Understeer. Tires?

[thomas kelley]

two engines cures all issues with traction front or rear lol
unless you are fat like me lol
tk

[steve welte]

4.50 vintage speeds aren't the problem. You do need to run the heck out of them until the outside square edge starts to round. Rupps are narrow in the front so rear width is critical. I currently use Kenda's on the front of all the karts since Chen Shin stopped producing 11/4.50/5. by the way a durometer check will show the Kenda's at 72 and the VS at 78 to 82. Personally I want my kart to drive through the turns without all the sliding around. Get enough power and speed and yes it breaks loose but not to the point of what some people think. I would suspect you may have a twist in the frame (not uncommon). Rupps with their geometry do not steer hard. Drive them with one hand in some cases.

[steve miller]

all good reading ...I usually cant tell if i have a push my stuffs so slow 8 outta 10 times I come off track at least one tire is always flat if not two ..!!!  hell I cant tell no difference ..sometimes it makes my karts seem better ..Lol..

[Kurt Bogerman]

Definitely many years of experience represented in these replies! Thanks, guys. I'll try to sort this out as much as possible before VKA Oreville, and I'll reply with the results. Fortunately, the kart still gets around a track, as is. I think I wouldn't be happier if it was perfect, because there'd be nothing to do, try, research, or discuss. But it's by no means perfect, hence the research, discussion, and experimentation!

In the next several days, I hope to bring the kart to work, where we have a nice, level, concrete floor, upon which I can take some measurements and analyze the frame situation.

Speaking of low hanging fruit... One thing that I noticed recently, but failed to acknowledge, is the fact that the steering arm of the RF spindle is bent. I think it has always been bent, but it's subtle, and I hadn't compared the two closely together to see the difference until recently. Realizing the significance of this, now, I contacted Mr. Stanton at RobRon, today, and he's sending me a pair of new spindles and a new steering shaft. The spindles are going to be ones with longer axles, so I'll have the option to space out the track width (in addition to correcting the steering arm geometry by simply not being bent!). The steering shaft is mostly an aesthetic concern (mine has rust pits in it), but it'll hopefully be clocked straighter than my original, too, which is just a minute or two off 12:00 no matter which way the hub and steering wheel are clocked. Obviously this will also be my opportunity to revisit the toe adjustment.

Also... My rear axle is an Azusa Flexpruf: 36" overall length, 32" shoulder to shoulder. This is 1" wider, shoulder to shoulder, than the axle that the kart had when I bought it. I have realized, since posting in an axle thread elsewhere (commenting about how mine was fine), that my Flexpruf axle does have some oscillation to it. I haven't measured it, but I've noticed that the engine rocks up and down slightly when it's running on a stand, so that axle will be replaced sooner than later. This begs the questions: Should I space out the front track by an inch, or any other amount, and continue to sport a 32" axle, or should I order a replica of my original 31" rear axle? Or both?

There's so many areas where, I'm realizing, there are opportunities for improvement. I have mixed feelings about that, but at least I can continue to pursue improvements and optimizations.

Thanks again, everyone, for all of your advice and consideration.

Kurt

[thomas kelley]

try to square up the front and rear track... with in a 1/2 inch you are good
azusa axles suck
go to the 4.50 tires and space them out so they are stretched a little
that my .02$
tk

[David Luciani]

first 
steve m,
you need to actually load a kart with a little excess wt before steering geometry gets to be an issue.
you'll never have a wt problem but still it would be nice if you invested in a few tires that hold air.
just sayin!  

kurt,
just trying to put the kart into a good track condition is an excellent mind set.
asking the guys for advise is a good idea too.

if it was me i'd do a search to find a good home brew method checking tire wts on each corner .

• one method , as i recall , hook a fish hook type scale to each tire . 
  
• place a sheet of paper under the tire and lift tire with fish wt. scale
  
• when the paper was able to be slid out you had your tire wt.
  

by scaling each tire corner you 'll be able to find a twist if it's there.

a  bent rear axle is more of engine damage /chain throw type concern but can screw up steering too.

d

[steve miller]

remember wide to slide ..!!
with an inch wider rear than you had it should have freed up chassis a little more not tighten it up ..
blow up the rears and pitch it in the corners ..it wont push ...lol..

david ., my 57 year old tires work great its the 2 lbs air in them and having them rolled under till the rims run on the ground that the tubes don't like ..lol..

[Kurt Bogerman]

Well... Part of the issue with comparing the kart's past performance to the present is the 25 years in between experiences!

On a funny note, one mistake that I made back in the day, after burning off the Carlisles that it came with, was to order up a set of 11x6-5 Super Slicks along with a fresh set of 4.10x3.5-4 fronts. Worse than the excessive size of the rears that I demanded, the tire shop ordered in sawtooth tires for the front rather than slicks. Talk about push! No front traction at all, and sticky steam rollers squeezed onto the stock width rear turbines! Did. Not. Turn. The burn of that experience probably has a lot to do with my suspicion of the somewhat wide rear tires that I'm running now: I'm afraid that I'm making the same mistake all over again. I guess I should take comfort in the general opinion that I'm making completely different mistakes this time, lol!

I had an interesting conversation with a co-worker who runs with his son in the Legends series. He re-explained some of these chassis concepts in a way that resonated with me, so I have some clearer ideas about what to look for when I get deeper into this analysis.

I did find an interesting article about chassis scales here:

kartdrome.com/index.php/technical-documents/how-to-weigh-your-kart

Without having a lot of chassis adjustment available on most vintage era karts, a lot of the info contained in that article is academic, but it is definitely interesting.

Thanks again guys,

Kurt

[ted johnson]

Weight jacking. Once you use Dave's fish scale-paper under the tire solution to determine diagonal weight bias, we always put the heavy front tire on a concrete block lying on its side, then piled about three guys on the light front axle and tire and we all jumped up and down on it. We kept it up until the front end weight was equal. It sure looked funny! It works fine with chrome moly. Don't know how well it'd work with mild steel or Shelby tubing. I remember a guy in Kissimmee, FL, permanently ruining his nearly new Rupp Mean Machine Sprint that way. The tubing bent like spaghetti. TJ

[Al Hasenfratz]

remember wide to slide ..!!
with an inch wider rear than you had it should have freed up chassis a little more not tighten it up ..
blow up the rears and pitch it in the corners  ..it wont push ...lol..

david ., my 57 year old tires work great its the 2 lbs air in them and having them rolled under till the rims run on the ground  that the tubes don't like ..lol..

My yellow kart understeered with a 36 axle, which is what it had when I got it. When ordering tires from our friend Gus, he suggested the narrower 34 axle and to not lock down the rear frame cushions so tight so the frame could flex more. It really helped. But it never pushed bad enough to give me blisters like Kurt showed me! He gets an "A" for effort! And I have no doubt he'll get it worked out. Now I'm curious how mine will scale out because I never weighed it.