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Discussion Starter · #1 ·
What do folks reckon to speedo accuracy on the Thruxton ?

I've been cruising at an indicated 80mph , but it doesn't actually feel that fast
 

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A coincidence in timing here: the other day I approached a speed indicator kindly set up by the cops. It showed 38 mph; my gauge showed 40. I'll have to check it a few more times, but I was going at a steady rate.
 

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A coincidence in timing here: the other day I approached a speed indicator kindly set up by the cops. It showed 38 mph; my gauge showed 40. I'll have to check it a few more times, but I was going at a steady rate.
Be careful here. Don't know about my Bonny's speedo yet but I do know that my '99 BMW R1100RT w/EZS sidecar varies as to how many mph faster shows when compared to my gps. At lower speeds like 20 mph the speedo shows 22 mph, gps shows 20 mph. At 60 on the speedo the gps shows about 55 mph. At 70 mph on speedo, gps shows about 62 mph.

Don't know why this is happening but I trust the gps and use it for my speedo. The R1100 has been modified with auto wheels/tires on all three points, now running 15 inch tires, not the 17 inch cycle wheels/tires that it originally came with.

Enjoy the day.

Karl
 

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Discussion Starter · #6 ·
thanks for the link, just realised my bike has a 17in front wheel which I presume will compound the problem
 

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I've never known an accurate speedo on any make of bike or car, I use a sat.nav against mine and at 70+ its about 3 mph fast, not so much on the lower speeds so watch out on the town Gatso's.
One of the more accurate ones Ive had.
 

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The thing that i find strange is blokes tell me when checking there speedo against the GPS reading they say the odometer reads correct , now i can not work out how if your speedometer is out than you odometer should be out the same amount
Am i wrong ? :confused:
 

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A coincidence in timing here: the other day I approached a speed indicator kindly set up by the cops. It showed 38 mph; my gauge showed 40. I'll have to check it a few more times, but I was going at a steady rate.
most read 4to6 mph faster then you are running
Be careful here. Don't know about my Bonny's speedo yet but I do know that my '99 BMW R1100RT w/EZS sidecar varies as to how many mph faster shows when compared to my gps. At lower speeds like 20 mph the speedo shows 22 mph, gps shows 20 mph. At 60 on the speedo the gps shows about 55 mph. At 70 mph on speedo, gps shows about 62 mph.

Don't know why this is happening but I trust the gps and use it for my speedo.
When speedos are off (which every bike I've ever had is), they are always off by a percentage, not a static amount. It just has to do with the ratio between the speedo ring or gear (depending on the kind of speedo sensor the given bike has) and the OD of the tire. So, that's why a speedo that is off by 1-2 MPH at 20 MPH can be off by 5 MPH or more at 80 MPH.

I don't know for sure why MC speedos are always off by a larger percentage than car speedos. My guess is that moto manufacturers know that there is a much greater likelihood of variability in the ultimate OD of the wheel and/or tire that will be run on a given model of bike across all of its owners out in the world compared to a car, where people very rarely go with anything different than what came on it. There are hefty fines for installing a speedo that reads low, so I suppose the err on the side of caution and make them all read about 5 percent high to give them a safe margin or error.
 

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The thing that i find strange is blokes tell me when checking there speedo against the GPS reading they say the odometer reads correct , now i can not work out how if your speedometer is out than you odometer should be out the same amount
Am i wrong ? :confused:
Yes, you're wrong. :D ;)

The speedo and odo may run off the same sensor (and on some bikes, they actually have different sensors , but this is rare), but they are attached to different inputs (gears in the case of analog instruments like our bikes) at the instrument end. It's just a matter of calibration - what one rotation of the wheel translates to on the other end.

I had a KTM that had a digital speedo and odo, and an adjustable front-wheel setting among 17", 19", and 21". If you had it on 21", the speedo would be 5 percent fast, but the odo would be spot-on. If you set it to 19", the speedo would be spot-on, but the odo would be 5 percent slow. :(
 
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