Rear suspension travel on a 61 bug

[Phil West]

Hi all,

At a race meet last year a steward took a photo of my car 50yds after the finish line doing 113mph coming off the power.  There was no more than 1 inch of tyre in contact with the dragstrip - car was practically off the ground.  I use AVO shocks set to maximum, setting 20/20.  Also I use metal flop stops on the springplates, I was just using the single metal spacer that came with the flop stops.

When I jack up the car the top of the slick is 9cm below the wing lip.  I have just made another spacer and re-installed the flop stops - the top of the slick is now 3.5cm below the wing (one extra plate made a big difference!) so the wheel is nearly in the same place whether the car is jacked up or not.  Actual max upward movement of the car on the rear shock abosorber itself is only around 1.5cm.  My question is - can anyone recommend a safe minimum amount of upward travel for the car on the rear suspension on a drag bug?  Car is swingaxle.

If anyone out there is using a similar setup at similar speeds - your slicks are hardly in contact with the ground at the top end!  Get a mate to take a photo after the finish line and you'll see what I mean.

Cheers
Phil

[richie]

Phil,how do you slow it down? if you get on the brakes quickly then it will unload the back end causing the situation you describe.

And I think it could do with more suspesion travel than that,what you have will cause the startline antics,it needs to be able to squat more at the start and absorb the bumps better at the top end

cheers richie,uk

[Roman]

What stops the upward movement? I have AVO shocks, part #TB436, 30 mm bars and even a bus tranny that moves the suspension up even more but no problems.
If you remove the shocks how much travel do you have then? BTW, I have home made limiter straps with steel wire that limits the downward movement to nearly straight axle.

[Phil West]

Hey Richie,

Actually I get 2 inches of downward travel on launch with the shocks on max setting so any softer and there would be too much squat on launch.  At the top end I'm pretty good about coming off the power, very gentle reduction on the loud pedal and no brakes until much later.

Roman,

There's plenty of available upwards play left in the rear shocks, so although they are making it harder for the car to move up, ultimately the physical limitation on upward movement is in the flop stops on the spring plates.  So if I were to unload rapidly on a bumpy track, the car would lift up 1.5cm on the rear shock and then hit the physically limit of travel on the springplate.  If the upwards force is strong enough the rear tyres would then lift right off the ground.  Or if I hit and bump and the car went down into it and then back up, the tyres may come off again.

Trying to balance that problem with the one I had before which is leaving more springplate travel so that the the tyres remain on the ground but have almost no contact on the ground because the car is able to lift up more.  It's a fairly fine line between the two.
Cheers
Phil

[Roman]

Now I understand, with down you mean down with the tire and vice versa. I meant the opposite, so now I know what you mean.
AVO can revalve your shocks for about £15 each, it takes them about three days. Just tell them you need the hardest setting you have now at #10 on the adjusters. I had the same problem with a bit to soft shocks, but the shipping from the UK back and forth was the same cost as selling the old ones and order new with the right valving from the start.