Chunky monkey needs a kit!

[Lardo]

Hi all, sorry to come in with my first post being a request for a build but I've been looking through the site and am still so full of confusion that I might never get round to it unless I get some help!

I'm looking to convert my Mongoose Tyax Super (2009 version) for a specific commute.
It would be a 5 mile ride each way, all tarmac with 259ft ascent and 315ft descent, then the reverse on the way home. It should be noted that the way home will follow a 12 hour minimum shift which leaves me fairly tired and that even fresh I would be pushing a bike up the entirety of the 300ft sustained climb over 2.6 miles of the return leg!

The reason for this outright failure is down to my considerable girth! I'm currently 140kg but really want to do something about it, hence the post here!

Given my weight and the ride details I have given, can anyone help me out with a build please? I am not particularly flush, so the cheaper the better initially, but longer term I may be able to add to it by swapping/upgrading as I go on.

I presume a front hub would be the cheaper option here but would be suitable for this application? I'm happy to consider home made LIPO kits as I've been using them for years on my RC car and am familiar with the safety implications.

It is worth stating that I cannot charge the battery at work, so need something that will do both legs of the commute on a charge.
I'm pretty handy mechanically so would hope I can do the build myself if I get some help with the spec.

Again, apologies for coming straight in with a request, but I have been reading for a while and need to jump in now if possible!

Thanks in advance,
Luke

 

[Deleted member 4366]

This kit with 201 rpm motor. For a battery, you'll need about 8aH of 12S lipos. Top speed will be about 20 mph.

http://www.bmsbattery.com/ebike-kits/347-bafang-350watts500watts-bpm-motor-e-bike-kit.html

Choose the thumb throttle option.

In addition to the kit, you'll need one of their torque arms and a spoke key

For managing your lipos, it's a good idea to get a wattmeter like this, which you'll have to do some modifications to fit it on your handlebars:

http://www.ebay.co.uk/itm/New-GT-Power-RC-130A-LCD-Battery-Balance-Watt-Meter-Power-Analyzer-Ver-2-0-dvz-/201048320816?pt=UK_BOI_Electrical_Test_Measurement_Equipment_ET&hash=item2ecf69eb30

You'll also need a free-wheel gear set, which costs about £8. Normally, I advise the DNP one because it has 11T top gear, but with your weight, a cheapo Shimano one will do with 14T top gear. You can always change it later if it's too slow for the motor.

 

[Alan Quay]

How many gears on the Mongoose? If it's 8 speed (and you want to keep it so) then you might have to go with Bafang CST. D8veh, do those DNP freewheels come in 8 speed?

If your Mongoose has Aluminium forks, then rear wheel drive is the best option. 250w is widely regarded as the limit on ally forks.

 

[Lardo]

Thanks guys, that's really helpful.
The Mongoose has an 8 speed cassette but I'm not really fussed if the replacement means I lose a gear.
I think it is an ally fork but am not 100% sure. Specs are here: http://www.evanscycles.com/products/mongoose/tyax-super-2009-mountain-bike-ec017395#features

 

[Deleted member 4366]

The DNP freewheel comes in 8 spd, but it's a bit wider, which means you need a slightly bigger dish in your wheel to centralise the rim. The CST is a better motor because it can take OP's cassette gears, but it's a higher speed wind, so not so efficient for low-speed climbing.

I've often used a 7 spd free-wheel on an 8 spd bike, nd it works OK.

 

[Lardo]

Low speed climbing is what this build will be about, so the best option for that is what I'd prefer.

 

[Lardo]

Are these the right options as listed above:

http://www.bmsbattery.com/ebike-parts/48-14-28-teeth-shimano-freewheel.html

http://www.bmsbattery.com/36v/450-a-pair-of-ebike-torque-arm.html

 

[Alan Quay]

BPM it is then. I fitted one to a friend's bike a few weeks ago. We bought the 500w version, but only run it at 250w. Works quite nicely like that, but she's about 60kilos soaking wet.

 

[Deleted member 4366]

Are these the right options as listed above:

http://www.bmsbattery.com/ebike-parts/48-14-28-teeth-shimano-freewheel.html

http://www.bmsbattery.com/36v/450-a-pair-of-ebike-torque-arm.html

Yes. Don't forget the spoke key.

 

[RobF]

I'm not sure which wheel you are looking at, but a heavy rider and a rear hub motor is a recipe for spoke problems.

 

[amigafan2003]

I'm not sure which wheel you are looking at, but a heavy rider and a rear hub motor is a recipe for spoke problems.

Nonsense.

A poorly built wheel is a recipe for spoke problems ;-)

 

[RobF]

Nonsense.

A poorly built wheel is a recipe for spoke problems ;-)

Exactly, which is what you get time and time again in a cheap kit.

You also get it in cheap Chinese bikes.

You also get it occasionally in expensive bikes.

A rear hub motor, disc brakes and a heavy rider tortures the spokes.

 

[trex]

you'd be better off with a £350 BBS01 18A 350W
http://wooshbikes.co.uk/?cdkit
It's easy to fit, pulls you uphill with ease and no broken spokes.

 

[Deleted member 4366]

Exactly, which is what you get time and time again in a cheap kit.

You also get it in cheap Chinese bikes.

You also get it occasionally in expensive bikes.

A rear hub motor, disc brakes and a heavy rider tortures the spokes.

The torque on the spokes is the same whether you have a crank or hub motor! The weight of the rider is the same whatever type of motor you have. Therefore, the only true variable is the expertise and knowledge that goes into the building of the wheel.

 

[RobF]

The torque on the spokes is the same whether you have a crank or hub motor! The weight of the rider is the same whatever type of motor you have. Therefore, the only true variable is the expertise and knowledge that goes into the building of the wheel.

That should be true, but doesn't explain why rear hub motors eat spokes.

My guess is the transmission of the torque is a bit different with a crank drive.

It goes via the chain to the cassette, which is attached to the axle, then - through the spokes obviously - to the wheel rim/tyre.

The torque of a hub motor acts directly on the spokes.

 

[trex]

the spokes are much longer on a non motor wheels, much less stress, much less awkward angles at the flange of the motor, more length to flex, less dishing.
Moreover, the shock wave from the motor spindle will have been reduced by the chain and freewheel.

 

[RobF]

the spokes are much longer on a non motor wheels, much less stress, much less awkward angles at the flange of the motor, more length to flex, less dishing.
Moreover, the shock wave from the motor spindle will have been reduced by the chain and freewheel.

Makes sense.

I was thinking about the shunt from the motor which, presumably, is why crank drives are harder on chains and sprockets.

 

[Deleted member 4366]

I think you're all trying to make generalisations out of specific cases. There's so many factors that cause the spokes to break that it's difficult to get a handle on the cause. I've had wheels completely fall apart on non-electric bikes, and I've known particular models of electric bike where there were no problms, then nearly every one had broken spokes, then it went away again as suddenly as it came without anybody changing anything (supposedly). Spoke length has nothing to do with it. I've seen 2-cross break, and then change to 1-cross, which solved the problem.
My own opinion for what it's worth is that the cause is a combination of elbow length compared with flange width and wire condition (hardness, roughness, etc)

 

[trex]

if you have never replaced just one broken spoke on a motor wheel before, prepare yourself for a steep learning curve.
On one post, a guy cut through his motor cable - presumably he's fed up with pulling it out from the controller each time he needs to remove the motor wheel. Recently, I was helping a friend replacing a broken spoke. Sod's law had it that it's got to be one that needed to be threaded from the inside of the wheel and on the freewheel side, so requiring removal of the freewheel and a fair bit of bending to get the spoke into position. Another time, the nipple fell inside the double skin rim, rookie's mistake you'd say. Honestly, replacing broken spokes is a messy job.

 

[Deleted member 4366]

It's the same on any bike. It can be even worse if you have hub-gears.