Learn Me Suspension? (Lowering springs and scrub radius)

I have an mk7 GTI that I tracked this year which I'm looking to get a little more out of next season. The GTI is a lot of fun to toss around the track, the level of grip it provided was particularly surprising. However, if I'm being honest the chassis while capable is also pretty numb, but I guess that should have been expected. I know this car will never be an e46 m3 or GT86 in terms of feel, but I'd like to see if there's anything I can do to enhance the feedback some while improving its' cornering capabilities at the same time.

Current mods:

Front control arm poly bushings

Strut bar

Falken Azenis RT615K

26mm RSB

Poly RSB endlinks

The next mod I'm looking at are lowering springs and camber plates. My main goal here is being able to increase negative camber in the front and the camber plate I'm looking at supposedly has to be used in conjunction with their springs. From what I understand, you don't want to go too low with just springs as it will ruin the suspension geometry. The question I have is, how do I figure out exactly what is too low for my car?

Here are the springs I'm thinking of buying:

https://www.ecstuning.com/b-racingline-parts/mk7-gti-vwr-sport-springs/vwr31g7gt~vwr/

They seem to be the only ones on the market for the GTI that at least try to match the stock shocks and again they have to be used with their camber plates that I want. In the end, I know coilovers are always the better option, but if I can stay within my budget while still improving that would be perfect. So how will "slightly" matched springs effect my suspenion? Will there be any negatives on the track under hard load? I guess what makes that more difficult to determine is they don't list the spring rate, which unfortunately seems to be pretty common.

Alternatively, would it be better to get an entry level coilover kit?

Next up, lighter weight wheels. All of which have different offsets from stock and offsets will impact scrub radius and scrub radius impacts steering feel. What wheel width and offset should I be looking at to change my scrub radius whereas it will provide more feedback? I'm not sure how to figure this out.

Maybe I'm going too deep, but I'd hate to waste money on mods that send me in the wrong direction.

Thanks.

For most strut based cars, keeping the control arms parallel to the road is more or less as low as you want to go.

For lowered cars, you should also be aware of how much travel is left in the struts.

You can get balljoint spacers to correct the geometry of the control arm and shorter struts to ensure you don't run out of travel on the struts.

Some have trimmed the tops of their strut shafts and ground them down to cut new threads to shorten the shafts, not ideal, but its a cheap solution.

For scrub radius, you get to play with the camber settings at the strut top and at the spindle to try and get a line drawn through the center of the strut to hit the ground in the middle of the front tire's contact patch.  You can also play with wheel offset as well to improve this.  This helps with torque steer among other things.

Porsche worked quite hard on this for the 924/944 which used MK1 Golf front suspension parts.

That said, strut based suspension is always going to be compromised due to the bad camber curves inherent in the design, so you have to make the most of it within the narrow range where you use it.

Scrub radius isn't a case of "x is perfect, anything else is bad."  There's a reasonable range that'll behave well (different for FWD vs RWD) and if you've got a way to adjust it (such as adjusting camber by tilting the strut), you can experiment a bit to see what feels best.  

Stefan pretty much nailed it. You can add in -camber with the plates, and then take some back out with crash bolts if you want to run less offset wheels and keep the scrub radius change to a minimum. 

I would also say: adding scrub radius will increase "feel", but at the downfall of amplified torque steer since the wheel/tire now have more leverage against the steering/suspension. I would instead look at decreasing the assist on the power steering; be it from reducing pump pressure (hydraulic) or fiddling with the electric assist, whichever the car has.

Nessumsar said:

I would instead look at decreasing the assist on the power steering; be it from reducing pump pressure (hydraulic) or fiddling with the electric assist, whichever the car has.

For the GTI, that's a simple as selecting sport driving mode or setting the steering to firm in the individual mode.

Some amount of scrub radius can also increase self centering (like caster).  I got a bit too close to 0 scrub on the Jeep at one point and the end result was the steering feeling kinda screwy and not centering well.  Adding wheel spacers (and more positive scrub) made it much better.  Too much would have given nasty bumpsteer, however.  

Lowering springs matched to stock shocks makes me a little nervous. Unless the factory shocks are way over-damped for the springs, I would think those new lowering springs would be way too soft. As in you'd blow through all your travel at the slightest provocation and nail the bumpstops. That's not good for ride or handling.

When negative scrub is implemented on fwd cars in order to reduce the effects of torque steer, is it safe to assume that their negative value isn't far from 0? Meaning that excessive amounts of either positive or negative scrub will increase steering effort and road feel?

If that's true, I guess my goal is to go further into the negative and away from 0...

So I would want to slightly increase my offset? Not sure if I'm looking at this correctly.

Increase your caster.   The GTI may be factory lowered ?    As mentioned above don't go too low.   How old/miles ae the struts/shocks. New ones can make a world of difference  Rear bar or bigger if it already has one.

Stefan said:

For most strut based cars, keeping the control arms parallel to the road is more or less as low as you want to go.

For lowered cars, you should also be aware of how much travel is left in the struts.

You can get balljoint spacers to correct the geometry of the control arm and shorter struts to ensure you don't run out of travel on the struts.

Some have trimmed the tops of their strut shafts and ground them down to cut new threads to shorten the shafts, not ideal, but its a cheap solution.

For scrub radius, you get to play with the camber settings at the strut top and at the spindle to try and get a line drawn through the center of the strut to hit the ground in the middle of the front tire's contact patch.  You can also play with wheel offset as well to improve this.  This helps with torque steer among other things.

Porsche worked quite hard on this for the 924/944 which used MK1 Golf front suspension parts.

That said, strut based suspension is always going to be compromised due to the bad camber curves inherent in the design, so you have to make the most of it within the narrow range where you use it.

Great info thanks. I'm starting to lean towards finding a camber kit that will mate to the stock suspension that way I won't need lowering springs.

red_stapler said:

Nessumsar said:

I would instead look at decreasing the assist on the power steering; be it from reducing pump pressure (hydraulic) or fiddling with the electric assist, whichever the car has.

For the GTI, that's a simple as selecting sport driving mode or setting the steering to firm in the individual mode.

The wheel has better weight to it in sport, but still feels too numb imo. 

Found this: http://www.ground-control-store.com/products/description.php/II=989

Will allow me to adjust camber and caster on stock suspension. Still not sure which direction I should go in regards to wheel offset though. Also, I assume negative camber will lead to negative scrub radius as well?

Some handy links for you:

https://en.wikipedia.org/wiki/Scrub_radius

http://www.moderntiredealer.com/article/712036/helping-your-customer-understand-why-wheel-offset-matters

http://www.car-engineer.com/suspension-design-definitions-and-effects-on-vehicle-behavior/

Thanks Stefan. So that clears up that pushing my wheels further outwards leads to positive scrub radius. But, I'm still a bit confused as to whether or not that's the direction that would yield my desired results. As I understand it, the larger that pivot point is the more road feel you're going to have. So as I push my wheels out by changing my offset (marginally), I'm essentially decreasing the width of my pivot, but also moving closer to positive scrub. 

A large amount of negative scrub can also increase steering effort, I assume road feel as well. At the same time negative scrub is used in fwd to decrease torque steer.

So I'm confused as to whether a larger negative scrub radius, say moving from -2 to -3 would yield more road feel than moving from -2 to -1. The latter of course being smaller in width, but closer to positive.

It seems like you could break even on scrub radius if you get wider, lower offset wheels, and compensate for the change in scrub radius by adding camber with the camber plates.