Sam's build thread

[Sydneykid]

They should be ok. The main problem comes from the angled bush casings. In top view they are probably at 45 degrees to each other and in front view the casings angle upwards toward the rear seat bases slightly too. The crush tubes will allow up down articulation ok within a given range but then the angle of the bushes starts to force the bush to distort and then the poly, even just for up/down movement starts to lock up. Laterally I think they'll be unreal with no more of that detached rear end sog like before.
Yeah I had read a bit about droop limiters, everything literally from cables to internal damper ones, but figured I'd just go for more roll resistance from the twist beam than from the springs. Apparently limiters can be a bit abrupt in the way they limit droop (only read it have no experience) but if the bushes act to limit droop which I think they will (car is still on jacks with the beam just hanging there level with the ground) then hopefully its nice and progressive.
I just got the rear calipers back and don't know whether to slap it all together and go for a drive or leave it all in pieces and just wait for the coilovers to arrive. I think I'd rather drive it now so that I have a good before and after reference for what the beam is doing rahther than change everything at once but that means garage time tonight and I'm sick as. I'll see how I go.

We use droop limiters on a number of race cars (mostly FWD and 4WD Production Cars where often the regs don't allow us to change the swaybars) , the most common method is an internal bump stop which can be selected to give some progression. This is not as abrupt as say a solid travel limiter like an alloy block or a steel strap. It's also handy to have adjustable rebound damping which can slow down the travel so that it takes longer than the wheel is unloaded to reach maximum droop. Plus it also can assist with a soft stop when it hits the travel limiter. Many ways to skin that cat.

I'll be interested in how reinforcing the torsion beam works out in regards to the anti roll rate. Personally I'd prefer to mount the swaybar on the body and have drop links to the control arms, no unsprung weight at all then, plus it gives anti roll adjustment which on the rear of a FWD car is a great handling tuning device. But I like the simplicity (and low cost) of your method.

Cheers
Gary

[sambb]

The reason why I did it was because as soon as the car three wheels it just glues the front down and I get awesome drive out of corners. Rightly or wrongly I just couldn't see how adding more roll stiffness with springs was going to aid in getting it to lift the inside rear. I figured less roll would just make it harder for the inside rear to lift because the beam allowed so much droop. I'd maxxed out the bar so to me the only answer was a custom 22mm bar (more unsprung weight) or boxing the beam so I went that way. But yeah I do loose roll stiffness adjustability so hopefully I can tune the rear end with track width changes (I was doing that a lot), the 1 way rebound/compression adjustability on the MCA dampers that are coming, and tyre pressure fiddling.
I'm getting the brakes on now so i'll hopefully have them bled tomorrow and i'll go for a run. Actually what I'm most scared of now is the welds just going ping! and letting go.

[sambb]

Yeah I've never seen a twist beam with an anti roll bar mounted to the body. I can understand why the factory don't do that when they can just throw a few more welds or gussets onto a beam, but its a wonder the aftermarket doesn't do it.

[Sydneykid]

The reason why I did it was because as soon as the car three wheels it just glues the front down and I get awesome drive out of corners. Rightly or wrongly I just couldn't see how adding more roll stiffness with springs was going to aid in getting it to lift the inside rear. I figured less roll would just make it harder for the inside rear to lift because the beam allowed so much droop. I'd maxxed out the bar so to me the only answer was a custom 22mm bar (more unsprung weight) or boxing the beam so I went that way. But yeah I do loose roll stiffness adjustability so hopefully I can tune the rear end with track width changes (I was doing that a lot), the 1 way rebound/compression adjustability on the MCA dampers that are coming, and tyre pressure fiddling.
I'm getting the brakes on now so i'll hopefully have them bled tomorrow and i'll go for a run. Actually what I'm most scared of now is the welds just going ping! and letting go.

Technically it's not the rear inside wheel lifting that increases the front end grip on turn in, it's due to the diagonal weight transfer onto the outside front wheel. The inside rear wheel lifting is just another symptom of that weight transfer. As long as the same amount of weight is transferred then it doesn't matter whether the inside rear wheel is on the ground on not. In fact keeping the inside rear wheel on the ground increases the weight transfer as the unsprung weight (of the inside rear wheel) wouldn't be working against the diagonal weight transfer.

Cheers
Gary

[sambb]

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.

[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.
Attachment 30470

[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.