This may be weird but I was riding with my wife following behind me in a car. I mentioned that I drove 60 mph at one point and didn't go below 50 mph. She said that I was wrong because she drove around 45 mph and sometimes even braked at 45. I never saw my speedometer go under 50. can our speedometers be that far off? I don't want to think I'm driving the speed limit and wind up getting ran over by a car!
Someone had a great "actual MPH" chart a while back. 100 on the speedo is even worse with actual just over 80 MPH as I remember.
Class?
I beleive it was stated its off by 10% I dont think the 100 being just over 80 is right as I ride up here in MI where the speed limit is 70 and everyone goes 80 and I am at 90 and keeping up just fine, 95 and I am passing everyone.
Quote from: tharpThis may be weird but I was riding with my wife following behind me in a car. I mentioned that I drove 60 mph at one point and didn't go below 50 mph. She said that I was wrong because she drove around 45 mph and sometimes even braked at 45. I never saw my speedometer go under 50. can our speedometers be that far off? I don't want to think I'm driving the speed limit and wind up getting ran over by a car!
Check the evil pumkin racing website for an excel spreadsheet that calculates mph for the GS500 based on tire circumference, gearing and rpm - enter your numbers and find out how fast you are really going when the speedometer says 60 - assuming, of course, that the tach is more accurate than the speedometer
http://www.evilpumpkinracing.com/gearing.xls
Yeah I rode 90 on a trip. My friend said we were doing about 80. When you take it up to 120 you usually pass everybody
And the speedo in your car following is probably 4 or 5% high too!
Check it against a GPS. The difference is rarely a linear percentage on a bike. The eror % usually gets larger at higher speeds.
Against my Garmin GPS, the GS is 10% fast. Indicated 70MPH on the GS's speedometer is exactly 63MPH on the GPS. 50MPH indicated is actually 45MPH.
That is actually 11.1 % high at both speeds. Have you tested it at higher speeds?
Hmm my math says 10% there....10% of 70 is 7 so 63, 10% of 50 is 5 so 45..11.1% is 7.77 so 62.23
And the speed difference does change with speed, ie its not a fixed rate of 5mph or 7mph but a percentage. So at 35mph its only 3.5mph off but at 80mph its 8mph off.
Quote from: JasonBHmm my math says 10% there....10% of 70 is 7 so 63, 10% of 50 is 5 so 45..11.1% is 7.77 so 62.23
Well... it's the percentage of the speed, not percentage of the speedometer. If actual speed is 63, to get an indicated 70 you would add ~11.1% of 63... So your speedo is reading 11.1% high at 63mph. If your speedo reads 10% high at 63mph, you'd be going 69.3mph.
I think there's confusion if you're calculating the actual speed's error in relation to the speedo, when it should be the speedo's error in relation to the actual speed. Make sense? Yeah, probably not...
Whatever... close enough... What are "nits" and why are they picked?
Quote from: bbanjoSomeone had a great "actual MPH" chart a while back.
Joris has one on his site, here:
http://www.bikepower.net/gs500e-power/modifications/appearance-related/speedometer/speedometerpage1.htmedit: My BBCode skills are lacking...
anyone have any idea off the top of their head what difference a 140/80 tire on the back would have on that chart. i assume the taller tire would throw the speedo off, but in this case would it start to make it more reliable? i ride pretty fast, usually around 80-90mph and pass everyone, so i must be going somewhere around there. any ideas? i suppose i could just put in a digi speedo... hm
Quote from: Zarathustraanyone have any idea off the top of their head what difference a 140/80 tire on the back would have on that chart.
Well, on paper, a 140/80-17 is 7% larger in diameter than a 130/70-17... But the speedo is connected to the front tire.
I have a couple of related charts on my site in Excel format. You can download and change the data to match your bike. One of the files is for calculating max speed (both mph and kph) and the other is for calculating the optimum shift point for your bike. The charts are obviously for "ideal" conditions and don't allow for rider weight and wind loads.
As it was said earlier, the rear tire does not affect the speedo. A larger rear tire will gear it down thus making it slower, you could have a 15t front sproket and an 80 size rear tire and it could actually be close to the stock 16t sproket 70 size rear tire combo. Not 100% sure on this though.