While comparing my speedometer readings to my GPS figures, I see that the bike reads approximately 8 - 10 mph slower than the gps at speeds over 40 mph.. I've done some light research and it suggests that the GPS is more accurate than the bike.
So, I'm wondering if a small change in gear ratio would make the speedo more accurate.
Has anyone pondered this idea and come up with a gear ratio that might result in a more accurate speedo reading?
And with all the technology out there, what's the reason that the speedo is so off the mark in the first place?
I installed a 17 tooth front sprocket on my '02 VFR800, sold now, with the OEM 43 tooth rear sprocket. I did this because I do a lot of highway driving and it reduces the RPM by ~500 rpm's and it helps fuel mileage somewhat. I checked the speedometer against my Garmin GPS V and it was exactly the same reading on both. I currently have a new 07 RWB VFR800 and will be doing the same once the OEM sprockets wear out.
[image: View Post]soichiro, on Oct 2 2008, 07:28 PM, said:
I have checked mine with my garmin. The speed-o was exactly 10% off across the board. It reads 10% high.
I just went up 2 teeth on the rear. How will that effect the speed-o?
It will be further off, you can figure it out by the gear ratio, or there is a calculator on speedohealer's website that will tell you.
[image: View Post]jeremy556, on Oct 2 2008, 07:06 PM, said:
[image: View Post]spud786, on Oct 2 2008, 08:54 PM, said:
might as well unplug the speedo>G<, thats probably a good 10mph difference
Maybe not since speed reads the cs sprocket?
Let me know
You can calculate it by figuring the difference between 16/45 and 16/47 or whatever the ratio is.
dont forget about what affect tires can make.
I checked my speed to my gps before new tires and it was 5-8 fast. After new tires (front an rear) it was only off 1-3. So I was going to buy a speedohealer but it won't account for the fact my tires are getting smaller every ride making my rear wheel rotate faster. In short know you have a + or - 3-8 and unless you always have a GPS you will never know your true speed.
The real question is why did they do this? My guess would have to be that its for legal reasons. If some guy crashed and his speedo said he was going 65, and he could somehow prove he was actually going 66, there would be a huge lawsuit. The odometer is pretty much dead on, so its not a technical limitation.
Unrelated, but remember that Honda had a class action lawsuit a while ago where the odometers in their cars was about 10% high, and they ended up having to extend everyone's factory warranty by 10%. I had a Honda Pilot at the time, but just missed out on the bonus warranty.
I just got around to ordering a speedo healer ($109 shipped seems like the going rate) because i went +2 in the rear and now it is way off. I verified it with my GPS and it was about 13% high. I'm annoyed that i can't have both the speedo and the odometer accurate.
As for the tire argument, yes it certainly does come into play as the circumference of the tire gets smaller, but 1 to 2 mph isn't really going to make a difference for most people (or get you pulled over), and the error does not change that much as speed increases. With the gearing change, its only 3 mph off at 20 mph, but its 11 mph off at 80.
My Speedo on my 83, Not digital of course reads 20km/h higher then my gps reads.
100km/h on the GPS is 120 on the speedo. SO I just guage it like that now. I know wherever I am if I am doing 80 im doing about 60 or so.
I used to be good at math...Anybody know how under my mileage is if I have a speedohealer installed. I really just want to accurately calculate MPG.
I don't think it's as simple as saying well, you reduced the speedo by 8% so increase the mileage by 8%, but I don't really feel like thinking about it. :mellow:
[image: View Post]CrazyInNYC, on Oct 3 2008, 06:43 PM, said:
I used to be good at math...Anybody know how under my mileage is if I have a speedohealer installed. I really just want to accurately calculate MPG.
I don't think it's as simple as saying well, you reduced the speedo by 8% so increase the mileage by 8%, but I don't really feel like thinking about it. :mellow:
I just bought a speedohealer and am wondering if anybody has installed one and if so how difficult was it. The guy on the phone said you just need to plug it into the speed sensor but before taking the fairings off and digging in I was hoping for a clue as to where to look.
[image: View Post]BITTERPRINTER, on Oct 3 2008, 05:54 PM, said:
[image: View Post]CrazyInNYC, on Oct 3 2008, 06:43 PM, said:
I used to be good at math...Anybody know how under my mileage is if I have a speedohealer installed. I really just want to accurately calculate MPG.
I don't think it's as simple as saying well, you reduced the speedo by 8% so increase the mileage by 8%, but I don't really feel like thinking about it. :mellow:
I just bought a speedohealer and am wondering if anybody has installed one and if so how difficult was it. The guy on the phone said you just need to plug it into the speed sensor but before taking the fairings off and digging in I was hoping for a clue as to where to look.
Thanks
Sorry, mine came with the bike. I think the speed sensor attaches to the bolt under front sprocket cover though.
[image: View Post]CrazyInNYC, on Oct 3 2008, 07:02 PM, said:
[image: View Post]BITTERPRINTER, on Oct 3 2008, 05:54 PM, said:
[image: View Post]CrazyInNYC, on Oct 3 2008, 06:43 PM, said:
I used to be good at math...Anybody know how under my mileage is if I have a speedohealer installed. I really just want to accurately calculate MPG.
I don't think it's as simple as saying well, you reduced the speedo by 8% so increase the mileage by 8%, but I don't really feel like thinking about it. :mellow:
I just bought a speedohealer and am wondering if anybody has installed one and if so how difficult was it. The guy on the phone said you just need to plug it into the speed sensor but before taking the fairings off and digging in I was hoping for a clue as to where to look.
Thanks
Sorry, mine came with the bike. I think the speed sensor attaches to the bolt under front sprocket cover though.
[image: View Post]CrazyInNYC, on Oct 3 2008, 06:43 PM, said:
I don't think it's as simple as saying well, you reduced the speedo by 8% so increase the mileage by 8%, but I don't really feel like thinking about it. :mellow:
Actually it is.
[image: View Post]BITTERPRINTER, on Oct 3 2008, 06:54 PM, said:
I just bought a speedohealer and am wondering if anybody has installed one and if so how difficult was it. The guy on the phone said you just need to plug it into the speed sensor but before taking the fairings off and digging in I was hoping for a clue as to where to look.
You will see a wire coming from the area of the countershaft sprocket, this is the sensor. You plug in between the sensor and the harness, then the speedohealer has a wire that leads to the speedohealer unit. I located mine under the seat. Very, very easy install.
[image: View Post]Alien TLR, on Oct 2 2008, 06:07 PM, said:
While comparing my speedometer readings to my GPS figures, I see that the bike reads approximately 8 - 10 mph slower than the gps at speeds over 40 mph.. I've done some light research and it suggests that the GPS is more accurate than the bike.
So, I'm wondering if a small change in gear ratio would make the speedo more accurate.
Has anyone pondered this idea and come up with a gear ratio that might result in a more accurate speedo reading?
And with all the technology out there, what's the reason that the speedo is so off the mark in the first place?
when i dropped 1 tooth on the front, then the speedo matched my gps...as if it matters :)
[image: View Post]VFR-SPORT, on Oct 2 2008, 04:13 PM, said:
I installed a 17 tooth front sprocket on my '02 VFR800, sold now, with the OEM 43 tooth rear sprocket. I did this because I do a lot of highway driving and it reduces the RPM by ~500 rpm's and it helps fuel mileage somewhat. I checked the speedometer against my Garmin GPS V and it was exactly the same reading on both. I currently have a new 07 RWB VFR800 and will be doing the same once the OEM sprockets wear out.
:+1:
Adding a tooth on the front sprocket put the speedo almost dead on. My GPS says the speedo still read a little high at 70 mph. For example, if the speedo said 71 mph, the GPS read would read 70 mph. Close enough for me!
After passing numerous "Your speed is..." mobile radar installations, it seems my '04's speedo is 10% 'optimistic'. Even if it's really 8% off, as many others are, that's close enough for me to think of as 10% and adjust my speed accordingly to be at, under or just over the speed limit wherever I am. I'm so used to compensating for it I really don't have to think much about it anymore.
What's weird tho is when I've been riding a lot, then drive my car a bit. I find myself thinking about how much I need to compensate for the speedo error while driving, which of course I don't need to do! :laugh:
One funny thing, too, is that on the rare occasion I hit 100 mph (indicated) on my VFR it's kind of a thrill to see triple digits, but then I realize I'm actually "only" doing 90-92 mph. Guess I'll just have to run it up to 110 mph indicated instead to actually get 'er up to 100. ;) ;p
BTW, I have a nice GPS unit in my car. I don't use it all the time, but I have found that my CR-V's speedo is 1 mph optimistic at all times, at least vs. the GPS unit. Another example of Honda's beancounters at work? :huh:
[image: View Post]BCsnowcat, on Oct 8 2008, 08:16 PM, said:
when i dropped 1 tooth on the front, then the speedo matched my gps...as if it matters :)
That is the exact opposite of what should happen! :blink:
Your speedo would be aprox. 15% fast at the point( if the 5th gen speedo is the 8% like the 6th gen?) and if your GPS says it's correct, I would sure return it for a working model! ;p
Adding a tooth would get it much closer! :biggrin:
End of thread · 24 posts recoveredWayback Machine snapshot 12 Apr 2010