Odometer and Speedometer not in sync?

[bobhamlin]

I've always just accepted the Japanese bikes' 10% differential between the speedometer and actual speed. Then I found out it applies to BMW, too. Since 10% is such an easy calc, it didn't bother me.

A little deeper, I DID resent that my bikes were accumulating 10% more miles than they actually were. But maybe they're not.

My latest excursion raised some doubt about the odometer being tied to the speedometer. So, last weekend, I clocked a 6-mile stretch using mile-markers. My odometer was only off by .1 mile. And that margin of error could have been me wandering back and forth in my lane.

1) Can someone confirm that the speedometer and odometer are independent in their calculations?

2) (If so) Can a marketing-type explain the logic for this (universal) disconnect? I always accepted the 10% speedometer fudge as a way to play loose with emissions rules because I assumed the odometer was in sync. But if the odometer is accurate, that reason is no longer valid since mpg is based on miles traveled. What am I missing?

[VulcanE]

I too have found that the odometer is pretty darn close to what my GPS gets, but I do know they are tied together, because if you use a speed-o-healer to correct your speedo, then your odometer will be off by the amount it took to correct the speedo.

it does make you wonder "What Were They Thinking"?

[goldstar225]

You ask the same questions that I have. My odometer was just about dead on (before my tire change) but the speedometer was off by about 9-10%. Every bike I've owned has been that way and it makes no sense to me. Now that I've changed to the Elite III 160-80 rear my speedometer is off by about 5% (high) and my odometer is off by about 4% (low). Why do the manufacturers not make both of them accurate?

[waterman]

Goldstar, I did the same tire size change as you but did not find my odometer to change much if any as compared to prior to the change. This summer when we did the trip to custer, my odometer was off by less than a mile on a 290 mile ride. This was confirmed by GPS. The speedometer is only off by 5% which is similar to yours.

[Jared]

If I remember right-when I did my iron butt ride, my odo showed 1050 and the gps showed 1034.

[blowndodge]

This is a "well-known" malady with the instrumentation on a Nomad. It is what it is. Why the calculations are not made from the same source for both the speedo and odo is a mystery to Nomad owners.

If one was really anal about it they could use a speedo healer to correct the speedometer then use a jumper wire around the speedo healer connector plug under the side case for the odometer reading; provided the odometer was accurate. The plug has I think 4 wires and one is for the speedometer and one is for the odometer.

[Yellow Jacket]

My 2006 brand new from the dealer had a 10% fast error on the speedometer. The odometer was 3% fast.

I installed a car tire with a 10% larger diameter than the stock MC tire.

My speedometer is now right on and the odometer is 7% slow.

As BD said, "It is what it is."

[bobhamlin]

Originally Posted by Yellow Jacket

As BD said, "It is what it is."

I'm not really questioning "what is." The problem is not limited to Nomads. Every metric bike I checked -- Japanese and European -- has the same issue with roughly the same percentages involved.

If true, this problem is a conscious, manufacturing decision (Or everybody has been block-copying the same original formula that inadvertantly substituted "meter" when they actually wanted "yard."

I've read speculations that legislation prevents bikes from under-reporting speed while mileage must be accurate within a tolerance. I don't buy that since imported cars should fall under the same legislative intent as imported bikes. But cars seem to report individual variations -- not universal patterns.

[blowndodge]

Not sure Bob. Why are Harley's speedometers dead on the money? Almost all Harley's are... go figure huh?

Metrics repeatedly making the same mistake; ie, converting meter to yard as you pointed out would be the biggest goof in an industry that prides itself as leading edge.

I wonder how accurate the BMW motorcycles speedometers are?

[bobhamlin]

Originally Posted by Blowndodge "Darksider"

I wonder how accurate the BMW motorcycles speedometers are?

Actually, finding that BMWs have the same problem was the first specific research I did.

A co-worker and her husband both have BMW 1200 somethings and very different riding styles. She was complaining to me one day that he was justifying exceeding the speed limit because BMW speedometers are known to be 10% off.

I tend to take the husband's side and told her that I knew Japanese bikes had that problem. I then went on to the internet and quickly found a BMW discussion about the 10% problem.

[isaiahsdad]

Ok, here goes. Speedometers and odometers are not linked. The odometer is actually mechanical in nature and the speedometer is static, or, it uses magnetic impulses to send its signal to the little needle. The odometer is connected directly to a gear in the front wheel (in most cases) that gear rotates, spinning a cable that goes into the back of the speedometer/odometer head assembly. It then connects to another gear and a hub. The gear connects directly to the odometer number assembly and is actually geared down to get your odometer reading. The hub is actually a "cup" of sorts with a magnet in one, or sometimes many parts of the hub. As the hub spins, another magnet on the needle hub, or disk, flickers every time the main hub passes it. There is a dampening spring to keep the needle from pulsing at lower speeds and some older speedometers actually do still pulse at low speeds. There are many variables that can effect the actual speed shown on the needle. Since the needles and there assemblies rotate on an axes, that Axel has lubricant that can be effected by weather, heat, moisture etc. So, that is the main reason why there can be such a difference between odometer and speedometer. Why are Harley's more accurate, they either use more magnets in the hub, to make it more accurate, or in the new models, it is all electronic. The pulses are actually calculated and measured like a digital clock. It is a more expensive system but the difference is only a few miles per hour. Most motorcycle companies don't really care to much about a couple miles per hour and are just trying to cut costs. In the industry, it has nothing to do with fuel economy, it has to do with saving money. When they dyno the bike before it rolls out the door, each speedometer has to be within a certain tolerance. And that is it. The EPA does not gage mpg based on the actual speedometer, but on there own equipment calibrated to the inch.

Of course the tire size has everything to do with the equation. The larger the tire, the more distance the tire covers per revolution. The system from the speedo/odometer gear on up has not changed so it cant tell if it is a 195/60, or a 180/70. It just goes by how many times the tire spins and translates that.

To sum it all up, a speedometer and odometer are no different than a tachometer. The all record revolutions per minute, or rpms. The speedometer just translates it to Miles per hour in stead of revolutions per minute. It is by no means an accurate system but better methods are out there. The most accurate, and constant method of calculating speed, and distance, is either the the good old stop watch and tape measure, or the GPS. GPS units use hyper accurate time pieces, calibrated from an atomic clock. It measures the time it takes a signal to travel from the satellite, to your GPS unit, then compares it to other satellites, some times as many as 12 to 14 to get your speed. But it is all based on time, and the ability to its accurate reading.

The best way to check your speedometer is against a GPS. GPS is also the best and most accurate way to gage distance and since it is all time based, it doesn't matter your position on the road, it is all time based.

Hope this helps.

[blowndodge]

Nomads built after 2000 have no odometer gear in the front wheel.

Prior to that the drive gear ran both speedo and odo so I'm unclear where that information came from.

Both speedo and odo are driven off the sensor underneath the left side cover. Refer to Owners Manual for more info to view wiring diagram.

[jd01]

I guess this is not just a problem with the "newer" Nomads with the electronic or digital odometers , as my 2001 has the older analog type odometer and is usually off as well. On the speedometer side, when I'm doing say 70, my GPS says I'm doing 66mph. On the other hand, when my wife and I are out riding, for every 100 miles she rides on her Honda (with digital odometer), my odometer reads 4 miles less. Go figure!

[isaiahsdad]

Originally Posted by Blowndodge "Darksider"

Nomads built after 2000 have no odometer gear in the front wheel.

Prior to that the drive gear ran both speedo and odo so I'm unclear where that information came from.

Both speedo and odo are driven off the sensor underneath the left side cover. Refer to Owners Manual for more info to view wiring diagram.

Yes, the drive gear does run both, it is what happens inside the speedometer unit that what I was talking about happens. Mine is a 99, and it is gear driven from the front wheel. If the newer models are sensor driven then it is a whole different story. I would be interested to see how the sensors are actually linked to show speed.

[Sin City Stan]

The 2009 Nomad is all electronic. Still not linked. At 83 indicated the GPS reads 80. A 46 mile trip indicated read 46.4 miles on the GPS.

Same pulse stream. Different percentage of error. It's odd both are not dead on. An internal calculation is made in the "brain" and this translates to the indicated speed and miles. It's just a matter of using the correct calculation (a few more decimal places). I think, they think, it's just not that important.

I guess it's really not. Unless you happen to be staring a RADAR gun down.