Author Topic: Motorising a Dahon Glide and fork modification.  (Read 777 times)

Motorising a Dahon Glide and fork modification.
« on: November 04, 2020, 05:28:51 pm »
As mentioned in the Grumble thread I'm looking at fitting an electric motor to my Dahon Glide to make my commute a little quicker and/or easier. I'm trying to take the quiet early train into work and cycle home to avoid the busier afternoon trains at the moment. Which is okay for now as I'm luckily only in the office two/three days a week but once that ramps up I'm not going to find the 27 mile ony-way trip sustainable.

Whilst the Dahon isn't the best bike for that sort of distance I can keep it behind my office door and not trust it to the easily accessible bike sheds.

I was happily looking at front wheel kits when I learnt that the Dahon has a narrow 74mm oln front fork and the majority of kits are for a conventional 100mm fork. But a folding bike kit with a narrow hub won't work as they are geared for 16-20" wheels and I'm running on 24". Simply re-rimming out to 24" is a bad idea or so I'm told. Unfortunately, a middrive kit won't work either due to the frame geometry around the bottom bracket.

Whilst searching around I did find aftermarket Dahon forks built to 100mm but of course they only seem to exist for their 20" models and not the 24".

So the current (ha!) plan is to get a fork that will take a 100mm hub and I've a few possible ways I could go about it that I'd like some advice with please. However I go about it I don't want a front end that'll collapse under me!:
  • I was thinking I could get the steel version of my current fork and cold set it wider. I've read of this being done on road bikes but usually only from 90/95 mm out to 100. Would going up from 74 to 100mm be too far? It feels too far. (As an aside I actually checked earlier and turns out I actually have a steel fork and not alloy like wot the Dahon site says.)
  • I've read of someone using a Tern fork and handlebar post on a Dahon bike, albeit a smaller wheeled model. Blogspot Link
    • I have found a Tern bike model that takes 24" wheels and a 100mm hub but the one place I've found the fork won't ship to the UK. And I think I'd need to buy the Tern handlepost to go with as well which is more expense.
    • The other route to go is getting a 24" fork and making it fit the Dahon headset arrangment - I've found a Schwinn childs fork new on eBay for £15. I guess my first question is is a childs fork going to be strong enough? I know kids are lighter and strain forks less but surely they're built to take some punishment? The Dahon forks have an internal thread with a copper washer and large bolt to preload the headset bearing with the base of the handlebar post clamping round the steerer like a conventional ahead stem. I've got two options here, either way I'll need to cut the steerer tube down but that's not too painful.
      • I need to double check my measurements (there are four different sizes of headset bolt out there) but I could get a tap and cut an internal thread in the Schwinn fork. I think I’m looking at a 1”x26tpi – does a normal fork have enough meat to do this?
      • The Tern fork uses a standard topcap and starnut to preload its headset, I’ve had a look and I can fit a topcap in and still close the handlebar hinge on my post provided I omit the washer. Would a starnut provide enough hold? I’m sure I’ve read that a standard ahead stem, once the stem is clamped up, can have the topcap removed entirely – my workmate seemed to think that the bolt on the Dahon helps to hold the fork in but it looks to me like it’s acting like a very odd shaped ahead stem. The only difference being that the length of steerer it clamps to is only about 15-20mm with a single pinch bolt. The Tern arrangement on the other hand is a longer section of steerer and a double pinchbolt. If I could get away with using a starnut though it saves a whole step of thread cutting and it’s one less tool to buy.

A few photos of the headset arrangement to show what I'm on about:

I know converting this bike is a bit of a compromise but I got the bike for free, if I bought an electic bike I'd have to go through the faff of selling this one. The cheaper new folding bikes tend to be limited on range and pretty much all have derailleur gears, this has an internal geared hub and a partial chaincase which should help protect it from the winter skog. They also tend to have smaller wheels and having borrowed a Brompton for a week I definitely feel like larger wheels roll better and some of my route isn't wonderfully surfaced.

I mean in an ideal world I'd just go out and get a Tern Vektron but it's £3500 and I think I can do this for <£600 all up.

ETA: For what it's worth the plan is to mount the frame frame battery to the headtube luggage mount sticking out the front there in the first photo. I figure that keeps more of the wiring confined to the front end and away from the hinge fold and it should balance the weight of the rear hub and luggage at the back. I tend to lift the bike unfolded for the stairs down from the train station as it's actually easier to carry that way than it is in its folded state.

Miles cycled 2014 = 3551.5 (Target 7300 :()
Miles cycled 2013 = 6141.4
Miles cycled 2012 = 4038.1

Re: Motorising a Dahon Glide and fork modification.
« Reply #1 on: November 05, 2020, 04:41:59 am »
That look like  a good free bike! From experience of riding a very similar Dahon fork loading won't be high but handlebar is. Looks a bit awkward as how to reproduce  headset bearing and handlebar clamp. That internal thread the aluminium 'plug' screws into won't be easy. I agree it seems to both preload the bearings and provide security for stem and handlebars. Maybe change the bar fold to simplify design?  All modifications would of course be at your own risk so don't bodge. Correct fork rake and caster will be critical to handling/stability. It's going to take proper engineering. How about looking for a 700c fork with a wide crown - say off a touring bike and shortening the blades? If you can find 531 or similar alloy fork then the rake can be reset. Although by the time you have shortened then they will be rather stiff. You may be able to find a frame builder who is interested and not to busy.. can you take the fork apart and find out what the bearings and tube diameters are? A pair of cheap Vernier callipers and an engineers steel rule to produce a drawing would be a good start.
The other point I would make is I often lift the front wheel on my Dahon when starting off so you may have FWD traction problems, but your planned battery location will help with this.

Re: Motorising a Dahon Glide and fork modification.
« Reply #2 on: November 05, 2020, 10:21:37 am »
The plug is steel for what it's worth. And if a starnut won't be enough security then the plan was to get a thread cutting tap and thread the steerer on the new fork, provided the wall is thick enough.

If those child forks will be sufficient I can get them for a tenner at the moment. And they're already the right length and have the brake bosses in the right place. From the photos the curve of them looks fairly similar.
Miles cycled 2014 = 3551.5 (Target 7300 :()
Miles cycled 2013 = 6141.4
Miles cycled 2012 = 4038.1

Re: Motorising a Dahon Glide and fork modification.
« Reply #3 on: November 06, 2020, 12:56:09 am »
I think you will be ok with the £10 forks, give them your considered opinion in any case steel fails gracefully. Even if if it exists a suitable tap to cut the thread will be expensive and require a heavy workshop vice to use it. Threads like that (usually external) can be cut on a lathe, I think you do need more than a standard aheadset cap to hold on your handlebars. If you ride like me there is quite a bit of pull and pushing. I remember a post on YACF showing a broken Dahon at the point of interest. The headset bearings are unlikely to 'just fit' the replacement fork. I expect it will be too small, so bushes will have to be turned up. A thread less plug turned up with the fork internally reamed to ensure a good sliding fit. shim underneath plug with washers cut from drinks cans  to get the bearing pre-load correct. Hope make an expanding plug that would give you a flat surface to shim against, or just use expoxy and a washer over a standard star-fangled variety, fitting that may damage any reamed surface. Paying pros is going to be expensive think you need to befriend a hobby engineer. There are a few on YACF.

Re: Motorising a Dahon Glide and fork modification.
« Reply #4 on: November 06, 2020, 01:17:18 pm »
You should be able to do it for less than £600.  Main cost is the battery.

How hilly is the route you are going to be riding on it? 
How much effort are you planning to put in?

Reason I ask is that a motor for a 20" wheel would work absolutely fine in a 24" wheel.  Only thing is it would provide assistance to a bit over the 15.5mph limit, maybe to 17 or 18mph, and it would be lacking a bit of torque for big climbs if the rider was not putting much effort in.  However, for most use it would be absolutely fine, and it would save you loads of unnecessary buggering around with forks.

One of the leading ebikes of around 15 years ago was the Ezee Torq.  It had a motor for a 20" wheel in a 700c wheel.  It could give assistance up to 25mph but wasn't a great climber.  What you would be doing would be a much less radical version of that.