How does weight affect go kart speed?

Introduction

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.

Given
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)

Formula

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
80	-0.844	-0.609	28.956	28.456	27.956	27.456	26.791
90	-0.739	-0.533	29.061	28.561	28.061	27.561	26.867
100	-0.633	-0.457	29.167	28.667	28.167	27.667	26.943
110	-0.528	-0.381	29.272	28.772	28.272	27.772	27.019
120	-0.422	-0.305	29.378	28.878	28.378	27.878	27.095
130	-0.317	-0.229	29.483	28.983	28.483	27.983	27.171
140	-0.211	-0.152	29.589	29.089	28.589	28.089	27.248
150	-0.106	-0.076	29.694	29.194	28.694	28.194	27.324
160	0.000	0.000	29.800	29.300	28.800	28.300	27.400
170	0.105	0.076	29.905	29.405	28.905	28.405	27.476
180	0.211	0.152	30.011	29.511	29.011	28.511	27.552
190	0.317	0.229	30.117	29.617	29.117	28.617	27.629
200	0.422	0.305	30.222	29.722	29.222	28.722	27.705
210	0.528	0.381	30.328	29.828	29.328	28.828	27.781
220	0.633	0.457	30.433	29.933	29.433	28.933	27.857
230	0.739	0.533	30.539	30.039	29.539	29.039	27.933
240	0.844	0.609	30.644	30.144	29.644	29.144	28.009
250	0.950	0.686	30.750	30.250	29.750	29.250	28.086
260	1.055	0.762	30.855	30.355	29.855	29.355	28.162
270	1.160	0.838	30.960	30.460	29.960	29.460	28.238
280	1.266	0.914	31.066	30.566	30.066	29.566	28.314
290	1.371	0.991	31.171	30.671	30.171	29.671	28.391
300	1.477	1.067	31.277	30.777	30.277	29.777	28.467
310	1.582	1.143	31.382	30.882	30.382	29.882	28.543

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.

	29.200	28.450	27.250
Weight (lbs)	Qualified 6.5	Elite 6.5 Times	Elite 9 Times
80	28.356	27.606	26.640
85	28.409	27.659	26.679
90	28.461	27.711	26.717
95	28.514	27.764	26.755
100	28.567	27.817	26.793
105	28.620	27.870	26.831
110	28.672	27.922	26.869
115	28.725	27.975	26.907
120	28.778	28.028	26.945
125	28.831	28.081	26.983
130	28.883	28.133	27.021
135	28.936	28.186	27.060
140	28.989	28.239	27.098
145	29.042	28.292	27.136
150	29.094	28.344	27.174
155	29.147	28.397	27.212
160	29.200	28.450	27.250
165	29.253	28.503	27.288
170	29.306	28.556	27.326
175	29.358	28.608	27.364
180	29.411	28.661	27.402
185	29.464	28.714	27.440
190	29.517	28.767	27.479
195	29.569	28.819	27.517
200	29.622	28.872	27.555
205	29.675	28.925	27.593
210	29.728	28.978	27.631
215	29.780	29.030	27.669
220	29.833	29.083	27.707
225	29.886	29.136	27.745
230	29.939	29.189	27.783
235	29.991	29.241	27.821
240	30.044	29.294	27.860
245	30.097	29.347	27.898
250	30.150	29.400	27.936
255	30.202	29.452	27.974
260	30.255	29.505	28.012
265	30.308	29.558	28.050
270	30.361	29.611	28.088
275	30.413	29.663	28.126
280	30.466	29.716	28.164
285	30.519	29.769	28.202
290	30.572	29.822	28.241
295	30.624	29.874	28.279
300	30.677	29.927	28.317
305	30.730	29.980	28.355
310	30.783	30.033	28.393
315	30.835	30.085	28.431
320	30.888	30.138	28.469
325	30.941	30.191	28.507
330	30.994	30.244	28.545
335	31.047	30.297	28.583
340	31.100	30.350	28.621
345	31.153	30.403	28.659
350	31.206	30.456	28.697
355	31.259	30.509	28.735
360	31.312	30.562	28.773
365	31.365	30.615	28.811
370	31.418	30.668	28.849
375	31.471	30.721	28.887
380	31.524	30.774	28.925
385	31.577	30.827	28.963
390	31.630	30.880	29.001
395	31.683	30.933	29.039
400	31.736	30.986	29.077
405	31.789	31.039	29.115
410	31.842	31.092	29.153

						Time Lost to Weight
Driver lbs	Low 5m/s	High 10 m/s	Joules to climb	6.5Hp	9Hp	6Hp	9 Hp
80	1,932	7,728	5,796	1.196	0.864	-0.844	-0.609
90	1,989	7,955	5,966	1.231	0.889	-0.739	-0.533
100	2,046	8,182	6,137	1.266	0.914	-0.633	-0.457
110	2,102	8,409	6,307	1.301	0.940	-0.528	-0.381
120	2,159	8,637	6,477	1.336	0.965	-0.422	-0.305
130	2,216	8,864	6,648	1.371	0.991	-0.317	-0.229
140	2,273	9,091	6,818	1.407	1.016	-0.211	-0.152
150	2,330	9,318	6,989	1.442	1.041	-0.106	-0.076
160	2,386	9,546	7,159	1.477	1.067	0.000	0.000
170	2,443	9,773	7,329	1.512	1.092	0.105	0.076
180	2,500	10,000	7,500	1.547	1.118	0.211	0.152
190	2,557	10,228	7,671	1.583	1.143	0.317	0.229
200	2,614	10,455	7,841	1.618	1.168	0.422	0.305
210	2,671	10,682	8,012	1.653	1.194	0.528	0.381
220	2,727	10,909	8,182	1.688	1.219	0.633	0.457
230	2,784	11,137	8,352	1.723	1.245	0.739	0.533
240	2,841	11,364	8,523	1.758	1.270	0.844	0.609
250	2,898	11,591	8,693	1.794	1.295	0.950	0.686
260	2,955	11,818	8,864	1.829	1.321	1.055	0.762
270	3,011	12,046	9,034	1.864	1.346	1.160	0.838
280	3,068	12,273	9,204	1.899	1.371	1.266	0.914
290	3,125	12,500	9,375	1.934	1.397	1.371	0.991
300	3,182	12,728	9,546	1.969	1.422	1.477	1.067
310	3,239	12,955	9,716	2.004	1.448	1.582	1.143699

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
80	340	36	155	9,350	1.929	1.393
90	350	41	159	9,625	1.986	1.434
100	360	45	164	9,900	2.043	1.475
110	370	50	168	10,175	2.099	1.516
120	380	55	173	10,450	2.156	1.557
130	390	59	177	10,725	2.213	1.598
140	400	64	182	11,000	2.269	1.639
150	410	68	186	11,275	2.326	1.680
160	420	73	191	11,550	2.383	1.721
170	430	77	195	11,825	2.440	1.762
180	440	82	200	12,100	2.496	1.803
190	450	86	205	12,375	2.553	1.844
200	460	91	209	12,650	2.610	1.885
210	470	95	214	12,925	2.667	1.926
220	480	100	218	13,200	2.723	1.967
230	490	105	223	13,475	2.780	2.008
240	500	109	227	13,750	2.837	2.049
250	510	114	232	14,025	2.894	2.090
260	520	118	236	14,300	2.950	2.131
270	530	123	241	14,575	3.007	2.172
280	540	127	245	14,850	3.064	2.213
290	550	132	250	15,125	3.120	2.254
300	560	136	255	15,400	3.177	2.295
310	570	141	259	15,675	3.234	2.336

Conclusion
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.

Heavy.