Jever98,
I've actually gave this a lot of thought when I got my first ebike. The areas I like to ride are very rocky. I find that a long derailleur arm is not always the ideal setup. Dispite my best efforts, I've occasionally place my bike in situations where the rear derailleur arm would 'Take one for the Team.'
SRAM Eagler AXS, hard hit on a rock drop, Brohemian Rhapsody Trail, Las Vegas Nevada.
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Being new to eMTB at the time, I found that on power moves such as a punchy climb, I was snapping chains frequently. I often thought about how much thicker chains chains used to be on the older 9 speed drivetrain setups. I also questioned why the need for 12 speeds on an eBike? I get 12 speeds on a traditional bike, but why an eBike? After all, I was receiving plenty of power from the bike, why not a more robust eight or nine speed system?
By going with a smaller cassette typically found on an eight or nine speed system, I could decrease the length of the derailleur arm and it would be less prone to rock strikes.
For those new to mountian biking, Shimano and others uses a letter suffix added to the rear derailleur model number to denote derailleur arm length. Shimano's primary designations are
SS for Short Cage,
GS for Medium Cage, and
SGS for Long Cage. One of the primary functions of a derailleur arm is to take up slack and keep tension on the chain as it is shifted between cogs. A larger cassette requires more chain and thus a longer derailleur arm to accomodate the increased length of chain. I would like to add that rocks are immensely attracted to longer derailleur arms. It's one of those 'Rules of nature' thingies.
There are several companies such as 'Box' which offers eight and nine speed systems for eMTB, that have a thick chain, semi wide range cassete , i.e. 11-42, and short derailleur cage. The financial cost for one of these drivetrains is minimal when compared to say a SRAM Eagle Type T drivetrain. If you find that the terrain you ride tends to snap chains, smash derailleurs, or you simply just want a piece of Old School, this may be the ticket to happiness and less fuss.
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Our Box Four tier is for those people who just want less fuss! You're fond of Prime 9, but know 8 is enough, and surely 11-42T is plenty of range for an 8-speed cassette. Our derailleur still has the Limited Slip clutch but now arrives with a more compact cage. The custom 8-speed chain is built...
boxcomponents.com
I tried one of these systems and it worked well. However, the cassette range impacted my riding, i.e. I was sweating my balls off on steep climbs. I live in Southern California which features a lot of mountain terrain and steep trails. I also like the 'Rock Crawling' type of trails found in the Nevada, Utah and Arizona areas. In my old age, I found I'd gotten spoiled riding with a wide range cassette. I went back to my SRAM AXS. As a side note, I have absolutely nothing to say bad about Shimano drivetrains, it's just that I love the locking derailleur arm on SRAM drivetrains. It makes working on a bike so much easier.
I currently use the SRAM 'T-Type' AXS drivetrain, coupled with a Bosch Race motor. It's a great system and I have felt no need to change. Occasionlly, I will have to replace the derailleur arm. It's one of those costs of doing business things. Swapping out a T-Type derailleur arm is a quick and easy process that does not require breaking the chain and takes only about few minutes to do.
T-Type replacement derailleur arm
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Below I'm going to discuss a seperate drivetrain topic for those who are interested:
While many riders like to increase chain ring size to increase top end speed, I found myself actually decreasing chain ring size, i.e. 26T - 28T, to increase bike range. My first eBike was an Orbea Rise with 65Nm motor and 360Wh battery. On steep climbs, I found that I was using a lot of boost. I was quickly draining my battery and thus ride length. I reasoned that if I went to a 26T or 28T chain ring, I could use 'Eco' mode more often and less boost. Decreasing chain ring size ultimately proved successful and I was able to increase overall range/ride distance by about 20%.
I average about 2,500 to 3,000 miles of riding annually. I was stretching chains out to 50% wear in about 400 to 500 miles. Because the SRAM AXS T-Type derailleur has no screw adjustment, the drivetrain requires a very exact chain length to shift properly. When the chain stretches to 50% wear, this increases overall chain length by about 6mm. A 6mm difference in chain length will directly impact T-Type shifting. The more the T-Type chain stretches, the worse your shifting will become. It's a very gradual degradation. So, if you find your T-Type drivetrain is no longer shifting smoothly or making noise, check your chain stretch. This will likely be the cause. A new chain will restore smooth and quiet shifting.
New style SRAM Type T chain (Note the thicker chain plate)
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Older style SRAM Eagle chain
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I'm not fond of replacing chains at 450 miles of use. I began experimenting with chain lubes. I reasoned that what was desgined for a traditional bike drive train may not be sufficient to withstand the torque and friction produced by an eBike motor. I trains in Southern California rains once a year, whether it needs to or not. Because of a lack of rain, the trails develop a very fine, talcum powder dirt that's abrasive. A wet lube severely attracts this abrasive dust. I've always used dry chain lubes, i.e. Rock n Roll Gold, Muc-Off Dry Lube, Squirt, White Lightening, etc. After a bit of experimentation, I've settled upon Dumonde 'Pro X Regular Formula', chain lube as my current favorite. It's marketed as a dry lube, but i'd describe it as a semi dry and wet lube. I was surprised by how well it the lubriction works. I noticed an immediate reduction in drivetrain noise and I no longer need to lube my chain before a ride. I now apply lubrication about every 5th or 6th ride. I currently have 1,000 miles on my chain and it's only at about 25% stretch. There is one definite downside to Dumonde Pro X, it attracts dirt and it requires a more frequent cleaning of the derailleur pulleys and chain.
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Be safe,
Rod
