suspension tuning

[Steven103]

Interesting thing to google. The ones I saw only measured bump steer? The principle is similar so I guess there are more expensive ones that measure the distance on two planes and leave you to do a bit of maths.

Astonished that you can retail those sorts of items for several £££ though. They cost the same as a decent pressure gauge and pyrometer LOL!

 

[Chip-mk1]

^^^^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.

Or just set your coilovers to minimum height, stick a camber gauge on, then put a jack under each sill and raise it 10mm at a time (on both sides to keep car level) and keep checking the guage.

 

[Tav]

Stiffer roll bar on the front of a front wheel drive car, not so sure that'd be a good idea.

 

[p@blo]

Stiffer roll bar on the front of a front wheel drive car, not so sure that'd be a good idea.

But what if its too soft in the first place?

 

[Chip-mk1]

Stiffer roll bar on the front of a front wheel drive car, not so sure that'd be a good idea.

What is making you say that?

 

[Steven103]

That comment reminds me of the "Clio aerodynamics" thread where a sizeable amount of members with not the slightest formal background in mechanical engineering, let alone aerodynamics, were guessing at the effect of the modifications someone had done to a track car, when it was modifications so complex you wouldn't even bother trying to guess whether they would have a positive or negative impact you'd just go straight to CFD or wind tunnel testing.

It really does not take any leap of the imagination to find yourself in the plausible situation where you add front roll stiffness to a point that, all other things being equal, you are reacting too much weight at the front too not cause understeer but by restricting the roll angle you are actually gaining more from controlling your contact patch.

In my eyes relative roll stiffness vs controlling the roll angle could be seen as the exact same type of not-immediately-obvious-trade-off as springs. How many of the general public would say "as soft as possible" to the question "how stiff should springs on a racing car be?"

/blabbering & ranting at general ignorance


EDIT: Infact whilst I'm on a rant, the phrases:

* body roll causes weight transfer
* weight transfer/body roll depends on springs
* fit stiff springs for less weight transfer
* low profile tyres are better
* small wheels are better

are the top 5 fastest ways to make my brain explode and bring out the inner keyboard warrior!

 

[MG cup]

Put the keyboard down love

 

[Steven103]

Haha I'm getting better! I still type out a reply to the silly threads, but can now hold backspace instead of clicking post and immediately go to a different website :L

I did lol at my complete inability to type the whole sentence in that 1600cc F4R thread though, so I too am guilty of contributing to Roy's "Influx of Idiots - Third Edition"

 

[Chip-mk1]

Small wheels are better on a 172. It means cheap tyres. Lol.

 

[Tav]

But what if its too soft in the first place?

Add spring rate, not roll bar stiffness.

My Polo has a pretty hefty roll bar on the front due to it making up half of the wishbone (it joins a track control arm to triangulate). Car has the habit of lifting the inside wheel or certainly unloading it heavily. So you can get quite a lot of under steer under power since the car doesn't have a locking diff. Preference now is to ditch the roll bar up front, up the spring rate to control roll at the front and then stiffen roll stiffness at the rear to aid turn in.

 

[NorthloopCup]

In an ideal world the entire package should be tuned as one, and the spring rates are normally one of the last things to be settled on. Damper rates/frequencies, camber, roll centres etc etc are all calculated and corrected first.

 

[Chip-mk1]

Add spring rate, not roll bar stiffness.

My Polo has a pretty hefty roll bar on the front due to it making up half of the wishbone (it joins a track control arm to triangulate). Car has the habit of lifting the inside wheel or certainly unloading it heavily. So you can get quite a lot of under steer under power since the car doesn't have a locking diff. Preference now is to ditch the roll bar up front, up the spring rate to control roll at the front and then stiffen roll stiffness at the rear to aid turn in.

And as a result of relying entirely on spring rate for all your roll resistance, the car doesnt like to dip under braking so the brakes now work less well?

Sorry but I will stick to a balance of ARB and Springs to get the right rate when im trying to make a car handle not just rely on springs alone.

 

[Steven103]

Small wheels are better on a 172. It means cheap tyres. Lol.

Yes I completely understand where the advantage comes from for Clios and I'm not suggesting everyone move to 17s and big tyres "because race car," the track (even race) cars on CS don't have the budget to make big wheels & tyres work. It's just the assumption that small = better, when it actual fact it's the complete opposite and wheel/tyre size is purely limited by mass, inertia and space under the wheel arch.

Likewise (as we're finding out now) the assumption that you want/need stiff springs, when in actual fact the very well established fundamentals of mechanics & vibrations all show that you want the softest springs possible to minimise contact patch variation and that minimum spring stiffness on a non-aero car is only limited by suspension travel and a desire to control the CP under roll (jacking, camber, roll steer etc.)


On an unrelated note, what are peoples' thoughts on where the instant centre is for a beam axle? Perpendicular to top mount and parallel to beam? Then RC as usual is the intercept of CP and vehicle centreline?

 

[Steven103]

Small wheels are better on a 172. It means cheap tyres. Lol.

Oh I completely understand the benefit of cheap I'm not suggesting CS ditches the 15" F1s and everyone move to 17s and big tyres "because race car," the track (even race) cars on CS don't have the budget to make big wheels & tyres work. I personally suspect that what actually makes 15s work on a Clio is actually having a much better aspect ratio for the tyre (since there are a whole bunch of grip mechanisms that get better with bigger sidewalls) rather than losing a tiny bit of unsprung mass and inertia (even if mass & inertia gets squared in a bunch of equations). It's just the assumption that small = better, when it actual fact it's the complete opposite and wheel/tyre size is purely limited by mass, inertia and space under the wheel arch.

Likewise (as we're finding out now) the assumption that you want/need stiff springs, when in actual fact the very well established fundamentals of mechanics & vibrations all show that you want the softest springs possible to minimise contact patch variation and that minimum spring stiffness on a non-aero car is only limited by suspension travel and a desire to control the CP under roll (jacking, camber, roll steer etc.)


On an unrelated note, what are peoples' thoughts on where the instant centre is for a beam axle? Perpendicular to top mount and parallel to beam? Then RC as usual is the intercept of CP and vehicle centreline?

 

[Steven103]

How's that happened LOL. Opps.

 

[NorthloopCup]

How's that happened LOL. Opps.

10 out of 10 for enthusiasm there mate! Lol! All I will say is sometimes you can look into things too deep and not actually gain anything as the end result. Trust me, I've spent a lot of time calculating things and pretty much just added confusion to myself along the way! Lol! The other enemy is cost. If your pockets are deep enough you can correct/re-design anything and everything, which is basically how the hubs came about.
Ultimately the Clio has a very potent chassis in factory form - even when only fitted with lowering springs, so all that's left to do is enhance that really. Keep it simple is what it's about from experience.

Fair play though mate.