Fastest Urban Folder - Single Speed? Options

[puppypilgrim]

yeah, looks much more appropriate with the lowered handlepost.
But without rear brake? Are you sure this is a good idea? If you have slippery, wet surface, front braking can become delicate.

I know, I know....why delete the rear brake on a singlespeed? Deleting the rear brake only makes sense on a ...wait a minute...FIXED GEAR! According to my bathroom scale, it now weighs 21 lbs (9.5 kgs). If I want it any lighter, it will be wheels and tires (I'm not there yet).

The reason I did it was to test the feel and look of the bike with just the front brake. I don't ride in the rain and its not a daily commuter bicycle. It's a play bike when its dry outside. I have also set it up so I can easily transition to a fixed gear whenever I feel ready. I need the magic ratio to avoid using a tensioner though.

A buddy set me up with a Dakine hydration pack so I'm good for day tripping.

[newsilver]

To quote the bandito in Blazing Sadles "We don need no stinkin rear brakes".

It is redundant because you will use your legs to start slowing and a GOOD front brake is all you need. If you are getting in trouble with just a front brake in the wet your are going to fast! Also your feet give a safer slowing because it is unlikely you will lock up the rear wheel until you are an expert on fixed or mucho macho. I've been riding fixed for 28 years and still have never locked up the rear, I know I could but like my tires to last and don't like the stress on my legs.

In NYC last week a kid on a fixie was throwing his weight forward and locking up the rear for every sudden stop or slow down. I asked him how long his tires lasted and he said 2 months!

[newsilver]

Sweet Pea

Another attempt at posting images?!

This is the Sweet Pea - It came with 14 inch wheels and because there really are no good tires and rims for 14" I changed to 16". The fork had to be extended by cutting and brazing (it needs to be painted). In the rear the 16" fit fine.

It came with a tiny gear so the major challenge was to get a chain line that allowed for a 54 tooth chain ring. The solution was to cut a U shape slot out of the underside of the chain stay and TIG weld in a U shaped piece of aluminum that gave enough room for the chain line.

Other changes - a taller seat post which at first I used a long single piece one but it was a little to short and did not have enough in the bike so it was putting to much stress on the seat tube, also it was to long when the bike was folded so did not pack well. The solution was the 2 part job you see now. It added weight but it now packs in a small bag I found.

I cut down the handle bars and added bar ends, brazed on bosses for a real front brake (the one it came with was scary).

It weighs roughly 20 lbs. and that is with very over built front and probably rear wheels, so if I spent another $500 on wheels and other parts I might get it down to 17-18lbs. But I do not feel the need it does every thing I want as is.

I bought the bike for $250 (the NYC bike shop was glad to move it) and spent $500 more on parts and welding at Chelsea Bikes on 26th street. Raphael the boss there did a fantastic job - he really knows his welding and heat treating! I highly recommend him for any work like this.

If the Uno had been on the market I would have bought it and made gearing changes but for like money I have a smaller folder and when I get it painted it looks way cooler!

[puppypilgrim]

Quick update: Was able to run the bike without the Surly Singleator chain tensioner by removing one chain link and experimenting with chain length. Seems to work fine and I've mashed it as hard as I can. Chain tension passes the Park Tools chain tension test and does not derail. I might have found a magic ratio that works with that particular cog height and teeth size. (IMG:style_emoticons/default/smile.gif)

It goes without saying it runs better without the tensioner. Somehow I was getting incorrect tension or insufficient chain wrap in push down mode and the chain was skipping climbing hills. I love singlespeed.

For those who know Vancouver, I cycled from Howe and Cordova in downtown (by the waterfront) back into Garden City and Granville Ave in Richmond. About 16.5 km and 40% of the trip involves hill climbing from the bottom of Cambie bridge to 41st then Oak street bridge. I took 57 minutes and that includes waiting on traffic lights for an average of 17 km/h - on a 65 gear inch singlespeed. I lost time of the hills because my chain was slipping. That was why I tried modifying the bike by removing the tensioner and playing with chain length.

Victor "Looking Forward to Climbing Hills" in Vancouver

[peteribach]

I might have found a magic ratio that works with that particular cog height and teeth size. (IMG:style_emoticons/default/smile.gif)

That is with 52T/14T?
Keep us posted if it still works after some time or chain gets some slack.

[puppypilgrim]

I might have found a magic ratio that works with that particular cog height and teeth size. (IMG:style_emoticons/default/smile.gif)

That is with 52T/14T?
Keep us posted if it still works after some time or chain gets some slack.

Assuming 406mm wheels and "normal" tires yields a rolling diameter of 19.25".

Previously, one poster has said he made his Dahon Mariner D7 into a singlespeed running 42t x 13t. His gear inch would be:
(19.25" x 42T) / 13T = 62.2 Gear Inches.

My Dahon Helios setup is (19.25" x 52T) / 16T = 62.6 Gear Inches. The common denominator is therefore 62 Gear Inches being one of the magic ratios for my generation of Dahon with their chain stay lengths.

EDIT: Another magic gear combination that will work is 59T x 16T = 71 gear inches according to my calculations.

[puppypilgrim]

Here is the revised Dahon Helios singlespeed after removal of the Surly Singleator:

(IMG:http://i43.tinypic.com/34hubz6.jpg)


1600x1200 pic: http://i44.tinypic.com/301isls.jpg

[newsilver]

It gets better and better!

I had to keep my brake cable long so that I could extend the handle bars for a good fold, what about yours?

[peteribach]

I had to keep my brake cable long so that I could extend the handle bars for a good fold, what about yours?

The 'over-the-axle' fold works as long as you don't mount a rack. Thus folding is much easier - no need to extend post nor to rotate bars.

[puppypilgrim]

It gets better and better!

I had to keep my brake cable long so that I could extend the handle bars for a good fold, what about yours?

I'm using the Dahon for quick trips to the store. I don't even bother doing a full fold. First step is to set the pedals so the left pedal is in the 6 o'clock position. Flip the handlebars down without rotating the handlebars to point the brake levers down (mine is cut narrow to 41cm). Undo frame hinge and fold in half. This leaves the seatpost sticking in the air but a small footprint. Unless people pay attention, most won't even "see" a bicycle at this point. The good aspect about this fold is that it doesn't require the precision alignment of resetting the seat post. Both the handlebar and frame secure back in pre-determined points.

The narrow width of the bar reduces leverage but I am OK with that. The short brake cable means it will be difficult to raise the handlebar for anyone significantly taller than me. That is a compromise I was willing to make to please my needs. After I took the photo in the above post, I reinstalled the rear brake for redundancy in the safety department. I did it after determining that I would not proceed with fixed gear on this bike and it would always only be a singlespeed.

I am ecstatic with how the bike looks, handles and feels after this round of work. It's solid and since it no longer creaks (cleaned and lubed the hinge joints) it feels more solid. It is unbelievably nimble. At 62 gear inches, I wish it had more top end speed but given the stop and go traffic and very consistent winds here, 62 works OK.

Now in case you are planning to use the magic gear calculator located here http://eehouse.org/fixin/javafmu.php to find a ratio that will work with your vertical drop outs, you might want to know that the Dahon Helios P8's chainstay length is 15.75" or 40 cm.

[dpeddle]

Great thread here. I have also been a fixie for many years in 700c format but just purchased the Dahon Hon Solo and I too can attest to the difference in handling in a fixie with small wheels. Fixies are the way to go. Who needs complications of figuring out what gear to be in....just RIDE!!!!!

[newsilver]

The 'over-the-axle' fold works as long as you don't mount a rack. Thus folding is much easier - no need to extend post nor to rotate bars.

Peter you are a genius!! I had assumed that my bar-ends would interfere with an over-the-axle fold so had not tried, after your post I gave it a quick go and voila, bob's your uncle, thar she blows!!! it folded right up with the bar-end slipping between the spokes of the rear wheel. Now the fold is smaller and I can cut off all that ugly extra front brake cable.
Thanks so much!

Dpeddle, You have the right attitude - glad you have joined the little wheeled tribe!

Puppypilgrim I had put a stupid question here for you but was tired and realized that it had been answered. Your bike is "a nice ride" as they say (I have been spending to much time on LNDFGSS!

[puppypilgrim]

Puppypilgrim I had put a stupid question here for you but was tired and realized that it had been answered. Your bike is "a nice ride" as they say (I have been spending to much time on LNDFGSS!

I'm not quite done. This afternoon I bought bar ends, a cone wrench, a freewheel tool, 2 quick links..... :0

[puppypilgrim]

I was rethinking why longer reach is so important when I stand and hammer. And it might be because one shifts balance point forward onto the pedals and more reach is needed to compensate, otherwise it gets unstable. datako, I am usually riding in crowded urban traffic, this might be a factor (?).
I test-mounted a long 130mm ahead stem (which I had lying around). The ahead stem makes the overall steering stiffer and the stand-and-hammer more relaxed. But I think 50mm stem might be ideal. Also this would still allow for the inside fold.

Peter, this is the reason why you need a longer stem when you stand and hammer.

[peteribach]

Peter, this is the reason why you need a longer stem when you stand and hammer.

Interesting read. While I didn't understand all it seems quite clear that Dahon's Biologic II geometry is quite upright and taller riders need more reach. In my case (6,2 ft tall) 5cm more would be just fine.