Camber, Caster, KPI, Steering Angle, AND YOU!
Nov 22, 2016, 10:32 AM
#1
Camber, Caster, KPI, Steering Angle, AND YOU!
Hey guys, ever wonder what adding caster really does? Beyond just knowing you probably don't have enough that is. Also you hear Kingpin inclination (KPI) takes away from camber while Caster adds it in steering. But at what rate?
Well, here you go. This is the equation for camber with regards to caster, steering angle, and kingpin inclination. Found online but have seen multiple times. I verified the numbers are accurate with a 3D model and brute force on a couple examples but equations and excel are certainly much easier.
One of the more traditional ways to go and ASP/STU legal, gives about 5.5deg of caster, ~-4deg camber, ~18deg of KPI. STU might run less camber, but the rate of changes remains constant. You can see there's a big jump from 0deg steering to 10deg steering where caster has its biggest change. By 20deg KPI is starting to have a big effect and by -30deg its overwhelming the change by caster. 30deg of steering is a big angle on Evos, not sure where we actually are physically limited but I would guess this is around the limit.
For a proper SM car, around 7deg of caster is possible now and soon I'll be up to 8deg. I noticed this year I was really hammering the inside tire with wheel spin so thinking about how to run less static camber. With 8deg camber, I think I can get away with only 3deg and maybe less (will elaborate below) to improve braking, accel, and tire wear. Net effect, faster car.
Camber gain in roll isn't tackled here, but stock uprights on heavily lowered cars are definitely in the camber loss range of bump or near it. My models are showing 2-3deg or roll is losing 2-3deg of camber, pretty much 1:1 loss. My setup with high KPI but also high slider axis angle, along with 2" of roll correction is closer to 0.5deg lost camber per deg of roll, or 0.5:1. So looking at the chart in 20 and 30% steering angles, I need less flat camber cause I lose significantly less in roll.
I'm actually pretty happy with where I'm getting on the setup possibilities of a McPherson Strut setup. Its not as good as proper SLA (Modeling that one too, super exciting possibility), but we can do better than what we're given. Look at the fast Porsches, Mustangs, and BMWs, they're all in that 8-10deg range of caster though I don't know what KPI they have.
Well, here you go. This is the equation for camber with regards to caster, steering angle, and kingpin inclination. Found online but have seen multiple times. I verified the numbers are accurate with a 3D model and brute force on a couple examples but equations and excel are certainly much easier.
One of the more traditional ways to go and ASP/STU legal, gives about 5.5deg of caster, ~-4deg camber, ~18deg of KPI. STU might run less camber, but the rate of changes remains constant. You can see there's a big jump from 0deg steering to 10deg steering where caster has its biggest change. By 20deg KPI is starting to have a big effect and by -30deg its overwhelming the change by caster. 30deg of steering is a big angle on Evos, not sure where we actually are physically limited but I would guess this is around the limit.
For a proper SM car, around 7deg of caster is possible now and soon I'll be up to 8deg. I noticed this year I was really hammering the inside tire with wheel spin so thinking about how to run less static camber. With 8deg camber, I think I can get away with only 3deg and maybe less (will elaborate below) to improve braking, accel, and tire wear. Net effect, faster car.
Camber gain in roll isn't tackled here, but stock uprights on heavily lowered cars are definitely in the camber loss range of bump or near it. My models are showing 2-3deg or roll is losing 2-3deg of camber, pretty much 1:1 loss. My setup with high KPI but also high slider axis angle, along with 2" of roll correction is closer to 0.5deg lost camber per deg of roll, or 0.5:1. So looking at the chart in 20 and 30% steering angles, I need less flat camber cause I lose significantly less in roll.
I'm actually pretty happy with where I'm getting on the setup possibilities of a McPherson Strut setup. Its not as good as proper SLA (Modeling that one too, super exciting possibility), but we can do better than what we're given. Look at the fast Porsches, Mustangs, and BMWs, they're all in that 8-10deg range of caster though I don't know what KPI they have.
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Construct (Nov 22, 2016)
Nov 22, 2016, 12:27 PM
#2
Interesting regarding camber loss and bump. Makes a better case for defeating roll with stiff springs.
Your kit with 2" of correction is huge compared to just a Whiteline kit
And this would allow for less stiff springs and or softer sway-bar with the camber loss ratio. Allowing more suspension independence.
Your kit with 2" of correction is huge compared to just a Whiteline kit
And this would allow for less stiff springs and or softer sway-bar with the camber loss ratio. Allowing more suspension independence.
Nov 22, 2016, 01:10 PM
#3
Yeah, we've all heard how SLA has real camber gain in bump and the generic benefits but what I care about is what the car does in roll since that's what we're really trying to control. If there is camber gain in bump, that means theres also camber loss in droop. So, whole car rolls but inside looses negative camber, outside gains neg camber, and both tires work harder.
I should do some screen shots and plots of the camber in my models in roll to show the gains/loss and why we have to start with -4deg on our compromised setups. It works, but its not as good as it could be for sure.
BTW, 4 sets are gone, 6 left at the initial batch price!
I should do some screen shots and plots of the camber in my models in roll to show the gains/loss and why we have to start with -4deg on our compromised setups. It works, but its not as good as it could be for sure.
BTW, 4 sets are gone, 6 left at the initial batch price!
Nov 22, 2016, 01:15 PM
#4
EvoM Guru
iTrader: (1)
Yeah, we've all heard how SLA has real camber gain in bump and the generic benefits but what I care about is what the car does in roll since that's what we're really trying to control. If there is camber gain in bump, that means theres also camber loss in droop. So, whole car rolls but inside looses negative camber, outside gains neg camber, and both tires work harder.
I should do some screen shots and plots of the camber in my models in roll to show the gains/loss and why we have to start with -4deg on our compromised setups. It works, but its not as good as it could be for sure.
BTW, 4 sets are gone, 6 left at the initial batch price!
I should do some screen shots and plots of the camber in my models in roll to show the gains/loss and why we have to start with -4deg on our compromised setups. It works, but its not as good as it could be for sure.
BTW, 4 sets are gone, 6 left at the initial batch price!
Nov 22, 2016, 01:28 PM
#6
EvoM Guru
iTrader: (1)
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Nov 22, 2016, 01:49 PM
#8
I don't have a plotted curve of the stock, I just have a model I can move around and gather data. But I can get some numbers about what I show that stock will do vs other scenarios.
I'm also not looking at scrub because its another thing that can be hugely variable depending on wheel/tire/spacer setup.
I'm also not looking at scrub because its another thing that can be hugely variable depending on wheel/tire/spacer setup.
Nov 22, 2016, 03:24 PM
#9
Yeah, we've all heard how SLA has real camber gain in bump and the generic benefits but what I care about is what the car does in roll since that's what we're really trying to control. If there is camber gain in bump, that means theres also camber loss in droop. So, whole car rolls but inside looses negative camber, outside gains neg camber, and both tires work harder.
I should do some screen shots and plots of the camber in my models in roll to show the gains/loss and why we have to start with -4deg on our compromised setups. It works, but its not as good as it could be for sure.
BTW, 4 sets are gone, 6 left at the initial batch price!
I should do some screen shots and plots of the camber in my models in roll to show the gains/loss and why we have to start with -4deg on our compromised setups. It works, but its not as good as it could be for sure.
BTW, 4 sets are gone, 6 left at the initial batch price!
And bare with me here as I am just learning and don't really know squat besides what I've read, but wouldn't camber loss on the inside tire in droop provide more grip on that tire? Assuming you had 3 degrees of static camber and 2 degrees of roll you'd have say 1 degree of droop camber per your above findings. I'd think this would increase grip on that unloaded tire.
Last edited by V.8MR; Nov 22, 2016 at 03:31 PM.
Dec 4, 2016, 09:32 AM
#10
Yeah, we've all heard how SLA has real camber gain in bump and the generic benefits but what I care about is what the car does in roll since that's what we're really trying to control. If there is camber gain in bump, that means theres also camber loss in droop. So, whole car rolls but inside looses negative camber, outside gains neg camber, and both tires work harder.
I should do some screen shots and plots of the camber in my models in roll to show the gains/loss and why we have to start with -4deg on our compromised setups. It works, but its not as good as it could be for sure.
BTW, 4 sets are gone, 6 left at the initial batch price!
I should do some screen shots and plots of the camber in my models in roll to show the gains/loss and why we have to start with -4deg on our compromised setups. It works, but its not as good as it could be for sure.
BTW, 4 sets are gone, 6 left at the initial batch price!
Dec 4, 2016, 02:02 PM
#13
Heh, thanks. Weight difference is 4lbs lighter from the original 11lbs steel unit. My original set was 5.5lbs lighter but then I found out the hard way how sever steering forces could be. Easily in excess of 500lbs on my car with race tires. So I made the steering arm about 0.6lbs heavier. Then I made chose to increase safety factory on a few areas which I'm sure most people would appreciate. I also put more effort into doubling the stiffness coupling steering to wheel position.
Overall I'm pretty stocked with how they've turned out. Its a good balance between weight, geometry correction, strength/stiffness, and price.
Overall I'm pretty stocked with how they've turned out. Its a good balance between weight, geometry correction, strength/stiffness, and price.
Dec 4, 2016, 02:09 PM
#14
They are killer for sure. I've been looking for these for awhile. I've seen other billet uprights but they didn't fix the geometry issues which to me didn't make sense. Spending $2k to drop 8 pounds alone (even if it isunsprung) is stupid. Correcting the geometry in the front however, is well worth it.
Do do they allow enough adjustment on the tie rod ends to run x arms?
Do do they allow enough adjustment on the tie rod ends to run x arms?
Dec 4, 2016, 04:08 PM
#15
That was my thought too. Weight reduction is just a bonus when the primary change should be roll center correction and bump steer. I can understand if someone just drag races there is another option that drops more weight but its a stock for stock replacement.
If I understand what you're asking, you are wondering if the tie rod replacement can extend long enough to work with the EvoX arms? I think yes, but I cant say 100% cause I haven't tried to fit it. On standard arms running aggressive camber I know I have to trim 1/2" from the rod end which I just do for the buyer depending one their setup and what they want. If its not trimmed the rod end stubs against the steering arm.
So there is enough adjustment work with an extra 1/2 of control arm by just not trimming the rod end. I cant say for sure what happens with low camber (less than 2degs) though but I think maintaining the minimum 1/2" of thread engagement shouldn't be an issue. I may on the next set make the coupler just a little longer so I have options for people depending on their setup.
As usual, when it comes to race cars no ones set up is the same so its been pretty tough to accommodate each possibility. Im just an engineer working on the side in his garage for the fun of it, so its no big deal for me to do custom things for each person.
If I understand what you're asking, you are wondering if the tie rod replacement can extend long enough to work with the EvoX arms? I think yes, but I cant say 100% cause I haven't tried to fit it. On standard arms running aggressive camber I know I have to trim 1/2" from the rod end which I just do for the buyer depending one their setup and what they want. If its not trimmed the rod end stubs against the steering arm.
So there is enough adjustment work with an extra 1/2 of control arm by just not trimming the rod end. I cant say for sure what happens with low camber (less than 2degs) though but I think maintaining the minimum 1/2" of thread engagement shouldn't be an issue. I may on the next set make the coupler just a little longer so I have options for people depending on their setup.
As usual, when it comes to race cars no ones set up is the same so its been pretty tough to accommodate each possibility. Im just an engineer working on the side in his garage for the fun of it, so its no big deal for me to do custom things for each person.