Is a drop in MPG accurate after the 17/44 gear change? - Wrist Twisters
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post #1 of 13 Old 06-13-2019, 10:55 PM Thread Starter
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Is a drop in MPG accurate after the 17/44 gear change?

I've only gone thru a few tanks since last weeks gear change, and I can really notice a few things changed. Some good and some I don't like so much.

One thing that happened was a drop in fuel economy. In two test (not enough to be certain) I went from 36~38 to 32. I know the gear change was only about 3.8% loss of torque, but also the old miles are not the new miles, right?

Meaning that the gears changed how the 919 sees a mile. IDK how far off the speedo was before, but so far this drop in MPG is at least 10% to maybe 15% and that doesn't seem right.

So far, the good is that 1st gear is much smoother, the bad is that I have to change my grip because for the first time, I'm going WOT. It's strange that I've never gone WOT on this bike before. I can feel the loss of torque, but I can also see the lower RPMS on the freeway.

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post #2 of 13 Old 06-14-2019, 10:10 AM
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KarlJay,
You are right on about the speedo error from the gearing change.
You bike is traveling 3.8 % further than your odo indicates, and 3.8 % faster than your speedo indicates.
But that doesn't explain the other 3/4s of the 13. 5%+/- loss of fuel economy.
Hmmm, maybe you are spending more time at bigger throttle openings than you think you are!
That would easily explain the other 3/4s of the loss.
Plus, you just changed your rear tire, correct?
Is your new tire larger in OD than what you took off?
That might make another 1 or 2 % difference.
Surely whatever the loss is from rests within the above, as it's been running nice and consistent for you all along, and you've not done any other work that could affect such things, correct?

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post #3 of 13 Old 06-14-2019, 12:31 PM
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It's probably that o-ring
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post #4 of 13 Old 06-14-2019, 01:56 PM Thread Starter
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Quote:
Originally Posted by marylandmike View Post
It's probably that o-ring
Surprisingly, that o-ring looks like all the other now. I did a clean, check and lube and I thought "oh shit, the o-ring is gone" and then I cleaned it off and there it was. I had to look close to see if it was torn or not, but it looks 100% intact. Maybe the hot-cold cycle and all the moving around in the grease got it to work it's way back in.

Either way, I'm still keeping an eye on it.
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post #5 of 13 Old 06-14-2019, 02:10 PM Thread Starter
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Quote:
Originally Posted by mcromo44 View Post
KarlJay,
You are right on about the speedo error from the gearing change.
You bike is traveling 3.8 % further than your odo indicates, and 3.8 % faster than your speedo indicates.
But that doesn't explain the other 3/4s of the 13. 5%+/- loss of fuel economy.
Hmmm, maybe you are spending more time at bigger throttle openings than you think you are!
That would easily explain the other 3/4s of the loss.
Plus, you just changed your rear tire, correct?
Is your new tire larger in OD than what you took off?
That might make another 1 or 2 % difference.
Surely whatever the loss is from rests within the above, as it's been running nice and consistent for you all along, and you've not done any other work that could affect such things, correct?
I've changed nothing else and the tire is the "same size" not counting for 10 years of wear on the old rear and different brand.

The "seat of the pants" dyno says a loss of torque and I've never been WOT on this bike before the gear change.

So I think I'm actually getting less MPG because of my riding style. I was never a WOT rider, but was aggressive and even more after the new tires because they were like glue compared to the old ones.

I'm thinking that my riding style would do better with a 16 front or I have to learn to be less aggressive. I'd probably be best off if I backed off a bit, but I'm having a lot of fun with these new tires. I really do enjoy the blast of torque right in the middle, it's just damn fun and now I have to go WOT to get what I had before. Strange that only a 3.8% change would make that much difference.

The 16T front would increase torque by 5.9% or 2.3% more torque than stock. I can't see 2.3% being that much, it would be damn close to stock, but would I actually be getting better MPG?

~15% really can't be just the speedo correction alone.

Does the PC III do any speedo correction or is it just fuel? I'm asking because the best setup might be a 16 sprocket and a PC III to get the smooth torque at the start. The 17 sprocket does fix the jerky part down low.

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post #6 of 13 Old 06-14-2019, 05:03 PM
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Well there's your problem, WOT. You might as well throw the concept of fuel economy out the window.
Still running that K&N filter? The only real way of tuning these bikes is with a pc111usb and the OEM air filter.

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post #7 of 13 Old 06-14-2019, 07:25 PM
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Quote:
Originally Posted by marylandmike View Post
It's probably that o-ring
This was Hilarious! Good one!

Or maybe the chain is too tight, or wheels are not aligned... LOL

But seriously, a new O-ring chain will also cost a bit in mechanical efficiency. It will get better as the o-rings wear a bit. In theory an X-ring chain has a slight advantage in that regard.

The fun factor of occasional WOT out weighs the small mpg penalty. I think I need new tires!

Mark
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post #8 of 13 Old 06-14-2019, 08:32 PM
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Quote:
Originally Posted by KarlJay View Post
Surprisingly, that o-ring looks like all the other now. I did a clean, check and lube and I thought "oh shit, the o-ring is gone" and then I cleaned it off and there it was. I had to look close to see if it was torn or not, but it looks 100% intact. Maybe the hot-cold cycle and all the moving around in the grease got it to work it's way back in.

Either way, I'm still keeping an eye on it.
That's great to hear!
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post #9 of 13 Old 06-15-2019, 12:15 AM Thread Starter
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Quote:
Originally Posted by Mark919 View Post
This was Hilarious! Good one!

Or maybe the chain is too tight, or wheels are not aligned... LOL

But seriously, a new O-ring chain will also cost a bit in mechanical efficiency. It will get better as the o-rings wear a bit. In theory an X-ring chain has a slight advantage in that regard.

The fun factor of occasional WOT out weighs the small mpg penalty. I think I need new tires!

Mark
Occasional?

Quote:
oc·ca·sion·al
/əˈkāZHənl/
adjective
occurring, appearing, or done infrequently and irregularly.
Sure, it's um, only occasional

Well I checked again today and it was 36 MPG and that's back in the ball park.
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post #10 of 13 Old 06-15-2019, 08:18 AM
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Quote:
Originally Posted by KarlJay View Post
Surprisingly, that o-ring looks like all the other now. I did a clean, check and lube and I thought "oh shit, the o-ring is gone" and then I cleaned it off and there it was. I had to look close to see if it was torn or not, but it looks 100% intact. Maybe the hot-cold cycle and all the moving around in the grease got it to work it's way back in.

Either way, I'm still keeping an eye on it.
It sounds as though your got away with it.
If you haven't already done it, I'd caliper the outside width of the rivet link's sideplates, and compare that dimension to those of the regular link's dimension.
Whatever difference there is should be in terms of a thousandths of an inch, and nothing remotely close to fractional!

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post #11 of 13 Old 06-15-2019, 02:26 PM Thread Starter
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Quote:
Originally Posted by mcromo44 View Post
It sounds as though your got away with it.
If you haven't already done it, I'd caliper the outside width of the rivet link's sideplates, and compare that dimension to those of the regular link's dimension.
Whatever difference there is should be in terms of a thousandths of an inch, and nothing remotely close to fractional!
I not only measured the outside and compared to other links, but I used a feeler gauge to measure the actual gap the o ring sits in and compared that to others.

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post #12 of 13 Old 06-15-2019, 05:32 PM
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Quote:
Originally Posted by KarlJay View Post
Quote:
Originally Posted by mcromo44 View Post
Hmmm, maybe you are spending more time at bigger throttle openings than you think you are!
That would easily explain the other 3/4s of the loss.
So I think I'm actually getting less MPG because of my riding style. I was never a WOT rider, but was aggressive and even more after the new tires because they were like glue compared to the old ones.

I have to learn to be less aggressive. I'd probably be best off if I backed off a bit,

Does the PC III do any speedo correction or is it just fuel? I'm asking because the best setup might be a 16 sprocket and a PC III to get the smooth torque at the start. The 17 sprocket does fix the jerky part down low.
Quote:
Originally Posted by Islandboy View Post
Well there's your problem, WOT. You might as well throw the concept of fuel economy out the window.
Still running that K&N filter? The only real way of tuning these bikes is with a pc111usb and the OEM air filter.
That makes sense, if you are opening it up a lot more, and as a result burning more fuel.

Personally, I don’t even pay attention to fuel mileage on my bike, but that’s just me. They get better than my 4runner. And I am riding it to enjoy it, push it, and have fun.

I had 15/43 sprockets on my 919, K&N air filter, PCIII tuned very rich in the low/mid range RPMs with the accelerator pump enabled to feed extra fuel when you crank the throttle (before/during the acceleration, instead of “catching up”), with Pirelli Angel tires.
The bike was very smooth accelerating, just more vibes than with the 17/44 set-up.

I just reset the trip odometer at every fill up and re-fueled before it hit 120 miles.

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post #13 of 13 Old 06-16-2019, 12:50 AM Thread Starter
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Quote:
Originally Posted by PC1978 View Post
That makes sense, if you are opening it up a lot more, and as a result burning more fuel.

Personally, I don’t even pay attention to fuel mileage on my bike, but that’s just me. They get better than my 4runner. And I am riding it to enjoy it, push it, and have fun.

I had 15/43 sprockets on my 919, K&N air filter, PCIII tuned very rich in the low/mid range RPMs with the accelerator pump enabled to feed extra fuel when you crank the throttle (before/during the acceleration, instead of “catching up”), with Pirelli Angel tires.
The bike was very smooth accelerating, just more vibes than with the 17/44 set-up.

I just reset the trip odometer at every fill up and re-fueled before it hit 120 miles.
I had no idea the PCIII had that level of tuning. Sounds like it should be on the list of things to get.

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