Author Topic: wheelie bars  (Read 2013 times)

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Offline cbr954

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wheelie bars
« on: April 29, 2015, 03:01:59 pm »
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!
03 CBR954RR, 72 750 chopper(970cc
F2 head), 2017 CRF450R, 2001 CR250R, 72 CB500, 79 XR250, 04 CRF50,70's soon to be rebuilt cb750 drag bike.

Offline dragracer

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Re: wheelie bars
« Reply #1 on: April 29, 2015, 07:51:44 pm »
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. 
 

Offline 754

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Re: wheelie bars
« Reply #2 on: April 29, 2015, 07:57:19 pm »
I like to run forks quite stiff..helps. Break the beam.. Too soft and it goes up..up..up..then breaks beam..hard to get good reaction time. Bar or no bar you want front end to stay down.
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Offline cbr954

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Re: wheelie bars
« Reply #3 on: April 29, 2015, 08:24:10 pm »
Thanks guys that helps a lot.  I know there is a lot to learn just needed a place to start from!  Will see how it goes.
03 CBR954RR, 72 750 chopper(970cc
F2 head), 2017 CRF450R, 2001 CR250R, 72 CB500, 79 XR250, 04 CRF50,70's soon to be rebuilt cb750 drag bike.

Offline dragracer

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Re: wheelie bars
« Reply #4 on: April 29, 2015, 08:45:18 pm »
Did i ask about your starting line control method?? Are you planning to use a two step or just bring the rpm's up and drop the clutch off the line? My suggestion is to get a launch rev limiter of some kind. A simple, easy, low and high side limiter is a Dynatek, DRL400. You will need a high side limiter anyway so why not just get something that does both.

To make a 2 step work correctly, you need to get an adjustable, switched cluth lever like the ones FBG sells. You want to figure out the point where your clutch just starts to engage, then you want to figure out electrically where the two step releases. The idea is to get the 2 step to release just before the bike starts to move so it launches at full throttle, and not on the low side rev limiter.

And thanks Frank for finishing my thought about the front forks. I started going down the path to discuss fork stiffness and moved forward before explaining why i mentioned fork travel.

Offline dragracer

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Re: wheelie bars
« Reply #5 on: April 29, 2015, 08:46:19 pm »
Thanks guys that helps a lot.  I know there is a lot to learn just needed a place to start from!  Will see how it goes.

If you follow what Frank and I detailed, you'll have a decent starting point.

Offline cbr954

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Re: wheelie bars
« Reply #6 on: April 30, 2015, 04:41:20 am »
Yeah I am running a msd mc-1 ignition with a 2 step box.  The bike came pretty well setup in that regards but didn't get any data that the was used as far as setup. 

I willl have to look into the front suspension aspect as it just has stock forks.  Need to look into stiffening them up.

Thanks for the info
03 CBR954RR, 72 750 chopper(970cc
F2 head), 2017 CRF450R, 2001 CR250R, 72 CB500, 79 XR250, 04 CRF50,70's soon to be rebuilt cb750 drag bike.

Offline POPS 911

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Re: wheelie bars
« Reply #7 on: April 30, 2015, 06:19:08 am »
FROM A GEORGE BRYCE SCHOOL [ STAR RACING ] : Paint your wheelie bars with a dose of white shoe polish ...... look at the wheels at the end of the run and lower the darkest black one or raise the whitest one a 1/2 turn at a time until it leaves straight.
The darkest is the highest one ..... the low one hits first and leans bike over on the high one .... then the bike drives away.  The reason it's dark is because you ride on it so long .... Going in the wrong direction. If you lower the dark one on the next run the bike will hit both and go straight. GB3
RAISE THE BARS FOR MORE TRACTION UNTIL YOU GET WHEEL HOP THEN TURN BACK A 1/2 TURN AND YOU ARE SET TO RUN .... GB3
This SCHOOL is at STAR RACING the GUY who sends PRO-STOCK bikes down 1320' at 197mph in 6+ seconds.

SHORT BARS = No way, wheel hop at the hit = Right FRANK ? Them long bars take some of the shock out of the hit, walk up and down the lanes look at them bars. I watched the young man run 227mph at SGMP 2014 fall event with NO BARS but he had a set of BALLS!!!!!!

Offline NalleyRacing

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Re: wheelie bars
« Reply #8 on: April 30, 2015, 06:42:19 am »
Sounds like Joey Gladstone Pops! 200+MPH in the 6's with a NO BAR bike. That is true talent

Offline dragracer

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Re: wheelie bars
« Reply #9 on: April 30, 2015, 07:03:03 am »
Yeah Pops, no bars  at 200 plus mph always means big balls. Lol

Offline jweeks

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Re: wheelie bars
« Reply #10 on: April 30, 2015, 07:28:43 pm »
I like to run forks quite stiff..helps. Break the beam.. Too soft and it goes up..up..up..then breaks beam..hard to get good reaction time. Bar or no bar you want front end to stay down.
If the front wheel goes up, you break the staged beam sooner than if the front wheel goes forward. Going forward, the rollout is greater than the distance up to stop blocking the staged beam  (starting the clocks.)
     I fought a bunny hop off of the line last season that had me redlighting far too often. My problem was with the lockup clutch that I couldn't figure out. Got the launch rpm down to the point that the bike bogged when the front wheel cam back to the pavement on launch. Took the lockup off, went back to a stock pressure plate, kept the soft springs and started going forward, not up. (Not on a CB750, but a GPZ) I also like a tie down strap for the front forks that limits their travel. Most of the major bike shops can get those straps for a reasonable price.

Offline Don R

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Re: wheelie bars
« Reply #11 on: May 06, 2015, 07:36:51 am »
 We run a dragster and the front wheel advise is correct for what we do. Rolling through the beam is more consistent than wheelieing up and out.  We have used the wheelie out of the beam plan when we were having a problem with pro tree reaction times but it's never as consistent. I wondered about limiting the fork travel, that's common on door cars with front suspension.
 When you do the math it's amazing how much R/T and ET tradeoff there is when staging even a fraction of an inch forward or back in the light beam. That's where a bike has the advantage, the rider should be able to just creep into the beams until the stage light comes on, that's the only spot you can know exactly where you are  in the beams and repeat with accuracy.
 Rolling in deeper can reduce the reaction time but adds to the E.T. useful only in heads up racing.
 
« Last Edit: May 06, 2015, 07:40:50 am by Don R »
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Offline Don R

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Re: wheelie bars
« Reply #12 on: May 07, 2015, 10:37:24 pm »
Thanks for the thread, I may build a set of old school bars for my drag bike resto project. I won't make them as short as I was planning.
If the things you own end up owning you, it's better to be owned by some cool things.

 

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