Modern Vespa

In the technical forum, both Jess and I have done GPS comparisons of our speedometers vs actual speed as verified by GPS. I realize that either of us could be off a little, so I'm not holding too much to the accuracy until I can get two scoots together, two GPS mounted on them, and then a passenger to take better readings. But until then, what we have is what we have.

I've made a chart and table showing both scoots overlapped. Curiously, Jess's starts further off than mine, but gets closer the faster he goes.

Has anyone else done this, and if so, how about adding to the data. Find a nice deserted flat location, hold a steady speed (it takes a couple seconds for the GPS to average out) and fill the chart out on the spot. Take a couple runs to verify your reading, and if possible, add a navigator to help.

Jess, I'm running about 4 pounds more air in my tires than recommended, which will ever so slightly add to the rolling radius. How about you?

Steve,

I was running about 1 psi over in each tire. Well warmed up, too -- didn't start doing measurements until I had done about 30 miles or so.

Jess

Ah, yes, my tires were warmed up, too, but not 30 miles worth. Maybe 10, though.

Someone replied to my GPS thread on another board that the Vespa Speedo is some sort of magnetic induction system, but I don't know how this effects any error. I'm used to dealing with cable driven speedos.

Comparing just my GPS numbers to the speedo, the error seems to be a straight ratio throughout the scale. I would expect that, given enough accuracy, I would see the same error ratio through the lower end of the scale as well.

My error could easily be something as simple as a poor measurement of the wheel circumference, i.e. they measured it with a different kind of tire. Yours seems to be correct up until 20 mph, which seems harder to explain.

Well, I didn't check lower than that. It could actually be higher than the GPS at 10 and 15 MPH. Mine doesn't look like a straight line, either, which could be an error in reading on my part, or not waiting until the GPS caught up.

That would be very interesting. So, are you going out to do more "research" tomorrow?

Ummmmm, no! (You California people... )

Doh! I forgot all about that whole "Ohio" thing. Bummer.

Difficult to quantify how much of an overall effect it would have on you results, but if you don't mind me asking, what's the "range" of your respective rider weights?

By the way, awesome stuff.

Good point! It could theorectically effect rolling radius. This would be a negative to the positive effect of having a navigator for more accurate readings. I guess I need to use a digital video to record the results.

I'm on the LX 150 (a 225# scooter) and weigh 175#

I'm on the GT200 (which is 310 pounds) and weigh, um, north of 200.

"I guess I need to use a digital video to record the results."

Careful--lazy people like me are always ready to take advantage of someone like yourself who's willing to do the work.

I hope you are patient! Scroll up to that weather forecast screen copy. It's getting cold here, with a possibility of wet snow this week. I'm getting pretty close to being done for the season other than those once a month nice days. Once the salt is on the road, the scooters and MG are parked until the second heavy rain in the spring.

Today was the first day I didn't ride the scooter to work since October 6.