Dogmans Featherweight ( yeah right) trail bike

[dogman dan]

Well, the battery is featherweight anyway. This time I wanted a motorized trail bike that I would actually pedal. Most rides will be quite slow, at the 5 mph speed my St Bernard runs. 2-3 miles long, so no need to lug a lot of battery or have a lot of watts.

Based on the Giant DS3 Full Suspension mountain bike I rode to work for 3 years. I no longer work, so time for the bike to become more fun. The bike is about 30 pounds, the motor 15, and the battery 3 pounds. So at sub 50 pounds ( try 71 pounds ), it's light compared to when it was a commuter.

The motor is the well broken in 9 continent 2812 motor I have been riding dirt with for years. It's the crazy slow winding model. Controller is a generic 9 fet 48v 20 amps typical in many motor kits. This one happened to come from E-BikeKit.com . The battery is Hobby King RC lipo. Two 6s 5 ah and one 2s 5 ah packs. Series connected for 14s, or "48v" 5ah. The battery weighs only 4 pounds. 8) Charges to 57.5v with my old 5 amps pingbattery charger. Occasionally I will balance charge with an RC charger.View attachment 4

Since the battery is so light, I didn't hesitate to take the easy way out, a simple seatpost rack. BTW, the seatpost is reinforced, with a smaller seatpost pounded up into the fat one. So carrying just 4 pounds, it should not need any extra bracing.

For now, and because most rides will take only about 2 ah of a 5 ah total capacity, I monitor the battery with a simple and cheap wattmeter mounted to the top of the battery box.

Other features different from the commuter version are a very nice fat rear tire. I ride through lots of deep sand in the dog running spot. I have a trail I follow, but the sand just blows in and fills the packed track. The fat 2.7 inch tire floats nice. 2.3 inch tire on the front. I've been wanting to use this tire for some time, but it was too fat to fit on the mongoose blackcomb dirt bike.

Nicest of all, I've been hoarding this virtually brand new marzocchi bomber fork for a year or so. Time to enjoy it. Boy howdy, a good fork on a FS bike makes all the difference.

The bike now has a top speed of about 18-19 mph, and beautiful throttle resolution at lower speeds. You can select 3 mph, or 3.5 mph, instead of having no choice under 5-8 mph. It's perfect for dawdling along with the dog, enjoying the sunrise over the Organ mountains east of my house.

All together I'm quite pleased with how it turned out. I really like not having a battery box crowding my knees, and carrying just 4 pounds of battery, I really cannot tell I'm carrying it "wrong". For a longer ride, I may tuck a second battery someplace, possibly even just in the back pocket of a riding jersey. Or maybe a small box on the handlebars. I have some slim 3s hardcase packs coming soon, so those could even tape to the frame in a pinch. ( I always say don't do that, but that's with the naked lipo)

I took about as long a dirt ride as I am physically able to nowdays this afternoon, and only used 3.5 ah to go about 6 miles. So I really won't need more than the tiny 4 pound battery unless I make a trip to the steeper mountain trails. The combination of slow motor and only 1200 watts maximum makes the ride naturally a watt sipper. The exact same ride with the exact same motor and 72v 40 amps controller often took about 8 ah. The lower power setup leads to a smoother riding style, rather than the usual jam throttle/jam brakes ride you tend to do with lots of watts on tap.

The old mongoose blackcomb bike is still up and running. I put a 2810 motor on it, and with 72v 10 ah of battery I'm still well equipped for the occasional hooligan ride on nearby dirt roads. 30 mph top speed on that, so plenty of danger when I need a cheap thrill.

 

[spinningmagnets]

That's a great well-balanced selection of components, suited for the job you have given it.

 

[arkmundi]

Thanks for the post and pictures! You're a master of ebike art.

 

[dingoEsride]

Hey! I have the same bike which I bought new about 13 years ago except mine is the DS/2 a nice bike but a little heavy for climbing without power, it was the fist that I electrified using lead on the same type carrier as you but it was bending so i converted another that had a bigger triangle, your solution would work great but is it a little rear heavy if you got some air or on a steep incline will it wheelie?

 

[dogman dan]

I think you are right, it's DS. Impossible for me to tell by the way the decal looks which it is. About a 2004 or 5 model bike I think. Originally it came with an OK but worn out fork, but nothing compared to the bomber it has now. A very heavy frame to pedal, but nice and stiff for a motor bike.

You can feel that weight there. I suppose it will be a problem with a really long steep hill. You definitely feel a light front wheel with it. The trails near my house don't have any long hills, so wheelie's are not a big problem. I would run more power for long hills of 20%, so this bike won't likely be asked to do that.

Though it does affect the handling, at only 4 pounds, it's easy to just lean on the bars a tiny bit to stick down the front wheel to crank a turn. It does have a slightly floaty front tire, like any rear drive two wheeler can, but it's not a wheelie monster.

I truly don't have any handling issues that are a problem. I've ridden with more weight on rear racks plenty, and know what it's like. You constantly feel like you are behind as you ride a twisty trail, you constantly keep having to catch up with what the bike is doing to you, rather than just making the bike do what you want. Pretty soon, you get far enough behind your turns to high side it. Very similar to snow skiing if you sit on the tails of the ski.

I might try a fork mount later, but for now it rides ok with only 4 pounds in the rack. Experience tells me it will ride tolerably good even if I put 8 pounds back there. Above 10 pounds, it will start to suck badly, and need a brace on the rack to save the seatpost.

 

[dogman dan]

I thought I had this thing weighing in at about 50 pounds. Try 71 pounds with the battery!!! Holy crap. I knew the bike wasn't sub 30 pound originaly, but it must have been closer to 45 pounds!

The bomber fork weighs more I suppose, as does fat tires with a big slug of slime inside. But man, I didn't realize that frame was such a tank. In it's day, it was entry level DH stuff. Pretty thick alloy tube, It's always ridden nice and stiff.

It could be worse, I just weighed my longtail too. 132 pounds with the battery. That I knew was over 100 pounds.