Vintage Karting Forum

I think I'm going to change up my tires for VKA Oreville. I've been using Vintage Speed tires on my Grand Prix at several events this year. I really like the looks of this combo, but I'm not sure that I chose the correct rear tires for the job.

Having 4" front wheels, I installed the VS 4.10-3.5x4 narrow fronts, but I may have erred on the side of sporty looks when I chose the 11-4.5x5 rears. Admittedly, this is my first season of karting since driving the same machine as a kid in the early '90s, so my line choices, brake points, etc., do lack consistency, but I feel like the kart consistently tends to understeer, and the steering wheel is heavy. I watch others steer crisply around corners, while my driving style has become one of fighting the wheel and using all of the throttle and all of my own mass to break the rear loose in order to negotiate the same corner.

I was offered some advice at TBO this past weekend suggesting that, amidst the shaking, flexing, and bouncing that's going on at speed, that rather than worrying about minutiae of toe adjustment or tire pressure, I need to work on some fundamental issues including using my core and legs to hold myself in the kart, using my arms solely for steering. I absolutely respect that advice, and I will definitely be focusing on those issues, but, having had the chance to drive some other karts this year, I really think something else is at play, too.

So back to tires...

I hypothesize this: I believe the main issue is that the wide rear tires are overpowering the narrow front tires, causing an understeer situation, and what I perceive as "heavy" steering feel is actually my tendency to use the steering wheel as a grip, from which I am swinging my body mass, in order to induce a corrective amount of oversteer. This resulted in at least one close call this weekend, as well as some trimmed grass, when oversteer got the better of me.

My proposed solution is this: I need to redistribute traction by changing tire sizes on the front, rear, or both. I have a set of four Kenda slicks ( two 4.10-3.5x4 & two 4.10-3.5x5) that I picked up at Northern Tool last winter. I could also purchase Cheng Shin tires in those same sizes, or get a pair of 4.10-3.5x5 Duro tires from Vintage Speed for just the rear. Then there's the question of whether to only go narrower on the rear, or also replace the fronts with the wider CS or Kenda options.

So...

(1) I am curious to know what the opinions of those more experienced than me might be, in response to my ponderings above.

(2) Chassis diagnostics aside, does anyone have direct experience and opinions regarding the Kenda tires vs Cheng Shin, or with the combinations of tire fitments that I'm considering?

Thanks in advance for your consideration!

-Kurt

push.. never had it until i put 22 lbs in the front tires
5" rears i only use on my duel's
tk

on rear karts i almost never use more than 4" wide tires in rear.
 i run skinnier fronts sometimes 3" sometimes 2.5"
if you have to much push from rear you can try to up tire pressure.
but best thing to do is go narrower on rear.

you should also check wt on each tire. 
you may have a twist in your frame.
often a twist in the frame will give you fits on the track.
this is especially true if you notice one side being harder to turn in.
d

So, It appears that the solution is that I need to mount a second engine?

Seriously, though, I appreciate your advice, Tom and Dave. While I will look into whether the frame is twisted, the low hanging fruit still sounds like trying narrower rear tires. Obviously, Cheng Shins have been popular in the absence of Carlisles, but does anyone have an opinion regarding the Kenda slicks?

Thanks,

Kurt

(09-03-2018, 10:23 PM)Kurt Bogerman Wrote: [ -> ]I think I'm going to change up my tires for VKA Oreville.  I've been using Vintage Speed tires on my Grand Prix at several events this year.  I really like the looks of this combo, but I'm not sure that I chose the correct rear tires for the job.

Having 4" front wheels, I installed the VS 4.10-3.5x4 narrow fronts, but I may have erred on the side of sporty looks when I chose the 11-4.5x5 rears.  Admittedly, this is my first season of karting since driving the same machine as a kid in the early '90s, so my line choices, brake points, etc., do lack consistency, but I feel like the kart consistently tends to understeer, and the steering wheel is heavy.  I watch others steer crisply around corners, while my driving style has become one of fighting the wheel and using all of the throttle and all of my own mass to break the rear loose in order to negotiate the same corner.  

I was offered some advice at TBO this past weekend suggesting that, amidst the shaking, flexing, and bouncing that's going on at speed, that rather than worrying about minutiae of toe adjustment or tire pressure, I need to work on some fundamental issues including using my core and legs to hold myself in the kart, using my arms solely for steering.  I absolutely respect that advice, and I will definitely be focusing on those issues, but, having had the chance to drive some other karts this year, I really think something else is at play, too.

So back to tires...  

I hypothesize this:  I believe the main issue is that the wide rear tires are overpowering the narrow front tires, causing an understeer situation, and what I perceive as "heavy" steering feel is actually my tendency to use the steering wheel as a grip, from which I am swinging my body mass, in order to induce a corrective amount of oversteer.  This resulted in at least one close call this weekend, as well as some trimmed grass, when oversteer got the better of me.

My proposed solution is this:  I need to redistribute traction by changing tire sizes on the front, rear, or both.  I have a set of four Kenda slicks ( two 4.10-3.5x4 & two 4.10-3.5x5) that I picked up at Northern Tool last winter.  I could also purchase Cheng Shin tires in those same sizes, or get a pair of 4.10-3.5x5 Duro tires from Vintage Speed for just the rear.  Then there's the question of whether to only go narrower on the rear, or also replace the fronts with the wider CS or Kenda options.

So...

(1)  I am curious to know what the opinions of those more experienced than me might be, in response to my ponderings above.

(2)  Chassis diagnostics aside, does anyone have direct experience and opinions regarding the Kenda tires vs Cheng Shin, or with the combinations of tire fitments that I'm considering?

Thanks in advance for your consideration!

-Kurt

I seriously doubt the tires are your problem,,,,since most guys with single engine rears karts run that same combo of Vintage Speeds.....( 4 or 5 in should make no diff on the front, overall height is app the same)

I personally have run the skinny Vintage Speeds on the front ( 2 in and 3.5in) and 4.5 on the rear  on my singles for years,,,Darts, Lancers, Bugs and  Hornets...

play wit tire pressure...usually 12 up front , 14 in the rear works  ( for me)

width of rear axle could be the problem????

bent chassis,,,????

don't waste your time and money on Kendas ( hard as a freakin rock)

my 2 cents worth
gw

Kurt - my experience has been that it doesn't take much of an imbalance in the weight distribution to have a very large effect on the handling. If you want to check yours out and feel up to a ride to the shore, I'd be happy to get the scales out and give you hand with it.

Bill.

All good advice. My G/P has always had that same combo of Vintage Speeds and handled close to neutral, for the most part. This past weekend I had the smaller Cheng Shins on there without the rear wheel spacers. and the kart seemed to like the narrower rear track width better. It was looser, and fun to drive with the oversteer but the tires sure took a beating. Probably could have got it neutral with pressure adjustments, but didn't fool with it. Was just having fun. I would suggest trying whatever tire combinations you have. Play with widths, pressures, and sizes etc. It's the only way to know for sure. Plus, you'll get real good at humping tires! Have fun....

The old n1ke has had Vintage Speed 4.10-3.50 X 4 narrows up front with Cheng Shin 4.10-3.50 X 4 regular width on the rear since it was new.
4" Go Powers all around with 1/2" spacers in the rears. 
It is as close to neutral as a single rear can be. 
19-21 PSI front and back. 
It's happy. 

 The new Photon is also neutral with 3.40-3.00 X 5 Cheng Shin narrow fronts, 4.10-3.50 X 5 Cheng Shin regulars in back with 1/2" spacers. 
CT Alloy wheels. 
 A BUNCH depends on weight distr. and front end numbers. 

I run almost the same pressures in the Photon with 5" wheels as in the n1ke with the 4" wheels. 
Both are 12° caster, 7° KPI, 0 to -1° camber. 
Oh, yeah, the 4" narrow Vintage Speeds wear like iron. 

TJ

all right on advice  ; 
   1) especially cking rear axle width.
    2) 1/4" diff.  save your $$=  Just pump up rear tire to 20 psi , front 8psi . with 20psi you'll have a smaller ground patch(narrow tire) you'll prob spin out, then  go down rear psi. from there.. 
    3)  Bent frame = Do the cheap tire jack. find level area ,lift front left &Rt. tires each one should have equal jack weight..other wise bent frame..
    4) Driving= blip throttle--->brake---> hit apex-----> throttle down...have fun..thk/u. gus..

Kurt,
My 63 GP had VS 4" on the front and CS 4.5x11.5 on the rear (no longer available)
My grandson's 65 GP has the 4.10x350 on the rear and 3" wide 5" fronts.
Both karts handle like a dream, like they are on rails. I have alsu used the VS 450 rears and they work great also.

First, do the front wheel lift trick like Gus said to see if the frame is fairly straight. If not you might be able to compensate with different rubber spacers on the front/rear frame sections unless your's is a one pice frame(I can't remember)

An important thing with Rupp karts is that you need to have neutral or 1/16" Toe Out in the front, it makes a big difference over any toe in. Rupp factory specs are 0-1/16" toe out so give that a try and mess with those tire pressures.

Also, make sure your rear axle is no wider than 36" overall and 32" shoulder to shoulder.

If the frame is twisted badly there isn't much you can do to make it handle, I had one like that and it was a fight to drive around left turns and easy on right turns.

Just my two cents,
Scott