Discrepancy between supposed and actual RPMs with stock sprockets

[eru000]

Hey guys.

I have stock sprockets on my bike (16/46). I've checked and verified that. According to the Gearing Commander website, there's a difference between what I see on my bike and what it says it should be. According to GC, my bike behaves has if it's at 15/46. I have a speedo healer and it's calibrated to GPS at 80mph.

On my bike my mental rule of thumb to calculate which gear I'm in is as follows:
5th gear: 65mph at 5500RPM
6th gear: 65mph at 5000RPM
These are almost exact (at least within the error tolerance of the stock tach)

According to Gearing Commander, it should be approximately those RPMs for a 15t/46t setup (5516/4937). It says stock should be 5171 and 4628. This is confusing to me, because the gearing is stock, not 15/46.

I've checked all the gear ratios and whatnot, comparing GC and the service manual. The site is correct.

I'm running Pilot Road 4's so it could be a circumference difference, but I've calculated that it'd have to be almost 5 inches less than "stock". I find that hard to believe on a tire with identical width and aspect ratio.

Any thoughts?

 

[Woody146]

Check out one of these...no more calculating.


[ame="http://www.amazon.com/Yamaha-2011-2012-Non-ABS-Healtech-Indicator/dp/B0062Z0CU0"]Amazon.com: Yamaha FZ8 2011-2012 Non-ABS Healtech Gipro X-type Gear Indicator: Automotive[/ame]

Here it is on my bike(newest mod)







That is weird though...

 

[eru000]

It's on my to-buy list, but I can't justify the cost at the moment. I just have those little rules of thumb for when I'm cruising on the interstate since I only really use 5th/6th for that.

 

[Rotaryknight]

since you have a speedo healer did you check the mph/RPM/Sprocket before the calibration?

 

[eru000]

since you have a speedo healer did you check the mph/RPM/Sprocket before the calibration?

Yes, it was about 7.5% over actual speed.

Hm, so what you're saying is that the website might be using the factory speedo values instead of real speed?

 

[Rotaryknight]

Yes, it was about 7.5% over actual speed.

Hm, so what you're saying is that the website might be using the factory speedo values instead of real speed?

I dont know about the use of factory speedo values. Many of these websites uses mechanical speed from calculating the gearing and tires. Mechanical speed is different than actual speed since it offers no variance in errors, numbers in mechanical speed is right 100% of the time.
On my completely stock gearing bike and stock tires, at 6000rpm top gear, my speedo (uncalibrated) reads 84 mph, the gearing commander website says 84.3 But actual GPS speed is 76 mph.

 

[eru000]

I dont know about the use of factory speedo values. Many of these websites uses mechanical speed from calculating the gearing and tires. Mechanical speed is different than actual speed since it offers no variance in errors, numbers in mechanical speed is right 100% of the time.
On my completely stock gearing bike and stock tires, at 6000rpm top gear, my speedo (uncalibrated) reads 84 mph, the gearing commander website says 84.3 But actual GPS speed is 76 mph.

Hm. That's weird.

 

[Rotaryknight]

Hm. That's weird.

Pretty sure the speed sensor on the bike calculates off the gearing equations just like the websites. It reads the final drive inside the transmission. It figures in stock chain, tires and sprockets. If it was a cable speedo reader it would be calculated by how many rotations it spins in a certain amount of time.