Speedometer correction?

[Carl722]

I noticed that I had to ride quite fast to keep up with traffic and mounted my GPS and checked my speedometer against it. My speedometer is turning 10% fast. I know they are a simple system but was wondering if there is a way to correct the speedometer.
Has anyone attempted or corrected theirs?

[Floyd Dolin]

We have personally discovered that the Honda motorcycle speedometer is not very accurate as has been mentioned in prior threads. My wife (on her Shadow) had mentioned that I was speeding. My speedometer on my H-D showed 70MPH and hers was 75MPH. When we got back from our trip we did a run with me driving her car and she on her bike. Same result. Her Shadow was off by approximately 5 MPH. Some have mentioned changing gear ratio, but I believe that it's just the nature of the beast.

[SnoGhost13]

Never checked my 08 VT750C2 from the factory but after putting a Metzeler ME880 170/80-15 on the rear it is pretty dead on. Tells me I had to be a bit off with the original 160/80-15 back there.

Sent from my SPH-D710 using Motorcycle.com App

[ButchA]

Originally Posted by Floyd Dolin

We have personally discovered that the Honda motorcycle speedometer is not very accurate as has been mentioned in prior threads. My wife (on her Shadow) had mentioned that I was speeding. My speedometer on my H-D showed 70MPH and hers was 75MPH. When we got back from our trip we did a run with me driving her car and she on her bike. Same result. Her Shadow was off by approximately 5 MPH. Some have mentioned changing gear ratio, but I believe that it's just the nature of the beast.

My wife and I did the same thing...

She drove her Chevy Cobalt at 70mph on a section of the interstate. Once it was safe to pass, I cruised up in the next lane and aligned myself with her side-by-side.

Chevy Cobalt ===> 70 mph
Shadow Aero 750 ===> 75 mph

[adlowe]

Originally Posted by Carl722

Has anyone attempted or corrected theirs?

The easiest way to correct yours would be to get a new faceplate printed, open up your speedometer and change it. Somewhere I might have a few links for outfits that can print them for you. I'll come back and edit them in if I find them.

Folks with speedometers that run off electrical signals (your bike -- and mine -- does NOT) have a couple of other options. There's an active thread on that right now.

[Earthling789]

I don't think I've ever had a car/truck/bike that was 100% accurate on the speedometer... most err on the low side of actual speed.... up to 10%.

I've tested by stopwatch method ... mile-marker to mile-marker (level, straight-stretch of highway) @ 60mph on the speedo should take 60-seconds. If it takes 62 seconds, you're 96.8% accurate, or running 58mph (0.968 x 60), conversely, if it takes only 58 seconds, you're 103.5% accurate, or actually running at 62mph!

I've found my wife's Fusion to be the most accurate vehicle in the stable... speedo is within 1-sec, marker to marker, so when her speedo reads 60, she's actually doing 59-ish.

My Shadow... at 60 on the speedo, was actually running 54-ish... 10% low... but that was with my older, nearly bald tires... I'm sure with my new tires, I'm probably within 5-6%, but still on the low side. (hard to use stopwatch method on the bike, but using my wife's car as a gauge, she said I was running dead-on at 55, side-by-side on the parkway, adjusting for her ~1mph offset... put me at 54-ish mph)

My '69 F250, however, has oversize tires, and at 60 on the speedo, I'm running actual speed of 67... so I have to really watch myself on the highway/Interstates... If I creep up to speed limit of 70 on the speedo, I'm actually running closer to 78.5!

[John Hopkins]

The only reason we really need a speedo is so that we can slow down when we see smokey, so if it's running a bit fast it might be a good thing..

John.

[Carl722]

I have a hypertech tuner for my truck. I changed the tire size and used the tuner to adjust the speedometer dead on with the GPS.

I haven't looked yet but I thought the bike speedometer was on a cable from the front wheel. That is common for older bikes, I haven't paid attention to the newer bikes speedometers to know if they are run off the gear case, if they are the rear tire size would be a factor. Just changing the face plate won't correct the odometer running up mileage more than what the bike is doing.

[Carl722]

I used to use the yard sticks but now I use the GPS to correct the speed because that is extremely accurate more so than police radar. My car is dead on without programming my truck with OEM tires was about 5% fast.

[adlowe]

Originally Posted by SnoGhost13

Never checked my 08 VT750C2 from the factory but after putting a Metzeler ME880 170/80-15 on the rear it is pretty dead on. Tells me I had to be a bit off with the original 160/80-15 back there.

The front wheel drives the speedometer.

Originally Posted by Earthling789

I don't think I've ever had a car/truck/bike that was 100% accurate on the speedometer... most err on the low side of actual speed.... up to 10%.

By law in the U.S. Almost ALL of the cars I've had have been very, very accurate -- the biggest variation on Chrysler, Ford & GM products that I've had is way less than 2%. Almost every Honda car I've owned has been slightly (about 2%) off. Every bike I've owned (Honda or otherwise) has been off by 5% to 10%.

Originally Posted by Carl722

I haven't looked yet but I thought the bike speedometer was on a cable from the front wheel. That is common for older bikes, I haven't paid attention to the newer bikes speedometers to know if they are run off the gear case, if they are the rear tire size would be a factor. Just changing the face plate won't correct the odometer running up mileage more than what the bike is doing.

You don't need to look for YOUR bike if it is a 1999 VT1100C2 (aka 1100 Shadow A.C.E.) -- it is a mechanical system and you can NOT fix it with an electronic device. Changing the tire will, of course, have an affect -- but you won't be getting a 10% overstatement out that way.

And, yes, changing the faceplate will NOT affect the odometer. Although driven by the same cable, it runs on a different system inside the speedometer housing so it is NOT tied into the same error as the speedometer needle. It can be completely different -- even right on the mark. They are two different gauges driven off the same front tire but for all practical purposes the tire is the only thing they have in common. Fixing the odometer, though, is NOT a question you have posed in this thread.

And you don't need to worry about other bikes having their speedometers driven by the gear case and/or rear tire.