Sale ends todayGet 30% off any course (excluding packages)

Ends in --- --- ---

False upshifts in data under braking

Professional Motorsport Data Analysis

Forum Posts



Tech Articles

Discussion and questions related to the course Professional Motorsport Data Analysis

= Resolved threads



I'm experiencing false upshifts in the data during braking. This happens even when the clutch isn't depressed or gears are changed. Any ideas? I believe I set the gear calculation correctly (speed/(rpm/1000)).

Attached Files

Can you post the logging or at least a screen capture with the Drive Speed and Engine Speed channels visible, not seeing the channels that are used to generated the gear position value makes it difficult to diagnose.

Of course, see attached.

Attached Files

This isn't a motorcyle, with an over-run clutch to reduce rear tyre lock-up?

Engine and wheel/gearbox output should be directly proportional in each gear and if not it would suggest some sort of slippage or sensor error?

Hmmm, if the output/wheel sensor is on one wheel, it may be dragging slightly under very hard braking - reading slower than the engine which would be effectively reading the average wheel speed?

Your engine speed is dropping at a non linear rate to your vehicle speed, this is causing the calculation to go out.

Ryan by Stephen Dean, on Flickr

It's a RWD circuit car. I think it could be rear lockup? I don't have wheel speed sensors to confirm. Speed is from GPS.

You could try a little more front bias and see if that makes a difference?

Maybe back of the rear's low speed rebound, it the dampers allow that?

Well, GPS speed is always slightly delayed (i.e. you JUST WENT XXX km/h), usually this is pretty accurate, but when the speed is changing rapidly, it always lags. There is a "Corrected GPS" calculation in I2 that may help -- or you just learn to use it for what it is. Or fit a rear drive speed sensor to your drive shaft if you are going to calculate the gear ratio.

I think that's pretty common, I get that in mine a lot, it's just the nature of calculated gear.

The only solution I know of, is to increase the gear detection delay. You want that to be just long enough to prevent the false calculations, but not so long as to cause lag in the detection. There's going to be a sweet spot there somewhere.

I had a chance to look at your data. Based on that, I would be using the following values for the Gear Table:

Gear Value

2 11.5

3 14.2

4 17.7

5 21.4

6 24.7

We usually reply within 12hrs (often sooner)

Need Help?

Need help choosing a course?

Experiencing website difficulties?

Or need to contact us for any other reason?