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How to weigh a kart – on the cheap!

We’ve discussed many times before (and will many times again!) how important weight distribution is to kart handling. It’s one of the key inputs to the kart, and yet most people have no idea what the weight distribution of their kart is. Calculating the weight distribution of your kart is pretty straightforward, and you can do it accurately enough with four cheap bathroom scales (which you can pick up for about ten bucks a pop). Make sure you get analog scales (like, the old school ones with a needle). The digital ones are a pain in the proverbial for the purposes of scaling karts.

There are two reasons to scale a go kart:

  1. To calculate the front/rear weight distribution.
  2. To check that the kart is straight and true.

Let’s look at front/rear weight distribution. First, find a nice, flat surface and lay out the scales so you can place the kart on them. Zip tie the brake pedal to the front crash bar to stop the kart from rolling around. Have the driver (fully dressed in race apparel preferably) sit in the kart and assume the normal driving position. Note down the weights at each corner, FL, FR, RL, RR.

I usually try to steer clear of mathematics in this blog (and those who know me well would know how hard that is for me, a natural born maths geek!), but in this case you’re going to have to survive just a little maths! To calculate our weight distribution, note down the following numbers:

(RL + RR + FL + FR) = Total weight
(RL + RR) = Rear weight
(FL + FR) = Front weight

Your rear weight percentage is Rear weight ÷ Total weight × 100.
Front weight percentage is Front weight ÷ Total weight × 100.

Those numbers (rear percentage and front percentage) should add up to 100, and if they don’t then you need to go back and check your numbers again because you’ve made a mistake somewhere along the way!

Now then, you’ve probably heard lots of people tell you that you want to shoot for 40:60 (front:rear) weight distribution in a kart, but the people that told you that were probably the sheep in the paddock that have never actually tested anything for themselves. You should probably ignore the rest of the advice they gave you too!

Here are some guidelines, based on REAL, actual testing, for what your weight distribution should probably be (Note that each figure is only a starting point, and you need to do your own testing to find out what works for your chassis, driver, and tyres):

Midgets/Rookies (Cadets, if you’re overseas) 47:53
National Classes (on SL1 tyres) 45:55
Clubman Classes (on MG Reds) 43:57
125 Classes (on MG Yellow or equivalent) 41:59

As an experiment, try moving a 3kg block of lead around the kart and see how it effects the distribution numbers. You’ll see how sensitive karts really are!

This blog got longer than I thought it would. Come back soon to find out how to use scales to check your kart for straightness.

You might also enjoy:

  1. Weigh your kart for straightness
  2. Seats (Pt 4) – Position
  3. The kart… Just. Won’t. Go!!
  4. Storing and transporting your kart
  5. Seats (Pt 3) – Position

4 Comments

  1. James Head
    26 December 2010

    Are these weight distribution figures based off the Phoenix by any chance? or is that just a generalization of what you should be aiming for?

    I own a 32/32 phoenix stealth that’s 5 and a half year’s old (I’ve only had the kart a year, and I use it in Clubman Heavy on club day’s with no problems), is there perhaps a secret weight distribution figure I should be aiming for in Clubman for the phoenix? or will the 43:57 still be the way to go.

    Another question, will the weight distribution be more critical and maybe perhaps should be changed for drivers that are light, heavy, superheavy, etc etc?

    • Col Fink
      4 February 2011

      They are based off Phoenix to an extent, because I’ve spent so much time playing with those karts. That said, the distribution figures are largely determined by the capacities of the tyres as much as they are by the design of the kart, so my experimentation with other kart brands thus far suggests that the numbers are “fairly” universal.

      My point was mainly that the “60/40″ figure you hear quoted all the time is not really an accurate description of what you’re shooting for, especially when you consider that rear track changes of 0.3% make a noticeable difference to the kart!

  2. Jamie Passlow
    5 July 2011

    If you go to http://www.jp-programming.com.au/freeware.html, there is a free program to do the weight calculations for you. It’s a simple .NET 2.0 program and there is a html version too.

    • Col Fink
      5 July 2011

      Cool, thanks Jamie! :)

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