Author Topic: Is your speedometer telling you the right MPH?  (Read 6250 times)

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Phxmark123

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Is your speedometer telling you the right MPH?
« on: July 11, 2008, 05:00:07 PM »
I had an idea that my speedometer wasn't correct when I was doing the speed limit on the freeway and everybody was passing me. Here's a tip to check out if yours is correct. I got my Magellan SporTrak Map hand held GPS and turned it on and let it find a satellite and took off down the road on my bike. I am guessing most hand held GPSes have a speedometer option. Mine does. I tested it in my Cadillac and it was right on so I cruised down the road and took a look at it and sure enough my speedometer was 5mph slower than the GPS. I was right.



Offline Markcb750

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Re: Is your speedometer telling you the right MPH?
« Reply #1 on: July 11, 2008, 06:19:10 PM »
According to the local Red LED speed limit indicators my speedometer on my '76 is off 10mph at 50...

Speedo says 50

Sign radar says 40

checked it four times through two different signs.


Not very good, no wonder kids in hopped up Civics give me the finger.
"Imagine the people who believe such things and who are not ashamed to ignore, totally, all the patient findings of thinking minds through all the centuries since the Bible was written. And it is these ignorant people, the most uneducated, the most unimaginative, the most unthinking among us, who would make themselves the guides and leaders of us all... I personally resent it bitterly." ~Isaac Asimov

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Offline markjenn

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Re: Is your speedometer telling you the right MPH?
« Reply #2 on: July 11, 2008, 07:29:47 PM »
Almost all GPS's have a speed function and in reasonably steady state conditions even the cheap ones are extremely accurate so this is a great way to calibrate our (usually 5% high but anywhere from 0% to 10% high) speedos.

Another good way is to go a steady 60mph on the freeway, watching the mileage markers.  The number of seconds you're off from 60 at each marker is approximately your speedo error in mph (e.g., if it takes 63 seconds, your speedo is about 3 mph high).

- Mark



jameseb444

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Re: Is your speedometer telling you the right MPH?
« Reply #3 on: July 11, 2008, 10:14:25 PM »
I asked the same question a while back and several responded saying their all about 10-15% off. The speedo usually says your going faster than you actually are. I was going 60 mph in a construction zone just to keep up with traffic. I figured everyone was going 55 mph which is normal for this part of the country. You can't drive fast enough for morons around here. Even old ladies pass me giving me the finger ;). You just can't go for a nice cruise anymore without pssing someone off.



Offline rbmgf7

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Re: Is your speedometer telling you the right MPH?
« Reply #4 on: July 12, 2008, 08:46:53 PM »
ditto. i try and do the speed limit and when i do, i get passed like i'm standing still. i figured on a road that's 45mph, i was doing maybe high 30 to 40.

when i get on the throttle from a stop, my speedo will hit about 35 and either stop for a few seconds or sometimes accelerate exponentially. i got on a road that was 45 and hit the gas, all of a sudden my speedo said i was doing 70 in 2nd.

maybe the mechanicals need lubing inside the instrumet unit.



Offline sandcastcb750

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Re: Is your speedometer telling you the right MPH?
« Reply #5 on: July 15, 2008, 02:59:48 PM »
Don't assume the motorcycle speedometer is optimistic; while most of my Hondas have been almost exact, my 1982 Goldwing reads 60mph when the GPS says 65mph. Could be a problem someday.



Phxmark123

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Re: Is your speedometer telling you the right MPH?
« Reply #6 on: July 15, 2008, 03:48:21 PM »
I thought I would throw this out there with out doing a little research. I wonder if there is an after market digital speedometer?



Gittfiddler

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Re: Is your speedometer telling you the right MPH?
« Reply #7 on: July 15, 2008, 04:30:34 PM »
anyone ever messed with the stock speedo to calibrate?



Offline winnipeg550guy

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Re: Is your speedometer telling you the right MPH?
« Reply #8 on: July 15, 2008, 05:35:16 PM »
Here's the solution I went with, also used GPS to calibrate cycle speedo, now it's spot on. Much in the same manner as done here. I'm considering removing stock speedo all together now.

http://www.houseofthud.com/bikecomputer.html

 Simple and cheap, Some models come with backlight as well and I've read other articles telling people to stay away from the wireless models.
« Last Edit: July 15, 2008, 05:38:35 PM by winnipeg550guy »
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Offline Uncle Ernie

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Re: Is your speedometer telling you the right MPH?
« Reply #9 on: July 15, 2008, 09:13:58 PM »
I already knew this simply because when I'm going an indicated 70, I can feel the draft as old people using walkers pass me while walking to the drug store.

What's depressing is now I KNOW my bike is even slower than I thought it was.  Maybe it's time to look for a stock airbox.
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Offline JaredJL

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Re: Is your speedometer telling you the right MPH?
« Reply #10 on: July 21, 2008, 10:11:54 PM »
mine is also off around 10mph or so... if it makes anyone feel any better.



fixahonda

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Re: Is your speedometer telling you the right MPH?
« Reply #11 on: July 23, 2008, 01:54:56 PM »
Mine is off by about 7 mph I'm pretty sure. It sucks too. The bike is screaming going "75" and I'm still getting passed out left and right.

The bike speedo looks pretty neat though. I could use a clock as well. I'll have to check into getting one of those dealies.



Offline gc8andy

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Re: Is your speedometer telling you the right MPH?
« Reply #12 on: July 23, 2008, 03:25:05 PM »
I think I am going to go with the Trail Tech Vaypor for a modern Spedo/Tach

http://trailtech.net/vapor.html
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NE550

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Re: Is your speedometer telling you the right MPH?
« Reply #13 on: July 25, 2008, 12:21:55 PM »
You got me thinking about mine.  I went by a police radar trailer and kept it steady at 50 mph, the sign registered 45.  I'm gonna try a little WD40 in the cable to see if it helps.  I'll let you know if it works or not.

Matt



joeyboy

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Re: Is your speedometer telling you the right MPH?
« Reply #14 on: July 26, 2008, 01:25:13 AM »
I noticed mine was off the same way as most everyone here.  I was being passed by everyone.  But how could this be on my bad motor scooter?  So it is like being at the firing range, I use kentucky windage, sort to speak.  I know how much it is off, and I internally calibrate.  In fact, the light went out in my speedo the other day, so at night, I reference the tach.  It all works out somehow.  It feels good doing 90-95 mph on the highway (or more like 75-80).



Offline Venturous

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Re: Is your speedometer telling you the right MPH?
« Reply #15 on: July 26, 2008, 05:45:15 AM »
Nearly every bike I've ridden since GPS's became common is off 5% to 10% with the exception of Harley, so not surprising these are. My solution is simple. I quite looking at the speedometer. I use my GPS for speed.
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Offline cadunkle

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Re: Is your speedometer telling you the right MPH?
« Reply #16 on: August 02, 2008, 01:02:38 PM »
This is all well and good to figure on how far off your speedometer is, but how does one go about calibrating the speedometer. Is this internal to the speedometer or are different tooth count on the speedometer gear or hub used? My bike is a '71 CB750 if it makes any difference.



Offline DonD

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Re: Is your speedometer telling you the right MPH?
« Reply #17 on: August 02, 2008, 05:31:39 PM »
Since my bike needs new speedometer/tach faces, I've considered re-calibrating it with the new faces.  I haven't thought about it too in-depth yet.  Maybe disassemble the units enough to remove the glass, put them back on the bike, and drive down a lonely road.  As the GPS unit would hit units divisible by 10, mark where the needle is on the speedo face.  Then I could create the custom face using those marks with the actual MPH.



Offline markjenn

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Re: Is your speedometer telling you the right MPH?
« Reply #18 on: August 04, 2008, 03:09:20 PM »
This is all well and good to figure on how far off your speedometer is, but how does one go about calibrating the speedometer. Is this internal to the speedometer or are different tooth count on the speedometer gear or hub used? My bike is a '71 CB750 if it makes any difference.

For bikes with electronic speedos, there is a device called the "Speedo Healer" which manipulates the electronic signals to make corrections.  But on a mechanically driven speedo, you really don't have any options, other than refacing the speedo.  For my V-Strom, someone took the trouble to do exactly this and I replaced my gauge faces and now have a dead-nuts accurate speedo.  But I don't think anyone is doing this for our old bikes so unless you're a graphic artist and have access to silk-screening facilities, probably not feasbile.

There may be ways to go inside the unit and tweak things, but I've never heard anyone do it.  Just getting in the sealed units is difficult without hacking them up.

One of those things you live with I guess - calibrate and then do the minor math in your head.  For most of my bikes which are off the typical 5 mph at freeway/highway speeds, I simply ride at an indicated 10 over which means I'm about 5 over.  Around town, I do 5 over which means I'm probably 2-3 over.  The only problem I have is that with my V-Strom speedo now spot on, I have to dial back on that bike.

- Mark



Offline muscle_car1

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Re: Is your speedometer telling you the right MPH?
« Reply #19 on: August 31, 2008, 12:32:54 PM »
I think I am going to go with the Trail Tech Vaypor for a modern Spedo/Tach

http://trailtech.net/vapor.html


Is this feasable?? For the cb
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Offline skamagedon

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Re: Is your speedometer telling you the right MPH?
« Reply #20 on: May 16, 2011, 09:24:50 AM »
I thought I would throw this out there with out doing a little research. I wonder if there is an after market digital speedometer?


    I use a Sigma bc1106 and it is accurate to 200mph, to 100th of a mile. i love it. other nifty features as well
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Offline bjatwood

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Re: Is your speedometer telling you the right MPH?
« Reply #21 on: August 12, 2011, 10:54:45 AM »
While my method for checking mine was not very scientific, I used a Honda Accord that I was passing a couple days ago that had a digital speedometer readout. The car speedo showed it  was going 62 and when I slowed my bike to match the cars speed mine showed I was doing 67 on my speedo. So now, I drive at 70 on the highway and stay with the flow of traffic quite nicely.
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Offline motocyconomad

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Re: Is your speedometer telling you the right MPH?
« Reply #22 on: August 12, 2011, 11:14:03 AM »
GPS is the speedo all I kept was the tacho put it right in the middle.

Ive been eyeing that Koso instrument clusters for a while   i just get nervous about hooking it all up.



Offline BobbyR

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Re: Is your speedometer telling you the right MPH?
« Reply #23 on: August 20, 2011, 10:42:50 AM »
I used a few of those roadside speed signs and they agreed with my speedo but I wonder how calibrated they are. A few weeks ago on a Parkway the speedo was reading 75mph and a gentleman that works for the County validated that speed was correct. He was going to put it in writing, but we have common acquaintances.  ;D ;D ;D ;D 
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Offline Bob Wessner

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Re: Is your speedometer telling you the right MPH?
« Reply #24 on: August 20, 2011, 11:08:45 AM »
I've found that my 750 is off by about 2 mph (low per the speedo) against a GPS. Similarly, my Honda CRV is off by about the same amount per the GPS. One can almost think this is deliberate for liability reasons.  ;)
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