Printable View
hey everyone, I am going to be racing an 09 masters from mars in Tucson at usa raceway in a couple weeks, its a new car to our team wondering about proper LR droop. right now to get the LR top bar to good dry slick angle with starting hole in frame puts me at about 12.75" from axle tube to frame does this sound close?
12-13 inches is where a lot of folks start on MB cars. You can use jack stands and stuff to measure but we like to just put the car on the ground at ride height and jack it up under the seat until the chain is taut. Then measure from axle tube to frame rail. This seems to be the most repeatable method of measurement. Also try to make sure your upper bar doesn't exceed 47 degrees at full travel. If it rolls past that, you could actually start to lose LR drive which just leaves you with roll-steer.
And be sure you are using a chain (or something) mounted TO THE AXLE TUBE as your travel limiter. You should not use a shock to limit travel for two reasons 1) you will eventually destroy that shock and 2) the allowed travel will change when you make bar adjustments.
yeah thats how ive been going at it, jack up left rear measure angle and change with chain for small adjustment ,bar for big adjustment. this is just in the shop so ill find how it actually works pretty soon. im at 45 degrees now for a dry set. would i want the droop back lower if its tacky or just bar?
We've found that less droop in the LR takes away some of the throttle push we pick up when the track is tacky. If the car still won't turn (on the gas) we usually raise the right upper or lower the left upper just depending on what it feels like it needs.
We like to run no more than 45 degrees on the left upper at full travel. Changing the travel limit is doing just that but if you adjust the bar on the frame you are changing the overall indexing properties of the birdcage up until full travel. By lowering the upper bar on the chassis and leaving the travel limiter alone you are taking some rear steer out of the car in addition to taking some drive out of that corner. It all depends on what the car needs.
Thanks alot for the advice, next weekend will be my first race in it at and its a big fast place, so its good to know im in the right general area. before when we were testing it wasnt even getting into the 12'' range because it was limited by a shock but i made a chain setup for it so that will give it alot more options. Again thanks for the advice
I have a question concerning drop and the limiter. This year we got a new car and had problems with the chain maxing out and the car being very evil. My thoughts are that the chain should only be used to prevent shock damage. I thought the j bar should have been dropped in the beginning.
What do you guys think?
Is the chain only to prevent shock damage? If the chain is maxed out, then shouldn't the left rear become unloaded? Is lowering the j bar the first option?
Thanks.
What do you mean by "the car being very evil"? The chain is not just to prevent shock damage. It is to limit travel and thereby prevent excessive roll oversteer and getting the bars at angles that are too much to generate downforce on that corner (drive angle).
I'm not sure why you went to the j-bar but I'm also not sure what the car was doing that was undesirable. J-bar adjustements are completely different.
The chain being maxed out does not unload the LR because the bars are still loading that corner as long as you are on the gas. The spring itself is usually unloaded well before you reach the limit of the chain unless you are running a super soft LR setup. This leads a lot of people to believe that the LR corner is "unloaded" but it is still loaded due to the angles of the bars (drive angle). If you let off the gas with the car loaded by the bars and off of the spring, it will free fall until the spring catches it. But as long as you are on the gas, the corner is loaded by the bars.
If you do not have enough damping from the shocks, you can bounce on and off the chain limiter and the car will feel evil. This is extremely bad if you attach the limiter to the front of the birdcage instead of the axle tube.Quote:
Originally Posted by bb14
Maybe this is what you are describing?
The chain is hooked to the rear bracket for the swing arm and runs forward to the birdcage. The car would enter fine and the turn hard left when the gas was picked up like the left rear was off of the ground. We have one many races and were trying a new setup. 500 lf, 350 rf, 200 lr and 275 rr. We could not any traction if turning under another car so we went back to a standard setup, 225 on rear and lowered the j bar and the car was much better. We used to run the chain to the axle tube but for some reason we hooked it to the birdcage this year. This coming year we are going to keep it much more simple.
Matt that was a really good explanation. These Mastersbuilt threads always lead to some interesting tech talk. I