Sam's build thread

[Sydneykid]

The dampers are an amazing improvement. Despite now probably being overdamped (they are valved/adjusted for 350lb springs but he H&R's are less than 200lb/in) they are like butter over bumps compared to the B8's which are far more crashy in comparison, yet feel great when you lean on them. As a damper comparison on the same rate of spring they are a cut way above. Super motivated now to press on and get the whole lot in.

You should confirm with Murray but usually he allows enough adjustment in the rebound to handle that sort of spring rate variation (ie; it shouldn't be over damped). When I'm spec'ing a single adjuster shock I aim for a ratio of 3 (rebound) to 1 (bump) ie; 1 click on the adjuster moves the rebound damping X% and the bump damping 1/3 of X%.

I'm sure you know but 200 lbs/inch is way too soft for an R spec tyre, I'm guessing around double that depending on the movement and leverage ratios between the spring and the wheel. On that subject, I'm sure you are also aware that not being a coil over design there are movement and leverage ratio differences between the shock and the spring as well.

It is quite common for Bilstein to engineer additional bump valving in the rear shocks of FWD vehicles and often they run higher nitrogen pressure. This helps the handling by supplementing the often too soft rear spring rates.


Cheers
Gary

[Notso Swift]

As a ball park the rears on a FWD competition cars should be 50% more than the front per kg of mass, then you look at anti roll bars
Remember this is wheel rate so you need to multiply the difference between the difference between the pivot to the hub centre vs the spring centre (lever ratio) Struts are as near as damnit a 1:1 ratio
So for ease of example if you have a 1000kg car with F60/R40 if you have 300 lbs on the front you would want to look at 400lbs on the back


The classic line for FWD is Shocks are more important on the front while springs are more important on the back! Gross over simplification of course

200lbs is what you would expect for road based set up, you can't live with SuperTourer style 1000lbs springs every day! Also it isn't good for the average Joe to have a car that wants to oversteer all the time, but as a FWD hillclimber you want to jet the rear rotating so you are using less lock and making the most of the fronts
(Of course you may decide you can only live with 200 in the back then you may try and do something like add a lot more ARB so at least you get rate on turn, but too much ARB and if your inside wheel hits a curb it will jack up the outside rear mid corner, making it skitty)

[Notso Swift]

Not sure about a much later Polo but toe control on a Mk1 Golf is severely lacking, you can feel the back end move around even a low speeds. Sure toe out the outside rear wheel sounds good for turn in but on high load corners (ie faster) there is more toe, when what you really want is toe out for slow corners (to aid direction change) but toe in for the fast corners for stability at high speeds.
On track you will lose more time in a fast corner than the slower ones. Not such an issue for hill climbs, but Turn 1 at Eastern Creek or Phillip Island... It isn't the popular set up but stability and drive confidence are worth a lot

[sambb]

'I'm not sure that adding a bolt in the middle would make any difference to the anti roll. It would still link the 2 wheels together with the same overall length. Shortening the overall length is the easiest method, so you could have 3 or 4 bolts, holes and mounts at each end. Just one bolt at each outer end would be the softest setting (longest bar to twist), then 2 bolts (shorter bar to twist), 3 bolts etc. '

actually yeah I see what you mean by the middle position not doing anything if bolted up since it'd just be twisting with the bar anyway. I really like the idea of the internal beam bar with a pair of mounts at each end if it means that you can run it 'long' or 'short'. Might creak and bang a bit with the inner mounts unbolted though but that'd be ok.

yeah definitely became aware that 200lb/in was too soft for the softs/mediums that I've run - Just a road reg competitor though so all on a shoe string budget. Yeah the damper mount point is well behind the spring seat and hub position on my car. The damping intricacies that result from that I leave in the capable hands of Josh. I will get on to him re the relationship between bump and rebound and each click setting. I'm guessing he's a tad busy with the WTAC car at the minute though so that one can wait at least until I get the fronts in. As it is the MCA's are 8kg fronts, 6kg rears. He initially wanted me to run 9kg fronts and 8kg rears but with the standard 20mm front bar and no rear bar. When I explained to him that I wanted to run a rear bar (cos I just couldnt see that not happening) he came back and suggested the 8:6kg split. Of the 8:6kg split he said that despite the different motion ratio on the rears that further soften the rear spring rate, that relative to the front and the weight that it is carrying that it is still a rear stiff setup especially when you factor in the rear bar. As it is rear springs are 100 bucks for a set so I can up the rear spring rate cheaply/easily down the track if need be so I was happy to take his lead. He was pretty adamant that I should move away from the whiteline 22mm front bar though and go back to standard, but we both agreed that it was worth trying on soft initially before pulling it out.

Notsoswift does the spring selection rule of thumb relate to torsion beam rear ended FWD cars just the same as IRS ones too? I only ask because from what I understand torsion beams have significantly higher rear roll centres (and steeper roll axis) than IRS cars which becomes a form of roll stiffness in itself. In your weight split example (if it was for an IRS car) wouldn't you have too much rear bias in a torsion beamed car relative to an IRS car if you threw the same springs at them? just trying to get my head around it based on the bits and pieces of theory that I know. I'll definitely aim to get the springs decided on first, then work out what to do with the front bar and rear toe will come last.

[sambb]

front bits
rear bits.

My shiny MCA bits. They run red series 1 way damping adjustment, separate stroke adjustment and height/spring perch adjustment, spherical top mount bearings, adjustable 1 way (camber) top plates, adjustable rear spring seat perches and revised front anti roll bar droplink pick up.. It came with a helper spring for the rears but there's seriously no rear beam droop with the new bushes so I may not even need them.

[rgvlee]

Same ones I was thinking of getting

[sambb]

I think the X series had been out with the blues previously. Josh has changed the position of the FARB droplink pickup on this new revision . I think mine are the first with that. Its now solid welded to the strut tube rather than a clamp which they apparently used to run. That's just FYI in case you do get them.

[rgvlee]

I've got adjustable drop links so should be fine

[HaydEn]

Crap photo and the tube I have at 1000mm is 150mm too long to fit in properly.

But as a reference. Sit the tube on the lower edge as pictured and put two 20mm welds at each end with an appropriate spacing, 30mm or so.

[sambb]

thanks for that mate. yeah I see what you mean. Is that your pic - are you considering doing the same?

[HaydEn]

thanks for that mate. yeah I see what you mean. Is that your pic - are you considering doing the same?

Yeah I thought i better take a picture of what i was poorly trying to explain.

Will eventually do it.

As rear sway bars for mk3's are far to expensive.

[sambb]

cool good stuff. keen to see how you weld it and what sort of result you get.
for a cheap add on bar from a wrecker, apparently the 1990's corollas had a bar internal to the beam - the type that bolts through the beam at either end. If you look up autospeed.com Julian edgar added one of them to the beam on their Honda insight project car.

[Sydneykid]

yeah definitely became aware that 200lb/in was too soft for the softs/mediums that I've run - Just a road reg competitor though so all on a shoe string budget. Yeah the damper mount point is well behind the spring seat and hub position on my car.

I'd have to measure it to be accurate but my guess is around 0.8 to 1 movement ratio and 0.8 to 1 leverage ratio, so the 200 lbs/inch at the spring would be 200 X 0.8 X 0.8 = 128 lbs/inch at the wheel (what the tyre feels). That's a slightly sporty road car rate.

The damping intricacies that result from that I leave in the capable hands of Josh. I will get on to him re the relationship between bump and rebound and each click setting. I'm guessing he's a tad busy with the WTAC car at the minute though so that one can wait at least until I get the fronts in.

Not that you can change the ratio, but it is important to know, so that you can give him feedback. In simple terms if you adjust say the fronts to give you more rebound (so that the weight doesn't transfer as fast off the front when you lift off the brakes) you need to know how much that affects the bump (too much of which may make it understeer on corner exit, which is what you are trying to overcome).

As it is the MCA's are 8kg fronts, 6kg rears. He initially wanted me to run 9kg fronts and 8kg rears but with the standard 20mm front bar and no rear bar. When I explained to him that I wanted to run a rear bar (cos I just couldnt see that not happening) he came back and suggested the 8:6kg split. Of the 8:6kg split he said that despite the different motion ratio on the rears that further soften the rear spring rate, that relative to the front and the weight that it is carrying that it is still a rear stiff setup especially when you factor in the rear bar. As it is rear springs are 100 bucks for a set so I can up the rear spring rate cheaply/easily down the track if need be so I was happy to take his lead.

The front struts on the Polo (like most VW's) have ~0.9 movement and leverage ratios, and I think 9kg's (504 lbs/inch) is far too high a spring rate (408 lbs/inch at the tyre). There's not any R /semi slick that likes that much spring on our rough tracks, especially on the front of a FWD car. Even 8kg/mm (362 lbs/inch at the tyre) is still a bit high, personally I'd run 7kgs/mm on the front.

I know Josh (and Murray) have a preference for higher spring rates and lower anti roll rates, but that comes from the vast rally car experience plus the days back when we weren't allowed to change the swaybars on Production race Cars, so we had to use the spring rates instead. Pretty much every race car (where it's allowed in the regs) have driver adjustable swaybars, that's because they are the easiest method of tuning the handling balance. It's pretty hard to pull a pit stop in the middle of a race to swap spring rates. This is the same philosophy as us being at a hillclimb, it's much easier between runs to adjust the swaybars than swap springs.

Keeping the above in mind, I wouldn't be running 8/6 springs rates. I'd be looking at something like 7/8, that should give around 317 lbs/inch on the front and 286 lbs/inch on the rear (at the tyre of course). Obviously it's important to confirm the movement and leverage ratios first though.


Cheers
Gary

[sambb]

I'm glad you said that because its worried me from the start that the front will be too stiff even at 8kg/mm. But my mates W172 clio is on 400lb/in fronts and it felt great which makes me think 450lb/in on the front wont be far off - just not sure. I'm easy with the back because that's so easy to change but if the front is too stiff then I have to commit to another 100 bucks for more coils and another strut removal job/alignment etc or changing down to the stock FARB at minimum (which is also a big job and might still be too stiff!). Whats your opinion of 8kg/mm on the stock 20mm bar vs the 22mm whiteline - still too front stiff? In that case I can still tune the rear bar and the damping.
My current BALANCE is great on 200lb/in spring front and rear (rising rate) springs with FARB on soft and RARB on hard and needing a bit more bar at the back. So if balance can be adjusted up in relative terms I agree with the 1:1.14 split you mention.
Got a question for you re FARB's and inside front wheel droop. I've always imagined that a softer front bar would allow the inside front to droop more easily - be pushed into the road more easily/independently by its strut. I asked Ortiz about that and he said that's a theory that has gained a lot of traction in Oz/NZ but which is totally false - the inside front tyre doesn't know if its a spring or an ARB or both pushing it into the road, if the roll resistance is the same then the inside front will do the same thing. I still can't get my head around that. Whats your take?
I think Ill see if he can send down a 7kg/mm pair for the front (exchange).

[sambb]

sorry another question Gary - I always thought you just times the spring rate by the motion ratio. I didn't know about leverage ratio factoring into that same equation to get your wheel rate. Whats leverage ratio and how does it differ to motion ratio?