| [ Total Views: 2081 | Total Replies: 13 | Thread Id: 104796 ] |
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 55slug
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| posted on January 21st, 2014 at 02:36 PM |
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Wheelie Bar mount questions....
Can anyone see issue with this. Couple of questions in my head, 1st is are the bar mounts too close (we can run a mount out of the holes and spread
the bars), 2ndly are we asking too much of the mount with the bars set up like that. I can see the mount being twisted downwards if it gets hit with
enough force, breaking studs and worse...
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dangerous
A.k.a.: Dave Butler Muffin Man
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| posted on January 22nd, 2014 at 07:47 AM |
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This is one area that I continually see bent, flared, or twisted, on nearly all VWs that have bars.
Now is the time to make this mount as rigid as you can,
so the bars themselves can to the job intended.
Often you will have to give in to a bolt-on arrangement for the actual bars,
(as opposed to a quick pin),
to eliminate the chance of the 'slop' that can appear in short order.
As you well know, most bars are outboard of the forks, so apply the majority of the force to the forks first.
But yours will be very hard on those studs in the gearbox.
I would be happy with the location, you have,
if you can transfer the forces back through the forks instead,
with some well thought out gussets and boxing-in,
plus some sort of anti-rotation appendage that will take the load away from those studs.
This can (and should) be on the forks,
but also on the gearbox too, in your case.
| Quote: | Originally
posted by westi
That's mad Alan.
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nasty
A.k.a.: Michael Nash
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| posted on January 23rd, 2014 at 08:27 PM |
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Will you need to spread the bars out past the forks so they clear the sump on the motor?
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modnrod
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| posted on January 23rd, 2014 at 10:26 PM |
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If you did need to spread the bars out like Michael said, and if you also need to brace the ends to stop rotation as Dave says and to take some of the
load off the forks, how about making another set of "slip-pipe" socket-mounts, but this time on the torsion housing?
Sorta hard to describe, but almost like a short "Y" on each side becoming each side leg near the end of the car.
That way it's all braced for load transferance, but can still be "quick-fit" (I assume for ease of trailer stuff?).
You can imagine all sorts of strange setups when not constrained by knowledge or experience! 
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55slug
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| posted on January 24th, 2014 at 03:30 AM |
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It's dry sumped so clears everything, will try and work with this and brace it all up as per Dangerous post. Remove able for trailer and street.
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Dak-A-Tak
A.k.a.: Peter Page
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| posted on January 25th, 2014 at 06:25 PM |
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I would make those slip in joints much longer for flex strengh , and then basic copy what you got there ,then put that on the other end of slip joints
under the tranny and have bracket tabs weld on chassis ( or forks for a pan car ) tubes there , to tie it all together , IT will be like a craddle
then .
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humpty
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| posted on February 5th, 2014 at 11:32 PM |
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This is possibly a dumb question.... And I don't mean to high jack the thread, but can one of you enlightened souls please explain why VW drag cars
all mount the wheelie bars off the framehorns/chassis, but all conventional drag car (non-rigid) have them mounted on the suspension?
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allanvw
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| posted on February 6th, 2014 at 05:52 AM |
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Comes down to the fact that VWs have independent rear suspension, not a big straight axle like a conventional drag car.
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modnrod
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| posted on February 6th, 2014 at 06:02 AM |
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On a conventional car Hump the diff nose (where tailshaft goes in) is angled downwards at rest, and at the hit the diff nose rotates upwards from the
torque. The rear suspension is set up so this twist is transferred through into trying to lift the front of the car (Instant Centres, etc), thereby
squashing the rear tyre harder into the track. That's one reason why well set up leaf spring rears "hit" so hard compared to 4-link, and 60ft so
well. Wheelie bars on these cars provide more yet more "twist" force on the tyres due to the length of the leverage, as well as acting as a limiter
function for raising the nose of the car.
An IRS rear has different I.C. angles and actions, and vastly less torque transference through the suspension, so much less leverage available. A
wheelie bar here is really just performing the nose-lift-limit function, so is frame mounted.
What's more important on IRS of any sort is to keep the angle of the rear trailing arms (especially short ones like ACVW) still slightly angled
downwards after launch. If the IRS arms are angled up the rear suspension goes into too much squat, and the weight of the car is actually trying to
lift the tyres off the ground, not squash them in further, so reducing traction effort.
Yes, just like a bike! 
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morgan
A.k.a.: morgan smith
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| posted on February 6th, 2014 at 04:21 PM |
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the weight of the car is actually trying to lift the tyres off the ground???? WTF
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modnrod
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| posted on February 6th, 2014 at 10:03 PM |
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OK, please don't excommunicate me yet!
Another way to describe it. The tyres are twisting around the axle centreline. If the arms are pointing upwards at the front, then the reactive forces
will try to push the arms further downwards, so it plants the tyre harder. If the arms are angled downwards at the front, then the reactive forces are
trying to lift the arms up into the car more, so it actually reduces tyre pressure into the ground. This can cause "pogo" effect, and also axle
tramp if it's bad enough. Either way, the tyres are trying to rotate around the axle centreline one direction or the other and trying to get to the
front of the car (as a reactive force from the torque).
Or just put bigger slicks on it to make it stick and hope you don't break mounts.
PS: really off topic, sorry 55.
I hope your bars work out man. Pics please!
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allanvw
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| posted on February 7th, 2014 at 01:29 PM |
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A wheelie bar has 2 uses.
1, as it says. stops big high wheelies
2, Traction control. When the hit comes on, the tyre compresses and deforms ( isn,t a round tyre anymore) and the wheelie bar hits the track which
unloads the weight on the tyre which inturn releases the tyre to become round again and also allows the tyre to slip which lets the motor get up into
the revs. Slippage is very important in drag racing. This video of Shawn Geers shows it all. The double hit of the wheelie wheels and the tyre
slippage
https://www.youtube.com/watch?v=ODhdXOLBRw8
Up until I started getting into the finer points of drag racing, I had never realized the 2nd part a wheelie bar does. Thought it was all in the
clutch
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humpty
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| posted on February 12th, 2014 at 11:15 AM |
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Cheers for clearing that up fellas.
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55slug
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| posted on February 14th, 2014 at 11:02 AM |
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Going with Dak-A-Taks sugestion, its tight but will work out sweet and spread the potential load.
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