If the speedometer is off, is the odometer also off?

snoozy · Post by **snoozy** » Sun Jun 15, 2014 5:41 pm

I had a pickup truck which i was trying to get the dash off of, which reqd disconnecting the speedometer cable. This also disconnected the odometer, something i found out when i had to run to the parts store. Since scooter speedos are conceded to be inaccurate, would this mean that the odometer is also off? This would mean that any mpg calculations would also be off, wouldn't it?

KrispyKreme · Post by **KrispyKreme** » Sun Jun 15, 2014 5:48 pm

While I don't have an answer, that is an excellent question. Can't wait for a reply.

az_slynch · Post by **az_slynch** » Sun Jun 15, 2014 7:38 pm

Not necessarily.

While both the speedometer needle and the odometer wheels are driven by the same cable, once the cable drive enters the speedometer housing, it drives both the speedometer and odometer through two very different mechanisms.

The speedometer needle drive is not directly connected to the cable drive. The cable drives a short shaft with a polarized magnetic bar on the end. This bar spins within a metal cup. The rotation of the bar applies a twisting force on this metal cup, which can be varied by adjusting how deep the bar spins within the cup. The cup connects to the speedometer needle via a shaft which balances on fine bearing surfaces. This shaft is linked to the speedometer chassis via a clock spring. The clock spring provides a resistive force against the rotation of the metal cup. The spring tension can be adjusted slightly, but is generally not recommended due to the fragile nature of the clock spring. The faster the speedometer cable spins, the faster the magnetic bar spins and the greater magnetic force it applies to the metal cup. As the magnetic force increases, it exceeds the resistive force of the clock spring and drives the needle upwards. As the cable speed decreases, the magnet creates less twisting force. As the force on the metal cup decreases, the resistive force of the clock spring pulls the needle downwards.

The odometer drive splits off of the speedometer drive once it enters the speedometer housing. Drive is transferred to the odometer gears through a series of worm gears and geared shafts. The pitch of the worm gears dictates the speed of shaft rotation and slows the drive speed down to a calculated fraction of the rotational rate of the speedometer drive. the gear drive runs the "tenths" wheel directly. A cam on the tenths wheel, opposite the odometer drive, clicks over the "ones" wheel once a single rotation is completed. An identical mechanism drives the "tens" wheel, "hundreds" wheel, "thousands" wheel, continuing on until the highest increment wheel is reached.

Due to the drive differences, you could break a drive gear in the odometer and the speedometer would still work. Conversely, you could break the clock spring in the speedometer and the odometer would still work.

As I mentioned in the speedometer drive description, it is an indirect coupling that can be adjusted by fiddling with spacing of the magnetic coupling or the clock spring tension. The odometer, being driven by gears, lacks this adjustability; the fixed ratios of the odometer drive will not vary and will not generate an odometer discrepancy. If there is a discrepancy in the odometer reading, it is more likely due to a variance in the rolling diameter of an installed tire. Stamped dimensions on a tire do not guarantee accuracy, as characteristics of the tread pattern and the tire's cross-section vary from model to model and manufacturer to manufacturer.

If you want an odometer accuracy, try running the OEM fitted tire. If you want speedometer accuracy, there are shops out there that can calibrate it for you.

scootERIK · Post by **scootERIK** » Sun Jun 15, 2014 8:47 pm

I have done some testing on my Buddy and it seems like the odometer is off by ~10%(1.1 miles on the odometer is ~1 mile in the real world.) Though if I did more accurate testing I think it would be less, maybe around 8%.

I didn't really notice it until I did some 100-200+ miles rides and the google maps distance didn't match my odometer.

KrispyKreme · Post by **KrispyKreme** » Sun Jun 15, 2014 9:39 pm

scootERIK wrote:I have done some testing on my Buddy and it seems like the odometer is off by ~10%(1.1 miles on the odometer is ~1 mile in the real world.) Though if I did more accurate testing I think it would be less, maybe around 8%.

I didn't really notice it until I did some 100-200+ miles rides and the google maps distance didn't match my odometer.

Both are off by a bit IMO. I aint sweatin the small stuff.

BuddyRaton · Post by **BuddyRaton** » Sun Jun 15, 2014 9:49 pm

WHY RED IS RED!!!!!

sc00ter · Post by **sc00ter** » Mon Jun 16, 2014 1:31 am

I just put Vee-Rubber tires on my wifes Buddy 125, and eventhough they are the same size as the stock tires, they look smaller in overall height!? Now the speedo reads faster than the scoot is going. Not sure by how much off, but it is noticible. Dont really care, the Vee's handle pretty good for the price. And the scoot gets lovingly maintained, so if the miles pile on faster it will just get some bonus maintanance.

snoozy · Post by **snoozy** » Mon Jun 16, 2014 1:38 am

BuddyRaton wrote:WHY RED IS RED!!!!!

Can you elaborate on this??

scootERIK · Post by **scootERIK** » Mon Jun 16, 2014 4:47 am

KrispyKreme wrote:
scootERIK wrote:I have done some testing on my Buddy and it seems like the odometer is off by ~10%(1.1 miles on the odometer is ~1 mile in the real world.) Though if I did more accurate testing I think it would be less, maybe around 8%.

I didn't really notice it until I did some 100-200+ miles rides and the google maps distance didn't match my odometer.
Both are off by a bit IMO. I aint sweatin the small stuff.

Small? My odometer is off by ~2,000 miles.

I figure the best way to deal with it is to ride more to make up for the miles that are "lost."

BuddyRaton · Post by **BuddyRaton** » Mon Jun 16, 2014 11:39 am

snoozy wrote:
BuddyRaton wrote:WHY RED IS RED!!!!!
Can you elaborate on this??

Please don't take it personally, however this is a topic that has been beaten to death, reanimated and beaten to death more times than Dr. Who!

I would guess that a quick search would show at least 50 threads regarding speedo inaccuracies.

It's been a long time since I read the original WHY RED IS RED thread, one thing to take from it is that we watch out for each other here! The other is that I was at 400 posts then...wow...time flies when you're on a scooter!

Welcome to MB...you have been RED in as a member!:mrgreen:

topic4954.html

viewtopic.php?t=4558&postdays=0&postorder=asc&start=50

snoozy · Post by **snoozy** » Mon Jun 16, 2014 5:30 pm

If red is red, does it necessarily follow that orange is orange?

I realize the speedometer thing has been beaten to death, but I only just thought about the connection to the odometer and the possible effect on MPG calculations. Me, I rarely drive faster than the guy ahead of me, so the speedometer is not really important. On a scooter, I figure if I'm keeping up with everybody else, I'll be alright.

snoozy · Post by **snoozy** » Mon Jun 16, 2014 5:31 pm

If red is red, does it necessarily follow that orange is orange?

I realize the speedometer thing has been beaten to death, but I only just thought about the connection to the odometer and the possible effect on MPG calculations. Me, I rarely drive faster than the guy ahead of me, so the speedometer is not really important. On a scooter, I figure if I'm keeping up with everybody else, I'll be alright.

BuddyRaton · Post by **BuddyRaton** » Mon Jun 16, 2014 5:52 pm

It is a very common misconception that because red is red orange must be orange, this just is not true.

This is in line with the proven facts that while blue is blueviolet is not indigo and olive may be olive but is not green while yellow is yellow and brown is really just a shitty color.

I hope this has cleared everything up for you

BuddyRaton · Post by **BuddyRaton** » Mon Jun 16, 2014 5:59 pm

This may help you out too

viewtopic.php?t=23411&highlight=odometer

az_slynch · Post by **az_slynch** » Mon Jun 16, 2014 11:00 pm

Nobody's ever asked the really important aspect of this question:

"How much is the rider's sanity off by?"

agrogod · Post by **agrogod** » Wed Jun 18, 2014 4:06 am

Hold on. wait a second, sanity I know I left it here somewhere. Just give me a minute I know I can find it.