PDA

View Full Version : Right rear bouncing



citiracer
07-12-2010, 12:09 PM
During our heat race this weekend our right rear was bouncing pretty severely coming off of turn 4. The car handled pretty well in 1 and 2 (a little loose off) and then I was having trouble getting into 3 (car wouldn't turn) and then in 4 it would just bounce something crazy on the right rear.
Based on the travel indicator, the shock did not bottom out and it didn't compress the spring enough to coil bind it. This was on a 225 RR spring.
All we did for the feature was tilt the car (6 turns in LR, 4 turns in LF, and 2turns out of RF) and add a little bite (2 more turns in LR). In the feature the car was good other than a bit free on entry.
Any idea what might have been causing this horrendous bouncing? The track was a bit rough but nobody else was bouncing like we were off of turn 4.

JJRT
07-12-2010, 12:39 PM
did you check your shock on a dyno

redfred
07-12-2010, 01:37 PM
Is the shock hanging up on the spring? check for marks on the shock. also check that the rear is not hanging up in the rear. Air pressure in the tire?

GRTLRBITE
07-12-2010, 03:19 PM
Add More Rebound In Rr. Maybe

citiracer
07-12-2010, 06:42 PM
Thanks for the replies. We run an Afco non-adjustable twin-tube on the RR. John Schulte does our shocks and valved them for our car/track. He does a great job and helps us at the track but he wasn't there last weekend. Last time he had the RR was five races ago and we haven't had any problem with it. The spring rolls straight and doesn't show any signs of buckling or catching the shock body. We run 8psi in our RR tire. It just did it this one heat race.
Here is what I THINK might have been happening: We didn't have enough "tilt" in the car and with it pushing on entry, once I finally got it around it was slamming over on the RR. Once we got the car tilted and freed up on entry, the problem went away. But I was just wondering what else might be going on. Even when we're not fast our car usually "looks" pretty good. But the bouncing was so bad my crew guys were looking for bent/broken parts after that heat race. It was strange. Like I said, the track was a little rough and maybe I was just hitting the one rut the wrong way that everybody else was missing. Who know :-)

redfred
07-12-2010, 10:08 PM
8lbs in the rr on a ruff track is a little low. It's to easy to roll that tire off the bead on a ruff track. You might want to bump that up to about 10lbs if it's ruff. Also depending on brand, the sidewalls might be a little to soft. McCreary are know to have very soft walls and don't handle ruff tracks well.

redfred
07-12-2010, 10:09 PM
Sorry meant American Racers. Old school here.

valken88
07-13-2010, 12:24 PM
You can run under 7lbs tire pressure because of our taller safety bead.

F22 RAPTOR
07-13-2010, 02:24 PM
During our heat race this weekend our right rear was bouncing pretty severely coming off of turn 4. The car handled pretty well in 1 and 2 (a little loose off) and then I was having trouble getting into 3 (car wouldn't turn) and then in 4 it would just bounce something crazy on the right rear.
Based on the travel indicator, the shock did not bottom out and it didn't compress the spring enough to coil bind it. This was on a 225 RR spring.
All we did for the feature was tilt the car (6 turns in LR, 4 turns in LF, and 2turns out of RF) and add a little bite (2 more turns in LR). In the feature the car was good other than a bit free on entry.
Any idea what might have been causing this horrendous bouncing? The track was a bit rough but nobody else was bouncing like we were off of turn 4.This has all the earmarks of a dampening issue in the RR. Either the shock is too soft on compression or too weak on rebound or both. You could have had something fail in the shock. Since its a dual tube it could be a busted bag, which would release gas into the oil and make dead spots in the dampening. I'm not knocking your shocks or even the guy that built them, but bags can fail and so can other parts. I built shocks for 6 years at Carrera and things can go wrong with anybody. Also, hand stroking the shock won't necessarily tell you anything, a dyno and an internal inspection are the only sure fire way to know whats going on.

CrumpRacing
07-13-2010, 03:36 PM
This has all the earmarks of a dampening issue in the RR. Either the shock is too soft on compression or too weak on rebound or both. You could have had something fail in the shock. Since its a dual tube it could be a busted bag, which would release gas into the oil and make dead spots in the dampening. I'm not knocking your shocks or even the guy that built them, but bags can fail and so can other parts. I built shocks for 6 years at Carrera and things can go wrong with anybody. Also, hand stroking the shock won't necessarily tell you anything, a dyno and an internal inspection are the only sure fire way to know whats going on.

I agree sounds like a shock issue to me. JMO

Crump

MasterSbilt_Racer
07-13-2010, 04:03 PM
I agree with the last few posters. Unless you have something goofy like a spring loaded droop limiter on the RR, it is most likely a shock problem.

BLAHBLAH
07-13-2010, 04:49 PM
did the wheel get packed with mud by any chance?

citiracer
07-14-2010, 06:56 AM
Thanks for all the replies. If we have the problem again, I'll get the shock on a dyno for sure.
The wheel didn't get packed with mud (to my knowledge). We run a metal wheel cover on both right sides.
The air pressure thing has me wondering. We have pretty much left air pressure alone as we are new to this and trying to keep the variables limited. We've been running LF8 RF10 LR6 RR8. I think we're going to try starting the night LF10 RF12 LR6 RR10 when the track is tacky/rough and then start dropping pressure down to our original numbers as the track slicks/smooths.
We spent a long time in the shop last night "gameplanning". We think our biggest problem is we seem to get hung up on ONE adjustment at the track and OVER focus on that (lately it's been bite/jacking the LR). There's a lot more on these cars that we can do and we know it. But we're also trying to keep it simple for a driver that has only been in a late model 5 times.
We're going to be a crate running with supers this weekend so nothing to lose. We're gonna take some bigger swings at the setup changes I think. At this point we feel that's the only way we're going to learn. We know what the adjustments DO, but we don't know HOW MUCH and how that's going to feel to the driver. That's what we're working on now.

DLM06
07-14-2010, 05:05 PM
If you are totally up on the bars then you could be bouncing on the tires. They act like a spring but with no shock to control them.

F22 RAPTOR
07-16-2010, 05:40 PM
If you are totally up on the bars then you could be bouncing on the tires. They act like a spring but with no shock to control them.

I doubt he's up on the bars on the RR, but I've been wrong before....

Graff Spee
07-17-2010, 05:30 PM
Simple, shock it up!!!