F:R weight bias and corner weights

[Martin]

But hey if its the only avenue open to me (since I have struts) and if I ever do get around to chucking it on some scales...

Ah, but you do have another much better option!
Put a packing plate on the top of the left front strut
This will make the shock longer and increase the weight on that corner
You'll need to mess around with the thickness of the plate - thats what low budget racers do

There is also a way to weight your corners at home using scales and a fulcrum lever
https://racemagazine.com.au/cars/bud...-weight-scales

[sambb]

cool. i'll get reading.

[sambb]

So with the packing plate method, you put it on scales and then try different height shims under whichever tyre/scale until everything is balanced. Once you have the height of each shim you then make up plates to the same height and fit them. Is that how its done.

[sambb]

But thinking about it, at any rate you would have to have adjustable links on your FARB if you got it corner weighted the way you are saying where there is no preload on the bar at the end step. Even taking our cars numbers once you add a driver it could be 80kg heavy on the RF. Once they adjust the collars to even that out (bars disconnected at this stage and assuming they aren't doing it with ballast) then there would be a ride height disparity between LF and RF. If you have non adjustable drop links and then just re attach the FARB then you will be preloading the bar which would throw the numbers out again. If the bar needs to be neutral at the end step then you would need adjustable drop links so that you could set the links to a neutral position where there was no bar preload and so that your numbers would stay as they were as set by the collars/shims yeah?
I know that bar preloading is used as a tuning tool on RWD live axles. I had a couple of books back when I had RWD cars that described how RARB preloading can counteract the rear steer that 4 link axles get when chassis torque pushes down through the tyres unevenly on a big launch. I read a thing by Mark Ortiz about how on some circuits that cars can deliberately be set up assymetrically. ie you could put ballast on one side of the car or even 'wedge' it nascar style with slightly different rate springs/preloads if that made the car much faster through one critical corner (ie like coming onto a straight where you could then pass) but didn't trade too much on other corners (like where it was hard for you to be passed or the total time lost off your lap would be comparatively small) ie tuning for the net gain. Makes your head hurt. The engineers that work all that out are freaks.
My mates clio will be getting corner weighted soon (its a McStrut + rear twist beam too) so i'll definitely get along to that to see how its done.

[Martin]

So with the packing plate method, you put it on scales and then try different height shims under whichever tyre/scale until everything is balanced. Once you have the height of each shim you then make up plates to the same height and fit them. Is that how its done.

Yep

The threads at the top of the shocks normally have 10mm~15mm excess which should be plenty for a small change like this

(I would not go to the trouble for 16kg with a diagonal of 50.6%)

[Martin]

Even taking our cars numbers once you add a driver it could be 80kg heavy on the RF.

No way will you end up with +80kg on the right front
Put a 100kg driver into the drivers seat, some of that weight will be born on the left, say 20%,
and only 60% of the rest will be on the front right, which is 48kg.

Once they adjust the collars to even that out (bars disconnected at this stage and assuming they aren't doing it with ballast) then there would be a ride height disparity between LF and RF. If you have non adjustable drop links and then just re attach the FARB then you will be preloading the bar which would throw the numbers out again. If the bar needs to be neutral at the end step then you would need adjustable drop links so that you could set the links to a neutral position where there was no bar preload and so that your numbers would stay as they were as set by the collars/shims yeah?

Yeah, you need a drop link that is threaded/adjustable at one end

I know that bar preloading is used as a tuning tool on RWD live axles. I had a couple of books back when I had RWD cars that described how RARB preloading can counteract the rear steer that 4 link axles get when chassis torque pushes down through the tyres unevenly on a big launch. I read a thing by Mark Ortiz about how on some circuits that cars can deliberately be set up assymetrically. ie you could put ballast on one side of the car or even 'wedge' it nascar style with slightly different rate springs/preloads if that made the car much faster through one critical corner (ie like coming onto a straight where you could then pass) but didn't trade too much on other corners (like where it was hard for you to be passed or the total time lost off your lap would be comparatively small) ie tuning for the net gain. Makes your head hurt. The engineers that work all that out are freaks.

There are far better solutions to a flawed design being made to handle big horsepower
Probably not relevant to a FWD McPherson strut Polo

I would not go down the path of preloading a swaybar
One obvious problem it would cause at the front of a FWD would be a loss of droop on one side and wheel spin galore

My mates clio will be getting corner weighted soon (its a McStrut + rear twist beam too) so i'll definitely get along to that to see how its done.

I've always hated rear beams but through the Pulsar racing I have observed benefits of that system,
rear camber control on a smooth track is far better than McPherson strut at the rear

[sambb]

So with the regard to packing the strut are you referring to the whole strut assembly - I'd imagined a spacer ring fitting between the strut top and strut tower, or are you talking about the damper itself. And with regard to the 80kg I was just pulling a number out of my bum as an example, I know it doesn't quite work like that, but it still remains that we don't know what the corner weights look like with a driver in the seat.
Yeah I'm hearing you on the FARB preload. Thinking about it more I'm sure it could be used to help square up static/ride weights but god knows what it would do in roll.
anyway out of all this its good to know the F:R weight split which should help with a few things, and that the car seems pretty well balanced L:R without a driver at least.
I'd just assumed your car was an irs N14 - do you run an N15? I wasn't sure if that was a twist beam or a solid beam on trailing arms.

[Martin]

I'd imagined a spacer ring fitting between the strut top and strut tower

Exactly - that's what I would do if I had a bent car and a significant weight differential and no appetite for coil overs

but it still remains that we don't know what the corner weights look like with a driver in the seat.

My FWD Pulsar N14 with me in the seat has a 49.9% diagonal split
The guy from improved production racing who is helping me to set the car up said we ain't gonna waste time trying to improve that

I remember when I removed the air con compressor and it's cast iron mounting plate,
I lost over 25kg from the right front, that made me happy
Removing the sound deadening from the floor saved 18kg
The front seats were also very heavy

One mistake I made, removing the heater, it does not weight that much and you need it to demist the windscreen when racing in the rain (especially at the start of the race, the windscreen fogs up standing on the grid!)

I'd just assumed your car was an irs N14 - do you run an N15? I wasn't sure if that was a twist beam or a solid beam on trailing arms.

Yes, mine is a N14 which has IRS, I run more than -4 degrees of negative camber at the rear
I've chased a few quick N15's which have a live rear beam and noticed the car body leaning over without hurting the rear camber (which is 0 degrees)