simon's learning what to do with the polo thread

[simon k]

In summary a strut tower to strut tower brace on a macstrut car is a no brainer. But spending the extra on a triangulated one may not be good value for money.

that's excellent Gary - that makes a lot of sense - thank you very much. I'll see what I can find in my scrap pile to make one up

I understand what you mean - I also had a look at the firewall on the Polo and it's very hard to get to, triangulating a brace back to it would mean disassembling all sorts of things and probably pulling the dash apart.

Thanks for the info on the tyres too

stealing this from Sam's thread...

We really want the front lower control arm pivot points pointing upwards towards the centre line, around crankshaft centre is a good rule of thumb. That's not the actual roll centre, it's a bit lower than that in a MacStrut car, but it's a pretty good indicator. Plus you want the car to gain camber on suspension compression, not lose it as would be the case with control arms parallel to the ground or even worse pointing downwards towards the centre.

...

Around 10 mm of negative rake is OK, measured at the jacking points just behind the front wheel and in front of the rear wheel. I confirm that and then translate it to the wheel to guard measurements for easier checking. Beware of damaged jacking pints of course.

I'm doing a Winton sprint this Sunday, so on Saturday I'll put the 15" wheels on and take 1" or so out of the rear and set up the front as you've said there. When I test fitted the 15" wheels there was a LOT of clearance between the tyres and the guards... I'll machine up some bits of nylon to put under the rear springs when the big wheels go back on

[sambb]

yeah the front rides pretty much at stock ride height to have "by eye" good control arm angles for roll centre. With 15's it looks ridiculous. When I have a full tank of fuel it is noticeably bum down (neg. raked).

The 'firewall' on our car is just a flimsy piece of tin. There is a huge gap behind it (houses all the wipers assemblies, air intakes and motors etc) and the real firewall which is right under the windscreen. Like Gary said it would give you zero gain to triangulate to it. So nice and easy straight across tower to tower for that one.

[h100vw]

then there's the rear, do things like this make any difference?

I have one like that, you could tell if the bolts came loose, it creaked going on and off the drive. Whether thats an indication of stiffness or not, who knows. Not sure I have the senses to pick it on the street...

It's modified from a mk5/6 GTI one. M8 nutserts into the body seat still fits etc

[Sydneykid]

A job for the machinist, what I'd suggest is a spacer (alloy) that enables the front outer ball joint to sit on top of the control arm instead of below it. That won't fix the roll centre (too low) problem but what it will do is assist in optimising the dynamic camber change. The pivot points will still be in the same place relative to each other hence the roll centre will still be at the same height. But the control arm will be lower on the outer than it is on the inner, hence as the suspension compresses (in roll) the negative camber will increase maintaining the tyre contact patch.

The above shouldn't affect the bump steer as the steering arm and lower control arm ball joints will still be in the relative positions. But I'd check it just to be sure,

The only way to really fix the roll centre problem would be a change in the upright to move the ball joint pivot point lower. Have you guys looked at an equivalent Audi upright? I recall on the early TT's there were 2 or 3 different uprights with different roll centres to compensate for the different models ride height. The one we ended up using was 18 mm or so lower, which raised the roll centre about 30 mm so well worth doing.

This also shouldn't affect the bump steer as the source vehicle should be OK in that regard, but again always worth checking.

Cheers
Gary

[simon k]

That won't fix the roll centre (too low) problem but what it will do is assist in optimising the dynamic camber change. The pivot points will still be in the same place relative to each other hence the roll centre will still be at the same height. But the control arm will be lower on the outer than it is on the inner, hence as the suspension compresses (in roll) the negative camber will increase maintaining the tyre contact patch.

that's a good one, should be quite an easy modification - on minis they use a balljoint extender that's about 1" thick, is that the amount of change you're looking at?

A job for the machinist, what I'd suggest is a spacer (alloy) that enables the front outer ball joint to sit on top of the control arm instead of below it.

Since the balljoint is currently sandwiched inside the control arm, is what you're suggesting there as simple as making a plate to sit inside the arm (just so it doesn't crush), then another plate to sit between the arm and the balljoint (and using longer/thicker bolts), or is it something more substantial?

edit: maybe like this...

The above shouldn't affect the bump steer as the steering arm and lower control arm ball joints will still be in the relative positions. But I'd check it just to be sure,

The only way to really fix the roll centre problem would be a change in the upright to move the ball joint pivot point lower. Have you guys looked at an equivalent Audi upright? I recall on the early TT's there were 2 or 3 different uprights with different roll centres to compensate for the different models ride height. The one we ended up using was 18 mm or so lower, which raised the roll centre about 30 mm so well worth doing.

This also shouldn't affect the bump steer as the source vehicle should be OK in that regard, but again always worth checking.

Cheers
Gary

very interesting - no upmarket wrecking yards near me, go Sam go!!

googling around I see what you mean about different uprights, here's a comparison from one SEAT to another

[simon k]

there's a good post on this exact subject on this page - saying the same (I think!) as you Gary - and almost directly stating that TT uprights are the go

VWVortex.com - Roll center adjusters/ball joint extenders

[simon k]

here's another interesting read: Roll Centre Correction - The Pinderwagen

[sambb]

I did look briefly into the audi upright. We know that Audi ball joints fit our upright so know that ball joints will fit in. I assume tie rod ends would be easy. The question is will the driveshafts fit ( I know track people in the UK have mentioned running Audi driveshafts as ours were getting expensive?) and will our struts match the upright too. Apparently the ones you want are Audi TT Mk1 pre-recall - the recall where they added the rear gurney flap on the boot and swap uprights. Apparently the thinking was that you shouldn't let people on the road have uprights with good camber gain because they will just grip grip and then let go when the tyre gives up. Far better to have an upright like ours probably that starts to plough understeer you the moment you go above 7/10ths so that you can always get it back and can never get to a point where you are at a fatal speed when you leave the road.

[simon k]

sometimes I amaze myself... I took the rear springs out and cut about 20mm off them, just by eye... put them in, measured the rake off the jacking points like Gary said, 10mm down in the bum. 185mm at the front and 175 at the back

[sambb]

wisdom right there. nice work.


That second post you added is a beauty. I wont try explaining roll centre/ball joint location to people ever again, I'll just send that.
I think the problem with ball joint extenders on our hubs is that you still cant lower the car easily without mangling the steering angles very quickly too. The steering rack simply cannot be raised and you'd have to go custom on the tie rod end side to correct there.

That's why the Audi TT spindles look the goods as I'm sure they'd have ball joint and tie rod end positions in step with one another. Didn't know they are alloy too!

That leaves the diameter of the receiver for the strut tube and the driveshaft fitment to confirm. If that's a go then you'd also be swapping brakes over with it, ABS sensors etc but that wouldn't be too bad - probably couldn't run 15's over those brakes though.

I could be wrong but I still swear I heard that even within MK1 Audi TT there were two different spindles and that the recall had something to do with that so not all spindles were created equal within that model.
-

[simon k]

seen this? Vehicle Suspension: Front View Online Suspension Simulator - need to take a bunch of measurements but interesting to play with once they're in there

definitely worth having a good look at some TT spindles, I'd be pretty confident that the strut tubes are the same size, the CVs are different but there ought to be some combination of parts that works

[sambb]

I've heard of Audi A3 driveshafts going in I think.

[simon k]

reasonably happy with the sprint at Winton today - tyres and suspension took 2.5 seconds off, and it was a much hotter day so that could easily account for another second - but not enough laps for the money - it works out at $7.50 per lap. 4 sessions of 4 laps plus 4 laps practice. Not enough seat time I reckon

my best time was in the last session, I'd learnt how to take some corners better by the end of the day, but my 2nd best time was in the first session when it was cooler.

Something was wrong during the 2nd session, the car just felt sluggish - after the chequered flag I was enjoying the feeling of the airconditioning cooling my hand through my glove... oh sh*t, idiot... I reckon that took 15kph out of the car on the main straight

During the 3rd and 4th sessions the temp gauge was getting up to the 110° mark, and I assume the ECU was cutting timing as it felt doughey after the first lap or so as the temp crept up. I could hit 160 along the main straight on the 1st & 2nd lap, struggled to get to 150 after that

I think I have also experienced boiled brake fluid for the first time; the pedal is spongy for the first half of its travel and will pump up pressure as if there is air in it. I'll bleed it after tea and see what comes out. I have a couple of bottles of the good high temp stuff that's been recommended on here, and it's probably time I fitted the new rotors and pads I bought last year.

[sambb]

That's a pretty fat improvement. Which tyres did you run? That's why I did my oil cooler - its always been known that oil temps get way up but they drag the water temps up too via the heat exchanger. Whether it dumps fuel or pulls timing I'm not sure but I haven't felt that yet. I know Sean in QLD temps says he's felt it quite often.

My mate is building a Clio RS and I nearly died when I saw how much the firewall/master cylinder moved. He made up a nice brace for it with associated heat shield and it is rock solid now, so after seeing that and after what you just mentoned I'm a bit inspired to do that now.

[simon k]

That's a pretty fat improvement. Which tyres did you run?

F: A050, R: R888R. I took the NT01s with me, but left them off. On paper the A050/R888R combo is the best, widest wheel, widest track and better tyres...

That's why I did my oil cooler - its always been known that oil temps get way up but they drag the water temps up too via the heat exchanger. Whether it dumps fuel or pulls timing I'm not sure but I haven't felt that yet. I know Sean in QLD temps says he's felt it quite often.

yeah - I read all of your posts about it - I'll go back and review... basically bypass the water heat exchanger and add a sandwich plate for the oil cooler, yeah?

My mate is building a Clio RS and I nearly died when I saw how much the firewall/master cylinder moved. He made up a nice brace for it with associated heat shield and it is rock solid now, so after seeing that and after what you just mentioned I'm a bit inspired to do that now.

I was talking more that I reckon there is a change in the pedal pressure when I was driving home. It just felt like the pedal was going further to the floor. I bled both fronts. The fluid was darker than I'd expect, and a little bit of air came out of the left. Not sure...