Need some help setting up wheelie bars. I have a couple of different sets, one short and one long. Stock frame with extended swingarm and struts. Running a MT drag slick. Need some info on a base line for bar height etc. Cant seem to find any decent info on setting up bars for bikes, lot of info for cars. Any help appreciated!
Alright, i see no one else has replied so i'll see if i can help. Since you have several sets to choose from, we now need to do some initial measurements. The first measurement to take is the wheelbase of the bike, axle to axle. With that number in mind, you want to pick a set of bars that are equal to the length of the wheelbase. Measure the lower bars to get the length. The general rule of thumb for wheelie bars- the length of the bars should be equal to or close to the wheel base of the bike in order to get proper weight transfer under power.
Now i'm going to assume the swingarm and the struts already have tabs welded on to mount the bars.
Attach the bars and determine visually if they are level. To do this correctly, you need to level the bike itself and then check across the wheelie bars, as close to the wheels as possible, to see if they are level. IF not, adjust the heim joint on the lowest side until the bars are level- again, the bike must be level itself when doing this step so you might need 2 levels.
Before the next step, air up the front tire and rear tire to the amount of pressure you intend to run while racing the bike. This is extremely important. Now look again at the bars that should now be level left to right. You want to see about 1 1/2 - 2 inches clearance under the wheels as a baseline. Adjust the lower heim joints to get this measurement. At this point you will need a piece of 2x4 wood, a level and an assistant. Roll the front wheel up on the 2x4. The wheelie bar wheels should not be touching the ground at this point. Now you will need to sit on the bike. At this time the wheels should be really close to touching the ground but not quite. You want to see a little daylight and allow just enough room for the wheels to roll freely. Adjust the bars up or down, evenly, until you get it right.
What i've explained will get you fairly close in making a straight pass while the bike is on the bars. You must be sure the rear wheel is aligned correctly before making a pass. Find the same fixed point on both sides of the bike to take this measurement. I use either the swingarm bolt or i measure from the crank centerline. To make a bike go straight on the bars, its imperative that the rear wheel is tracking straight in the swingarm- its only on 3 wheels at the point and the rear wheel is what actually "steers" the bike. If you have shoe ploish or "dial in", paint the wheelie bar wheels. This is an aid to visually see on the track surface, which one of the wheels on the bars contacted the ground first or if you got lucky, both will leave even length marks. You will need someone up on the line to confirm the marks- video is best so he/she can show you. The next car/bike up will likely erase the marks before you can come back to the line yourself to look.
So now you've made a pass and the bike didn't go straight. It now time to tweak the height of the bars on one side only to correct the path. If the bars are level and at the right height but the bike steers left right off the hit, This means the right wheel is too low and is "throwing" the bike left because its hitting the ground first. Adjust the heim joint to raise the bar on the right side only. Sometimes a full turn is enough- you just have to do trial and error on the next pass. If the bike goes to the right off the hit, then the left bar needs to be raised because it hitting the ground first and driving the bike right. I think by now you get the concept of bar adjustment to make the bike go straight.
One more thing, the front fork travel can have a major affect on whether or not the bike will actually ride back on the bars. If the frontend is too spongy and extends too when you drop the clutch, the bars will hit the ground before the bike carries the front tire and you will be riding on 4 wheels instead of 3. Again, you want to carry the front wheel off the line in order for the weight to transfer and the bars to plant the tire. Otherwise, it could unload rear tire and cause you to spin. At the same time, if the bars are too high to begin with, off the hit the bike will pogo and again unload the rear tire. This could make for a very unsafe launch.
Well, there's my take on wheelie bar selection and adjustment. I'm sure others will chime in with better information. I only wanted to share my opinion on the questions you asked.