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I have 2004 Rockster and every time I rode it, it seemed like the speedo is off. So I get a speedo app for my phone and go for a drive. My speedo is off by 8 miles an hour fast. I have looked over the bike and I can find no indication that it was an ABS model with the ABS removed. The rear gear is stamp 31/11.

Anyone give me an idea on how to true up the speedo or get it in the ballpark?

Thanks,
Dan...

Speedos generally 'over-read' anyway. Manufacturers set them with a 'tolerance' that HAS to over -read. IE - for a genuine 50, they'll read more than that. It means that anyone looking at the speedo to gauge that their speed below the current limit is guaranteed to be below that limit.

EG - if you were watching your speedo in a 60 limit, and it was reading 60, but then the cops pulled you because you were ACTUALLY doing 68 (or more), because the speedo was under-reading; then you'd have a very valid claim against the manufacturer of the vehicle.



at what speed were you testing it, and was it reading under or over? (ie if your gps says 50, was the speedo reading 42 or 58??).

mine reads high as well, at 80 mph on the speedo, GPS says 74-75ish

I don't worry about it. might save a ticket

Beginning to look like it is endemic to the bike.

I tested at 20, 40, 60 and 70. It was right about 8 - 10 mph fast. Which is better then slow when it comes to potential speeding tickets LOL.


Dan...

Postby kirby » Sun Dec 04, 2016 6:06 pm

That's about right for the average machine. The rockster has the speedo drive on the rear drive ala r1100s. It is sensitive to the tire diameter. All 180/55 tires are not exactly the same. A little diference will make a difference. Having said that most speedos read a bit high on motos as a general rule. From 4% to 10% high.
Most Rocksters have a .7 ratio of 6th gear soo...
engine rpm in top gear X .7 / 2.82 = wheel rpm X circumference of wheel (pi X dia.) in inches / 12 = feet per min / 5280 =miles per min X 60 = mph.
4000 rpm X .7=2800/2.82=993 rpmXdia 6.55 feet/5280=1.23 miles per minX60=73.9 mph

Play around with that and you can see the difference a couple inches makes!

Remow2112 wrote:Beginning to look like it is endemic to the bike.

I tested at 20, 40, 60 and 70. It was right about 8 - 10 mph fast. Which is better then slow when it comes to potential speeding tickets LOL.


Dan...

it's 'endemic' to every vehicle on the road....

about the only vehicle that 'needs' absolutely accurate speed measuring equipment are aircraft where even a small over reading of actual speed could result in a stall at landing/take-off... catastrophically.

Mine indicates 5 mph fast virtually thru the whole range versus my GPS.

Dusty Burman
64 F Phoenix, AZ

So this means we are piling up less miles than the odo shows?

That is correct. If your speedo is fast. If it is slow there would be more miles then those showing.

I am good with the speedo being off. Just about every hotrod I have owned and changed the tires on has the speedo off some amount. As long as I know the amount of offset I can deal.

Thanks!
Dan...

WhiteDog wrote:So this means we are piling up less miles than the odo shows?