Need high-speed GPS vs MPH confirmation

I did some regression, hill climb testing and found:

• 85 mph indicated - 83 mph Trip B average speed
• 90 mph indicated - 88 mph Trip B average speed
• GPS indicated 96 mph was maximum speed

So now I'm really confused. I've seen the trip meter average speed come in at 1 mph under ordinary speeds. But this was the first time I had occasion to do high-speed runs up the hill and found the trip meter registered a lower average speed than the indicated.

I am working on reading the GPS trip log to see if I have enough data to compare the two. I may go out and try again Saturday morning, when the temperatures are closer to 70F, to see if I can replicate these results. But I thought I'd ask the community.

If you have a GPS unit and opportunity for high-speed tests, 85 mph or higher, see if you can find any evidence of a difference between the trip meter average speed, indicated and GPS. Given the high speeds, please be careful and since this is a holiday weekend, please don't annoy the police.

There is no great rush on this, so carefully folks, carefully. If you can, have a co-pilot do all of the data collection or set-up a video camera to take all of the measurements. Nothing should distract you from handling the car safely.

Thanks,
Bob Wilson

 

The indicated appears to read 1 mph higher than true. The trip meter reading a little low, OK, I can buy a 2 mph difference. But the GPS peak has me wondering.

Bob Wilson

 

Thanks,

I just finished analysis of the GPS track and the trip meter agrees with the GPS data. I'm happy and have updated my hill-climb chart:


So this is consistent with my earlier results showing Shell 87 having higher energy content than Shell 89. Sad to say, I don't have straight gas values but straight gas is getting harder and harder to locate. Regardless, I'm reasonably happy with these results.

Bob Wilson