Topic: Speedometer Calibration

[Loudpipe]

My speedometer is off by about 5 mph (reads high) at sub-50mph speeds. Is this something that I can adjust, or will it need to go to a shop to be fixed?

[OldSchool_IsCool]

Same problem on my bike.  I simply subtract 5 from the reading to calibrate my brain.  Tho it does skew the odometer reading I 'zpose.

[eldar]

Is it off below or above? You could change this by changing tire size.

[Loudpipe]

I would rather just get the speedo properly calibrated.  A decent motorcycle should be able to do this, right?

[eldar]

tell you the truth, I am not sure if ours can be calibrated. Maybe pull the speedo out of its chrome ocver and clean it and maybe lube the insides lightly. Could help, cant hurt.

[oldbiker]

No provision was made to calibrate speedos. Anyway I believe by law there is a 10% tolerance allowed. Certainly that was the case in the UK.

[eldar]

There is supposed to be, unless of course the cop is having a slow day or is pissed!

[Ernie]

its my understanding that all these old honda's are off quite a bit-between 5 and 10 mph

[eldar]

Probably because of different tire sizes and such. Mine is within 2 mph or so. But every bike of course is going to be different. So you either need to remember to always mod your speed by whatever amount, or change tire size to bring it closer to actual speed.

[MRieck]

 Mine reads very high as I went to an 18" front from the stock 19". I've wondered if the needle itself could be reset to adjust for the difference i.e.  set the needle 1/4" below the 0 mark.

[eldar]

I dont know. It is a pain to pull them part and when I last did, The needle looked pretty fragile and easy to break. I also did not see any type of set screw holding it on. I think it is glued.

[MikeDeB]

My speedometer is off by about 5 mph (reads high) at sub-50mph speeds. Is this something that I can adjust, or will it need to go to a shop to be fixed?

I'm afraid the answer is no to your questions.  The odometer is gear driven off of the cable drive whereas the speedometer is driven by a magnet (which means that your odometer is spot on while your speedo is off a few mph).  At the opposite end of the needle on the speedo shaft is a bell.  Under the bell is a round magnet that is driven by the speedo cable.  As the magnet rotates, the resistance between the magnet and the bell causes the bell to move.  What keeps the bell/needle from moving too far is a hairspring located between the bell and the needle.  This hairspring also returns the needle to a lower indication as the bike slows.

The calibration would occur at the hairspring.  Changing it's length would alter the speed indication.  To calibrate the speedo you, or a shop, would have to know what the exact speed indication should be for a given rpm of the cable and adjust the length of the hairspring accordingly.  I don't know of any shops that can do this and if there was one the cost would be fairly high as this is a labor intensive operation.

I've included a pic of a tach since they work on the same principle.  This particular one is a K1 (same as the K0 & K2).  The circular piece with the four holes is the bell.  The magnet is below it.  In the K3-K8 gauges the bell actually looks like a bell.

[liaudio]

a bell?  like a "ding-dong" bell?  or like a bell housing?

[MikeDeB]

a bell?  like a "ding-dong" bell?  or like a bell housing?

Bell housing.

[benny365]

Alot of it being off has to do with the tire.  With my old tires I was of 5 mph on the high side.  After new tires it is real close to being right on.  Think about it, your tire expands or shrinks over time thus increasing or decreasing the time it takes for the tire to make one revolution.

[MikeDeB]

Alot of it being off has to do with the tire.  With my old tires I was of 5 mph on the high side.  After new tires it is real close to being right on.  Think about it, your tire expands or shrinks over time thus increasing or decreasing the time it takes for the tire to make one revolution.

True.  And most bikes leave the factory reading up to 10% high with brand new stock sized tires.

[nickjtc]

When I had the speedo apart from Sophie to get rid of the cracked face I noticed that there was a stamp on the back which said 1 mile = 1400 revs (or something similar). So my guess is that the speedo and odometer are set to work based on a number of wheel revolutions per set distance, assuming a standard tyre size.So the only way to change the speedo would be to change the number of revolutions it has to make to read a certain speed....smaller or larger tyre circumference.

I never cease to wonder why some enterprising soul hasn't figured a way to scrap the guts of the speedo/tacho and replace them with electronic bits....surely it wouldn't be hard to do??

As others have said it's no secret that Honda and the other Japanese manufacturers have always made their instruments optimistic, by up to 10%. How else could spotty face youths brag about the huge speeds they get out of their bikes?? I remember when the (enforced) moped craze was on in England in the '70's it was always speed that the riders were bragging about. Erroneous, always, because in those days speedo inaccurracy could be very significant!

[MikeDeB]

When I had the speedo apart from Sophie to get rid of the cracked face I noticed that there was a stamp on the back which said 1 mile = 1400 revs (or something similar). So my guess is that the speedo and odometer are set to work based on a number of wheel revolutions per set distance, assuming a standard tyre size.So the only way to change the speedo would be to change the number of revolutions it has to make to read a certain speed....smaller or larger tyre circumference.

I never cease to wonder why some enterprising soul hasn't figured a way to scrap the guts of the speedo/tacho and replace them with electronic bits....surely it wouldn't be hard to do??

As others have said it's no secret that Honda and the other Japanese manufacturers have always made their instruments optimistic, by up to 10%. How else could spotty face youths brag about the huge speeds they get out of their bikes?? I remember when the (enforced) moped craze was on in England in the '70's it was always speed that the riders were bragging about. Erroneous, always, because in those days speedo inaccurracy could be very significant!

It's not just the Japanese.  My Ducs are off a bit as well.

[croquesaveur]

When I travel large distances I bungie my GPS receiver between my clocks.  Up to about 100km/h (~65mph) my speedometer exaggerates my speed by about 5km/h (~3mph).  At very high speeds this error gets very big.  When my speedometer reads 140km/h (~90mph) I'm actually going at about 128km/h (~76mph).

I was very disappointed the first time I thought I had hit the ton (160km/h).  It turned out I was only going about 140km/h (~90mph). 

The fastest GPS-confirmed speed I've ever obtained on my bike is 157km/h.

Incidentally my BMW (car) speedometer is also optimistic but by a consistent, smaller amount: about 5km/h (~3mph).

I think it makes sense that if a speedometer is going to be inaccurate it be optimistic rather than pessimistic because:
1) It would really piss people off to get a speeding ticket when they thought they were complying with the laws.
2) People prefer to think their vehicle is faster (rather than slower) than it really is.

In my experience all speedometers are optimistic to some degree and I've never seen one that is pessimistic.

[Bob Wessner]

In my experience all speedometers are optimistic to some degree and I've never seen one that is pessimistic.

Not to sound like I'm paranoid  but think how much faster your new car rolls through warranty or your contracted lease miles are eaten up, if the odometer is equally "optimistic."

[nickjtc]

In my experience all speedometers are optimistic to some degree and I've never seen one that is pessimistic.

Not to sound like I'm paranoid  but think how much faster your new car rolls through warranty or your contracted lease miles are eaten up, if the odometer is equally "optimistic."

Now, now, Bob. That sounds just a tinch cynical!

[Pinhead]

And if your odometer reads high, you're actually getting worse gas mileage than your'd be figuring.

[Ernie]

jeez the news just keeps getting worse

[burmashave]

With all this misinformation, I smell a class action lawsuit 

[nickjtc]

With all this misinformation, I smell a class action lawsuit 

The OEMs are just covering their butts. They don't want a bunch of owners complaining that they were going faster than the speedos indicated, so they err on the side of optimistic speed instrumentation.

And in reality, how often does, say, a warranty situation happen just as a vehicle is about to leave warranty....??