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Author Topic:   rolling over
modracer15
Dirt Roller

Total posts: 14
posted May 05, 2004 10:16 PM  
I have a '02 harris asphalt car that I switched over to dirt this season, and I am having a terrible time getting it to hook up, or even roll over at all. I am running the long panhard bar behind the rear end at about 7 degrees down. 250# spring on the left rear, 175 on the RR, 750# on the left front and 650# on the RF. 58% rear and 52% cross. The track I am racing at is very fast and stays tacky all night. The guys are just blowing me away. The front guys are all picking their LF up 10-12" at least. I dont know if this asphalt car will do that with the motor shifted to the left, but I have to do something. Thanks.

zeroracing
Dirt Forum Champ
Total posts: 1875
posted May 05, 2004 10:30 PM  
your number 1 problem is the panhard bar. take it off and put on a short bar on the front. goes from left side of pinoin to left side of frame. and put about 4 inches of rake in it and it will roll alot more.
also what rear suspension are you running.

modracer15
Dirt Roller

Total posts: 14
posted May 05, 2004 10:34 PM  
we have thought about doing that, that is what everyone is running here. They sent us a mount for the chassis, but im not sure where to mount it, there is not square tubing on that left side like a dirt car has. should i just weld one in there?

modracer15
Dirt Roller

Total posts: 14
posted May 05, 2004 10:35 PM  
It is a 3 link.

mdsteacher
Dirt Maniac

Total posts: 145
posted May 05, 2004 10:54 PM  
I also have the same problem, except my chassis is a much older Harris combo chassis that I run on dirt. It has almost no roll as well. It is a 3-link with panhard behind rear end. I thought about putting a panhard clamp mount on a roll bar (no square tubing either) and attach to the left side of the rearend with one of those panhard/pinion mounts for Ford 9-inch. Then put in a short bar and remove the one behind the rear.
Is there any other considerations here? I have an old chain mounted torque arm.
Zero, you've helped me in the past with this same car, but I never had the time to change to a new panhard location because I'm not 100% confident I'll do the right thing.

[This message has been edited by mdsteacher (edited May 05, 2004).]

zeroracing
Dirt Forum Champ
Total posts: 1875
posted May 05, 2004 11:27 PM  
pm me your email, and i will take some pics of mine on the car so you can see it good.

mod70
unregistered Total posts: 1875
posted May 05, 2004 11:37 PM           send a private message to zeroracing   Edit/Delete Message   Reply w/QuoteBBBBBB
15, you are going to want to weld in some square tubing for a short bar mount. You're lookin' at alot of stress on that piece. As a quick fix, however, try putting more angle in the pan bar. I'd go upwards of 15 deg. to really get it to roll over on the RR to plant it. Don't worry about how high you pick up the LF. Most of those guys doing that are running some type of 4 link or verriation. Worry about how she handles more than runnin' like a 3 legged dog. You should swap the front springs too. The stiffer LF is going to want to loosen you up. %'s sound about right. Good luck man.

mod70
unregistered Total posts: 1875
posted May 05, 2004 11:42 PM           send a private message to zeroracing   Edit/Delete Message   Reply w/QuoteBBBBBB
As for mdsteacher's idea, don't know if thats such a good idea. Like I told 15, you're looking a alot of stress there. I've got square tubing on mine, and bent the h*ll out of it last year. It's alot less work to replace that than rollbar tubing. I'd hate to see you bend a critical bar like that! What you think Z?

modracer15
Dirt Roller

Total posts: 14
posted May 06, 2004 12:40 AM  
mod70, can you explain to me how the geometry works on the suspension when the car goes through the corner, it doesnt make a whole lot of sense to me. Thanks.

CUSTOMPERFORMANCE
Dirt Forum Champ
Total posts: 1172
posted May 06, 2004 03:40 AM  
What is being run for the toplink/third link ? solid bar spring bar or biscuit bar? Aslo i would run a lighter lr spring closer to 200 lbs everything else looks pretty good.

NJantz
Dirt Forum Champ
Total posts: 755
posted May 06, 2004 05:56 AM  
Howe makes a panhard bar mount that slips over a 1.75 od DOM round tube. Very strong piece and only two bolts hold it on. http://www.howeracing.com/Suspension/Index-PanhardMounts-CastClamp.htm

I just switched to this style over the winter and installed a .125 wall tube for a frame post.

[This message has been edited by NJantz (edited May 06, 2004).]

[This message has been edited by NJantz (edited May 06, 2004).]

zeroracing
Dirt Forum Champ
Total posts: 1875
posted May 06, 2004 06:53 AM  
i use 1.5 inch od tubing and dont have any problems at all. .120 wall thickness.
"The stiffer LF is going to want to loosen you up" the stiffer lf will tighten up on entry only and not effect exit.
as far as the mount i would recomend using a good square tube or dom tubing.
as far as geometry, i am not sure what your talking about, i mean how the panhard bar effects it or just the whole rearend in gerneral.
as the car hikes up it will pull the rearend to the left. you will notice tire rubing the frame when you get the car really hiked up.
mod70 is right, dont worry about how highthe front tire is off the ground, go by feel for set up.
what angles are you running in your bars?
good luck
jason
and if your in doubt about its strength then beef it up on the panhard mount.
also the first place you will bend it is on the pinoin, they are very week. all of them are, i was talking with the afco owner and they just take so much abuse they bend easy.
goodluck

02racing
Dirt Full Roller

Total posts: 54
posted May 06, 2004 07:10 AM  

 
This is how we did our short bar and we run 4 inches of rake like zero said. I like it alot more than my long bar. It help the car roll over a ton.

modracer15
Dirt Roller

Total posts: 14
posted May 06, 2004 07:12 AM  
Thanks for all of the help and ideas, Ill give it a try and let you know how it turns out.

modracer15
Dirt Roller

Total posts: 14
posted May 06, 2004 07:15 AM  
one more question, its kinda dumb, but what do you mean when you say "rake"?

02racing
Dirt Full Roller

Total posts: 54
posted May 06, 2004 07:19 AM  
If you put it in the second hole up on the pinion side and it measures 10 inches from ground to center of heim then put chassis side at 14 inches from ground to center of heim and you have 4 inches of rake or angle to the pinion

modracer15
Dirt Roller

Total posts: 14
posted May 06, 2004 07:23 AM  
that makes sense, thanks

mod70
unregistered Total posts: 14
posted May 06, 2004 10:25 AM           send a private message to modracer15   Edit/Delete Message   Reply w/QuoteBBBBBB
Wow 15, you just asked the mother of all questions! I'll give it a shot, but this might take a while. First let's try to visulize (spelling?) how corrner weights affect the car through the turn. Draw an 'X' and imagine looking down on the car from above, the top of the 'X' being the front of the car. As the car turns left, if most of the weight is supported by the RF & LR you can see the line points toward the outside of the turn. The car will want to follow that line and push, or be tight. If, instead, more weight is supported by the LF & RR, it's pointed toward the inside of the turn, and will be loose. That's a pretty simplistic view of it, because of the dynamic nature of weight transfer in a race car, but it's a good place to start. As you dive the front end down in braking, the corner which is stiffer will hold more weight. When you turn, the weight will transfer to the right, and as you accelerate, it will move toward the rear, eventually ending up mostly (but not completely) on the rears, once again on the stiffer corner.
As far as what is happening with the movement of the rear end durring cornering, as the weight transfers to the right, the RR will move up in relation to the frame, and the LR falls down. As the control arm on the RR moves toward horizontal, it will push the RR toward the back of the car, and pull it forward as it goes past horizontal. The LR control arm will swing down at the wheel, and pull the LR forward, thus giving you 'rear steer' and cocking the rear end to the right. This is usually prefered on a dirt track, as it helps the rear to pivot around the corner.
Now for the pan/J/short bar. I don't like to think of it as moving the rear end, so much as moving the chassis around the rear end. As the weight of the chassis is applied to the bar, and as the LR falls away durring cornering, the angle of the bar determines how that weight rotates around the rear end. More angle will try to throw the chassis over the rear end, placing more wieght on top of the RR, where less angle will try to shove the rear end out, placing more side force on the RR. I know it's alot of info to soak up, and I'm shure I'm missing some things, but that's the best I can 'splain it without using my hands! Hope this helps you to get a grasp on what's happening back there. You might look into geting a subscription to "Circle Track Mag." It's the best mag. out there when it comes to explaining suspentions, as well as alot of other info. I'm shure if you do a search for it they've got a website.
As for zero's note that the stiffer LF will want to tighten on entry, I'm not shure about that. The stiffer LF should wand to de-wedge, or remove cross weight from the car, but I'm not saying that I'm any kind of genius about this. It will affect entry more than exit for shure, but I really think it would cause the car to be looser rather than tighter. Hey Z, maybe you know something I don't. After all, I'm still learning too.

CUSTOMPERFORMANCE
Dirt Forum Champ
Total posts: 1172
posted May 06, 2004 11:32 AM  
What ride heigths are you running? I know the asphalt and dirt ride heigths are different, dirt is about 1 1/2 -2 " higher than asphalt.

NJantz
Dirt Forum Champ
Total posts: 755
posted May 06, 2004 01:04 PM  
02RACING- I like your adjustable mounts for your suspension linkage instead of the traditional holes in brackets method of mounting! Did you build that or did the chassis builder? What kind of chassis is that? thanks

[This message has been edited by NJantz (edited May 06, 2004).]

02racing
Dirt Full Roller

Total posts: 54
posted May 06, 2004 03:43 PM  
NJANTZ we built that we made them on the mill we did it like that so we could make smaller adjustments. The car is a local built car or was it is a 94 frickey but this winter we restubed it and went with nova lowers and pinto spindles and from three link to z-link. Plus we lenghtened the wheel base.

modracer15
Dirt Roller

Total posts: 14
posted May 06, 2004 09:23 PM  
thanks mod70, that really helps on understanding more how the suspension works. I think we figured something else that might be throwing us off, our upper a-frame on the left side is quite a bit longer than the right side, and Harris said that was probaly throwing our front roll center off quite a bit.

zeroracing
Dirt Forum Champ
Total posts: 1875
posted May 13, 2004 05:41 AM  
"As for zero's note that the stiffer LF will want to tighten on entry, I'm not shure about that. The stiffer LF should wand to de-wedge, or remove cross weight from the car, but I'm not saying that I'm any kind of genius about this. It will affect entry more than exit for shure, but I really think it would cause the car to be looser rather than tighter. Hey Z, maybe you know something I don't. After all, I'm still learning too."

it will tighten entry because it will take wedge out of the car on entry, which means it will plant the rr compared to the lr so when you get on the brakes, you will be outstopping with the rr tire, comparied to the lr. so this will help to tighten up the car on entry.

the mroe wedge you run the looser the entry and the tighter the exit.

with wedge your loading the lr tire. when you do this and get on the brakes, it will outstop with the lr comparied to the rr so the car will be loose, and when you get on the gas the lr will outbite the rr so it will be tight.
thats why i raise the lf spring to tighten up entry. it makes the car have less wedge on the brakes.


also a change in the lf spring will not effect exit AT ALL. only springs that recieve the wieght will effect that part of the corner. so that means the right side springs effect both entry and exit, and the lr effects only exit.
yes i know about unloading, but where the weight goes when the spring begins to unload is determined by the recieving springs. so on entry if you unload the lr and the weight all goes into the rf then you hold your cross. the weight can not go in thin air, so your recieving springs are the only ones that make the difference on that part of the corner.

[This message has been edited by zeroracing (edited May 13, 2004).]

zeroracing
Dirt Forum Champ
Total posts: 1875
posted May 13, 2004 05:51 AM  
also when you talk to somebody about rake, they are meaning the hieght difference between the frame mount and the pinoin.

modracer15
Dirt Roller

Total posts: 14
posted May 13, 2004 08:15 PM  
I am running one of harris' new pull bars with the spring that you can adjust. Where should I run that spring? and what affect does the pull bar have in general?

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