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  #1  
Old 06-12-2015, 11:54 AM
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Bike vs GPS Speedometer Accuracy

When driving in the car, I've noticed the car and GPS speedometers pretty much indicate the same speeds. When riding the bike, I've noticed a good bit of deviation.

Not being familiar with the mechanics of speedometers in cars and bikes, is it better to use a GPS for speed accuracy?

Thoughts?
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Old 06-12-2015, 01:42 PM
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Re: Bike vs GPS Speedometer Accuracy

All my beemers have been off - when I'm doing 60 mph indicated - actually going about 56 mph. Always indicating faster than actual.
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Old 06-12-2015, 03:03 PM
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Re: Bike vs GPS Speedometer Accuracy

Quote:
Originally Posted by ppalac
When driving in the car, I've noticed the car and GPS speedometers pretty much indicate the same speeds. When riding the bike, I've noticed a good bit of deviation.

Not being familiar with the mechanics of speedometers in cars and bikes, is it better to use a GPS for speed accuracy?

Thoughts?

The GPS should be very accurate. Speedos in cars had to be accurate during the 85mph-max-on-gauge days, but tended to be about 10% optimistic. (Probably legally safer to read faster than slower when inaccurate).

I've heard it said that rear tire slippage at high speeds adds some inaccuracy, if the speedo is driven by the rear wheel.

My 85 K100RS speedo is about 10% optimistic. My 2015 k1300s speedo is maybe 1-2 mph fast, but that seems the same at 100 as at 35. My 2012 Infiniti speedo is pretty close, according to GPS built into my radar detector. My 98 Ford Windstar is pretty consistently 3 mph optimistic at all speeds above 20.
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Old 06-12-2015, 03:38 PM
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Re: Bike vs GPS Speedometer Accuracy

Hi Perry

I've never saw a speedometer with exact reading or showing less speed than actual, usually they "exaggerates" speeds, from 5% at low speed to 10-15% at high speed. I think is for a "brain effect" you see more speed then you go at less...

this variation is sensitive to the tyre wear, usually the sensors are in mechanical parts, when the tyre is new the amount of RPM is different compared with a used tyre that has more RPM at the same real speed.

GPS speedometer is truly accurate because is a average lecture from at least 3 satellites, and the most important, is the same speed calibrated police radars

btw, Fiona (my K13R) shows 175 when GPS shows 160 --> 50 ---> 45 90 - 80 more or less , in Km/h-->
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Old 06-12-2015, 04:06 PM
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Re: Bike vs GPS Speedometer Accuracy

I personally wouldn't trust a GPS speedo 100% of the time. There are periodic issues with the satellites, tree coverage issues, local anomalies, etc. that affect their accuracy. I use survey grade GPS and can see some of the "noise" that gets received with my post-processing software.
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Old 06-12-2015, 04:34 PM
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Re: Bike vs GPS Speedometer Accuracy

Quote:
Originally Posted by brucev
All my beemers have been off - when I'm doing 60 mph indicated - actually going about 56 mph. Always indicating faster than actual.

I have noticed about the same difference as Bruce with my speedo vs GPS on the K1300R.

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Old 06-12-2015, 04:36 PM
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Re: Bike vs GPS Speedometer Accuracy

The panigale actually states the % error in the owners manual. (3 % , I think)
My BMW RNineT analog speedo reads way high
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Old 06-12-2015, 09:39 PM
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Re: Bike vs GPS Speedometer Accuracy

Quote:
Originally Posted by brucev
All my beemers have been off - when I'm doing 60 mph indicated - actually going about 56 mph. Always indicating faster than actual.
The K1200S was nearly perfect !!
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Old 06-13-2015, 09:11 AM
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Re: Bike vs GPS Speedometer Accuracy

Quote:
Originally Posted by cabnfvr
The K1200S was nearly perfect !!

Wow. First I've heard.

Really appreciate the responses. When lock'n in the cruise, I feel better about using the GPS speedo. I just need to stop getting lazy about the surprise 60 -> 45mph streets as I ended up with a paper souvenir. BAH!
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