Friday, August 17, 2007

da Vinci Tandems

I've been a serious cyclist for about 30 years now, with most of my miles on the road but significant mountain bike time several years ago. Up until a few years ago, I'd only ridden a tandem bicycle a few times; being a paid bike wrench for over 10 years as a youth gave me several opportunities. Only one ride was for more than 20 miles...and that was more than 25 years ago.

I bought this 26"-wheeled 1998 da Vinci Joint Venture early in 2004 and joined the tandem community. Since then, I've had about 4000 miles on two different da Vinci tandems with several different stokers, mostly my three children who are currently 8, 11, and 13 years old. The two adults I rode with were absolute novice cyclists, one being blind. Therefore, I have some experience with the da Vinci system, but not with an experienced adult stoker, and that might make a difference...see below. We sold that first tandem to a family on the East Coast and bought a custom-ordered 700c-wheeled da Vinci in early 2006.

I've discovered several things about the unique da Vinci drivetrain system: first, it's great with kids. They can coast when they want, push when they want, and when I'm really spinning, I don't pull their feet out of their shoes. We almost never ride with our cranks in sync...if we do, it's by chance. On the other hand, I've never missed it either. 99% of our climbing is done in the saddle. In fact, I only stand up to give the ol' butt a break occasionally. My stoker kids stand up all the time (sometimes too often) to take butt breaks. It seems like they always stop pedaling right at the steepest sections. But when it comes to ease of adaption to the whole tandem thing, the ICS (Independant Coasting System) gives us quite a bit of flexibility. It's at it's best with kids and inexperienced adults in the back. That's not to say it won't work for old-hand cyclists either; I just have no experience with it in that regard. As a captain, I love it. I wouldn't trade the ICS for anything.

The four chainrings are also very cool. Because the two crank chainrings are 34 teeth while the intermediate freewheels are about half that size, the whole middle jackshaft assembly spins twice as fast as the cranks. This means that the chainrings only need to be half the size of "normal" rings to give the same gearing. Very cool. This means that the 12-18-24-30 front chainrings are equal to 24-36-48-60 standard rings. Because they're so small, they never get caught up in while loading into the van, etc. They shift faster and easier than any triple I've ever ridden; this is to be expected, since they're actually Shimano HyperGlide cogs!! And the gear range is absolutely HUGE!! I'm currently running a 12x28 10-speed rear that gives us a 23 to 135 inch range from lowest to highest. You never need to worry about running out of top end...not with that 60x12 top gear.

And the 24 equivalent smallest ring, with a 28 or 30 big cog on the back end is plenty low for us. In fact, it's not the lack of low gears that bother me, it's my own steering problem keeping the bike straight and not wandering all over the road at speeds under 2.5 mph that limit our steep uphill creeping speed. Not many other 40-speed bikes out there either.

The 26" wheels we had on the first da Vinci are no big deal. I found a nice tire from Soma that's 1.1" wide and only 230 grams. At 110 PSI it rides very well. We're only 235-255 lbs depending on which kid stokes, so we're a very lightweight team. For heavier pairs, there's lots of quality 26" tires to choose from. The big knock on 26" road tandems is the lack of top end. Again, a 60x12 takes care of that just fine...

However, I prefer the 700c wheels we have on the latest tandem. There's plenty of tire selection and they just seem faster. I don't think they are; our average speed is about the same. I'm sure it's a psychological thing...

I expected some sort of weight penalty when I bought into the da Vinci drivetrain, and I'm sure there is one, but either bike still weighs almost exactly 35 lbs, which I think is reasonable. You can "lock-out" the ICS if you want, as well. To do so, you replace the two freewheels on the intermediate bottom bracket with a pair of fixed gears, thereby "locking" the two cranks together as with a traditional tandem. You still get the advantage of the smaller chainrings and 4-way front shifting. You can switch back and forth between ICS and fixed for the price of the time needed to exchange the cogs...about 20-30 minutes (with practice), I'd guess. According to the builder in Colorado (a great guy, by the way), he very rarely has to send out the parts to do this. Most teams like the ICS better than fixed, according to him.

Disadvantages? Well, that middle bottom bracket with the two single-speed freewheels on one side and four cogs on the other is more complicated than a normal tandem. I can foresee that a strong pair of experienced adults that are more evenly matched than me and my various stokers would not need some of the benefits I find so attractive, but for me, it's just the ticket.

By the way, I've found the Large-Small da Vinci sizing to be rather flexible. My usual stokers are my children at 13, 11, and 8 years old now. They all started at 10, 8, and 7 (youngest had to grow just a bit to fit; he was too short when we first got the tandem). They're currently 5'3", 4'8", and 3'10" tall respectively. They all fit on the bike fine, though I have to remove the shock-post and run a different saddle all the way down for the youngest.

The 13-year-old daughter is nice to ride with because of the time we spend together. Where else can an old guy spend so many hours with his teenage daughter? She's not all that strong and doesn't like to push very hard, though she doesn't mind longer 60+ mile rides if we take enough rest stops along the way. If the speed ever gets above about 24-25mph (usually on the down-hills) she starts calling for me to apply the brakes. A speed demon she's not.

The 11-year-old boy, on the other hand, is much faster both on the flats and especially the downhills. He doesn't talk much, but likes to put his helmet down and hammer. Our average speed is about 1-2mph higher than with the girl. He tells me "Faster, Dad, faster!!," on every downhill. His longest ride is a metric century (62.5 miles) and he was very tired at the end.

The 8-year-old is only just barely big enough to reach the pedals. He's a real fireplug up hills, though; I think his strength-to-weight ratio is higher than the other two. When he stands up on the pedals, I can really feel the turbo-boost kick in. His longest outing is 45 miles so far--he still talks about that ride and wants to do hills when we go out. A real chip off the old block, if I do say so myself.

My two adult stokers have been my wife (5'2") for a few rides and a blind gal (5'7" but heavier than I am) whom I took for a couple or three rides last summer. Neither of these women are experienced cyclists by any stretch of the imagination, but we were easily up and riding on the tandem with virtually no issues. The daVinci ICS makes this especially easy.

I can't say enough good things about the ICS system, especially if the captain is much more experienced than the stoker, as is the case with me. It allows me to ride the tandem almost as I would a single bike, without any of the worries about dragging the stokers legs (as was previously mentioned), concerns about coordination of coasting periods, or even being effected when the stoker wants to stand up and coast for a butt-break. Starting out is particularly easy with no whacked shins for either rider...ever. I ordered the new bike with daVinci's cool three-hole stoker cranks (no extra charge, by the way).

They makes a big difference, as they allow the stoker to have either 130, 150, or 170mm crank lengths just by moving the pedals from hole to hole. Because I tend to run a rather high cadence (usually from 90-110 rpm) I used to hear constant requests from the back seat to slow the feet down when on our older tandem (with fixed 170mm stoker cranks). Well, by using the 150mm option (where I normally have the stoker pedals mounted), it allows the stoker to run the same cadence as I but at a lower overall foot speed--no more complaints. Furthermore, I am able to use the 130mm super-short option with my youngest. This made all the difference in allowing him to fit the bike well.

Over time, as the stokers get more used to the faster cadence of the captain, you can simply move the pedals out to a more normal 170 mm length.

In our case, I'm about to try the 170mm with my daughter, though my wife (as infrequently as she rides) will likely prefer the 150mm forever. Since both boys are not long-of-leg yet, they'll stay at 150mm and 130mm for some time, I imagine. When a growth spurt hits, it's so easy to change to a different hole.

Our bike was "custom" ordered from da Vinci last spring, but with standard Large-Small sizing. We picked the exact color we wanted and I was able to spec every component. The front cockpit fits me exactly the same as my best-fitting single bike. I can move right from the one to the other without feeling even the slightest difference in fit.

This was important to me, though some captains don't mind (some even prefer) a different fit. Our frame was still made by hand by the same fellows that build da Vinci "custom" bikes; it's a pretty small shop. The biggest advantage of a custom builder would be for custom tube choices if you're an unusually light or very heavy team as well as the obvious custom sizing if needed, most especially for a longer top-tube in the rear cockpit. This can make a world of difference for stokers experienced on single-bikes. Because all of my stokers are small, the 28.3" rear top tube of the daVinci is fine.

I wanted a 57-58cm captain's top tube with a rear seat tube in the sub-45cm range. Their stock sizing fit this just fine so I didn't have to pay the custom size up-charge. I do have two different seatposts and attached saddles that I swap (15-second job) depending on who rides. I run the shock-post in the middle of it's height range for my daughter and wife and run it all the way down for my oldest boy, but I replace the post and seat for a set with very low profile for the littlest stoker.

Oh, and by the way, if you're set on another custom builder, daVinci does sell the jackshaft assembly separately, with a choice of steel, aluminum, or titanium shells to fit whatever frame material you prefer. Check out da Vinci Tandems for further info. However, I would not hesitate to recommend daVinci themselves for the frame. They know their product best and are an absolutely top-notch outfit. In fact, I know their painter does work for a number of other frame builders and I believe they do contract frame work as well, though I could be mistaken.

By the way, I've got an IRD 10-speed 12-28 mounted on the new da Vinci. It's the "10-speed Elite Road Conversion Cassette" type that allows for Campy spacing on a Shimano-compatible freehub. This is in conjunction with a 9-speed SRAM chain, as I have not found any 10-speed chains long enough for the da Vinci (which uses 124 links) and didn't want to purchase two and splice. I'm leery of the strength of a spliced chain. I suppose I could use two master links, but haven't gone to the trouble yet.

The only problem we've had is that two of the spacers between the cogs were too thin for the 9-speed chain. This caused the chain to rub on the next largest cog at times and ghost-shift on to it under load on occasion. I firmly believe this is caused by the 9-speed chain and has nothing to do with the cassette itself. I solved it by replacing the two spacers with slightly thicker ones. The new spacers were thicker by .05 mm (yes, that's 1/2 of 1/10 of a millimeter). Not very much difference in thickness, I know, but it's enough that we've not had a single problem in the 3400 miles we've put on the bike.

I share some folks concerns about carrier-mounted cogs, which most high-end cassettes use to save weight. However, I believe that is most relevant on tandems using the larger rear cog sizes (like 32 or 34) and with strong full-sized stokers...especially off-road. Our cassette has a maximum of 28 teeth, we ride on the road exclusively, and my largest regular stoker just barely tips 90 pounds. Needless to say, we're not a powerhouse team. If this is a concern, you can use the Comp versions of the IRD; they don't use carriers for the larger cogs.

Be aware that daVinci's ICS will not "make" a team faster in and of itself. Fast teams are those with two strong riders who cooperate well with each other; the ICS's advantages lie in those times when the two of you purposely do not want to cooperate, like when one wants to take a break from pedaling and the other does not. Or when one rider is screwing around getting a cleat back in the pedal and you still need to get across the intersection. This happens to us all the time.

On the other hand, I do not believe that the ICS will slow down a strong coordinated team either (other than the pound or so weight penalty the jackshaft imposes). The ICS really shines in those circumstances like mine (small kids and/or non-cyclist spouse). If we didn't have a daVinci, I'm sure we wouldn't ride at all. The single bike is plenty fun, but the tandem is at least twice as much fun.

And yes, there's a real temptation for the weaker rider (usually the
stoker) to allow the stronger rider (usually the captain) to rickshaw them about. I can attest to this mightily as my kids have learned just how fast they have to pedal to keep the jackshaft's freewheel pawls from ratcheting (which I could easily hear), but to not really add much to the propulsion effort.

The only complaint I have about the whole rickshaw issue is when we're riding with friends. For example, they usually cruise at about 15-16mph over a 50-60 mile relatively flat ride. On a single bike, I have no problem with 18-19mph in the front pulling them all. But on the tandem, with one of the kids on the back, I really struggle to keep a steady 14-15mph. It's close enough to the speed of our friends; we can almost hang, but not quite. We get very tired of pulling into every rest stop just as they all are ready to take off again, but I guess it doesn't bother my stoker kids enough to get them to crank just a bit harder.

On the other hand, there are no kids on these rides other than my stokers and we do get to spend an awful lot of time talking just between the two of us. I guess in the long run, I don't even mind playing the rickshaw driver all that much. We're out and having fun together, we enjoy the nature, and I get one hell of a workout, which is what I wanted all along...

Tuesday, August 14, 2007

Tippin' the Saddle

I've mentioned before that I wasn't entirely satisfied with the stock saddle angle on the nifty leather Vespa GTV250ie seat. I felt that the front of the saddle didn't give enough support while braking; my weight would naturally shift forward and I tended to slide off the front of the seat unless I braced my feet against the leg shield. I decided that something had to be done. Here's a shot of the stock angle. Notice the nose is slightly lower than the tail and that the hinge under the nose cannot be seen.

In these two photos, you can see the four silver bolts that hold the saddle to it's plastic frame-plate. In the second shot, the lower right bolt has already been removed. These bolts require a 4mm Allen wrench (hex key). Once the bolts are removed, the saddle and it's rear chrome-plastic supports can easily be lifted off. Keep in mind that the rear bolts should be reinstalled without spacers or modification, unless you also want to raise the rear of the saddle. This might be the case, if you've got longer legs, but wasn't what I was personally after.

I decided that it would be a simple matter to install a pair of spacers under the nose of the saddle along with the necessary longer bolts. Here's a photo of the original bolts (the short one to the far right) along with 50mm and 40mm length potential replacements. Specifically, these are all 6mm in diameter with 1mm thread pitch, by the way. I wasn't sure which would give me a comfortable angle, and not wanting to return to the hardware store, I bought both sizes; you can never have too many bolts in the spair-parts stock, ya' know. As it turns out, the 40mm worked best; the spacers needed to support the 50mm bolts raised the nose of the saddle too much. I'll go into some details on that a bit later.

Here's a photo of the 1/2" outside diameter x 3/4" long nylon spacers (those of you with good eyes will notice that there's actually one 1/2" spacer and one 1/4" spacer together) and three 3/4" washers I used. The lowest washer lies next to the head of the bolt, just as on the original setup. The other two washers sandwich the spacers and sit between the saddle itself and the plastic frame/pet-carrier lid. The re-installation of the saddle with the longer bolts and spacers required one more hand than God gave me; I enlisted the help of my oldest boy to hold the saddle frame steady while I positioned all the loose pieces.

Once the bolts were tightened and the frame/carrier lid closed, the saddle now has a definitely higher nose. Notice how the front hinge is easily seen under the bottom of the saddle now. At first, I installed the 50mm bolts and appropriate 1" of spacers. That turned out to be a bit much. Yes, the front of the saddle was raised nicely, but so was the middle portion, where my thighs sit. I found it uncomfortable--the constant pressure on my thighs, that is. I felt like I was sitting on a bench with my butt hanging slightly off the back. Not pleasant.

A week went by and I grew sure that I needed less tilt. I again had the boy hold the saddle frame while I removed 1/4" of spacer and slid in the 40mm bolts. The resulting tilt was ever-so-slightly less, but seems to make all the difference.

After riding this setup for six weeks now, I can report it's a vast improvement over both the stock angle as well as my first attempt with it's too-high angle. I no longer slide forward on the saddle, nor is the pressure on my thighs uncomfortable.

The GTV saddle's angle has now reached a happy equilibrium.