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Discussion Starter · #1 ·
I having been going over the whole 60 vs 70 series front tire for my SV and the speedo accuracy. We know that our speedos are reading about 10% fast with the 60 series front tires. I was looking for a calculator that could tell me the percentage difference in speedo reading between the 60 and 70 series tires. I came across this http://www.discounttire.com/dtcs/infoTireMath.dos tire calc that can handle motorcycle widths. The 70 series with will make you read about 4% slower than you're really going, for a total error of about 6% too high left over. Just thought Id share.
 

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speedo error varies depending on tire profile(brand/model) and tire wear even on the same size tires.
the only tires I have experienced 10% error with is dunlops, all others closer to 5-6%
 

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Discussion Starter · #3 ·
Ivan said:
Not accurate.

The /70 is the ratio of the tire SIDEWALL to the width of the tire. It does not measure the circumference of the tire. For example, a 70 tire may have a very flat profile while another brand may have a 60 tire but the center of the tire is very pointy (read Dunlop to Michelin).
Well considering there is no easy way to calculate the true circumference from sidewall markings, aspect ratio is as good as we have for a simple calc. It going to be a descent estimate sticking to the same brand/model of a tire. Its not perfectly accurate calculating these things on car either, but its a start without looking up things on a mfg website and doing the math by hand. Thing is, most of the tire calculators Ive found online are based on the one at miata.net which only handles tires down to 145 width. So this at least is a step in the right direction.
 

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automotive tires have a square profile, you are also always riding on the outer circumference, with a bike, speedo error also depends on your lean angle, twistier roads, more lean angle riding , more error, that doesn't happen with a cage
 

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ls14ever said:
seriously people you are making this way more complex than it needs to be. Ever heard of estimates?
no, I don't care how fast I am going, your the one who originally questioned the error, everybody else is pointing out the variebles, there are a lot of them for motocycles compared to cars
 

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RandyO said:
speedo error varies depending on tire profile(brand/model) and tire wear even on the same size tires.
the only tires I have experienced 10% error with is dunlops, all others closer to 5-6%
So if I get a 120/70 Michelin for my front, I'll have little or no speedo error? Glad someone finally cleared this up! Thanks! :)
 

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650Hooligan said:
So if I get a 120/70 Michelin for my front, I'll have little or no speedo error?  Glad someone finally cleared this up!  Thanks! :)
don't know, never run a Michelin the only 120/70s I have run are Pirelli MT60Rs and Avon Distanzias.
 

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One advantage of your speedo running slower will be fewer miles on your odo right? Seems like that would be good for resell and such.
 

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With my GPS on the SV and the stock d220 front tire, I estimated that the odometer is off by roughly 2%. That I can live with. But the 10% error on the speedo? If there was some way to correct the speedo, but keep the odo where it is. I'm all for it! Otherwise, I'll stick with my GPS for trips and working the math in my head while commuting...




Moi
 

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VTSVSY said:
With my GPS on the SV and the stock d220 front tire, I estimated that the odometer is off by roughly 2%. That I can live with. But the 10% error on the speedo? If there was some way to correct the speedo, but keep the odo where it is. I'm all for it! Otherwise, I'll stick with my GPS for trips and working the math in my head while commuting...
Ummm...you have a GPS at least--doesn't that tell you mph?

I don't know--I have been riding around the same traffic with my bike as I do my car, and I travel about the same speeds, and at no time do I ever feel like I am traveling slower than what my speedo says. I typically ride about 70, 75, or 80, which is faster than most other traffic and keeps me ahead of everyone. Same with my car.

Also, as I have said before, on my old SV650 I was clocked going 72mph by a cop and sure enough that's how fast my speedo said I was going. I was also clocked at 90mph by a cop on my Gixxer 1000 (and yes that's what my speedo said), a bike that most people said had a speedo error of up to 15%! That's BS and I got the ticket to prove it!

I'm not going to spend $100 on a GPS just to see how fast I am "really" going. Everyone seems to want to buy the idea that cars and motorcycles are slower than their speedos say, and yet no one questions that perhaps GPS is not as accurate as people think. Both sides are acting on faith and hearsay. Who decides if GPS really is accurate? If you can't get a clear triangulation on satellites, the reading could be off anyway.

I don't trust GPS any more than I trust speedometers. But as far as I am concerned, I am travelling as fast as my speedo says--and the cops agree!
 

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Yes, my GPS show the speed. And Yes, I've used it in several other vehicles as well. The speedo in my car reads to within 1 mph of my gps, and my brothers car reads about 2 mph fast at highway speeds. Those errors can be contributed to tire type/make/wear. My SV can't say that!

Maybe you were one of the lucky ones who got a correctly calibrated speedo on their SV?




Moi
 
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