Street Touring Hatchback (STH) discussion/setup

[xXDavidCXx]

Howdy,



So, put on the 034 rear bar (soft setting) and bumped the rear springs to 500 in-lb (Apparently the ST XTA kit is 400 front, 260 rear). Autox yesterday. For sure a step in the right direction. For the first time, really tossing the car into a corner would get the back moving. But not really enough. Still pretty bad understeer unless you really tried to drive like an idiot.

For the rear springs, 8" 2.5" ID coil overs put me right into the butter zone in the middle of the rear adjuster at my current ride heights. Which was handy, because I had some springs sitting on the shelf.

For the next event, I'll try going to the 550's I had sitting beside those, and bump the rear bar to the stiff setting. Going to add some helper springs as well. On the lift, the rear springs/top adjusters aren't _quite_ completely free of the OE spring centering bulge, but its darn close. I don't think they could ever get loose enough to actually come completely out of the seat in usage (when cornering, the rear bar would keep enough pressure on the inside rear I think), but helpers will mean I don't need to think about it when jacking the car, if I go stiffer yet, etc.

Mark

Just go right to 700-800 in/lb springs.

The motion ratio in the rear is almost 1/2 of the front, meaning a 50 in/lb increase is hardly noticible.

If you get helpers, also get a spring coupler so the two springs don’t slip around.

With an 8 inch spring, I would not bother, considering you will need another corner balance and alignment. It’s not worth the hassle.

 

[JackRabbitSLIM]

For the next event, I'll try going to the 550's I had sitting beside those, and bump the rear bar to the stiff setting. Going to add some helper springs as well. On the lift, the rear springs/top adjusters aren't _quite_ completely free of the OE spring centering bulge, but its darn close. I don't think they could ever get loose enough to actually come completely out of the seat in usage (when cornering, the rear bar would keep enough pressure on the inside rear I think), but helpers will mean I don't need to think about it when jacking the car, if I go stiffer yet, etc.

I really think the understeering STH cars are a result of a problem at the front, not the rear. Most people on here have a setup close to what you are saying you'll change to and still understeer. No one is complaining about being to loose. I dare you to put the 550s on the front, leave the rear springs, stiffen the rear bar, and add rear toe out. If it's not better, I'll buy you a hockey stick.

I know, I know, understeering means add rear rate. That's only going to help if the front is in it's happy place. These cars have 1000 lbs on each front corner, the front needs to be propped up. My STX type R would always understeer no matter how much rear rate I threw at it. Once I added enough front spring the car changed completely. Ask around for what other heavy FWD/AWD people have for spring rates/bars.

Andy Hollis DM on FWD:
"Build your spring rates around the corner weights, and adjust bars to get the roll angle from there. if you do too much with springs, you'll reduce grip on bumpy surfaces. Since bar rates go up in rate exponentially, it's the only real way to large amounts of roll stiffness."

"So how do we make the car stop understeering? One way, is to decamber the rear, as you have been doing lately. But that is a fairly sudden breakaway, and actually doesn't make the car any faster (it just feels better than "riding out the push"). Here's another key point: Under steer is when the slip angle of the front tires is larger than the rear tires. One way to open up the effective slip angle of the rear tires (reducing understeer) is through toe-out in the rear. This "steers" the rear tire to a larger arc than it would otherwise be at. You will be amazed at how much rear toe-out you can run in autocross. And it's free. Try something like 1/4" total to start, but don't be afraid to go up to 1/2" total."

 

[marka]

Howdy,

Changing front springs is a PITA. Changing rears will take me about 45 minutes.

And yes, that means I'm just getting the ride height back where it was and not bothering with corner balance / alignment. My assumption is that if the ride height is close to the same, there won't be significant differences in alignment (toe in particular) so I can play with this until the balance is closer, then fine tune more.

I need to order some helpers. Maybe I'll get some 700 in-lb springs too. For that rate, does 7" work better than 8", assuming I have height adjusters on the top w/the OE rubber perch in the bottom?

And I'm still not wanting to add toe to either end. The car's driven less on the street now than before, but it still happens. Given that in GS form with zero front camber and no toe it was more balanced, it sure seems like I should be able to get the car more balanced without needing to add toe.

Mark

 

[bfury5]

I really think the understeering STH cars are a result of a problem at the front, not the rear. Most people on here have a setup close to what you are saying you'll change to and still understeer. No one is complaining about being to loose. I dare you to put the 550s on the front, leave the rear springs, stiffen the rear bar, and add rear toe out. If it's not better, I'll buy you a hockey stick.

This is one of the changes I'm contemplating for next year, however as has been said a bunch of places I'm going to toe-out in the rear (because free) and see how that goes first. At this point, my car isn't understeering if I can remember to drive it correctly, so I'm focusing more on my driving and *slight* suspension tweaks until the end of the season up in New England. I've got enough changes coming over the winter that I'm just going to wait to do them all.

 

[marka]

Howdy,

Just go right to 700-800 in/lb springs.

You people are a bad influence. Added 7" long 700 in-lb springs to my helper/spacer order.

Mark

 

[JackRabbitSLIM]

Can someone measure the 034 rear bar for both settings? "A" is the straight arm length, "C" is basically the hypotenuse dimension.

 

[GTIfan99]

Howdy,



You people are a bad influence. Added 7" long 700 in-lb springs to my helper/spacer order.

Mark

Yes, but this is one of the best threads in the whole forum. I find myself only really wanting to talk to motorsports people on the forums anymore. The farther you stray, the more derp there is. lol

 

[xXDavidCXx]

Yes, but this is one of the best threads in the whole forum. I find myself only really wanting to talk to motorsports people on the forums anymore. The farther you stray, the more derp there is. lol

This thread has grown beyond my wildest dreams.

Thanks to all who have contributed to learning and discussing all things MK7 and racing, and to helping each other learn more about our cars.

 

[xXDavidCXx]

I really think the understeering STH cars are a result of a problem at the front, not the rear. Most people on here have a setup close to what you are saying you'll change to and still understeer. No one is complaining about being to loose. I dare you to put the 550s on the front, leave the rear springs, stiffen the rear bar, and add rear toe out. If it's not better, I'll buy you a hockey stick.

I know, I know, understeering means add rear rate. That's only going to help if the front is in it's happy place. These cars have 1000 lbs on each front corner, the front needs to be propped up. My STX type R would always understeer no matter how much rear rate I threw at it. Once I added enough front spring the car changed completely. Ask around for what other heavy FWD/AWD people have for spring rates/bars.

Andy Hollis DM on FWD:
"Build your spring rates around the corner weights, and adjust bars to get the roll angle from there. if you do too much with springs, you'll reduce grip on bumpy surfaces. Since bar rates go up in rate exponentially, it's the only real way to large amounts of roll stiffness."

"So how do we make the car stop understeering? One way, is to decamber the rear, as you have been doing lately. But that is a fairly sudden breakaway, and actually doesn't make the car any faster (it just feels better than "riding out the push"). Here's another key point: Under steer is when the slip angle of the front tires is larger than the rear tires. One way to open up the effective slip angle of the rear tires (reducing understeer) is through toe-out in the rear. This "steers" the rear tire to a larger arc than it would otherwise be at. You will be amazed at how much rear toe-out you can run in autocross. And it's free. Try something like 1/4" total to start, but don't be afraid to go up to 1/2" total."

For me, the short story is I’ve increased the front rate from 400 to 425, raised the front ride height and decreased front rebound.

I think what you are alluding to when say make the front end happy, is to not overload the front tires.

This can also be done with higher front tire pressure, which I may test this weekend.

I entered this season woefully unaware of what slapping on 400 in/lb springs front and rear would do.

Thanks for continuing to push me to rethink my setup ideas and the underlying theories.

 

[Mini7]

This thread has grown beyond my wildest dreams.

Thanks to all who have contributed to learning and discussing all things MK7 and racing, and to helping each other learn more about our cars.

Couldn’t agree more!

 

[theDoktor]

Can someone measure the 034 rear bar for both settings? "A" is the straight arm length, "C" is basically the hypotenuse dimension.
View attachment 186622

I couldn't find my measurements, but the rate I calculated was 509 in/lbs. (softest setting).

 

[xXDavidCXx]

Helpful link to convert toe from inches to degrees.

https://robrobinette.com/ConvertToe...-In&text=0.0625" x 4 = 0.25",0.58º, not 1.16º.

 

[xXDavidCXx]

I think I'll go back to more rear camber, and 1/4 inch toe out. Is this recommendation total toe or each side is 1/4 inch?

 

[Mini7]

I think I'll go back to more rear camber, and 1/4 inch toe out. Is this recommendation total toe or each side is 1/4 inch?

1/4” is a lot. I’m thinking it’s a total toe measurement. Super loose coming up. Lol

 

[Mini7]

The post said to start at 1/4”, but don’t be afraid to go as much as 1/2” total toe.