Scaling a Kart - How to get rid of cross wt and balance it

Brian Degulis · Posted: Sun Dec 30, 2012 7:28 am Post subject:

Is the 43/57 ratio from front to rear a guide for all karts? Is the goal to get as close as you to equal weight side to side? Is the seat ever moved side to side to acomplish that?

Brian

kyle luttrell

Chris Parks · Posted: Mon Dec 31, 2012 7:05 am Post subject:

Dan Haynes · Posted: Mon Dec 31, 2012 9:23 am Post subject:

We need about 30lbs. of lead to make weight. I typically scale it adding only about 20lbs. to get close to the 43/57. After that we go to the track and see how the handling is and add the rest as needed based on handling. We often move weight around from one weekend to the next, and sometimes from morning to afternoon, depending on conditions.

Like Chris said, there is no magic number. Those are guidelines to get you started. We have run as low as 41% on the front and it handled great.
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Blaise Haynes
#3 Arrow X1-CIK
TaG
Cook Racing Engines Parilla Leopard

Eric Alexander · Joined: 19 Jun 2011 Posts: 121

I like to think of it like this: numbers give you a reference point but the handling is the main point. Its alot like tire pressures, you fine tune the kart with tire pressures using past settings as a start reference - not absolutes.

Data like tempertures, pressures, and corner weights are all numerical references to further understand tuning and help make adjustments. But the chassis handling is the main focus - not the numerical data. The handling drives the changes. The data is merely a reference scale along the way.

Tony (Toe-Knee!) Morrison · Joined: 15 Nov 2007 Posts: 28

These suggestions are plausible solutions, but seat position will not cause opposite diagonal corner weights to be high/high. Seat position will make diagonals high/low. -Before you make any changes, make your BEST effort to determine WHY the corners weights are 'off'. Possible causes include; axle height is asymmetrical (high/low on one side), spindles are not installed symmetically, a bent spindle, or the frame is bent... -When you take it apart, to move it into your basement, do a complete examine of the whole chassis for cracks, bends, etc. Lay the unassembled frame, on something flat. Look at the frame rails; they should be flat, on that 'flat' piece. (It doesn't need to be level, but it MUST be flat). While the chassis is on the 'flat', measure from the 'flat piece' to the spindle mounts.
- After you reassemble the chassis, measure from the axle to the bottom of the frame rails. You might install your SPARE spindles, to see if that helps. -Do a thorough analysis, and you will find the cause, which will allow you to fix it with the least amount of labor, and cost. -Have fun, you will learn something, and save yourself some money! (Which can be spent on more toys!)
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-Toe-Knee!

Brian Degulis · Posted: Mon Dec 31, 2012 12:28 pm Post subject:

Thanks I'm working on a Top Kart that I put a CRF250 on so the engine is heavier than a typical shifter. I'm 175 lbs and here is what I get for weight distribution this is me my gear and around 50% fuel.

LF 87 RF 92 LR 128 RR 132

The kart handles OK I'm just having some trouble on a hard right hair pin. If I push it a little to hard it hops or jumps in the rear and trys to break my ribs. I haven't done anything other than a rough basic set up on the front end. Tires are Vega whites.

Thanks

Brian

kyle luttrell · Posted: Mon Dec 31, 2012 1:18 pm Post subject:

kyle luttrell · Posted: Mon Dec 31, 2012 1:23 pm Post subject:

Eric Alexander · Joined: 19 Jun 2011 Posts: 121

Brian Degulis · Posted: Mon Dec 31, 2012 2:51 pm Post subject:

Good info one of those threads is one I started dealing with a 125 shifter. I removed some castor and that solved the problem. I guess I wanted to start with weight distribution because of the engine weight and side to side seat position required to clear the wider engine. I weighed after changing the seat and seat position. I think I had more weight in the rear than I do now so I guess I should try it before doing anything else.

This 4 stroke engine has less RPM than a 2 stroke and an enormous amount of torqe. I'm just getting this kart set up and I know I'm geared wrong. I'm 17/24 and I'm done shifting and @ 12500 RPM half way down the straight. I put a 23 on and ordered 22thru 20. This kart jumps around 3/4 thru the turn pretty much when I'm accelerating out of it. Do you think it might be momentarily breaking free on acceleration and then grabbing? It's all new to me does that make any sense?

Brian

Dan Haynes · Posted: Mon Dec 31, 2012 3:26 pm Post subject:

Kyle,
I understand all of that. When we run in high grip conditions we usually have less front weight. Cooler, slicker conditions we usually have a little more nose weight and sometimes raise the lead up a little.
_________________
Blaise Haynes
#3 Arrow X1-CIK
TaG
Cook Racing Engines Parilla Leopard

Chris Parks · Posted: Mon Dec 31, 2012 5:46 pm Post subject:

As a general rule hard numbers are only a reference after you have gotten the kart working how you want it. If it is hopping out of one corner it has a problem and if that problem if fixed then it will be better to drive everywhere else as well, you just don't recognise that due it not actually hopping on those other corners. There is a mountain of information in this forum but it is not recent, in fact you have to go back to near the beginning and it only lasted a few years. Take the time to read and understand it and you will have a better idea of how kart dynamics work, either that or you will be totally confused.
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understeer happens on road courses and usually is pronounced with a British accent. Push happens on ovals and usually is pronounced through a wad of chew. Other than that, I don't think there's a difference - Jim Derrig

Chris

Brian Degulis · Posted: Tue Jan 01, 2013 8:44 am Post subject:

I've done that. I've also searched elsewhere and this is one of the best references I've found http://www.crg-america.com/pdfs/CRG_Kart_Tuning_Manual.pdf I still like hearing ideas from both the experienced and the novice. After 27 years of building tug boats I've learned that good ideas can come from both.

Brian

Ambrose Buldo · Posted: Tue Jan 01, 2013 2:02 pm Post subject:

Well.. I too took the kart apart, gave it a good cleaning and re-assambled. I confrmed rear axle hieight is same both sides. I confirmed rear axle is straight andsymetricial.

I then moved seat forward about 1". I also reduced seat back angle a bit (Leaned more forward). I am about as far forward as I can be while still being comfortabe.

I also put brand new equal circumfance rain tres on # 20 PSI

So I started out before moving seat with 84 65 = 149 40%
99 123 60%

This gave me 83.5 69 - 152.5 = 41.1%
99.5 119 = 58.9

Then I went to the Left spindle where I had washers above and 2 washers below (same on other side) and switched the left front to 1 above and 3 below. This netted the fllowing

70 84 = 154 41.5%
112 106 58.5%

Suggestions? While better, I really do not like the the sindles in front set uneven;y.
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Ambrose Buldo - AKA Racer27
Old Tappan, NJ 07675
Current: Citation FC2000 (For Sale), Madza RX8, VW Eos
Kart for myself: Intrepid Silverstone Pro w/HPV3 --- With a ROK TAG engine waiting in wings
Kart for Daughter: 2001 Birel ARC-100