Street Touring Hatchback (STH) discussion/setup

[xXDavidCXx]

And yes, I'm also VERY surprised that this setup is tighter than the GS one.

It's because the companies that sell these coilovers, to include Ohlins, keep the rear wheel rate lower than the front, but to the consumer the spring rates are often even, which "looks" okay. This keeps the handling towards under-steer, which is safer for those who just bolt-on the coils and go.

What you need in STH to have a setup that rotates like GS is a much higher rear spring rate. Read up on this thread for the past few pages to see my results as I increased the rear spring rate.

 

[xXDavidCXx]

Vorshlag plates.

The stock plate still has to mount to the top of the Ohlins stack for reference.
View attachment 184268View attachment 184269View attachment 184270

You have plenty of room for a corner balance. I have about the same.

 

[Mini7]

Good.

Cant be much difference in stack height between GC and Vorshlag.

 

[marka]

Howdy,

So, I'm looking at replacing the rear springs in the ST XTA setup I have. The top perch looks like it will work fine with standard coil over springs. Apparently they're 60mm, but I imagine they'd also work with 2.5" springs.

For the bottom, are folks just using the stock pigtail spring perch or something else?

Any idea on appropriate free lengths for springs in the 400 to 500 in-lb range?

I'd prefer not to have the springs be completely free at full droop. Guessing that means I'll need some helpers as well?

Appreciate any pointers toward how folks are setting this up to work with standard flat on both ends coil over springs.

Mark

 

[JackRabbitSLIM]

Hey Mark,

I've been meaning to tell you that I don't think that Strano (22mm for those unfamiliar) bar is even getting your rear inside off the ground. And also, every video I have seen (mine and Piehl) from that last Pittrace event all cars are pushing like crazy.

I've got some 2.5" ID 7" springs 7Ks and 500s if you want to try them out this season before deciding what you want.

If I were building I'd go with something like 500F/800R. For reference, Lugod's STX Focus ST ran 650F/1500R, I think Tipple (not sure if this is helping or hurting my argument) said his STH Civic was 600F/900R.

 

[marka]

Howdy,

Yeah. I've got an 034 25.x bar sitting on my workbench. It'll be on there for the next event.

Looks like the ST XTA spring rates are 400/~260 (front/rear) and stock is 182/238. So that may well explain some of my push as compared to the GS setup.

I've got some coilover springs from various previous cars/lifes. I'll probably throw something in there for the rear to get the split more like it was on the OE springs, but I'm wanting to do it in a way where the spring isn't clunking around / falling out at full droop. I've had that with other competition only cars and don't want to deal with it again.

Mark

 

[xXDavidCXx]

Hey Mark,

I've been meaning to tell you that I don't think that Strano (22mm for those unfamiliar) bar is even getting your rear inside off the ground. And also, every video I have seen (mine and Piehl) from that last Pittrace event all cars are pushing like crazy.

I've got some 2.5" ID 7" springs 7Ks and 500s if you want to try them out this season before deciding what you want.

If I were building I'd go with something like 500F/800R. For reference, Lugod's STX Focus ST ran 650F/1500R, I think Tipple (not sure if this is helping or hurting my argument) said his STH Civic was 600F/900R.

The reference numbers you posted are not useful without at least the wheel rate, but suspension frequency would be better.

 

[xXDavidCXx]

Howdy,

So, I'm looking at replacing the rear springs in the ST XTA setup I have. The top perch looks like it will work fine with standard coil over springs. Apparently they're 60mm, but I imagine they'd also work with 2.5" springs.

For the bottom, are folks just using the stock pigtail spring perch or something else?

Any idea on appropriate free lengths for springs in the 400 to 500 in-lb range?

I'd prefer not to have the springs be completely free at full droop. Guessing that means I'll need some helpers as well?

Appreciate any pointers toward how folks are setting this up to work with standard flat on both ends coil over springs.

Mark

I used standard 2.5 id Hypercoil springs. They fit fine in the lower OEM rubber spring seat.

Get 8 inch if you have that option.

I'm using 6 inch with a helper spring, and a spring divider.

 

[JackRabbitSLIM]

The reference numbers you posted are not useful without at least the wheel rate, but suspension frequency would be better.

I attached a calculator for both of those pages ago. I don't have the measurements for the 034 rear bar, with some assumptions, the wheel rates would be around 1000F/900R (in roll, so including swaybars) and suspension frequencies of around 2.3F/2.4R.

I was going to say this before when you guys were talking about suspension frequencies, I'm wondering what you think that is telling you? The natural frequencies and those bump charts of the "rear catching up to the front" all assume some specific decay amount. Now, do you (the general "you") think you have your dampers set to the exact critical damping setting? I very much doubt it, and I don't know why it would matter to anyone. Yes we hit bumps during autocross, but is keeping those traces lined up worth more than tuning your dampers to give you handling you want?

Dave, you just dropped your front damping way down at the last event, and your performance was better, right? And you are at LAP, where the bumps are actually pretty bad in certain places. Did you think your ride frequency was unchanged? With the rear full stiff, you are certainly over-damped (more damping, less weight), meaning the oscillation dies without overshoot. The front by contrast is heavier and your damping is far less due to your setting, so you could be underdamped. Don't forget that the y-axis unit on the shock dyno's is a force unit, same as your spring. So when you change your damping you are changing everything about those decay graphs. My whole point in typing all this BS is that you really don't care about this, you just think you do.

 

[xXDavidCXx]

All I was asking about the spring rate of the other cars, was to post the wheel rates, so we can make a better connection between a FOST running 1500R springs and my setup.

 

[bfury5]

If I were building I'd go with something like 500F/800R. For reference, Lugod's STX Focus ST ran 650F/1500R, I think Tipple (not sure if this is helping or hurting my argument) said his STH Civic was 600F/900R.

Quick dive down google shows the Focus ST is ~.5 rear motion ration, so makes sense to see the rear spring rate that much higher.

500/800 for this car seems fitting, I might be upping soon to see what sort of effect it has on driver input. I'm under-tired as well so when I upsize next year I'd rather have the springs on already.

Howdy,

Yeah. I've got an 034 25.x bar sitting on my workbench. It'll be on there for the next event.

Looks like the ST XTA spring rates are 400/~260 (front/rear) and stock is 182/238. So that may well explain some of my push as compared to the GS setup.

I run the 034 bar right now and that would definitely help, but as others have mentioned the rear spring would be the best bet.

 

[bfury5]

I attached a calculator for both of those pages ago. I don't have the measurements for the 034 rear bar, with some assumptions, the wheel rates would be around 1000F/900R (in roll, so including swaybars) and suspension frequencies of around 2.3F/2.4R.

I was going to say this before when you guys were talking about suspension frequencies, I'm wondering what you think that is telling you? The natural frequencies and those bump charts of the "rear catching up to the front" all assume some specific decay amount. Now, do you (the general "you") think you have your dampers set to the exact critical damping setting? I very much doubt it, and I don't know why it would matter to anyone. Yes we hit bumps during autocross, but is keeping those traces lined up worth more than tuning your dampers to give you handling you want?

View attachment 184418

I like the points you're making here. Personally, I use the math as a way to make the best estimates I can to determine the springrates and damper performance in terms of how the car handles bumps. After that, I see the damping adjustments as a tool to use to tailor the car to my liking. A lot of this has to do with the damping curves built into the damper as well. While it's not quite "black magic", I certainly put a lot of trust in the guy who built my suspension to give me a suspension I can work with and fine tune. Does altering damping effect ride frequencies? Absolutely, but I feel comfortable making those changes knowing my "base" setup should act a certain way. Increasing or decreasing front or rear at that point is based on feel.

And all of this doesn't even take into account tire pressure or tire construction, both of which can wildly effect tire springrate and compliance over bumps as well.

 

[xXDavidCXx]

Howdy,

Yeah. I've got an 034 25.x bar sitting on my workbench. It'll be on there for the next event.

Looks like the ST XTA spring rates are 400/~260 (front/rear) and stock is 182/238. So that may well explain some of my push as compared to the GS setup.

I've got some coilover springs from various previous cars/lifes. I'll probably throw something in there for the rear to get the split more like it was on the OE springs, but I'm wanting to do it in a way where the spring isn't clunking around / falling out at full droop. I've had that with other competition only cars and don't want to deal with it again.

Mark

You know you could just swap springs front to rear and that will make a big change in balance.

 

[JackRabbitSLIM]

All I was asking about the spring rate of the other cars, was to post the wheel rates, so we can make a better connection between a FOST running 1500R springs and my setup.

Sorry about that. The FoST and Si are both strut front and divorced multi-link rear, so the motion ratios are in the same ball park.

 

[xXDavidCXx]

I attached a calculator for both of those pages ago. I don't have the measurements for the 034 rear bar, with some assumptions, the wheel rates would be around 1000F/900R (in roll, so including swaybars) and suspension frequencies of around 2.3F/2.4R.

I was going to say this before when you guys were talking about suspension frequencies, I'm wondering what you think that is telling you? The natural frequencies and those bump charts of the "rear catching up to the front" all assume some specific decay amount. Now, do you (the general "you") think you have your dampers set to the exact critical damping setting? I very much doubt it, and I don't know why it would matter to anyone. Yes we hit bumps during autocross, but is keeping those traces lined up worth more than tuning your dampers to give you handling you want?

Dave, you just dropped your front damping way down at the last event, and your performance was better, right? And you are at LAP, where the bumps are actually pretty bad in certain places. Did you think your ride frequency was unchanged? With the rear full stiff, you are certainly over-damped (more damping, less weight), meaning the oscillation dies without overshoot. The front by contrast is heavier and your damping is far less due to your setting, so you could be underdamped. Don't forget that the y-axis unit on the shock dyno's is a force unit, same as your spring. So when you change your damping you are changing everything about those decay graphs. My whole point in typing all this BS is that you really don't care about this, you just think you do.

View attachment 184418

After driving around for a few weeks on these springs, I'll offer the following observations:
1. The front shocks are valved much higher than needed for the included 400 in/lb springs.
2. The rear shocks are valved such that higher spring rates can be used and still fall within the 0.6-0.7 critical damping range.

At full soft, the rear shocks dampen a single bump with at least two obvious oscillations. 10 clicks stiffer on the rear shocks on the same bump feels about in in 0.5-0.7 critical damped range. One bump and a quick return to neutral, but not harsh.

At the next race I'll leave the shocks at theses settings and manage rear grip with changes to tire pressure.