[The Old Coot]

I got a chance to check the speedo on my today and it's about 5 mph fast. Is that normal for the Enfield?

[Richard230]

That is normal for my 2011 B5.

[sumaris]

Mine reads about 10KPH faster than the speed on my GPS

[Ice]

 Speedometers "optimistic" by a few MPH is normal for most bikes.

[no bs]

I've always suspected the speedo was "optimistic" on the g5. I recently acquired a garmin that shows mph, and i'll post the unit's speed vs. indicated speed when I figure out the damn thing.

[wildbill]

I think you will find most are very accurate where they have to be around the 30 to 35 mph mark or built up areas/safety zones and once they get to 60 mph read that little bit fast. not only in bikes but cars too.

[Arizoni]

In Phoenix, where I live they have signs that show how fast approaching traffic is moving.  They use radar to figure out the speed.

When I'm approaching these signs on my G5, they indicate I'm going very close to the speed indicated on my  speedometer.

I've also read a lot of posts where riders on the C5's are actually traveling 5 mph slower than their speedometer shows.

I think part of the reason for this is, my G5 is running 19 inch wheels.  The C5's are running 18 inch wheels.

At any given speed, the C5's 18 inch wheels are spinning faster than my 19 inch wheels.

Since both motorcycles are using the same speedometer and the same gear system in the speedometer drive, I think the faster turning C5's wheels give the speedometer the error they are seeing.

The difference between the 18 inch and the 19 inch wheels gives the 18 inch wheels about a 6 percent faster rotation speed.  That would show up as a 6 percent difference on the speedometer.

At a speed of 50 mph that 6 percent would be about 3 mph and given the errors in a mechanical speedometer I can see where this might be read as a 5 mph error.

[SteveThackery]

Mine read 5mph fast at 30, and 3mph fast at 70.

I improved it by taking the needle off and shifting it back by 3mph.  I then bent the needle stop so it pointed at 0mph again when stationary.

So now it is 2mph fast at 30, and spot on at 70.

[Blairio]

Should there not be different speedo drive ratios for the different wheel sizes? That was the norm back in the day.

Also, my cheap bicycle computer ($20) worked perfectly when I fitted it to my old Francis barnet, although its top speed is now 58 rather than 65!

[The Old Coot]

Arizoni, my C5 has a 19 front wheel so that's not what's going on.

I know almost every bike I have had the speedo is fast on. The KLR is like the C5, about 5 mph. The Versys was fast but not that much and having a VSS on the counter sprocket when I changed for a 15 to a 16 tooth it is now almost dead on.

So are they set like this for bragging rights? or to try and get riders to go a bit slower? 

[Richard230]

I have two BMW motorcycles and both read 8% fast.  Apparently this is typical of most modern motorcycles, according to many internet postings about the subject.  Manufacturers claim that they deliberately do this to compensate for tire wear (?) and future changes in replacement tire rolling radii (and sometimes they say that it is required by DOT regulations).  But I believe (always liking a good conspiracy theory) that manufacturers make their speedometers read fast to increase reported top speeds.  Fooling with the speedometer to show a high top speed is sure a lot cheaper than inserting more horsepower into the engine.  (LOL)

[Captwilly]

Yep 5 mph off on my C5, pretty consistent through the range though. My Triumph Scrambler is dead on per GPS and traffic radars. So I guess it varies.

[barenekd]

Most bikes read about 10% fast, however my Enfield was a bit more accurate, maybe about 5% fast.
All the cars my wife and I've had in the last 20 years were actually quite accurate
Bare

[upintheair]

This discussion is one reason that I went with the Koso North America T&T speedometer/tach combination from Nfield Gear.  It is extremely accurate, so much so that when I had K70 tires installed in place of the skidmasters, I had to remeasure the circumference (9 mm difference, smaller) and enter it into the appropriate place in the programming sequence.  The only anomaly was that the shop knocked one of the magnets out of one of the internal wrenching bolts and put it back in wrong pole up.  That caused me some head-scratching as to the error in speed reading, but a quick check of polarity showed one odd one, so I turned that one around and everything was back to normal.  The shop thought that the unit was made specifically for my B5 because it fits so good.

[heloego]

IIRC the DOT regs allow for a +/- 5mph error in speedos sold in all new vehicles. Regardless of the manufacturers' logic, variation will be found in many new vehicles sold. The logic behind the DOT's allowance (amazing as it is) is because of the different tire outside diameters available, and some reasonable leeway had to be allowed or everyone would be spending half their time paying speeding citations. If you look up the DOT regs you'll find more than a few handy things to help fight some of those citations, as 90% of the traffic court judges, both local and Federal have no clue about this, and the police don't particularly care ("My radar is calibrated").
That said, if the variance proves an issue Steve, myself, and at least one other member of this forum have popped the needle off and reset it back slightly to correct it.