Aluminum vs Steel frame

[leamcorp]

I didn't want to hijack another posters thread, so I'm starting a new one. This was regarding Link using Schwinn S-40 for his Ebike. After seeing that, I've posted this,

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Link, Schwinn S-40 is an aluminum bike. No problem with the dropout? I thought everyone is suggesting that we get a steel bike.

I too like better quality bike/components and been having hard time finding a steel bike. In order to get steel, its either cheap department store bike (less than $150) or high end custom bike (over $1000 for frame alone).

So for rear wheel hub, is aluminum bike okay? It will make my next build much easier since its easier to find mid-grade aluminum bike with very good quality folk/components set.

Link's response was,
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It's rear drops are quite thick (8mm, IIRC), so it should be fine with less powerful hubs. I ran a 48V 40A Golden Motor on it for a while without a torque arm, and it seemed to be okay. (I think that's probably pushing it, though, since the Golden is pretty torquey.)

That being said, I really don't think it's worth the risk just to save $25 on a torque arm.
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So my question is - if paired with Torque arm(s), is aluminum frame strong enough for BMC rear hub motor with 48v Lifepo4. How'bout 72v 35amp setup.

The bike I'm thinking of is Specialized Rockhopper Comp hardtail.

Cheers

 

[Link]

If a torque arm does its job right, it should take most or all of the stress off the drops. So, really, any frame is okay as long as you have a good torque arm or two.

 

[Sacman]

If a torque arm does its job right, it should take most or all of the stress off the drops. So, really, any frame is okay as long as you have a good torque arm or two.

...provided the strut member you attach the torque arm to is strong enough to take the torque. :wink:

 

[Link]

Yar, we're assuming this isn't a carbon road bike, right?

 

[docnjoj]

Many of the walbarf bikes that say they are Alloy have steel forks and rear triangles. Bring Your magnet!
otherDoc

 

[leamcorp]

The bike is aluminum and here's what it say - "Specialized M4 Manipulated Alloy frame, fully butted, ORE DT, forged dropouts w/ replaceable 98954020 hanger"

I have a several torque arm - from hi-power cycle and amped bike.

As for the connecting member, I've used 1/2" steel loop strap with silicone cushion. Do a search on steel loop strap on McMaster.com

On my current setup (48v BL36 on steel front fork), the only problem I had was on the rear rack mount. The hole where rack screws in (on the frame) came right off. I guess it wasn't design for 30lb of weight bouncing around. I'm using the steel loop strap to hold the rack at this point.

 

[dogman dan]

Steel bike frames are dime a dozen at the fleas and garage sales. They are starting to pile up like beer cans at my house. I keep buying em at 10 buck prices for one or two components. Why not start with a frame like that, and then get a good set of suspension forks for it? If it is a good bike to start with, all you will need is maybe a new derailur and a bunch of cables. If it's really trashed, another 10 buck bike or two will provide all the shifters or straight front wheels you need. The thrill is in the hunt anyway. The one I bought last weekend was a pretty high quality bike, but when I put a shock fork on it, it rocks now. It's my peadling bike for the mountain trails now. It definitely has a rear gearmotor in its future.

 

[leamcorp]

The problem with that solution is difficulty finding right frame that will accept the newer components. For example, most of the cheap bikes from Walmart uses either threaded or 1" non thread for fork. Most of the newer components uses 1 1/8" and is non threaded. While there are 1" non threaded forks around, its now non standard and more limited in selection.

The other thing is the weight. One Walmart bike I saw, Mongoose XR250 weighted 46lb to start (and its aluminum). The Specialized Rockhopper I'm looking at is 27lb, which is big difference. While weight is less of a concern for Ebike, I still would like to have a lighter bike since I pedal most of the time (and I'm a weight weenie for my regular bikes).

Since lot of people are using aluminum bike with rear hub, I like to know if they had any issue with their dropout (when used with torque arms).

 

[lepton]

I'm using a rear mounted X5 on an aluminum Specialized FSR XC (aluminum swing arm and drop outs) with a torque arm fabricated from 1/4" steel and bolted to the brake caliper mount on the swing arm. Running at 72 volts for about six months now. No problems yet.

 

[leamcorp]

I'm using a rear mounted X5 on an aluminum Specialized FSR XC (aluminum swing arm and drop outs) with a torque arm fabricated from 1/4" steel and bolted to the brake caliper mount on the swing arm. Running at 72 volts for about six months now. No problems yet.

Cool, that will make my choices easier - now to that hardtail I've been eyeing at my LBS Cheers.