Geometry advice
Discussion
I started a topic in Suspension & Braking but it's like the Marie Celeste in there 
If anyone's got anything to add I'm all 
http://www.pistonheads.com/gassing/topic.asp?h=0&a...
If anyone's got anything to add I'm all http://www.pistonheads.com/gassing/topic.asp?h=0&a...
Nope, no corner weighting done. Part of me thinks take it to a specialist and let them set it all up for me, but another part of me wants to understand the setup so I can fine tune it for myself.
The pic I've added does show my track arms angled upwards in a stationery position. Could it be that?
The pic I've added does show my track arms angled upwards in a stationery position. Could it be that?
If you measure ride height from the corner of each outrigger to the ground and its about 150mm front and 160mm rear, the steering rods are not far off parallel.
It then comes down to whether all the wheels are pointing in the same directions and cambers are even.
Sounds like you need to be involved in the geo process and some specialists are more than happy to have the customer involved, some of my customers watch the geo and then go up my test track and either ask for a more benign or more agressive set up and I'm not alone in enjoying driver feedback because you learn every day.
It then comes down to whether all the wheels are pointing in the same directions and cambers are even.
Sounds like you need to be involved in the geo process and some specialists are more than happy to have the customer involved, some of my customers watch the geo and then go up my test track and either ask for a more benign or more agressive set up and I'm not alone in enjoying driver feedback because you learn every day.
Edited by Ab Shocks on Tuesday 10th June 17:21
First of forget all the rubbish that is talked on the suspension threads about having wishbones parallel with the ground*, it's the most misinformed rubbish and i wish people would stop spouting it. For a start the orientation of the wishbone isn't even important, if any of it were important it would be the line through the ball joint to inner wishbone bush, what the wishbone does itself inbetween these two points is of no importance at all.
What you're describing in your car could be down to several factors including scrub radius (i see you have non-std wheels), gyroscopic effects, bump steer, subconscious steering inputs etc etc
First point of interest would be to post up your current suspension geometry so we can take look at it.
What you're describing in your car could be down to several factors including scrub radius (i see you have non-std wheels), gyroscopic effects, bump steer, subconscious steering inputs etc etc
First point of interest would be to post up your current suspension geometry so we can take look at it.
- If you want to eliminate bump steer as far as possible you should have the steering arm describing an arc on the intersection of the lines from the upper and lower wishbone, called their centre of instantaneous rotation. In reality this rarely occurs, indeed you can introduce some characteristics into the behaviour of the car by having some bump steer deliberately in the system.
trackcar said:
First of forget all the rubbish that is talked on the suspension threads about having wishbones parallel with the ground*, it's the most misinformed rubbish and i wish people would stop spouting it. For a start the orientation of the wishbone isn't even important, if any of it were important it would be the line through the ball joint to inner wishbone bush, what the wishbone does itself inbetween these two points is of no importance at all.
What you're describing in your car could be down to several factors including scrub radius (i see you have non-std wheels), gyroscopic effects, bump steer, subconscious steering inputs etc etc
First point of interest would be to post up your current suspension geometry so we can take look at it.
Joolz, from various threads on here,I thought the level front wishbones was the starting point for setting ride height?What you're describing in your car could be down to several factors including scrub radius (i see you have non-std wheels), gyroscopic effects, bump steer, subconscious steering inputs etc etc
First point of interest would be to post up your current suspension geometry so we can take look at it.
- If you want to eliminate bump steer as far as possible you should have the steering arm describing an arc on the intersection of the lines from the upper and lower wishbone, called their centre of instantaneous rotation. In reality this rarely occurs, indeed you can introduce some characteristics into the behaviour of the car by having some bump steer deliberately in the system.
personally, I would rather measure from the main chassis rails.
Any thoughts on measurements for these points?
Edited by AntonyJ on Tuesday 10th June 19:35
Edited by AntonyJ on Tuesday 10th June 19:45
AntonyJ said:
trackcar said:
First of forget all the rubbish that is talked on the suspension threads about having wishbones parallel with the ground*, it's the most misinformed rubbish and i wish people would stop spouting it. For a start the orientation of the wishbone isn't even important, if any of it were important it would be the line through the ball joint to inner wishbone bush, what the wishbone does itself inbetween these two points is of no importance at all.
What you're describing in your car could be down to several factors including scrub radius (i see you have non-std wheels), gyroscopic effects, bump steer, subconscious steering inputs etc etc
First point of interest would be to post up your current suspension geometry so we can take look at it.
Joolz, from various threads on here,I thought the level front wishbones was the starting point for setting ride height?What you're describing in your car could be down to several factors including scrub radius (i see you have non-std wheels), gyroscopic effects, bump steer, subconscious steering inputs etc etc
First point of interest would be to post up your current suspension geometry so we can take look at it.
- If you want to eliminate bump steer as far as possible you should have the steering arm describing an arc on the intersection of the lines from the upper and lower wishbone, called their centre of instantaneous rotation. In reality this rarely occurs, indeed you can introduce some characteristics into the behaviour of the car by having some bump steer deliberately in the system.
If not having replaced my outriggers, I would rather measure from the main chassis rails.
Any thoughts on measurements for these points?
Edited by AntonyJ on Tuesday 10th June 19:35
If it's road use I use this rule of thumb :
set it high enough so you can get over speed bumps, into your office car park, into the wife/girlfriend's favourite shopping centre car park and down your favourite bumpy windy hooning road without bottoming out too often whilst still feeling reasonably flat and low and agile, that's about the right height
What that height is in mm on your particular car on any particular day / fuel load is anyone's guess, and it'll be different to someone else's guess who doesn't drive your road, park in your car park or have to contend with your speed bumps and your fuel/luggage load.
Now that might not sound like a particularly useful bit of information (people for some reason get hung up on achieving the nirvana 150mm or 165mm or whatever is the current vogue..) but it's about the most useful info you'll ever need for ride heights on the road. In short: make it high enough that you can actually use it
and if you do like a bit of aero-stability it's wise to make the rear a bit higher than the front but how much higher is up to you, it'll change depending again on how much fuel you carry, how many shoes your wife bought from the shopping centre. Just make it a bit higher most of the time and you'll be fine! You don't have to be all scientific for road use, you just have to be sensible.HRG said:
Typical, I've got receipts for every nut and washer on the car, my old geo settings but not the ones since I replaced the rack. 
My "old" settings are broadly similar to the current ones, are they of any use?
Post what you've got and we'll see if it's about right or miles off or somewhere in between My "old" settings are broadly similar to the current ones, are they of any use?
trackcar said:
AntonyJ said:
trackcar said:
First of forget all the rubbish that is talked on the suspension threads about having wishbones parallel with the ground*, it's the most misinformed rubbish and i wish people would stop spouting it. For a start the orientation of the wishbone isn't even important, if any of it were important it would be the line through the ball joint to inner wishbone bush, what the wishbone does itself inbetween these two points is of no importance at all.
What you're describing in your car could be down to several factors including scrub radius (i see you have non-std wheels), gyroscopic effects, bump steer, subconscious steering inputs etc etc
First point of interest would be to post up your current suspension geometry so we can take look at it.
Joolz, from various threads on here,I thought the level front wishbones was the starting point for setting ride height?What you're describing in your car could be down to several factors including scrub radius (i see you have non-std wheels), gyroscopic effects, bump steer, subconscious steering inputs etc etc
First point of interest would be to post up your current suspension geometry so we can take look at it.
- If you want to eliminate bump steer as far as possible you should have the steering arm describing an arc on the intersection of the lines from the upper and lower wishbone, called their centre of instantaneous rotation. In reality this rarely occurs, indeed you can introduce some characteristics into the behaviour of the car by having some bump steer deliberately in the system.
If not having replaced my outriggers, I would rather measure from the main chassis rails.
Any thoughts on measurements for these points?
Edited by AntonyJ on Tuesday 10th June 19:35
If it's road use I use this rule of thumb :
set it high enough so you can get over speed bumps, into your office car park, into the wife/girlfriend's favourite shopping centre car park and down your favourite bumpy windy hooning road without bottoming out too often whilst still feeling reasonably flat and low and agile, that's about the right height
What that height is in mm on your particular car on any particular day / fuel load is anyone's guess, and it'll be different to someone else's guess who doesn't drive your road, park in your car park or have to contend with your speed bumps and your fuel/luggage load.
Now that might not sound like a particularly useful bit of information (people for some reason get hung up on achieving the nirvana 150mm or 165mm or whatever is the current vogue..) but it's about the most useful info you'll ever need for ride heights on the road. In short: make it high enough that you can actually use it
and if you do like a bit of aero-stability it's wise to make the rear a bit higher than the front but how much higher is up to you, it'll change depending again on how much fuel you carry, how many shoes your wife bought from the shopping centre. Just make it a bit higher most of the time and you'll be fine! You don't have to be all scientific for road use, you just have to be sensible.Oh dear, I knew this would start Joo off, he hates the level wishbne theory.but more importantly he hates one stop suspension solutions.
Let's go back to the ride height discussion, what was said a long time ago on a thread was that if lower wishbones and steering rods were roughly level or slightly pointing upwards that this was no bad thing and Guglielmi and other race teams subscribe to this in general.
Unfortunately people take this as cast in stone and start using spirit levels to ensure perfection.
As for packing out racks, I know who started that nonsense and he ought to know better because very few tivs bump steer, in fact its more common for them to toe in under bump. BUT NOT ALL,ONLY SOME
I advocate a pull down test on all cars with the dampers turned down, just to see what the car does in bump and then counter with more or less toe.
I'll show you how this works at the Griff Growl.
Let's go back to the ride height discussion, what was said a long time ago on a thread was that if lower wishbones and steering rods were roughly level or slightly pointing upwards that this was no bad thing and Guglielmi and other race teams subscribe to this in general.
Unfortunately people take this as cast in stone and start using spirit levels to ensure perfection.
As for packing out racks, I know who started that nonsense and he ought to know better because very few tivs bump steer, in fact its more common for them to toe in under bump. BUT NOT ALL,ONLY SOME
I advocate a pull down test on all cars with the dampers turned down, just to see what the car does in bump and then counter with more or less toe.
I'll show you how this works at the Griff Growl.
I do hate it you're right mainly because it achieves nothing and is of absolutely no importance whatsoever, it's best people just put it out of their minds, but because it's mentioned as some sort of handling fast-track it keeps getting mentioned time and again and it makes me go Grrrrrrrrr!! Now of course it's not inconceivable that in the course of setting a car up it happens to come out with the the intersection of ball joint to inner bush level, but you shouldn't strive for that if it doesn't give you the ride height and usability that you require from the car.
There's a culture that's grown up around suspension of one kit fits all solutions and this is a shame because it assumes that all the cars are the same and everyone wants the same thing from their car.
Still, it does give me a chance to dust the soap box off
mainly because it achieves nothing and is of absolutely no importance whatsoever, it's best people just put it out of their minds, but because it's mentioned as some sort of handling fast-track it keeps getting mentioned time and again and it makes me go Grrrrrrrrr!! Now of course it's not inconceivable that in the course of setting a car up it happens to come out with the the intersection of ball joint to inner bush level, but you shouldn't strive for that if it doesn't give you the ride height and usability that you require from the car.There's a culture that's grown up around suspension of one kit fits all solutions and this is a shame because it assumes that all the cars are the same and everyone wants the same thing from their car.
Still, it does give me a chance to dust the soap box off
I do understand your frustration Joo, I now set up 2 or 3 MX-5 cars a week and they turn up with data sheets from the Yank forums from some geezers called Icehawk and Lanny who run completely different suspension set ups, one of them is a circuit racer for Gods sake and I have to point out the lack of merit in trying to set up a car exactly the same as somebody of that ilk (probably 25 stone as well)
Right, here we go with the pre rack replacement settings. The caster will be different as I've fitted 2 x 3mm spacers so I can use the later upper balljoints. I know camber is improved on the left front but otherwise the settings are broadly similar.
Front
Caster
Left 5.21
Right 5.45
Camber
Left -0.10
Right -0.42
Toe
Left 0.06
Right 0.04
Total 0.10
Rear
Camber
Left -0.54
Right -0.58
Toe
Left -0.01
Right 0.11
Total 0.10
Thrust Angle -0.06
Secondary Angles
SAI
Left 13.31
Right 14.17
Included Angle
Left 13.22
Right 13.35
Setback
Front 7mm
Rear 8mm
Track width difference -7mm
wheel base diff -1mm
Front
Caster
Left 5.21
Right 5.45
Camber
Left -0.10
Right -0.42
Toe
Left 0.06
Right 0.04
Total 0.10
Rear
Camber
Left -0.54
Right -0.58
Toe
Left -0.01
Right 0.11
Total 0.10
Thrust Angle -0.06
Secondary Angles
SAI
Left 13.31
Right 14.17
Included Angle
Left 13.22
Right 13.35
Setback
Front 7mm
Rear 8mm
Track width difference -7mm
wheel base diff -1mm
HRG said:
Right, here we go with the pre rack replacement settings. The caster will be different as I've fitted 2 x 3mm spacers so I can use the later upper balljoints. I know camber is improved on the left front but otherwise the settings are broadly similar.
Front
Caster
Left 5.21. Good
Right 5.45. Good
Camber
Left -0.10. -0.75
Right -0.42.-0.75
Toe
Left 0.06. 0.06
Right 0.04. 0.06
Total 0.10. 0.12
Rear
Camber
Left -0.54. -1.2
Right -0.58 -1.2
Toe
Left -0.01. 0.12
Right 0.11. 0.12
Total 0.10. 0.24
Thrust Angle -0.06
I want 0 thrust
Secondary Angles
SAI
Left 13.31
Right 14.17
Included Angle
Left 13.22
Right 13.35
Setback
Front 7mm
Rear 8mm
Track width difference -7mm
wheel base diff -1mm
Alongside I have put numbers I would send you out on a test drive to see how you got onFront
Caster
Left 5.21. Good
Right 5.45. Good
Camber
Left -0.10. -0.75
Right -0.42.-0.75
Toe
Left 0.06. 0.06
Right 0.04. 0.06
Total 0.10. 0.12
Rear
Camber
Left -0.54. -1.2
Right -0.58 -1.2
Toe
Left -0.01. 0.12
Right 0.11. 0.12
Total 0.10. 0.24
Thrust Angle -0.06
I want 0 thrust
Secondary Angles
SAI
Left 13.31
Right 14.17
Included Angle
Left 13.22
Right 13.35
Setback
Front 7mm
Rear 8mm
Track width difference -7mm
wheel base diff -1mm
Oh yes, more traction on the rear from the increased toe and better high speed stability from the increased camber with less tramlining.
On the front, more and even camber promotes a nice crisp turn in with better grip from slightly improved toe balance but that was only a gnats cock uut.
On the front, more and even camber promotes a nice crisp turn in with better grip from slightly improved toe balance but that was only a gnats cock uut.
Lot's of stuff said that I don't understand in suspension .. like adding rear toe to gain you traction, makes no sense and I've tried this when I first saw it mentioned and couldn't tell any difference. You have a grip circle to work within .. why would you trade fore/aft traction by introducing a lateral slip angle? How many dragsters do you see running negative camber and toe in? Not many .. then again how many dragsters do you see with vertical wheels on live axles with no rear toe at all? Lots .. You can't tell me the drag racing fraternity (who've been doing this kind of thing a long long time) have been doing it wrong all these years? Adding toe will always lose you straightline speed once you've run out of hp to spin the tyres too.
Looking at your figures above the first thing that strikes me is you have very little camber in performance terms (and unequal on the front), so no need to use one thin spacer either side of the new top ball joint as you're probably not trying to put eh ball joint very far through teh upper wishbone so don't need it centrall mounted .. put them both a the front of the ball joint to get your trail back where it should be and that will lift the steering arms .. Derek seems to find most of his TVRs toe-in on compression and yet I see exactly the opposite in all the ones I test so IMO the last thing you need is lower steering arms (gives you the same effect as raising the steering rack) .. if you are running your car any lower than std then this advice is doubly important, get the steering arms up or the rack down.
You need to equalise the rear toe up though, you can visualise it as crabbing from the rear of the car but worse still you have one side toeing out .. big no-no.
There's not a lot you can do with the rest of it without getting the oxy-acetylene kit out
So that lot should at least get you a car that's going straight ahead down the road with the front bump steer back where the factory had it .. then see what the car's like and if it's still misbehaving and you think it's a suspension/geometry/other issue try winding the dampers full stiff (to limit their movement in any given time interval) and see if it improves or gets worse, then try it full soft and see .. that should give you an idea of is it's the physical suspension movement causing the issue .. put the ride comfort to the back of your mind and just concentrate on the trajectory of the car ..
after that if you're still struggling just get it as good as you can then let the tyres do more suspension work by letting some air out and see what happens, after that if it's still misbehaving it's time to hand it over to someone as it'd be very difficult to go through all the permutations in a forum ..
Looking at your figures above the first thing that strikes me is you have very little camber in performance terms (and unequal on the front), so no need to use one thin spacer either side of the new top ball joint as you're probably not trying to put eh ball joint very far through teh upper wishbone so don't need it centrall mounted .. put them both a the front of the ball joint to get your trail back where it should be and that will lift the steering arms .. Derek seems to find most of his TVRs toe-in on compression and yet I see exactly the opposite in all the ones I test so IMO the last thing you need is lower steering arms (gives you the same effect as raising the steering rack) .. if you are running your car any lower than std then this advice is doubly important, get the steering arms up or the rack down.
You need to equalise the rear toe up though, you can visualise it as crabbing from the rear of the car but worse still you have one side toeing out .. big no-no.
There's not a lot you can do with the rest of it without getting the oxy-acetylene kit out
So that lot should at least get you a car that's going straight ahead down the road with the front bump steer back where the factory had it .. then see what the car's like and if it's still misbehaving and you think it's a suspension/geometry/other issue try winding the dampers full stiff (to limit their movement in any given time interval) and see if it improves or gets worse, then try it full soft and see .. that should give you an idea of is it's the physical suspension movement causing the issue .. put the ride comfort to the back of your mind and just concentrate on the trajectory of the car ..
after that if you're still struggling just get it as good as you can then let the tyres do more suspension work by letting some air out and see what happens, after that if it's still misbehaving it's time to hand it over to someone as it'd be very difficult to go through all the permutations in a forum ..
Excellent advice chaps, thanks.
Couple of things, I can't use the 6mm spacers as my later style upper ball joints do foul the wishbone. That 0.10 on the left front was as far as she'd go until I swapped the spacers after the rack refurb. IIRC the right camber is now about 0.45. Bear in mind my upper and lower wishbones have both been replaced so they could be out a bit on tolerances anyway.
What I don't understand is setting the ride height. On bikes, which I'm a bit more familiar with, you raise/lower the forks or adjust eccentrics on the swing arm to alter the attitude then set the preload to adjust the amount of sag and then finally damp it down to your preferences. If I'm trying to raise the ride height on preload alone am I in danger of setting it too hard before I actually reach the ride height that's recommended?
Is getting the amount of camber/toe etc right more important than the height the car actually sits relative to the ground?
Couple of things, I can't use the 6mm spacers as my later style upper ball joints do foul the wishbone. That 0.10 on the left front was as far as she'd go until I swapped the spacers after the rack refurb. IIRC the right camber is now about 0.45. Bear in mind my upper and lower wishbones have both been replaced so they could be out a bit on tolerances anyway.
What I don't understand is setting the ride height. On bikes, which I'm a bit more familiar with, you raise/lower the forks or adjust eccentrics on the swing arm to alter the attitude then set the preload to adjust the amount of sag and then finally damp it down to your preferences. If I'm trying to raise the ride height on preload alone am I in danger of setting it too hard before I actually reach the ride height that's recommended?
Is getting the amount of camber/toe etc right more important than the height the car actually sits relative to the ground?
Forget the word preload, it's only of any importance when the damper is at full extension (full droop) .. as you wind the spring up the damper with the weight of the car on it you are NOT compressing the spring until you run out of damper extension, therefore the preload is of no consequence .. when you wind the spring seat up don't think of compressing the spring, think of making the damper longer when it's carrying the weight of the car. Hope that makes sense.
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