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Discussion Starter #1
I just bought my 2012 vulcan classic lt. It was new left over stock. I have put about 700 miles on it now. I noticed when driving down the highway I get passed a lot. So I decide to take my handheld gps with me down the road. My speedo is off by about 5 mph. So 60 is 55, 70 is 65. I have read where people have put on bigger tires and different pulley to bring the rpms down on the highway. Would a bigger tire correct the speedometer some too?? If so what size are you guys using.
 

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Discussion Starter #3
That is true will help with tickets. lol It also make me wonder about the odometer. If it saying I have more miles on it then I really do. I will have to check that some time
 

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That is true will help with tickets. lol It also make me wonder about the odometer. If it saying I have more miles on it then I really do. I will have to check that some time
That is correct - it does!
 

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The 9's speedo has been found to be as much as 10% optimistic, tho 6% seems to be the more common number.. Every one of them reads fast unless you overdrive with pulleys or go to a larger-diameter rear tire.
 

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Discussion Starter #6
How about the odometer?? Are those accurate?? I can live with the speedometer being off as long as the miles are correct. I understand that 5 mph really is not that much. But that would be an extra 50 miles for every 600 miles road.
 

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How about the odometer?? Are those accurate?? I can live with the speedometer being off as long as the miles are correct. I understand that 5 mph really is not that much. But that would be an extra 50 miles for every 600 miles road.
The odometer measures distance based on a calibration value for the rear tire diameter. Since that value is obviously not accurate, your odometer will be afflicted the same way the speedo is.

Every speedo has a margin of error, but bikes are bad in general and the 900 seems to be one of the worst offenders.
 

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Speedo Healer is an electronic gadget that allows you to correct the speedometer and odometer readings. Just google Speedo Healer for sellers.

I recently heard praise for the Speedo Healer from a GoodWing rider, who said it's available for cars and motorcycles.

But I know nothing about them,
Grandpa
 

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Discussion Starter #10 (Edited)
Ok I have been reading some post on this. I think I am just getting confused now. Every one has an speedo that's off. K well some say their odometer is right some say they are off too. Some say they put on a 170/80r15 tire others 200/70r15 tire. Stock is 180/70r15. OK first what is the difference in tire 170 and 200??

A taller tire makes the speedo read slower?? so 55 could really be 60
A smaller tire makes speedo read faster?? so 70 could really be 60

Or one could change the pulley front, rear or both. Which will also change the speedo. But by changing either pulley makes the speedo read slower. so 50 could really be 70

Now how do these changes affect the odometer?? I understand any of these will change rpms and shift points.
 

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This is pretty much the reason that you'll ALMOST never be pulled over for doing 5-7 MPH above the speed limit.
 

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Ok I have been reading some post on this. I think I am just getting confused now. Every one has an speedo that's off. K well some say their odometer is right some say they are off too. Some say they put on a 170/80r15 tire others 200/70r15 tire. Stock is 180/70r15. OK first what is the difference in tire 170 and 200??

A taller tire makes the speedo read slower?? so 55 could really be 60
A smaller tire makes speedo read faster?? so 70 could really be 60

Or one could change the pulley front, rear or both. Which will also change the speedo. But by changing either pulley makes the speedo read slower. so 50 could really be 70

Now how do these changes affect the odometer?? I understand any of these will change rpms and shift points.
Hopefully I can provide something that resembles an answer:

Tire size: The first number is the width of the tire in millimeters. The second number is the height of the sidewall as a percentage of the width. the remaining information is the tire type (R=Radial) and rim size (15 inches.)

180/70R15 is 180mm wide with a 126mm sidwall.
170/80/R15 is 170mm wide with a 136mm sidewall.
200/70/R15 is 200mm wide with a 140mm sidewall.

Without taking actual tire thickness in the middle contact patch of the tire or contour, the stock tire would be the shortest tire of the three.

What I am no 100% sure of is where the speed sensor is located. I believe it is sensor on the output of the transmission. The electronics will send the signals to both the Odometer and Speedo circuits. These will then interprit the signals to give the desired reading. Since the Odometer is 100% digital, it will display more accurately than the speedo. The speedo must convert the digital input to an analog current to operate the needle. There is always a degree of loss in this process making indicated speed display slightly different than actual speed.

A taller tire results in slightly more distance travelled per rotation when compared to stock. This means that the actual speed will be higher when compared to the speedo versus stock. I personally noticed the difference when I changed from the stock tire to a 170/80R15. According to my GPS, when i held firm at 60mph indicated, the stock tire would read 54mph (a full 10% drop). when I changed to the taller tire my actuall speed increased to 57mph at 60mph indicated. Still low but much closer. I am sure that tire wear played a little factor on the stock tire reading so low. I checked here recently when i put on my lastest rear tire. My actual speeds did increase approx. 1mph (from 56mpg to 57mph) when the new tire was installed (same 170/80R15 was used).

During one IBA certification ride I put on 1183 miles according to the odometer. The GPS read 1174 for the trip. That is a variance of approx. 0.7% between the two.

I guess my point here is that both tire height and wear will impact both your indicated speed variance and the odometer reading. Your odometer reading will be more accurate.

I have no knowledge on how changing the pulley(s) would impact actual v. indicated speeds. This is not something I have done to my ride. However, if the speed is measured at the drive shaft rather that at the wheel hub I would expect the pulley to impact actual speed when compared to indicated speed.

There also is a lot of misinformation out there about speedometer readings and their legality. In the United Stated, the federal laws governing speedomteters only apply to commercial vehicles. These laws specify a 10% variance between actual and indicated (+ or -) when measured at 55mph. Commercial regulations are much tighter than non-commercial. There is no regulation on non-commercial vehicle (aka motorcycles) speedometers and their accuracy.

As always, this information is personal knowledge and experience. If anything I have said is false, please correct me so that I can learn, but please provide citable references.
 

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Discussion Starter #13 (Edited)
Dranzaz That's is a pretty good explanation.

Well I went for a small ride today with the gps. Had my kid hold it and checked the mph along with the odometer. I only went 25 miles on the odometer. gps read 25.3 so it will be adding ghost miles. Does the 200 or 170 tire fit fine?? Is there an advantage to one or the other??

According to this tire size calculator a 200 would put it pretty close. should add 2.65 mph and 170 about 1.9mph at 60 mph.http://www.tacomaworld.com/forum/tirecalc.php?tires=180-70r15-200-70r15

If I understand this gear commander right http://www.gearingcommander.com/ adding a 34 tooth front pully should add 3.6 mph adding rear 62 tooth pulley 3.7mph both pulley 7.6 mph looking at 3420 rpms.

So if I did a front pulley speedometer should be at 60 mph and gps 60.3 If I understand this correctly.

my speedometer vs gps
25 / 24.5
30 / 29
45 / 42.3
55 / 52.6
60 / 56.7
65 / 62
70 / 66
 

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Does the 200 or 170 tire fit fine?? Is there an advantage to one or the other??
The wider 200 tire will give you a more comfortable ride and will handle grooves in the pavement (like cracks and chewed up for resurfacing) better. The thinner 170 tire will give better cornering and lean responsiveness, but it will try and follow the grooves.

The 200 will reportedly fit without any modification to the drive system. Although I have read were some have removed the belt cover, "just to be safe."

As to the pulleys, I am sure you will get the desired affect, I just cannot speak personally to any actual first hand knowledge. All I know is that I used to swap sprockets on a Suzuki I had. I had one set for highway riding that gave me lower RPMs and thus better fuel economy. I had another set for city driving to give me better launches off the line and acceleration in traffic. But with those I could match the chain to my setup. Have not done the needed research yet on belts and pulley swaps to feel comfortable making that attempt, yet. Maybe next year. Other more pressing bike projects I am looking at first.
 

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if your speedometer indicates too much it does not matter, as long as I do not interfere with traffic. just run and enjoy the ride, that's why you drive a motorcycle. then if it is a mil shorter or longer to the target does not so much. :)
 

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Discussion Starter #16 (Edited)
It does not really it just an annoyance. You would think with today's technology it could be just a simple program fix in the computer. I just don't like having those extra ghost miles on. Resale.. I know it not a lot but in 10000 it adds up. I originally was just waning to know why I was getting passed all the time and way to correct it if I wanted to.
 

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I have matched my bike with my friends, and they have been checked by radar. I also checked my bike with my son's car. We are all going 5 slower than indicated at highway speeds, just keep it in mind and relax. 80 means 75 no tickets......
 

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Discussion Starter #18 (Edited)
I know I just did the math. Mute point I guess. lol

I am kinda picky about stuff. Girlfriend would say anal. But what does she know. Just so you guys I have been enjoying the bike though.
 

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I know I just did the math. Mute point I guess. lol

I am kinda picky about stuff. Girlfriend would say anal. But what does she know. Just so you guys I have been enjoying the bike though.
The next time you're riding on the Interstate make a mental note of the mileage, including the tenths at the exact time you pass a mile marker post then see what it is a mile down the road and so on. That will tell you how much odo error you're dealing with. I've installed one of the circuit boards that corrects the speedo because I'm now running a 200 rear. It was just for fun because there's no cops checking speed around here. Anyway, getting to the plug end of the speed sensor on the engine was a major pain in the butt. Wish I hadn't bothered.
 

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Discussion Starter #20 (Edited)
I took the gps with me and for every 50 miles I gain a .5 in 115 miles I gained 2 miles
If the pattern continues I would say the odometer is about 2.2 percent off. The speedometer is about 6 percent off.

I think if I did anything I would due the front pulley only.
 
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