Found myself in a tight spot - Battery life vs. energy spent

[EnduroDad2k]

Hi all, I had one of those 'live and learn' moments yesterday that I would love some advice on - What mode is best to make it up a long steady climb? Is it better to get up more quickly using more power for a shorter duration? Or drop it to a low gear and crawl in eco mode for a much longer period?

I was riding up in Downieville California which has a legendary 15mi. downhill. I figured I would ride it down with the motor mostly turned off, then head back up a more gentle 18mi. dirt road to my car. The classic EMTB "shuttle" scenario.

The15mi downhill portion was a blast, I only used 5% charge on a couple climbs.

That left 95% charge for 18 miles back to the car, no problem, right? Even with a long climb (6,000ft) it seemed doable if I kept it on power level low (eco 1 - active 3). I'm on a 2021 Trance X e+ Pro 3 with a 625Wh battery, 175lbs.

I knew it would be a LONG climb back to the car, but I underestimated how quickly I was burning through the battery. I started the climb in Active (level 3) and pushed pretty hard to keep energy use down. But 8 miles in I was down to 45%, it was getting dark, cold, and I was in the middle of nowhere alone. And looking at the remaining 10 miles on my trailforks app it was nearly a solid incline all the way. I wasn't going to make it at that pace.

So I dropped down to Tour 2 mode and pushed as hard as I could, then when I was on last indicator light I dropped to Eco 1. I finally made it to the top with just under 5% battery remaining but I hit the wall physically about half way up and had to dig deep to make it.

So here's my question: When faced with a steady incline on a dirt road and need to make the battery last as long as possible, what is the ideal power mode? Would it make sense to turn it down to Eco 1 mode and crawl up in a slow, low gear? Or would it make more sense to keep it in Active 3 mode and make it to the top much more quickly?

I certainly learned the hard way that steady hillclimbs will devour my 625w battery very quickly!

Many thanks!

The route:

The massive trees:

My son the beneficiary of my shuttle misadventure:

 

[hyfly25c]

Hi,
my take would the the following:
your bike support in % of rider input - i.e.the more you push yourselfes the more the motor will support
and in consequence quicker deplete your battery.

I think its a matter of work over time - so
if you switch to lower support, your climb is slower; as your ride takes longer, over time your own input
accumulates to a higher amount. So in the end your battery lasts longer, as you work more yourself

 

[RustyIron]

I've programmed a special mode that I use when the ride gives me concerns about range. The assist level is 2/10, and the maximum torque is 27 Nm. This results in a higher leg/motor input ratio, and it limits the amount of assistance. But this is half of the equation.

The total energy required to move the bike over a given trail is greater when the speeds are higher. When riding up hills or on the level, I keep my speed down to that which I'd be rolling if on an acoustic bike. Generally, that's about 6 mph.

You can test this out for yourself on one of your regular routes. Ride it at a moderate speed and low level of assistance, then see how much battery you have left at the end. Next time, ride fast with a lot of assistance, and look at the difference in battery usage.

 

[steve_sordy]

I agree with @hyfly25c. Just stay in Eco and grind your way up in easy gears.

I once went round a 15-mile trail in Wales and used up my 378Whr battery. The following year I took my young grandson on his hardtail. I followed him and was in Eco the whole time. I only used 1 bar but I was working well into the second. So, let's say 30-35% used. I was astonished, I'd even taken my spare battery this time and not used it!

 

[jeanmarc]

I've programmed a special mode that I use when the ride gives me concerns about range. The assist level is 2/10, and the maximum torque is 27 Nm. This results in a higher leg/motor input ratio, and it limits the amount of assistance. But this is half of the equation.

The total energy required to move the bike over a given trail is greater when the speeds are higher. When riding up hills or on the level, I keep my speed down to that which I'd be rolling if on an acoustic bike. Generally, that's about 6 mph.

You can test this out for yourself on one of your regular routes. Ride it at a moderate speed and low level of assistance, then see how much battery you have left at the end. Next time, ride fast with a lot of assistance, and look at the difference in battery usage.

How can you do that on a Giant bike?

 

[RustyIron]

How can you do that on a Giant bike?

I don't own a Giant, so don't know about the programability. But the part about riding at the lowest level of assist and sensible speeds should be self evident. Do that, and your range will improve.

There's one more thing that increases range. I haven't done this myself, but some of my friends do it. They ride at higher levels of assist, and they're slender ladies. Now I'm in no way recommending that you become a slender lady, but this is 2021, and if that's what you choose to do, it's your business.

For the foreseeable future, I intend to keep riding at lower levels of assistance, and retain my manhood.

 

[hyfly25c]

With the Giant Ride Control app - you can customize support-% for the different modes; you can choose from 3 different % values
for each mode.
I have dropped Eco+ to just 75% - instead of 100% and reduced the higher levels as well so the difference is not too much beween the modes.

 

[TR5_20]

Now I'm in no way recommending that you become a slender lady, but this is 2021, and if that's what you choose to do, it's your business.

Hey, Rusty, has the New Year still not reached your part of the world?

 

[Mikerb]

Whilst all the various motors differ in terms their support modes they all have cadence and torque sensors to determine how much assistance is provided. With some of the motors you can set a max for each mode but its not really necessary because you can regulate the level of assist by how much torque you put through the cranks............so the key is keep the gearing low and spin. Mot motors also reach peak efficiency at higher cadences.
Something that probably makes just as much difference is to spend a couple of minutes with a couple of CO2 cannisters and up your tyre pressures to 30 psi plus. Secondly take the line of least resistance on the shuttle and maintain momentum and a constant speed.

 

[RustyIron]

Hey, Rusty, has the New Year still not reached your part of the world?

Clearly, I'm a bloody idiot. That's why you shouldn't listen to anything I say. Since I retired, it's not infrequent that I don't even know what day it is. I have to think twice to remember the month. But I can tell you off the top of my head what the weather will be for the next week, trail conditions, and how many hours until sunset.

 

[EnduroDad2k]

Thanks everyone for the advice! Next time I find myself making poor decisions like this I’ll stick with high cadence and low gearing.

I’ve been contemplating a switch to an Orbea Rise lately, but I’m glad I had the full fat for this weekend’s death climb!

 

[MountainBoy]

Thanks everyone for the advice! Next time I find myself making poor decisions like this I’ll stick with high cadence and low gearing.

I’ve been contemplating a switch to an Orbea Rise lately, but I’m glad I had the full fat for this weekend’s death climb!

Yes, high cadence is key because it puts the motor in a more efficient RPM range. It aalo smooths out the natural variation in crank speed as it goes through each revolution.