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Discussion Starter #1 (Edited)
Just checked out the bike speedo read out in comparison with MCN Ride GPS logger, without disclosing the speed, bike reading was indicating 17mph, yes 17mph above the data recorded on the GPS logger
I just cannot believe the variation, has anybody checked their bike out, or have any comments as to why there should be such a difference
 

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Just checked out the bike speedo read out in comparison with MCN Ride GPS logger, without disclosing the speed, bike reading was indicating 17mph, yes 17mph above the data recorded on the GPS logger
I just cannot believe the variation, has anybody checked their bike out, or have any comments as to why there should be such a difference
This is common on ALOT of sportbikes. I have seen the Japanese sportbikes read 20+ mph over what the actual speed they were moving. The faster your actual speed the higher the error. Most 600's will read as high as 180+ mph top speed and we all know thats not going to happen. They even make devices that will fix the speedo inaccuracy like this one here.

http://www.calsportbike.com/sh/
 

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Just checked out the bike speedo read out in comparison with MCN Ride GPS logger, without disclosing the speed, bike reading was indicating 17mph, yes 17mph above the data recorded on the GPS logger
I just cannot believe the variation, has anybody checked their bike out, or have any comments as to why there should be such a difference
Pretty common, my mk5 Golf speedo reads 80 mph when the tomtom says 72 mph
 

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There is no limit to how high they are allowed to read, they just are not allowed to read lower than actual speed. Most car manufacturers will spec a 5-10% over read in speedo's. Japanese manufacturers tend to be a little higher. You don't calculate it by how many mph or kmh out it is, it's in percentage. So i.e a speedo that is 5% out would read 105 at 100 actual 210 at 200 actual, etc, etc
 

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So you not disclosing the speed actually makes your statement worth nothing really at all because we don't know the percentage it was out by
 

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ALL Japanese motorcycles read fast (7~10% is the standard) and have for as long as I have been involved in bikes. My 910R reads much more accurately than my friend's Yamaha cruiser.

Also remember that different tires can change accuracy as can tire wear and pressure....and forget everything if you change gearing.

Gearing changes are the real reason the "Speedo Healers" were brought to market.
 

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Also remember that different tires can change accuracy as can tire wear and pressure....and forget everything if you change gearing.

Gearing changes are the real reason the "Speedo Healers" were brought to market.
gearing doesn't effect Aprilias.....speedo reads off the sprocket bolts, something Aprilia got right :laughing:
 

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There is no limit to how high they are allowed to read, they just are not allowed to read lower than actual speed. Most car manufacturers will spec a 5-10% over read in speedo's. Japanese manufacturers tend to be a little higher. You don't calculate it by how many mph or kmh out it is, it's in percentage. So i.e a speedo that is 5% out would read 105 at 100 actual 210 at 200 actual, etc, etc
On my Golf it is not a percentage, it reads around 2 mph fast at 50mph, 8mph at 70 and is back to 2 mph at 90mph
 

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gearing doesn't effect Aprilias.....speedo reads off the sprocket bolts, something Aprilia got right :laughing:
Or Ducati's, they also read wheel speed.

Thinking about it so did my 1969 Bonneville as well :)
 

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18% to be precise
Maybe that's how they got the 312 to do '312kph' ? it would only need to actually be doing 265kph to show th magic 312 kph
 

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the faster u go, the faster its going to be out.... also what do u think happens to a rubber tyre when its spun extremely fast?? it expands. a tire at 160mph will be a fair size bigger than a tire spinning at 40, has nothing to do with percentages out cos it will be different at different speeds.
 

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it doesnt matter if its from the front wheel, or the gearbox.. i think the most popular inaccurate speedo was the first hayabusa.. lol top speed of around 315kmh, and it would show 350. lol.
 

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gearing doesn't effect Aprilias.....speedo reads off the sprocket bolts, something Aprilia got right :laughing:
Only problem with that is if you're spinning the tire....or make a significant change in tire profile.

"Back in the day" most Jap bike speedos were driven off the front axle (some still are).
Lot's of Euro bikes off the rear axle (John's Turnip as he stated).

Regardless....accuracy has always been suspect and always optimistic in readings.
 

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If your tire was expanding that much at speed, don't you think it would be having clearance issues with fenders\huggers? Not saying they don't expand, just I wouldn't imagine them expanding quite that much. However if the reading was taken from the sprocket and you changed the final gear ratio, then it would be a relatively linear percentage that the reading would be out by..... Just sayin.....
 

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gearing doesn't effect Aprilias.....speedo reads off the sprocket bolts, something Aprilia got right :laughing:
....Until the sensor packs up (£80+please) - my Ducati uses the same method. Adding lightness by changing the steel bolts for Titanium (too expensive) and your speedo stops working too.
New rears after pounding up and down the M4 and squaring off my Bridgestones seems to make a noticeable difference to speed/revs but it can only be 2-3%. Getting on the edges of course can make ~15% difference.
 
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