Sam's build thread

[Sydneykid]

Yeah that's a good point re the hanging inside rear acting as a counterweight, I hadn't thought of that. Actually I should clarify inside rear wheel skimming the deck or at the point of un-adhering is the target in medium radius corners from what I've felt. That way it'll be lifting in tight corners to help the car rotate and still on the deck in fast open corners so that I make it to the others side!
A lot of what I've been guided by are articles written by Mark Ortiz who writes for racecar engineering. Here's one of his articles re FWD race car setup: April 2000 only some of it is applicable to what we're talking about now but was all I could find quickly.
He's written some other really good articles about using 'castor jacking' in FWD cars to help the inside front to get more front percent in a corner. Basically using lots of castor coupled with positive steering offset/positive scrub radius, jacks the diagonally opposite wheels of inside front and outside rear causing them to have more % (obviously the outside rear can't get more % when the inside rear is in the air but it'll help at the front when the outside front % goes up dramatically with three wheeling). Its primarily used in RWD race series that use locked rear diffs (eg supercars and lots of US stuff apparently) so that the car would lift the inside rear and enhance turn in but has benefits for FWD too. It seemed to make sense for FWD cars especially open diff ones (mine was at the time) so I thought I'd try it. The effects was pretty dramatic on my car. I have 6+ degrees positive castor and ran spacers at the front out to ET20. The car always felt great that way. A co driver at the eastern ck tarmac rally sprints couldn't believe how my car was turning in in the pouring wet on worn mediums. At the next round I forgot my spacers and the car was completely turd, like a different car pig understeering, not rotating and spinning up the inside front worse than before. I'll try to find that article.
Really I'll just have to drive it and see how it goes. If the rear is too stiff even with the front bar on hard then I won't run any castor jacking promoting scrubs if they are going to help it even more. Its going to be interesting that's for sure.

I have actually met Mark Ortiz at a Claude Rouelle race car engineering seminar in the early 00's. As well as reading all of his articles on FWD race cars in the 90’s as at the time I was working with a couple of SuperTourer teams (Nissan Primera and Honda Accord). I have also used a lot of his theories turned into practise when I was the technical designer at Whiteline and on countless FWD and 4WD race cars since. In my library I have most of his articles in Race Car Engineering and they are well and truly worn and dog eared from the use.

You may have already seen it, but just in case, Mark responded to a question in 2015 on FWD race cars with twist beam rear suspension (the question came from a guy with a Polo GTi 9N)
April 2000

Caster is easy, the more the better, but I could write pages on scrub radius, it’s a complex subject. VW’s in general tend have zero to negative scrub radius in an attempt to alleviate the torque steer. So adding a bit of positive radius is a good thing, but be careful with ripple strips as with too much positive they will grab the inside front wheel and can rotate the chassis rather quickly. As a rule of thumb I wouldn’t suggest going over 75 mm in a short wheel base car like a Polo.

As you probably already know, hillclimb tracks vary a lot and what you find works at say King Edward Park won’t work on Mt Straight at Bathurst. So be prepared for quite drastic chassis set differences, particularly the rear. Being able to adjust the rear camber, toe and anti roll is a big help.

Cheers
Gary

[sambb]

Man you've had the life I should have gone after. I'm envious. Ha yeah I had a feeling you might have already been across those articles. One of the engineers at work was reading Race car engineering once and I picked it up and have every episode since. Thankfully I have a very generous sister who foots the considerable subscription. Mark Ortiz is a legend. I think that article might have been me. We went back and forth over email for ages until we got to the root cause of the problem which turned out to be the ESP doing strange things when one wheel was in the air and straightening the car up on me. In slow speeds it would 3 wheel happily but in the faster stuff I could eventually feel the brakes kicking in here and there and ironically trying to throw me off the road. I now run events with the steering angle sensor unplugged which kills the ESP and allows me to left foot brake except for the mountain straight hillclimb and Huntley where I like the safety net. Before we got to the bottom of it though he asked if he could publish it and took bits and pieces of correspondence and stitched it all together which is probably why it reads a bit funny. For someone of that calibre to respond to a guy in the streets emails though is pretty cool.
I totally get what you mean regarding positive scrub radius and ripple strips. The first outing with my wavetrac on a tight left uphill hairpin and the steering wheel literally felt trapped at the apex lock that I had on. I had to absolutely muscle the wheel to get it straightened up. The extra drive on the inside front from the LSD and the scrub feedback made it pretty physical compared to what it had been but it was faster that way so I've kept it like that and adapted. From playing around with spacers and going by feel it feels like ET30 is about centre pin steering and then as you start to go outboard from that things start to improve again so I assume ET20 which is what I've run for the last year or so is about 10mm positive scrub - same as factory probably just out the other way.
I've done the Panorama hillclimb rounds for the last two years and yeah it is pretty daunting - mountain straight is not getting any less scary. The speed that you turn into Griffins bend at and the car going rear light over the crest into Suliman Pk isn't any less scary and I was loosing a tonne of time there chickening out on the throttle. Definitely need a different setup for Bathurst. Problem is my normal setup feels great on day 1 going up the esses where I'm way more competitive so I've tended to leave it alone other than dropping some air out of the rears for the mountain striaght runs. I wonder if a touch of front end toe in on day 2 might make the car a little less reactive too. The other thing I was thinking is that with the coilovers I may be able to play with rear ride height eg drop it at the rear to stabilise it for mountain straight but have it raked slightly for the esses. Thanks for your advice so far. I love hearing from suspension people that do FWD.

edit: I'd seen pics of the bracing, coilover conversion etc they were doing to MK3 rear beams when I first saw beam boxing. I asked Ortiz about it and he confirmed that it was an option. I never would have done it if he hadn't confirmed that it was viable.

edit2: sorry don't mean to mislead anyone into doing the wrong thing. It is the brake pedal switch that I unplug which allows left foot brake, NOT the steering angle sensor. Disconnect that and the steering goes impossibly heavy.

[sambb]

So I finally drove the car for the first time today with the new beam in place. The problem was bleeding the brakes. It had sat for so long that the lines must have drained well dry. I had only bought a litre of fluid to get me out of trouble and it took all that to clear up the rears. I actually had my 7 year old son sitting in the foot well pushing on the pedal with both hands like a minion but the problem was synchronising open/closed with him which was quite comical. I got it good enough to trundle down to the local euro shop and they got it sorted for me.
Then I could take it for a proper run through the national park and it was pretty awesome. Its all new and chromy in my mind so hopefully its not placebo but it feels a tiny bit more rear stiff than before. Because I've done bushes and the beam at once I can't be certain that that 'extra' bit of stiffness I'm feeling isn't the bushes rather than extra roll stiffness, but it felt super taught, direct, enhanced the steering and felt very comfortable going quick. I'm on 195 UHP street tyres so its hard to say really how it will go in event setup but I'm elated that it worked, didn't seem to sacrifice anything (including ride comfort to any great extent) and is a definite improvement. Best of all the engineers decision to use 3mm and the amount of welds that he did to approximate the roll stiffness that I had before with the bar, was spot on.
So I'm super happy. The car is straight back into the garage tonight. The front is coming off so that I can measure up a nudge bar against the bumper bar, drill it and then take it down to get some mounting nuts welded on so that my spotties/nudge bar will be removable for the twilight rallysprints which are coming up. If I get better over the next few days I'll polish the headlights too so that light rays have some chance of making it out of them! Finished product will look like this which was how I ran last years old car.

[guile]

nice write up mate, picture in your last post is not working though...

[seangti]

Great to hear it's all gone well Sam. I've been quietly following your progress.

A pressurised brake pressure bleeding kit is a brilliant investment. Something like this: Motive Products Power Bleeder Kits - Free Shipping on Orders Over $99 at Summit Racing. I've got one, can't recall the brand, makes the bleeding very easy.

Re the headlights, I had tried the Turtle branded headlight restoration kit on them, but was ordinary (as you've noticed). I paid a dude to come fix up the headlights on the red polo, which were much worse than yours, and he did a brilliant job. Might be worth outsourcing.

[sambb]

thanks fellas. Sean I was looking at them on ebay but had no way of getting one quick enough. I'll definitely get one for the next bleed. Down at European Autotech they said they basically use them too. I asked about whether or not they use the output test VCDS style of bleeding cos I was worried air might have gotten up inside the ABS distributor. They said they only run that test after a new module has been fitted because there's a risk it can overheat the pump if there's too much air in it and it runs for too long, so I was happy with them just cramming in the fluid from the master cylinder. I have a really good pedal now so the brakes are ready for the rallysprint.
Yeah my last of headlights I did with a home kit and they came up about 85% and it was a pretty hateful task which I swore I'd never repeat, but I just paid for my MCA's so now I'm skint and will have to eat my words. If I get them half good an acquaintance has a UV heat resistant film (just like a car wrap) that he puts on headlights to keep them in good nick for longer so I might try that this time. My others were smashed to smitherines when I was shunted up the back of the 4WD in the crash so sadly they are gone.

here's that pic. hope it loads this time.

[Sydneykid]

For an emergency one man pressure bleeder at a race meeting once I used a spare brake master cylinder cap, grabbed a spare tyre valve stem and fitted it through a hole I drilled in the cap. I used the 12 volt electric tyre pump that I used for quick tyre pressure adjustments, just flick the switch on on the pump while the bleed valve is open. Not for too long as it blows the cap off the master cylinder. Need to refill the master cylinder regularly of course. Total cost = one tyre valve stem.

Cheers
Gary

[Sydneykid]

I totally get what you mean regarding positive scrub radius and ripple strips. The first outing with my wavetrac on a tight left uphill hairpin and the steering wheel literally felt trapped at the apex lock that I had on. I had to absolutely muscle the wheel to get it straightened up. The extra drive on the inside front from the LSD and the scrub feedback made it pretty physical compared to what it had been but it was faster that way so I've kept it like that and adapted. From playing around with spacers and going by feel it feels like ET30 is about centre pin steering and then as you start to go outboard from that things start to improve again so I assume ET20 which is what I've run for the last year or so is about 10mm positive scrub - same as factory probably just out the other way.
I've done the Panorama hillclimb rounds for the last two years and yeah it is pretty daunting - mountain straight is not getting any less scary. The speed that you turn into Griffins bend at and the car going rear light over the crest into Suliman Pk isn't any less scary and I was loosing a tonne of time there chickening out on the throttle. Definitely need a different setup for Bathurst. Problem is my normal setup feels great on day 1 going up the esses where I'm way more competitive so I've tended to leave it alone other than dropping some air out of the rears for the mountain striaght runs. I wonder if a touch of front end toe in on day 2 might make the car a little less reactive too. The other thing I was thinking is that with the coilovers I may be able to play with rear ride height eg drop it at the rear to stabilise it for mountain straight but have it raked slightly for the esses. Thanks for your advice so far. I love hearing from suspension people that do FWD.

A quick way to check the scrub radius is rub some chalk across the tyre tread, say 50 mm wide. Then lower the car and with just a bit of weight on the tyre turn the steering wheel. Roll the car back and you can see where the centre of rotation of the tyre is, measure from there to the centre of the tyre and that's the scrub radius.

For the Esses Hillclimb I'd run about 4 mm of toe out (2 mm per side = 4 mm total) on the front and about 6 mm of toe out on the rear, with quite lot of rear antiroll. Without a rear adj swaybar I'd try running the dampers a bit stiffer. I'd also run it with about 10 mm of rake (nose down) to give some more weight transfer onto the front outside tyre. It shouldn't need more than 10 mm but don't be afraid to experiment.

For the Mt Straight Hillclimb I'd run about 2 mm of toe out (1 mm per side = 2 mm total) on the front and about 4 mm of toe out on the rear, with a bit less rear antiroll. Without a rear adj swaybar I'd try running the dampers a bit softer. Unfortunately you are adjusting bump and rebound together so I would suggest small steps, maybe 2 clicks at a time. If you are finding it still oversteering on the longer, high G force corners then I'd try lowering the rear ride height so that its has zero rake or maybe even a little bit rear down.

Murray should be able to supply you with a graph of what the damper curves look like, usually the rebound adjustment changes the damping about 2 to 3 times compared to the bump damping.

Cheers
Gary

[sambb]

"Murray should be able to supply you with a graph of what the damper curves look like, usually the rebound adjustment changes the damping about 2 to 3 times compared to the bump damping."

glad you mentioned that because I was wondering if bump/rebound were coupled or not. Yeah I'll ask for sure about what step changes I can expect in each.
To be honest I've always run the front with zero static toe because coupled with the castor changes and OE ackerman, I had no idea what effect it'd be having as you put the lock on. I was sort of hedging my bets. Rear toe is probably the most conflicting thing I read/hear about within FWD circles. Some say if you are very rear stiff then you don't need toe out at the rear at all and toe in is preferable, others say not beyond zero toe or it becomes treacherous and others say it depends more on your roll axis (what you alluded to). I was reading an article recently that was saying that rear toe has its greatest effect in faster corners because the rear stays more loaded than in tight corners where braking forces have the weight transferring more onto the fronts in the corner - any thoughts on that?
I can and will experiment on the front but the rear is much harder as it means calipers,discs, stubs-bearing off. I have my eibcah adjusters but I think that might be the last thing after I get used to the new rear and the coilovers and setting them up. I presume that if I adjust my rear static ride height I won't affect the corner weighting to much. From what I've seen of other polo's on the scales the rear cross weights are very even so hopefully that means I can adjust evenly up or down at the back and not be adversely affecting the front.

[Sydneykid]

"Murray should be able to supply you with a graph of what the damper curves look like, usually the rebound adjustment changes the damping about 2 to 3 times compared to the bump damping."

glad you mentioned that because I was wondering if bump/rebound were coupled or not. Yeah I'll ask for sure about what step changes I can expect in each.
To be honest I've always run the front with zero static toe because coupled with the castor changes and OE ackerman, I had no idea what effect it'd be having as you put the lock on. I was sort of hedging my bets. Rear toe is probably the most conflicting thing I read/hear about within FWD circles. Some say if you are very rear stiff then you don't need toe out at the rear at all and toe in is preferable, others say not beyond zero toe or it becomes treacherous and others say it depends more on your roll axis (what you alluded to). I was reading an article recently that was saying that rear toe has its greatest effect in faster corners because the rear stays more loaded than in tight corners where braking forces have the weight transferring more onto the fronts in the corner - any thoughts on that?
I can and will experiment on the front but the rear is much harder as it means calipers,discs, stubs-bearing off. I have my eibcah adjusters but I think that might be the last thing after I get used to the new rear and the coilovers and setting them up. I presume that if I adjust my rear static ride height I won't affect the corner weighting to much. From what I've seen of other polo's on the scales the rear cross weights are very even so hopefully that means I can adjust evenly up or down at the back and not be adversely affecting the front.

It's handy to know what the steps are in the adjuster but more importantly the relationship between the bump and rebound adjustments. There is no doubt that Murray knows his stuff but the real question is what has he compromised on to keep the price down?

Rear toe settings on a FWD car (I always run toe out) are very different to rear toe settings on a RWD car (I always run toe in) and a lot of what we read confuses that. A 4WD (with rear drive primarily) like a Skyline is more RWD in its toe settings whereas Evo's and WRX's (with primarily FWD) are more like a FWD in their settings. Best to ignore anything but specifically FWD when discussing rear toe settings.

Toe out is what we call an "unstable" condition, it makes the rear end lively, responsive to inputs from the throttle, brakes and steering. Conceptually we run toe out so that the rear is light under brakes and deceleration so that it responds to steering inputs for corner turn in. We want the rear end to step out slightly when there is negative longitudinal G force with steering lock applied, that way it points the front of the car at the corner apex. So we use less steering lock to negotiate any given corner. It also means that we can get on the power earlier as the car is pointed straighter earlier in the corner (we can wind off steering lock sooner).

As a result I would always suggest running toe out on the rear of a FWD car, the question is how much? Firstly it's driver dependant, some drivers just don't like the nervous/fidgety rear end feeling and it actually slows them down. Other drivers don't even notice it, they just find the car more responsive to their inputs. Secondly it's track dependant, high speed corners with long flowing entries (sustained high lateral G force) aren't the place for lots of rear toe out. Whereas tight corners that demand short sharp entries are prime territory for plenty of rear toe out. Bumpy braking areas are also worthy of respect when it comes to how much rear toe to run.

To answer your "more effect" question, keeping the above in mind, I would suggest that the best effect (for lots of rear toe out) is in the tighter corners. Whereas the effect of a lot of toe out in higher speed longer corners can be too much, so we reduce it, but I never have run zero or toe in on any circuit in Australia on a FWD car.

I understand the difficulty in changing toe using the Specialty Products shims, that's why I'd suggest using a mid range toe out (say 2 mm per side = 4 mm) and then trimming out any excessive rear end nervousness by lowering the ride height. Or vice versa. Once you have been to a track you will then know how much toe out you can run. There is no right or wrong technically, a lot comes down to how comfortable/confident the driver feels. If it feels comfortable, cosy and safe then it definitely needs more toe out, if it frightens the crap out of you under brakes then it probably needs less.

Corner weights wise, in regards to a twist beam, as long as you adjust the pair equally (precisely to the mm) then the corner weights shouldn't change. The first trick is balancing for any permanent twist in the beam, which is tricky. Because adjusting the spring seat heights (to achieve corner weight balance) maybe introducing a twist in the beam, hence preload in the anti roll. My suggestion would be set the spring seat heights the same on the rear (to achieve the desired ride height) and then use the front spring seat heights to achieve the diagonal balance. That will minimise the preload in the twist beam and avoid any uneven anti roll.

Cheers
Gary

[sambb]

Thanks for the response Gary. You managed to answer pretty much everything I was wondering about so thanks very much for taking an interest in the setup and offering your ideas. The tracks in the state hillclimbs and the rally sprints are all very tight point and shoot sorts of circuits so rear toe out looks to be the way to go. I'll just have to trim the rear with tyre pressure, ride height and the damping when doing the fast stuff. Next step I guess is to get it aligned and see where each rear wheel is pointing andindividually set them up from there for the right angles. It has static 1.5 degrees negative camber which I'll probably leave in place. thanks mate.

[sambb]

I've had the front off the car primarily so that I could get the bumper off and nuts welded onto the back of it in locations where I can easily run bolts through from the front to mount my nudge bar and spottie for the twilight rallysprints that are coming up. While I was at it I decided to plumb up a cabin actuated intercooler water spray. Onmy last car the water spray was manual and boost activated. Now that I have a proper sized front mount the water spray whilst underway is not that critical but its still a big benefit to have a water spray to chill the IC down prior to a hillclimb run especially if you have the AC on with the fans running at the same time. It makes for a very chilly IC off the line and would also work very well for drag folk. So what I did was pop off the rear wiper fitting off the wiper reservoir pump (its the one on the inside). Cut the pipe about an inch up from the fitting. I basically then just plumbed in a Y -piece with it angled/biased towards the IC. If you use silicon 4mm tubing it just push fits over the ribbed wiper tubing that you cut and is secure and will not leak. I ran a test and even though you are now activating two nozzles, there is tonnes of pressure at the new nozzle head. I haven't got the IC nozzles in place yet. My old SMIC nozzle doesn't work at close range very well on the tall SEAT sport IC. I tried some irrigation fittings (1/2 and 1/4 circle) and neither of them gave good coverage either, so i'll suss out what the EVO's use ad go from there down the track.

[sambb]

So when I had the bumper off, as well as getting the nuts welded into the back, I angle ground the top upturned lip off the top edge of the bumper. I did this so that air getting through a cut out I made would run straight onto the core rather than hit the lip and be deflected upwards and also so that the boost piping which was sitting very close to the sharp edge of the bumper would be safe. I'm glad I did de-lip it because the cutout location was bang on and will let a tonne of extra air straight onto the core when I run in hillclimbs without the number plate or nudge bar.

[sambb]

While I was in there I also made up a CAI feed. If you just take some tin snips you can put in two cuts on either side of the flap that sits under the mouth and then just flex the flap up and down and it will break free cleanly. There's a ready made slope built into the mouth that lets you just drill some self tapers into the radiator support and mount whatever shaped feed you make. Mine is 175mm wide at the front narrowing to 145mm at the top and the edges are folded up at a height that allows it all to tuck in under the slats when the grille is fitted. It basically picks off air that otherwise sails straight over the top of the radiator through a void and into the engine bay and channels it up. It'll also prevent the CAI sucking air straight off the top of the radiator in traffic or at hillclimbs/drags after queueing up. To finish I taped up the slits moulded into the panel above the CAI since it'll just let pressurised air running up the ramp towards the mouth to escape out the top and across the underside of the bonnet.
Main thing is when the number plate is back on you wouldn't know anything had happened.

[Sydneykid]

Thanks for the response Gary. You managed to answer pretty much everything I was wondering about so thanks very much for taking an interest in the setup and offering your ideas. The tracks in the state hillclimbs and the rally sprints are all very tight point and shoot sorts of circuits so rear toe out looks to be the way to go. I'll just have to trim the rear with tyre pressure, ride height and the damping when doing the fast stuff. Next step I guess is to get it aligned and see where each rear wheel is pointing andindividually set them up from there for the right angles. It has static 1.5 degrees negative camber which I'll probably leave in place. thanks mate.

I've probably given you enough to think about already, but just one more......

With twist beam rear suspension the roll centre changes according to the angle of the trailing arm. A trailing arm that is, say, parallel to the ground has a higher roll centre than one where the trailing arm points downwards towards the wheel. As a result changing the ride height (RH), which obviously changes the centre of gravity (CoG), also changes the roll centre (CoR). The CoG moves 100% with the RH but the CoR moves around 40% on a Polo (from memory). ie; lower the car 10 mm and the CoG moves down 10 mm but the CoR only moves 4 mm. Hence when we lower it we reduce the roll couple (RC) by 60% (ie; 6 mm). Conversely if we raise the RH 10 mm the RC increases by 6 mm.

As a result of all 3 (CoG, CoR and RC) changing at once ride height changes are a very powerful handling tuning tool, it's a big hammer so don't hit it too hard. A few mm at a time and feel for the effect.

Hope to catch up at a hillclimb sometime next year
Cheers
Gary