Need high-speed GPS vs MPH confirmation

[bwilson4web]

Hi,

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

[grahamy]

Originally Posted by bwilson4web

Hi,

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.

Thanks,
Bob Wilson

Trust the trip meter average rather than the readout. Lacking GPS and having only a Tomtom GPS I find a cosistent mph readout 2 mph less. It has to be more accurate -- confirmed by other GPS systems I've used. Toyota just wants to save us speeding tickets.
Or have I missed something here?

grahamy

[bwilson4web]

Originally Posted by grahamy

Trust the trip meter average rather than the readout. Lacking GPS and having only a Tomtom GPS I find a cosistent mph readout 2 mph less. It has to be more accurate -- confirmed by other GPS systems I've used. Toyota just wants to save us speeding tickets.
Or have I missed something here?

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

[qbee42]

Originally Posted by bwilson4web

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

It's not unusual for a GPS system to post high peaks. What happens is the GPS misses a fix, so when the next one is calculated the position has moved farther than expected. The peak speed is higher than expected, but the average is okay. We see this quite frequently when hiking in the woods, where trees disprupt the GPS signal. Sometimes my maximum speed will be 20 mph, which is a tad fast for walking.

Tom

[WPWoodJr]

The GPS peak could be due to an inaccurate location reading. It depends on how often the GPS reading is taken. The more often its taken, the more a slight inaccuracy will skew the results.

[bwilson4web]

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