simon's learning what to do with the polo thread

[Sydneykid]

For caster my process is relatively simple. The text book is plus and minus 20 degrees of wheel movement, but I don't really care about the text book number. I just want as much caster as I can get, I have never been able to physically get more caster than works (on a production based car). What I am really interested in is making sure that the camber change is the same side to side. So whatever test I apply it must be the same side to side. My usual process is half a turn one way, measure camber, then half a turn the other way, measure camber. Do the same on the other side and compare them. Then pick the side with the least amount, add some more adjustment and remeasure. Repeat until the readings are the same.

The only reason for the 20 degrees is that's the common amount of steering lock used by most aligners, so we can compare car A with car B (ie; mine has 6.5. degrees, what does yours have?). Personally I don't care, it only matters that it's the same side to side and I have as much caster as I can get.

If you do want to be able to compare them either do the 20 degree test yourself or take it to an alignment shop and get then to check the caster. Either way just count how many turns of the steering wheel = 20 degrees. Then you never have to go back or measure the 20 degrees ever again, well until you change the steering ratio anyway.

With race cars it's kinda useful as when competitors ask what caster we run I can honestly say that I don't know.

Cheers
Gary

[Sydneykid]

edit 2: measuring caster, check this out... https://disco3.co.uk/gallery/albums/...ent%5B1%5D.pdf

Thrust angle correction, yep that's relevant on a FWD car.

Cheers
Gary

[simon k]

What I am really interested in is making sure that the camber change is the same side to side. So whatever test I apply it must be the same side to side. My usual process is half a turn one way, measure camber, then half a turn the other way, measure camber. Do the same on the other side and compare them. Then pick the side with the least amount, add some more adjustment and remeasure. Repeat until the readings are the same.

yes - that's the right way to look at it, the actual number is irrelevant, it's the change that counts - like putting a car on a dyno, I want the number to get better, the number isn't relevant

With race cars it's kinda useful as when competitors ask what caster we run I can honestly say that I don't know.

lol, good call - "how much caster mate?", "...enough..."

[sambb]

I generally left the ball joint in the hub. I jack the hole front end and disconnect the FARB. Then I go nuts with WD/CRC etc and get it soaking while I do the next few things. On the difficult side I knock out the tie rod end so that the hub can swivel a bit more which helps with that last little bit at getting the strut base to pop out. Disconnect /clear all the brake lines etc. With struts I compress the springs - with coilovers I measure where the collars had been and drop them down to remove any spring preload. Spread the hub with a spreading tool (hex key ground into an elliptical shape). With my spreader I fluked its size/shape so that I turn it to spread the hub and at its maximum I take out the 1/2in drive and the key stays put holding the hub open. I then lump hammer the only real part of the hub side to side till it wont go any further and then start rocking the hub side to side and getting a tilt on it while hitting until the strut base pops out and hopefully doesn't mash a brake line in the process. The B8's were definitely harder than my MCA's. Wont help you now that you don't have a spring seat anymore but I had a special length rod that I used to fit under the spring seat and I'd get a little upwards force into the spring seat with a second jack, just enough to hold it up a tad for those last hits. The advantage of the MCA;s with their separate damper stroke and spring preload setup is that I can wind the damper stroke/strut base upwards to shorten the hole strut and it nearly lifts clean out after a couple of hits. The B8's were definitely harder to extract. Yeah there's no reason why you couldn't knock out the ball joint on that difficult side. I don't think you'd need to take the drive shaft out. That, with a tie rod end knocked out too would let you swing it away from the control arm/ball joint and then you could knock it out easier. I did it that way when I stripped my last Polo and I do remember thinking why the hell didn't I always do it like this.

[simon k]

had another sprint at the local track yesterday, I'm reasonably happy. I took 0.5 seconds off my best time which was in the 2nd session of the day, and most people said the track was a second and a half slower than usual, so I'll take that

I only did 1 lap of my first session, as I went to move into the lineup to enter the circuit my power steering stopped working. It had been working fine, I turned the ignition off and back on again but still no-worky. I went out anyway and did a lap but it was way to heavy for me. I had my laptop so checked the codes and it said no communications to the steering module - checked the fuse and sure enough, hairline crack through it - I'd let my tyres down right before I went to line up, I guess the extra caster plus low tyre pressures and maybe the fuse was old as well. It's one of the thin strip type fuses on top of the battery, one was broken when I first bought the car, I'd replaced a couple but not this one... I borrowed a socket and put a piece of wire across it.

It's a lot easier to drive fast through turns now, though the car still picks up its inside rear wheel, I can feel it and someone said 3-4" or so. I haven't seen any photos, but the front tyres weren't scrubbing the sidewalls like usual and I could feed it from one corner to the next. Braking from ~130kph at the end of the straight is fun, I reckon the backend is almost off the ground, it's like it lifts up and steps out to the right just a little bit. A load cell on each spring seat would be a fun engineering exercise...

It still won't give me any oversteer, any attempt results in tyre juddery understeer - I don't even get a squirm from the back. The nose is sitting a little lower than the rear - I recall some conversations b/w Sam and Gary about negative rake. The front is only low because I hadn't adjusted it from where I dropped it on the ground last weekend, I did lift it up a few mm but maybe it needs 1/2" or so.

I also had a problem with the inlet manifold hose popping off the 90° MAF pipe. I was using the standard spring clip and (rubber) hose, the hose was very soft and warm. I put a screw clamp on it this morning, will find one for the other end, and maybe buy a silicone hose (and yes Sam, hair spray...)

[sambb]

Good to hear it was better. I saw your time relative to your last visit there and it was 0.5 sec, I was thinking hmm maybe you're not going to be happy with how it turned out, but it sounds like it was better.
What spring rate did you work the fronts out to be? What rear springs did you have in - the cut ones or the H&R's?
So even a little midcorner lift couldn't get the rear a bit lively? If you're really stick you can run the rear pressures higher than the fronts which helps the back slide a bit. Dunno - if the rake you had is because the front is too low then maybe an overly low front roll centre was making the front feel softer than if the ride height was up a bit?? To my thinking if you'd have lowered the rear though then you'd be making the rear more stable, not less, and therefore less likely to oversteer so I don't think it'd have been that. Or maybe with the front springs you are running its still a tad soft for the track and its crying out for a FARB that'd give a bit more support to the front when the inside rear starts unloading. I only say that because even for the street (with 400lb springs) when I went back from the whiteline front bar to standard, I can noticeably feel the car leaning on that outside front a bit harder now. I think that'll help my current diff work a little better at hillclimbs/on cold tyres/on bumpy tracks, but may have injured myself on smooth fast tracks with that choice. Just thinking out loud.

[simon k]

Good to hear it was better. I saw your time relative to your last visit there and it was 0.5 sec, I was thinking hmm maybe you're not going to be happy with how it turned out, but it sounds like it was better.

yeah, I was a bit surprised that I hadn't picked up much time, but then as other people were saying they'd dropped a fair bit of time so it's fine. I'd missed my first session, and it had warmed up quite a lot coming in to the second - not good for boost

What spring rate did you work the fronts out to be? What rear springs did you have in - the cut ones or the H&R's?
So even a little midcorner lift couldn't get the rear a bit lively? If you're really stick you can run the rear pressures higher than the fronts which helps the back slide a bit. Dunno - if the rake you had is because the front is too low then maybe an overly low front roll centre was making the front feel softer than if the ride height was up a bit?? To my thinking if you'd have lowered the rear though then you'd be making the rear more stable, not less, and therefore less likely to oversteer so I don't think it'd have been that.

Nup, even a big mid-corner lift wouldn't unsettle it. I did think about putting more air in the rear tyres, but I think once the weight is on that outside front and the inside rear has picked up, then the outside rear is always going to just follow the fronts around. Breaking traction isn't going to happen easily.

My fronts are 4.9kg/275lb, the rears are the cut Hondas that are theoretically at just about the same at 5kg/280lb.
If yours are still the front 7kg/392lb and 8kg/448lb, then you're a lot stiffer.

(BTW the H&Rs have gone to someone else in Melbourne).

Or maybe with the front springs you are running its still a tad soft for the track and its crying out for a FARB that'd give a bit more support to the front when the inside rear starts unloading. I only say that because even for the street (with 400lb springs) when I went back from the whiteline front bar to standard, I can noticeably feel the car leaning on that outside front a bit harder now. I think that'll help my current diff work a little better at hillclimbs/on cold tyres/on bumpy tracks, but may have injured myself on smooth fast tracks with that choice. Just thinking out loud.

If you reckon you can feel the car resting on the outside front without the fat FARB then it's what I'm feeling. I don't want to make the front any stiffer, it's borderline uncomfortable on my commute so maybe it's time for that. Sparesbox has them for $222 (20% off) for the next couple of days, but I'm running out of things to sell...

[sambb]

Yeah it sounds like we have a similar F:R roll stiffness distribution - me carrying a bit more of it in the rear with spring and you with the bar. I'm just stiffer overall but considering you're not on R specs you're probalbly in a good spot. If FARB's were easier to fit I'd send mine down for you to try but unfortunately its a committed fit up. Yeah I think power on traction on corner exit is better with the softer OE FARB but you can feel the car taking a bit more roll angle than previously through a constant radius corner and it definitely rides rougher roads better ie isn't as figety over broken surfaces and follows undulations smoother without crashing. As it is I'm not keen to move my 22mm FARB on just yet until I've been back on the circuit with the OE bar and i'll want to run the car with the plate diff. I suspect with the added front end traction a plate diff will inherently bring, that possibly I wont need to run the softer bar to achieve that and i'll probably feel the need to go back to the stiffer FARB down the track.

[Sydneykid]

Two quick observations;
The problem with the Polo's is getting the rear roll centre (RC) low enough, it really needs to be subterranean, at least 50 mm below ground level. But that's not possible with the torsion beam, well not without some extensive re engineering. So the best we can do is to lower the rear ride height which reduces the RC plus the centre of gravity (CoG). Both of them then help to reduce the amount of weight transfer to the front outside wheel, which is what causes the mid corner and exit understeer.

A heavier front swaybar is a bandaid, it also helps to reduce the amount of weight transfer to the front outside wheel but it has a downside in increasing the roll stiffness which may push it too high so the tyres lose traction. That's why on the FWD race cars we don't run a lot of front anti roll, because we control the amount of diagonal weight transfer with the rear swaybar and the low(er) RC and CoG.

So first tip, make sure the front RC isn't too low (keep the control arms pointing down towards the wheel) and then lower the rear ride height. Around 10 mm negative (rear down) rake is a good place to start. Yes, it looks funny, but it works.

Tip 2, rear toe out, on tight (low speed) circuits we run up to 8 mm toe out (4 mm each side), at fast flowing circuits it doesn't ever get less than 4 mm (2 mm each side). If we ran the "fast circuit" toe out settings on a "slow circuit" it would cost upwards of half a second a lap due to reduced corner entry speed (understeer). So it is very important.


Cheers
Gary

[simon k]

got it - setup changes this weekend - thanks Gary

I have some leftover pieces of coilover sleeve, I could (but probably won't) make them into rear height adjusters... the rear is pretty low so I'll just lift the front up and see what its like

[sambb]

Ok so even a negatively raked torsion beam rear ended car will likely still have a higher rear roll centre than an IRS car with positive rake.
Simon i'll get a pic of my weird looking rake up on here in a bit. It looks like a standard car with a safe in the boot.

[simon k]

It looks like a standard car with a safe in the boot.

cool... I'll pretend I have several dead bodies

[Sydneykid]

Ok so even a negatively raked torsion beam rear ended car will likely still have a higher rear roll centre than an IRS car with positive rake.

Yep, sort of. The double wishbone IRS cars have very adjustable RC, but for CoG reasons we run them with fairly flat rake. Strut based IRS cars are not as user friendly and in general we have to run negative rake with them to get the RC close to where we want it. With some we still can't get it low enough. On cars with beam axle style rear suspension we run a Mumford link and can get the RC wherever we want it. With torsion beam rear suspension I'd like to try a Mumford link, but it would require some engineering. Possibly even removing the torsion beam all together.

Cheers
Gary

[simon k]

With torsion beam rear suspension I'd like to try a Mumford link, but it would require some engineering. Possibly even removing the torsion beam all together.

That's the name of it... I read it in another post of yours a while ago, forgot it, then couldn't find it again




Obviously that's a live axle that doesn't bend so it's transferring load from one side of the car to the other, I can't visualise what it actually does... I'll read up

fun little CAD exercise if nothing else...

[Sydneykid]

That's the name of it... I read it in another post of yours a while ago, forgot it, then couldn't find it again


[ATTACH=CONFIG]39144[/ATTACH]

Obviously that's a live axle that doesn't bend so it's transferring load from one side of the car to the other, I can't visualise what it actually does... I'll read up

fun little CAD exercise if nothing else...

It operates like a panhard rod or a Watts link in locating the wheels laterally, but they are both limited to an above ground RC. As far above ground as the brackets on a panhard and the centre pivot in the case of the Watts. A Mumford enables a much lower RC, even below ground ie; where the outer links cross over if extended virtually.

On the Polo the torsion beam is what locates the wheels laterally, as well as acting as a swaybar. So I'd like to try removing the torsion beam and replacing its function with a Mumford link and a separate swaybar. Would make a huge difference, with fully independent suspension, solid lateral location, separate swaybar adjustment and a tuneable RC.

A useful reference;
Suspension linkages for solid (rear) axles...

For accuracy it doesn't "transfer load from one side to the other" it transfers the lateral load to the chassis via the pivot points (that are mounted to brackets attached to the chassis).


Cheers
Gary