• Howdy! we're looking for donations to finish custom knowledgebase software for this forum. Please see our Funding drive thread

Hill Climbing eBike

Jan 3, 2022
Front View.jpg

Rear View.jpg

This is just to get the thread started.

I had a mountain bike with a cracked rear swingarm.

So my goal is to build a Hill Climbing eBike because in the place I live there are plowed fire roads which are so steep in some places you can barely climb them on foot much less the regular eBike designed for flat conditions.

Lot's of work was done grinding down the rear hub to make it lighter weight.

I'll be using another of the motors like the one I recently rewound.

My hope is something like 10" of good rear wheel suspension.

You can see a battery which was also featured in a different thread about MBM "Manual Battery Management".
Wondering if you went out far enough on the length of the back swingarm.

I have yet to find a hill this thing wants to pop up the front wheel on. I have a 36t chainring on the front now (its a 48T in the pic) but haven't had the time to try it out going straight up a downhill trail. With a 42T cog on the back it should make it. These days I use it exclusively in the Lower Sierras, so nothing but overland; steep hills, often all granite no soil.

MoneyPit said:
Wondering if you went out far enough on the length of the back swingarm.

The swingarm is still as yet "undefined" as far as length.

I forget the exact numbers but the stock swingarm was roughly 15" and I'm looking at the new one being 30" or near that.

But it really could be longer or shorter up to the limit of the amount of square tube I have to weld.

Overall wheelbase should be around 52" - 56" which is a foot longer than most bicycles.

Also... the motor will be direct drive through a #219 chain and sprocket going from 10 tooth to 94 tooth so it will be a fixed ratio.

Your multiple gear ratio would be helpful for when you go faster but this is entirely focused on a specific insanely steep section of fire road that connects an entire ridgeline. Once I can cross that obstacle the entire rim of a long ridge becomes all mine.

And the views are hundred million dollar views.... inflation you know.

People used to say "million dollar views".

Lot's of grinding done on the hub as well as the aluminum rim to take off at least a pound of weight.

Normally there is a heavy steel axle but I bought a raw hollow aluminum tube and threaded them from the ends so that's another pound saved.

And even the spacers are aluminum.

It weighs a little more than a standard bicycle wheel but is not too bad.

Compared to a 15 lb hub motor it's much lighter.

The motor is only about two to three pounds and will produce at least two horsepower at peak which will be somewhere around 18 mph.
My problem with this is that it is too nice a bike.

My ( horridly overweight, cant-climb-uphills-so-they-say) 15lb hub motor.... goes so hard.... up big hills.. I get far up them.. then.. crash and the bike tumbles down 40-50 feet and smashes all its nice bits.. to even smaller... bits.

Tumbling end over end. You get the idea.

Its a significant problem when climbing hills. Smashed bits at the bottom. Traction being what it is.. and how it is affected by angles.

Gravity only half works on a 45* angle. I'm saying. This is where the (weight) distribution comes in to play, I think. You cannot lose that traction, and if you do, you spin and stop the forward speed vector velocity. Tumbling (usually) ensues.

Be sure to get some good crash bars, bash guards, and lever-protectors. Fork bumpstops. I do wanna see how far, and how hard, this bike can go. Lol. I like purpose built bikes. They are great. GL w the project. Bike is really cool . Why such a small diameter rear wheel? That sure is some driven sprocket. Lol.

I look forward to the project.
DogDipstick said:
My problem with this is that it is too nice a bike.

It's actually going to be pretty light weight so my "hope" is to crash softly.

The goal is very simple... be able to get up one choke point to open up a big area to ride in.

Most of the fire road is more level but it's still steep.

And the main bike is actually very old.

This is my "junk parts" ebike. (use up a lot of old stuff)

The battery is made with two wheelchair battery packs blended together from my mother's wheelchair that broke.
SafeDiscDancing said:
DogDipstick said:
My problem with this is that it is too nice a bike.

It's actually going to be pretty light weight so my "hope" is to crash softly.

Excellent thinking.
Motor Apart.jpg

So these motors have a sleeve that is aluminum that conducts heat very effectively to the outside for cooling.

You can magnify the cooling capacity with more aluminum.

Motor Together.jpg

That sprocket was ground down very carefully when starting with a #35 chain spacing.

Take a #35 sprocket and grind it down into a #219 sprocket.

Cheap Chinese base part at about $4.

Sometimes I just build stuff for the heck of it.

I needed to extend my disc brake from 180mm to 203mm so I just went ahead and did it.

Could I have bought that? Sure.

Some days I like little projects that get done in a few hours and not go on for months.

So this is the intended general shape of the swingarm.


The bottom bracket shell metal was cannibalized from an old frame and cut in half.

The bottom bracket cartridge is for a fat bike.

Somehow it will magically turn out perfect and look like it was all done on purpose in the end.

At least that's how it usually works.
Spring Fever

I know that when you start a thread like this the expectation is that it's like a sort of ongoing series with enough "action" to keep it interesting.

But my village is doing a bizarre "fake lockdown" (a long story) which has dulled my buzz on ebikes for the moment.

The weather is fantastic though and I spent today hiking and it's like a ghost town now so really weird.

Like one of those Science Fiction movies where everyone dies and you are the last person on earth.

Anyway... I do plan to get onto this and normally this time of year is our heaviest rainy season which is optimal for hobby efforts but this time it's sunny, dry and warm.

And if we don't get rain soon it's looking like another drought.

Got the welding bottles filled up.

Was a bit shocked at prices now... 87 cu/ft oxygen and 75 cu/ft acetylene.. four sparking flints... two pounds of welding rod came to:

:( $168

Yikes !!!

But the guy at the supply store asked:

"So when was the last time you filled up?"

...and I realized it was a decade ago. Plus, in California everything is expensive so it's pretty much the inflated world we are into now.

Did a practice weld and it's amazing how quickly the skill returns.


On my local "fake lockdown" situation the local newspaper is starting to run stories about how everyone hates this idea and that it was a mistake so the tide is turning.

I even tried a ride on my primary ebike today but it's a little premature because the "rogue committee" meets today to decide to end it or double down. Was getting hostile looks from the Karens.

My "guess" is it ends officially as was first suggested on Jan 31.
99t4 said:
Like your earthquake strap (lol).

Well it is California and I live on an older less active fault line. The reason I'm building this for Hill Climbing is because the hills came into existence because of earthquakes.

But I have in the past accidentally nearly tipped them over when welding.

The valves are delicate and if they smacked the cement it would certainly break them and if I was welding at the time you can imagine a very nasty situation.

Two screws and some wire... took me five minutes.
SafeDiscDancing said:
Two screws and some wire... took me five minutes.
Welll, OK. In the photo it looks like fuzzy yarn.
First Weld

Freewheel 1.jpg

The threaded part was from an old steel hub I chopped up.

Freewheel 2.jpg

And it bolts to the hub.

Freewheel 3.jpg

I'd like to countersink those bolts but that will come later.

After the weld I did a little cleanup so a little grinding on the inside and sanding.
How long have you been welding, how many welds have you done in the past?
Was that the wire feed mig, you had bottles of gas and I dont think tig uses gas, I know arc stick welding doesnt.
Mig seems like more of a learning curve, what speed to put the line feed at, what wire, what diameter of wire but theres tons of resources out there.

To me I know that bead isnt perfect but I do not know if its bad, for non critical and hobbyist welding beads I think yours would hold up.
calab said:
How long have you been welding, how many welds have you done in the past?
To me I know that bead isnt perfect but I do not know if its bad, for non critical and hobbyist welding beads I think yours would hold up.

I'm 60 years old. I have been hobby welding since I was 16.

At times I can go a decade between welds, but it comes back quickly.
I dont see much of it I just envisioned the pedal and a long stick because I never see them with the big bottles because they are off camera, while the mig machine is right next to them. All of it is such a skill but more with tig.

Voltron said:
Tig does use gas.
Hence the acronym, Tungsten Inert Gas.
Twin Towers.jpg

The chain stays.

Those holes will hold the aluminum axle.

Structurally I probably could have left the end open, but I used some thin metal so very little added weight.

In those holes there is a metal tube that matches the axle size.

The idea is to permit the axle to be tightened without crimping the square tube.
calab said:
I doubt the extra weight would really hinder anything man

I'm being VERY weight conscious on this build. Every place I can I'm switching to aluminum or going to smaller sized bolts and adding sleeves to get it to fit.

The shock absorber has about a half inch mounting hole and there is no way I'm going to jam a big bolt in there that weighs half a pound when I can do it for maybe a tenth of a pound. Every pound counts.

If a part breaks I can upgrade.

The core philosophy is to create a Hill Climbing ebike that weighs about the same as other light weight ebikes.

But... I just didn't want an open square tube in the back.

And so far I've been very impressed with how light weight it is.

The biggest weight is the rear tire itself which is maybe four to five pounds.

Also the motor is only two pounds and produces two horsepower so that's pretty good too.

Battery is light at about ten pounds. (300 wh)

The square tube is 1/16" thickness so not that bad as far as weight.

Total weight of the bike? Hmmm... 50 lbs? 60 lbs?
To cap off the end the extra grams of an extra 1/8" won't harm nuffin' but better to cap it off then leave it open :thumb:
Morning End Caps.jpg

This shows why I had to cap the ends.

There is such a thing as style and beauty and I'm not going to do ugly just to save that last ounce.

We all have our limits to idealism.

Also... I'm thinking I can narrow this a bit. Those axle spacers could be reduced by at least 1/4" on each side. Clearance is nice, but that's just excessive. Maybe even closer to 1/2".