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Message started by Kris01 on 02/21/14 at 17:39:37

Title: Speedometer accuracy?
Post by Kris01 on 02/21/14 at 17:39:37

Ok, so I've read that the stock speedometer is about 14% off. Does it read too fast or too slow? In other words, if my speedometer is reading 50, am I actually going 57 or 43 mph?

I've also read that a 140/90-15 rear tire will help the speedometer read more accurately. How much closer to actual speed?

Has anyone ever checked the stock speedometer against a GPS or a calibrated bicycle speedometer?

Title: Re: Speedometer accuracy?
Post by verslagen1 on 02/21/14 at 18:51:00

I doubt that it's that far off.
and yes, 140/90-15 fixes it, so it's more like 5 or 6%
but it sure to vary.
and yes, more than 1 person has checked it.

fyi, all (all as in everything) speedos are fast, otherwise everyone would be getting tickets.

Title: Re: Speedometer accuracy?
Post by Serowbot on 02/21/14 at 21:20:32

Most bike speedo's read 5 to 7mph higher than you are actually going... (probably some legal thing,... or just to make you feel fast)...
;D...
90 profile rear tire does a fair job correcting this...

Title: Re: Speedometer accuracy?
Post by ToesNose on 02/22/14 at 05:24:29

Yea my stock speedo was around 5Mph over actual speed.

Title: Re: Speedometer accuracy?
Post by Kris01 on 02/22/14 at 12:35:13

I live in a small town where 30 mph means 30 mph, not 31. So if I change to a 140/90-15 I should be ok and not worry too much about getting a ticket (provided I ride at the speed limit)?

Title: Re: Speedometer accuracy?
Post by Serowbot on 02/22/14 at 13:58:01

Yuppers... ... but, don't come cryin' to me if I'm wrong... ;D...
..(tires vary a little bit by brand and style + there's tire wear)...
No speedo's 100% accurate...

140/90-15 is as close as ya' gonna' get... :-?...

Title: Re: Speedometer accuracy?
Post by pgambr on 02/22/14 at 22:50:17

I always thought my speedo was a little slow but, the gps said it was bang on. Why does the tire size matter though? The measuring device is in the front and it doesn't know what's going on in the back? :-?

Title: Re: Speedometer accuracy?
Post by justin_o_guy2 on 02/23/14 at 00:16:32

Speedo drive comes outta the engine block, r/ side.. If the rear wheel was 3 inches tall, the speedo would be tellin ya you were running 70 when you were movin about 5 miles per hour,,

Title: Re: Speedometer accuracy?
Post by Dave on 02/24/14 at 07:46:24

5146404C4353210 wrote:

Some motorcyles use the front wheel to drive the speedo. This was done so that rear wheel spin would not show a false mileage, and sprocket/gearing changes would not affect the speedometer accuracy.

The Savage speedometer drive is from the transmission - so having a larger or smaller back tire does make a difference. Larger tires travel more distance with each revolution......and the speedometer is not able to compensate for the tire changes.

Title: Re: Speedometer accuracy?
Post by pgambr on 02/24/14 at 07:51:17

Thanks JOG & Dave. I must of been thinking about the KLR, I hope or I just gaffed that one. :D

Title: Re: Speedometer accuracy?
Post by old_rider on 02/24/14 at 07:58:02

Well, you could do what I did. I put a bicycle and a gps on the handle bars, that way if you get stopped and the police officer says you were doing 31 in a 30, you just tell him his gear is off and needs recalibrated cause you have three instruments telling you the same speed.
If you get the dell 100 bicycle speedo, the top/avg. speeds are stored, so if the tell you that you were doing % over the speed limit, just call it up and say... um nope... looky here.

Title: Re: Speedometer accuracy?
Post by Serowbot on 02/24/14 at 08:10:24

But oldrider,... that would require actually going the speed limit... :-/...

Title: Re: Speedometer accuracy?
Post by old_rider on 02/24/14 at 08:21:58

I ain't gonna lie, down here on Highway 98, the mean speed is 10 miles an hour over posted (minimum), if you aren't doing that you are causing a problem (I cause a lot of problems). Even through a posted 35 mph construction area (with a double the fine sign) people are doing 50, but not in my lane :) The area was previously 45mph, but they have cones and concrete to block off the construction crew areas (concrete walls were they are actually working) because they KNOW someone would run off the road and hit some worker or equipment when it rains.
About once a week the state or county will put up a speed trap, but its not often enough, they drive VERY offensively down here, and I don't mean offensive as in the other side of defense... I mean offensive in the term used for Aholes that don't care about others and think they own the road.

Title: Re: Speedometer accuracy?
Post by paulchristi on 02/25/14 at 05:31:57

I always try to be a good driver, but.....two weeks ago I was popped for going 30 in a 25 mph construction zone. There was a line of cars pulling away from me (I was last in the line after a signal), and the cop just pulled in behind the line and pulled me over. Fair? no. Was I speeding? yes.

I brought this up to a cop friend, and he said "When you go fishing, do you only try to catch the biggest fish?"

I'd rather spend my money on something else, so it's the speed limit for me from now on.

Title: Re: Speedometer accuracy?
Post by Kris01 on 02/25/14 at 18:30:45

I agree completely. Any time I've ever been caught speeding I had absolutely no reason to complain. I was speeding...no excuses. Do the crime, do the time. My money is better spent elsewhere.