Speedo Accuracy

mo650chopper · Posted: August 31, 2005, 9:43 pm Post subject: Speedo Accuracy

Was wondering about accuracy of stock XS speedo's? Specificly a 1980 model. I got a Speeding ticket, 1st one in 10 Years, on the way home from work today for doing 75 MPH in a 60 MPH Zone. I never seen my speedo read above 70 MPH, more like 68 MPH. I would like to know but it seems 7 MPH off is quite a bit too much "Tolerence" for my liking.

grizld1 · Posted: August 31, 2005, 10:07 pm Post subject: Re: Speedo Accuracy

Hmmmm. The error usually goes t'other way--reading a tad higher than actual speed. What size front wheel ya got on that scoot? If you're running a 21" front end, you'll have in the neighborhood of 10% lowside error right there, which would do the dirty deed to ya.

mo650chopper · Posted: September 1, 2005, 6:19 am Post subject: Re: Speedo Accuracy

I'm running a 19" tire. I actually thought it was reading slower as well just by the traffic around me. I still think the reading the officer had was the big F350 dually coming up behind me. I pleaded my case as much as possible with out making matters worse.

grizld1 · Posted: September 1, 2005, 8:32 am Post subject: Re: Speedo Accuracy

Let's see if I've got this straight--you're running down the road on a 45+mpg motorcycle, tempting the good citizen in the Yuppie warwagon to vent his frustration over his monster fuel bill by closing up and trying to run you over; so this diligent, fair-minded public servant pulls you over and gives you a ticket for speeding, since he can't ticket you for presenting an attractive target. Sounds logical to me!

mo650chopper · Posted: September 1, 2005, 1:23 pm Post subject: Re: Speedo Accuracy

I guess the money I'm saving on gas can now support the wonderful town of Byrnes Mill, Mo. Can you Spell "SPEED TRAP"

fire2235fighter · Posted: September 1, 2005, 5:28 pm Post subject: Re: Speedo Accuracy

take it to court and fight it the cop probley won't show

kingwj · Posted: September 6, 2005, 8:00 pm Post subject: Re: Speedo Accuracy

I hate that cops steal your money and don't even follow the rules. He will get up there and recite his script of BS about calibrating and following rules and you will be poorer. If there was a Ford 350 behind you I would wager big bucks he clocked the truck and not you, biggest reflection wins. Cop radar sucks big time, it isn't even required to measure a vehicle going 55 to be certified. Remember the tree that was clocked going 85 mph? Do you know that nothing has changed with police radar since that incident. Your only satisfaction may be to tell the officer that cops have a higher incidence of testicular cancer than the general population and encourage him to use his radar every chance he gets so he can give his nuts a many small, measured doses of microwave radiation.

xs650mike · Posted: October 10, 2005, 6:51 pm Post subject: Re: Speedo Accuracy

When I checked the 85 mph "EPA" speedo on my '82 650 against the CHP's informational roadside radar at an indicated speed of 55 my actual speed was 60 mph. I got a 140 mph speedo from an XS750 Special and mounted it on the bike and it was dead accurate according to the radar. I put the 85 mph speedo on my 400 to replace the one busted in a collision with a deer. On the 400 it was dead accurate, the 400 has an 18" front wheel. Apparently those 85 mph jobs are calibrated for an 18" front wheel and read slower than the actual road speed. Rolling Eyes

Bear that in mind so as to avoid tickets.

Phred · Posted: October 12, 2005, 8:39 pm Post subject: Re: Speedo Accuracy

Ah, yes.....the famous Byrnes Mill Speed Trap strikes again! BTW, kingwj is right-if the F350 was anywhere close to you he would have reflected the stronger signal back. The cops are *SUPPOSED* to be taught that large vehicles often are read even when the radar gun is "aimed" elsewhere. Of course, it's harder for a low-life biker to convince the judge the cop is wrong than a respected yuppie in his $50,000 cowboy cadilac, who will have his lawyer take care of it anyway.

xs650mike · Posted: October 12, 2005, 8:55 pm Post subject: Re: Speedo Accuracy

Right you are Phred, for many years the California Highway Patrol refused to use radar for just this reason, it was too easy to get a false reading. Then when they did start using it they only used it on sparsely travelled roads where they knew they were getting a reading on the targeted vehicle. Now they have the infamous forward looking computing radar in their cars and will have you before you even see them. The first you will see the cop is when he's turning his car around before you even get there, then he pull in behind you and turns on the red lights. Most of the CHP officers will cut you a break if you're contrite and didn't do anything dangerous. They'll generally write you for a lower, less expensive speed. My friend Tim got radared on his Ducati 916 at 90 mph and the cop wrote him for 65 in a 55 zone. As Tim was signing the ticket the cop asked him, "How do you like your Ducati?" Tim said, "A lot less than I did before you ticketed me!" He has since traded the 916 for a more sedate ST2 sport tourer.

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