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Folding Bikes Discuss the unique features and issues of folding bikes. Also a great place to learn what folding bike will work best for your needs.

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Old 09-20-07, 10:25 PM   #1
Pine Cone
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Folder Mods and Bike Handling

While it might be out of place to discuss bicycles here, I have noticed that one very unique thing about folding bikes that is very different from most bicycles is the attachment of the handlebars to the stem or stempost.

The 2006/20077 Downtube Mini is like many folders in that the handlebars attach directly to the stempost. This makes the handlebars centered on the pivot point of the forks.



Most bicyles have some sort of stem like this one, which extends the handlebars forward of the pivot point of the forks.



Adding barends or using funny handlebars like these Scott AT4s also move the pivot point forward if you move your hands onto the barends or the forward portions of the handlebars.


You could also add a conventional stem and some funny looking handlebars and end up with something like this...



What I have found with these mods is that moving the pivot point forward by adding a longer stem makes the bike steer more predictably and be less twitchy. Thinking about the change in geometry it makes sense. When the handlebars are centered on the pivot point a small movement of the handlebars moves the steering angle a larger amount when compared with using any stem which moves that pivot point forward. The Mini with a 130 mm stem handles much better at speeds above 25 miles per hour when compared with the stock 2006/2007 stempost. In the 2007/2008 bikes Yan has added an adjustable stempost which requires an additional stem and improves handling by moving the handlebars forward.

The fold is smaller with the handlebars centered on the stempost, but from my experience bike handling is much improved by adding a stem which moves the bars forward.

Has anyone else noticed this change in bike handling associated with changes in handlebar position? Anyone have bars that sweep backwards like bikes had back in the good old days (whenever they were)?
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Old 09-20-07, 11:10 PM   #2
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Pinecone, you get full marks here!
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Old 09-20-07, 11:51 PM   #3
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Interesting post and nice photos however I think that you will find that most folders that mount the handlebars on to of the stem post have an angled stem post that moves the bars forward of the pivot line. In your first photo the stem post appears to be about 10 deg ahead which moves the handlebars about 2" ahead of the pivot line. This is less adaptable than getting to the same location with an in line stem post and an offset stem but it folds better and should be lighter. I believe that Birdy offer a couple of different angles and I assume that some other manufactururs also do so.

None of the above of course affects your comment about perceived stability improvement if the offset is greater.

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Old 09-20-07, 11:55 PM   #4
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Looking at those versions, it is noticable that the original stem riser angles forwards a bit, while the newer stem is in line with the steering axis. Can you confirm that?

[edit] D'oh! beaten to the post by energyandair! [/edit]
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Old 09-21-07, 12:10 AM   #5
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PineCone:

I have added a 140mm stem onto my Mini. I did it for the reach and comfort, but it makes the handling a bit nicer too as you have pointed out.
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Old 09-21-07, 12:19 AM   #6
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Quote:
Originally Posted by jur View Post
Looking at those versions, it is noticable that the original stem riser angles forwards a bit, while the newer stem is in line with the steering axis. Can you confirm that?

[edit] D'oh! beaten to the post by energyandair! [/edit]
The older stem does angle forward, but the consequence of that is to make it impossible to switch from inside fold to outside fold with the stempost without moving the angle to the rear. The older post has two parts held together with a split pin hammered through the two pieces.

The angled stempost doesn't offset the handlebars forward very much, maybe 2 to 4 cm, so shorter than any conventional stem for threaded or threadless bars.

I also like to keep the handlebars low to keep more weight on the front wheel and less on the rear. I had to be very careful to keep the stock Mini from popping a wheely when I started pedaling on the hill just before my office. With the original setup I had a hard time keeping the front wheel on the ground when I started in a lowish gear. More weight on the front wheel and hands also means less weight on your butt and seat which makes longer rides much more comfortable. Lower handlebars also = more aero and my average commute time dropped by about 4% after I switched to the lower bar position. Win win win as far as I can tell...
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Old 09-21-07, 12:25 AM   #7
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Hi
I found this article eye-opening. http://www.pulse-jets.com/phpbb2/files/block40_125.pdf See picture 40.1 for T = trail.
Quote: "..way to increase the stability of a bicycle is to increase T (fork trail)."
According to my simple measurements increasing Merc's trail & stability would mean bending front fork backwords - contrary to what I believed.
Using bar-ends seems to help me too.
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Old 09-21-07, 01:27 AM   #8
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Concerning Raleigh 20s, I think I read in Sheldon's Digest that because of the nylon bush the R20 uses it is not possible to ride "no hands" ??.....well, I've found with the Wasp's long stem it is possible and very stable,....thanks to Jur's inverted seat post creation. However, I am thinking of making a LONG stem riser with a quill and using a normal headset to get rid of the q/r set up.
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Old 09-21-07, 01:32 AM   #9
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Interesting points and BEAUTIFUL photographs. They make my efforts look shameful.

How do those longer stems affect folded size?

I'm quite sure that putting an extension on the steering post of my Merc would widen the folded size hugely. I suppose the manufacturers of folders mount the bars directly to the steering post to enable the fold to be compact. Doing so forces compromises like shrinking the cockpit size and creating very direct steering. Personally, I really like the rapid, agile handling of the Merc. I've been riding my new bike mostly for the last three weeks and going to the pub last night on the Merc, I reallly enjoyed the upright position and the agile handling. It's a bit of a shock when you first get on one, but you soon learn to ride it safely. It's accelleration is incredible in the 45 inch bottom gear. It's a blast in town duringb rush hour across the many mini roundabouts. It goes from 0 - 10 miles an hour in 0.25 of a second and zips in and out like lightning, leaving lumbering car drivers with their mouths open (maybe they're just thinking, 'Look at that mad kamikazi b*stard').
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Old 09-21-07, 04:15 AM   #10
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I'm quite sure that putting an extension on the steering post of my Merc would widen the folded size hugely. I suppose the manufacturers of folders mount the bars directly to the steering post to enable the fold to be compact. Doing so forces compromises like shrinking the cockpit size and creating very direct steering.
In terms of reduced cockpit size, Dahon "created" biologic geometry to off-set this compromise and other companies have done similar things. It seems to do the trick.

In terms of steering, I'd agree that an extended stem makes the ride more stable, yet increases folding size, but I think another significant reason why manufacturers don't include extended stems is because they don't want riders pulling back on the handlebar in order to obtain leverage. Incidentally, which would be the bigger issue: the headset being over-stressed or the handlebar post snapping off? My gut feeling is the latter.

By the way SC, you have a BEAUTIFUL backyard!
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Old 09-21-07, 06:01 AM   #11
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Since I take my mini on the train all the time, I cannot afford even a moderate increase in fold size, so I have not done anything to the handlebar on mine. Were I to take it for an extended tour, I would probably change something, mainly for the aerodynamics. But ... let me change the subject!

I changed the TIRES on my mini:
front-- Big Apple (fattest tire I could find)
rear-- Primo Comet (thinnest tire I could find)
The effect is that the front axle is now 18 mm higher than the rear axle; this rotates the whole bike backwards a little over one degree. The wheelbase is shortened a tiny bit (about 0.17 mm?), not enough to make a difference. The relaxed frame angles, however, increase stability significantly. I can now ride no hands!
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Old 09-21-07, 06:02 AM   #12
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I put a 130mm stem on my NS with some carbon bars and bar extensions, I put a quick release on the stem so that the bars can be rotated, so that the bar ends don't stick out when folded. It's comfortable having the extra reach and it does seem to give a slightly more stable ride. Picture here:
http://www.box.net/shared/3c3bd9h4dy
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Old 09-21-07, 08:43 AM   #13
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Quote:
Originally Posted by Pine Cone View Post
The fold is smaller with the handlebars centered on the stempost, but from my experience bike handling is much improved by adding a stem which moves the bars forward.

Has anyone else noticed this change in bike handling associated with changes in handlebar position? Anyone have bars that sweep backwards like bikes had back in the good old days (whenever they were)?
Yep ... and I agree that a more forward position on the Mini improves handling considerably.
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Old 09-21-07, 08:47 AM   #14
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By the way SC, you have a BEAUTIFUL backyard!
LOL! I live in a golf course development. The pond is where an extended duck family hangs out...
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Old 09-21-07, 09:03 AM   #15
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The pond is where an extended duck family hangs out...
Are you Tony Soprano?
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Old 09-21-07, 10:12 AM   #16
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How do those longer stems affect folded size?
The only way I can get a compact fold it to remove the handlebars from the stempost, fold the stempost, fold the frame, and then place the handlebars on top of the racks, wheels, and frame. Then I use Velcro one-wrap to attach the handlebars to the rack. I also use the Velcro one-wrap to attach the fork to the seat stay to keep the bike from unfolding. I can easily roll the bike holding onto the seat.

The fold is almost as compact as it would be with smaller bars, but it probably adds a minute to the folding time. I will try to post a picture of the folded bike sometime next week.

I don't do a daily fold, so it is not much of an issue for me. If I folded it on a daily basis I would probably use the old stempost, stock handlebars, and add the longest barends I could find. Barends can usually be adjusted so they go around or through the front wheel when folded (inside handlebar fold) and add almost nothing to the final folded size.

I also like the idea of using the big front tire and small rear tire to add stability by changing the frame angles.
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Old 09-21-07, 11:24 AM   #17
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Quote:
Originally Posted by Pine Cone View Post

I also like the idea of using the big front tire and small rear tire to add stability by changing the frame angles.
How much would the fatter tyres calm down the handling. I noticed a while back that taking fat nobbly tyres off my mountain bike and putting road tyres onto the wheels entirely changed the handling. Not only was the bike much faster as you'd expect, but the handling was entirely different - much twitchier and more agile. I'm wondering if that was what made the reported change up above. Going the other way, changing skinny stelvios for wider marathons (going from 28x406 to 40x406) made my new bike much less twitchy.
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Old 09-21-07, 01:59 PM   #18
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PINE: used to put on longer stems on my BMXs to get a more stable ride... it does feel less twitchy farther from the pivot point (is it the pivot point, or more cockpit space?)... I'm not a big guy, but I also used to put sway back seatposts too (the ones that angle the seat back, not straight... not sure if they still have them now)... wonder if putting one of those on would make for an even more stable ride... if the mini is to mini...

Where'd you get that stem in the 2nd pic?
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Old 09-21-07, 04:14 PM   #19
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Where'd you get that stem in the 2nd pic?
It's an old Girven flex-stem. They have an elastomer so the idea is they would give you some of the benefits of front suspension. Works OK, but I wanted lower handlebars.

I picked up a few of them when they were being closed out for cheap...
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