The New And Improved Unofficial R65 Forum V2

Technical Discussion => BMW Technical Q&A, Primarily R65 => Topic started by: Zamp on May 26, 2015, 05:59:42 PM

Title: speedometer accuracy?
Post by: Zamp on May 26, 2015, 05:59:42 PM

I recently adopted an R65ls. When I checked the speedometer with my GPS it showed 7 mph optimistic. Is that the norm..

 California High Way Patrol safety month,  and on certain roads, and fwys Hwy 2 they will ticket for 3 miles over the speed limit.

Thanks

Title: Re: speedometer accuracy?
Post by: nhmaf on May 26, 2015, 07:59:12 PM

They are usually 3-5% optimistic, though 7% is still within the realm of possibilities.   It is only a requirement that the speedometer NEVER register BELOW actual speed, and BMW took that to heart on these clocks.

In spite of the optimistic velocity readings, the odometer on these (when it is working) are generally quite accurate.

Another thing to consider is that you might have a transplanted/replaced speedometer or final drive on your bike.   They are calibrated to the final drive ratio, which would be either 31/9 or 32/9 (stamped in the gray metal near where the final drive unit bolts to the swingarm).   The speedometer dial face was a "Wxxxx" (4 digit number) printed on it near the bottom - check your final drive numbers (it will be a fraction like what I typed above) and your 4-digit speedometer "W"  code and report back - we can tell ya if they properly match up.   The W number is the number of revolutions per mile on US calibrated speedometers.

Title: Re: speedometer accuracy?
Post by: mrclubike on May 26, 2015, 09:40:15 PM

mine  is very accurate with my GPS within  2MPH at 60

Title: Re: speedometer accuracy?
Post by: Barry on May 27, 2015, 02:59:08 AM

Depending on the speed you checked it at it's probably within BMW's spec which is to over read by a maximum of 10% plus 2.4 MPH.  I go through one of those radar signs every day and mine is +6 MPH at 40 MPH That's in spec but it's kind of depressing to realise how slow you are really going.

My old car speedo was the same and I could safely drive +5 MPH over the limit without fear of actually exceeding it. By contrast my new to me car which is a 2009 is absolutely spot on the exact speed every time.

Title: Re: speedometer accuracy?
Post by: Motu on May 27, 2015, 05:18:32 AM

Mine is 8kph optimistic, checked with a GPS - I sit on 110kph and am still legal at our 100kph limit (plus 4kph discretion) It seems to get more accurate at higher speeds, and the tacho is accurate, so sit at 4,000 to 4,500rpm.

Title: Re: speedometer accuracy?
Post by: Red_Hen on May 27, 2015, 07:00:24 AM

Mine is right on due to having fellow member Terry Vrla, aka Wirespokes overhaul my speedo - he does great work in the event your instruments are in need of repair!

Title: Re: speedometer accuracy?
Post by: Zamp on May 27, 2015, 11:37:39 AM

 I check the rear drive 32/9, and there is a long number 51511 07500 on top of the speedo face.. rear tire 120/90.

Not too uncommon, optimistic speedo will keep me from getting a talking to.

Thanks for the good info.

Cheers

Title: Re: speedometer accuracy?
Post by: Barry on May 27, 2015, 01:30:12 PM

The speedo ratio to match a 32/9 final drive is 1318 so you should have W1318 printed low down on the dial just under the MPH.
Most  120/90 tires are usually very close in diameter to the the stock 4.00

Title: Re: speedometer accuracy?
Post by: Ed Miller on May 29, 2015, 02:11:08 PM

Mine used to quit reading accurately if I went over 85 mph.  It would just stay at 85.

Title: Re: speedometer accuracy?
Post by: Luca on May 29, 2015, 05:49:39 PM

Quote

Mine used to quit reading accurately if I went over 85 mph.  It would just stay at 85.

how did you fix it?  Mine still has that problem  :D