simon's learning what to do with the polo thread

[sambb]

simin I found the spring rates I'd had measured at Eibacj in a press or was quoted from the manufacturer.
aftermarket spring kit spring rates

Blood hell thats a good gain from just some rears and a bar. Must have been a nice surprise to see that.
The H&R definitely look progressive but I'm pretty sure that they coil bind once the droop is taken out of them to a remaining few coils that give a linear rate from then on. H&R in the fatherland said 27N/mm so I can only assume that's not in a press from full free length because the initial take up would be softer than that.
Lifting a wheel does mess with any system that looks at wheel speeds. I always thought cruise control was more of a MAF thing but it makes sense that it would disengage if it thinks you've locked a wheel which is how it would look to the ESP when the elevated wheel slows down compared to the others.

[simon k]

Gary, I'll measure the current rear springs (ex-honda front minus 4")fter work. Knowing the rates of those would be interesting

[Sydneykid]

25 n/mm = 142 lbs/inch, 27 n/mm = 154 lbs/inch.

For a combo car (road and track) with mac struts much over 200 lbs/inch spring gets a bit stiff and doesn't give a lot of (track) gain in comparisons to the (road) pain.

From the picture it certainly needs a lot more negative camber at that front spring and anti roll rate.

You can measure the "effective" rear anti roll rate, but it's a lot of effort for a number that on its own won't mean much. I use it as a basis of comparison between swaybars rather than an absolute number, unlike say an actual spring rate that has some meaning. The process is to put the car on the scales at the rear, on jack stands at the front and then jack up one rear wheel. Try 10 mm, 20 mm maybe even 30 mm, with the maximum being limited to it reaching zero weight. Then read off the weight reduction on the other side and measure the distance the lifted wheel moves.

Was 250 kgs now 100 kgs = 150 kgs reduction
Movement 30 mm
150 / 30 = 5 kgs / mm or 280 lbs /inch

Adding more anti roll (thicker rear swaybar)
Was 250 kgs now 70 kgs = 180 kgs reduction
Movement 30 mm
180 / 30 = 6 kgs / mm or 335 lbs /inch

As a comparison the FWD race cars measure twice that.

Of course it's affected by leverage and movement ratios, bush flex, tyre distortion, chassis twist etc etc. I can do the mathematics and work out the twist rate of any given piece of material, hollow or sold, but it doesn't replace an actual measurement on the car, because of all of those other factors.

Have some fun, try it with the swaybar added and then without, just with the twist beam supplying the anti roll. I'd guess something around 4 times the rate with the swaybar.

Hope that makes sense.
Cheers
Gary

[sambb]

Got to agree re road comfort. My 8kg/mm rears (447lb) are 290lb/in at the wheel are mega on the track but make Sydney roads feel like a fire trail. The 6kg rears (335lb) were 214lb/in at the wheel and were far more tolerable on the road, yet still a lot stiffer than the H&R rears that'd been in there. Plan was to hang onto those 6kg's for the street but I lent them to my mate to try in his Clio that runs a B14 kit and after a cracker of a hillclimb event at Ringwood he wont give them back!

[simon k]

25 n/mm = 142 lbs/inch, 27 n/mm = 154 lbs/inch.

For a combo car (road and track) with mac struts much over 200 lbs/inch spring gets a bit stiff and doesn't give a lot of (track) gain in comparisons to the (road) pain.

From the picture it certainly needs a lot more negative camber at that front spring and anti roll rate.

cool - I was quietly hoping that the picture would hold some clues to setup needs...

does anyone know if there is a thicker stock front bar from another car that fits the polo? is there something from a Golf maybe?

Try 10 mm, 20 mm maybe even 30 mm, with the maximum being limited to it reaching zero weight. Then read off the weight reduction on the other side and measure the distance the lifted wheel moves.

it does *mostly* make sense - I understand that it's a comparison tool, same as putting a car on a chassis dyno, it's only a useful exercise when you're comparing before and after changes on the same car

when you say "jack up one rear wheel", do you mean put the jack under the spring base, or the jacking point on the sill or somewhere at the back? I don't think it'd make sense to put it under the spring base because the weight on that scale would go to zero as soon as the balloon is taken out of the tyre

just to put in my own words

1. lift up the front of the car (to keep the car on the same plane when the rears are put on the scales?)
2. put scales under the rear wheels
3. put a jack under the left rear (on the body at a standard point that's always used for this procedure)
4. jack it up 10mm
5. record the weight on both scales
6. repeat 4 and 5 with increasing heights until the left rear has lifted off the scale
7. do the maths, nod head knowingly at the results, adjust stuff, repeat

Have some fun, try it with the swaybar added and then without, just with the twist beam supplying the anti roll. I'd guess something around 4 times the rate with the swaybar.

I don't think I want to go back to driving it without the rear bar, it's really made it a lot nicer to drive

I'm getting a bit too busy though - I'm doing things to the Polo, trying to sort out my mini for the June long weekend, and a CRX race car was dropped off at my house last night to supply, install and wire up a megasquirt ready for a sprint in May.... and do my day job....

[sambb]

no not that I know of. You can look at Ultra racing or Whiteline for bars and beyond that is ridiculously expensive H&R bars and VW racing stuff.

[Sydneykid]

Responses as follows;


1. lift up the front of the car (to keep the car on the same plane when the rears are put on the scales?)
The same plane isn't necessary, it just goes up on jack stands so that the front springs don't compress when you jack up one side of the rear


2. put scales under the rear wheels
Yep


3. put a jack under the left rear (on the body at a standard point that's always used for this procedure)
Nope, put the jack under the spring seat (or other convenient spot on the trailing arm)


4. jack it up 10mm
Jack the left wheel up 10 mm


5. record the weight on both scales
The only weight that matters is the right rear (the one you aren't jacking up).
The reason for the left scale is simply so you know when to stop jacking (there needs to be some weight on that wheel)


6. repeat 4 and 5 with increasing heights until the left rear has lifted off the scale
Yep, note the measurements (of the left wheel movement) and the weights (of the right wheel)


7. do the maths, nod head knowingly at the results, adjust stuff, repeat
Definitely, the knowing nod is important, plus a "Yep, that's what I thought" always helps.


Cheers
Gary

[Sydneykid]

I don't think I want to go back to driving it without the rear bar, it's really made it a lot nicer to drive

I was just suggesting that it would be interesting to compare the anti roll with and without the rear swaybar. Not that you should remove the rear bar and drive it, once anyone has experienced a FWD car with increased rear anti roll they never want to go back

Cheers
Gary

[Sydneykid]

I understand that it's a comparison tool, same as putting a car on a chassis dyno, it's only a useful exercise when you're comparing before and after changes on the same car.

I actually use the same method on completely different FWD cars. For example I recently helped out with the set up on a Mazda 3 (won its class at the Bathurst 6 Hour) and there were 3 choices of rear swaybar, the SP25 one, a 22 mm solid and 24 mm solid with 2 x 2 adjustment holes. I measured them and the SP25 and the 22 mm didn't have enough anti roll. The 24 mm on full hard measured fairly similar to the anti roll that I used on the Integras previously at Bathurst (also class winners). Plus it showed that the bushed links were taking too much away from the swaybar (in lost motion), so I recommended ball joint links.

It's a comparison for sure but it is transferable to different cars.

Cheers
Gary

[simon k]

I actually use the same method on completely different FWD cars. For example I recently helped out with the set up on a Mazda 3 (won its class at the Bathurst 6 Hour) and there were 3 choices of rear swaybar, the SP25 one, a 22 mm solid and 24 mm solid with 2 x 2 adjustment holes. I measured them and the SP25 and the 22 mm didn't have enough anti roll. The 24 mm on full hard measured fairly similar to the anti roll that I used on the Integras previously at Bathurst (also class winners). Plus it showed that the bushed links were taking too much away from the swaybar (in lost motion), so I recommended ball joint links.

It's a comparison for sure but it is transferable to different cars.

Cheers
Gary

ahh.... drawing on significant quantities of knowledge and experience to derive exceptional outcomes.... I suppose that could work too