Toe in rear, too little or too much
07-27-2009, 10:28 AM
#1
Melting Slicks
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Toe in rear, too little or too much
I am told to use 1/32 inch for a total of 1/16 Rear.
I had my car aligned today and he ended up giving me closer to 1/60 for a total of 1/30
Front was almost neutral but slightly Toe in
Q
How does car handle with less or more REAR toe in ?
I know toe out is BAD, but how does 1/64 inch toe handle compared to 1/32 ?
tia
Rune
I had my car aligned today and he ended up giving me closer to 1/60 for a total of 1/30
Front was almost neutral but slightly Toe in
Q
How does car handle with less or more REAR toe in ?
I know toe out is BAD, but how does 1/64 inch toe handle compared to 1/32 ?
tia
Rune
07-27-2009, 11:44 AM
#2
Melting Slicks
As you transfer weight to the outside tire, if it has more toe in, you get more (relatively speaking) understeer. This is because you are putting more weight on a rear tire that is pointed to the inside of the turn, which steers the rear of the car into the corner, and you have to increase your steering to match it. The term for this is "roll understeer" and most cars have some of it built into the baisic geometry. That is, as the car rolls, the outside tire toes in a very slight amount to increase the stability of the car... In order to avoid problems with roll oversteer, some c5z autocrossers used to run a lot of rear toe in to create more roll understeer... The height of the rear of the car makes a big difference in how much or how little roll understeer that you get. Lower it too much and you will find out about roll oversteer....
You are down in the mud as being able to feel much difference between this small amount and zero.
I usually change toe in 1/16 of an inch (total toe) increments, simply because it is hard to feel much less than that.
That said, as you get close to zero, because of bushing flex, toe can become more "edgy". That is, if you have a bit of toe in and go to a similar amount of toe out, because the bushings compress the other way, the effects of a small amount of toe change can be exaggerated, and you might notice a bit more difference.
It also depends on the tires you are running, some are more rubbery and tend to wander more as you go from toe in to toe out...
Suggest that you mark your tie rods, and if you find the back end being unruly, crank in about 1/6 of a turn (one flat on the nut) of toe in on each side.
You are down in the mud as being able to feel much difference between this small amount and zero.
I usually change toe in 1/16 of an inch (total toe) increments, simply because it is hard to feel much less than that.
That said, as you get close to zero, because of bushing flex, toe can become more "edgy". That is, if you have a bit of toe in and go to a similar amount of toe out, because the bushings compress the other way, the effects of a small amount of toe change can be exaggerated, and you might notice a bit more difference.
It also depends on the tires you are running, some are more rubbery and tend to wander more as you go from toe in to toe out...
Suggest that you mark your tie rods, and if you find the back end being unruly, crank in about 1/6 of a turn (one flat on the nut) of toe in on each side.
07-27-2009, 04:49 PM
#3
Melting Slicks
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Thanks, very informative.
With solid bushings from pfadt and R888 tires and sometimes Hoosiers, i feel the car is pushing a little too much on the front (understeer). then i used to have 1/16 on each side. (1.5 mm)
Now i will try with 0.5 mm and see how she does.
SPA and Nurburgring here i come!
Rune
With solid bushings from pfadt and R888 tires and sometimes Hoosiers, i feel the car is pushing a little too much on the front (understeer). then i used to have 1/16 on each side. (1.5 mm)
Now i will try with 0.5 mm and see how she does.
SPA and Nurburgring here i come!
Rune
07-27-2009, 07:07 PM
#4
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What shocks are you running? I seriously doubt you are pushing on corner exit due to toe settings you listed. I agree with Solo, but I just don't think you'll see much of a difference. Also, unless the Vette is different than other IRS cars I've owned(and I could be wrong not having the Vette very long)but flex in the rear bushings will allow more toe-in upon acceleration due to the wheels driving the A-arms forward.
I run an 1/8" total toe in the rear and the car works great. But again, I'm a new Vette pilot and could be wrong.
Don
I run an 1/8" total toe in the rear and the car works great. But again, I'm a new Vette pilot and could be wrong.
Don
07-27-2009, 11:16 PM
#7
Drifting
What sways are you running? If they are adjustable, and you have a push, soften the front or stiffen the rear a tad.....see if that helps.......but, you might try a bit of toe OUT in the front....say 1/8th to 3/16 total toe out....that might settle her down too.
Last edited by CP Thunder; 07-27-2009 at 11:20 PM.
07-27-2009, 11:33 PM
#8
Burning Brakes
You might also leave the rear toe as is and change the front to a slight toe out. This will give you a sharper/crisper turn-in and may alleviate the understeer you say you're experiencing.
Just a thought...
Just a thought...
07-28-2009, 07:19 AM
#9
Racer
Wait a minute...........you lost me here. Toe out in the front will make the car turn in quicker ? Doesn't the weight go to the outside wheel, and that wheel is now pointing against the turn as opposed to toe-in would bring the wheel on a tighter turning radius ? I don't know, just got through doing the alignment on the car myself and went with zero toe in the back, 1/16" toe-in on each side fo the front. According to GM specs for the C6Z06, 0.00 to 0.10 + toe for the front. Please set me straight on this.
07-28-2009, 09:42 AM
#10
Burning Brakes
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Wait a minute...........you lost me here. Toe out in the front will make the car turn in quicker ? Doesn't the weight go to the outside wheel, and that wheel is now pointing against the turn as opposed to toe-in would bring the wheel on a tighter turning radius ? I don't know, just got through doing the alignment on the car myself and went with zero toe in the back, 1/16" toe-in on each side fo the front. According to GM specs for the C6Z06, 0.00 to 0.10 + toe for the front. Please set me straight on this.
This explains it: http://www.davidfarmerstuff.com/Toe-Ackerman.pdf
07-28-2009, 10:06 AM
#11
Melting Slicks
Wait a minute...........you lost me here. Toe out in the front will make the car turn in quicker ? Doesn't the weight go to the outside wheel, and that wheel is now pointing against the turn as opposed to toe-in would bring the wheel on a tighter turning radius ? I don't know, just got through doing the alignment on the car myself and went with zero toe in the back, 1/16" toe-in on each side fo the front. According to GM specs for the C6Z06, 0.00 to 0.10 + toe for the front. Please set me straight on this.
A good friend who does vehicle dynamics for a living explained it this way. You can't generate lateral g until you get the slip angles up. Slip angles in the front get changed as fast as you can turn the steering wheel. Slip angles in the back don't change until after you generate lateral g. If the car understeers, then you can generate a change in lateral g faster and that's what governs transient response.
This is why you want some understeer particularily in an autocross car, where fast transient response is really important. Now don't confuse some understeer to something that pushes like a pig in steady state cornering. That is where tuning comes in, you want some understeer, that is you always want the front working a little bit harder than the back, but as I like to say,
"To be fast, you want the front end to bite and the back end to follow".
That type of setup will get you around the corners fast, and, since you have margin on the back end, you will be able to put down more power on corner exit. To my mind too many people try to make the car too netrual, or even loose, thinking that is a fast way around, when it really isn't...
07-28-2009, 11:51 AM
#12
Burning Brakes
Great follow-ups, thanks guys!!!
You guys are way smarter at that stuff than me, clearly. I'm more the driver than the scientist and only know what I've picked up over the years along with the physics that I know from always having been intrigued with how the universe works.
I of course, say all this and yet always used to set up my C5s with .01 thrust angle, 0 toe on all four corners and 1.5* neg. camber up front and 1* in back. Mainly because, while my cars spent MUCH of their life on track, I still drove them on the street too. Usually driving them to/from the track events they were in. I found the 0 toe, 1* neg. camber a nice compromise (certainly far from optimal) that worked for the C5.
The C6 is not too different but still different indeed.
You guys are way smarter at that stuff than me, clearly. I'm more the driver than the scientist and only know what I've picked up over the years along with the physics that I know from always having been intrigued with how the universe works.
I of course, say all this and yet always used to set up my C5s with .01 thrust angle, 0 toe on all four corners and 1.5* neg. camber up front and 1* in back. Mainly because, while my cars spent MUCH of their life on track, I still drove them on the street too. Usually driving them to/from the track events they were in. I found the 0 toe, 1* neg. camber a nice compromise (certainly far from optimal) that worked for the C5.
The C6 is not too different but still different indeed.
07-28-2009, 03:01 PM
#13
Racer
cgh1 is correct, toe out in the front improves the transient response, although it is counterinutitive. Things that increase understeer (bigger bars and stiffer front shocks, as well as toe out in the front) improve the transient response and turn in. They can (in too large a dose) also make the car push like a pig, but it will be a pig that turns in really fast and THEN plows like a pig...
A good friend who does vehicle dynamics for a living explained it this way. You can't generate lateral g until you get the slip angles up. Slip angles in the front get changed as fast as you can turn the steering wheel. Slip angles in the back don't change until after you generate lateral g. If the car understeers, then you can generate a change in lateral g faster and that's what governs transient response.
This is why you want some understeer particularily in an autocross car, where fast transient response is really important. Now don't confuse some understeer to something that pushes like a pig in steady state cornering. That is where tuning comes in, you want some understeer, that is you always want the front working a little bit harder than the back, but as I like to say,
"To be fast, you want the front end to bite and the back end to follow".
That type of setup will get you around the corners fast, and, since you have margin on the back end, you will be able to put down more power on corner exit. To my mind too many people try to make the car too netrual, or even loose, thinking that is a fast way around, when it really isn't...
A good friend who does vehicle dynamics for a living explained it this way. You can't generate lateral g until you get the slip angles up. Slip angles in the front get changed as fast as you can turn the steering wheel. Slip angles in the back don't change until after you generate lateral g. If the car understeers, then you can generate a change in lateral g faster and that's what governs transient response.
This is why you want some understeer particularily in an autocross car, where fast transient response is really important. Now don't confuse some understeer to something that pushes like a pig in steady state cornering. That is where tuning comes in, you want some understeer, that is you always want the front working a little bit harder than the back, but as I like to say,
"To be fast, you want the front end to bite and the back end to follow".
That type of setup will get you around the corners fast, and, since you have margin on the back end, you will be able to put down more power on corner exit. To my mind too many people try to make the car too netrual, or even loose, thinking that is a fast way around, when it really isn't...
07-28-2009, 03:12 PM
#14
Racer
Great follow-ups, thanks guys!!!
You guys are way smarter at that stuff than me, clearly. I'm more the driver than the scientist and only know what I've picked up over the years along with the physics that I know from always having been intrigued with how the universe works.
I of course, say all this and yet always used to set up my C5s with .01 thrust angle, 0 toe on all four corners and 1.5* neg. camber up front and 1* in back. Mainly because, while my cars spent MUCH of their life on track, I still drove them on the street too. Usually driving them to/from the track events they were in. I found the 0 toe, 1* neg. camber a nice compromise (certainly far from optimal) that worked for the C5.
The C6 is not too different but still different indeed.
You guys are way smarter at that stuff than me, clearly. I'm more the driver than the scientist and only know what I've picked up over the years along with the physics that I know from always having been intrigued with how the universe works.
I of course, say all this and yet always used to set up my C5s with .01 thrust angle, 0 toe on all four corners and 1.5* neg. camber up front and 1* in back. Mainly because, while my cars spent MUCH of their life on track, I still drove them on the street too. Usually driving them to/from the track events they were in. I found the 0 toe, 1* neg. camber a nice compromise (certainly far from optimal) that worked for the C5.
The C6 is not too different but still different indeed.
