can static toe settings combat bumpsteer induced push??
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From: MA
can static toe settings combat bumpsteer induced push??
my experiences this year seem to indicate yes. as my car got lower, smaller amounts of front toe-out would cause more understeer mid-corner. ie, at less then 1/16" total front toe-out the car would be fine with a 4.75" ride height. adding another 1/16" of toe-out would cause the car to pick up a mild mid-corner push (more-so then what it already has). at higher ride heights the car seemed less sensitive to toe changes.
this seems to hold consistant with varying amounts of bumpsteer as ride height changes. lower ride heights move the car into a steeper portion of the bumpsteer curve, higher ride heights obviously put you in the shallower portion of the curve. iirc, the eg chassis suffers from toe-out in bump and toe-in in droop. a high static toe-out setting would then be further exaggerated on the outside front as the car rolls while at the same time being dialed out on the inside front. i think it's also safe to assume that the outside front will toe out faster then the inside front would toe-in. where am i going with all this??
when looking at the stock ackerman affect, and taking into account what i said above, it would seem logical that with high static toe-out (more then 1/32" total, for arguments sake) in the front you could essentially increase your total toe out dramatically when running at a low ride height. essentially, you start out with 1/8" total toe-out, but after feeding in 10* of steering lock (and the toe change due to the stock ackerman affect) and factoring in the amount of body roll and corresponding outside front toe-out change (and significantly smaller inside toe-in change) you end up with a substantially higher total toe-out.
this may not seem bad at first, but it would seem that since the outside front determines the path the front of the car takes, if you increased your total toe-out too far your inside front is forced to slide sideways (or at least outside it's optimal slip angle) which would increase the chances of spinning your inside front and deny you your ultimate front grip.
so now the question is, if this theory is true, could toe in combat this problem? true, the car might turn in a little slower but if it's generating more grip at mid-corner to track out, i don't see this as a problem. shock settings and swaybars can effect turn-in response as well as roll centre's, so this side effect could probably be dialed back out relatively easily. am i totally off base here? general convention says toe-out the front, but does that assume zero bump steer or an SCCA legal 5"+ ride height?? feedback and flames are welcome.
nate-who isn't really worried about, just curious.
this seems to hold consistant with varying amounts of bumpsteer as ride height changes. lower ride heights move the car into a steeper portion of the bumpsteer curve, higher ride heights obviously put you in the shallower portion of the curve. iirc, the eg chassis suffers from toe-out in bump and toe-in in droop. a high static toe-out setting would then be further exaggerated on the outside front as the car rolls while at the same time being dialed out on the inside front. i think it's also safe to assume that the outside front will toe out faster then the inside front would toe-in. where am i going with all this??
when looking at the stock ackerman affect, and taking into account what i said above, it would seem logical that with high static toe-out (more then 1/32" total, for arguments sake) in the front you could essentially increase your total toe out dramatically when running at a low ride height. essentially, you start out with 1/8" total toe-out, but after feeding in 10* of steering lock (and the toe change due to the stock ackerman affect) and factoring in the amount of body roll and corresponding outside front toe-out change (and significantly smaller inside toe-in change) you end up with a substantially higher total toe-out.
this may not seem bad at first, but it would seem that since the outside front determines the path the front of the car takes, if you increased your total toe-out too far your inside front is forced to slide sideways (or at least outside it's optimal slip angle) which would increase the chances of spinning your inside front and deny you your ultimate front grip.
so now the question is, if this theory is true, could toe in combat this problem? true, the car might turn in a little slower but if it's generating more grip at mid-corner to track out, i don't see this as a problem. shock settings and swaybars can effect turn-in response as well as roll centre's, so this side effect could probably be dialed back out relatively easily. am i totally off base here? general convention says toe-out the front, but does that assume zero bump steer or an SCCA legal 5"+ ride height?? feedback and flames are welcome.
nate-who isn't really worried about, just curious.
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From: Atlanta, GA
Re: can static toe settings combat bumpsteer induced push?? (solo-x)
I concur. Toe out upfront is used for turn-in, and it will adversely effect mid corner grip. Ackerman in racing situations is bad...some racecars will actually goto negative ackerman.
Example, me in Topeka. 1/2" toe out is BAD... It will also cause your street tires to get *odd* wear patterns on the way home to Florida
Example, me in Topeka. 1/2" toe out is BAD... It will also cause your street tires to get *odd* wear patterns on the way home to Florida
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From: MA
Re: can static toe settings combat bumpsteer induced push?? (PseudoRealityX)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by PseudoRealityX »</TD></TR><TR><TD CLASS="quote">I concur. Toe out upfront is used for turn-in, and it will adversely effect mid corner grip. Ackerman in racing situations is bad...some racecars will actually goto negative ackerman.
Example, me in Topeka. 1/2" toe out is BAD... It will also cause your street tires to get *odd* wear patterns on the way home to Florida</TD></TR></TABLE>
but how does that relate to bumpsteer? i assume that there is a point where the tires will be pointed in a direction in relation to each other that will optimize mid-corner grip. in a situation where there is a lot of toe-out bumpsteer combined with ackerman i would think that a small amount of toe-in may actually get you closer to this ideal then static toe-out or even zero toe.
and i can't entirely agree that ackerman is a "bad" thing. why do you say it is?
fwiw, large steering angles at low speeds (walking speed) in dirt parking lots with 1/8" total toe out made my inside front scrub quite noticeably. that's with zero body roll.
nate
Example, me in Topeka. 1/2" toe out is BAD... It will also cause your street tires to get *odd* wear patterns on the way home to Florida
</TD></TR></TABLE>but how does that relate to bumpsteer? i assume that there is a point where the tires will be pointed in a direction in relation to each other that will optimize mid-corner grip. in a situation where there is a lot of toe-out bumpsteer combined with ackerman i would think that a small amount of toe-in may actually get you closer to this ideal then static toe-out or even zero toe.
and i can't entirely agree that ackerman is a "bad" thing. why do you say it is?
fwiw, large steering angles at low speeds (walking speed) in dirt parking lots with 1/8" total toe out made my inside front scrub quite noticeably. that's with zero body roll.
nate
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From: Atlanta, GA
Re: can static toe settings combat bumpsteer induced push?? (solo-x)
From a buddy of mine who I showed this to...
"For a car racing around, the outside wheel has a lot more weight on it than the inside, and the optimum slip angle for the outside wheel is greater than for the inside. So, if you have the wheels pointed in the right direction for 0 slip(100% ackerman), the with the outside wheel sliping more than the inside, you need the wheels parrallel or perhaps "toed in" to get the path after slip to be the same as 100% ackerman with zero slip. Bump steer of course effects this, and since he's getting overall roll toe out, then he is gaining more ackerman effect on roll, which means static toe-in can be a good comprimise to get the wheels pointed in the right direction in the middle of the turn.
Bottom line is, you need to look at the interaction of the ackerman and bumpsteer to get the wheels pointed in the right way, which will mean the outside wheel will be at more slip than the inside. How much more slip? can't say without tire data, could it be enough that you need a net toe-in on the front mid-corner? possibly, but that might be a bit much, however a little static toe-in could result in the wheels being pointed the right way in the middle of a corner.'
Better than I could have explained it for sure.
"For a car racing around, the outside wheel has a lot more weight on it than the inside, and the optimum slip angle for the outside wheel is greater than for the inside. So, if you have the wheels pointed in the right direction for 0 slip(100% ackerman), the with the outside wheel sliping more than the inside, you need the wheels parrallel or perhaps "toed in" to get the path after slip to be the same as 100% ackerman with zero slip. Bump steer of course effects this, and since he's getting overall roll toe out, then he is gaining more ackerman effect on roll, which means static toe-in can be a good comprimise to get the wheels pointed in the right direction in the middle of the turn.
Bottom line is, you need to look at the interaction of the ackerman and bumpsteer to get the wheels pointed in the right way, which will mean the outside wheel will be at more slip than the inside. How much more slip? can't say without tire data, could it be enough that you need a net toe-in on the front mid-corner? possibly, but that might be a bit much, however a little static toe-in could result in the wheels being pointed the right way in the middle of a corner.'
Better than I could have explained it for sure.
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From: MA
Re: can static toe settings combat bumpsteer induced push?? (PseudoRealityX)
wow. that explains it very well indeed. now the difficult part, finding the ever illusive "ideal" point for front static toe setting. 
i've tried most things on the negative end of the spectrum, now i guess i'll try some things on the positive end. i'd be interested in hearing what your friend has to say about the dynamic toe change of the rear suspension on these pigs too.
nate
i've tried most things on the negative end of the spectrum, now i guess i'll try some things on the positive end. i'd be interested in hearing what your friend has to say about the dynamic toe change of the rear suspension on these pigs too.nate
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From: Atlanta, GA
Re: can static toe settings combat bumpsteer induced push?? (solo-x)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by solo-x »</TD></TR><TR><TD CLASS="quote">i'd be interested in hearing what your friend has to say about the dynamic toe change of the rear suspension on these pigs too.
nate</TD></TR></TABLE>
What specifics can you give me? I'm interested out of curiosity. And Jim won't be back till Monday... he went home(and to an autocross) for the weekend. I'll definately show this to him when he gets back.
This is actually something I've been talking to him for a while about after my experiences at Nationals.....might try something fairly dramatic to get rid of the push associated with my big front bar on the MR2. I can deal with less than razor sharp turn-in with my driving, but getting around steady state stuff is where I felt my car could be a lot faster....even with all the camber I could ever want.
nate</TD></TR></TABLE>
What specifics can you give me? I'm interested out of curiosity. And Jim won't be back till Monday... he went home(and to an autocross) for the weekend. I'll definately show this to him when he gets back.
This is actually something I've been talking to him for a while about after my experiences at Nationals.....might try something fairly dramatic to get rid of the push associated with my big front bar on the MR2. I can deal with less than razor sharp turn-in with my driving, but getting around steady state stuff is where I felt my car could be a lot faster....even with all the camber I could ever want.
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From: MA
Re: can static toe settings combat bumpsteer induced push?? (PseudoRealityX)
well, other then toe-in on compression and toe-out in droop there really isn't anythig more specific. i'm just wondering if you could get the car low enough to get really far into the rear bumpsteer curve you might be able to excede the outside tire's slip angle by running more rear toe in. however, i'd bet with both front and rear toe in (particularly enough rear toe in to acheive what i'm talking about) the car wouldn't ever want to turn in, so the mid-corner push may (big assumption here) be fixed, but now the car doesn't turn in for ****. does anyone else have any opinions, or should jesse and me just continue this conversation in im's?
nate
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From: Shiny side up dammit, MO
Re: can static toe settings combat bumpsteer induced push?? (solo-x)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by solo-x »</TD></TR><TR><TD CLASS="quote"> does anyone else have any opinions, or should jesse and me just continue this conversation in im's?
nate</TD></TR></TABLE>
no. i am interested in this as well. you make some interesting points, and while i don't have quite the comprehension of slip angle and the like, i think i understand what's goin' on.
but it is my opinion that the amounts of toe-in required for this theory (when applied to our cars) are soo negligable that it would be just as well to zero the toe out. and, now correct me if i wrong here 'cause i may be wrong, couldn't you control the amount of toe change by effectively limiting the travel of the suspension in the rear? how much toe change is there at the spring rates we (nate in particular since he runs ridiculous spring rates ) run. 0.05? 0.005? 0.0005?
and aren't we also forgetting that we need to be able to control the deflection of that rear trailing arm bushing to the nth degree to really be able to test this stuff?
personally i'm more concerned with trying to achieve more caster up front so i won't have to run so low to get the camber i want, but that's just me.
nate</TD></TR></TABLE>
no. i am interested in this as well. you make some interesting points, and while i don't have quite the comprehension of slip angle and the like, i think i understand what's goin' on.
but it is my opinion that the amounts of toe-in required for this theory (when applied to our cars) are soo negligable that it would be just as well to zero the toe out. and, now correct me if i wrong here 'cause i may be wrong, couldn't you control the amount of toe change by effectively limiting the travel of the suspension in the rear? how much toe change is there at the spring rates we (nate in particular since he runs ridiculous spring rates
) run. 0.05? 0.005? 0.0005?and aren't we also forgetting that we need to be able to control the deflection of that rear trailing arm bushing to the nth degree to really be able to test this stuff?
personally i'm more concerned with trying to achieve more caster up front so i won't have to run so low to get the camber i want, but that's just me.
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From: Atlanta, GA
Re: can static toe settings combat bumpsteer induced push?? (carl_aka_carlos)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by carl_aka_carlos »</TD></TR><TR><TD CLASS="quote">
personally i'm more concerned with trying to achieve more caster up front so i won't have to run so low to get the camber i want, but that's just me. </TD></TR></TABLE>
But then again, when you can play with a lot of suspension pieces, caster isn't always a great thing.
It's variable by how much you turn the wheel. More dynamic camber on the tighter curves. A long fast sweeper will get little camber gain from caster, while a tight 120 or 180 will get you a lot more.
Plus, it effects weight jacking.
Of course, I know of some faster prepared cars that have come the conclusion that caster IS a good solution for autocross situations.
personally i'm more concerned with trying to achieve more caster up front so i won't have to run so low to get the camber i want, but that's just me. </TD></TR></TABLE>
But then again, when you can play with a lot of suspension pieces, caster isn't always a great thing.
It's variable by how much you turn the wheel. More dynamic camber on the tighter curves. A long fast sweeper will get little camber gain from caster, while a tight 120 or 180 will get you a lot more.
Plus, it effects weight jacking.
Of course, I know of some faster prepared cars that have come the conclusion that caster IS a good solution for autocross situations.
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Re: can static toe settings combat bumpsteer induced push?? (PseudoRealityX)
What's interesting is what Carrol Smith found. In one of his early books, he said, scientifically, less Ackerman is better, and he went on to say why.
Fast forward to his last book, Engineer To Win. They finally took a car to the track and played around with Ackerman settings. Guess what? The more Ackerman they set up, the faster the car was, and the more comfortable to the driver (probably the two are related.) Granted this was on a "real" race car, not our weenie production-based cars, but still....
Fast forward to his last book, Engineer To Win. They finally took a car to the track and played around with Ackerman settings. Guess what? The more Ackerman they set up, the faster the car was, and the more comfortable to the driver (probably the two are related.) Granted this was on a "real" race car, not our weenie production-based cars, but still....
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From: Shiny side up dammit, MO
Re: can static toe settings combat bumpsteer induced push?? (PseudoRealityX)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by PseudoRealityX »</TD></TR><TR><TD CLASS="quote">
But then again, when you can play with a lot of suspension pieces, caster isn't always a great thing.
It's variable by how much you turn the wheel. More dynamic camber on the tighter curves. A long fast sweeper will get little camber gain from caster, while a tight 120 or 180 will get you a lot more.
Plus, it effects weight jacking.
Of course, I know of some faster prepared cars that have come the conclusion that caster IS a good solution for autocross situations.</TD></TR></TABLE>
i understand that caster affects camber dynamically but what i'm saying is that I could get away with only running ~2* of negative camber if I had the ability to gain more caster, especially with my soft suspension.
But then again, when you can play with a lot of suspension pieces, caster isn't always a great thing.
It's variable by how much you turn the wheel. More dynamic camber on the tighter curves. A long fast sweeper will get little camber gain from caster, while a tight 120 or 180 will get you a lot more.
Plus, it effects weight jacking.
Of course, I know of some faster prepared cars that have come the conclusion that caster IS a good solution for autocross situations.</TD></TR></TABLE>
i understand that caster affects camber dynamically but what i'm saying is that I could get away with only running ~2* of negative camber if I had the ability to gain more caster, especially with my soft suspension.
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