What's your fuel mileage usage like?

[don_vanecek]

Well now you got me worried, guess I'll have to see what it does at the higher speeds, at this time the other riders-were I in the lead-would tell me I was pretty much always five over. Lets see now, where were the local cops putting their radar trailer, you know they have these small trailers with a flashing sign telling you your speed, saw it about two days ago or so..... 

Actually I think it stays pretty constant, I don't find myself zooming past the traffric around me-usually I'm just going with the flow-as most everyone around here seems to drive 5 to 10 over.   

[Cdnlouie]

For speeds under 60 your only going to be about 5-8mph over, and most of those speed radars are in the slower speed zones, so pretty hard to tell or hold a consistent speed.  A GPS will confirm, and it makes sense that the more revolutions your wheel spins the larger the discrepancy, so normally it is not a problem for any legal limits, but a very good thing to keep in mind if you are pushing the limits and relying on your speedo for accuracy.

Hey...any good riding out your way?  I am planning a western trip next summer and might scoot through your territory.  We can test your speedo accuracy  :D.

[don_vanecek]

Well you know, small hills, corn fields, bean fields, loss hills on the Iowa side, come on by!

OK, so who is our math wiz, Vision in 5th gear, rear tire Avon 110/90, speedo says 60 tach says 5400, what is real speed, next quiz, Vision in 5th gear, same tire, speedo says 70, tach says 6300, real speed is ??. 

Fudge factor, sort of tricky to keep speedo exactly on speed and look at tach and of course the road-so tach reading could be 100 plus or minus. 

Common, this should just be a math problem, we need the Visions final gear ratio, circumferance of tire, we know the engine speed, there figures should all be on the internet someway, common math wiz!   

[Cdnlouie]

Don...next time I'm out with the GPS I will note the speed corrections and post them for you. The math hurts my head. But at 60 it is out 5-8mph and at 70 you are closer to the 8mph so that it where it will bite you in the ...let's say wallet for now, if you end up running a radar trap.

The rear tire and rpm's really don't matter because it is the front tire ratio that has changed and lowered the speedometer reading as a result.  The circumference is larger on the front and covering more road than the smaller 90/90 tire for the same rpm's so it is like the front tire has slowed down in revolutions and as a result your going faster than you think.

Fortunately, this error is almost neglible on the lower speeds where most speed traps are.  I start thinking about it when I go over 50mph and start keeping to the actual speed limit and not pushing it say 5mph over.

Hardly anyone has really noticed this until we started using GPS.  I just thought my buddies were all slowpokes and the Vision never complained, but at highway speeds I always wondered why everyone tended to drag back from me and this pretty much explains it.

Have fun anyway... ;)

[don_vanecek]

Basically the same here, I couldn't understand why the two guys I was with weren't moving along when the speed limit changed and so passed them thinking that they thought that I, on the smaller bike (they were on a Ventura and sprint) didn't want to move up to the higher limit-in reality they were already going the limit.

Actually it wasn't until the fall of last year that the friend on the Ventura told me if he followed me I was always going five over or so.

I still think it would be an interesting math problem and since it's about checking true speed the front tire only plays in the problem as your checking the accuracy of the speedo.

[Brian Moffet]

I still think it would be an interesting math problem and since it's about checking true speed the front tire only plays in the problem as your checking the accuracy of the speedo.

Actually no.  The drive train is basically going through the back wheel :-)

The basic formula is RPM / <gear ratio> / <rear-end ratio> * <circumference rear tire in inches> * 60 / 12 / 5280

gives you miles per hour.

I found on lucky's site that the overall gear ratio for the Vision in 5th gear is 6.59.  So, assuming that the rear tire circumference is 75 inches, you get:

5000 / 6.59 * 75 * 60  / 12 / 5280

which gives you 53.89 miles per hour at 5000 RPM.  Now I am guessing on the rear tire circumference and am probably a little large. I am at work and the bike is in the garage.

Brian

[Cdnlouie]

Yes... you fellows are both right and speedo accuracy is what we were talking about, and it seems that Brian enjoys the math challenge so you should be able to get your answer that way too, although the fact that the rear tire circumference changes with speed (and air pressure), could throw a wrench in your accuracy (which may well be the most common cause of small speedo errors) there  :-\. I'm a fan of technology doing it for me, but certainly appreciate the thoughtful theory.

Sometimes it is easier to not think too hard... ;D

[Brian Moffet]

yeah, I usually just use a GPS :-)

Brian

[Rick G]

I usually have a problem running away from people I ride with, but the speedo has nothing to do with it. My friend David Bright , commented that he usually rides a maximum of 5 mph over the limit and I countered with " I usually ride 5 mph over double the speed limit"  . LOL
I'll have to watch it though, the Hualipie Police have acquired  a 6 passenger Ford pickup , which looks like any one of the thousands that are seen around here, except it has a light bar INSIDE the cab at the top of the windshield. I was lucky enough to see it in action , aimed at someone else and again sitting still at the Gas and Grub mini mart in Truxton. I'll have to keep a weather eye open for it , when I'm riding through the reservation.