Mychron 5S 2T - GPS speed accuracy

Ok I dug up my sheet from 2021, I ran one test using someone’s old MyChron expansion setup and only had enough length to get it to the Right Front wheel, so its not perfect, but here’s one lap of G&J Kartway A-Config with wheelspeed sensor vs MyChron 5S GPS.

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Definitely worse than I remembered, but in the end I’m not racing Nationals here, so I decided it was fine enough.

I think that show error more than tire size change. Sometimes at slower speeds the wheel is faster. Sometimes the wheel is slower. If wheel expanded at speed it would always increase relative to GPS at lower speed

May the difference be related to the sensor being on the front right instead of the rear axle? Visible difference is only at low speed, at higher speed on the straights it’s really minimal.
Sometimes GPS is higher and sometimes axle is higher: may it be related to turn direction and front right being on the inside or outside of the turn? Front wheel are not axle connected so they are free to rotate at their speed.

That was my first thought, too. @Bokeno_Racing i am not familiar with that track, so does it look like the tire was measuring a farther distance around the outside of the track (ccw)?

In my clutch slip thread, I’ve wondered about this same error, so I’m going to write up a turn radius calc to compensate. If I get anywhere with that, I’ll post the relevant stuff here

Yeah I definitely think that’s part of it. Some long, big radius corners to build up that error, and a very very tight final chicane where there’s bound to be some mismatch

G&J A-Config reference:

This depends on the duration of top speed segments for a given track, as well as the length of a race/drive session.

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I can see how having the sensor on a front wheel would diverge the two measures (GPS vs Wheel Speed), but then why does it diverge at the end of every braking zone? In reality the outside front tire always travels further than the inside front. Is the act of braking and weight shift compressing the tires also affecting the measurement? Could you flip the sensor to the other front wheel and average the two readings to see how much they diverge from the GPS? Given the area under the curves between braking zones 3 and 4 are very similar and being two different directions, leads me to believe that GPS is pretty close.

Andy,
TM KZ R2
14,600 rpm
17/23 gear
5s2t GPS. 85mph
Calculated 93mph

Pretty big Delta……gps latency ???

Cheers,
Bill Gillespie
Lake City, Fl

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Could be a tire circumference difference but I’m getting a different top speed. I confirmed the ratios and primary are the same as the R2.