Body Roll and spring size.

[Bob_n_Cincy]

Right now I am running the 818S spring package 350F/275R with no sway bar.

42527

In the picture above I suspect I am less than 1 G on some old 205/45/16 federal tires.
The body roll shows about 4" difference between sides of the car.
My 818S yellow shocks only have 4" total travel.
I suspect my left side shocks are in full compression and my right sides are in full extension in the above picture.

Do you agree with me and if so what should I do to fix it.
Thanks
Bob

[Buzz Skyline]

I would probably try installing a sway bar first. If you have the donor bar, at least it will be a cheap option. After that, I would consider stiffer springs.

I don't have the sway bar installed in mine yet either. I was planning to see how things went without it, but you've done the experiment for me.

[Buzz Skyline]

How's the over steer with that set up? I'm no expert on suspensions, but the problem with adding a front sway bar is that it would dial back your oversteer and increase understeer. If you like the way the tail moves now, then stiffer springs would be better than a sway bar, I'm guessing.

[RM1SepEx]

There are pros and cons to both approaches... FFR did the development work with help from KONI and the 17MM bar, I would start there. Remember they have many hrs of development between springs, shock rates etc... Why reinvent the wheel?

If you have an R, $ for new tires all the time and a development track... go for a custom setup to match your driving style.

I used to buy tires for my FMod from development efforts of national SCCA roadracers. Loved those low use tires, they just kept swapping em out to eliminate tires from the setup variable... I bought slicks with only one or two short heat cycles for our autocross efforts and got to thrash them for a season or more!

Most of us can't generate the data that requires hrs of seat time, esp if you are an autocross junkie. And you could spend hrs going down the road of developing a bad setup.

[Buzz Skyline]

I agree with Dan generally, but I've had lots of luck making changes here and there with my autocross and rallycross cars. Provided you only change one thing at a time, it's not hard to avoid making a huge mistake.

I've found that tinkering with anti-sway bars seems best for adjusting over/under steer, while springs are better for reducing roll and improving cornering (the car settles into it's cornering stance quicker with stiffer springs). I generally avoid messing with my dampers because I find it much harder to understand and control their effects.

My impression is that FFR added the roll bar specifically to dial in some understeer and make the car a bit safer on the street. If you like the over/understeer you have then I would certainly avoid adding a roll bar to begin with. (Adding a roll bar, btw, will effectively make it like you have stiffer springs because both sides get involved when you compress the suspension on either side.)

Of course, stiffer springs are going to cost more than putting on the donor roll bar, and you might want to find an expert to help you decide what stiffness springs to choose. Among other things, it's important to make sure the front and back suspensions don't have the same resonance frequency. Resonance depends both on the spring stiffness (k) and the mass attached to the spring (m). You should make sure that the ratio k/m is different for the front and back of the car.

We used a great reference source to come up with our spring set up. I'll try to remember what that was.

[xxguitarist]

Speaking from our time on the R package springs/shocks, with stiff up front, we were pretty happy with the balance without any sway bar. I'd give the stiffer springs a shot, and dial up damping proportionally.

We didn't have our body on when we were running hoosiers, but I can say that we were not contacting the front bump stops while running the car very aggressively.

[RM1SepEx]

Andrew, the R package setup was developed w/o a bar, correct? I would imagine that the R package would be unbearable on a street driven car. Once you start down the racing development road street driving generally suffers.

So Bob, if that turbo 818S is a race only car and you go with the R setup... great place to start, if you are starting with an S arrangement and want to periodically autocross... go the other route.

Every time I've developed a street car to autocross, I've developed it right off street drive ability. EX setup a Miata to autocross well and here in Maine due to lowering, increased spring rates and bigger bars, you need to be related to a dentist and a mechanic as the roads will shake and crunch you into trouble...

[C.Plavan]

I have found 375 pound springs up front and 600 pound in the rear (no sways) were WAY BETTER than the the stock setup (300/500). I may go even a little stiffer. I increased the rebound 50% all the way around also. There- I saved some more people money..... :)

[xxguitarist]

Dan, agreed that too much autox setup can degrade road driving quite a bit. We do have friends who street drive STR/STS miatas though. They just might come out an inch shorter after it!

We will be considering some stiffer springs for the rear of our car. It's currently using the majority of the available travel, and possibly riding on the bump stops on accel. We'll have to get a camera on it to be sure.

If getting the rear range proper results in more oversteer bias, we'll probably correct that with aero or a front sway.
Could be handy to use aero, then you have a neutral car at speed, and a little oversteer bias in the tight slow spots.

[Bob_n_Cincy]

Right now I am running the 818S spring package 350F/275R with no sway bar.



Thanks for the responses, keep them coming.
The car as set up now suffers from snap oversteer.
It is possible but not easy for us to do a front sway bar as our front gas tank is in the way.
Bob

[xxguitarist]

Snap oversteer on lift, or do you just mean rapid oversteer on throttle mid corner?

[Bob_n_Cincy]

Snap oversteer on lift, or do you just mean rapid oversteer on throttle mid corner?

Andrew
here is a typical mid corner spin

https://youtu.be/vjj8IcT11FQ

[xxguitarist]

I dont notice a big tone change right before the rear lets loose, so i'm assuming you were on engine braking, and also braking. I wouldn't call that snap oversteer, but would say it was oversteering by about a third of the way through the corner.
The tires will be a big limiting factor for you, and it could be that the spring rates you're using makes it easier to really unload the rear. We've only used 235/255 split Dunlop Z2s for street tires for autox, which felt balanced, and 245 hoosiers square, which interestingly also felt balanced, but can always use more accel grip!

Have you checked your rear toe?

Barring an oddity with handling, it may just be a frequent result of trail braking. (fix with fast hands, and oddly, getting back on the throttle) I can get our ES Miata with a HUGE front bar to let loose by trail braking in certain ways, and Tamra used to like to spin it on lift :-)

[Mitch Wright]

I agree with Andrew, I would sort out what tires and sizes before spend a bunch of money. The track suggested set up for the R is 300Frt 500 Rear with all the aero and front bar. I am not sure that would be the hot ticket for AutoX and I am not an AutoX guy but I would also start by adding spring to the car. The snap oversteer can also be from bottoming out the rear understeer from bottoming out the front.

[Bob_n_Cincy]

Thanks everyone,
I have decided springs, tires and rims.
9x17-45 with 235/40-17 R888 fronts
9x17-35 with 255/40-17 R888 rears. Mike wants me to jump to 275s.
For springs, I am thinking the 818R setup of 500R 300F or Chads setup 600R 375F
Thanks
Bob

[Tamra]

Thanks everyone,
I have decided springs, tires and rims.
9x17-45 with 235/40-17 R888 fronts
9x17-35 with 255/40-17 R888 rears. Mike wants me to jump to 275s.
For springs, I am thinking the 818R setup of 500R 300F or Chads setup 600R 375F
Thanks
Bob

I believe you will rub on the rears. We have 17x8 et 45 with 255/50-17s for our street setup and they rub on the lower arm at autox due to tire deflection. They are fine for more "normal" driving.

Also we are running the 500lb springs on the front, not the rear.

[xxguitarist]

With what Tamra said, you'll be aprox 0.1" closer to the rear control arm than us, but the tire will be supported better. Alignment around this problem and/or wide tire arms could fix this, assuming adjustable lateral links.

The fronts will rub at full lock also.

[C.Plavan]

Dont forget I have the APR wing on the rear with the 600lbs springs. Bob, you may want to run even stiffer on the front.

[Bob_n_Cincy]

I believe you will rub on the rears. We have 17x8 et 45 with 255/50-17s for our street setup and they rub on the lower arm at autox due to tire deflection. They are fine for more "normal" driving.
Also we are running the 500lb springs on the front, not the rear.


With what Tamra said, you'll be aprox 0.1" closer to the rear control arm than us, but the tire will be supported better. Alignment around this problem and/or wide tire arms could fix this, assuming adjustable lateral links. The fronts will rub at full lock also.


Dont forget I have the APR wing on the rear with the 600lbs springs. Bob, you may want to run even stiffer on the front.

Last week we tested 17x9-35 255/40-17 on front and rear.
We had 3/8" clearance on the lower trailing arm.
I do see that much deflection during hard acceleration. We are also changing our lateral links to tubes with rod ends to prevent deflection.
42560

Here is a picture of the 17x9-35 255/40-17 in the front barely rubbing at full lock.
We have our suspension moved out to the wagon holes.
42559

Chad, don't forget we have 600 lbs of ballast right in front of the fire wall.
I will take your advice and go stiffer in front.

Thanks to all.
Bob

[xxguitarist]

It's not acceleration that will eat up your clearance, it's the lateral deflection of the tires under cornering Gs.

Watch the tire shift on the wheel: (start at 10:20)

http://www.youtube.com/watch?v=fGKCo6nQ24g

[Bob_n_Cincy]

It's not acceleration that will eat up your clearance, it's the lateral deflection of the tires under cornering Gs.

Watch the tire shift on the wheel: (start at 10:20)

Wow
Thanks Andrew,
I thought the tire would only deflect at the bottom. That video clearly shows it is much higher. I may have to add a little more curve to the trailing arms.
Bob

[xxguitarist]

Bob,
Yes- the whole sidewall flexes, and the tread portion more-or-less stays concentric with the hub, it could cause clearance problems even at the top sidewall area.

[D Clary]

If you autoX you definitely need to go with the stiffer springs. When you are dealing with fractions of a second you don't have time to wait for the car to roll back and forth in transition. But to optimize autoX you will damage you're street ability. I have been autoXing my mustang for about 7 years and it has gotten faster every year but it is a kidney punch to drive on the street.

[Bob_n_Cincy]

If you autoX you definitely need to go with the stiffer springs. When you are dealing with fractions of a second you don't have time to wait for the car to roll back and forth in transition. But to optimize autoX you will damage you're street ability. I have been autoXing my mustang for about 7 years and it has gotten faster every year but it is a kidney punch to drive on the street.

We are in our 3rd season of autoX, but hope to do some track days this summer. I would like to keep this car streetable. Maybe our second 818 will become an R that is track only.
Bob

[xxguitarist]

Sure you know it, but autox & road course setups tend to be pretty different.

Autox favors transitions, so you have lots of front spring or bar as required by class. Cars tend to be understeer to neutral bias.
Track favors sweepers, so rates tend to be more balanced, and cars tend to be neutral to oversteer biased.

"streetable" is too personal for us to speak to it for you. Hopefully in a few more weeks we'll be able to comment on our opinions, the inspection checklist is getting smaller!

[D Clary]

I kind of have a different feeling, I like neutral to overs teer in autox to try to get the car to rotate quickly, in track there is room to trail brake and get the car to rotate with different positions on the track but stull very different set ups.

[Bob_n_Cincy]

I'm going to follow chad lead and go with 600R/350f springs.
Bob

[Tamra]

Bob, I'll be interested to see how it goes. I think you know from our setup, that if we had those spring rates, we would be running 600 front and 350 rear. But who knows, maybe with the rear weight bias it will work for you. When do you expect to have them installed and go to your next autox?

I'll just leave this here any case anyone wants a cheat sheet:

http://i1374.photobucket.com/albums/ag408/wrx818/Build/Suspension%20setup_zpslat3hnqw.png (http://s1374.photobucket.com/user/wrx818/media/Build/Suspension%20setup_zpslat3hnqw.png.html)

[Bob_n_Cincy]

Bob, I'll be interested to see how it goes. I think you know from our setup, that if we had those spring rates, we would be running 600 front and 350 rear. But who knows, maybe with the rear weight bias it will work for you. When do you expect to have them installed and go to your next autox?


Thanks Tamara,
Here is some rough calculations.
With Michael and I both in the car there is about 1500 lbs (750lbs per tire) on the rear axle.
During a 1.0G corner the rear outside tire adds 600lbs. (1500 x 1.0G x 12"cg-rc height / 30" half of axle length
With 275 springs and 2" of travel we are well into the bump stop.

Michael and I have been on family vacation on Hilton head island for the last 2 weeks. We have lots of parts waiting at home when we get back this weekend.
Wheels, tires, springs, lateral links, oil cooler and an accusump. The next autocross for us is on the 28th in Wilmington, OH.
Bob

[Bob_n_Cincy]

I just put on some 600 springs on the rear to test at an autocross this weekend.
with the shocks off the car, I put zero preload on the springs. I just snug up against the top perch.
When I installed the shocks the spring compressed about 3/4" and the ride height was 5 1/8"
I can get to 4" ride height by adjusting the spring collar. The problem I see is that the spring will come out of it's perch by 1" if the tire gets unloaded will driving.
Does anyone know a solution.
Bob

[JeromeS13]

Helper springs.

https://www.pegasusautoracing.com/productselection.asp?Product=1876

[Mitch Wright]

Bob,

I would be really surprised if you had a problem with the spring coming out of the perch. With the rebound damping the wheel won't fall fast enough. I having run many cars that were that way, it was never an issue. Now if you plan to rally the car and will be getting some air that would be a different story.

[Bob_n_Cincy]

Helper springs.

https://www.pegasusautoracing.com/productselection.asp?Product=1876


Bob,

I would be really surprised if you had a problem with the spring coming out of the perch. With the rebound damping the wheel won't fall fast enough. I having run many cars that were that way, it was never an issue. Now if you plan to rally the car and will be getting some air that would be a different story.

Thanks Jerome and Mitch.

I'll try it this weekend without the spring tenders. no time to get them.
I will go-pro it to see how it works out.

I have been know top tripod Mike's impreza all the way around a sweeper.
Good thing this has a lower center of gravity.
Bob

[xxguitarist]

Bob, move shock mounts to the "R" position bolt hole, you'll get a little static drop, and can keep your springs with a tiny bit of preload, without the helper springs.

I would not run the springs loose at full droop.

[Bob_n_Cincy]

Bob, move shock mounts to the "R" position bolt hole, you'll get a little static drop, and can keep your springs with a tiny bit of preload, without the helper springs.

I would not run the springs loose at full droop.

Thanks Andrew,
I am going a completely different direction. I'll let you know if it works out.
Bob

[Bob_n_Cincy]

I am trying to stop some fender rub in the front.
I was thinking about spacing the bump stop in the shock lower.
The shock body would hit the bump stop before tire hits the fender.
Is this acceptable to do?
Bob

[Bob_n_Cincy]

I am trying to stop some fender rub in the front.
I was thinking about spacing the bump stop in the shock lower.
The shock body would hit the bump stop before tire hits the fender.
Is this acceptable to do?
Bob
Anybody have a comment on this?
Bob

[BuzzSkyline]

I've always tried to avoid using the bump stop as a suspension element. You end up with an extremely non-linear suspension. Of course there are problems with all the other solutions too (cranking up the coil overs, narrower tires, smaller diameter tires, stiffer springs, roll bar, etc.). I wonder if there's a way to raise or modify the fender?

[Tamra]

I wouldn't use the bump stop... sudden spring rate to infinity could cause some poor handling characteristics I imagine. I would go up in front spring rate or some other combination that BuzzSkyline listed.

[C.Plavan]

You noticed how they fixed the issue with the new fenders right? Everyone is fighting the same tire rub issue.

[Mitch Wright]

I agree with Tamra and Buzz, add bump stop is not the way to go and will create a list of handling troubles. you have some good suggestions above.
In mocking up my body while waiting parts it looks like a little room can be gained by moving the bottom rear of the fender out about an 1 1/2 inches. I have only played around with it and taking crud measurements I was gaining a 1/4" at the center of the flare.

[C.Plavan]

I agree with Tamra and Buzz, add bump stop is not the way to go and will create a list of handling troubles. you have some good suggestions above.
In mocking up my body while waiting parts it looks like a little room can be gained by moving the bottom rear of the fender out about an 1 1/2 inches. I have only played around with it and taking crud measurements I was gaining a 1/4" at the center of the flare.

It's going to rub on the inside of the flare on the fender. I'll take pictures of where mine does.
Bump stops are bad.

Really only 3 options:
1. Raise car/stiffen springs
2. Make spacers to raise fenders and hood. Then live with the funny gap of raising the hood.
3. Super small tires or try new front end, which may/may not help.

[Bob_n_Cincy]

It's going to rub on the inside of the flare on the fender. I'll take pictures of where mine does.
Bump stops are bad.

Really only 3 options:
1. Raise car/stiffen springs
2. Make spacers to raise fenders and hood. Then live with the funny gap of raising the hood.
3. Super small tires or try new front end, which may/may not help.

Thanks Everyone.
I been messing with my front suspension all afternoon.
At 2.5" RH (Ride Height) my tires rub when turning.
A 4.5 RH is where I want my normal ride height.
At 6" RH the angled upper bay joint jams.

If I have 1/2" safety factor on each end. Is 2.5" total vertical travel enough?
I have 350 springs on the front. Is that enough?
I don't understand how the R guys are doing it without cutting 2" out of your fenders.
Bob

As a side note. The bump stop that comes with the yellow shocks is about 400 lbs. when it is squished to 1/2"

[Bob_n_Cincy]

I've always tried to avoid using the bump stop as a suspension element. You end up with an extremely non-linear suspension. Of course there are problems with all the other solutions too (cranking up the coil overs, narrower tires, smaller diameter tires, stiffer springs, roll bar, etc.). I wonder if there's a way to raise or modify the fender?


I wouldn't use the bump stop... sudden spring rate to infinity could cause some poor handling characteristics I imagine. I would go up in front spring rate or some other combination that BuzzSkyline listed.

I understand that using the bump stop will give me an exponential spring curve. But we don't have very much choice with the small static clearance between the tire and fender.
I could put a note on the steering wheel that says.
Only hit bumps while going straight at slow speeds. :confused:
Bob

[Erik W. Treves]

http://thefactoryfiveforum.com/attachment.php?attachmentid=43482&d=1436495654

[C.Plavan]

http://thefactoryfiveforum.com/attachment.php?attachmentid=43482&d=1436495654

Thats childs play :)

http://i.imgur.com/vbmJ3bll.jpg