Vintage Karting Forum

Al,

Thanks for your help, here on the forum, and especially at the track last weekend. I enjoyed our conversations.

When you say you switched from a 36" axle to 34", are you describing the width between shoulders or overall. These terms confuse me because the advertised length of the 3/4" stubs varies. I assume that your axles have 2" stubs and shoulder to shoulder measurements of 32" and 30", respectively?

I was also meaning to ask you: What is the width of the turbine wheel spacers you used on the rear whenever you ran 11x4.5-5 tires? I understand that adding spacers would add another variable to my quest, probably in direct opposition to my original theories, but, as you know, the stock wheels are barely within the minimum recommended width range for those tires. I wonder if widening the rear wheels, thereby flattening out the tread, would allow the sidewalls and tread to perform their functions more independently and more consistently on the track?

(09-07-2018, 09:26 PM)Kurt Bogerman Wrote: [ -> ]Al,

Thanks for your help, here on the forum, and especially at the track last weekend.  I enjoyed our conversations.

When you say you switched from a 36" axle to 34", are you describing the width between shoulders or overall.  These terms confuse me because the advertised length of the 3/4" stubs varies.  I assume that your axles have 2" stubs and shoulder to shoulder measurements of 32" and 30", respectively?  

I was also meaning to ask you:   What is the width of the turbine wheel spacers you used on the rear whenever you ran 11x4.5-5 tires?  I understand that adding spacers would add another variable to my quest, probably in direct opposition to my original theories, but, as you know, the stock wheels are barely within the minimum recommended width range for those tires.  I wonder if widening the rear wheels, thereby flattening out the tread, would allow the sidewalls and tread to perform their functions more independently and more consistently on the track?

Without pulling it apart it measures about 30 inches between shoulders. Spacers were 1/2 inch thick. It's fun to make changes to make things better, but you can chase your tail if you change more than 1 thing at a time. Or like me, neglect to write it down thinking "I'll remember what I did". Enjoy.

Here's what I did to scale our karts.  Tedious for sure, but cheap.
Bought 4 identical cheapo bathroom scales at Target.
Set them on concrete floor.  Put a straight 2X4 across two scales at a time (6 combinations), with carpenter's level atop.  Shims beneath scales to get level.  (Mark the floor to simplify the process next time.)
Sit in kart with helmet on, like you race.  Make sure wheels are steered perfectly straight ahead.
Recruit someone to read the scales for you, and write the numbers down.

I'd love to say that the results are lots of races won... maybe someday!

yes same for me ..maybe someday... !!!
I did buy a tire gauge this year so I could go real fast ..but I lost it before I got to avon so that aint gonna help me none ..

Kurt,I don't remember was your kart a one or two piece GP? For you or anyone with experience,does lengthening or shortening the wheel base change any thing ? Much? Just asking because I just acquired a 2 piece GP.
John

Hi, John!

Your GK800 is one of the other karts I tried at Avon in June. It was light and responsive, as was Romero's Brand-X. If it was just your GoKart, I'd write it off as the difference between brands, but the Brand-X is too similar to ignore.

Mine is a two-piece frame. I honestly have never played with the wheelbase. I have always had mine assembled in the longer wheelbase position. With respect to my goal of more responsive steering, that might be a cheap adjustment to play with, too. Al's yellow GP is a two-piece, as well. Maybe he has experience experimenting with that?

-Kurt

How tight do you have your frame mounting bolts behind the seat?

Brian,

As is, the bushings are just tight enough to provide slight compression without being loose enough to spin and slip around.

I have been wondering... If I progressively snug them up, that might begin to apply the jacking effort of the steering geometry more directly to the rear frame, allowing the inside rear tire to lift in a corner. Right now, there is definitely some of that movement lost in the flexibility of the two piece frame. At rest, the inside front tire definitely lifts, but, with weight on the chassis, most of that movement is taken up by the bushings rather than forcing the inside rear to lift.

I assume that the chassis jacking effect manifests itself differently at speed, but I'm not sure what the range of adjustment might be, and to what effect. More opportunities for experimentation.! Al H. is right, there's plenty of opportunities to really complicate things, changing too many things at once!

As of now, I've put on new RobRon spindles, and a full set of Kenda 4.10x3.5 tires on Azusalite wheels. The front and rear track widths are within 3/4" of each other. I have set the tow at about 1/16" out. I hope to fine tune that today!

Tighten the rubber bushings should make the kart push more, we delt with the problem on my brothers grand prix, biggest difference was when we did tires, but loosening the bushing to where you have them now did help.

"If I progressively snug them up, that might begin to apply the jacking effort of the steering geometry more directly to the rear frame, allowing the inside rear tire to lift in a corner."   wrong wrong wrong

arrrrghhhh,  
KURT, you aren't listening to your advise.

a vintage straight front axle , rear engine kart IS NEVER INCLINED TO "LIFT THE REAR INSIDE TIRE" EVER.

You'll only see that when the kart bicycles which you definitely don't want to experience. 
on rears you want the front inside tire to jack up the EXACT OPPOSITE of the more modern space framed karts.
if you do it right it'll lift as much as 3"-4" while the back snaps out in a short slide then digs in for the straight.
you'll more or less pivot on the planted tire.
mind you that kind of driving sometimes takes years to learn and some never figger it out.

to explain , in your mind you make a triangle out of your kart layout .
the narrow end of triangles resist twist while the wider end lifts easily.
that is because the wider end can  exert alot more leverage.
rear karts have wide front =>narrower rear 
space frames have narrower front => wider rear. 
where ever the wider section is it will lift the tire when you do a sharp turn

so to keep it simple 

• karts with a straight front axle needs to lift the FRONT inside tire in a corner.
  
• karts with front y style axles need to lift the REAR inside tire when cornering.
  
  

Understanding that difference is critical if you are gonna do effective, safe modifications to your kart.

early karts were designed to lift the front tire leaving you with full rear steer and only one tire contact in the front wheel.
back then sticky tires didn't exist so they built frames to use what was available to the best effect.
this is called rear steer and this design makes for fast slide cornering.

as the tire grip increased in the mid 70's the karts started acting a bit insane and were modified to run the stickier tires. 
to combat this the rear axles were stiffened by making them bigger diameter and the rear width was changed.
 with that the geometry reversed and new frame designs forward started being designed for stickier tires .

to be fair a rear engined  kart can be modified to run sticky tires.
this is best attempted by someone totally familiar with frame mods and tuning.
it'll then have rear lift but it'll be a twitchy ride requiring alot of skill to keep it in control.

so rules to live by when adjusting

• modern karts are made and run wide rear tracks = adjust for rear tire lift.
  
• straight axle vintage karts run a narrower rear axle with front inside lifting.
  

hope this helps
d