Where’s my caster?

[Usr117063]

My wishbone bushes are powerflex adjustable, you can effectively correct some roll centre without touching the lower joints, so your caster stays the same. You would lose camber and some geometry's would change slightly. I talked about this with balance motorsport a while back and said we could just set max camber via the adjustable struts on the asts which would still net 2.6 camber or something.

@Steven103 Thanks for clarifying that, I couldnt believe they would be like that.

But then why is frayz caster 2.4 when it should be 3?

 

[Eddie555]

Ah so im reading these h2 and h5 is basically the rake of the car, Which in effect changes the caster angle... I think i know where my 1 degree got lost.. I had raised the ride height of my rears by about 12mm.. It makes a lot more sense now..

@ZachB @frayz It would be interesting to see what your measurements are from wheel centre to arch on your fronts and rears to sort of compare the rake of our cars..

I will add to this... I know that to get a true and precise caster angle i will need to get my car cornerweighted for the correct balance and work on caster from there on.. This has been a very good discussion..
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[frayz]

Ah so im reading these h2 and h5 is basically the rake of the car, Which in effect changes the caster angle... I think i know where my 1 degree got lost.. I had raised the ride height of my rears by about 12mm.. It makes a lot more sense now..

@ZachB @frayz It would be interesting to see what your measurements are from wheel centre to arch on your fronts and rears to sort of compare the rake of our cars..
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As said in my first post, I decreased the take of the car by dropping the rear ride height than what it was when it sat on the Eibachs.
So in theory, I should have increased my caster. Although I don’t think it would be of any noticeable amount when measured.

 

[Eddie555]

As said in my first post, I decreased the take of the car by dropping the rear ride height than what it was when it sat on the Eibachs.
So in theory, I should have increased my caster. Although I don’t think it would be of any noticeable amount when measured.

Ah i must have missed that part.. [emoji854]

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[Usr117063]

@Eddie555 Will measure tomorrow mate. I just realised that rake is changing the number its not actually altering the dynamic camber, the intercept that goes through the joints to the ground points either further forward or backward with the rake change. But you will have a change in mechanical trail so if there was a lot of forward rake the steering would be slightly lighter (I think.. All of what I said I think )

 

[Steven103]

Unless I've misunderstood the timeline, you've measured castor whilst at an unknown ride height & rake, then changed the majority of the front end, then measured castor again at a different unknown ride height/rake?

On top of that as nothing is obviously bent, fitted incorrectly and there's no adjustment left it seems a bit of a pointless thing to worry about. I know it's not really what you want to hear as it doesn't get you back to this 3 degree target.

Unfortunately pretty much anything you touch changes everything. Take camber bolts for example. They change camber. But because of where in the system the change is made, they also unintentionally change track width, toe, king pin inclination, scrub radius, ride height, roll centre, pitch centre, anti dive blah blah blah.

If you wanted something to do during lock down, you could set the car to the standard ride height (if the ASTs even go that high) then measure H5-H2 to see where castor is compared to standard Renault hardpoints?

 

[Usr117063]

@Steven103 Is what I just said correct because you know what you are talking about 😁

I was just checking up on anti dive as you just wrote. Does the roll centre correction kits that lower the bottom joint decrease the anti dive slightly?

 

[Usr117063]

@Steven103 Wouldnt the camber bolts change the dynamic scrub radius but not static?

Sorry lots of questions but Im trying to get my head round suspension geometry so I can start making more informed changes to the alignments and such!

 

[frayz]

Unless I've misunderstood the timeline, you've measured castor whilst at an unknown ride height & rake, then changed the majority of the front end, then measured castor again at a different unknown ride height/rake?

On top of that as nothing is obviously bent, fitted incorrectly and there's no adjustment left it seems a bit of a pointless thing to worry about. I know it's not really what you want to hear as it doesn't get you back to this 3 degree target.

Unfortunately pretty much anything you touch changes everything. Take camber bolts for example. They change camber. But because of where in the system the change is made, they also unintentionally change track width, toe, king pin inclination, scrub radius, ride height, roll centre, pitch centre, anti dive blah blah blah.

If you wanted something to do during lock down, you could set the car to the standard ride height (if the ASTs even go that high) then measure H5-H2 to see where castor is compared to standard Renault hardpoints?

Thanks for the valued input Steven, and agree with what you’re saying.

But on basic terms irrespective of what changes I’ve made since, my car still never had and never has had more than 2.4 degrees of caster.
Many others with seemingly with no mods that would significantly affect the caster angle have got more than the 3 degrees supposed to be worn by the Cup chassis cars.

I’ve added a timeline and modifications just to give some perspective.

 

[Usr117063]

Ph1 subframe

 

[Usr117063]

@Mbeau Was breaking a FF 182 and not to far from you, not sure if he has a subframe but it might be worth it to rule things

 

[Steven103]

But on basic terms irrespective of what changes I’ve made since, my car still never had and never has had more than 2.4 degrees of caster.

I see where you're going. Not much consolation but it might just be luck of the draw in terms of body, turret and sub frame tolerances. Does your car have the elongated cut outs on the turret for the topmount? This would increase castor.

@Steven103 Is what I just said correct because you know what you are talking about 😁

I was just checking up on anti dive as you just wrote. Does the roll centre correction kits that lower the bottom joint decrease the anti dive slightly?

Yes on castor.

My first thought as to why anti dive changes is that camber bolts move the wheel centre slightly up/down in Z relative to the body. Straight away this moves the contact patch relative to the topmount and wishbone, which are two of the points that you use on a mcpherson strut to draw lines to work out the % of anti dive.

RC kit in short no: if you draw anti dive in conventional 2D with lines then moving the outboard lower balljoint does nothing. Lengthier speculation: you get a slightly different height for roll centre when you draw a real wishbone (i.e. non-symmetrical and inclined in all three axes rather than the perfect things drawn in textbooks) with 3D planes versus 2D lines so I wouldn't be surprised to find that the same happens for anti dive.

@Steven103 Wouldnt the camber bolts change the dynamic scrub radius but not static?

Sorry lots of questions but Im trying to get my head round suspension geometry so I can start making more informed changes to the alignments and such!

What do you mean by dynamic? Steered but not driving forwards?

Reason for it changing when static is because king pin inclination changes. Camber bolts would shorten/lengthen the strut ever so slightly and the turret doesn't move, so this length is taken up by the lower ball joint moving, which moves the steering axis a little. And as above the wheel centre/contact patch has moved which is the other component of KPI.

 

[Usr117063]

Thanks for the write up, I understand about the rc kit and anti dive now.

About the scrub radius that it changes with suspension travel, and that the camber bolts would change the 'path' it takes, for example it might have been more linear before but now its progressive. Just a thought.

 

[frayz]

I see where you're going. Not much consolation but it might just be luck of the draw in terms of body, turret and sub frame tolerances. Does your car have the elongated cut outs on the turret for the topmount? This would increase castor.

Yeah.
With regards to tolerance stack I’m guessing this is all it can be, just a shame it differs by so much.
My top mount holes are fixed and concentric so no ability to move this back to increase the caster here unless I swap to an eccentric version.

Just leaves me with the lower arm bushings but more likely the ball joint mounting holes. In the grand scheme of it, 0.5 degrees is nothing, just would have liked to enjoy the benefits of a bit more caster.

 

[Usr117063]

It’s a whole degree out. It should be 3.3

How do you know the previous owner didn’t have a wack and replace the subframe but used a 172 one?

 

[Usr117063]

What’s this on yours? If it’s same as the cup then it’s just bad luck, at least rule it out

My pics
172 cup
View attachment 1218644
ph1
View attachment 1218645

 

[frayz]

It’s a whole degree out. It should be 3.3

How do you know the previous owner didn’t have a wack and replace the subframe but used a 172 one?

Because the previous owner was a good mate and I know the entire cars history. It’s all original paint, panels and glass.

 

[Usr117063]

 

[Usr117063]

 

[Usr117063]

@Eddie555 around 310-320 both rear and front right side it was hard to tell.

 

[frayz]

Been busy doing other bits today so not had time to measure.

 

[boko]

Hello
I have kw v2 on my ph2 172.
Running -3 deg camber(camber bolt setup)
What is the best way to setup caster and on what value ?
Car is running only on track days.

 

[Usr117063]

Hello
I have kw v2 on my ph2 172.
Running -3 deg camber(camber bolt setup)
What is the best way to setup caster and on what value ?
Car is running only on track days.

This is the easiest way to obtain more (link). Then theres wishbone bushings that you can use, I use powerflex adjustable wishbone bushings although mine are set only for camber you can dial in more caster with them (but less camber and changes other geomtry) There are loads of ways of doing which I havnt done but these 2 are the easiest. Mine is around 4.7

BC Racing Solid Top Mounts - Renault Clio Mk2 RS172 / RS182

BC Racing solid top mounts replace the standard rubber mounts and are designed for competition only as they generally are harsher and more noisy for general road use. They work great for weekend and trackday cars as well. The BC Racing top mounts improve

www.kamracing.co.uk

 

[boko]

This is the easiest way to obtain more (link). Then theres wishbone bushings that you can use, I use powerflex adjustable wishbone bushings although mine are set only for camber you can dial in more caster with them (but less camber and changes other geomtry) There are loads of ways of doing which I havnt done but these 2 are the easiest. Mine is around 4.7

BC Racing Solid Top Mounts - Renault Clio Mk2 RS172 / RS182

BC Racing solid top mounts replace the standard rubber mounts and are designed for competition only as they generally are harsher and more noisy for general road use. They work great for weekend and trackday cars as well. The BC Racing top mounts improve

www.kamracing.co.uk

Thanks for answer.
Can you please send one more time link,i can not open it?

 

[Usr117063]

BC Racing Solid Top Mounts - Renault Clio Mk2 RS172 / RS182

BC Racing solid top mounts replace the standard rubber mounts and are designed for competition only as they generally are harsher and more noisy for general road use. They work great for weekend and trackday cars as well. The BC Racing top mounts improve

www.kamracing.co.uk

Bc top mounts

Thanks for answer.
Can you please send one more time link,i can not open it?

 

[boko]

This one?