Ep8 chainring 28 or 30t

[Gismo6303]

Hello, I've an orbea rise witch has au 32t chainring. I want less tooth. Is anyone know wich brand made a 28 or 30t chainring for the ep8 please?

 

[ebsocalmtb]

why would you want less teeth to the chainring? I already have a hard time using the 32t with a 51t rear cog as it is. I have a much faster cadence then most, and the 32/51 combo would need a cadence that can exceed 110-115 in order to maximize it.

 

[Gismo6303]

I've very high gardien climb near my house and where I go in holidays. On the 51 rear cog I climb at a 60-70 cadence. I prefer near 90. And I've to put a lots of efforts in for climb.

 

[Gary]

Any 30t 4bolt 104bcd narrow wide chainring will fit. Be aware though. 104 spacing was never designed to be used with chainrings smaller than 32t so any aftermarket 30t will be offset (either at the bolt mounting points or with spacers) so that the chain does not foul the spider. So carefully check your frame has sufficient clearance. If you're using a chainguide you'll also need to re space it and it will no. Longer be able to be lowered sufficiently to stop chain bounce off the top.
Cheap good quality rings are readily available via Ali express/eBay


If you're still struggling and on a 29er. Consider swapping to a smaller rear wheel. (basically down gearing by 2 front chainring teeth).

Having said a that.. 90rpm cadence doesn't actually make a whole lot of sense on a genuinely super steep climb.

Whatever it is you're climbing at the moment at 60rpm in 32x51 will already be slower than walking pace.

 

[ebsocalmtb]

I've very high gardien climb near my house and where I go in holidays. On the 51 rear cog I climb at a 60-70 cadence. I prefer near 90. And I've to put a lots of efforts in for climb.

I don't quite get it. Here in Laguna, our rides have climbs with grades in excess of 20% and many of them have 2.5KM long climbs with average grades that are 17%. From my experience, there is no way that you would ever want/need a 28/51 or 30/51 to accomplish these climbs. The motor puts out the most power in the 60-70 range. Spinning the motor up to 90rpm, is going to cause a trail off of assist output from the motor, and require that you are putting more leg power in, likely reducing your ability to complete the climb.

I get it, I have a fast cadence too, and adjusting to an ebike took me a while. The truth is, to get the most of out of these, you need to understand how to work best with them and get the most out of them. For me, the way that works is that I lower my cadence in order to allow the motor to operate in it's max amperage draw range, and get the most out of the motor. Basically, you're using the assist settings to keep the gearing that you want/need to use in check.

 

[Gismo6303]

I want to use mostly eco and motor off. I've 90km and 2400m d+ to do in one ride with only the frame battery, not the extender. I can't put the bike in trail or boost. And with eco I've more strength to apply in the climb in lower gear than my analog bike wich is in 26" 28-48t

 

[Gary]

Yeah. fair enough!
I generally like higher cadences too and also ride my Eeb switched off a fair bit. But would pretty much never pedal at 90rpm at slower speeds than walking pace for more than a second or so at a time. it's simply not as stable or good for traction as slightly lower cadences with a little more torque would be.
I've no idea what your steep climbs are like though.

 

[Gismo6303]

It's mostly hard rock or packed track with root. Some with loose rocks hand sized

 

[Gary]

The motor puts out the most power in the 60-70 range. Spinning the motor up to 90rpm, is going to cause a trail off of assist output from the motor, and require that you are putting more leg power in

I don't think you understand how power actually works.
At a higher cadence with lower gearing you don't need so much leg force to achieve the same power output
And the Shimano motor's assistance level doesn't actually start taper off noticeably until around 100rpm... Where it then begins to "trail off" as you put it until 120rpm. Where assistance has dropped off hugely.
I pedal between 100 - 120rpm most of the ride whenever I commute on my (shimano) Emtb as it gets me where I need to be quickly but keeps my HR in my aerobic zone.

 

[ebsocalmtb]

I don't think you understand how power actually works.

You have a habit, of curt, very condescending responses, which is a pretty neat trait that leads to me not desiring being involved in threads you post in. No skin off either of our butts... and neither of us are going to lose sleep over it... but certainly, it detracts from the whole experience. Either way, I'll respond to this one and then go back to not reading your posts.

I had a whole response typed out here... but I just deleted it, realizing that a back and forth is pointless for me, and exactly what you seem to look for. I digress... Your perception of what I understand and what I don't is incorrect. I suggest you look into near field weakening and consider that the electric motor is going to consume/output more power with a higher load and a lower rpm. In that situation, the motor is producing max torque/power and the shimano firmware will allow 80%+ assist levels provided the rider isn't outputting a power level that is such that 3x the rider power, exceeds the motors max total output. I have yet to see a shimano motor continue the full assistance level it is capable of past 90rpm.

On the physical, non motor side situation, of course higher cadence and lowering gearing means reduced leg force. In my case, my assumption was that the OP was trying to figure out how to climb a steep grade, on an ebike and in that case, going to a 90-100rpm cadence, is working against what the motor wants to do. You are simply better off pedaling softer at a lower rpm and letting the motor consume it's max amperage and not dig into near field weakening which is reducing power and efficiency.

TLDR: because of how 3 phase motors work, eco and high rpm, does not necessarily end up more efficient then trail/boost and lower rpm because NFW is less efficient and you lose power to heat generation.

 

[Gismo6303]

I don't know for the motor, just my feeling is this one : I'm not good at low rpm. I'm better at high rpm. I can sustain hours at high rpm but only a few few seconds,minutes in best case at low rpm. Low rpm put my in too high heart bpm.
I can put bike in trail mode but it suck too much battery, and I need to speed up for keeping a good lvl of effort. Sometime it's not technically possible, and I don't search that. I'm searching comfort for doing a 8h+ effort and keep my 360w battery up for the whole ride.

I just feel the need of a lowering gear. I often looks for a lower gear in my ride.

 

[Gary]

Except. If you'd actually been paying attention. the OP already stated his reason for wanting to run lower gearing to pedal at a higher cadence is because he wants his motor to output less assistance. Not MOAR.

Kinda weird to block someone AND type a long direct reply that'll be hidden from them. I guess some folk simply can't cope with adult discussion.
Cest la vie