Will it fit?
The JR will fit most bicycles with rim brakes. The diameter of the axle cannot be greater than 10mm (fits 3/8”). The diameter of the hub flanges, where the spokes attach, should not be greater than 52mm (2”). The clearance from the forks to the spokes should be more than 12mm (1/2”). These are very common dimensions. In general, simple, inexpensive bicycles seem to allow its installation better than expensive ones. Features such as carbon-fiber forks, or beefy shocks on the front tend to be more problematic, but not always. A couple customers experienced multiple failures within a mile or so after installing the counter “properly” on a brand-new bike, and unfortunately they had to buy different axles/rims in order to be able to use it.
There is now a right-hand version that fits bikes with disc brakes, but the larger hubs can be an issue. See the “Special Sale” page for details.
5 digit or 6?
Both counters produce the same resolution of approximately 9 to 10 centimeters per “count”. On 700c x 35 tires, this is almost exactly 11,000 counts per kilometer after including the 1.001 SCPF. Smaller tire will have greater counts/km. The 5-digit will “roll over” at approximately 10km, and the 6-digit at about 100km. Both units can be used to measure any length of course. Rollovers are easily handled by adding a “one” in front of the data like an auto speedometer. A 5-digit requires fewer numbers to be recorded “in the field”, and may lessen transcription errors.
The manufacturer of the counter specifies the unit should not exceed 5,000 counts per minute, which equates to 27kph, or 17 mph on 700c x 35 tires, and slower on 26” tires. Many people have exceeded this briefly during routine riding without incident, however the limit exists, and failures have occurred. In one case, the user admitted to routinely exceeded 35 mph on a long downhill.
Lubrication / maintenance:
If there is any resistance to turning, first examine the setup. If there is resistance or excessive noise during operation, something is binding. Try a little oil - it's possible that this will seek out the binding and smooth out the operation.
Properly installed it does make a little noise, but sometimes prior to failure it sounds louder. It’s likely the unit was bent laying the bike down, or otherwise catching the counter on something loading or riding the bike. Possibly it’s getting worn out. In normal operation there should be little noise, and no “grinding” sound. Oil is often the cure for noise.
Personally I’ve bent up a few of my counters, and it isn’t the end of the world. It can however end the day’s measuring. Once I crammed my bike into the back of the car, and bent the chassis. Another time, I ran off the trail I was riding, and a twig got into the chassis / gear and fouled things up. Last, my kickstand gave out, with the bike/ curb in the wrong spot as it fell. I fixed this one with a little twist of the chassis.
If you recognize the sound it makes is “different”, check to make sure the unit spins freely and the gears aren’t binding. If the gears mesh too tightly, you may have bent the chassis slightly. I’ve bent a couple straight, usually a slight tug on the counter is all it takes to get the gears to mesh properly again.
Can it be reset?
The counter does not have a reset button. Over the years Jones Counters have never had them. The counter is part of the measurement process, and the process includes review by a state certifier. Having people reset their count in the middle of a measurement, unless fully explained, can lead to confusion. Thus no great demand for a resettable counter has yet arisen.