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View Full Version : car plow into corner front roll center issue? or something else?



cgs
06-15-2012, 11:23 PM
so im at wits end here. the track is hooked up, let off the gas get on the brake and the car wants to push to the wall, the harder you push the brakes the more it wants to push. i have to throw the car in extremely hard ro get it to rotate. when the track dries out it still wants to push into the corner but not as bad. here is my set up and what ive done and tried to do :

03 bms metric clip nova lowers pinto spindles
lf 700 93 shock
rf 950 95 shock all bilstien gas shocks
lr 325 swing arm (217 corrected and on the arm) 94
rr 175 2link in front shock on rear
48 cross
52.5 left
56 rear
1in of rr trail
wheel weights: 576lf 480rf
690 674
i'm running out of ideas on what to do. I've run an 850 rf spring with 100 lr bite ive gone down from 200rr spring to 175, tried a 2off rr, moved the rear end over 1in, tried left side weight at 53.5, 1in of rr trail, lowered frame j bar/raised pinion, no rf brake. found rear master cylinder to be a 1in, changed it to a 7/8. i have gauges on the brakes and i can get 800lbs on the rear and 100 lbs on the front brakes. found the brake biass slide adjust too tight. adjusted it to willwoods specs. thoght it was a carb problem changed that. i was running mechanical advance in the distributor ( very easy to start) so i thought the weights were hanging up so i locked it out. i do run cheapo pads so im going to by some good ones this week. car rolls over about 2-3 inches on the right side. this car hikes up also. tried a heavy compression shock on lr. anybody have a clue what im missing? would front roll center be off? is the rf wheel weight too light causing the the rf to not get grip?
the reason im running a 2link/swing arm is because my track gets awefully rough. like moto cross rough.

jsf74
06-16-2012, 01:37 AM
I'm no pro but does anyone else think those front springs are way too stiff?

26-62 racing
06-16-2012, 01:46 AM
Just a thought, and you sound very frustrated from working your tail off to fix the problem. But with that much rear weight and the right rear tailing 1''. Is the rear end driving the car,and the front tires cannot over come the rear push to turn the car? And with the right side trailing the rear end is pointed to the wall , also driving the car to the wall. Hope this helps.

Mike
26B owner driver

cavemod
06-16-2012, 12:36 PM
I ran a 2link clamped on left z swing arm on the rr a couple years ago and had pretty much the same thing when I started with it.this is what i suggest which some may say is wrong but it helped a ton.change the rf spring to a 750 (950 way to stiff w nova lowers)on the rear go to a 225 spring on the lr(when on the bars the car is just sitting on the spring and doesn't know what spring it has) make sure bite is around 75lbs or less.when i drove the car i had to make sure to be off the brakes by the apex of the corner or it pushed like a dump truck be on the gas to get the car to turn also trail the rr 1/4".you never mentioned how much split you got in your j bar.another thing is try and get front wheel split under 125#.This may sound whacked out but it may a ton of difference in my car i shaved a full second off my lap times.Remember don't touch the brakes in the corner or it will push.Caster is+2 lf and +5 on the rf more is better.I got this info from a guy who ran this setup on a usmts car back in 05 and finished 2nd in rookie points.

cgs
06-16-2012, 03:08 PM
I can try running lower rear weight.. Haven't tried that yet

cgs
06-16-2012, 05:42 PM
My car is bent mind you, lf rr 6.25
Rf and lr 7. It sound like you are saying to get the car up quicker on the lr bar which is on the gas. Once the car is rotated it's a rocket ship. Just won a dry slick race last weekend.it being tight isn't too bad when it's dry. Off the gas and on the brakes is where it pushes to the wall

powerslide
06-16-2012, 11:12 PM
I think u mentioned it but did u make sure your balance bar isn't binding up int the pedal?

cgs
06-16-2012, 11:23 PM
Powerslide-
That was what I found. When I bought the car the two yokes for masters were up tight to the pedal and the bearing wouldn't slide back and forth. And made sure that the bar didn't contact the peddle housing when the brakes were applied.

cgs
06-16-2012, 11:31 PM
Pieman- hey something you said about cheap pads hit me. That is exactly what happens. The car rotates good the first two or three laps then it goes to hell. I'll try some good pads and see what happens. What pads do you recommend ? Hawk 30's ok?

powerslide
06-17-2012, 01:16 PM
Something else. Is the car picking up a lot of weight from the tacky track causing the change in handling?

cgs
06-17-2012, 03:26 PM
Powerslide-
As in what? Mud?
You're right more towards the back and right side. I think I will bring a scale and record what is added on back and side. Good thought powerslide

powerslide
06-18-2012, 02:05 PM
Powerslide-
As in what? Mud?
You're right more towards the back and right side. I think I will bring a scale and record what is added on back and side. Good thought powerslide

Exactly mud. Some of the late model teams have put a tarp like material under the deck on the lr and RR

cgs
06-18-2012, 04:13 PM
Will pull bar length or angle have any affect at entry off the throttle?

Flyin Iowan
06-18-2012, 09:56 PM
Have you checked your calipers? is the RF sticking? does the LF work? Also check to see if the RF lower a-frame is hitting the rotor.

cgs
06-18-2012, 11:20 PM
I disconnected the right front caliper. It was a little better at entry but still not rotating like I want. The left front locks up in the gravel when driving on my property so I'm assuming it works. I will check to see if the rotor is hitting the a frame. Thanks

Sportmod Rookie
06-19-2012, 07:45 AM
Just a thought, and you sound very frustrated from working your tail off to fix the problem. But with that much rear weight and the right rear tailing 1''. Is the rear end driving the car,and the front tires cannot over come the rear push to turn the car? And with the right side trailing the rear end is pointed to the wall , also driving the car to the wall. Hope this helps.

Mike
26B owner driver


I believe this guy has the correct answer. I had a bunch of RR trail in my car cuz i was having the same problem. I was explaining my problem to a local guy with a lot of experience and he told me to take it to a 1/2" of trail. Thought he was crazy and it was going to make it worse because i always heard trail the RR to make it loose. Trust me.... made it 100 times better. Its just like the guy above was saying. If you take it out it will allow your rear end to slide and not just blast you into the wall like a rocket ship. Try it in hot laps or heat race. If you dont like it you can easily change it back.

cgs
06-19-2012, 10:24 AM
Thanks. I actually just took a half inch out before I posted anything about my problem. Just waiting to go racing again to try. Had to go party in Vegas:)

cgs
06-19-2012, 03:14 PM
Also my j bar is center with 9'' pinion and 4 inch of split.

cgs
06-20-2012, 10:03 PM
Just curious, how is everyones rear end centered? The reason I ask is the driveshaft is straight in the car but looking down both rotors to stock frame rails the rr rotor is inset a couple of inches and the lr is just outside or so. I don't know what is correct because my car is an abomination that is no longer what BMS built in 2003.

Sportmod Rookie
06-21-2012, 12:46 PM
Call BMS and talk to Brandon. He should be able to help you.

outacontrol
06-21-2012, 10:32 PM
Stiffen that RR, it will rotate much better on the gas.

cgs
06-21-2012, 11:16 PM
im having a tight problem into the corner off the gas . the track i run on is 3/8 fair amount of banking heavy adobe mud. full throttle down the staight away, right before the corner off the gas, get the car rotated and smash the pedal through the fire wall all the way around the corner from the start of the corner to the end of the corner and down the straight away.

so what kind of track/ track conditions do you use the "on throttle into the corner "type of driving style?

Sportmod Rookie
06-26-2012, 08:08 AM
so.....im curious. did it work better?

cgs
06-26-2012, 02:23 PM
sportmod rookie-

i havent been able to try anything yet. this week was the fair. i will let everyone know what happens on sunday:) i'm going to put good pads on the rear , run a 4off on lr and 2 off on rr and take a percent out of rear weight and see what happens. not all at the same time tho. hopefully the track will give me some practice laps between heats and main...

autoshop
06-28-2012, 11:09 AM
petaluma speedway?

I would try even springs in front.800's
flatten out the lr bar angle.
try a 225 in front on rr
53.5 ls weight
56% rear
48.5 cross
1/2" trail in RR

should get you in the ball park.
If still too tight raise the rr bar up

heats and mains are differant setups if at petaluma, track is so close to water table that it affects setups. What works good in heat may not even be close for main. running the even springs in front helps when the track changes during the race. car stays more constant.

dualdj1
06-29-2012, 11:58 AM
950 was the RF Autoshop.

That RF weight seems real low, and it's hurting your cross. if you can take some rear out that should help, but try getting your fronts a little closer. if the frame is bent, it's gonna mess up your ride heights and geometry a bit, unless you can move ballast around, but it should still help. Think it's just too much rear %, if you can get it down to 54 you'll see a huge difference. try leaving it lower on fuel, if you're still ok on weight.

cgs
06-29-2012, 02:34 PM
autoshop-
ya its petaluma. lately its been dry wich is awesome cause i love dry slicks!! we will see what happens this week now that the flat track motor cycles are out of the way.just curious why i would want to put a havier spring in the right rear? that will tighten up entry off the throttle right? i have had a heavier spring in rr (200) wich made it tighter from what i recall.

dualdj1-
i thought the front was a little light on the rf too. the only way i can get that back is by upping cross weight. so maybe a lighter rf spring to counteract the up in cross wieght to get the front weights more even???
this weekend im going to lower rear weight by taking fuel out and moving battery forward and adding more left side weight by sucking in lr and moving rr out an inch. i will keep everyone posted

autoshop
07-02-2012, 10:50 AM
stiffing the rr will help it rotate on the gas,
adjust springs for entry
panhard bar for middle
bar angle for exit

the reason I suggest even springs in front is the weight comes back not favoring either side when it comes back.
With the 950 rf when the weight loads the rf, on excell the weight goes straight back to the rr with a softer rr the spring takes longer to react so the lr drives harder than the rr
the rr spring in front is a freer setup , for a dry slick moving the rr spring to the rear will add a lot of drive off but may make the middle too tight.
in times past petaluma never got dry unless it was a playday,

pay close attention to the tide tables when it's wet. In what order your main event runs will make your adjustment.

The tide going out when wet makes for a drier track earlier in the night but if the tide starts coming back in at 8-30 to 9 the track will hold the moister.

Don't let the tides trip you up like it does most teams running there for the first times

a 6 shock on the lf
6 or 7 on rf if tacky
4 shock lr wet
7-2 shock lr dry
4 shock wet rr
3 shock dry rr

dualdj1
07-02-2012, 11:52 AM
dualdj1-
i thought the front was a little light on the rf too. the only way i can get that back is by upping cross weight. so maybe a lighter rf spring to counteract the up in cross wieght to get the front weights more even???
this weekend im going to lower rear weight by taking fuel out and moving battery forward and adding more left side weight by sucking in lr and moving rr out an inch. i will keep everyone posted

More cross and less rear will help. and think Autoshop has some good suggestions for you as well. Not sure what else you could do to even weights besides just adding lead, if you don't have any balast you can move. Maybe moving the battery around will help.

cgs
07-02-2012, 02:37 PM
alright everyone, time to post about what happened :)

so i went ahead and lowered rear weight to 55%
sucked in lr and moved rr out 1in
put on some good pads on rears
and lower my front springs to 700lf and 800rf

much looser on turn entry!!! very happy with turn entry now. was leading the main for 7 or 8 laps till i jumped the cusion :( ended up 2nd after jumping the cusion for a second time and passing back the two cars that passed me in the last turn of the last lap.

now what i did notice is that the right side frame rail is digging into the ground when going into turn one. rf shock travel indacator was at 4+ inches. so im going to put in an 850 right front spring for now. going to hanford this weekend for a two day show.
thanks you every one for your help.

dualdj1
07-03-2012, 09:39 AM
why not try going back to your 950, and see what difference it makes? Maybe it won't be too much, with the way your car is. And if it is, then you know that's the change that made the difference for you, and can adjust accordingly.

autoshop
07-03-2012, 11:26 AM
Chris:

I ran 5.14 at hanford 5.43/5.67 at Petaluma to give you a idea the differance in length's of the track.

Hanford slicks off and takes rubber on most two day shows if the second one is during the day.

if both are at night could be heavy both nights.Hanford's a fun track to run ,big banks no crash walls except the front straightaway.

if it slicks off you may want to drop the rr bar down in front so the rr sucks forward in the corners or move the rr spring to the rear of the housing.

Good luck........