Tech Talk

Desparate for some setup help. Been fighting a chronic loose middle off condition. 1/4 mile 22 degree track. Metric chassis, 602 crate, 8" Goodyears
55% cross, 57% left, 47.7% rear, 1.25" front sway bar, 3" stagger.
LF 869# RF 794#
800#spring 900#spring
#5 shock #6 shock (shocks are Pro WB's)
140/125/116 158/161/165 tire temps

LR 954# RR 563#
175#spring 125#spring
4-6 shock #4 shock
137/137/136 172/180/179 tire temps

In front we can use screw in BJs and tube uppers. MC is right of center.
In rear we can raise front uppers 1". Soft rubber bushings in the front uppers.

The soft springs in the rear have helped alot with bite off the corner. Soft springs were good advice from trustworthy regulars.

Next step of testing is front springs. Any advice would be welcome.

Make sure the rear axle tube is not hitting the frame

hi ,
you need more cross%...like 60%..with a metric..
your cross temp average is 24* cooler...

also try more bar..or more pre-load..

and less rear stagger.... like 1.5"

you also need more camber / caster in the RF..try 4.5 to 5*..
and less in the LF..
and then re take temps..

you mite then be tight from the middle off,.... ?

if it is id think about adding some spring to the RR ,
like a 150lb,175 lb.. or/ and a rubber...

I've been on the lookout for rear suspension binding. Been testing lots of different rear spring combo's and found a rub in the LR spring bucket that scrapes the powdercoat off the top of the spring. Gotta trim some flashing to fix that. I don't think its a smoking gun...

Found my old 8mm video camera and am going to strap it under the car to see whats going on

Racer 270 thanks for the input. I've tried higher cross weights but that just makes the car push bad and be loose off. Last time I accidentally went in with 59% I balded the RF in 25 laps.

I've tried cranking on the bar preload but again I've never made the car tight. Right now I'm sticking with 1.5 turns on the bar as a baseline till I get a better setup in the car. I think the 1.25" bar is the biggest 'stock' bar thats available.

As for stagger I raced most of last season with 1.5" or less with the same problems. 2.5 to 3" is optimum for the track so again I'd like to get a better baseline setup in the car before I tweak it with stagger. BUT it is NEXT on my test night list to try less anyway.

For camber I'm at 5.7 LF and -5.5 on the FR. Caster is 3.0 LF and 3.5RF. I chase camber and pressures to get the tire temps better. Overall the numbers above are typical.

Raced most of last year with 225/175 rear springs. Tried higher and lower and all different splits. At least with the rates now I'm at full throttle drivng off in both the high and low grooves.

fighting a chronic loose middle off,

if it's stepping out , that's too much stagger...
or to little cross../ bite... if it were spinning the tires..

too much toe out can also make it loose off... a bit..

your tire temps need help.. , to average out...correctly..that's going to take more cross%

even with that much camber in the RF...
the tire is still rolling under or pushing ,by the RF temp.

..that much stagger is too much...and the last thing you should add , to get it to turn...))

more spring in the RR , will add temp. to the LF...witch you need..

your rear temps on the LR.is flat across....so it's not slipping..

from 1.5" to 3" of rear stagger is a tun of difference ,
i could see no reason it could act the same...???

is the rear end in in the car square..?

maybe it's tight in ,
and then jumping to a loose , when you go for the gas..?
because the RF is not working all that grate..!

to get a better base line ,
you need to get better tire temps first...

then make tweaks ans adjustments..

quote :>

I've tried higher cross weights but that just makes the car push bad and be loose off. Last time I accidentally went in with 59% I balded the RF in 25 laps.
< end quote:

you should have tried to find a happy spot with less Bar pre load... and a little less cross..
and with the RF.. tire showing the temps it has now... no wonder you killed it..in 25 laps...
it rolled under..on you..with more push in the RF..

inho , you never got it to a happy spot when you ran 1.5" of rear stagger..
ans 3" is just way to much stagger..one LR tire daggers , and the rr skips... and you end up with total less grip in the rear tires,...!
not to mention it very hard on the drive line.., and you end up loosing some speed on the straights... with that much stagger..

one more idea...
maybe you have a brake push... , and it just don't recover from it , tell it snaps to loose.... when you go for the gas..?

try more rear brake ,( as much as the driver can stand)...and cut some RF brake also..

and you can also try less air in the LF..,

then it will do more then just cut into the turn,

the hole car will rotate...

Try a smaller bar. Looks a little big for the front spring pkg. And the banking.
Also if the tire temps say you need more camber. You need more camber. Trust the tire temps.
Do the front suspension geo. Take the time and do it right. It will pay off in the end. Tall ball joints. Do wonders. If u can use them. Have fun race hard, trust your gut.

racer270 - Thinking you are correct in re-evaluating my stagger. It was the first thing I played with at the start of last season when the car was at its worst. Checked my tire bank and the best I can do is 2.25" for now. I have a new tire coming to me (one new tire every 2 races) and I can shoot for 1.5". It is stepping out some so going down on stagger should help.

Checked the rear end for square as best I could with strings and lasers. Looks good.

redneckracer- I have worked the front geometry with 1" taller lowers and a 1" taller RF. MC is 4" right of center and moves out to 14" right of center with dive and roll. At some point past 2" of dive it goes somewhere crazy. The metric spindles are hard to work with.

Waddaya think about going up on the front spring rates? Thinking about going up 50# for the next race. I have adjustable mounts on the uppers and could try adding antidive too.

"Have fun race hard" is whats its all about. Best advice from my wife last year was "Knock off the math and drive the damn car!" Should make a tee shirt with that one.

I ran a metric car for a lot of years. One thing I learned (at least for ym setups) was that they don't like any preload on the bar. Every time I added any preload at all the car was tight in the center. We always ran the bar neutral, period.

Just food for thought.

Quote posted by timmj:racer270 - Thinking you are correct in re-evaluating my stagger. It was the first thing I played with at the start of last season when the car was at its worst. Checked my tire bank and the best I can do is 2.25" for now. I have a new tire coming to me (one new tire every 2 races) and I can shoot for 1.5". It is stepping out some so going down on stagger should help.

Checked the rear end for square as best I could with strings and lasers. Looks good.

redneckracer- I have worked the front geometry with 1" taller lowers and a 1" taller RF. MC is 4" right of center and moves out to 14" right of center with dive and roll. At some point past 2" of dive it goes somewhere crazy. The metric spindles are hard to work with.

Waddaya think about going up on the front spring rates? Thinking about going up 50# for the next race. I have adjustable mounts on the uppers and could try adding antidive too.

"Have fun race hard" is whats its all about. Best advice from my wife last year was "Knock off the math and drive the damn car!" Should make a tee shirt with that one.


i run the same tire size on the Left and the right rear..
i make all the stagger on psi alone...!!

ie 12 to 14 psi lr.... and ~25 psi ~ in the rr...

you need to take & keep good tire temps..
racing cars is about 98% the car and 2% driver....lol
so stay up on the math..!!!

and i run my bar with ..:
so slack high and low...on the left up link..!

from 1/4" ...to 3/8"... high and low...///
this gives you the ability to adjust the car...for the middle.....and with slack... the bar loads slower ,
but unloads harder....
sending more weight to the left front..,
then a pre loaded , or neutral set bar could..
this will allow you to hit a very low and late apex..!!
& drive it were they ain't...

i was looking at you caster #
FR. Caster is 3.0 LF and 3.5RF. I chase camber and pressures to get the tire temps better. Overall the numbers above are typical.
not much of a split. try 1.5 lf and 5.5 rf for a 4 deg split. you will notice that the car almost enters the corner by its self. should help in the middle of the corner.

I dont have any end links on my sway bar. Its bolted on the right and has a slapper on the left. Are you saying the mounting angle of the bar has an effect on the loading and unloading?

I have not played with caster much at all. I was running around 2 degrees split and reduced it down to 0.5 on advice from another racer. I pitted next to the multiple time track champion last year and was able to glean bits of information from him and his crew after the races once they got liquered up.
He ran no caster split and claimed the car was smoother in transition out of the turn that way. One of those drivers that ran the same qualifying time every week no mater how hot and slick the track was.

In regards to caster I've been scratching my head about how my upper A-arm mounts are installed. The right upper mount is parralel to the lower which is toe'd in on a metric. So the right front has no caster change in dive. The left upper mount is toe'd out (parallel with the upper right mount) while the lower is toe'd in (stock position). So the left front is gaining caster in dive. So I've got some dymanic wedge thing going on.

Pre-race I made some improvements to bumpsteer, reset caster to 0.75 right and 3.6 left, increased RF camber to 5.6, decreased rear %, and decreased rear stagger to 2.25". Caster and camber in the RF are maxed out to keep the Arm from hitting the shock.

Pre and post race weights 56% cross, 57.6% left, and 46.6% rear

Feature tire temps (25 laps no cautions)

LF 179 174 156 RF 203 206 213
LR 154 172 169 RR 140 195 200

Car was best its been for 5 or 6 laps then pushing and plowing the RF. I was convinced a spring settled or something and jacked up the cross. I was suprised the post race % was the same as the garage.

The car was much improved with the caster changes going in and coming out of the turns. Way easier to hold a line. Still a little loose off but better.

Still need a solution to tighen the car with less crossweight.

Bump stop the left rear, you can run lower cross and as soon as you get to the throttle theres your cross.

Quote posted by timmj:Pre-race I made some improvements to bumpsteer, reset caster to 0.75 right and 3.6 left, increased RF camber to 5.6, decreased rear %, and decreased rear stagger to 2.25". Caster and camber in the RF are maxed out to keep the Arm from hitting the shock.

Pre and post race weights 56% cross, 57.6% left, and 46.6% rear

Feature tire temps (25 laps no cautions)

LF 179 174 156 RF 203 206 213
LR 154 172 169 RR 140 195 200

Car was best its been for 5 or 6 laps then pushing and plowing the RF. I was convinced a spring settled or something and jacked up the cross. I was suprised the post race % was the same as the garage.

The car was much improved with the caster changes going in and coming out of the turns. Way easier to hold a line. Still a little loose off but better.

Still need a solution to tighen the car with less crossweight.



Should that read "reset caster to .75 left and 3.6 right?"

Quote posted by crewchief99:Quote posted by timmj:Pre-race I made some improvements to bumpsteer, reset caster to 0.75 right and 3.6 left, increased RF camber to 5.6, decreased rear %, and decreased rear stagger to 2.25". Caster and camber in the RF are maxed out to keep the Arm from hitting the shock.

Pre and post race weights 56% cross, 57.6% left, and 46.6% rear

Feature tire temps (25 laps no cautions)

LF 179 174 156 RF 203 206 213
LR 154 172 169 RR 140 195 200

Car was best its been for 5 or 6 laps then pushing and plowing the RF. I was convinced a spring settled or something and jacked up the cross. I was surprised the post race % was the same as the garage.

The car was much improved with the caster changes going in and coming out of the turns. Way easier to hold a line. Still a little loose off but better.

Still need a solution to tighten the car with less cross weight.



Should that read "reset caster to .75 left and 3.6 right?"


your still to high on cross%
the first 5 or 6 laps were good tell the psi & temps came up...

it's pushing , in the middle because of to much cross ,
and too much sway bar..

it's pushing / then it's snapping loose

because you got to much rear stagger..,it will step out , no matter how much cross you add also..

your tire temps show to much air in both rear tires..& the LF...!

you need to pay attention to your tire temps..and drop the cross..& use less sway bar..
and less stagger..
as has been suggested..,
you can then bump stop the LR...for the bite you need coming off...

Typed in the caster wrong it is 0.75 left and 3.6 right.

I bumped up the rear pressures based on practice tire temps. I need to anticipate the higher pressures for the features. Didn't get heat race temps since I won it and opted for the photo and then scales.

Cross will go down. Stagger will go down. Practice is next. Thinking hard about the bump stop suggestion. Is a bump stop common for this type of car or is it more radical??

Any adjustment I can make with front springs instead of trying a smaller bar??

yes. try 850 lf 800 rf. try toset it back at the same weights and heights. run the bar neutral. not slack set it with you in the car. less camber lf more camber rf. is the rear locked or open. if locked more stagger. if open it don't matter just get ride heigt correct.

rember a bigger type bar works faster and harder. adding rate to rf. if looking at doing bumps. there are lots of post on here that talk about them. but most of it is for latemodels. if you try it. and it don't work atleast you tried it.

SO, went up on the RF spring and down to 1.5" stagger and got these caution filled feature tire temps:
LF 850# RF 900#
170 140 134 172 170 170

LR 175# RR 125#
132 135 135 152 162 156

Yes the RR has too much air. New tire mis-behaving. Front average higher than rear average.

SO, for practice I lowered both front springs and got:
LF 800# RF 850#
157 146 140 179 173 177

LR 175# RR 125#
153 154 154 183 181 178

Averages looking good but still spinning the tires off at 55% cross limit. Would lowering the front spring rates allow me to run more cross without pushing 10 laps in?

Took a video of my LR shock (old 8mm camera and gaffers tape) to investigate bump stop potential and found there was no squat to speak of in acceleration. The 50# spring split ain't gonna let it go down. Just can't get anything on the darn LR!

you need more camber / caster , in the RF...asap..!
you won't to see 10^+ across that tire..
btw- the RF needs some air ,,,like 1 psi... the average is 176*
and it's rolling under ..a tad..!

that should stop the push ,... the contact patch is not working as good as it could be,,!


drop the LF spring to a 650lb

try 1/2psi less in both rear tires..

if your still not , getting down travel in the LR
try the 900 lb in the RF again...
that will add heat to the LR , and keep it off the RF....

you don't need more cross% , you need more weight on the LR

My old metric had a 700 r/f and a 800 l/f on a flat 1/4 mile. 51% cross and 225 across the rear with a lowered 4 link rollcenter. If you want the car to turn the same and get more bite at throttle then put a bumpstop in and fill the shaft with shims till it starts to push.

you'll notice that the push will get worse as you keep going down on front spring rates. it's not setup, it's geometry.

Quote posted by boas51:you'll notice that the push will get worse as you keep going down on front spring rates. it's not setup, it's geometry. Very true, If your bumpsteer is not correct and you are trying to run to low of a chassis height on a metric it will not behave well.