Recalibrating Speedometer

[Ziraya]

A week or so ago I was going down a 25mph road, pretty much flat, and I passed one of those road side radar units, the kind that displays your speed, well it said I was going 23mph where my speedo said 25, it might have only been 2 miles an hour difference but it was apparently enough that most of the cars coming up behind me felt they had to pass. I'd like to fix it if I can, but I don't have access to a gps unit or radar gun, and don't remember where that unit was.

It is an '88 so I can imagine after twenty years the springs might have worn out a little, so would the best solution be to order a replacement spring? Or does anybody make a digital system fitted to the SB's 'dashboard', maybe just a mounting plate I can use with some brand name thing

[mikehelms]

A week or so ago I was going down a 25mph road, pretty much flat, and I passed one of those road side radar units, the kind that displays your speed, well it said I was going 23mph where my speedo said 25, it might have only been 2 miles an hour difference but it was apparently enough that most of the cars coming up behind me felt they had to pass.

The 2 mph difference probably wasn't what made cars want to pass you.

Most speedometers are calibrated to read a bit optimistic. My Ducati speedo reads 70 mph - GPS says I'm going 67 or 68. Ditto for my car.

Speedometers are finicky things ... I'd just live with the 2 mph difference, and not risk making it worse.

-- Mike

[keithw]

There might be a calibration adjustment on the inside. Unfortunately before you mess with it you need a calibration source, like a GPS or radar. Unless you're really good with tiny fiddly bits things go down hill really fast. Or you can pay a professional speedo shop to do it.

The bottom line is that it isn't worth it. Make a mental note that 27mph is really 25mph. At work a lot of the vehicles had badly calibrated speedos. They would put a label on it saying something like "indicated 58, actual 60".

Speedos are almost never calibrated very well. That's one reason you almost never will get a ticket for going just a few mph over the limit.

keithw

[Ziraya]

Alright, I can live with it, but how bout this, can I reset my odometer? it's over 30k so rewinding it would take forever even if that works

[keithw]

Legally there are two times you can reset an odometer. If it is broken you can reset it to zero or the estimated mileage when you repair it. If you install a new one it can be left at zero or changed to reflect the estimated mileage. In either case you need to let the new owner know that the odometer reading does not reflect the actual mileage.

Turning it backwards isn't practical as it would take weeks. Some can be taken apart and reset. Depends on how it was put together. Some have tiny screws but others are crimped. The crimped ones are tough to get apart.

keithw

[66SIX]

Or you could just take it apart .
And not tell anyone.
Wow my 15 year old Elite has no miles on it .
I also re-did the face plate ,I guess I should have put in ( may not be actual mileage )

[eliteguy50]

An sb reading 30k on the odometer? Are you sure? Every sb I have odometer I have ever seen rolls over at 10k not 100k. The white is tenths of a mile.

Install a bigger front tire to correct the speedo.

[devenex]

The easiest way to knock out atleast some of that speedo optimism is to put a larger front tire on. All these honda scooter seem to be ~10% optimistic w/ stock tires.

[swimmingfree]

so what size wood you need to put on the front a 3.00 to get the 10% down to 0 ???
swimmingfree

[Wheelman-111]

Greetings:

At around 7-8% optimistic, (2/25 =8/100) your perfect groundspeed correction is to take the 2.50 front tire,
(15" total diamater) and make it 8% bigger. That'd be 16.2". A 3.00x10 tire would get you almost there - 16" nominal - but still retain a hair of optimism for pesky ticket prevention. Trouble is, does it fit within the forks and fender?

Most of the Big Four (and even rustic Harley-Davidson) went to all-electronic speed devices for several reasons, not the least of which is the easy programmability. (H-D in particular sells their basic engine packages with a wide variety of tire sizes and diameters.) There's a "convertor box" to gear up - or down - from miles to KPH, but fine-tuning to 5 or 10 percent just isn't feasible with a mechanical device.

[eliteguy50]

I run a 2.75x10 and that fits with the forks at full compression.