Print

Please login or register.
1 Hour 1 Day 1 Week 1 Month Forever
Login with username, password and session length

[tunafish_phd]

I know there's another active post about this currently, but I didn't want this to get buried on the 3rd page of a thread for future folks. I'll keep the main part of this updated as I gain more info.

Hello all!

I finally got my 40t rear in, installed it, and have done some initial testing.

'23 Ribelle RS - Testing a 15/40 sprocket setup

(If you don't actually care about data, or my opinions, skip to the <=====> mark for the TL;DR:)

My initial thoughts: Yep. Its a lot slower off the line, basically took the bike from "I'm in danger" to "man, I'm barely beating liter bikes now"

More thoughtful thoughts:
My speedometer now PERFECTLY matches GPS - WIN
My Odometer now PERFECTLY matches GPS - WIN
I can hit 125 MPH per GPS speed now - WIN
I did not have to change my chain during this, there was enough adjustability in the rear that it wasn't an issue. - WIN
I REALLY REALLY REALLY wish there was a full torque spec manual floating around somewhere. -  NEUTRAL
Efficiency took a very harsh negative dive. More thoughts on that one below. - BIG LOSS

(if you dgaf about why I think I got the efficiency loss, skip to the <----->)

Lets talk about that efficiency loss. Grab some coffee and strap in.

With ICE we're very used to discussing efficiency coming from lower RPMs or "the less the motor turns, the more efficient it should be". I think thats true for ICE engines and I think its completely wrong for EV's. Electric motors are torque machines, their draw relates directly to much torque they are supplying as opposed to how fast they are spinning. In a vacuum, keeping an electric motor spinning at 6k rpm isn't much if anymore draw than keeping it spinning at 6 rpm, the big issue we run into is resistances. Wind, rolling, friction, etc. So for us to keep speed on the highway, we're not just keeping the motor running, we're overcoming wind resistance, rolling resistance and friction. In the 44t setup, we have gearing assisting us in overcoming those resistances. By reducing the gear ratio, that extra torque has to come from somewhere, and in our case, the only place to make that up is going to be directly from the motor itself. So whereas with the 44t setup, it might take 10-12 (number from memory of flipping through screens on the highway) torque to "keep speed" its now drawing 15-17 (based on evidence from a single ride) using the 40t setup.

By changing my gear ratio, I have effectively increased the amount of torque the motor itself needs to supply to overcome the same resistances and achieve the same speeds. Basically, since I lost some gearing advantage, that has to be made up somewhere, in this case it seems to be motor battery draw.

<------>

By the numbers (Speeds are all GPS speeds, wh/mi are average observed during riding. Keep in mind I have a lot more data for the 44t at this point):
70mph - 44t: 190 wh/mi average. 40t: 250 wh/mi average
50mph - 44t: 120 wh/mli average. 40t: 170 wh/mi average

By %/distance - 20 mile loop 85% City, 5% 70mph freeway, 10% 50mph highway
44t - 8-10% battery removed at end of loop (this is the average over the last few weeks)
40t - 19% battery used (single data point)


Conclusion about the 40t:
I'm really torn here.
I like the win's I got for Speedo, Odo.
The efficiency hit is pretty harsh.
I REALLY liked feeling like I was going to die every time I grabbed a handful of throttle with the 44t sprocket. Now its merely exciting. Its not "slow" it still beats liter bikes, but only just barely now.
I don't really care about the 125MPH limit so much. Every now and then its fun to hit, but I don't make a lot of trips to Mexico these days.

Next steps:
I think I'm going to stick with the 40t for a week or so, just to get some more data, but as of right now, I'm leaning towards going back to the 44t
I'm interested in trying a 16t in the front, but I'm pretty sure this will be VERY similar to going to a 41t in the rear (.017 difference in gear ratio and I don't have to buy the tool)

<================>
TL;DR:
40T fixed speedometer and odometer issues. Can actually do 125 per GPS now. Bike less fast off the line or out of a dig. Bike is WAY less efficient.

[HoodRichOG]

Damn, totally sucks about the energy loss. Thanks for sharing your findings!

Wanted to do the same, but losing efficiency sucks. Wish we could just have an option to correct the speedo somehow.

[Ashveratu]

I don't understand all this fuss about the speedometer. I never have time to look at it while passing everyone 

[PWM]

Good info...cannot get away from the dynamics of street riding...for steady state operation say highway speed the difference SB nill, no?

[tunafish_phd]

Steady state riding at highway speeds my energy draw went up be almost 50%!

[Richard230]

Steady state riding at highway speeds my energy draw went up be almost 50%!

 

[jotjotde]

Thank you for sharing this (for me) totally unexpected outcome!

[MVetter]

by show of hands who here believes that the data collection in this thread might, just might, be flawed

[iopean]

by show of hands who here believes that the data collection in this thread might, just might, be flawed

Hard to say either way without more data points.

I've had two Suzukis previously and they both underread by about 10%, can't say it ever bothered me.  For electric bikes, I'd just want the guessometer  to mean an accurate distance - meaning 100 miles to mean a hundred miles and not 10% less at 90 miles.

[tunafish_phd]

by show of hands who here believes that the data collection in this thread might, just might, be flawed

Which part? I just reported exactly my experience. I'd like to know how you'd like me to collect more data to help prove what I've learned.

Edit: Prove maybe too strong a word.. Verify is probably a better way to put that?

[IRideElectric]

I'm sorry to ask (since I don't have a bunch of time to look/think about this in greater detail), but my first question that doesn't seem clear to me: stated efficiency is significantly lost at highway speeds, but it wasn't clear, so, is the highway speed efficiency comparison same speedo speeds from 44t to 40t, or same gps speeds? (ie. are we talking 65mph by both speedo's, or 65mph by gps, and yes I understand 40t speedo=gps speed now, since same speedo speeds from 44t wouldn't be actually same speeds)

Also, realized when you mentioned odometer now reads accurately, it just occurred to me (sorry, maybe I'm slow here ) but this would have implications for warranty if odometer read 10% higher than actual (as in, you exceed your warranty miles sooner). Just stating as this seems sketchy, like if a manufacturer was allowed 10% higher speedo/odo, wouldn't it be in their best interest to always make sure it's at the max instead of accurate? Just asking to see if I'm wrong here.

[HoodRichOG]

My understanding is the odo reads correctly while the speedo reads incorrectly. The bike knows the real speed, it just displays a different one on the dash for some reason.

[MVetter]

Which part? I just reported exactly my experience. I'd like to know how you'd like me to collect more data to help prove what I've learned.

Edit: Prove maybe too strong a word.. Verify is probably a better way to put that?

We're going to need more data, but there's a chance that, when you changed the gearing, you also interfered with the range calculations algorithm. If the speedo is based on motor RPM and now that's all out of whack with reality, there's a good chance this threw a wrench at Wh/mi and SoC algorithms. I'd be interested to see if the SoC gets miscalculated. Really I'd like to watch the voltage and log that but most people aren't able to access such data.

[tunafish_phd]

Hmm. That would be interesting. You're right, technically I think changing the gearing would interfere with the WH/Mi calculation. Thats why I also included my SOC for a known distance.

Let me talk through my interpretation of what you said about the wh/mi calculation..

Lets assume the motor has no knowledge of actual mileage, because I believe it does not. If I change the gearing, the electronics should have no way of knowing that the distance in a "mile" has changed. Now that we've corrected for mileage/speed by changing sprocket sizes, it would make sense that it takes more energy to go an actual mile because you're physically traveling further "per mile" according to the computer.


I'll go drive a larger, cruise control centric loop this evening and repeat it tomorrow evening with the different sprocket to see where I wind up with with SOC. That should at least get at the total electrons consumed while staying in as controlled an environment as possible. Will also note down any data I can find flipping through the menu's.

Will report back with findings. In the mean time. If you or anyone else has any other data points you'd like me to collect, let me know!

[ultrarnr]

The odometer on my Ribelle is not perfect but it is close. My trip odometer for today's commute shows. 61.6 miles. My GPS shows 60.4 miles. But of course my speedometer is 10% off like everyone else's. Just a data point for this discussion.