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how off is a stock speedo?

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I noticed in town today on two occasions that my speed was off when clocked by a mobile radar unit....I think 40mph on my dash it was showing 36-37. Are vfr's known to read higher than they are actually going? In addition to having a speedometer not correct the idea that I am giving away free miles is not acceptable. I am due for a chain and sproket because I noticed that portions of my chain is stretched which is making it harder to find an ideal chain adjustment.  If speed is off by as much as 10% then I want to choose a sproket that will make up for the difference as close as possible anyway.

thanks

Joel

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I do believe that all motorcycle speedos are off. Given that the tire has a round profile rather than flat like a car, it is impossible to have a consistant and accurate speed reading.  Your speed indicated will be one thing riding totally upright and another when corning or hitting the twisties. To change the gearing will not correct this for all your riding.  It is the nature of the beast. Just be aware of it and move on.  Or you could get yourself a GPS and rely on that for your precise speed.

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I have calculated, based on both road-side radar and a GPS, that my fifth gen speedos, all of them, consistently register as ~8% optimistic. YMMV

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It's a very common issue with most bike speedometers. 8-10% is the norm. However the odometer is spot on, even

if the speedometer is off. So if you change your speedometer reading by regearing, your odometer will then be off.

 

When I went to the 45-tooth rear sprocket I installed a bicycle computer that I set to the correct speed reading. And

a GPS will work too.

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I use the Speedo Healer V3 unit (bought used from a goldwing) to accurately represent my speedo. I need it to be accurate because I do enjoy riding the bike fast. It under-reports the mileage though, but it won't really matter because I don't plan to ever sell this VFR.

 

that may change do to recent troubles with it lmao. 

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My VFR is down a tooth on the front sprocket so it was off 15.7%. I got tired of doing the math in my head so installed a SpeedHealer yeah the mileage is now off 15.7 percent.   

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44 minutes ago, thepretender said:

My VFR is down a tooth on the front sprocket so it was off 15.7%.

 

Methinks your arithmetic is faulty. Your '02 VFR came with 16/43 gearing, so a 15 tooth sprocket changes the gearing only by ~6%.

How'd you come up with the 15.7% value?

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2 hours ago, Urbanengineer said:

I use the Speedo Healer V3 unit (bought used from a goldwing) to accurately represent my speedo. I need it to be accurate because I do enjoy riding the bike fast. It under-reports the mileage though, but it won't really matter because I don't plan to ever sell this VFR.

 Why would it under-report mileage if the speed is set accurate?

 

If you set the speedohealer to -99% it would yes I reckon.. :tongue:

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My stock 03 is off by approximately 5 kms/hr.


Sent from my iPhone using Tapatalk

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12 hours ago, Lorne said:

 

Methinks your arithmetic is faulty. Your '02 VFR came with 16/43 gearing, so a 15 tooth sprocket changes the gearing only by ~6%.

How'd you come up with the 15.7% value?

Used GPS (phone) to get real mph then use math to calculate from reported mph difference is 15.7%.

Nylon thingy on sensor is shot so for next couple of days getting 0 mph and 0 miles per gallon 😁

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13 hours ago, Lorne said:

 

Methinks your arithmetic is faulty. Your '02 VFR came with 16/43 gearing, so a 15 tooth sprocket changes the gearing only by ~6%.

How'd you come up with the 15.7% value?

If the mileage was already off to begin with, and you add some more it could add up to that much. I added 2 teeth at the rear and

mine is now off around 12-15%.

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13 hours ago, thepretender said:

Used GPS (phone) to get real mph then use math to calculate from reported mph difference is 15.7%.

Nylon thingy on sensor is shot so for next couple of days getting 0 mph and 0 miles per gallon 😁

 

Ah, now I see what you meant.

 

Btw, it simply isn't possible to have both an accurate speedo and an accurate odometer on 3rd, 5th, or 6th Gen VFRs. My examples all had speedos that read about 5-6% high while their odos were near spot on. (checking against mile markers keeps the mind occupied on long rides through the American west )

 

Btw, I assume most other Hondas are the same but can only comment on the ones I've owned.

 

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Every Honda, Suzuki, Kawasaki, and Yamaha I've ever owned all read high on the speedometer. The only bikes

I've ever owned that were on the money as far as speedometer/odometer readings were a '71 and '73 Triumph

Bonneville.

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I put a SpeedoDRD on mine. I find the 10% error extremely irritating... "let's see... Speedometer says 70, so I'm actually doing about 63... Limit is 55... I can probably get away with 10 over..." I'm fairly capable of doing math in my head, but it detracts from my enjoyment. I used to ignore it when I didn't feel like thinking about it... One $300 ticket later, I decided it would be cheaper to deal with the odometer error. Granted, I knew I was speeding, but I didn't think I was pushing it that hard. 

 

I've heard a few different explanations for the practice... Whether it is safety, or marketing or just a small piece of some convoluted plot of the illuminati, it needs to end. Dear motorcycle manufacturers: please don't sell me bikes with broken gauges! 

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Apparently they used to get sued over the speed over reporting... so they just made everyone think they were faster than they were and made the odo accurate and the speedos high reading. 

 

When the tire is nearly worn out it reads higher than when it’s new. 

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I never knew about lawsuits over that - I just figured they were trying to save me (and my license) from myself!  :blush:

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I never heard of any lawsuits during that time, and the Brit bikes were spot on, just the Japanese bikes were so far off. I think they

just wanted the bikes to look like they were going faster than they were. Then they could say that their smaller bikes could go X number

of miles per hour. Pure marketing I think.

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This is the best explanation I can find for factory speedo error.

 

From the RACQ WEB PAGE

Quote

Australian Speedo accuracy standards 

Australian Design Rule 18 sets out the accuracy standards for vehicle speedos. 

Until July 2006 this rule specified an accuracy of +/- 10 percent of the vehicle’s true speed when the vehicle was travelling above 40km/h.

That is, at a true vehicle speed of 100km/h the speedo could indicate between 90km/h and 110km/h.

An odometer accuracy of +/- 4 percent was also a requirement.

From July 1 2006 a new standard began its phase in and by 1 July 2007 all new vehicles had to comply. The new standard requires that:

  • The speedo must not indicate a speed less than the vehicle’s true speed or a speed greater than the vehicle’s true speed by an amount more than 10 percent plus 4 km/h. 
  • Odometer accuracy is no longer defined.

What this means:

  • For a vehicle travelling at a true speed of 100km/h, the speedo must read between 100km/h and 114km/h.  The effect of this is that many drivers will find that at 100km/h they are driving up to 14km/h below the speed limit if they rely on the vehicle’s speedo. 
  • The speedo must always read 'safe', meaning the vehicle must not travel faster than the speed indicated by the speedo. 

This change was made to align Australian vehicle rules with those already in place in Europe.  It applies to all Australian motor vehicles except mopeds.

Dealers will generally not attempt to correct speedo error unless it exceeds the legal requirements.

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Possible, but that seems pretty recent, and all Japanese motorcycle speedometers from the early 60's on have all been optimistic.

I still think they did it just so it would look like you were going faster than you really were. Early Japanese bikes were all under 500 cc

basically, so higher than normal speeds would have been a real plus. It's like "Look at this, our 350 twins will hit 100 mph", when they

really are only doing about 90 mph.

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1 hour ago, FJ12Ryder said:

Possible, but that seems pretty recent, and all Japanese motorcycle speedometers from the early 60's on have all been optimistic.

I still think they did it just so it would look like you were going faster than you really were. Early Japanese bikes were all under 500 cc

basically, so higher than normal speeds would have been a real plus. It's like "Look at this, our 350 twins will hit 100 mph", when they

really are only doing about 90 mph.

The question is which market for Japanese bikes has had a requirement favouring over reading speedos the longest? Make one bike that meets the tightest regs.

 

I can see the promotional/marketing motivation in the days when cross referencing speedos between bikes was more hit and miss! (but I do have in the shed a 1990 VT250L with an exact reading +/-1 kph mechanical speedo and it will do a hundred on a gps!)

 

I also see a safety/speed related accident liability angle. (And I suffer a Suzuki with a 10% over reading speedo that drives me nuts, Why is all the traffic passing me?)

 

The only answer I got for the vfr is to gear the cogs the way you like it and add some brand of speedo healer.

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