Belly Tank Build Diary

[SPARKY]

I was trying to give you a way to get some idea how easy it is to twist you frame  ie how stiff it is in torsion.  High torque engines can twist the frames way more than most suspect which lead to unloading the right rear wheel

[JAL AKA JL222]

JL 222

I have no idea which cars made the "footsteps".   I would assume that most were higher horsepower cars by the length and depth of the spin marks and how far down the track they were.  I assume that some were liners by the width of the track  but most had fairly wide rear wheel spacing.

I assumed that most were spools, but that is pure assumption on my part.

   How would a spool spin one tire and not the other?

                   jl222

[SPARKY]

the frame sets up an oscillation      twisting and/or back and forth      that is what causes the footstep pattern the tires are loaded and unloaded

[JAL AKA JL222]

the frame sets up an oscillation      twisting and/or back and forth      that is what causes the footstep pattern the tires are loaded and unloaded

maybe in an open rear end but not a locked one without leaving a spin mark from both tires. doubt a frame would twist back and forth that quick at speed.
 
  That would also put more load diagonally on the front tires severely affecting steering.

    Sounds like motorcycle tracks.

                     JL222

     

[SPARKY]

it is real hard to leave a tire track when the tire is off the ground

[Rex Schimmer]

This discussion is exactly why, in my opinion, suspension is a requirement at the salt.At best the salt, these days, is never absolutely smooth, combine this with tires ran at high pressures invites poor traction. The tires are bouncing from one high spot to the next. This could possibly be combined with the bending and twisting frequencies of the chassis to have a frequency that allows the wheels to be unloaded in a cyclic manner which is almost impossible to change. The addition of a supple suspension system at least gives you a tool to have some affect on this potential phenomenon. In a car with out actual suspension the only "spring" that you can easily adjust is the inflation pressure of the tires which can also introduce some unanticipated traites. One of the big challenges of non suspension cars ,as I see it, is getting the corner weights set. You need to have a method of raising and or lowering the corners to get the wheel weights set, with a suspended car that adjustability is part of the package.   

In my way of thinking the perfect chassis for Bonneville would have high stiffness in both bending and torsion and would be combined with a suspension with a relatively low natural frequency.

Rex

[JAL AKA JL222]

  Hey....Sparky you experienced this oscillation in your car how did you know and how did it feel or effect the handling?

  Also, what was the distance between the groves?

               JL222


                 

[SPARKY]

it hunted real bad and I kept asking everyone i thought might have an idea----finally a circle track chassis builder put me on to scrub radius and caster and how it affects things..  so i got rid of the scrub radius and went down to 2 degs caster and went to a torsen diff huge difference and i kept stiffening up the chassis and it got better and better  then  I preloaded my right rear 140# which also preloaded my chassis 

High torque engs try to lift the right rear tire  I also now have wheel speed sensors on both rear wheels as well as driveshaft and trans input shaft  I am exploring load cells on rear chassis mount points as part of my research as I explore much more eng torque in high gear.

I got my hats using poor boy traction control a PG/GV combo no torque converter  I now have 6 gears and air shift violence..I am contemplating really stepping up the power  it will change lots of stuff and I am really exploring what it will take to maintain a stable car. I do not want to go back to the way I started.

[desotoman]

Thanks for the post Sparky. 

Tom G.

[SPARKY]

thanks Tom. 
The chassis builder explained to me that large scrub radius and lsrge caster were the way circle guys could weight load the RR tire coming out of a corner--  when you see them putting in lots of  steering wheel action  they are not trying to catch the car with frt wheel action they trying to make the RR bite.   I was doing in a much smaller way as I "chased the hunt"  I put it on chassis scales and proved that it just made it worse..  that why roadster guys say  dont steer if the car hunts- a lot of them have lots of caster and scrub radius.  YMMV  :naughty

[JAL AKA JL222]

 
  Sparky .... looks like your handling problem was front end problems no mention of side-to-side tire spinning or how it felt.

  But you did go to a torsion diff. why?

So after your many course walks observing these spin marks can you tell us how long these marks were and how often from side to side in estimated feet?

                    JL222 

[bubruins]

Lot of good info in the past page for people planning on running a solid axle lakester! IMO the dream for any racer is to have enough downforce that traction is not an issue. At some point, the downforce would be sufficient to ensure there was 100% grip and no slip for either wheel on any surface. I have not seen many Bonneville builds that utilize thousands of pounds of downforce because the drag cost would be too high. That does lead to the question - how much downforce is enough to dampen those vibrations for a solid axle lakester? 200lb? 500lb? 1000lb?

[JAL AKA JL222]

   Sparky .... those spin marks might be from unsprung cars.

  We all have heard the EH EH EH [car sounds] of some vehicles during a run.

  Sitting in our pits a solid suspended roadster came by being pulled about 10 mph;

the rear tires bumping up and seeing air under them

                   JL222 

[SPARKY]

I never said my car made evenly spaced  footsteps.  I just saw multiple set of them multiple times. Between open rear, track bumps and a very twist prone frame my rear facing camera revealed very uneven salt spray coming from my tires, eventually ended up with 2500# on rear axle but my car at first had no torsional rigidity.

The torsen has a very unique ability--torque basis it works like a wheel speed governor ( differs from spool  if one wheel has less traction it transfers more power to the tire that has the best traction until it is overpowered)

As to spacing  figure out how far a car travels at the speed you are going to run to run. The suspension of a solid axle vech. is the tire deflection.  The reaction time of the tire deflection determines how far up the tire tread moves when you.

at 300 you are covering 4.4' or 528 inches every 1/100 of a second. 5.28" every 1/1000 of a second

My personal opinion is the is no suspension that can react fast enough to deal with pot holes and bumps   you just have a more stable system by trying to make the tire pressure work as best as you can

I run 65 in my Goodyear 17" front tires and 90 in my 25" Goodyear rear tires

[JAL AKA JL222]

  Sparky.... can you answer the QUESTION???

  How far were the spin marks that you observed on your many course walks and side to side in ft.

   Just an estimate.

   It's amazing that you don't think suspension doesn't react at speed but gives incite to how you think.

  why do you think other race cars have suspension such as road racing?

   More to come

   222 CAMARO blown gas altered 287 at THE 21/4 with suspension and a smooth ride.

                                JL222