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Discussion Starter #1
This has me scratching my head:

I have a 2013 CCT with 16K miles on it now. Tire replacement time I changed out the E3's to Commander II's. The slightly taller rear tire (60 vs. 65) puts my speedometer right on the money. I was riding with my buddy on his HD Ultra last weekend and when both of our GPS's showed 70mph His HD's speedometer was at 72 and mine showed 70. Usually HD's have the most accurate speedometer in the motorcycle world from my experiences.

Twice we filled up and I was also kicking his butt in mileage. He'd add 3.3 gallons and I'd add 3.1 gallons. All good fun teasing. But here is the rub. Our route planned on both of our GPS's showed this loop was 140 miles. On our fill up his trip meter was right on the money with the GPS and my trip meter showed 131 miles or LOWER than actual. I've never seen an odometer read slow before.

As we departed our separate ways I hit the "home" button on my GPS and it showed 81 miles. I reset my trip meter and followed the exact route and it came out to 77.5 miles on my trip meter or about 6% slow exactly what the loop we rode showed!

Has anyone noticed this on their CCT's? This is the first time I've seen this on a motorcycle that the odometer was slower than actual miles traveled.
 

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I've heard a lot of people over the years say they changed their tire to "correct" their factory speedometer reading. I've never owned a bike that didn't come stock almost perfect (maybe one to three MPH at most off) which wasn't enough for me to care so I never messed with it. Usually it was sport bikes. I think every cruiser I've had was dead on.

If you changed your aspect ratio but kept the same width of the tire then you will have an off reading. If you increase outer diameter then you should be going faster than the speedometer reads. I'm not 100% sure but likely Victory uses a Hall effect/pulse generator which gets a reading off the transmission.

The speedometer on your bike is setup to read X amount of revolutions with X amount of stock outside diameter tire = x distance/speed. Now you have a higher outside diameter so you're traveling farther per revolution but the bike doesn't know that.
 

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On my vision the speed-o is two miles a hour off. Radar says 60 speed-o shows 58 but then I'm running a CT in back.
Trip meter is off by 1 mile doing trip like you did. No GPS
 

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I read somewhere that most motorcycle speedo / odo's are off by up to 10% .
 

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Discussion Starter #5
On my vision the speed-o is two miles a hour off. Radar says 60 speed-o shows 58 but then I'm running a CT in back.
Trip meter is off by 1 mile doing trip like you did. No GPS
Mine with E3's was 58 at 60 as well. Now it's right on the money but I don't understand why the odometer would now be 6% slow? You'd think the speedometer would be a linear math function moving either fast or slow at the same rate of change?
 

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Mine with E3's was 58 at 60 as well. Now it's right on the money but I don't understand why the odometer would now be 6% slow? You'd think the speedometer would be a linear math function moving either fast or slow at the same rate of change?
That's true unless it's algorithm is designed to reflect accurate mileage and inaccurate speed. Which somehow would not surprise me........
 

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My trip meter always reads more miles than Lacy's, which indicates her rear tire/wheel diameter must be a little taller. My speedo is also about 3 mph optimistic compared to hers. When those values are dependent on the number of revolutions your rear tire might make, changing that number alters those values. Larger diameter=slower speedo, fewer miles on odo.
 

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Discussion Starter #8
But a 65 series tire compared to a 60 series does not translate to 6%less tire revolutions. :crzy:
 

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It really depends on both numbers the width and the aspect ratio. But it could be out that much. There are speedometer correctors that can adjust and get you right on. If you do use one of these make sure your tire is half worn when you set it. That way your error will not be in all one direction, you'll end up with a +/-.
 

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Who really knows why the odometer is off but at least it's not showing excessive miles on your bike. I also just replaced both tires on my '13 CCT (14.3K miles at the time) but stayed with original tires and sizes. My speedo is about 3 MPH off. NBD.
 

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Ha, this is fun. Math!

180/60R16 = 108 sidewall
180/65R16 = 117 sidewall

According to the circumference calculator:

60 series = 76.9 circumference / 823.5 RPMs per mile
65 series = 79.2 circumference / 800.3 RPMs per mile

So.... theoretically there's about a 3% difference in circumference. But remember we're using a circle so it is a linear increase based on RPMs. It may be off by .5% at 1000 RPMs and 2.5% at 5000 RPMs.

I think.......

Research is fun.

Bottom line though, if the stock tire gave you accurate mileage but inaccurate speed.... then why would a different sized wheel correct one without altering the other? I am having a good time trying to figure all the formulas and math out.
 

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Discussion Starter #12
:ltr:
Ha, this is fun. Math!

180/60R16 = 108 sidewall
180/65R16 = 117 sidewall

117/108= .923

So...... a 7.7 % difference. If I did all that right. Don't do a lot of math here past 2+2 in Mississippi.
You didn't! :ltr:
 

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I think it's an error built in, so that with new tires of the correct size and used up tires of the correct size will end up in a window of speed that's not to far one way or the other from the indicated speed.
 

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Discussion Starter #14
Circumference of 180/60/16 = 76.982 "
Circumference of 180/60/16 = 79.209

difference 2.8% :D
 

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I think your slower then what speed-o says so if you get a speeding ticket you can't go back to Vic and clam its there fault
 
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