group n spring rates?

[NorthloopCup]

Sorry - yes it is slightly confusing I am running 300lb/in front springs and 400lb/in*rear springs they are they actual spring rates

Lol yes just a bit! In that case I maintain my original recommendation, and I'd be tempted to go straight in for the kill with a 500lb rear spring.

What is the actual issue your suffering or experiencing Sam? Apologies I've only skim read :S

 

[sam JFM]

Well no particular issues apart from I feel it might be a little soft due to the amount of damping I have had to dial in on track, and I got the general feel that my spring rates were low compared to others.

It's such a faf trying spring rates out as every time you change a front spring you have to sort the geo out again!

 

[NorthloopCup]

Well no particular issues apart from I feel it might be a little soft due to the amount of damping I have had to dial in on track, and I got the general feel that my spring rates were low compared to others.

It's such a faf trying spring rates out as every time you change a front spring you have to sort the geo out again!

How low do you run the front of your car Sam? If you use the same way you'd measure a dirty girl, how many fingers can you get in between the front wheel and the arch? I run mine very low and I can only just about get 2 fingers in (1" 1/4 ish). Only reason I ask is it will give me an idea of how far out the front roll centres are. This will obviously be corrected with the kit your having, but it will also have a vast improvement to how your suspension works as it currently is. I still think you need to go stiffer but you will be pleasantly surprised at how much difference it adds to the car.

 

[sam JFM]

How low do you run the front of your car Sam? If you use the same way you'd measure a dirty girl, how many fingers can you get in between the front wheel and the arch? I run mine very low and I can only just about get 2 fingers in (1" 1/4 ish). Only reason I ask is it will give me an idea of how far out the front roll centres are. This will obviously be corrected with the kit your having, but it will also have a vast improvement to how your suspension works as it currently is. I still think you need to go stiffer but you will be pleasantly surprised at how much difference it adds to the car.

All I can tell you is what I originally set it too (Front ride height (hub centre to bottom of wheel arch) 407mm ) due to someone currently having possession of my hubs lol

 

[p@blo]

Be interesting to see how you compare Sam. Whats the corresponding value at the back?

 

[sam JFM]

well my Rake (measured from the top of the jack point holes to the floor): 20mm back to front

 

[NorthloopCup]

All I can tell you is what I originally set it too (Front ride height (hub centre to bottom of wheel arch) 407mm ) due to someone currently having possession of my hubs lol

Flol yeah I'd forgotten about that!!! I'll have a measure up on mine later on and report back.

 

[NorthloopCup]

All I can tell you is what I originally set it too (Front ride height (hub centre to bottom of wheel arch) 407mm ) due to someone currently having possession of my hubs lol

I've just measured mine from the same reference points and it comes in at 314mm.

 

[sam JFM]

So how far are my roll centers out?

 

[NorthloopCup]

So how far are my roll centers out?

Difficult to say without seeing the car at its current ride height, but it will be out. Mines currently set ridiculously low anyway so it's possibly not representative tbh.

 

[sam JFM]

Update to this,

Very happy with the handling, BUT it bottoms out over the big bumps

So

If I up the spring rates to 350F and 250R That should help with the bottoming out but, will it change the balance or will the balance still be the same and just resist bottoming out? Also I currently have 7" springs on the front and 5" on the rear so I am contemplating increasing the length to 8" and 6"?

 

[sam JFM]

http://www.rallygallery.com/Picture...014_ABR&PhotoID=abr14_74_mrol0574&FitWindow=0

http://www.rallygallery.com/Picture...014_ABR&PhotoID=abr14_74_mrol1663&FitWindow=0

Some pictures from the weekend at Abingdon - still scrubbing the outside of the tyres. scroll through the pictures and see what you think.

Too soft at the front?

Sam


NorthloopCup

 

[NorthloopCup]

http://www.rallygallery.com/Picture...014_ABR&PhotoID=abr14_74_mrol0574&FitWindow=0

http://www.rallygallery.com/Picture...014_ABR&PhotoID=abr14_74_mrol1663&FitWindow=0

Some pictures from the weekend at Abingdon - still scrubbing the outside of the tyres. scroll through the pictures and see what you think.

Too soft at the front?

Sam


@NorthloopCup

What camber you running up front mate? I'd be tempted to say it's not stiff enough all round tbh. Maybe more so at the rear. N/S/F on the first picture is still running a bit of negative camber as well so it shows that something's working!

 

[Ph1 Tom]

That's too soft front and rear.

 

[sam JFM]

Its quite interesting looking at those pictures from a suspension point of view.

Three degs neg on the fronts (to try to stop the scrubbing) but it has worn the insides too! so too much camber!

Am I right in thinking its the softness of the suspension that is causing the tyres to roll as it goes into positive camber? (the tyres are at about 32-33 Psi in those pictures which is too much really)

 

[NorthloopCup]

Its quite interesting looking at those pictures from a suspension point of view.

Three degs neg on the fronts (to try to stop the scrubbing) but it has worn the insides too! so too much camber!

Am I right in thinking its the softness of the suspension that is causing the tyres to roll as it goes into positive camber? (the tyres are at about 32-33 Psi in those pictures which is too much really)

Lose half a degree of camber as a starting point. The roll is a combination of spring rates and damper valving.

 

[sam JFM]

Lose half a degree of camber as a starting point. The roll is a combination of spring rates and damper valving.

That is where it was set last time one - my plan was to go back to 2.5.

Yeh I don't think the dampers are perfectly suited to what im doing but I cant afford anymore!

 

[Steven103]

Its quite interesting looking at those pictures from a suspension point of view.

Three degs neg on the fronts (to try to stop the scrubbing) but it has worn the insides too! so too much camber!

Am I right in thinking its the softness of the suspension that is causing the tyres to roll as it goes into positive camber? (the tyres are at about 32-33 Psi in those pictures which is too much really)

Pictures are indeed fascinating. It's actually how vehicle dynamics started and how the first analysis were done before people knew what and why cars behave the way they do.

I think a massive amount of the cars on Cliosport would benefit from going back to basics and actually thinking about things rather than just essentially everyone copying Burpspeed because they have the quickest Clio. Though naturally it's therefore not a bad thing to copy!

33 PSI (2.1 bar ish) isn't a million miles off and would actually begin to offset the increased inside shoulder wear you'd associate with too much negative camber. In general what is actually happening is the geometry associated with a Clio means that the camber angle changes a lot in roll (dynamic camber angle) and so if you have a large roll angle (e.g. soft springs, soft roll bar, high lateral force from running a wide track or slicks etc.) you get very poor tyre performance as it's never being used at it's optimum angle (which is not dead upright as people think, it's actually around -0.5deg for something called "camber thrust" but there are entire books on this). The excessive roll angle causes excessive dynamic camber change which causes the sidewalls to fall over themselves.

So you want to reduce roll angle. Without an adjustable FARB this means springs and dynamic camber is the reason stiff springs make such a difference to Clios. But if you fit stiffer springs then it just means the spring deflects less and the tyre sidewall deflects more and so the sidewall falls over itself and the problem remains to some extent (the total force going through the tyre sidewall and spring remains constant no matter what spring rate you have - quite obvious when you think the weight of the car doesn't change!) Clearly this is bad for tyre life and actually extremely bad for grip because of the exact way tyres work (but again people have dedicated their entire lives to how tyres work) because they respond very poorly to large variations in the contact patch force (and clearly if the sidewall is folding over there is a lot of force!)

Do you have the RC correction kit? A well placed roll centre reduces roll angle and therefore improves dynamic camber angle. Frankly I don't think anyone has done the analysis to decide where a good RC height actually is, but no doubt putting it near to standard (what the RC kit tries to do) is better than nothing.

So clearly you need to strike a balance: a soft enough spring so that the spring is doing all the deflection and not the sidewall (to stop the sidewall falling over itself) but a stiff enough spring to nail down the roll angle (to reduce dynamic camber change so that the sidewall doesn't fall over itself). Roll angle is determined only by springs/ARB (and the force causing it to roll obviously), the damping rate only changes the amount of time the car takes to reach it's maximum roll angle. For a rally car which doesn't really do long settled corners you might find with stiff damping you're rarely in a corner long enough to reach the maximum roll angle. So from this point of view - increasing the (low speed) bump damping may help, but nowhere near as much as springs/ARB/tyre pressures.

And this is where CS opinions are so, so useful. Because plenty of people will now comment who've been through 7 spring rates and found the ideal balance between limiting roll and limiting sidewall deflection. For a Clio on sticky tyres with decent quality dampers this seems to be around the 500lb mark as I'm sure MG Cup, Northloop, Chip et. al. have also found.

Does your Clio go on bumpy stuff with the same spring rates? What the Clio world could really do with (even more so for you rally folk) is a stiffer FARB. That way you can limit roll angle to improve dynamic camber AND run softer springs to improve the contact patch. But that's a bit of a project for someone. (You'd also have to do a new RARB to massively up the rear roll stiffness to keep the same handling balance)



Soz 4 long reply. I don't know, I just got the impression you just sound interested to learn "why" and not just "what can I buy becauseracecar"

TLDR: Others with 500lb ish springs will confirm, but generally you probably want to go stiffer as you can more in dynamic camber control than you loose through all the bad things associated with a car being too stiff.

Infact can you just correct me please - is this a rally car or I have made that idea up in my head lol? Does it ever see slippery surfaces? Because camber angles and spring rates are probably the last things to copy from people who run on a flat circuit!

 

[sam JFM]

Pictures are indeed fascinating. It's actually how vehicle dynamics started and how the first analysis were done before people knew what and why cars behave the way they do.

I think a massive amount of the cars on Cliosport would benefit from going back to basics and actually thinking about things rather than just essentially everyone copying Burpspeed because they have the quickest Clio. Though naturally it's therefore not a bad thing to copy!

33 PSI (2.1 bar ish) isn't a million miles off and would actually begin to offset the increased inside shoulder wear you'd associate with too much negative camber. In general what is actually happening is the geometry associated with a Clio means that the camber angle changes a lot in roll (dynamic camber angle) and so if you have a large roll angle (e.g. soft springs, soft roll bar, high lateral force from running a wide track or slicks etc.) you get very poor tyre performance as it's never being used at it's optimum angle (which is not dead upright as people think, it's actually around -0.5deg for something called "camber thrust" but there are entire books on this). The excessive roll angle causes excessive dynamic camber change which causes the sidewalls to fall over themselves.

So you want to reduce roll angle. Without an adjustable FARB this means springs and dynamic camber is the reason stiff springs make such a difference to Clios. But if you fit stiffer springs then it just means the spring deflects less and the tyre sidewall deflects more (the total force going through the tyre sidewall and spring remains constant no matter what spring rate you have - quite obvious when you think the weight of the car doesn't change!) Clearly this is bad for tyre life and actually extremely bad for grip because of the exact way tyres work (but again people have dedicated their entire lives to how tyres work) because they respond very poorly to large variations in the contact patch force (and clearly if the sidewall is folding over there is a lot of force!)

Do you have the RC correction kit? A well placed roll centre reduces roll angle and therefore improves dynamic camber angle. Frankly I don't think anyone has done the analysis to decide where a good RC height actually is, but no doubt putting it near to standard (what the RC kit tries to do) is better than nothing.

So clearly you need to strike a balance: a soft enough spring so that the spring is doing all the deflection and not the sidewall (to stop the sidewall falling over itself) but a stiff enough spring to nail down the roll angle (to reduce dynamic camber change so that the sidewall doesn't fall over itself)

And this is where CS opinions are so, so useful. Because plenty of people will now comment who've been through 7 spring rates and found the ideal balance between limiting roll and limiting sidewall deflection. For a Clio on sticky tyres with decent quality dampers this seems to be around the 500lb mark as I'm sure MG Cup, Northloop, Chip et. al. have also found.

Does your Clio go on bumpy stuff with the same spring rates? What the Clio world could really do with (even more so for you rally folk) is a stiffer FARB. That way you can limit roll angle to improve dynamic camber AND run softer springs to improve the contact patch. But that's a bit of a project for someone. (You'd also have to do a new RARB to massively up the rear roll stiffness to keep the same handling balance)


Soz 4 long reply. I don't know, I just got the impression you just sound interested to learn "why" and not just "what can I buy becauseracecar"

TLDR: Others with 500lb ish springs will confirm, but generally you probably want to go stiffer as you can more in dynamic camber control than you loose through all the bad things associated with a car being too stiff.

Thanks for the great reply!

Yes I am interested - I find it all really interesting, if you understand why something is happening you have half a chance of making it better!

There is always bumpy stuff and therein lies the problem - hard enough for the fast smooth stuff and soft enough of the broken tarmac. not to mention spring length and ride height!

I am going to have to do something about it, I have had plenty of track time or events to get a feel for what its doing (apart from wrecking tyres!!) and I now need to decide how to optimise what I've got.... A front ARB would be good

 

[sam JFM]

Thanks for the great reply!

Yes I am interested - I find it all really interesting, if you understand why something is happening you have half a chance of making it better!

There is always bumpy stuff and therein lies the problem - hard enough for the fast smooth stuff and soft enough of the broken tarmac. not to mention spring length and ride height!

I am going to have to do something about it, I have had plenty of track time or events to get a feel for what its doing (apart from wrecking tyres!!) and I now need to decide how to optimise what I've got.... A front ARB would be good

P.s Yes it is a rally car, poverty tarmac spec!

 

[Steven103]

Go out on a limb - make a new front anti roll bar

As I sort of said roll stiffness is what the Clio really wants. And everyone gives it roll stiffness with stiff springs. But obviously this somewhat affects how it copes with bumps! By making a stiffer roll bar you can therefore achieve a high roll stiffness (therefore meeting the goal) without compromising the thing by fitting rock hard springs.

Just to give an idea of how bad the spring choice is for bumps, suspension "stiffness" is usually worked out by calculating the resonant frequency of the car body (ride frequency). Point is a stripped clio with a 500lb rear spring is well into the "moderate downforce" category of suspension stiffness - except it's all wasted because Clios have no downforce!

 

[Ph1 Tom]

Adjustable bladed ARB for the front would be great. Something Cornering Force could do perhaps. http://www.corneringforce.com/anti_roll_bars.html

 

[NorthloopCup]

Adjustable bladed ARB for the front would be great. Something Cornering Force could do perhaps. http://www.corneringforce.com/anti_roll_bars.html

There's more to it than that though mate. You need to valve the dampers to suit, get the spring rates correct, optimise the roll centres etc etc (and not all in that order!) before you can get the correct calculations to do an adjustable arb. If you've got a spare 2-3k this would undoubtably be THE best money you'd ever spent on making a Clio an even better handling car.

 

[EVOgone]

Do you need to ensure both the wishbone and the steering arm angles are corrected ? Do you visually measure it by the being parallel to each other or just to the ground?

 

[mark123]

I have 450 up front and I wouldn't want to be that stiff on even a relatively smooth rally like Abingdon. More like 200-250 and help control roll with a FARB as mentioned.

Circuits I would go stiffer and not be bothered about FARB.

 

[sam JFM]

But you cant buy a FARB. I am currently running 300lb fronts and 200lb rears so I am considering upping it by 50lb

 

[ed55j]

I went for 350lb 9inch springs on the front of my road rally car, they work well on mixed surfaces and feel spot on.

 

[sam JFM]

I went for 350lb 9inch springs on the front of my road rally car, they work well on mixed surfaces and feel spot on.

What dampers are they on?

I should imagine that a RR car would/should be softer than a tar car? (you guys have quite a lot of rough stuff don't you?)

 

[ed55j]

They are bilsteins. The rough stuff is usually only a small percentage of the rallies,i try to take it easy and then push on on the tarmac which is where the clio excels.

 

[NorthloopCup]

Do you need to ensure both the wishbone and the steering arm angles are corrected ? Do you visually measure it by the being parallel to each other or just to the ground?

Yes and no mate. You need to measure the bump steer ideally and whatever the best position is would be where you'd leave the steering arms. This can vary between upwards or downward towards the hub and parallel to the ground. It all depends on which position gives the least amount of bump steer.
Clios when lowered do suffer with massive bump steer though on the original hubs. The Ackerman angle ain't all that good neither but that's another story for another day.

 

[Steven103]

To add to Northloop's 4:30am (?!?!) comments...


Bumpsteer occurs whenever the arc described by the steering arm (blue line) is different in any way (length, angle, radius etc.) to the arc described by the wishbone (red line for arguments sake) when you look at the car approximately head on. So to eliminate bumpsteer the two lines need to completely overlap.

The difficult to imagine part is that they only have to overlap when you view the wishbone dead on. Because cars have inclined wishbones (from a side view, to give some anti-dive force under braking) "dead on" is actually a bit of a funny angle and not quite head on to the rest of the car.

The perfect steering arm (for bumpsteer only, ackermann would be set to zero if you did this which is bad) would be parallel to the wishbone from the front view, inline with both inner wishbone bushes in the side view and be exactly the same length as the wishbone. So you'd potentially have to raise/lower the entire steering rack as well as fit a "correction kit" to get it all lined up properly in all planes.


I am sure that makes very little sense unless you can picture it in 3D and know what it should look like xD There's probably a great animation of all this on youtube or something...

 

[NorthloopCup]

To add to Northloop's 4:30am (?!?!) comments...


Bumpsteer occurs whenever the arc described by the steering arm (blue line) is different in any way (length, angle, radius etc.) to the arc described by the wishbone (red line for arguments sake) when you look at the car approximately head on. So to eliminate bumpsteer the two lines need to completely overlap.

The difficult to imagine part is that they only have to overlap when you view the wishbone dead on. Because cars have inclined wishbones (from a side view, to give some anti-dive force under braking) "dead on" is actually a bit of a funny angle and not quite head on to the rest of the car.

The perfect steering arm (for bumpsteer only, ackermann would be set to zero if you did this which is bad) would be parallel to the wishbone from the front view, inline with both inner wishbone bushes in the side view and be exactly the same length as the wishbone. So you'd potentially have to raise/lower the entire steering rack as well as fit a "correction kit" to get it all lined up properly in all planes.


I am sure that makes very little sense unless you can picture it in 3D and know what it should look like xD There's probably a great animation of all this on youtube or something...

I still need to put my gopro in the wheel arch and go out and do some filming. I'll see what I can do as it would make for potentially the most boring, yet interesting video! Lol

 

[Steven103]

I still need to put my gopro in the wheel arch and go out and do some filming. I'll see what I can do as it would make for potentially the most boring, yet interesting video! Lol

As you say interesting to see something moving, but boring because it does exactly what you're expecting.


Pointing it at OE wishbone bushes could be interesting, likewise maybe some rear beam action to see it flex.

 

[NorthloopCup]

As you say interesting to see something moving, but boring because it does exactly what you're expecting.


Pointing it at OE wishbone bushes could be interesting, likewise maybe some rear beam action to see it flex.

I'm on cup racer wishbones so I doubt there will be much movement tbh. I'll have to get some filming done.