Sam's build thread

[Sydneykid]

I'm stoked you said that regarding negative rake. I've tried that many different springs/heights to run the car raked, level and slightly bum down and always found that the latter gave the best handling despite everyone telling me its not right. Ive always run the front ride height at what would give level control arm piviots. Of course I can go up a tad and will if you think it'll help. One thing I've always been unsure of is working out the LCA pivot point to work off when comparing its height to the balljoint. The OE setup has anti-dive built into it as the front LCA pivot is much lower than the rear. So do I measure the rear LCA pivot height, the front, and then take an average. Or once I know the LCA inner pivot axis, do I work out a point along it that lines up in top view with the balljoint and that becomes a virtual inner pivot - make sense? Because at the moment I'm just working off the front inner pivot/bolt centre.

The inner (front) lower control arm bush pivot point and the ball joint pivot point are the references. So the first job is to identify exactly where the ball joint pivots. The bush pivot point is easy, it's the centre of the bolt. Depending on the car and what's in the way I use a steel rule, a piece of string or a laser pointer to determine the roll centre. If the engine is out, with nothing in the way, it can be exact, but that hardly even happens, so approximations are fine. In a production based car it's not like we can adjust the roll centre in tiny increments like we can in an F3 or a V8Supercar anyway.

FWIW, we call the rear lower control arm bush a caster bush, because that's what it mainly controls, the amount of caster.

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.

The problem with anti dive (under brakes) geometry is that it creates lift on acceleration. Taking weight off the front wheels when they most need it. Lowering the rear caster bush is something we do on Golfs and WRX's for example, that's why there are aftermarket kits for it. You might want to have a think about how to achieve that on your Polo.

I do remember Ortiz somewhere saying that the only thing on a rear twist beam that would limit how low you should/could go is ground clearance - alright i'll whip out the lowest collar initially and see what it gets me.
Today I jacked the car so that it was 2wheeling. The inner rear main spring was wholly over the threads and two of the helper coils had started to unbind on the back edge so maybe keep the helpers in?

Yep, at that ride height keeping the helpers would be my suggestion.

It would be hard to get the rear too low for roll centre purposes, your limit is ultimately going to be retaining enough suspension travel. The revised thinking around FWD race cars and rear suspension geometry mostly came from SuperTourers, at best they ran zero rake and that was with adj roll centres. We just don't want too much weight transfer from the rear inner to the front outer tyre. Plus less roll helps keep the inside front wheel on the ground for more drive off the corners.

Cheers
Gary

[sambb]

Ok cool. Before I installed my audi TT ball joints I did the line of intersection thing and worked out their pivot centres. Working off the front LCA inner bolt will be easy. I'll have a look at what I can achieve with some front ride height fiddling. On my rear inner LCA bushes I did install offset bushes but not to take away some of the anti dive - I put them in the castor position thinking that was what the car was lacking most and with the subframe eccentric bolts gained a tad over a degree of positive castor - up to 6 and a bit degrees now.
I'm sending back the unused 8kg/mm fronts on Monday. I'm really torn between going for 7kg/mm or 8kg/mm for the rears. I could run 6kg/mm on the street and then swap in the 8's for the track but I'm thinking I could try the 7kg/mm to be in the car always and just drop the RARB when I'm on the street. Still to'ing and fro'ing over that one but have the weekend to think about it.
When I got my quick toe and go done the other day after I fut the coilovers I found that I have zero toe on my left rear and +3mm on the right rear so I'm going to have to get the eibach shims in to sort that too. There was also a bit of preload on the rear bar with the ride heights set so I'll have to adjust out one of my droplinks to counter that.

[sambb]

No I've decided to not be a pussy and just get the 8kg/mm rears so I'll get that happening today.

Got another question for you Gary concerning rear track. Once I get it the front aligned and can see what will fit under the arches ill basically space it out as much as I can. I think with the extra camber I can get now, 12mm spacers on ET40 rims will fit plus the car has extra track from the ball joint mod.
So how wide can you go on the front before you must start following it with the rear end especially considering how rear stiff the car will be? Just maintain the OE front:rear relationship or is there a rule of thumb to follow eg F:R track widths based off say F:R weight splits or roll stiffness distribution? Do you normally set and forget rear track once you've decided and tune with bars/dampers/ride height instead or do you use it often to tune the car? I have used it in the past but that and tyre pressure was all that was available to me but a few more things have opened up to me now.

[sambb]

Gary got another one for you: the 8kg/mm rear recommendation, does that still hold true considering I do primarily hillclimbs. While it might be right for circuit stuff I'm just wondering whether that'll be too aggressive for hillclimbs with dirty stone cold tyres. Just final checking before I order them.

[Sydneykid]

No I've decided to not be a pussy and just get the 8kg/mm rears so I'll get that happening today.

Got another question for you Gary concerning rear track. Once I get it the front aligned and can see what will fit under the arches ill basically space it out as much as I can. I think with the extra camber I can get now, 12mm spacers on ET40 rims will fit plus the car has extra track from the ball joint mod.
So how wide can you go on the front before you must start following it with the rear end especially considering how rear stiff the car will be? Just maintain the OE front:rear relationship or is there a rule of thumb to follow eg F:R track widths based off say F:R weight splits or roll stiffness distribution? Do you normally set and forget rear track once you've decided and tune with bars/dampers/ride height instead or do you use it often to tune the car? I have used it in the past but that and tyre pressure was all that was available to me but a few more things have opened up to me now.

The maximum front track is pretty much always determined (limited) by the scrub radius, which for a FWD car usually means around 25 mm positive (the pivot point ~25 mm inside the tyre centre contact patch). On a RWD we can get to as much as 75 mm, but that much creates too large a load on the steering in a FWD car, hit a ripple strip or track edge and with engine torque it will pull the steering wheel out your hands.

Once I have the front track established I then equal it with the rear if possible. Having the rear track wider than the front can cause issues with front tyres missing the ripple strips or track edge (nice apex) and then rear tyre jumping over it. With a combination of a high (relative) rear spring rate and low (relative) rear of chassis weight it can pitch a lot of weight transfer off the inside rear tyre and onto the front outside tyre. Having the rear track noticeably narrower than the front makes it easier for diagonal weight transfer under lateral G. So my default is to keep the front and rear tracks pretty much the same.

Keeping in mind that widening the track softens the effective (at the wheel) spring and anti roll rate.

Cheers
Gary

[Sydneykid]

Gary got another one for you: the 8kg/mm rear recommendation, does that still hold true considering I do primarily hillclimbs. While it might be right for circuit stuff I'm just wondering whether that'll be too aggressive for hillclimbs with dirty stone cold tyres. Just final checking before I order them.

No real black and white answer I'm afraid. It depends on what tyres you are running, the temperature on the day, the track surface, the track layout etc. When I was running a FWD car in hillclimbs I ran very soft (compound) tyres and didn't warm the fronts up too much, no big tyre smokin burn outs. As I didn't want huge tyre temperature differentials front to rear. I also used to take the rear wheels off and stick them in the sun between runs.

It's circular reference, #1 we don't want too much weight transfer off the front for the take off, so a high spring rate is a necessity (because you don't have separate bump and rebound adj in the shocks). But #2 we don't want too high a spring rate such that it rotates at the first corner. My preference would be the highest spring rate it can handle to optimise #1 and then use the swaybar to minimise #2. No amount of swaybar is going to help with #1.

I'm afraid the only real answer is to try it, sorry.

Cheers
Gary

[sambb]

thanks. I was thinkng that re the temp differentia after the 'tyre warming'. In the interest of preserving clutch/gearbox/LSD I've always saved it for the last 2 runs and to be honest haveound little difference anyway and yes have gone very sideways on the opening corners probably as a result.
lAlright i'll have my hands full with lots of jobs to set it up. I pulled the pin on tomorrow nights rallysprint - just way too under prepared. List of things to do on suspension:
1. raise front slightly and check that I still have enough droop.
2. install 8kg/mm rears and remove one locking ring to get it a bit lower and check bump travel.
3. adjust out one of my RARB links to remove some bar preload that is there. Prob should do bars with 70kg weight in the drivers seat.
4. fit eibach shim to right rear which has +3mm toe. Left is nearly zero so result hopefully squared up at zero toe each side.
4. machine my hub centric rings so that they mate up to my bigger spacers properly so I can match front and rear tracks.

also fit brake ducts, setup spottie, fit airbox = ready for december 7 rallysprint.

[Sydneykid]

You want some toe out on the rear, minimum 2 mm each side, 3 mm would be OK.
I'd also run some toe out on the front, around 2 mm per side would be good.

Cheers
Gary

[seangti]

4. fit eibach shim to right rear which has +3mm toe. Left is nearly zero so result hopefully squared up at zero toe each side.

Howdy man, do you know if the shims can be rotated to be camber or toe centric? I've never actually seen the shim and how they fit on the car. I've got whiteline shims.

Got my car aligned last week and my guy suggested more rear camber. Not sure how it'd be possible to go about that.

[sambb]

Yeah I think both are possible. I've seen ones where there's two discs the fit over the top of one another. On a 2 axis lookup table you choose the camber and toe you want which gives you a pair of numbers that you align the discs to. HOW TO: Fit Adjustable camber/toe EZ-Shims to the rear beam / stub axle. I assume the eibachs work the same way but to be honest I havent even opened the packet yet.

[Sydneykid]

Yeah I think both are possible. I've seen ones where there's two discs the fit over the top of one another. On a 2 axis lookup table you choose the camber and toe you want which gives you a pair of numbers that you align the discs to. HOW TO: Fit Adjustable camber/toe EZ-Shims to the rear beam / stub axle. I assume the eibachs work the same way but to be honest I havent even opened the packet yet.

Eibach sell rebadged Specialty Products shims, so they do both toe and camber.

I think the Eibach Polo shims are Golf Mk4 Specialty products shims. If you can find the original part number I can confirm that.

Cheers
Gary

[sambb]

Yep mine were bought as Eibach but now that I check them out they are Speciality Products company. On the main sticker on the back the part# is 5.75200K. There is also a small part#99720 printed in the bottom left back of the box.

[sambb]

Just took delivery of a K&N Apollo. Basically a pod in a cone box arrangement. Got to admit that I'm a bit over making things and when I found that I could get a genuine one (be careful the rip jobs are everywhere) for a decent price I thought what the hey. I was actually after a K&N Orion which is a bit bigger but the prices were a bit too high. So when I took it out of the box I freaked because it is very compact, but I rana tape measure over it and it has more area than the OE K&N drop in filter for the OE box. That filter had an area of 249cm square and the Apollo has 280cm square. Also the Apollo filter has 25% more pleats so it has decently more filter surface area. Also the OE box breathes through a 60mm bellmouth and this one has a massive bellmouth base that tapers down to an ID of 64mm which is a very close match to the MAF intake which this will but right up against so I'm hoping it'll flow better. I'll get some pics up once its fitted.
I was going to build a partition in the engine bay that sealed against the underside of the bonnet. I thought that was legal because at a community show recently the Police pursuit cars were there and they had the exact same arrangement. I was just told though that they don't have to adhere to the NSW rule that says the pod can be visible in its partition but basically a hand isn't able to get in to touch the pod. When I found that I was going to have to box it in fully I just went with the K&N pod.
I'll be putting my K&N OE drop in replacement filter up on the classifieds soon so if anyone is interested let me know. To be honest I mostly ran paper filters cos I don't trust filters I can see through especially when I wasn't running it oiled, so the filter is in pretty new condition.

[sambb]

[NGT18T]

just a suggestion, if you get a 90d bend off the maf into the k&n then it would eliminate the bends and shorten the flexi hose. good setup though i love how much room the engine bay has with just moving those big bulky batteries