rear agitator effect on speedometer
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rear agitator effect on speedometer
Will installing a rear 18 inch agitator on a 09 streetglide cause the speedometer to display an inaccurate speed due to the taller wheel size. If so is there a way to fix it.
I have had this problem in my jeep when lifted and changed axle gearing but was able to change the speedometer gear to correct it
to. I called harley and they said it shouldnt change but were not sure. The parts manager said if it did change it would only be minimal and harley didn't have any way to correct the speedometer reading if it was off. This is a an after thought cause I bought the chrome agitators and will be installed next week. If the speedometer is off by a fair amount I will more than likely sell them and buy a set of rampage escalade rims
I have had this problem in my jeep when lifted and changed axle gearing but was able to change the speedometer gear to correct it
to. I called harley and they said it shouldnt change but were not sure. The parts manager said if it did change it would only be minimal and harley didn't have any way to correct the speedometer reading if it was off. This is a an after thought cause I bought the chrome agitators and will be installed next week. If the speedometer is off by a fair amount I will more than likely sell them and buy a set of rampage escalade rims
Last edited by hog95023; Oct 16, 2011 at 08:36 AM.
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I thought I read a thread in here someplace indicating the tire and rim combo was 1 inch taller in the rear and the front was the same height as stock even though it was 19. Due to low profile tire as you indicate.
I can't find that thread that gives the height difference and the good folks at harley couldn't provide any numbers either. Guess I am just Monday night quarterbacking and should have been more thorough in research cause I've been looking almost as long as one of the other members here lol.
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yes it will throw off the speed-o-meter..find the circumference of the old tire (diameter x 3.14) and the circumference of the new tire ....find the ratio change (in percent) of the two and you will know how much the change is in the speedometer....you need to remember the actual speed change will change as you speed up and slow down ie., at 50mph on the speedometer you may be 10 mph off but at 25 mph on the speedometer you will only be 5mph off (these are just made up numbers to give you an idea how it works)..
Last edited by mrfikser; Oct 16, 2011 at 09:51 AM.
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I made this change last year. The rear tire specs can be taken from the H-D website.
I looked up 2010 SG & a 2011 CVO SG, which uses the agititator wheels.
The profile of the tire makes up for most of the 2" inch difference in diameter, (16" vs. 18"). The difference is approx. 3% larger for the agitator combo.
At the end of the day my speedo is very close when compared to a GPS. Also, your rear tire will wear reducing the diameter over time. Worst case is my speedo is reading a low, and I am probably putting on slightly more miles than the odometer reads. Nothing to lose sleep over. Make the change.
2010 SG rear tire - 180/65B16 81H - tire diameter 25.33" (796 revolutions per mile)
2011 CVO agitator rear - 180/55B18 80H - tire diameter 26.18" (770 revolutions per mile)
I got the tire diameters from Dunlops site for D407's, which is what was stock.
http://www.dunlopmotorcycle.com/tire...ire.asp?id=107
I looked up 2010 SG & a 2011 CVO SG, which uses the agititator wheels.
The profile of the tire makes up for most of the 2" inch difference in diameter, (16" vs. 18"). The difference is approx. 3% larger for the agitator combo.
At the end of the day my speedo is very close when compared to a GPS. Also, your rear tire will wear reducing the diameter over time. Worst case is my speedo is reading a low, and I am probably putting on slightly more miles than the odometer reads. Nothing to lose sleep over. Make the change.
2010 SG rear tire - 180/65B16 81H - tire diameter 25.33" (796 revolutions per mile)
2011 CVO agitator rear - 180/55B18 80H - tire diameter 26.18" (770 revolutions per mile)
I got the tire diameters from Dunlops site for D407's, which is what was stock.
http://www.dunlopmotorcycle.com/tire...ire.asp?id=107
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*edit* ramair's post is probably more accurate than mine, i used a tire size calculator to get my dimensions, not the info from dunlop. but the overall effect is the same, negligible. probably well within the +/- tolerances of the speedo.
the calculator that i use can be found at http://www.csgnetwork.com/tiresizescalc.html
its a good tool to have bookmarked.
Last edited by skratch; Oct 16, 2011 at 10:09 AM.
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If the wheel was turning at 1000 rpm, the bike would have an actual speed of 75.4 mph on the 180/65B16 81H's.
If you put on the 180/55B18 80H's and run the bike at the exact same rpm, which would turn the wheel at the exact same speed (1000 rpm), the bike would have an actual speed of 77.9 mph
The bikes engine rpm is what determines what the speedo reads. The speedo will be off by 2.5mph. To me, that difference is insignificant.
btw, mrfikser is correct. 1/2 the speed = 1/2 the error.
If you put on the 180/55B18 80H's and run the bike at the exact same rpm, which would turn the wheel at the exact same speed (1000 rpm), the bike would have an actual speed of 77.9 mph
The bikes engine rpm is what determines what the speedo reads. The speedo will be off by 2.5mph. To me, that difference is insignificant.
btw, mrfikser is correct. 1/2 the speed = 1/2 the error.
Last edited by KylePutzier; Oct 16, 2011 at 10:45 AM.