Inertianinja

I have a 2017 Specialized Sirrus (https://www.specialized.com/us/en/sirrus/p/115192)
8-speed, 700C wheels, rim brakes, aluminum frame.

I am looking at this kit on Aliexpress: https://www.aliexpress.com/item/32949276245.html (48V, 1500W)
This battery: https://www.aliexpress.com/item/32971240462.html (48V 17.5Ah Samsung)
This torque arm: https://www.aliexpress.com/item/1622635692.html

Any reason this kit wouldn't work for the Sirrus?

I emailed the seller but wasn't able to get an answer about whether the hub would fit an 8-speed cassette.

2old

I could be wrong, but don't see a cassette in their description. Also, some Direct Drive rear hubs are > 135mm with 8-speed freewheels, so you would need to decide whether you want to "spread" your frame (I wouldn't). Might also ask on endless sphere.

Inertianinja

Might be on a different tab of the site - but they offer a 7 speed cassette as a $5 upgrade. The bike is an 8-speed, so I'm not clear on whether it'd work.
The description does say the motor is good for 135-142mm rear spacing, so i assume that's OK?

2old

Pretty sure 7-speed is narrower than 8, so you would need to change those components (cassette and shifter), although depending on your cassette it may be possible to remove one gear from the "8".

Doc_Wui

It's most likely a kit that only uses freewheel compatible motors. THey offer to sell you a 7 speed 14-34T freewheel for $5.

I personally keep the 3 speed front derauilleur on conversions. On one bike, I had to change to a 6 speed freewheel because the frame was too narrow for a 7 speed, but most of the time, you don't need all the gears with a motor. What you will miss is that Shimano freewheels only go down to 14T. DNP does sell a freewheel with 11T, and you will probably want that to avoid spinning out the pedals at higher speeds.

Inertianinja

That looks right about the freewheel. The bike does have a triple chainring up front. I'm thinking that if the 7-speed freewhweel cassette will work with the bike, I won't miss the loss of gears. This isn't my primary bike and I'm not really spinning on it - just using it for rolling around. If this works it could become a commuter.

Same question, though - any reason this kit wouldn't work with the Sirrus?

Doc_Wui

What makes a kit not work?
1. When the motor doesn't fit in the dropouts,.
2. Motor turned out too slow. Conversely some motors are too fast for the user.
3. Crappy pedal assist, like when level 1 and level5 act the same.

Bonzo Banana

I know many don't like front wheel motor hubs but for heavier riders they don't slip and you have the advantage that you have 2 wheel drive, you can easily switch the bike back to a normal bike, you can still use your high quality freehub based gearing, they are much easier to fit and tend to be more reliable as simpler and don't have as much weight on them. Lots of reasons to consider a front wheel motor hub. As a heavy rider I tend to get more punctures on the rear because that is where more of my weight is which is another reason to favour a motor on the front wheel.

A freewheel is a junk component in my opinion especially those very low quality 8 or 9 speed freewheels you sometimes see on low end ebikes. Much better to have a high quality freehub based drivetrain like your Sirrus already has.

GMoser85

What Front hub motor do you use? I am a bigger guy and looking to convert my cargo bike.

2old

I'm not that big (6'1", 180) but loved a 36V, 350w geared front hub system, but disliked a 48V 1200w. Try to test ride something comparable if you're leaning toward a larger motor.

Bonzo Banana

I just use a violamart front hub motor, it was a very cheap package costing me about £100-110 with the battery an additional purchase. I bought a cheap s/hand mountain bike for £5, a 48V 12.5Ah battery for about £140-150 and a 7 speed freehub rear wheel for £10 including postage. The mountain bike originally came with low end single wall rim wheels, the whole bike cost me about £300 in build costs but with the parts I didn't need I guess I have £20-30 of parts to sell although they will probably end up on a beater bike frame I have.

GMoser85

Awesome, thank you for the information! How do they hold up in the rain? That's biggest concern going with a cheap set up.

Bonzo Banana

I think water ingress is an issue on all ebikes, I've certainly seen it as a issue on mid-drive motors, Bosch etc which can be very expensive. I'm a fair weather cyclist with regards my ebike so unsure how this cheap ebike compares to more expensive models but at least the controller box is separate so can be high up and isolated better from the rain, many motors include the main circuit within the motor assembly and I've certainly seen LCD screens that have suffered due to water ingress. It feels to me ebikes are ok for light rain and exposure but real downpours can maybe cause issues. Maybe front motor hubs are more exposed then rear motor hubs. It feels like the rider could be a barrier to rain getting to the rear motor hub plus there maybe more physical barriers at the rear like rear rack etc. The front hub in comparison seems to be hitting the rain first with nothing blocking it. I hadn't thought about it before but maybe one disadvantage to add to front hub motors. Obviously if the seals are in perfect condition and well designed then no problem but such seals aren't always perfect. I've seen where grease in mid-drive and geared hub motors has been emulsified due to water ingress and I've seen rust too. It feels like you need to be proactive protecting your ebike from rain, checking water entry points etc. If water gets into a hub motor gravity would surely help it find its way out.

Doc_Wui

LAst year was a bad year for water and my ebikes. I had one inexpensive ebike get water inside the controller, but luckily I had disconnected the battery after coming home soaking wet, The next day, when I reconnected it, the bike didn't run and I heard the water sizzling, Immediately powered down and washed it out with rubbing alcohol.

My wife's DIY bike had the controller over the rear wheel. When she rode thru a deep puddle, the throttle shorted out.The last incident was another DIY bike where I had the electronics in a box, but the wiring exited from the top. Water from back wheel eventually dripped down the wires and caused errors. Over the winter, I addressed all these issues. Installed fenders. Moved the electronics and exposed connectors into water resistant cpntroller boxes (sold for this purpose). Looks far better too,

Didn't talk about handlebar controls/displays. When transporting these bikes, I rubber band plastic bags over then, but they do resist light rain..

MNebiker

The bike I wanted to convert to an ebike had a good quality 24spd freehub drive train that shifted super smooth. But all the rear wheel kits at the time were set up to use a 7spd freewheel. I preferred keeping the original drive train intact so I opted for an eBikeling 700c 500W 36V geared motor front wheel kit, and added a beefy torque arm to the front fork. 4000+ miles later everything continues to work fine. I have noticed no significant difference in handling after the conversion. It seems like the motor in front and battery on the rear carrier help balance each other. I'm a big guy, so I did swap the 700c32 tires for 700c35. The local trails run though crowded parks with picnic and beach areas - I turn off the electric in those areas and the bike rides just like it did before the conversion.

The only traction problem was some spin if you hit the throttle hard from a stop - but I ride it only in PAS mode. In fact, I eliminated the throttle completely when I added some larger ergo hand grips.

I was surprised and pleased with the eBikeling kit quality. Plus - they are in Chicago, not China, and have decent customer service.

2old

FWIW, I'm satisfied with ebikeling too. Their kit was exceptional for the price and their CS is very good. I've called them ten or so times and was able to talk to someone at least 80% of the time.

chas58

MNebiker

Hope this helps, but 6, 7, 8 speed all use the same spacing, chain, indexing. The only difference is limiting the range of the derailer. I've put a 7speed freewheel e-hub on an 8 speed bike with no issues.

For what it is worth, the width of a tooth is the same for most all gears (except of course 1/8" track bikes and single speeds), meaning you can use an 11 speed chain on a 7 speed cassette. the indexing and the outer width of the chain is different, but the internal width is the same.

2InertianinjaFront forks are not in any, any way designed for the torque of a hub motor. Steel will bend if something goes wrong, but many alloy front forks have put people in the hospital (or occasionally morgue) because they fail suddenly and when you loose your front wheel at speed, well...

I would rather get a hub motor designed for a modern cassette (rather than the antiquated feewheel) than to put something on the front fork. And by no means put a 1500 watt motor on a front hub. 500watts is starting to get dangerous. Its not at all hard for the torque of a small motor to rip open the fork's dropouts.

@Inertianinja I have a bike like the Sirius (its the crossroads). That is about perfect for a non mountain bike ebike in my opinion. Not so sure I'd want to go too fast on those brakes though (I have built half a dozen ebikes over the years). Make sure you have some high end brake pads and you should be fine.

The specs state "32mm tires" but an ebike like that will be a lot nicer with 38-40mm tires. Trust me.

"V-brakes are dependable and easy to maintain, so you won't have to worry about brake bleeds or labor-intensive maintenance to have awesome stopping power. " Ok, that quote (from the web page link above) made me kinda laugh.

Inertianinja

chas58 I’m actually not looking to go super fast on it - not much faster than you’d go on a road bike anyway. I’m really more concerned about torque getting up hills without losing a ton of speed.

I still haven’t been able to get a clear picture of what kit to buy for the conversion, though!

2old

Your best bet is a mid-drive if you ride in hilly terrain. I've had excellent success with a Luna BBS02 at 52V, but 48V will work well too.

chas58

I like my bike to feel like I'm doing work peddling - which for me means a small motor and a small battery (i.e. 36v). But, I'm a strong cyclist and not a typical e-bike rider.
For a small motor, i like a Q100 at 260rpm and 36volts - that is about 20mph. Alternatively, a Q100 rated at 200rpm but run at 48volts will do about the same speed (but with a 30% more power).
For reference, that is a 350 watt motor (or 500 watt at 48v) doing 20mph. You can always have a 1500 watt motor and just use a fraction of the power. Its nice to have some reserve power, but that is going to cost you $$$ and weight. Its going to be so much stronger than your legs that you are going to be tempted to let it do all the work. ;-)

But if you are doing hills (especially if they are long or if you are carrying a lot of weight), a mid drive is what you want (Bafang BBS02). That will allow the motor to use the gearing on your bike. If you spend a lot of time (say more than 5 minutes) with a hub motor going full throttle but half its cruising speed, something will over heat. If you are not grinding up long hills at full throttle (and lower speed) a hub motor is lighter and cheaper and less maintenance.

Inertianinja

I think I want to go rear drive rather than mid-drive.
I’d like the option to use the motor without pedaling, and I would prefer not to add stress on the chain. There seem to be plenty of kits out there, just not clear which will work with my rear spacing and cassette.

chas58

Understood. My rear drive bikes work just fine with no motor.

If you don't want to go more than 500 watts (36v x 20 amps or 48volts x 15 amps), and want light, this is what I use (Q100)
https://bmsbattery.com/ebike/577-162...ebike-kit.html
(Note that shipping from china will come close to doubling the price listed on the website)

For a little more weight, the Q128 will take about 50% more power if you need that.

You probably want the "C" version - as that takes a standard 8 speed cassette. (the standard version will take a screw on 7 speed "freewheel" which works fine too if you don't mind using a cheap ($20) gear-set in the rear).
https://bmsbattery.com/motor/768-167...8v/213-rpm-201
https://bmsbattery.com/motor/651-163...l#/213-rpm-201


Bafang makes some good motors as does Mac.


Really though, your biggest expense is gonna be that battery.