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Originally Posted by jur
(Post 7622884)
I will need lots of practise to get it down to the sub-15s what I routinely do on the Yeah. For one thing, I have to figure out what to do with the crank arms, what the most optimum position is. I have tried to follow the (excellent Australian) manual's directions, but that didn't seem to help. I will just have to work out the best one for myself like I did on the Yeah. Part of the problem is the cranks move when folding so they don't end up where you think. http://www.kinetics.org.uk/assets/mu.../birdfold.mpeg |
Originally Posted by jur
(Post 7622884)
Comparative Geometry - Birdy vs Swift [all dimensions in mm]:
Wheelbase: 1010 vs 1030 (longer is better?) Effective top tube: 585 vs 550 (longer is better for taller riders) Head angle: 71º vs 72º Seat angle: 73º vs 72º Trail: 63 vs 36 BB height: 290 both (depends on tyre width) Stepover height: 535 vs 640 Chainstay length: 430 vs 410 Head tube length: 88 vs 125 rear dropout: 135 both The Birdy's wheel flop factor is quite strong, resulting from a slack head angle and lots of mass in front of (and therefore above) the steering axis, partially due to the sports stem. So the front wheel has quite a strong tendency to flop sideways. The flop is not dependent on speed - it wants to happen at any speed. The Birdy also has quite a large trail; ie the wheel contact point is behind the steering axis, like in a shopping trolley wheel. So at speed, the trail tends to straighten the wheel out - the faster, the more you get. This ought to make the bike very ridable hands-off. So with trail and flop you have these opposing forces, one of which is speed dependent - the wheel flop factor steers away from the middle at any speed, while the trail steers to the middle at highish speeds. At low speed, the flop factor is stronger than the trail, so the bike veers off. At high speed, the trail is stronger than the flop, but now there is over-correction from any disturbance so the bike now veers in the opposite direction, and back again, and so on, resulting in shimmy at high speed. Possibly the comfort stem which is further backwards may be more stable. The Swift, which also can't be ridden hands-off for long stretches, has not exhibited any tendency to shimmy under similar conditions. The slightly steeper seat tube angle has the effect that as the seatpost is set higher, the saddle has to be set back further to end up in the same spot as for the Swift. Fitment: Most of my other folding bikes have a 55cm effective top tube. This is logical as it corresponds to a medium sized bike, and makers obviously want their bikes to fit as many customers as possible. However, the Birdy has a 58.5cm effective top tube, so it caters for slightly taller riders which is great since I am on the edge of being too tall for a size medium. I like a more forward body posture, arms and body roughly at 45º from vertical. I use the Peter White approach to fitting, and this has the result that all my bikes end up being very similar in fit - the relative position of saddle, pedals and handlebars are the same on all bikes. The preferred fit has resulted in the Birdy saddle going back as far as it can go; the sport stempost places the handlebars smack in the right spot. The lowest setting results in the handlebars at saddle level. So the Birdy fits me with no mods. The slightly longer effective top tube, plus that there is a lot of seatpost left over for extension, makes the Birdy suitable for taller riders as well. (I am average at 5'10".) Pacific Cycles claims to 6'4" and 110kg, including luggage. I think that claim has substance. |
I think all Birdy bikes have hands off shimmy due to the folding mechanism, but thankfully no hands on shimmy.
The difference between even the Marathon Racers and the Stelvios is night and day. I recently had to ride with a Racer on the back and was dropped by folks that don't usually drop me! The Birdy Maxis is even worse. Of course, nearly all of the performance difference between one bike and the next is due to the wheels and tires, at least on flat surfaces. The 24 spoke wheel with a relatively light rim is great. The Maxis is not so great, but gives a more confident ride. That is where I think the only real trade off comes in with a small wheeled bike. If you ride thin tires on small wheels, there is a danger that the wheel can sink into a pothole or grate. |
I run Stelvios on my Birdy and have got two slow leaks over the past two months from potholes that I was not able to see or avoid in time. There definitely is a trade off when running skinny, high pressure tires on small wheels. I have since been only pumping the tires to 100 in the front and 110 in the back instead of the 120 maximum. We'll see if that helps any.
In contrast, I have run over tons of stuff on my Dahon with Marathon Racers and have yet to get a flat. Speed wise, the Birdy is only slightly faster, maybe because the wheels are smaller and it is geared slightly lower? Of course, the ride on the Birdy is a lot smoother :). |
Jeffy--fun experiment. Do you have multiple average speed differences?
Jur--I left out the most important comment. That is the most thoroughly detailed and well thought out review I have ever read. Hats off. You are an upstanding member of this online community. You are coming dangerously close to Sheldon Brown status. |
A thorough and readable report. These kinds of details are good to hear about. Congrats on your very nice new toy!
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I think I did about just under a mile no-handed the other day on the Bike Friday. The Birdy looks like fun. Thanks for the great write-up!!!
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Originally Posted by pm124
(Post 7629207)
You are coming dangerously close to Sheldon Brown status.
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Originally Posted by invisiblehand
(Post 7625225)
So the effective top tube length is the horizontal distance between the seat post and saddle. Given you have the sport stem post, what is the effective stem length?
Further thinking about it made me realise that the seat tube is welded so it comes out behind the bottom bracket shell, so we are looking at apples and oranges. If the seat tube came out on the BB shell as in the Swift, the effective top tubes would be about the same for the 2! So we're back at the size medium. :p That explains why the effective stem looks to be about the same again. And why I couldn't ride it with the comfort stempost. :twitchy: Having said that, the sport stempost still offers taller riders who like a more sporty posture a roomier cockpit because the cockpit stretches if seat and handlebar are kept at the same height. |
To improve the gearing I installed the Vuelta 58T chainring I had lying around (after getting a 60T for the Swift). It improved the gearing to 31-91". Quite good for most riding. The nice thing is, the bigger ring is only about 1/2 tooth bigger in radius that the original, so it still fits nicely between the chain guards without sticking out. In fact it is now level instead of slightly recessed.
The interesting thing is, the first time I went up a steep slope, the chain climbed off twice and wedged itself between guard and ring. It's a credit to the tough plastic that the guard didn't break right off. This happened twice and then never again. A bit of a puzzle. I blame a slightly dusty chain which had more friction to the teeth so instead of slipping into the tooth valley, the chain stuck on the tip and so climbed off. Checking last night I saw the chainline isn't centered on the middle of the cassette, making the line more acute in low gears, further strengthening my conclusion. After almost 2 weeks of commuting, I haven't changed any of my initial impressions. I would like some faster tyres but will probably first wear this set out. I have found by pulling the brake cable housing towards the back giving it more freedom, I am able to get the back wheel past the brake pads without having to deflate it. :thumb: |
Originally Posted by jur
(Post 7673386)
I would like some faster tyres but will probably first wear this set out.
I have found by pulling the brake cable housing towards the back giving it more freedom, I am able to get the back wheel past the brake pads without having to deflate it. :thumb: The rear brakes are a bit of a PITA both because of clearance with the original pads and because its not practical to change to Koolstop pads as the clearance gets worse. I plan to eventually change the brakes to parallel action brakes (Magura, Avid, XT or LX) which should fix the problem. David |
Both good ideas. Gives me a legitimate excuse to upgrade! :)
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Hi jur,
I also wanted to add my congratulations! I can't wait to see the future mods... Barry |
Originally Posted by pm124
(Post 7607710)
If the chain does not fall off when you fold it, you can put it in a low gear, but I wouldn't put it in the lowest, as it bends the chain quite a bit. I use an Ultegra medium cage. It doesn't gather as much chain as it should in part because road derailleurs have weaker springs than mountain derailleurs. The XT works great.
Originally Posted by pm124
(Post 7607710)
Those tires are about -2-3MPH relative to the Stelvios, but are almost indestructible. In the US and Europe, Schwalbe is now listing the Kojak in 355. That will also take 1.2 pounds off of your bike.
Plus the rear tyre threatened to blow off the rim 3 times during commuting last week. I was JRA and had just gone over a very minor bump when I felt the rear brake rubbing in a spot. Checking showed the tyre bead perched on top of the rim. :eek: I was able to save a blowout all 3 times. The LBS agreed on a new tyre, so I got a Marathon Racer instead after paying in the difference, and installed a Slime liner for proper puncture protection. We're going on a tour next weekend: day 1 day 2 day 3 day 4 - retracing day 3 Got me some Deuter panniers (with Ortlieb catches) for the trip and commuted with them for a shakedown. Perfectly happy. :thumb: |
Partial repost from NorCal:
I rode my Birdy up Page Mill today! :D http://www.bikely.com/maps/bike-path...y-scenic-hilly Oh, and yes, I was creaking, whistling and rattling the whole way. Descending through the twisties, I had a new sound...then I realized I was scraping the little chain guard on sharp right-handers. ;) And on a straight descent (probably going 25-30) I tried again no-handed, no issues (I did keep my hands close to the bars just in case). Plus, had a couple of entertaining encounters on the way home... First was on Alameda de las Pulgas. Some guy on a road bike passed me, working hard. Once he felt he had gotten far enough ahead, he sat up and relaxed. Well, we got to a bit of a hill, and I was able to make up the difference. He didn't notice until I was right on his ass, then he looked back, saw me, and stood up to mash up the rest of the little hill. Unfortunately for me it leveled out, I can't keep up on flat ground. Guess he didn't like the idea of being passed by a girl on a clown bike. :p Then by El Camino, met a woman on a comfort bike and had an interesting conversation as we waited for the light: Her: That's a really cool-looking bike! Me: Thanks! Her (dead serious): Is that a road-racing bike? Me: Um, no, it's a folding bike. Her: A what? Me: Folding. It folds up, small (made some hand motions to illustrate). Her: You have got to be kidding me!!! So you can take it on the bus??? I was having a hard time holding back the laughter...I mean, I can't think of too many bikes that look farther from a road-racing bike. :lol: |
it will be interesting to see whether you notice a difference. I found the Racer to be sluggish. Did you replace both tires? The front matters almost as much as the rear.
I have a 349 wheelset and used a Brompton Green with great success. I've had a higher average speed with that tire than with a Stelvio+Slime liner and only 2 flats in 1500 miles. Let us know how the tour goes. |
I did a Palomares Road loop for the first time today on my Birdy. I actually started in Pleasanton, heading south on Foothill Rd (the route is plotted going the opposite direction).
http://www.bikely.com/maps/bike-path/217409 Not too much bike noise for me since I tightened everything this past weekend. My climbing skills leave much to be desired as I had to stop a couple of times going up Palomares Road to catch my breath. It still feels a little unnatural for me when I am out of the saddle compared to riding a full sized bike, so I typically spend most of the time in the saddle on climbs. I'm thinking it's somewhat due to the more upright riding position, or maybe I just need to practice the technique more. |
Originally Posted by jeffy1021
(Post 7751171)
It still feels a little unnatural for me when I am out of the saddle compared to riding a full sized bike, so I typically spend most of the time in the saddle on climbs. I'm thinking it's somewhat due to the more upright riding position, or maybe I just need to practice the technique more.
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Originally Posted by pm124
(Post 7751031)
it will be interesting to see whether you notice a difference. I found the Racer to be sluggish. Did you replace both tires? The front matters almost as much as the rear.
David |
Originally Posted by msincredible
(Post 7751492)
I have found that on steeper hills (15-20%) the Birdy really wants to wheelie, particularly when I have a heavy backpack on. To compensate, I really have to get my weight over the front wheel, which feels unnatural ergonomically for climbing. Maybe what you are feeling is related?
The other issue is, climbing out of the saddle places the body more forwards, so unless you have bar-ends or brake hoods to hold on to, it feels awkward. Bar-ends are a huge help in climbing out of the saddle. :thumb: |
Hmmm, possibly the stempost.
Also, I should probably define "heavy backpack". When I have it on (with my laptop and portable drives and all the stuff I need for work) it's typically around 25 lbs, which is about 25% of my body weight, and it is larger than my torso. Guess that might have a significant effect. :o |
Originally Posted by msincredible
(Post 7753773)
Hmmm, possibly the stempost.
Also, I should probably define "heavy backpack". When I have it on (with my laptop and portable drives and all the stuff I need for work) it's typically around 25 lbs, which is about 25% of my body weight, and it is larger than my torso. Guess that might have a significant effect. :o |
I picked up a used 2006 Silver that came with a plain straight extension on the comfort handlepost with an ahead stem, and it handles very much like a full sized bike. The ability to use whatever stem you want allows for a greater degree af cockpit adjustment. I seem to remember seeing the plain extension listed as an accessory but not sure about availability.
Also installed an Avid Magnesium V brake set that I had laying about and there are no clearance problems with either functionality or wheel removal. |
Originally Posted by jur
(Post 7752855)
Bar-ends are a huge help in climbing out of the saddle. :thumb:
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In a big hurry, I wheelied away from a stop sign yesterday on my Birdy right in view of a patrol car... had to talk my way out of an exhibition of speed ticket... ;)
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Originally Posted by SesameCrunch
(Post 7754550)
Say, you can hang your backpack off your handlebars in those steep sections. Counterweight!:thumb:
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It has crossed my mind to use my Birdy for light trails and off road. Aside from the gearing, could I throw some knobbies on there and use it for that purpose? I've seen off-road tires offered for the Birdy, but I can't seem to find a place that actually sells it as an accessory. Changing to the stiffer elastometer also seems like it would be a good idea as well. Any thoughts?
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Originally Posted by jeffy1021
(Post 7785120)
It has crossed my mind to use my Birdy for light trails and off road. Aside from the gearing, could I throw some knobbies on there and use it for that purpose? I've seen off-road tires offered for the Birdy, but I can't seem to find a place that actually sells it as an accessory. Changing to the stiffer elastometer also seems like it would be a good idea as well. Any thoughts?
Knobbies would be great if you can find them, I only had the stock tires. The other issue is clearance. I have to carry over big tree roots, loose sand, and big rocks. Calgary's Fish Creek Park http://paularickert.net/albums/userpics/calgary01.JPG Russian Ridge http://paularickert.net/albums/userp...ianridge02.JPG Water Dog Park http://paularickert.net/albums/userpics/waterdog01.JPG |
Originally Posted by msincredible
(Post 7753773)
Hmmm, possibly the stempost.
Also, I should probably define "heavy backpack". When I have it on (with my laptop and portable drives and all the stuff I need for work) it's typically around 25 lbs, which is about 25% of my body weight, and it is larger than my torso. Guess that might have a significant effect. :o http://www.dotbike.com/ProductsP2121.aspx?TRACK%3dDPL http://www.dotbike.com/ProductsP2122.aspx?TRACK%3dDDI - this is the new version of the one I have |
Originally Posted by msincredible
(Post 7787428)
Water Dog Park
http://paularickert.net/albums/userpics/waterdog01.JPG I've done extensive off road riding as well. It shines on pack dirt trails, but not very useful for deep ruts, powdery dust, deep mud, and so forth. Though moderate mud doesn't seem to matter much. It is an outstanding all around bike for international touring. I can't afford the Intego version, so I rely on 2 chainrings in mountainous areas with steep climbs. Kind of a ghetto solution b/c the chain falls off when the bike is folded. This is a problem b/c one always folds right before eating, and not everywhere in the developing world has a sink with soap available. (Or in NYC for that matter.) With my chainline, the bike automatically shifts onto the low front ring when progressing to low gears and then back to the high ring when going into high gears. Not for everyone, but cheap! |
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