Post by otiscampbell on Apr 4, 2013 18:41:17 GMT -6
I've set up modifieds, mostly, in my 7 years of working on race cars. (Prior to mods, we raced karts.) Now, we are running a division of cars that are older asphalt late models with a perimeter chassis--our car has both truck arm and 3-link mounts. On dirt, we are running a 3-link with a J-Bar and a pull-bar and considering I didn't do much but square the rear and scale the car, it didn't handle too bad last season.
Now that we are in the final stretch before our first race, I want to get a good baseline setup down and one of the things about this car that bugged me was the J-Bar--or the fact that I didn't have a starting measurement for a baseline like the modified had.
My question for all of you setup experts is actually 2:
1. What is the best way to determine the J-Bar angle if all you have is one of those cheap angle finders? 2. What is a good starting point for the J-Bar angle? And as a follow-up, where should I start on the pinion side of the bar?
My thought is to figure out a starting angle and then determine where that is on the chassis side and then move it up and down to get different angles and take measurements so I can make changes at the track, if needed.
The track is a 1/2-mile clay. One turn is a little tighter than the other... My driver drove (and was most-comfortable) in modifieds so he would rather have the car a little more free than tight.
The easy way is to measure the hieght differences between the heims om the j-bar. Not sure where to start but I would say around 6 to 6-1/2 inches of rake. The frame mount should be higher than the pinion mount. Start with the pinion side at the centerline of the pinion, based on a nine inch rearend.
The weight, track width, tires, and track surface will all play into the set-up.
Post by otiscampbell on Apr 5, 2013 6:10:33 GMT -6
Thanks for the reply. I was going to post everything else about this car in a different thread because, like I said, I'm looking for some help on a good starting base-line.
Right now, the car weighs approx 3050# with driver (3000# minimum). I will likely take it up to 3100-3150# because when we hit the scales after the last race last year with 1/2 of a cell of fuel, we were at 3002#...which is a little too close to being DQed for comfort. The tires are Hoosier D35s on 10" rims. I don't have the track width on me...but the track surface usually has grip unless they run us at the end of the night. I expect our first race to go dry-slick, though, because of the wind this time of year and other factors.
One odd thing compared to what I know about the mods... Another racer who is familiar with these cars told me to only run "a few degrees" of J-Bar angle. It could be because the bar is mounted on the lowest hole on the pinion side (it is a Quck-Change, not a 9") so running less angle helps compensate for this.
My overall goal is to get the car good enough to qualify near the front and have some adjustability in the setup so I can compensate when the track slicks off.
Post by flipflopoo1oo on Mar 3, 2014 16:54:16 GMT -6
J-bars come in many off-sets as well as bushed and quick adjustable and walking! One hole up and bolt to bolt measurements is best to give a base degree depending on offset bend! Pinion movement by twist and lift comes into play with all adjustments, so keep any in mind with other changes changing j-bar and pinion angle as well as rear end offset with movements and ajustments! A simple ride height change will change so much as to where you want to go with most things! A biscuit on a right trailing arm to allow for some controlled movement ( if legal) helps save many adjustments when its all where you want things! This allows for instant steer going in and closing more on exit! Adjustable fully with limits!