Converting a Thorn Nomad to a mid drive motor

[arnsider]

Hi,
I have a twenty-one-year-old Thorn Nomad that I would like to convert to an E-bike using a Chinese crank drive unit.
All Nomads were built using Fillet brazed 735 Steel Tubing with a small breather hole drilled in the bottom bracket to ventilate the seat tube.
I've looked at a few conversion contractors web sites and they state that only Alloy frames are suitable to take mid-drive motors.
Can anyone here confirm or clarify this statement?

[rjb]

Having fitted a Tongsheng mid drive to my tandem although an aluminium frame I see no reason why a steel frame wouldn't be suitable.
Search this forum for "Tongsheng". There's several results for fitting this unit to steel frames
Here's one

After a year of reading up on ebike kits I've purchased a Tongsheng tsdz2 with the intention of fitting to my Pino tanden. Although I ride standard tandems regularly it is for fairly short distances without attempting the challenging hills. As my usual Pino tandem partner is neither particularly fir or strong I find that longer trips or those that go in hilly areas leave me pretty tired and sore. Hence the purchase. Initially I have fitted it to my old Claude Butler Dalesman of 1984 vintage. I was an easy fit and is a good match for the 7 speed cluster with its 34 tooth bottom gear. I have so far had just one charge of the 17 amp hour battery through it with some encouraging results. The total mileage according to my satnav is 55 with some serious climbs included. As I live in the Harrogate area there are plenty of hills to go at and one of the many dealt with was the Middle Tongue route up to Greenhow from Pateley Bridge. If it can climb that without problems it can climb anything. The system does not stop me working fairly hard but not to the usual level of sweaty exhaustion. Average speed is increased significantly though the speed limiter does tail off the power just under 16 mph, cycling beyond that is possible but there is a noticeable increase in effort that makes it feel not really worth it. As a torque sensor system, riding seems very natural and gear changing is easy. I think that it should work very well on the Pino with its Sachs 3x7 gears. If there is anything worth posting in the meantime I will.

[Audax67]

Well, steel is an alloy. They were probably thinking of alloy as opposed to carbon.

BTW, I'd research drive train wear before fitting a mid-drive unit. Some of them can put a hell of a strain on the chain and wear through derailleur cogs & cassettes at a hell of a rate. Hub drives are much kinder.

[rjb]

I've had my Tongsheng mid drive for 3000 miles on our tandem. Can't say I've noticed any issues with increased wear. If anything it's the opposite possibly due to less gear changing, reduced cyclic loading on the transmission as the motor carries the cranks over top dead centre. What's the consentsus of those members who have fitted one.

[Audax67]

Bloke I was talking to about it said 1500 km per chain.

[rjb]

Even on the tandem we rotate a pair of chains every 500 miles so that's 1500 miles each with no appreciable wear. (And tandems are notoriously heavy on transmission wear.) We know of another cyclist on a solo who is still on his original chain at over 4000 miles. Chainline may be compromised by the motor offset but with care when fitting can be minimised.

[Bonzo Banana]

Steel would be the ideal frame material for an ebike conversion typically. They are more likely to be overbuilt and its a denser material. It's really down to the frame design though. If its a lightweight frame with butted tubes and thinner sections either steel or aluminium it is more likely to fail. Using something a bit overbuilt is better. Carbon fibre is definitely less than ideal, its a performance material and not typically that overbuilt and its strength is often localised and designed for normal use not homebrew ebikes.

MId-drive should wear out drivetrains faster but its all about the details and how they are used. Changing gear under load on a mid-drive ebike is notorious for wearing down the drivetrain faster. Either a gear change sensor or pulling the brake levers enough to switch off the motor to allow a gear change is best practice. Obviously if you have 3 or 4 times a normal rider going through the drivetrain it will wear faster but when you are in a lower gear to climb hills the chain is over the largest rear sprocket which holds the chain more securely. It's the high gears at the back (smallest cogs) that are more likely to be worn faster if you try to use those gears and operate the motor at the same time. Ultimately you can reduce drivetrain wear with good practice but its never going to be as good as a hub motor which massively reduces drivetrain wear and can extend drivetrain life up to 4x over a conventional bike.

[rjb]

The Tongsheng has a torque sensor system so easing off on the pedals as you change gear also reduces the motor output, thus minimising transmission wear. Experienced cyclists know that it's wise to back off a fraction as you change gear. Who amongst us changes gear under full power.

[bikes4two]

• You can get a load of bo**ox talked about chain wear - I had a TSDZ2 250w on a Dawes Galaxy and I changed the chain at 4,500Km as my wear gauge indicated it'd just started to 'stretch' a bit. (and I'm rather sloppy about chain cleaning, lubing etc)

• I get good chain life because I ride my TSDZ2 mainly in ECO mode

• However, if Sir Chris Hoy were ridding my bike with a 750w motor in it, then I guess the chain (and everything else) wouldn't last as long.

• Put it another way, if you're fitting a mid drive motor to get you back to riding, power-wise, the way you used to, then drive train wear will be no different to the way it used to be.

• If however you're ploughing up 1 in 4 hills at max assist, then don't expect miracles from your drive train.

[Cowsham]

Rear hub every time when Retro fitting -- mid drive OK when it's built into the frame but there's problems when parts become obsolete or unavailable. With rear hub the drive is smooth and parts easy to get/change.

Also the mid drive Retro fitted spoils the whole look of the bike.

[the snail]

Rear hub every time when Retro fitting -- mid drive OK when it's built into the frame but there's problems when parts become obsolete or unavailable. With rear hub the drive is smooth and parts easy to get/change.

Also the mid drive Retro fitted spoils the whole look of the bike.

Not true. The bafang and ts drives are pretty neat, don't spoil the look of the bike imo, and spares are readily available.

[PH]

I think your Nomad will make an ideal candidate for a conversion, they're built tough so there'll be no issues strength strength or flex. I don't recognise the Reynolds number, is it 725? Whatever it is, they'll have chosen beefier tubing to suit it's heavy duty purpose.
I've never owned a hub motor E-bike, the couple I test rode didn't have the same natural feel as all the mid motor ones I tried, so I went with that, admittedly I didn't try all possible variations. What I'd heard about drive wear was a concern, it gets repeated so often you come to assume it has to be true. Mine is lasting as long as I'd expect on a non assisted bike with the same use and maintenance or lack of.

[arnsider]

Wow! Many thanks to all for such a response. I do own a Whyte Coniston E-bike and I'm very pleased with it.
It's three years old and has done seven thousand miles without motor or battery problems, but it won't last forever.
It is a punt, but I'm sure the right configuration is out there for my Nomad.
A few of the guys I ride with have rear-drive Orbeas and they all like them. Would a top-end rear hub be a better bet?

[Audax67]

I'm a hub-drive user but I've never ridden a mid-drive bike so I'm biased. Mine's great but (a) I had to squeeze a 135mm axle into 130mm dropouts, which ain't healthy. And (b), I suppose, mid-drive motors can use torque sensors to control the amount of extra oomph they give you, whereas hub motors (mine at least) can only tell whether you're pedalling or not.

Re drive-train wear, this puts a reason to it: https://youtu.be/IWsJFKzOOmA Basically, if you're an experienced rider you should be fine: it's beginners who ride in sack-of-spuds mode that do in their drive trains. Je me coucherai mois con.

[stodd]

I suppose, mid-drive motors can use torque sensors to control the amount of extra oomph they give you, whereas hub motors (mine at least) can only tell whether you're pedalling or not.

It is commonest for mid-drive motors to use torque sensing and for hub motors to use some form of cadence sensing, but there are quite a few exceptions in both directions.

There's a huge range of quality with cadence sensing systems; mainly differences within the controller. Very few use the cadence other than an on/off 'are you pedalling' switch. Avoid pure speed controllers that give full power up to selected speed; Controllers where the setting controls current and max assisted speed are the best cadence sensing systems.