VR-4 or 300Z.
What's up with that? My professional drift buddy last night was saying how me having aftermarket suspension thats set stiff helps because the toe on the rear tires won't even "activate" until a great deal of pressure is put down on the shocks or something. *shrugs* I'm clueless.
What's up with that? My professional drift buddy last night was saying how me having aftermarket suspension thats set stiff helps because the toe on the rear tires won't even "activate" until a great deal of pressure is put down on the shocks or something. *shrugs* I'm clueless.
05-21-2004, 01:53 AM
#3
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Join Date: Jul 2002
Posts: 2,315
that is a completely different topic, what your 'pro' buddy was talking about was the dtss system. it's called dynamic track steering system or some b.s. do a search and many good topics will come up on it. fluid dynamics eliminated it because it can at times make the car 'unpredictable.'
fluid, my first car was a gxl and i never noticed how much of a difference having a limited slip makes until now. i now have a sport and it's night and day. i'm looking forward to swap in my turbo rear soon. good info
fluid, my first car was a gxl and i never noticed how much of a difference having a limited slip makes until now. i now have a sport and it's night and day. i'm looking forward to swap in my turbo rear soon. good info
05-21-2004, 10:37 AM
#6
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Join Date: May 2002
Location: California
Posts: 22,465
yeah my t2 really had that stable feeling, it never ever felt bad ever. even spinning into the bushes it felt composed
why do you have a big rear bar and a small front? i'm reading about the speedsource its cars and they dont run a rear bar at all?
why do you have a big rear bar and a small front? i'm reading about the speedsource its cars and they dont run a rear bar at all?
05-21-2004, 04:14 PM
#7
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Thread Starter
Join Date: Dec 2003
Location: Corvallis, Oregon
Posts: 419
Spring rates, shock stiffness, anti-sway bar thickness, front and rear camber, rear toe angle, LSD or no LSD, tire pressures, and front / rear weight bias affect a car's tendency to understeer or oversteer.
With stiffer rear springs or shocks, you can eliminate the rear anti-sway bar and keep the neutral handling. Generally, a thicker rear bar will cause the rear to rotate more in a hard turn. If it is too stiff, the rear will rotate all the way around in a spin (oversteer). Stock FCs (all that I have driven, at least) have some pretty substantial understeer before about .5 g lateral acceleration when the DTSS kicks in and adds some toe-in to the outside rear hub.
You can use many combinations of the items mentioned above to affect the car's neutrality, and if you already have comparitively stiff rear springs / shocks, you might be able to get rid of the rear anti-sway bar. Also, track cars usually get set up to have some slight understeer while autocross cars (mine) can get away with having a loose rear end due to the lower speeds on the course and smaller consequences of spinning out.
I ran w/o the rear bar for a couple weeks, and the FC felt like my old Integra as far as handling balance. I have tokico HP nonadjustable struts and Eibach springs, so I was unable to choose a stiffer rear shock setting or spring rate. Adding the stiffer rear anti sway bar not only reduced body roll, but helped the car to rotate around turns instead of pushing and plowing.
With stiffer rear springs or shocks, you can eliminate the rear anti-sway bar and keep the neutral handling. Generally, a thicker rear bar will cause the rear to rotate more in a hard turn. If it is too stiff, the rear will rotate all the way around in a spin (oversteer). Stock FCs (all that I have driven, at least) have some pretty substantial understeer before about .5 g lateral acceleration when the DTSS kicks in and adds some toe-in to the outside rear hub.
You can use many combinations of the items mentioned above to affect the car's neutrality, and if you already have comparitively stiff rear springs / shocks, you might be able to get rid of the rear anti-sway bar. Also, track cars usually get set up to have some slight understeer while autocross cars (mine) can get away with having a loose rear end due to the lower speeds on the course and smaller consequences of spinning out.
I ran w/o the rear bar for a couple weeks, and the FC felt like my old Integra as far as handling balance. I have tokico HP nonadjustable struts and Eibach springs, so I was unable to choose a stiffer rear shock setting or spring rate. Adding the stiffer rear anti sway bar not only reduced body roll, but helped the car to rotate around turns instead of pushing and plowing.
05-21-2004, 05:38 PM
#8
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Join Date: Nov 2003
Location: Woodstock, Georgia
Posts: 583
I'm using 5-way adjustable Tokico's and I have them set at 4, and I'm using Eibach springs too. I was cornering a couple days ago and I wasn't pushing myself, mainly cause it was my 1st time on the road, but later on when I pushed myelf a little harder, I could feel the car understeer on the 90 degree turns. Should I soften up the front or something? Loose front stiff back = less understeer/more oversteer?
05-21-2004, 06:29 PM
#9
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Join Date: May 2002
Location: California
Posts: 22,465
Originally Posted by Lionheart240' date='May 21 2004, 02:38 PM
I'm using 5-way adjustable Tokico's and I have them set at 4, and I'm using Eibach springs too. I was cornering a couple days ago and I wasn't pushing myself, mainly cause it was my 1st time on the road, but later on when I pushed myelf a little harder, I could feel the car understeer on the 90 degree turns. Should I soften up the front or something? Loose front stiff back = less understeer/more oversteer?
05-21-2004, 06:31 PM
#10
Senior Member
Join Date: May 2002
Location: California
Posts: 22,465
Originally Posted by Fluid Dynamics' date='May 21 2004, 01:14 PM
Spring rates, shock stiffness, anti-sway bar thickness, front and rear camber, rear toe angle, LSD or no LSD, tire pressures, and front / rear weight bias affect a car's tendency to understeer or oversteer.
With stiffer rear springs or shocks, you can eliminate the rear anti-sway bar and keep the neutral handling. Generally, a thicker rear bar will cause the rear to rotate more in a hard turn. If it is too stiff, the rear will rotate all the way around in a spin (oversteer). Stock FCs (all that I have driven, at least) have some pretty substantial understeer before about .5 g lateral acceleration when the DTSS kicks in and adds some toe-in to the outside rear hub.
You can use many combinations of the items mentioned above to affect the car's neutrality, and if you already have comparitively stiff rear springs / shocks, you might be able to get rid of the rear anti-sway bar. Also, track cars usually get set up to have some slight understeer while autocross cars (mine) can get away with having a loose rear end due to the lower speeds on the course and smaller consequences of spinning out.
I ran w/o the rear bar for a couple weeks, and the FC felt like my old Integra as far as handling balance. I have tokico HP nonadjustable struts and Eibach springs, so I was unable to choose a stiffer rear shock setting or spring rate. Adding the stiffer rear anti sway bar not only reduced body roll, but helped the car to rotate around turns instead of pushing and plowing.
With stiffer rear springs or shocks, you can eliminate the rear anti-sway bar and keep the neutral handling. Generally, a thicker rear bar will cause the rear to rotate more in a hard turn. If it is too stiff, the rear will rotate all the way around in a spin (oversteer). Stock FCs (all that I have driven, at least) have some pretty substantial understeer before about .5 g lateral acceleration when the DTSS kicks in and adds some toe-in to the outside rear hub.
You can use many combinations of the items mentioned above to affect the car's neutrality, and if you already have comparitively stiff rear springs / shocks, you might be able to get rid of the rear anti-sway bar. Also, track cars usually get set up to have some slight understeer while autocross cars (mine) can get away with having a loose rear end due to the lower speeds on the course and smaller consequences of spinning out.
I ran w/o the rear bar for a couple weeks, and the FC felt like my old Integra as far as handling balance. I have tokico HP nonadjustable struts and Eibach springs, so I was unable to choose a stiffer rear shock setting or spring rate. Adding the stiffer rear anti sway bar not only reduced body roll, but helped the car to rotate around turns instead of pushing and plowing.