Speedo Accuracy

[Guest highplainsrider]

Before I changed the front sprocket from a 16 tooth a 15 tooth, I wanted to get an accurate reading on my actual speed. I mounted my GPS and went for a ride. The stock speedometer is surprisingly accurate. At 75 Mph indicated with the stock gearing in 6th gear I was reading 74 Mph on the GPS. RPM's were about 5,200.
 
After switching to the 15 tooth front sprocket, speedo accuracy was exactly the same which leads me to the conclusion that the speed is measured with a wheel sensor instead of at the transmission. Good news for people who want to play around with different sprockets for this bike. RPM's at 75 Mph hour in 6th gear with the 15 tooth sprocket were roughly 250 RPM higher.
 
It live at high altitude in Colorado, so I am just trying to get the bike's acceleration closer to what you guys at lower elevations are fortunate to experience. Installing a full exhaust and a 2 wheel dynoworks flash yielded no real performance increases that I could detect. If anything, I would say the the exhaust and tune sacrificed a little bottom end for a very slight top end increase.
 
I wish I tried the sprocket change first. $28 dollars versus over $1,100 for an exhaust and tune. The off the line performance increase going from 16 to 15 is very noticeable but not extreme. I also have a 47 tooth rear that I plan on installing with a longer chain. The stock 110 link chain is not long enough even with the 15 tooth on the front.

[rustyshackles]

My experience has been similar. At speeds above 70 mph or so speedometer indicated 1-2 mph faster than GPS.

[happy01]

Before I changed the front sprocket from a 16 tooth a 15 tooth, I wanted to get an accurate reading on my actual speed. I mounted my GPS and went for a ride. The stock speedometer is surprisingly accurate. At 75 Mph indicated with the stock gearing in 6th gear I was reading 74 Mph on the GPS. RPM's were about 5,200. 
After switching to the 15 tooth front sprocket, speedo accuracy was exactly the same which leads me to the conclusion that the speed is measured with a wheel sensor instead of at the transmission. Good news for people who want to play around with different sprockets for this bike. RPM's at 75 Mph hour in 6th gear with the 15 tooth sprocket were roughly 250 RPM higher.
 
It live at high altitude in Colorado, so I am just trying to get the bike's acceleration closer to what you guys at lower elevations are fortunate to experience. Installing a full exhaust and a 2 wheel dynoworks flash yielded no real performance increases that I could detect. If anything, I would say the the exhaust and tune sacrificed a little bottom end for a very slight top end increase.
 
I wish I tried the sprocket change first. $28 dollars versus over $1,100 for an exhaust and tune. The off the line performance increase going from 16 to 15 is very noticeable but not extreme. I also have a 47 tooth rear that I plan on installing with a longer chain. The stock 110 link chain is not long enough even with the 15 tooth on the front.

At 70mph mine shows 77mph on dash..

[wessie]

My experience is more akin to @happy01 - satnav shows speeds up to 10% lower - if the speed is from the ABS/TCS sensors then the reading will alter as the tyres wear and expand or contract depending on ambient temperature and riding stlye.

[adjuster]

Anyone know for sure on this?
My 2014 FZ09 had no ABS/TCS, so it had to be gear box based. I never changed anything on that bike but it was a few mph faster indicated than what the GPS showed from my phone. At 50 on the bike, it's more like 57 on the GPS. At higher speeds on the FZ, I was paying more attention to traffic to spend much time reading the GPS/phone that was in my tank bag's clear flap/lid.
 
But I have not checked on the FJ09 yet. It would be very nice if the ABS sensors were used, then any gear changes would not create a need for a Speedo DRD.
 
But it would also mean you can not get your exact MPH corrected with a Speedo DRD either.
 
 

[zimbob]

Perhaps you should check the speed again. I would like to put a 15 tooth primary gear on so im following this.Has anyone done a speed healer on this bike?

[suncoaster]

Checked last weekend, used a dedicated GPS speedo device and also a phone app (Speedometer GPS), on a 100km slab ride:
88 on speedo = 80 on GPS
110 on speedo = 100 on GPS
These were rough readings. I'd set the throttle lock to the speed, then glance at the instrument in the tank bag or the phone in the holder.
 
Interestingly my car shows the opposite, it's speedo reads low, so I've been unknowingly speeding..

[zimbob]

So a full 10% off. The 15 tooth gear is 5% the other is just the way it was originally? I know the radar signs along the road that show your speed always show 2 or 3 mph less than what my speedometer shows at 50 mph.I wish they just made it accurate.I guess a manufacturer never got sued for overstating the speed.
 

[dedsxy47]

Used a Garmin GPS on a long ride zip tied to the bars.  I was able to compare speeds at many different MPH and found only about 1-2 miles an hour difference most of the time.  I have had bikes in the past which were nearly 10% off when compared to the speedo and 2 separate GPS's all at the same time.  Of course my tires are new and I had perfect weather with long roads to really perform a good comparison.  I do think bikes in the same model can have differences from each other though.  In the future I plan to use a different GPS to confirm the accuracy.  Sort of like a science experiment, well I guess it is an experiment.  At least I get to ride while I gather data, ha ha.

[rockinsv]

My speedometer seems to be right on. I've had my son riding the bike and us talking through a Sena and it registered identical to my truck speedometer at 70mph.

[keithu]

I've never seen a chain drive motorcycle that took speed from the transmission. Every chain drive bike I've owned used a front wheel sensor for speed. Since the FJ needs wheel speed sensors for ABS and traction control, it makes sense to use that data for speedometer/odo output, too.

[JJM]

I've never seen a chain drive motorcycle that took speed from the transmission. Every chain drive bike I've owned used a front wheel sensor for speed. Since the FJ needs wheel speed sensors for ABS and traction control, it makes sense to use that data for speedometer/odo output, too.

 
What kind of bikes have you ridden because my previous 4 (suzuki, 2 yamahas, and a Harley) did not have front wheel sensors.

[wessie]

I've never seen a chain drive motorcycle that took speed from the transmission. Every chain drive bike I've owned used a front wheel sensor for speed. Since the FJ needs wheel speed sensors for ABS and traction control, it makes sense to use that data for speedometer/odo output, too.

Honda had a sensor on the front sprocket on a VFR750 and CBR600 I owned in the 1990s for the speedo & odo

[fanowater]

Surprised the drop from 16 to 15 only increased rpm's by 250. Was thinking of going the other way for an upcoming trip to get better gas mileage, but may not bother now.
 
I have always found my bikes to be optimistic by around 5-10% (Says 77 mph, but going 74).
Regardless of where the sensor is or what type, you're actual speed will be affected by tire wear. Hopefully, if using an ABS/TC sensor, it is from the front since wear is so much less than on the rear.
 
FWIW, my FJ reads identical to my buds BMW (GPS based speed reading). I find the highway radar speed flashers to be handy checks - they say my Yamaha is about 10% optimistic at low speeds (40 mph or lower) and about roughly correct at higher speeds.

[fanowater]

Wessie is right about chain drive bikes not all using cable drive speedo's. My Triumph Daytona, Speed Triple and Ducati 996 all had an internal pickup - and none of them had ABS or TC.
My 750 SS had a cable drive and it broke constantly!