Smith Speedo accuracy

Smith Speedo accuracy

I'd read how accurate Smith speedos can be and here's another test that confirms it. Unbelievable steady needle reading in past Peel made me search out prior for some reality check.


http://www.motorcyclespecs.co.za/model/ ... ter_72.htm
Norton is to be commended for the accuracy of their speedometer. We tested accuracy at both 60 and 80 miles per hour. The speedo was consistently optimistic but by less than one mph at either speed. At 60 the percentage error was less than one and a half while at 80 mph it dropped to just over one percent. The Harley edged out the Norton by six one hundreds of a percentage point for speedo accuracy at 60 mph but was out of the ball park upon increasing speed to 80. It read about six miles per hour under actual speed—almost an eight percent error. It is interesting to note that the Harley and the Trident were the only two bikes that went faster than their instrument indicated. We could detect no lag in tachometer performance. We did find it necessary to concentrate on instrument location as our left hand searched for the various light and turn signal controls. The tach and speedo are separated just enough to make it difficult to take in their respective information simultaneously. We would like to see a trip meter added. It's a handy little addition and can save the rider from those old empty gas tank blues.

Steve
It is interesting that you posted this at this time as I had the 74 850 out today testing with a tire that I switched (front to back) Avon AM-26 with a fresh skin up on the front. I took the Garmin Nuvi 680GPS and tracked the MPH with the smith clock. I found that I was about 3 MPH faster on the smith clock as per GPS. Pretty consistent through the speed range.
Regards,
Tom
CNN

You can get arround 3% variation , with tyre wear . Tyre size / aspect ratio gets into it too . Based on the 26 in Dia. Circumferance traditionally applied .

The Gendarme traditionally used CHRONOMETRIC instruments , renowned for their accuracy . The 61 triumphs went in 1 mph imcrements , before overhaul.



The Bonnevilles had to run 140 m.p.h. speedos , in case the mufflers ' fell off ' .

This thing's not too bad , eh steve . Just the thing for a woodsman .

Yes
I was pretty much nuts on with the speed when my back tire was at the tread wear indicator marks.
Very cool thread.
Cheers
Tom
CNN

Yes certainly tire circumference matters unless within range of factory issue. I had a weird thing happen topping out on Peel, once, Tach needle stabilized at 6000 but speedo suddenly jumped up a few mph, it felt like the rear tire had expanded and tach needle dropped some but not the speedo needle. I've seen my scooter tire expand reving on center stand, but that was well below triple digits indicated. There was a 40 ft drop over 1/4 mile section when this occurred and maybe a following breeze. Speedo needle was steady to read so something else messing with it. It was only hard to read d/t wind buffet, so i had to put shield on it to make sure of the sight. Peel eventually wore that drive out some 1000's of miles later. Modern cars and bikes all tend to read 2 mph faster than road speed. I've GPS now to check next time it matters.

Chronometric gets my vote, & seeing that clockwork/metronomic flick is even cooler with the tacho..
Could try a bicycle speedo on the front wheel for comparative purposes..