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Need help understanding speedo and odometer

Old 06-30-2010, 05:17 AM
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Need help understanding speedo and odometer

Help me out here. I have looked through some of the threads about the speedo healer and understand that I do need one. I need to understand how many miles I am getting out of a tank of gas after my sprocket change.

I am now running a 16 / 43 instead of the stock 16 / 41. I did find out that when my speedo reads 65 I am acually going 55. Is this consistant throughout the speedometer or does it change as speed decreases and increases?

Also, I know my odometer is ticking faster now. How do I find out how many miles I am getting on a tank of gas?

I appreciate the help because I am going on a long 3k mile trip and don't have time to order a speedo healer before hand. If I can just do a calculation that would be great.

Thanks,

Nick

Last edited by Grasshopper; 06-30-2010 at 05:19 AM.
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Old 06-30-2010, 05:44 AM
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Originally Posted by Grasshopper View Post
Help me out here. I have looked through some of the threads about the speedo healer and understand that I do need one. I need to understand how many miles I am getting out of a tank of gas after my sprocket change.

I am now running a 16 / 43 instead of the stock 16 / 41. I did find out that when my speedo reads 65 I am acually going 55. Is this consistant throughout the speedometer or does it change as speed decreases and increases?

Also, I know my odometer is ticking faster now. How do I find out how many miles I am getting on a tank of gas?

I appreciate the help because I am going on a long 3k mile trip and don't have time to order a speedo healer before hand. If I can just do a calculation that would be great.

Thanks,

Nick
Use this to calculate all your changes and needs...

http://www.tweety.se/download.php?fi...aring VTR3.xls
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Old 06-30-2010, 05:50 AM
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It's a percentage error, so it will change.
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Old 06-30-2010, 06:01 AM
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Yeah... But with those sprockets the difference in total is 4.65% so a reasonable calculation would be 5% total to keep it simple... That's how much less you get out of your tank because of your change... That and some realworld test on your bike and you can figure out your tank range pretty accurately on the uncorrected number on your bike, ie when trip says X go fill up...
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Old 06-30-2010, 08:15 AM
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The speedometer also comes stock with around a 5% error so your total error is -9.6%. I have the same 16x43 gearing as you and get an indicated 120 miles per tank exactly when riding in the mountains. So my actual range is right around 110 actual miles. I have started carrying an MSR fuel bottle under the seat as a reserve.

That got a little off track so to summarize, with your gearing you will be going about 10% slower than your speedometer indicates and racking up 10% more mileage on the odometer than you actually travel.
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Old 06-30-2010, 08:28 AM
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u can fit something under the seat??????? lol i can get a glove in there if I'm lucky....
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Old 06-30-2010, 08:57 AM
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Originally Posted by nothing View Post
u can fit something under the seat??????? lol i can get a glove in there if I'm lucky....
I can fit a water bottle, the toolkit, a first aid kit, a tire patch and inflation kit, spare socks, gloves, a long sleeve shirt, a flashlight, a multitool and my registration papers.

The light stuff and the water bottles go to the outside of the subframe, the only thing to watch for is not blocking airflow to the R/R, so I often leave the right side empty, that'd free up a lot more room. And I did gain the use of most the battery box recently with my A123 batteries, so I now have even more room.

But on to the question at hand. I am now running 16/43 and while the Speedohealer site said I should be at -9.6% I found that to actually get it correct (per GPS) I needed -13.3%

However my rear tire is fairly worn now, and it might be a bit under inflated so that may be part of it.
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Old 06-30-2010, 09:02 AM
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This is great info. I've been riding quite spirited lately and I'm getting an indicated 115 to 120 before reserve comes on. This thing swallows gas.
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Old 06-30-2010, 09:23 AM
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Originally Posted by Grasshopper View Post
This is great info. I've been riding quite spirited lately and I'm getting an indicated 115 to 120 before reserve comes on. This thing swallows gas.
It's all in how you ride. I have run out at 90 and have made it to 145 before, some here on the forum average more than I have ever gotten.
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Old 06-30-2010, 11:36 AM
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Ok, speaking of the 10% error. If I have an indicated 120 miles on my odometer do I multiply that by 0.10 to get the actual mile number?

Last edited by Grasshopper; 06-30-2010 at 11:42 AM.
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Old 06-30-2010, 11:41 AM
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Then subtract 12 from 120 and that is my actual mile number of 108 correct?
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Old 06-30-2010, 11:44 AM
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Originally Posted by Grasshopper View Post
I did find out that when my speedo reads 65 I am acually going 55. Is this consistant throughout the speedometer or does it change as speed decreases and increases?
Thanks,

Nick
I been running that gearing for around 12 yrs now and yes between the gearing change and the stock speedo error the reading is right at 10% (well 9.xxx) through out the entire range. That is one reason I haven't really bothered with a speedo healer. It would be nice but even this old Marine can do the 10% correction in my head, no worries.

Cheers,
Mike
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Old 06-30-2010, 11:45 AM
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If you are off by -10% then: multiply by .90
or by .10 and subtract that from it.

so 120 = 108mph
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Old 06-30-2010, 11:46 AM
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Originally Posted by Grasshopper View Post
Ok, speaking of the 10% error. If I have an indicated 120 miles on my odometer do I multiply that by 0.10 to get the actual mile number?
This is where it get a little tricky, while the stock speedo reads about 5% high the ODO is dead on. So to figure out your mileage use the 5% from the gearing change to figure out this number.
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Old 06-30-2010, 12:32 PM
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So instead of multiplying by .10 multiply by .5?
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Old 06-30-2010, 12:37 PM
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Originally Posted by Grasshopper View Post
So instead of multiplying by .10 multiply by .5?
It would be .05
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Old 06-30-2010, 12:49 PM
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Right, that's what I meant. Thanks for your help
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Old 06-30-2010, 02:06 PM
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How is the odo off by 5% less than the speedo? I thought it got it's signal from the speedo sensor as well.

Lazn do you have a write up for your battery?
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Old 06-30-2010, 02:15 PM
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Originally Posted by zwoehr View Post
How is the odo off by 5% less than the speedo? I thought it got it's signal from the speedo sensor as well.

Lazn do you have a write up for your battery?
Because stock the speedo is around 5% optimistic while the ODO is pretty much dead on.
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Old 06-30-2010, 02:24 PM
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Originally Posted by zwoehr View Post
Lazn do you have a write up for your battery?
Yep linked in my signature: https://www.superhawkforum.com/forum...990#post265990
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