Birdy Monocoque Review
Model: Alivio
In Australia, the new Birdy monocoque frame range is still presented along the older scheme where color denotes model. More frame colors are actually available from Pacific Cycles but the size of the local market is quite small so this is probably not a bad business decision. The downside is it does stick you with a color that you might not like.
I decided to buy the entry-level bike since I like to change the componentry to what I want. The rationale is that the cheaper installed bits don't result in a big loss when upgrading them to exactly what I want. This meant the cream-colored 8sp Alivio model. They also have a black Rohloff and a deep blue 24sp Shimano Intego, and a brushed silver 9sp LX. The difference between the LX model and the Alivio is mostly limited to a different model Velo saddle (who cares if that's to be replaced anyway) and different derailer plus one more gear. Other bits are I think much the same. So the Alivio model presents a significant price advantage if the only real difference is a rear derailer, one less gear and the gear shifter - less than $100 cost all up, whereas the selling price difference is $450 or so. It's easy to see the economic sense in the Alivio - even if you upgraded it all to the same level as the LX, you'd still end up way in front.
You can find this model in the Pacific 2008 pdf catalog line-up; the local importer (St Kilda Cycles) orders just one color from each model range to limit stock.
Presentation/looks
Color: Metallic cream frame, with mostly black anodised componentry
In my case, originally I wasn't very enthusiatic about the cream color. Up close though, it is very nice indeed - it is the same metallic cream/off-white some cars are done up in these days, very striking, like a pearl. The black componentry shows up well against the cream frame. But so does every little speck of dirt.
The flowing lines of the monocoque frame is a significant departure from the agricultural looks of the first generation frame. The forks are unchanged, but the fork above anything else is what defines the looks of the Birdy - weird-looking? sure; agricultural? bl**dy oath; but it is a bit like the bike's badge - it defines it, it is unique to the Birdy. Bottom line is, it's a Birdy and that fork is as much a part of the package as the stylish Birdy logo.
On the front of the head tube you'll find Pacific Cycles' logo.
Suspension:
On to riding. This is where the Birdy excels, where the weird-looking fork is fully justified. I have the tyres pumped to the maximum of 90psi. The traction on gravel surfaces sucked but I was more interested in feeling the detailed effect of the full suspension rather than the tyre plushness.
I was not disappointed. Riding over rough surface is very good indeed - you are aware that you are riding over bumps but they totally lose any harshness or jarring they would otherwise have. Taking corners at speed is improved since road holding over rough surface is better, as dangerous bouncing is eliminated. The suspension imparts almost exactly the same feel as soft Big Apple tyres. It is debatable whether a rigid frame with soft Big Apples isn't a better alternative; but with the Birdy you have the option of installing fast tyres such as the Stelvio or Kojak but still have the benefit of the soft ride.
The Birdy fork has a leading link suspension, meaning the moving link is in front, ie leads, the rigid fork member. (The Pacific Reach forks are a trailing link suspension.) The leading link curves up and comes back together over the wheel where the damped spring is located. The wheel is mounted on the leading link.
I can see the leading link vibrating rapidly with the road surface bumps when riding along. I haven't seen this movement on any other bike, probably because the range of motion is amplified by the lever arm length at the spring. This movement is a great visual feedback of the forks absorbing road vibration.
Pedalling rapidly with cadence > 100rpm, I noticed some minor bouncing of the rear elastomer. I might get the stiffer green elastomer in case I do fast road rides. The red is just right for normal sort of riding. Replacing the elastomer is dead simple requiring no tools - just pull it off with the rear swingarm latch unhooked, and push on the other one, a 10s job; you can carry the spare elastomer with you in the saddle bag and swap it at any time during any ride. In any case it would probably be a big help in trying to develop a very smooth pedalling style.
Steering/handling:
The steering responsiveness (often called twitchiness) is not what I expected. Small wheels due to their low mass and small size have low angular moment around the steering axis, and this, as well as the steering geometry and tyre profile, is responsible for a small wheeler's light, responsive steering. Not so the Birdy. It feels much more like a large-wheeled bike. Part of the explanation is that the steering assembly's metalworks are "far away" from the steering axis, and there is quite a lot of it, so the angular moment is increased over a simple fork. From examining the geometry (see later) the trail is also large, resulting in "heavier" steering. I'm not seeing this as a plus or a minus - it is just different.
The Birdy cannot be ridden hands-off *at all*. I haven't read about others' experience in this regard; but when I took my hands off the bars going at a reasonably fast speed, the front developed *instant* and violent shimmy. There is mention in the Australian manual that if there is shimmy while riding hands-on, the front suspension pivots have to be tightened, but that is not my case - the pivots are positively tight. No, this is plain hands-off shimmy as most bikes will develop under the right conditions. I have studied this phenomenon in some detail and all I can say is the Birdy is a very bad case. Riding at low speed where shimmy doesn't develop, resulted in the bike veering all over, completely uncontrollable. So no hands-off riding ever, period. Further discussion for the reason is under the Geometry heading.
The above does not impact on normal riding - I found the Birdy as stable and easily controllable as any other bike.
At this stage due to not having any other tyres to try, I can't say how much of the steering performance is due to tyre profile.
Gearing:
The 8sp gearing ranges from 30" to 87". Low end is adequate but I am used to higher gearing at the top end. For average riding it is adequate. I have a spare Schlumpf Speed Drive and may install this at a later date; time will tell.
The level is Alivio and I find it works quite as well as the XT stuff I have on the Swift and Yeah, albeit a bit louder. I may leave it at 8 speed as chains are cheap and I can have a couple of spare chains ready to swap to extend cassette life.
Braking:
The braking isn't stellar but it is adequate. At this stage I am blaming the pad quality; I use higher quality pads and expect braking to improve once I replace the pads with better ones. The pad adjustment may also be out. I had to re-set the rear pads after removing the back wheel (see Little Things) and they seem much better. But since I have developed the habit of not using the back brakes unless I really *have* to, the front brakes have to be perfect.
Braking from the leading link has the effect that the suspension is stretched open when braking. This works against the weight resting heavily on the front during braking, so there is very little, if any, diving during braking, unlike a telescopic suspension which can dive deeply when braking hard. Pacific Cycles make a point of this but don't say why this is good. I can think of 2 reasons: that during sudden sharp braking you don't have a sudden unexpected weight shift forwards, and also that during sustained braking, the suspension travel and operation is largely unaffected.
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.
Folding:
The Birdy back end folds along similar lines to the Brompton, but where the Brompton wheel ends up directly below the top tube necessitating that characteristic hump, the Birdy's rear swingarm rotates slightly sideways so the back wheel ends up just to the left of the top tube, allowing freedom of top tube design. The seatpost locks the back in place. The handlebars fold on the other side of the frame as the front wheel, effectively holding it in place, so it is a nice package when folded without bits swinging everywhere when trying to carry it. The 2 wheels and seatpost form a balanced tripod so it stands when folded.
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.
The front wheel folding is straightforward but also needs practise to get it smooth. I will need to optimise the position of the securing screw that holds the wheel in folded position - it seems too tight.
The front wheel assembly is rotated outwards to fold and rotated back in after the rear swingarm is folded. It stops against the rear derailer and sticks out rather far - another reason for looking at slimming down the derailer. A low profile XT Shadow might be a great choice; I have one on the Swift and might put the planned Ultegra on the Swift instead. The front hub is narrow-flanged and that also makes the folded size a little narrower.
Engineering/quality
General: The Birdy is a very well thought out design. From the standard equipment to the folding details to the optional equipment, everything just works. The build quality is good too; there are no blemishes, the welds are as good as these can get, the wheels are true and everything is straight. Seatpost doesn't slip and has handy laser-marked height indicators.
Cabling: The cables are routed internally lending a clean uncluttered look. The RD cable is pulled out to the rear when folding, and pushes back through to the front when unfolding. A frame screw that sticks out to the side promotes the pushing back of the cable; if the cable is located too wide, outside the reach of this screw, the cable may not be pushed back in properly and you get this large loop of cable that you have to push back manually. This happened to me the first time before I knew what that screw was for. That screw looks like an afterthought. When unfolding, you get this scraping sound and it took me a while to trace where it was coming from - it's that cable getting pushed back.
Stempost hinge: The stempost hinge just oozes Teutonic quality. I disassembled mine to replace the upper half of the stempost with the sports version. The hinge parts are machined from solid aluminium. The upper and lower hinge halves are identical so only one piece has to be mass-produced, and therefore they fit together as perfectly as manufacturing tolerances allow. Thin washers furnish rotating bearing surfaces. The hinge jaws have a tapered lip over which a matching V-shaped channel fits to clamp them together. The lever - also machined from solid - which operates the mechanism, folds flat against the hinge face, unlike the older design where the lever sticks straight up. The steel hinge axle has an eccentric portion for operating a rod going to the V-clamp at the front. There is one screw for adjusting clamp tension which is double positively retained - a lock nut plus the lock nut itself is a nylock. No chance of that combo working loose, ever. One screw adjusts the hinge bearing preload and 2 screws hold the lever in place on the axle. All those screws are fixed in place with blue Loctite. I think spring washers or something similar would be better. But those screws will not result in a loose hinge when unscrewing. When the hinge is closed there is zero detectable play. It is miles and miles in front of the Dahon hinge. Probably costs more as well - but for such a safety critical part there must be no skimping in design and quality.
Installed equipment:
Stempost: sport version, but originally it came with the comfort version. It is height adjustable with a brass button locking into holes which keeps the alignment right and is a safety backup in case the QR is loose.
Brake levers: Avid FR5; these are my favourite - light weight, good looks and low cost.
Brakes: Avid Single Digit 5 V-brakes
Rims: Alex DV15, 24 spoke
Rear Hub: Shimano Parallax 32 hole (laced to 24h rim), 3x lacing
Front hub: Birdy special with radial lacing; I like the look of this hub. It breathes quality. It is a narrow flange
hub to clear the fork members, with axle spacers to make it 100mm wide.
Tyres: Maxxis Birdy 355x37 with Kevlar puncture protection
Velo comfort saddle
Alivio 8sp gearing
Optional equipment:
Mudguards: I opted for permanently installed mudguards as Melbourne gets rain all year round. The installation instructions that came with them (produced by the original Australian importers) are as good as they get. Pity the supplied parts no longer exactly match the description. I had to mess around a bit to figure out exactly what went where. And I had a few screws left over afterwards.
The mudguards provide good coverage. The back one has a protective strip that it rests on when folded.
Rear rack: For general and commuting duty I got the folding Mono rack. Another quality item with exactly matching parts and bushes at the swivelling members.
The top mounting position is just forwards of the seatpost under the older frame's seatpost clamp. This caused problems with slipping seatposts so the new frame has a conventional clamp instead. Weirdly, I was supplied no mounting screw for this position.
The bottom mounting point is at the top of the swingarm. I had to remove the powder coating on the holes to allow the tightly-fitting bushes to go in.
Front lowrider racks: This is stock standard and easy to install. Nothing special to report except that they are very nicely thought out, as usual.
torsional/twist test:
This is one stiff frame. I do detect some flex in the handlepost and handlebar assembly when pulling sideways hard, but it is less than I expected. The monocogue frame's shape gives a lot of extra stiffness.
Annoying Little Things:
I can't remove the back wheel. Unhooking the brake noodle releases the brake arms but the acute angle of the pads with arms means one end of the pads move away from the rim much less than the other end, and it's just not enough. So to remove the back wheel I either have to deflate the tyre or undo a brake pad. Both options suck. Pumping the tyre afterwards maybe sucks less. The quick release acorn nut also snags on the derailer so that also has to be removed to remove the wheel. Hardly quick release.
Unhooking the front brake noodle is fiddly because it is upside down, interfering with itself.
No bottle cage fittings! What is it with so many folding bike makers - do they think riders don't need to drink?? I have a tool for installing rivnuts and have previously installed some on my Yeah with good success. The Birdy top tube may also get a pair but I will need to get expert advice on this.
The seat post is not long enough to form a balanced tripod with the mudguards installed, so it falls over. I will have to make an extension for it.
The new monocoque frame has less freedom for carrying the frame; the only handy place is in the triangle in front of the seat tube. The package is less balanced and the Birdy angles down when carrying it, but the strain on the hand is still OK.
The handlebars when folding down snag against the rear axle. It would be better if it can go past that point; I can do this by pushing the adjustable stempost all the way in but that is an extra folding step I'd like to avoid.
The cables at the handlebars are not great - I will have to neaten them up a bit. At the moment they are of unequal length.
Dirt isn't cream-colored - it is at the opposite end of the spectrum. The nice cream paint shows off every speck of dirt with great clarity.
Overall performance:
Is it as fast as my Swift? Not even close. But the Swift is way lighter, has better gearing and has speedy tyres installed, so hardly a fair comparison.
How about against the Yeah? I have been commuting with the Yeah for a few months now. Well, the Yeah's Primo Comets are faster, and it has ultra-wide gearing, so again not a good comparison. The Birdy as is, is perhaps 5% slower than the Yeah. But it is a whole lot nicer to ride due to the suspension. Then again, the Yeah cost me $100 (before upgrades) not $1530 (before upgrades).