Speedo correction with 15T front sprocket and OEM inaccuracy


sti491

Member
Has anyone used a speedo correction device after going to a 15T front sprocket. I have played with the calculator on-line. It's somewhere between a 12.5 to 15% total correction.

To avoid trial and error testing, I'm wondering if anyone that has done this knows the best percentage change to program in?

I'm looking for best speedo accuracy between 40MPH to 80MPH actual.

Thanks.
 

TN6R

Member
I have -1/+1 sprockets and chain in my drawer ready to install but haven't gotten around to it yet. I've read that some riders just calibrate the speedohealer with their GPS. That's the route I'm planning to take. Other than that, I wasn't able to find any plug and play solution.

Did you already install your sprocket?
 

Marthy

World Most Bad A$$ 6R
Elite Member

sti491

Member
I have -1/+1 sprockets and chain in my drawer ready to install but haven't gotten around to it yet. I've read that some riders just calibrate the speedohealer with their GPS. That's the route I'm planning to take. Other than that, I wasn't able to find any plug and play solution.

Did you already install your sprocket?
Yes. I have a separate post on it.

I can calibrate with GPS, but the percentage it is off changes if you are at 35 mph vs 70 mph. Ultimately as I understand it, you have to pick a percentage change to program in. It doesn't really matter how you got it. It's either going to be more accurate at low speeds, or high speeds depending on what you go with.

It is a kinda rough estimate.
 

sti491

Member
I have my Excel tool on my other PC at home. I remember that 17T front sprocket is about spot on. I can check it out this evening...
Thanks Martin. If a 17 tooth is say, + 6%, does it stand to reason a 15 toothis -6%? But then I also need the OEM descrepency to add in.
 

Marthy

World Most Bad A$$ 6R
Elite Member

sti491

Member
Yep. I was closer to 13% for my calculation at various speeds, so we are close. I think one iteration I had was 12.5%.

Thanks.
 

TN6R

Member
Do you guys see any benefit in going -1/+1 vs just -1,0? My gear ratio would be 3.13 with -1/+1 vs -1,0 which is 3.06. If there's virtually no difference, then I'll probably just stick with the -1/0 set up.

I am pretty sure I can use a stock chain on either set up too but I bought a larger 120 link chain to be on the safe side. Some guys are saying I'll be good with my stock chain because the total teeth count on -1/+1 is the same as stock at 62. Would I need to knock out a link on my stock chain if I go with -1/0?
 

sti491

Member
Do you guys see any benefit in going -1/+1 vs just -1,0? My gear ratio would be 3.13 with -1/+1 vs -1,0 which is 3.06. If there's virtually no difference, then I'll probably just stick with the -1/0 set up.

I am pretty sure I can use a stock chain on either set up too but I bought a larger 120 link chain to be on the safe side. Some guys are saying I'll be good with my stock chain because the total teeth count on -1/+1 is the same as stock at 62. Would I need to knock out a link on my stock chain if I go with -1/0?
I can't speak for others preferences in riding style or need for speed, But after exhaust, PC5, Martin's excellent map, airbox mod, advancing the timing.... and now -1 front sprocket, I don't see the need for additional rear sprocket changes for acceleration. I had to change my riding position to avoid wheelies in 1st gear with my front sprocket. Personally, even stronger gearing would make my bike more difficult to street ride smoothly I think.

-1/0 does not require any chain change. I'd try that first see how you like it. It's easier to change the front sprocket that the back.
 

sti491

Member
I installed a 12 O'clock Labs SpeedoDRD Y1 Speedometer Calibrator last night. Pretty much plug & play, then program, which as easy. It was too windy to ride yesterday, and I will be gone today so I may not get to dial it in until tomorrow afternoon. I started at a -13% correction value.

Got it on Amazon for $70. Speedo Healer was over $100, plus this unit is VERY small which is good for my tight underseat area already crowded with my PV5 and alarm. I forgot to take a pic of it on my bike, but I included the pic from Amazon below. It plugs into the same piggy back plug as my gear indicator, which is also the same plug that you tap the pink wire for your PC5 speed sensor, so I have a lot going on down there. Heck, it seems like I have added miles of wire to my bike in last month. So many hard to reach plug-ins; My fingers are bleeding' mate!

While I was in there I took the liberty to try all short velocity stacks in the airbox, that's cut wide open. It will be interesting if I can feel any difference or sound. I don't think my airbox could get any louder!

Just call me Shorty... or you can call me Ray....
 

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sti491

Member
And the magic number is....drum roll please....: 13%.

Plus, Yay, I got it first try! That really surprised me. I calculated it using the gear tooth change and guesstimating the OEM speedo error, and by using my phone GPS, and by advice here. I'd figure I'd need some trial & error, but it is spot on. Happy times!
 


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