Downtube 9FS folding bike review - my take

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neptronix   100 GW

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Downtube 9FS folding bike review - my take

Post by neptronix » Apr 25 2018 7:00pm

So yeah, i live in goathead country and have became pretty tired of pulling thorns out of tires and having tubes mutilated after every ride, even with tube liners, puncture proof tires, sealants, etc.
I decided that my next bike would have motorcycle tires, period.

So i went on a quest to find a 20 inch wheeled bike that fit a long legged 6 foot person, which is not an easy task at all.
After spending weeks reading reviews,i decided to buy a Downtube 9FS demo model which was slightly discounted due to various nicks on the paint and whatnot, but said to be low mileage. The dual suspension was a huge selling point, as 20 inch wheels are not exactly known for ride quality.

Based on the reviews i'd seen elsewhere, it seemed to be a solid bike.
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The good:

+ It fits a tall human like me. The seat has a long range of adjustability, and so do the handlebars.
+ The bike is small but the wheelbase is actually identical to a mid sized bike. It's a little on the twitchy side when a large human rides it, but it's not too bad.
+ The front fork appears to not be a proprietary long stem type, so you could replace it with something better.
+ The handlebars and seat tube do not flex nearly as much as other folding bikes i've ridden do. ( probably due to their large diameter ).
+ The folding mechanisms are pretty solid and stout. I didn't experience any shaking or wobbling due to them.
+ Rear wheel is 135mm and front is 100mm, so this is compatible with standard hub motors.
+ The pedaling position is nice. It puts you a little bit behind the cranks, which i find comfortable.

The bad:

+ The included bell rings when you hit bumps. OK, it's a cheap bike but this is so annoying that it'd be better without the bell.
+ The front fork appears to have 40mm of travel, but hits a bump stop at 20mm. Basically, it's worthless because you can expect it to clunk/thunk on every major bump / curb drop.
+ The rear spring provides better suspension than the front fork, but is so short that there's no possibility of replacing it with something better.
+ I've had the folding pedals unfold on me more than once and surprise me while riding.
+ The folding mechanism is positioned exactly where pant legs would move as you pedal. This results in various kinds of pants i wear constantly getting caught in the mechanism as i pedal. I would only ride this bike with a lower leg strap, skinny jeans, or shorts.
+ Either the rear swingarm or bottom bracket area is extremely flexy. You can feel it flex as you change gears and turn while pedaling. It's pretty unnerving. And i'm not a super heavy guy, just 180lbs.
+ The rear dropouts do not make adding a hub easy because of their design.

So all in all, i'd put this bike in the 'do not convert' category. It has some unfortunate flex points and does not feel certain under pedal power. These issues will just get worse at higher speeds.
My first major build: 8T MAC motor on a Trek 4500.
The new all-arounder: Leafmotor 1500w on a Turner O2 full suspension.
The wheelie machine: 20" Rear Magic Pie II on a Trek 4300 MTB

"The best time to plant a tree was 20 years ago. The second best time is now."- Chinese Proverb

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cal3thousand   1.21 GW

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Re: Downtube 9FS folding bike review - my take

Post by cal3thousand » Apr 27 2018 4:19pm

That's an excellent review. There's certainly a place in the market for frames like this. Too bad, this one had some issues.
Get a Cycle Analyst and a Multimeter, you're still a noob if you don't have at least one of each.

Planning on posting questions or buying anything on this site? Put up your country (at minimum) on your profile. This is a worldwide forum and we haven't reached clairvoyance.

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Re: Downtube 9FS folding bike review - my take

Post by neptronix » Apr 27 2018 8:22pm

Thanks. Yeah, i was really hopeful it was 'the one'. The only comparable bike i can think of is the airnimal rhino:
http://airnimal.eu/products/rhino/white/

But i'm not really willing to buy one of those expensive bikes on a guess that it won't be a flexy nightmare, like every other single folding bike i've ridden.

I've decided to just stick with narrow 700c wheeled bikes, as there's less surface area to pick up goatheads.. i figure that will be the least path of resistance for where i live.
My first major build: 8T MAC motor on a Trek 4500.
The new all-arounder: Leafmotor 1500w on a Turner O2 full suspension.
The wheelie machine: 20" Rear Magic Pie II on a Trek 4300 MTB

"The best time to plant a tree was 20 years ago. The second best time is now."- Chinese Proverb

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Alan B   100 GW

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Re: Downtube 9FS folding bike review - my take

Post by Alan B » Apr 27 2018 8:53pm

Sorry it didn't work out. That folding coupler is in a bad spot. I seem to recall some other folks who converted a different model of bike, or perhaps an earlier variation, and suffered failures of some important frame or fork elements. Perhaps it was discussed in Jeremy's old folder thread.

The Swift folding bike is a good folding bike to convert, though it does not have suspension and clearance for moped tires might be an issue. Xootr was making them but they stopped recently. I have heard they have some inventory remaining but you have to call them, they don't advertise it on the website anymore.

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Re: Downtube 9FS folding bike review - my take

Post by chvidgov.bc.ca » Apr 27 2018 9:12pm

Try the Cannondale Hooligan 8, if you can find one. Love mine...way better than the Dahon Speed 21 I had in the old days, which your review reminded me of. Very good review. I also had my eye on the Swift, back in the day when they were readily available. These small bikes are too fun to ruin with flex issues when their excellent rigidity is sacrificed to the folding dream. Its too bad about that front fork.

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Re: Downtube 9FS folding bike review - my take

Post by Raisedeyebrows » Apr 27 2018 10:11pm

My Ecobike Vatavio seems well built, no suspension but the frame is rock solid, not too heavy and not much flex. Rides nicely even going down hills at high speeds (high folding bike speeds anyway). Too bad they went out of business, I really enjoy riding the bike.
Image
Yuba Mundo w/BBSHD
Specialized Hard Rock w/9c clone, statoraid, hubsink
Trek Fuel 90 w/BBSHD
Above all run on 14s4p 52v li-ion
Ecobike folder 36v
Currie Flyer scooter 24v on 24ah of SLA

Every trip made with electric bike is one less car trip, saves money, no toxic fumes, less noise, less impact on roads.

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Re: Downtube 9FS folding bike review - my take

Post by docw009 » Apr 28 2018 3:29pm

Our Downtube 8FS bought new last year. Q100 hub motor added. 36V 10s-3P (8.4AH) or 10S-2P (4AH) in bag.

18 mph is about the max speed. It's my wife's bike and she never goes over 15 mph.
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neptronix   100 GW

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Re: Downtube 9FS folding bike review - my take

Post by neptronix » Apr 28 2018 5:16pm

Yeah, poky speeds seem appropriate for a bike like this.
And wow, that thing has a much longer fork than my 9fs. Why did i pay extra again? :P

The hooligan does look like you could adapt a suspension fork to it and make it into a nice bike.

Oh well... off to sell the 9FS.
My first major build: 8T MAC motor on a Trek 4500.
The new all-arounder: Leafmotor 1500w on a Turner O2 full suspension.
The wheelie machine: 20" Rear Magic Pie II on a Trek 4300 MTB

"The best time to plant a tree was 20 years ago. The second best time is now."- Chinese Proverb

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Re: Downtube 9FS folding bike review - my take

Post by ElementX » Jul 31 2018 6:47pm

I have a Downtube 9FS from 2009 (or 2010) that was briefly running a 500w rear hub from ampedbikes. I enjoyed it, but back then my battery was SLA's so that just added too much weight and effort for my liking. I think the hardtail version with front suspension fork would have been a much better platform to build on.

mwkeefer had a good build thread: viewtopic.php?t=13124

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Re: Downtube 9FS folding bike review - my take

Post by neptronix » Aug 08 2018 12:36pm

mwkeefer is the one that inspired me to do this build, telling me that his did 40mph when i was friends with him. It was one of the reasons i tried the frame out.
I read everything on the internet i could find about these bikes. Did not find any information about the problems i experienced with this bike.

I don't think anyone should be exceeding 20mph on this, and i have a feeling that mike's 40mph number was a downhill figure.

I have a cannondale hooligan ATM that i'm looking to build up soon.
My first major build: 8T MAC motor on a Trek 4500.
The new all-arounder: Leafmotor 1500w on a Turner O2 full suspension.
The wheelie machine: 20" Rear Magic Pie II on a Trek 4300 MTB

"The best time to plant a tree was 20 years ago. The second best time is now."- Chinese Proverb

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Re: Downtube 9FS folding bike review - my take

Post by ElementX » Aug 10 2018 2:08pm

I completely agree, I have found that 20mph is the realistic max for 20"-wheeled bikes. The smaller wheels are just too squirrelly above 15mph, which requires a lot more focus and effort. My 9FS was inspired by YPedal's Downtube project, but I've gone through this dance with three different folders over the years. I think the 9FS is a really nice bike, but isn't a good platform for big/heavy motors. I think it would shine running a 250w mini geared hub though.

I'm thinking of selling my 9FS too. Need to fund some other projects, so I have about 3 folding bikes to sell off lol. If you sells yours, let me know how much you get for it. I gotta figure out what these are worth these days.

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Re: Downtube 9FS folding bike review - my take

Post by ElementX » Aug 10 2018 2:17pm

docw009 wrote:
Apr 28 2018 3:29pm
Our Downtube 8FS bought new last year. Q100 hub motor added. 36V 10s-3P (8.4AH) or 10S-2P (4AH) in bag.
Image
18 mph is about the max speed. It's my wife's bike and she never goes over 15 mph.
neptronix wrote: And wow, that thing has a much longer fork than my 9fs. Why did i pay extra again? :P

Damn I just noticed those monster 20" forks too! They must have put in real ones at some point.

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Re: Downtube 9FS folding bike review - my take

Post by Alan B » Aug 10 2018 2:52pm

Some 20" bikes handle higher speed better than others. Frame and fork geometry, stiffness and other factors make a difference. Not all 20" bikes are made equally.

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Re: Downtube 9FS folding bike review - my take

Post by neptronix » Aug 10 2018 9:48pm

That squirrely feeling mostly comes from a short wheelbase.
Most 20" bikes are designed to be compact..

So there's nothing *really* wrong with the wheels themselves, just common geometry.

On that note, the 9FS had a pretty decently sized wheelbase. It just flexed and clunked way more than my liking... and that's before i even put a motor on it.
My first major build: 8T MAC motor on a Trek 4500.
The new all-arounder: Leafmotor 1500w on a Turner O2 full suspension.
The wheelie machine: 20" Rear Magic Pie II on a Trek 4300 MTB

"The best time to plant a tree was 20 years ago. The second best time is now."- Chinese Proverb

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