suspension tuning

[bozothenutter]

Hi,

I want to reduce bodyroll on my car (spax RSX coilovers...I know I know.....)
i'm guessing the best way is to increase spring rates.
so the question is, should the increase be proprtional front to rear since I am happy with the balance of the car at the moment?
Does anybody make progressive springs for coilovers? eibach would have you use composite springs ie two shorter ones of a different rate (ERS system)
the springs currently are 60/40nm f/r

 

[NorthloopCup]

Increase the front rates to 70/80 and up the rears to the same. You will also find that a lot of body roll is induced by the roll centres if the car is lowered by a significant amount.

 

[Steven103]

Correct, to maintain the same over/understeer balance spring rates need to be adjusted proportionally to each other.

Increasing both the front and rear to 70/80 will change the relative roll stiffness to give more oversteer (or less understeer, depending on what his current balance is). I'm not saying 70/80 both ends is wrong, the standard car needs more roll stiffness at the rear afterall, I'm just saying OP has specifically said he's happy with the balance of the car.

I presume he is wanting to reduce roll angle in order to better control camber change in roll.

 

[Chip-mk1]

Its a shame a firmer ARB isnt readily available for the front TBH!

 

[NorthloopCup]

Correct, to maintain the same over/understeer balance spring rates need to be adjusted proportionally to each other.

Increasing both the front and rear to 70/80 will change the relative roll stiffness to give more oversteer (or less understeer, depending on what his current balance is). I'm not saying 70/80 both ends is wrong, the standard car needs more roll stiffness at the rear afterall, I'm just saying OP has specifically said he's happy with the balance of the car.

I presume he is wanting to reduce roll angle in order to better control camber change in roll.

From my own experience 60 fronts allow too much body roll and it feels like front end is falling over itself, but it's all personal preference really. A lot comes down to what the car is used for as well. If it's road use I quite like the 60/40 setup (I have had this) but if it's used on track I'd be tempted with 80f/100r. I prefer a slightly softer front personally.

The biggest handling improvement comes from roll centre correction.

 

[NorthloopCup]

Its a shame a firmer ARB isnt readily available for the front TBH!

Same can be said for the rear as well chip. Whitelines don't work as good as everyone's led to believe.

 

[Chip-mk1]

Same can be said for the rear as well chip. Whitelines don't work as good as everyone's led to believe.

Agreed, although the rear is far easier to knock something up for TBH as its such a simple layout.

Its the front that really needs it though, thats only reason I specifically mentioned the front.
The rear is easily controlled with springs really without it being horrible on the road or adversely effecting braking performance, where as the front really is crying out for a firmer roll bar.

 

[Steven103]

I didn't mean to call into question your judgement or preference of spring rates, you're one of the much better placed members on CS to be giving that opinion, so sorry if it came across like that. I tried to word my reply really carefully to say that the OP is 100% correct in terms of the question he asked (changing in proportion to keep the front/rear relative roll stiffness the same), and that the balance will change with your recommendation but that the balance changing towards more oversteer (rather less understeer) is definitely not necessarily a bad thing on the standard car.

TBH I'm shocked Dan@MAD etc. haven't come up with an F & R ARB, especially as you more serious trackday/racing lot keeping mentioning the b word (bladed).

 

[MG cup]

One of the traders has one in the pipeline. I can't remember which one though??

 

[Steven103]

Dan SJM IIRC.

 

[bozothenutter]

NorthloopCup, I have the rear coilover setup, does the 70/80 still apply or should i halve it

so i'll increase the fronts to 70 and the rearsand the rears to 45 (1.166*40) and work from there.....

any idea's on progressive springs? something that starts at 60 and ends at 80 sounds good.....

 

[p@blo]

bozothenutter - would the progressive springs not make it difficult to judge where the benefit was coming from? This is the main reason I avoided using them and just bought multiple sets of single rate to experiment with. You can go fairly high rate wise up front - mine are currently way above the rates mentioned in this thread (doesn't go on the road) in an effort to bodge camber shift from the stock 'clio RS' geo. As Mark/Northloop says the roll centre correction on the clio 2 cup and his own interpretation seems a sensible idea.

My tuppence worth would be to adjust the front initially then dial in more on the rear depending on how forgiving you want it to be. Mine is still comparatively soft at the back (~50n with rear coliover and ARB) although intend on upping it marginally and getting rid of the ARB.

 

[bozothenutter]

Ok, mine still is a daily...but I think I can handle a a bit more stiffness and lack in comfort
Not is a position to experiment a lot (unless i can find lots of springs second hand...)
Good idea though to start at the front first, make that as stiff as I think I want to live with, and then match the rear.

won't making the rear too stiff make the it jumpy?

 

[Chip-mk1]

Ok, mine still is a daily...but I think I can handle a a bit more stiffness and lack in comfort
Not is a position to experiment a lot (unless i can find lots of springs second hand...)
Good idea though to start at the front first, make that as stiff as I think I want to live with, and then match the rear.

won't making the rear too stiff make the it jumpy?

Making either end stiff will make it jumpier over bumps.

Also:
Making the front stiffer relative to the rear will make it understeer more
Making the rear stiffer relative to the front will make it oversteer more

 

[p@blo]

bozothenutter worth looking on ebay NL, UK & DE for second hand Eibach springs key word 'ERS', 'race' or similar. Race teams periodically sell them as i've had several sets myself this way. Would've thought for still using it on the road you'd be fine with up to 80-90N up front on the oem 'RS' hubs & around 50N rear.

 

[p@blo]

Also:
Making the front stiffer relative to the rear will make it understeer more

But wouldn't stiffening front rate (to a point) also help limit the extent of understeer associated with static/dynamic camber trransition from the oem hub arrangement? Granted its a bodge.

 

[bozothenutter]

Making either end stiff will make it jumpier over bumps.

Also:
Making the front stiffer relative to the rear will make it understeer more
Making the rear stiffer relative to the front will make it oversteer more

thanks these basics i know...
more thinking about the roll..ie setting it up to be as stiff and jumpy as i want a daily to be, while keeping the same balance.
I have some jumpy roads around for testing.
The plan was always to match the rears to the fronts.

 

[Goodj]

Making either end stiff will make it jumpier over bumps.

Also:
Making the front stiffer relative to the rear will make it understeer more
Making the rear stiffer relative to the front will make it oversteer more

boom. Everything you need to know.

Besides, a degree of roll is good for a better understanding of where your chassis is at at any given corner.

Alternatively, yeah, firm everything up to the max and get a chiropractor

 

[p@blo]

Besides, a degree of roll is good for a better understanding of where your chassis is at at any given corner.

Seems Ktec have this down to a fine art lately.

They see me rollin' They hatin'

 

[Goodj]

Hear Ktec have this down to a fine art lately.

They see me rollin' They hatin'?

Where's that bloke from manchester who sold a car to buy coilovers for another car, but didn't have the car.
then bought another car using more finance.
then sold it to get more finance for a cheaper car, with different coilovers.... on moar finance.

It was all ok because he sold phones at some retail estate, so he was nuff baller.....

he knew about roll rates, particularly in relation to the FIAT 500. I think optimum value was 5, through a hedge and into a field...


EDIT: LBRENCH!

 

[p@blo]

thanks these basics i know...
more thinking about the roll..ie setting it up to be as stiff and jumpy as i want a daily to be, while keeping the same balance.
I have some jumpy roads around for testing.
The plan was always to match the rears to the fronts.

What is your current rear spring rate? Did you say you'd fitted a rear arb?

 

[NorthloopCup]

@NorthloopCup, I have the rear coilover setup, does the 70/80 still apply or should i halve it

so i'll increase the fronts to 70 and the rearsand the rears to 45 (1.166*40) and work from there.....

any idea's on progressive springs? something that starts at 60 and ends at 80 sounds good.....

Yes mate the 70/80 still applies as I figured it was the rear coilover setup that you had. What's the primary use of the car mate? If it's mainly road use I'd be very tempted to run an 80 front and a 60 rear. You could even start with the 80 fronts first and see what it's like. I know that KW suggest upping the front spring rates to 80 on the v2's and leaving the rears (spring sits in the original location) in a bid to reduce understeer.
60n is about 330lbs in spring rate terms, so if the car is used on the road (including bumpy ones) I think you'll be fine with this at the rear.

 

[NorthloopCup]

Seems Ktec have this down to a fine art lately.

They see me rollin' They hatin'

I'm searching but drawing a blank?? Any links?

 

[p@blo]

I'm searching but drawing a blank?? Any links?

Only seen the one pic on fb Mark. Not clear if someone punted it from the side or if they've just spooned it and managed to roll it on a wide open airfield. For sheer comedy value, I'm hoping its the latter. Lol.

 

[NorthloopCup]

Only seen the one pic on fb Mark. Not clear if someone punted it from the side or if they've just spooned it and managed to roll it on a wide open airfield. For sheer comedy value, I'm hoping its the latter. Lol.

Ah I see! Lol!

 

[p@blo]

Yes mate the 70/80 still applies as I figured it was the rear coilover setup that you had. What's the primary use of the car mate? If it's mainly road use I'd be very tempted to run an 80 front and a 60 rear. You could even start with the 80 fronts first and see what it's like. I know that KW suggest upping the front spring rates to 80 on the v2's and leaving the rears (spring sits in the original location) in a bid to reduce understeer.
60n is about 330lbs in spring rate terms, so if the car is used on the road (including bumpy ones) I think you'll be fine with this at the rear.

Just a thought bozothenutter, but maybe worth upping rear platform height before opting for the heavier rate springs? Would at least give a flavour of what Mark is suggesting at no extra cost.

NorthloopCup - guessing you're not running much rake Mark?

 

[NorthloopCup]

@NorthloopCup - guessing you're not running much rake Mark?

No mate I don't. It's around 10mm front to back when I last measured it.

 

[Steven103]

Wasn't Llbrench the guy who claimed to have 6 PS3s under his bed, in about 2005?

Since this thread has kinda gone waywards and camber change is being mention (which I'd always assumed was OP's reason for wanting to limit roll angle), anyone got a measured/approximated figure for camber change? Deg/mm would be the handiest format?

 

[Chip-mk1]

Wasn't Llbrench the guy who claimed to have 6 PS3s under his bed, in about 2005?

Since this thread has kinda gone waywards, anyone got a measured/approximated figure for camber change? Deg/mm would be the handiest format?

Degrees measured where? On the bolts or on the top mount?

If I had to make a total guess it would be about a 2 mm per degree at the bolts and about 3 times that at the top mount.

 

[Steven103]

Sorry I mean camber change due to bump. (In the context of a thread about limiting roll, I was assuming he wanted to limit roll angle to limit camber change due to roll)

In my defence I did say Deg/mm Maybe spring off , damper on & measure is a rainy (dry) day thing.

Edit: I spose if I'm going to say that ^^^ then you could tell me to eff off and do 1 divided by your last post if I want my deg/mm

 

[Chip-mk1]

Sorry I mean camber change due to bump. (In the context of a thread about limiting roll, I was assuming he wanted to limit roll angle to limit camber change due to roll)

In my defence I did say Deg/mm Maybe spring off , damper on & measure is a rainy (dry) day thing.

Ah fair enough, Ive not measured it on the clio.

Easy enough to do though, like you say just take the spring off and jack it up and down with a camber gauge on.

I suspect its going to vary a LOT based on your starting height though, as the wishbone is so near to flat.


Ie measure it on a car at standard height and it will have nothing at all to do with the figures from one lowered 50mm, if you drop them both by say 10 or 20 mm of compresison from their respective starting points.

 

[Steven103]

I've no experience of more complex (anything beyond static RC) McPherson geometry so it'd definitely be interesting - double wishbone definitely does not give a true linear response, but the rate of change is so tiny it could be reasonably considered linear over the working range, so would be very interesting to compare with a McPherson strut in that sense.

Sorry for going off topic (maybe there needs to be a non-clio VD "anything goes" thread...)

 

[Chip-mk1]

No one will mind that sort of OT mate.


The camber change as im sure you are aware but just mentioning for discussion, is caused by two factors, the first is the shortening of the distance from bottom balljoint to top mount, and the second one which has more impact is the change in distance from the centre line of the top mount to the centreline of the bottom balljoint cause by the wishbone moving in an arc.

If the wishbone passes horizontal then the change will start to go from decreasing camber (getter more neg, so essentially an increase in terms of how most people think of it) to the opposte and your camber will start coming back from negative towards positive.

Thats why I am saying that a lowered car will respond so differently to a standard height car for the same change, as they are at such different points in the arc of the wishbone.

Thats what the roll centre correction kit sold on here recently aims to rectify.

 

[bozothenutter]

Thanks guys, i was hoping this would happen, some good discussion on an interesting subject

 

[p@blo]

I've no experience of more complex (anything beyond static RC) McPherson geometry so it'd definitely be interesting - double wishbone definitely does not give a true linear response, but the rate of change is so tiny it could be reasonably considered linear over the working range, so would be very interesting to compare with a McPherson strut in that sense.

Steven103 - Planning on measuring up when i swap the hubs on mine too. As you say, spring off the strut seems the best way. What gauge you using for measuring up?

Be interesting to get a feel for the difference between the two hub types. Also be interesting to try and compare over the range of caster adjustment too.

 

[bozothenutter]

just seen this on the dutch forum (is actually a UK forum link)

http://www.306gti6.com/forum/showthread.php?id=146338

any thoughts?

 

[Chip-mk1]

just seen this on the dutch forum (is actually a UK forum link)

http://www.306gti6.com/forum/showthread.php?id=146338

any thoughts?

Quite popular things with the VW crew too, the theory is sound and they tend to work quite well for a while, the only issue is that they exert more levarage on the balljoint location hole in the hub and therefore can elongate it over time.

Thats why the kit that james and mark does bottoms out on a flat flange to flat surface and is more positively located, to try and prevent that happening.

But as a cheap alternative these are great, and I would happily buy some if they were readily available in the right size for a clio.
You should do the track rod as well though IMHO, as otherwise you could potentially end up making things worse not better as the bottom arm will be corrected but the track rod wont.

 

[Steven103]

Steven103 - Planning on measuring up when i swap the hubs on mine too. As you say, spring off the strut seems the best way. What gauge you using for measuring up?

Be interesting to get a feel for the difference between the two hub types. Also be interesting to try and compare over the range of caster adjustment too.

I'd use some really short M12*1.25 bolts to clamp a steel rule to the hub. Have a big set square on the floor. Taking a wishbone angle of 0deg (to the horizontal) as 0mm bump - purely because it's a convenient starting point. Also the entire point of doing deg/mm and having a reference point is that it doesn't matter what angle the wishbones are at if you produce data for the whole working range of the suspension. Use a jack to apply bump/droop. I'll be using the inverse sine button on the trusty casio scientific since I don't have a camber gauge.

It's likely my Clio will never see a track so all this is out of interest rather than it being useful, therefore a steel rule seems more than accurate. If I did it "for real" I'd A) be doing it on a flatpatch and B) certainly just be replicating pickup points & balljoint locations in CAD to do a proper analysis.

Certainly the most difficult part I can see of any of this is determining the C of G height which really is the key to optimising anything rather than "correcting" it or improving it by guesstimation. What I'd really like to see would be some aggressive anti dive geometry, allowing someone to do something interesting with bigger rear brakes.

It would seem no-one's really gone to town on developing geometry. I know Chase Racing's chassis guy (spotted a few Formula Student tee shirts so they're definitely very capable guys) has done some pitch analysis by way of suspension frequencies, but that's by far the most advanced thing I've seen on CS which I think is a shame.

 

[NorthloopCup]

^^^^do a google search for bump steer gauge and copy the design idea would be my advice for measuring camber change Steven103
It will keep your readings consistent.

 

[underdog]

just seen this on the dutch forum (is actually a UK forum link)

http://www.306gti6.com/forum/showthread.php?id=146338

any thoughts?

Great find that. iv been searching for something similar for my focus and i cant find anything like that. if it was honda civic you can buy extended ball joints by buddy club