Steel or aluminium frame to fit hub motor

[Wayners]

There are two bikes in my area going for under £100 suitable for fitting hub motor.
One aluminium frame and another older bike with steel a frame.
I'm unsure about aluminium? I read steel is always better..
Thoughts?

 

[sjpt]

Cheap steel is never very good; heavy and harsh. Quality steel (eg 531 etc or even good Cro_moly) is good. Aluminium can be harsh; the main downside is that you need to be very careful fitting a front hub motor to aluminium forks. Many aluminium frames come with steel forks.

 

[Wayners]

Hi. Thanks for replying.

They are both specialised branded bikes and I want to fit a rear hub.
The aluminium bike has v brakes but will take disc front and back.

The steel bike is over 20 years old but has disc mount on fork only.
I'm thinking that will be best option?

 

[Woosh]

Do you have pictures? The shape of the frame is important too.

 

[saneagle]

Hi. Thanks for replying.

They are both specialised branded bikes and I want to fit a rear hub.
The aluminium bike has v brakes but will take disc front and back.

The steel bike is over 20 years old but has disc mount on fork only.
I'm thinking that will be best option?

I'd say go for whichever one gives disc brakes front and rear. You need enough space for the battery. Don't get anything with horizontal drop-outs. The rest isn't much difference.

 

[Bonzo Banana]

Cheap steel is never very good; heavy and harsh. Quality steel (eg 531 etc or even good Cro_moly) is good. Aluminium can be harsh; the main downside is that you need to be very careful fitting a front hub motor to aluminium forks. Many aluminium frames come with steel forks.

I personally feel high tensile steel frames and forks are the right choice for many ebike conversions. The issue with chromoly steel is its often butted and heat treated and rusts just as fast as high tensile steel so the thin butted sections can be compromised by corrosion. Chromoly frames were the only performance option before aluminium and carbon fibre frames and then became more of a niche in the market place. Fuji-ta the biggest bike manufacturer in the world by volume I don't think even bothers with chromoly anymore, they robot weld higher quality high tensile steel and phosphate dip it afterwards. They have a ridiculously low failure rate of something like 0.2% far lower than other materials and I'm assuming that is within the factory and reported faults from importers who use that factory. No reason for high tensile to be harsh at all although can be. Before road bikes had carbon fibre forks it was common for forks to be high tensile steel for comfort with a nice springy feeling. The Brompton uses a mixture of steel types in its frame construction which it can do becaused of its brazzed construction and I believe it is the high tensile tubes that provide most of the comfort flexing i.e. the main downtube. I totally accept high tensile steel bike frames can be heavy but I don't accept the harshness criticism. I've ridden cheap high tensile steel bikes and they are fantastic in comfort terms compared to almost all aluminium frame bikes. I have a GT Timberline with a chromoly frame and that is super heavy and harsh and I think they designed it that way for sheer durability for off-road use.

Also there are a huge variety of high tensile steels used in bike frame production, off the top of my head there are; 1010,1020,1040,1060 and various others I'm sure. Fuji-ta I think uses a high tensile steel that is 1040 or 1060 which is lighter and stronger than many of the entry level less advanced chromoly tubes.

The issue is if you are choosing an old bike for an ebike project its more likely a lightweight chromoly frame will be compromised with fatigue or corrosion.

Halfords sends 10s of thousands of bikes to Africa as their main bike charity and pretty much all the bikes they send are high tensile steel due to its great lifespan and durability. People there expect bikes to last decades really and they get huge abuse. I personally think weight is less of an issue when your bike has a motor. Also the Buffalo bike that is popular in Africa is high tensile steel. It doesn't make sense to me when adding a motor to a bike which adds weight and extra stresses to the bike to fit it to a weaker lighter performance frame that is perhaps end of life.

 

[saneagle]

Steel goes rusty in wet UK weather. Aluminium doesn't. Steel is stronger for the motor, but aluminium is strong enough for any rear 250w motor. A torque arm should be fitted for any power more.

Aluminium can crack with age due to fatigue. Steel doesn't.

Cheap steel frames are fine. Aluminium frames are actually stiffer than steel, so should give a slightly harsher ride, but I never noticed any difference when riding, and I've used both types many times.

As I already said, the other factors are more important than the frame material. Frame failures of any type are extremely rare, so that's not really a consideration.

 

[Wayners]

Update

I bought the specialised hardrock second hand. So aluminium frame.
Thinking about which kit to put on now.

Rear hub or I'm interested in a centre drive. Just for the interest and to see how it fits and rides, but will probably get rear hub.
I'll sleep on it

I'm surprised how light it is Vs my steel frame bike. Real easy to get in the car. Well happy with it for under £100

 

[saneagle]

Update

I bought the specialised hardrock second hand. So aluminium frame.
Thinking about which kit to put on now.

Rear hub or I'm interested in a centre drive. Just for the interest and to see how it fits and rides, but will probably get rear hub.
I'll sleep on it

I'm surprised how light it is Vs my steel frame bike. Real easy to get in the car. Well happy with it for under £100

Mid motor only mnakes sense for off-road riding. For everything else rear hub-motor gives a better ride, it's cheaper and more reliable.

 

[Woosh]

you should try both hub and crank motors if you have the opportunity. Crank motors are a little bit more expensive but give you better weight distribution and torque control.

 

[Bikes4two]

Mid motor only mnakes sense for off-road riding.

I've only ever ridden a rear hub for a short time so no real experience of one, so I'd be interested to hear why you think mid drive 'makes sense' for off-road riding especially as so many leisure ebikes come with mid drive units,

For everything else rear hub-motor gives a better ride,

Aren't all hub motors cadence sensing which from my limited experience doesn't give the more 'natural' assist that torque sensing motors give.

 

[saneagle]

I've only ever ridden a rear hub for a short time so no real experience of one, so I'd be interested to hear why you think mid drive 'makes sense' for off-road riding especially as so many leisure ebikes come with mid drive units,Aren't all hub motors cadence sensing which from my limited experience doesn't give the more 'natural' assist that torque sensing motors give.

With a mid motor, you can have lighter wheels so suspension works better. The central mass gives better handling. Also, you can get higher torque and lower speed. Those attributes give you an advantage when doing serious off-road riding. It's a slight advantage for normal riding on the road compared with a hub-motor, but then you have to consider the disadvantages.

With a mid motor, you have to be in the right gear all the time because it will rev out in the lower gears, which makes riding more frantic and less relaxing compared with a hub-motor that doesn't care what gear you're in, nor when you change gear. The mid motor's high torque in the low gears makes the ride jerky, and if you have to do a quick stop when in a high gear and don't get time to change down, it's difficult to get started again and it can damage your gears and chain.

The hub-motor just gives constant torque to help you pedal. It's a more comfortable ride. You can start in any gear and you can pedal as hard or easy as you choose. In the old days with crappy batteries and 36v, hill climbing was a problem, but now with 48v and higher power batteries, anybody can get the torque they need for their worst hills.

To summarise, for my rides, which are touring, commuting, shopping and generally riding around, I find hub-motors more relaxing. That's not less effort to pedal. It's not beeing lazy. It's just a smoother ride and less to do except pedalling. That's quite important too for winter commuting when you have cold hands. Weight distribution isn't important for shopping or riding on roads. Regardless of anything else, I'd always choose a hub-motor for that type of riding, because it gives a better ride, but then you add the other advantages of lower cost, lower maintenance, better reliability, lower running costs, ability to bail you out if you have a chain or gears problem and less noise, the mid motor is left a long way behind.

 

[saneagle]

Aren't all hub motors cadence sensing which from my limited experience doesn't give the more 'natural' assist that torque sensing motors give.

The type of pedal sensor isn't restricted to the type of motor. You can have a torque sensor with whatever motor you want, or you can have a cadence sensor. People choose cadence sensors because they're cheap and simple. I always say that if you want a bike that feels natural, get a natural bike. You wanted an electric bike for a reason. Why would you want to get power in the worst possible way, when you can choose how much power you want whenever you want?

 

[Bikes4two]

Thanks for your lengthy reply @saneagle as it's always good to hear opposing views and I have to say that the way you described the ride from a mid drive are opposite to my observations entirely.

As an unassisted rider of many decades I find the torque sensing system of the TSDZ2 mid drive ride as near identical in it's 'ride 'n' feel' characteristics to that of my unassisted days but with of course the proportional (to my own efforts) power uplift that others have described as having bionic legs.

But hey, that's why some folk like marmite and others don't

Best wishes, B4t