Pully change, speedo ratio
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Cruiser
Joined: Aug 2012
Posts: 190
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From: Wichita KS
Pully change, speedo ratio
I just changed to a 30 tooth pully from the stock 32 tooth on my '10 WG. I have a Zippers T-Max tuner and can edit the speedometer ratio, but does anyone have the formula to figure the difference? If I can't figure it out today with using math, I can borrow a hand-held GPS tomorrow to see how fast I'm going vs. what my speedo shows and edit it that way. Just wanted to see if anyone knows how I should figure the ratio so I can do it today. I'm prone to attract the attention of the law so I want the speedo to be set right.
One more question for future reference... can I use the stock belt length with a 30/70 pully combo?
One more question for future reference... can I use the stock belt length with a 30/70 pully combo?
Seasoned HDF Member
Joined: Jul 2008
Posts: 9,282
Likes: 1,139
From: southeast PA
Divide 66 by 32 and you get a ratio of 2.0625
Divide 66 by 30 and the new ratio is 2.200
If you go by the pulley teeth number in the speedo cal you have to reverse the old with the new, since it's set up for the rear pulley, not the front one.
I found the most accurate way to do it is your method with the GPS. Using the indicated vs. true speed will give the best results. I spoke to Zippers about this and they say this is the way to go.
Divide 66 by 30 and the new ratio is 2.200
If you go by the pulley teeth number in the speedo cal you have to reverse the old with the new, since it's set up for the rear pulley, not the front one.
I found the most accurate way to do it is your method with the GPS. Using the indicated vs. true speed will give the best results. I spoke to Zippers about this and they say this is the way to go.
Thread Starter
|
Cruiser
Joined: Aug 2012
Posts: 190
Likes: 0
From: Wichita KS
Divide 66 by 32 and you get a ratio of 2.0625
Divide 66 by 30 and the new ratio is 2.200
If you go by the pulley teeth number in the speedo cal you have to reverse the old with the new, since it's set up for the rear pulley, not the front one.
I found the most accurate way to do it is your method with the GPS. Using the indicated vs. true speed will give the best results. I spoke to Zippers about this and they say this is the way to go.
Divide 66 by 30 and the new ratio is 2.200
If you go by the pulley teeth number in the speedo cal you have to reverse the old with the new, since it's set up for the rear pulley, not the front one.
I found the most accurate way to do it is your method with the GPS. Using the indicated vs. true speed will give the best results. I spoke to Zippers about this and they say this is the way to go.
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