Hello, Very heavy rider pondering.....

Matt Jones

Finding my (electric) wheels
Oct 13, 2013
20
2
A, A
Hi, I signed up the this site while back, every now and then I flirt with getting an ebike, but then I talk my way out of it.
Now, I suspect I am a little different from your average overweight rider, and while I am very 'overweight' (23 stone/ 146 kilos ) I am far from a dead weight. I trained for Strongman for while and am very gym focused. I squat 280kg and deadlift 320kg, so I have some pretty powerful legs. (I don't know? maybe that makes me more of a typical overweight rider?) I have ridden Bikes all my life, I commute an 8 mile round trip daily, and at weekends will do trips of 12-20 miles for 'relaxation' while powering up hills takes it out of me a bit these days (46 years old) It is by no means a problem.

The idea of eBikes has always interested me from a tech perspective, but each time I think about it I talk myself out of the idea, as I seem to obliterate, or even destroy the Safe working loads of the ones I see advertised, and I worry about burning motors out.

The other half of me thinks, its not like I'll be sitting on the damn thing expecting the motor to do all the work, Surely +250w is +250w however you cut it? and considering I blitz past much lighter riders on my 29er mountain bike now, then there is not going to be a huge (or increased) strain on the motor all the while I am doing the largest part of the work myself?

As for other aspects of increased wear, I have been riding quality bikes for decades, (Giant, Cannondale, GT, Kona etc) and the only thing that wears fast is Bottom Brackets and Pedals, On two occasions I've pinged a couple of spokes on the rear wheel, but in decades of cycling twice is nothing really is it?, although I do worry that perhaps adding a potential 250w to whatever I currently generate might be a bit torque-ey for a rear wheel?

What is the consensus for us heavier guys?
 
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Woosh

Trade Member
May 19, 2012
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Hello Matt,

Your weight is not a problem, your strength is, as you said, you can destroy the bike.

How tall are you Matt?
 
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Matt Jones

Finding my (electric) wheels
Oct 13, 2013
20
2
A, A
Hi Woosh,

I am 5'11.

When you say the strength would be the problem, would that be in the same way as it would a conventional bike, or would there be new things to consider regarding the motor?
 

Woosh

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May 19, 2012
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the weak point in most e-bikes is the crankset in your case.
Most e-bikes are built for assist riding, that is the rider puts in less energy than the motor. Your case is different, imagine you put 320kg force onto your pedal, the ordinary M8 allen crank bolts are not going to hold. Your legs would ovalize the BB spindle in no time. You need a Hollowtech or GXP crankset and good pedals to take your strength. Furthermore, you can put in a lot of torsional bend to the bottom bracket shell and the frame, so a frame with strong tubes is advisable.
That rules out practically all the Chinese bikes with one exception, the Woosh Rio MTB.

http://wooshbikes.co.uk/?rio-mtb
 
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D8ve

Esteemed Pedelecer
Jan 30, 2013
2,142
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Ignore the 250 watt number. It's a manufacturing rated limit.
To sell bikes they rate more powerful motors as 250 watt but have peak powers that can hit 750 watts. But that would drain the battery in 40 mins. The 15 mph limit is also interesting some bikes will do 18 mph?
 
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Artstu

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Aug 2, 2009
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I'm not so sure the bottom bracket is a major weakness, track sprinters put out some serious power. I'm not sure if they need anything special to cope.


It'll be the axles on any hub motor that will be the weak link I imagine due to the weight load.
 
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Woosh

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May 19, 2012
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It'll be the axles on any hub motor that will be the weak link I imagine due to the weight load.
the axle of the hub motors on the Rios is supported by 4 ball bearings arstu.

(2 x 61805-2RS and 2 x 61904-2RS)

This is one of the 61904-2RS



On CD bikes, the axles of the wheel hubs are supported by only two ball bearings and they are usually smaller in size than those fitted in hub motors. They are not as long lasting.

Here is one:

 
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Artstu

Esteemed Pedelecer
Aug 2, 2009
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It's my understanding that it is the gap from the bearing to frame on the freewheel design is the weakness and where they bend.
Perhaps I'm not up to date and that issue has been resolved with newer cassette type axles with bearings much further outboard?
 

Woosh

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May 19, 2012
20,379
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the two 61805s are on the outside, the 61904s are on the inside. They are longer lasting. When they need replacing, we replace Chinese bearings with French ones...
 
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It's my understanding that it is the gap from the bearing to frame on the freewheel design is the weakness and where they bend.
Perhaps I'm not up to date and that issue has been resolved with newer cassette type axles with bearings much further outboard?
That wasn't a problem for the axle, which is many times stronger on a hub-motor than a conventional one (not counting the latest through axles). instead, it was a problem for the motor. There was such a long unsupported part of the gear-set that it gave a constant bending force to the threaded boss when you used top gear, which eventually snapped off the boss; however, the motors that suffered that (mainly BPM in the UK, MACs and some DDs in USA) were modified to strengthen the boss. I haven't heard of that happening for years.

I think OP could get what he wants by buying a cheapish steel-framed bike and adding a rear Bafang BPM kit with a very low winding speed - no more than 201 rpm. 48v is probably better than 36v. Strictly speaking, it's not legal, but there shouldn't be a problem if you limit it to 15 mph. A 201 rpm one will only do 15 mph anyway. If OP wants legal, a 250w BPM would be OK, but you still need a low winding speed. At 36v and 20A it'll give strong torque and would be pretty robust.