Aerodynamic vs. vehicle stabilty

[nebulous]

Rex
A P.S. to my last post
Rock climbers need a lot of caster for weight jacking. Think how much steering imput it takes to change lanes at 60mph. Think what just a little weight jack at 200mph could do to a rectangle wheel layout that "some vehicles" have!
Jack

[SPARKY]

When I was running '39 Chevy hubs with my 21" Goodyears I had almost 3.5" positive scrub radius with 15 deg caster---turn the wheels and I got a lot of weight jacking.  Above 160 the Rat started to hunt and wander his way down the race course if the Course was hard you could keep him gathered up fairly good if it was tractionaly challenged so was I! 

 I change wheels & hubs and got scrub radius down to 3/8" positive very little weight jacking and now the Rat goes pretty straight now. I will have 5 deg max when I relocate the axle.

The big tail feathers kept me from going completely around---The Rat has a flat bottom and 3.5" rake on a 209" wheel base with my smallest 25" rear tires

[Rex Schimmer]

One of the things that we are not talking about which I think in the case of Jack's cars could be very important are the gyroscopic forces developed by the wheels. A 20 inch diameter wheel at 200 mph is turning at almost 3400 rpm, it takes a pretty large amount of force to try to make that wheel deviate from its path, especially if the rate of deviation is fast. This force is what keeps bicycles and motorcycles from falling over at speed and the way Jack's cars are designed with very narrow tracks I would think that this force would also be a great contributor to keeping his cars vertical (bottom side down) and going straight.

Just another thought to ponder.

Rex

[Seldom Seen Slim]

Rex, as an aside to your comment about the gyroscopic forces of a fast-spinning wheel -- I've often tried steering the bike at speeds of 200, and it's bloody near impossible to move the handlebars.  Steering, when needed, is done more with hanging an elbow out in the breeze on the side toward which I want to go.  If I did manage to turn the bars -- I'm always afraid that they'll be too hard to turn back and I'll fold the front wheel under and do a high-side catapult.

[Gu11ett]

If the steering and frame geometry is correct, the front wheel will return to straight ahead when you decrease your input. That is if you are not already way out of shape or something else is providing input.

[John Burk]

With a rectangular foot print weight jacking requires scrub .

[nebulous]

John
I agree with the scrub comment. Jack

[Constant Kinetics]

Back to gyroscopic wheel force, that is why gran prix motorcycle riders throw their knees out to steer. The wheels spinning that fast want to remain plumb and the rider must create drag and counterbalance to navigate through the turns.
Also, way back to a question  i asked earlier this post, could a rider change his riding position during a run to act like a dynamic ballast? I used to drag race my old Maxim X, a naturally aspirated 700cc bike that ran very well. In one race, because of the low number of bikes that showed up at the track that weekend, i went up against a N2O breathing 1300CC 'Busa. I had an excellent light, my opponent did not. Being so overmatched, i was a little too hard on the throttle out of the hole and had my bike travelling up on it's rear wheel until i found 4th gear. Because my opponent had a poor light and wasn't ahead of me, i thought i might have a shot and rather than ease out of the throttle, i stood up on the footpegs and leaned out over the front fender desperate to keep the lead. Would it be possible to do something similar if the rear wheel was to have trouble hooking up or the bike started to develop a high speed wobble?
                                                                 -Chad-

[Dynoroom]

Back to gyroscopic wheel force, that is why gran prix motorcycle riders throw their knees out to steer. The wheels spinning that fast want to remain plumb and the rider must create drag and counterbalance to navigate through the turns.
Also, way back to a question  i asked earlier this post, could a rider change his riding position during a run to act like a dynamic ballast? I used to drag race my old Maxim X, a naturally aspirated 700cc bike that ran very well. In one race, because of the low number of bikes that showed up at the track that weekend, i went up against a N2O breathing 1300CC 'Busa. I had an excellent light, my opponent did not. Being so overmatched, i was a little too hard on the throttle out of the hole and had my bike travelling up on it's rear wheel until i found 4th gear. Because my opponent had a poor light and wasn't ahead of me, i thought i might have a shot and rather than ease out of the throttle, i stood up on the footpegs and leaned out over the front fender desperate to keep the lead. Would it be possible to do something similar if the rear wheel was to have trouble hooking up or the bike started to develop a high speed wobble?
                                                                 -Chad-

Did you win?

And I think you'll find the answer is yes but maybe to a lesser degree.
You sure do have a bunch of questions. My advice is "kiss". 

[jl222]

Back to gyroscopic wheel force, that is why gran prix motorcycle riders throw their knees out to steer. The wheels spinning that fast want to remain plumb and the rider must create drag and counterbalance to navigate through the turns.
Also, way back to a question  i asked earlier this post, could a rider change his riding position during a run to act like a dynamic ballast? I used to drag race my old Maxim X, a naturally aspirated 700cc bike that ran very well. In one race, because of the low number of bikes that showed up at the track that weekend, i went up against a N2O breathing 1300CC 'Busa. I had an excellent light, my opponent did not. Being so overmatched, i was a little too hard on the throttle out of the hole and had my bike travelling up on it's rear wheel until i found 4th gear. Because my opponent had a poor light and wasn't ahead of me, i thought i might have a shot and rather than ease out of the throttle, i stood up on the footpegs and leaned out over the front fender desperate to keep the lead. Would it be possible to do something similar if the rear wheel was to have trouble hooking up or the bike started to develop a high speed wobble?
                                                                 -Chad-

  As far as the high speed wobble ....just jump off but don't let your leathers or boot get stuck on the footpeg [ like Ron Cook]
and make sure you have your aerodynamic leathers and helmet on so you will not tumble but just slide head first through the timing lights with no loss in speed.

    JL222

[Constant Kinetics]

Hopefully, a steering damper and CVT will keep me straight and hooked up, i'd rather not bail off a mostly hand made bike.
I didn't win against the 'Busa, but he didn't pass me until about 60 feet from the finish. I do ask a lot of questions here, but looking dumb on a forum is much better than the look i'll have if i show up to my first speed week and don't get to run.

[maj]

Using every piece of information available is far from dumb.

For the body position, weight bias thing , may be usable on an open bike but my APS and many others in APS/MPS are fairly fixed in position due to the bodywork and seat design ,

[jl222]

Hopefully, a steering damper and CVT will keep me straight and hooked up, i'd rather not bail off a mostly hand made bike.
I didn't win against the 'Busa, but he didn't pass me until about 60 feet from the finish. I do ask a lot of questions here, but looking dumb on a forum is much better than the look i'll have if i show up to my first speed week and don't get to run.

  I'm surprised the bike guys have not advised you to Not stand up on footpegs and lean forward at high speed. On U-tube there's
a video of a top fuel harley rider getting blown off his bike when his glove caught the air.


                                JL222

[joea]

cuz he might not be riding a top fuel harley...

Joe

[Constant Kinetics]

JL222
   Do you know the name of that video? I figured there would come a point where that wouldn't work considering 1/8th mile speeds are much slower than LSR speeds, i was just wondering if i could slide forwards up to the fairing to help fight some of the high speed handling problems.
                                                              -Chad-