How does weight affect go kart speed?
Many years ago I had to coach a heavier driver with the goal of helping them qualify for the higher powered 9HP karts at Sykart. This would allow them to get out of the 6HP karts and drive the faster 9HP karts. As part of that mission I added weight to my own kart so we could both roll at around 350lbs. Now normally I roll around 200lbs so this was a great opportunity to see exactly what effect an extra 150lbs had on my lap times.
Well as expected, it totally killed my speed. What was unexpected was just HOW MUCH it killed my speed. We quickly realized that Sykarts qualification system that issues a handicap for lighter drivers was disproportionately biased towards lighter drivers. So on behalf of my student I had to go through the exercise of proving it, and had to try and convince Sykart to adjust their weight based ranking system.
Sykart did adjust their qualification system after this analysis.
So the rest of this document is basically the analysis and study as I looked into exactly how weight affects the speed of a go kart and lap times.
If you’ve ever raced at a go kart track, you’ll quickly realize there is something about weight that either helps you or hold you back. I’ve seen many debates about weight, some believe it’s an advantage to weigh more or that being light is a disadvantage. I must tell you, I’m not in that camp. Adding weight will kill your speed, and in this article we’re going to look at how I applied Newtons Kinetic Formulas to explore the effect of driver weight on lap times at Sykart Indoor Karting track during one winter season.
Newtons formulas tell us that any movement requires energy made up of the combination of weight and speed. If something weighs more then it needs more energy to travel at the same speed as something that weigh less.
You might want to apply some of these tricks yourself on your track because just going through the process will give you a better insight about your situation.
How to analyze exact sector times on your go kart track.
The first step was to find a Google Maps satellite image of the building that holds the track. Next was to use a track map and try to scale it exactly to the proportions of the building.
Next I created a scale image in photoshop then imported the image into Geogebra and scaled the image so that 1 unit = 1 meter in real life. This allows very precise measurements of arcs and line segments and you can start to get an idea of the total length of the track and each of its segments.
Here are estimated measurements of the approximate fast line, superimposed over a scale model of the building, taken from Google Earth satellite picture of Sykart
Next I took Go Pro videos of the track, and stepped through the videos one frame at a time. This allowed me to count the number of frames through each section and gave a measurement of the speed in meters per second.
One frame of a 60 frame per second video is 1/60th of a second. By observing the wheels next to marks on the track and by noting hand and foot movements you can get fairly accurate estimates of the time spent in corners and on straights. As you know what the lengths of these sections are you can estimate your speed using time/distance.
By mapping the speeds of each section onto a spreadsheet, I was able to create these charts.
The following charts take into account an analysis of the driving line, using GoPro Video to find the distances and speeds through each section, and then measuring the total amount of acceleration and deceleration per lap. (see Chart 1). The calculations use a driver weight baseline of 160lbs and show how +/- 10lbs affect lap times.
Chart 1: Speeds and G forces of the turns were calculated, and adjusted for driver weight.
This chart shows the range of velocity in m/s, from an average Sykart lap where there are 3 deceleration / acceleration zones, two sharp brake zones and a two phased brake zone at around 18 seconds into the lap.
Creating Time / Weight Charts
Using Newtons kinetic formulas, based upon the energy required to move the mass of driver and kart, we can calculate the amount of time it takes the power of your engine to reach maximum velocity. This allows us to build a chart of expected lap times given the weight of the driver.
Kart weight = 119 kilos (taken from scales)
6.5 hp = 4847.049168 Joules per second Power Capacity of Engine
9.0 hp = 6711.298848 Joules per second Power Capacity of Engine
(Sykart has 2 different kart types, a 6.5hp and a 9hp model)
k = mv²/2 Where k= kinetic energy in joules, m=mass in kg, v= velocity in m/s
1 hp = 745.699872 Joules/second
Whats a good time?
|Driver lbs||6Hp||9 Hp||Above Avg 6.5||Good 6.5||Expert||Godly||Expert 9 Hp|
Becoming 9HP Qualified.
At the time of writing, the Sykart qualification times (given weight) to drive the higher powered karts are. They have created this system of weight brackets to simplify the qualification process. Its actually a very cool setup that lets newer drivers develop their skills in the pursuit of the higher powered club karts. It also makes some allowance for the speed handicap that extra weight creates.
0 – 150lbs = 30.200 lap times or lower
151 – 200lbs = 30.500 lap times or lower
201 – 250lbs = 30.750 lap times or lower
251 – 300lbs = 31.000 lap times or lower
300 + = 31.250 lap times or lower
What the calculations tell us is that if Qualification Times @ 160lbs = 30.500 then the weight adjusted equivalent time for a driver at 250lbs should be 30.500 + 0.950 = 31.45, but because of the Sykart Bracketed Weight Class System, the 250lb driver is actually required to beat 30.750. So there is a relative handicap to the heavier driver of 0.700 seconds. That is, for the 250lb driver it is like being 160lbs and having to hit a 29.8 in order to qualify instead of a 30.5.
While this is a little bit biased and possibly unfair, it should also be noted that beating these times are incredibly easy even if you have average skills.
For a 300lb driver an equivalent weight adjusted time would be 30.500 + 1.477 = 31.977 seconds, etc. But they are expected to hit under 31.000, more than a .9 second handicap difference. This is like being 160lbs and having to beat a 29.300.
The driver at 140lbs would have an equivalent adjusted time of 30.500 – 0.211 = 30.289, so they also are at a little disadvantage to the 160lb driver, but only by about 0.200 so they are not hurt as badly as the heavy driver but they are still like a 160lb driver who has to hit 30.300 instead of 30.500, so there is some handicap.
And a 210lb driver would be 30.500 + 0.528 = 31.028, so they are a little closer to the asked time of 30.750. A difference of 0.278. So it is like being 160lbs and having to beat a 30.200.
The current qual times favour the driver between 150 to 170lbs, and become increasingly more difficult for the drivers above and below this range, particularly those above this range.
While these times are achievable, it must skew the skill levels of the 9hp qualified drivers and the volume of drivers who become qualified must disproportionately skew into the 150lb to 180lb range.
Personally I have found that running 30.3’s at 200lbs is easily achievable in all karts, where you are reasonably on line, under most track conditions and under race conditions I would expect to run in the low 29’s.
30.3@200 is a weight adjusted time of 29.878 @160
Currently we are asking a 200lb driver to run 30.5 – 4.22 = 30.078 weight adjusted times.
But what is the equivalent time to a 330lb driver?
30.078 + 1.700 = 31.778
But currently they are expected to run below a 31.250
The following chart raises the bar slightly to 30.3 for a 160lb driver, then shows a relative qual time for all weights on the blue line. This is the suggestion of where Sykarts Qual times should actually be.
The red line is an Elite driving time, for the 6.5HP karts which is in line with best times of drivers winning league races.
The orange line is an Elite Driving time for 9HP karts, given top league finishes.
Isn’t interesting how differences in weight create a linear handicap?
Here is a Table for Qualification, and Elite 6.5HP and 9HP Times. If you can hit the elite times here then you are in a very special class and could compete nationally. The Qualification times are where you would want to be if you are shooting to be amongst the top drivers.
|Weight (lbs)||Qualified 6.5||Elite 6.5 Times||Elite 9 Times|
|Time Lost to Weight|
|Driver lbs||Low 5m/s||High 10 m/s||Joules to climb||6.5Hp||9Hp||6Hp||9 Hp|
The chart above basically confirms the old theory that for every 10lbs you lose 0.100 seconds per lap.
Possible errors: It doesn’t take into account things like clutch slippage and extra binding in slow corners to heavier drivers, so heavier drivers might actually have even more of a penalty, consider this best case scenario..
If you know driver weights then you can adjust their lap times into a baseline time. If a driver is 230lbs in a 9hp kart, then you subtract 0.533 from their time and you get the 160lb driver time. If a driver is 140lbs in the same kart then you add 0.152 to their lap time.
How much time it takes to go from dead stop to vmax at 11m/s, given weight of driver
|Driver lbs||Driver+kart lbs||Driver Kilos||Driver+kart Kilos||joules at 11m/s||6hp T to vMax||9hp T to vMax|
So at the end of the day Sykart Adjusted their timing requirements and made it easier for heavier drivers to get into the 9HP club up from the 6HP club.
On most tracks I have visited 10lbs will cost you about 0.100 seconds per lap, this is the result of the cumulative effect of the acceleration zones. This is the easy rule of thumb, but if you have more or less corners this could obviously vary quite a lot.
Weight handicaps are real, and for this reason most well run indoor karting leagues will have strict weight requirements and use ballast to equal things out.
This could be a good thing, because the easiest way you can improve your lap times is to lose some weight. Managing your weight becomes a very important part of the sport and hobby of indoor karting. If you are struggling with your weight, you might consider a keto diet and intermittent fasting (I’ll discuss this elsewhere). Keto is insane at stripping the weight off, you can easily strip 0.100 off your lap time every 2 weeks.
I have an article here on site that talks about what you can actually do if you are a heavier driver.
Meanwhile good luck, and I’ll see you on track.