Wednesday, October 25, 2017

Titanium tandem by Waltly

I've already documented my previous tandem projects here before. The primary use of the tandems is for family bike rides with the kids. Two years ago I replaced my old Bike Friday tandem with the Experia tandem and have been happy with the results. Heather has still been using the modified Raleigh I acquired several years ago, but it's very heavy and never has been a very good fit for her. Now that the kids are both tall enough to ride a full sized tandem, it is time to consider replacing the Raleigh. The primary challenge is getting a good fit for a tandem pilot who rides a 50 cm road bike, and with the potential to fit a stoker who is taller (our 13 year old is already taller than her mom). The M/S sized tandem by Cannondale comes close, but is still a little big. So, getting a good fit would probably require a custom frame. In order to keep costs down (the goal was to build the complete tandem for a price close a stock Cannondale tandem), I went with a titanium frame made by Waltly in Xiamen, China.

I've been following Waltly for a few years as I've considered our options when upgrading tandems, along with Titanproduct and XACD. As I understand it, all three of them build OEM frames for various bike companies, and well as offering custom frames direct to consumer. All of them can be found on Alibaba or Aliexpress, along with a few others that I'm less familiar with. Just during the last few months, Waltly has re-done their web site to be by far the most professional looking I've seen, including a nice form to fill out for requesting a quote.

I initially contacted Waltly through a link on their web page and got a response the same day from Amy. Her English is pretty good, and she generally responded to my mails quickly given the 13 hour time difference. I sent her a picture of a frame with similar geometry and specified all of the key dimensions. Waltly's process is to quote a price, and then to ask for 50% of the cost to be paid up front before their engineers start making detailed drawings.

I made two key choices that dictated a number of the other details. One was the the Boost through axle standard. This means 148x12 rear and 110x15 front axles. This is an MTB standard that is relatively new, but I think makes a lot of sense for tandems, especially the wider front wheel (rear hubs wider than 148 have been used on tandems before). I did this because I want durable wheels and because I hope the standard becomes sufficiently common (for MTBs if not for tandems) that there will be many stock wheel options available in the future. The second choice I made was to try as much as possible to replicate the geometry of Heather's road bike on the front end of the tandem, but simultaneously eliminate the toe overlap that her road bike suffers from, because I think toe overlap is much more important to avoid on a tandem. Both of these choices led to the decision to have Waltly make a custom fork to go with the frame because no stock carbon tandem forks currently offer the wider spacing, and because I needed a higher than usual fork offset. My original proposal was parallel 73 degree seat and head tubes, but this was putting the front wheel far too close to the front bottom bracket. Eventually I settled on a 71 degree head tube. While this may make the handling a little more sluggish, it is frequently done on smaller frames, including Cannondale's smallest road tandem. With the slacker head tube it is possible to extend the fork offset to 55 mm while still having a reasonable amount of trail. I asked Waltly to allow for 700C tires between 32 mm and 40 mm width, with the idea that I would have the option of 32mm road tires or 40mm gravel tires. The distance between front and rear bottom brackets was determined by two considerations. First, I want the option of a Gates belt drive in the future, and second I want the spacing as far apart as possible to accommodate taller stokers, so I chose the largest spacing that will support a Gates drive.

After making my initial specifications and paying the deposit, we went through several iterations of drawings before I decided they were ready. Much of this had to do with trying to increase the distance between front bottom bracket and front axle because of the toe overlap problem. Now that I've done this I realize I could probably have used something like Bike CAD to figure that out beforehand and get through the process much faster, but Amy was patient and responsive with my continual tweaks. The final drawings looked like this:

In addition to the frame and fork, I asked for an adjustable stoker stem. About 6 weeks after I approved the drawings, Amy sent me an email with a set of detailed photos of the finished product.

When I gave my approval based on the photos, the frame, fork and stem were shipped by DHL, and arrived in the US just 3 days later. The build quality of the frame looked great. I'm not an expert on titanium welding, but the welds on the finished frame all look very neat. As I got started on the build I discovered that Waltly had made a mistake on the stoker stem, building it for a 28.6 mm diameter seatpost rather than the 31.6 mm diameter I had specified. I sent Amy a photo, she consulted with the engineers and builders, and they agreed that they had made a mistake. They created a new stem as I had specified and sent it to me at no charge. I commend Waltly for their responsiveness in fixing their error.

Before completing the build, I added some yellow and green paint using stencils. I love the look of titanium, but wanted to add a little more color to go with the yellow and green trim I was adding to the bike. I think this is a great solution for customizing a titanium frame that's relatively easy to do and still allows the titanium color to show through. The saddles don't match the rest of the scheme as well because they happened to be preferred saddles from previous bikes.

I built the bike up using a SRAM Rival drivetrain with mechanical disc brakes so that I could add bar-top auxiliary brake levers.

I used Sugino XD cranks front and rear. We wanted a low gearing range, and don't particularly need high end gears because we don't go that fast, so I used what's currently being referred to as "subcompact" gearing: 46/30 chainrings with 11-32 cassette. This is of course not something SRAM designed their 2x11 road groups for, and I found I had some difficulty getting the front derailleur to avoid overshifting and dropping the chain to the outside. The Sugino cranks are designed as a triple, so I installed a chain guard in the position of the outer chainring, and it seems to have solved the problem for now.

The one mistake I made in my design was forgetting to specify a front derailleur mount, which was my original intention. There are many clamp-on front derailleurs available, so it wasn't a big deal, except for the fact that the location of the water bottle mounts on the rear seat tube have limited the range of movement available to me for vertical placement of the front derailleur. So far I have been able to get things working. If I were to do it again, I would want either a derailleur mount with a wide vertical range, or put the bottle cage mount in a different location.

For the captain's pedals, I happened to already have a pair of old Shimano M324 pedals. To go with the yellow color theme, I took them apart and painted the main body with the same yellow paint I used elsewhere, and did the same on the platform pedals I currently have installed on the rear. I also found some gold anodized chainrings for the timing chain. They were originally intended for BMX bikes, so they required a 1/8" timing chain.

The wheels were custom built by, using Hope Pro 4 hubs and Velocity Chukker rims. When we discovered that they offered colored spokes, we couldn't resist paying a little extra to get yellow spokes, which turned out to match the existing yellow trim very well. Currently the wheels have Kenda Happy Medium 40mm tires installed.

I included mounts for rear racks in the design. I built the bike with 203mm discs front and rear for maximum braking power. Waltly only had post mounts available for 160 mm rear rotors, so I used a 160-203 mm adapter on the rear brakes. The fork had IS mounts.

Even with the 700x40C tires, there is plenty of clearance. I tried inserting a MTB wheel in the frame with 27.5x2.1 tires and they appear to fit, so that will be an option we consider in the future for riding gravel roads.

Overall I had a great experience working with Waltly and would definitely do it again.

Sunday, March 26, 2017

Garmin Varia mount for Topeak racks

Last year I finally upgraded from the traditional style bike speedometer (with wires and magnets) I had been using for over a decade to a GPS-based computer, the Garmin Edge 25. Compared to the larger and more expensive ones, it's pretty basic, but it does the things I need, and it also supports external sensors. Over the winter I acquired my first external sensor: the Garmin Varia rearview radar. It allows a rider to monitor the location of vehicles approaching from behind within about 300 feet, and also functions as a tail light that gets brighter and blinks faster as cars approach. I really like it, and I think it's especially useful here in west Texas, where there are a lot of narrow roads with high speed limits, and enough wind to make it sometimes difficult to hear vehicles approaching from behind.

The Varia uses a Garmin quarter-turn mount, and comes with a seatpost version of the mount. Two of my bikes have Topeak rear luggage racks that seem to me better mount points for the Varia than the seatpost. The Topea racks have a bracket on the rear for attaching a reflector (included with the rack) that looks like this:

This seems like an ideal mount point for the Varia, but of course nobody makes a Garmin mount that is designed to attach to something like that, so I designed one. The starting point for the design was the Garmin mount insert used by K-Edge:

K-Edge makes a number of different after-market mounts, all of which use the same plastic insert. I could have tried to replicate this myself, but as I've discovered from buying a less expensive after-market mount, a secure attachment requires getting the dimensions of the interface points right, and K-Edge have clearly already done so, so for $5 I can leverage their design and just focus on the interface with the Topeak rack. As shown in the picture, the insert comes with 2 M3 angle-head screws which are designed to screw into the metal mount. In this case, I needed a bracket that was thick enough to accommodate the screws and hold corresponding M3 nuts on the back side.

The design I came up with is this T-shaped bracket, which I had 3D printed by Shapeways.

It is 4 mm thick. The angled rack attachment holes are for angle-head M5 screws. To attach this to the rack requires 3 angle-head M5 screws and corresponding nuts. I used 12 mm screws and nylon-insert lock nuts, but plain nuts will probably work fine. Two M3 nuts are needed because they are not included with the K-Edge mount insert.

Bracket installation begins with inserting the M3 nuts into their corresponding recessed holes on the back of the bracket.

The bracket is then attached to the rack with the 3 bolts.

The K-Edge insert is attached to the bracket using the M3 screws. This is done after the bracket is already attached to the rack because the K-Edge insert slightly overlaps the top M5 screw.

At this point, the Varia can be attached.

Wednesday, September 21, 2016

3D printed cable guide for X-Peria tandem fork

In my original entry about the X-Peria tandem, I noted that the fork did not have an obvious method for routing the cable to the disc brake, but that there was a screw hole on the inside of the left fork blade. My solution was a 3D-printed bracket designed to attach to the screw hole and reach around behind the fork blade where the cable would pass through it.

I used OpenSCAD, a free CAD software to create the design. This is an OpenSCAD rendering:

Note that the hole for the screw mount has a flared shape to accommodate an angle-head screw, so as to minimize the amount the screw protrudes into the space inside the fork. The OpenSCAD source code for this design is below:

guidelength = 20;
width = 15;
cablesize = 5;
thickness = 1.5;
screwhole = 5;
len1 = 5;
len2 = 5;
th2 = 2.5;
angle = 70;
bendradius = 10;


r2 = screwhole/2+4;
cr = cablesize/2;
ofs = width/2-r2;
d = (guidelength-width)/2;

rotate(angle) {
difference () {
    union () {
        // cable guide outer
        translate([0, 0, -d]) cylinder(guidelength, r=cr+thickness);

        // connector section 1
        translate([0, -th2/2, 0]) cube([len1, th2, width]);

        // connector bend
        translate([len1, -th2/2-bendradius, 0]) rotate([0, 0, 90])
        rotate_extrude(angle=-angle) {
            translate([bendradius, 0, 0]) square([th2, width]);

    // cable guide hole
    translate([0, 0, -d-0.01]) cylinder(guidelength+0.02, r=cr);

// connector section 2
translate([len1, -bendradius-th2/2, 0]) rotate([0, 0, -angle])
translate([len2, bendradius+th2/2, width/2]) rotate([90, 0, 0])
translate([0, 0, -th2/2])
    difference() {
        hull() {
            cylinder(th2, r=r2);
            translate([-len2/2, -ofs, 0]) cylinder(th2, r=r2);
            translate([-len2/2, ofs, 0]) cylinder(th2, r=r2);
            translate([-len2-1, -width/2, 0]) cube([1, width, th2]);
        translate([-len2-r2, -width/2-0.05, -0.05]) cube([r2, width+0.1, th2+0.1]);

        // Screw hole
        translate([0, 0, -0.05]) cylinder(th2+0.1, r=screwhole/2);

        // flared hold for angle head screw
        translate([0, 0, -1]) cylinder(screwhole/2, screwhole, screwhole/2);

The part was printed in white ABS plastic by Shapeways. I have produced other parts using Shapeways before and have found the results to be very high quality. A couple of weeks after placing my order, the cable guide arrived.

The hole for the cable was actually just a little too tight for the cable to fit, so I widened it slightly with a drill. This is actually the second version of the design, the result of some changes I made to my first design after I had a chance to test it on the bike. Here is the final product, installed on the bike.

Monday, September 19, 2016

Custom mounts for Topeak Explorer rack

I have the Topeak Explorer rack on two of my bikes, the Raleigh Olympian and the X-Peria tandem. This rack comes with adjustable steel rails that attach to the upper part of the rack.

These rails are designed to be bent to fit the particular frame on which they are mounted, and can fit nearly any frame, provided there is a set of mount points to attach to. In the case of both the Raleigh and X-Peria tandem, there are no upper eyelets, so in both cases I made my own mounts to attach to other available mount points.

In the case of the Raleigh frame, I used the rear brake mount. The custom mount was made from 1/8" (3.175 mm) aluminum sheet. Because I intended for the mount to be specific to this bike and therefore not adjustable, I cut out the shape I had in mind in paper first to ensure that all of the holes were in the right place. I cut the aluminum to the shape I wanted with a circular saw (a fairly crude tool for this sort of job, but it's what I had available and it cuts the aluminum of that thickness relatively easily). I drilled the holes, and used a sander to smooth all of the edges. Bending the aluminum sheet to the desired shape takes a lot of leverage, so I used the holes to attach the ends of the cut out piece to some long pieces of scrap wood. I was eventually able to get the mount into the shape I wanted, but the aluminum got pretty scratched up in the process, so I did some more sanding on the finished product to remove all of the scratches, leaving it with a brushed look.

Here's the whole rack, held perfectly level by the custom mount.

The X-Peria tandem does not have dedicated upper rack mounts, nor does it have a caliper brake mount in the rear, since it is a disc brake frame. As I noted in my original blog about the tandem, there is a seatstay bridge where one would expect a caliper brake mount, which has a threaded hole underneath, possibly for mounting a fender. I used the same method and gauge of sheet aluminum to create the fender mount for the X-Peria. Since I happened to have some white paint close to the color of the bike, I painted this one.

The threaded hole on the frame is for an M4 screw (similar to what is used on water bottle mounts), but there is not a lot of clearance, so instead of a standard water bottle bolt (below left), I used an angle head screw (right).

Combined with a hole to match the shape, the screw protrudes only a minimal amount, leaving more tire clearance.

This is what the finished product looks like, installed.

Wednesday, August 24, 2016

MC286 with SRAM 1x

SRAM has been pushing their 1x groups for road use lately, and has taken it a step further with the recent release of the SRAM Apex 1x group. One important aspect of the new group for anyone trying to build a cyclocross bike on a budget was the release of a new version of the PG-1130 cassette: a 11-42 cassette that is compatible with the 10-speed freehub standard that is found on older road wheels and is still in use on MTB wheels.

At the time I was buying the frames and parts for these bikes, I noted in my post about components that my choice to buy Mavic's budget-oriented Crossride MTB wheels forced me to use only 10 of the 11 cogs in the Shimano 105 cassette because MTB wheels are still using the 10-speed freehub standard. Building a cyclocross bike with the Crossride wheels and SRAM 1x at the time would have required using an XD cassette and buying the XD driver that is available for this particular Mavic hub (which retails for $100). The ability to use a wide range cassette that is compatible with the built-in freehub on stock MTB wheels reduces the cost of a SRAM 1x build significantly.

Since Heather likes the SRAM shifters on her road bike better than Shimano, this summer I decided to convert her cyclocross bike to SRAM 1x so I could use the Shimano 105 group on another bike. For the conversion, I used SRAM Rival brake levers and right shifter, Rival crankset with 42t chainring, Apex derailleur, and the aforementioned PG-1130 cassette.

The original setup consisted of a 50-34 crankset and 11-32 cassette. The new setup results in a lowest gear (42/42 for a 1:1 gear ratio) that is slightly lower than the original 34/32. The highest gear, a 42/11, is approximately equivalent to a 50/13, meaning that the new setup replicates the original setup minus the highest gear of 50/12 (since the 11 tooth cog was never installed). Having ridden my cyclocross bike for over a year, I don't believe I've ever used the 50/12, so I don't believe this is particularly important for the type of riding we do (or most riders do) on this kind of bike.

Gearing range is clearly not a problem, but the other possible caveat to a 1x conversion is gear spacing. I did some spreadsheet analysis of the gear ratios on the original 2x10 setup compared to the 1x11 setup and found that the difference is not that large. The 12-32 cassette has a maximum jump in gear ratios of nearly 16%, between the 19 and 22 tooth cogs. The 11-42 has a maximum jump of 18%, between the 13 and 15 tooth cogs. Perhaps more importantly, that larger jump is closer to the edge of the range in less used gears, where the largest jump was previously in the middle. The difference should not be particularly noticeable to most riders.

Based on our experience so far, I think the SRAM 1x groups are an excellent choice for cyclocross and gravel bikes. It's not surprising to see so many bikes coming out with this setup from the bike bike brands.

Sunday, December 20, 2015

X-Peria 5200 Tandem

It's now been over 5 years since I bought the Bike Friday Family Tandem. I have no regrets about it, but I'm ready for something new. I eventually gave up on the conversion to drop handlebars, because even with the various tweaks I made, shifting never worked quite as well as the original shifters did, so I put the original flat handlebars back earlier this year. The telescoping seatpost was important when my kids were shorter, but now the kids are tall enough to fit some full size tandem frames. I also found the Bike Friday to be fairly heavy (around 50 pounds) and I felt that the frame lacked stiffness, a feature that can be partly attributed to its geometry.

My requirements for a new tandem were:
  • Full size frame that's a reasonable weight.
  • $1500 or less. I don't know how long my kids are going to be interested in riding with me on the tandem, so I want to avoid putting too much money into something that might not be used much.
  • Fit a tall rider (me) in front and a shorter rider in the rear.
The Cannondale Road Tandem 2 comes in over $3000, and newer used ones routinely sell on eBay for nearly 70-80% of that. One other option is the KHS Milano, which has a list price of $2000 for an aluminum road tandem with disc brakes and Shimano Tiagra. The only way to get a good road tandem for less than that is to buy used. The problem with most older used tandems (with the notable exception of Cannondales) is that most 1990s and early 2000s tandems had level top tubes that work great for two riders of similar size but would be much to tall in the back for me. Sloping top tubes that can accommodate a larger height differential have become much more common on tandems in the last 10 years, but many of those newer tandems are usually out of my price range. There is a steady stream of used tandems on eBay, but the number of older used road tandems of the appropriate size and price range turns out to be relatively small, and the number of those sellers willing to ship a tandem (a necessity when you live in west Texas) is smaller still.

After searching eBay for some time, I eventually stumbled onto a listing for the X-Peria 5200 tandem frame, which was being offered new for somewhere around $500 by the French online bike shop CR2V. The frame is offered in two sizes, the larger of which is pretty close to the correct measurements for me. At this price I decided I could build my own for something close to my target price. CR2V has a number of eBay listings for frames that they offer to ship internationally, but there are more options available directly on their web site, which is how I eventually ordered my frame. The site is completely in French, so I had to navigate it with the help of Google translate at times. It turns out the $500 price tag included the eccentric bottom bracket but did not include a fork, however they do offer a package with BB, fork and headset for about $90 more. Shipping to the USA is not available as part of the normal checkout process on their site, but after some emails back and forth with them, they offered to ship to the USA for an additional 100 EUR. Total cost was just over 700 USD including shipping. When I placed the order, they had just run out of stock, so there was some delay while a new frame was ordered from the manufacturer, which took nearly 3 weeks. After the frame was finally shipped, it was only a little more than a week until the frame arrived.

At first glance, the frame has a lot in common with a Cannondale, but a closer inspection shows that the welds don't look nearly as clean as can be expected on a Cannondale. I would compare it to the quality of frame one typically sees on lower end aluminum road bikes in a local bike shop. While X-Peria is clearly a French company, it's not clear to me whether the frames are made in France or somewhere in Asia. Regardless, as long as the frame holds up, it suits my purposes just fine. The combined weight of frame, fork, headset and eccentric bottom bracket is about 9 pounds.

The specifications on X-Peria's web site do not specify whether the fork is aluminum or steel, but I believe it is steel because the fork blades look too small to be aluminum, and the junction of the steerer tube (which is clearly aluminum) and fork crown suggests an interface between two different metals rather than a single continuous piece of metal.

The frame has post mounts for 180 mm brake discs front and rear. I used 203 mm brake discs with 180-203 Shimano adapters and Shimano BR-R317 cable-actuated brakes.

The rear dropout spacing is 135 mm, so it's compatible with 29er MTB wheels. Nearly all higher end 29ers now use through axles, so most quick-release 29er disc brake wheels are targeted at less expensive bikes, which gave me a number of good options at a reasonable price, particularly since cost and durability were higher priorities for me than weight. I ended up with these 32-spoke WTB SX19 wheels. 36 and 40 spoke wheels are common on tandems, but it's difficult to find pre-built wheels with more than 32, and I think these will be sufficient for me. The tires shown here are 37 mm Continental Contact, though their actual width appears to be a bit less than 37 mm. Both wheels fit in the frame easily. The fork could easily fit 40 mm tires or bigger, but the rear doesn't have much extra space.

For the drivetrain, I bought used Shimano Ultegra 6603 shifters (3x10 speed) and a 9-speed Shimano Deore XT rear derailleur. (Shimano 10-speed road shifters will work with 9-speed MTB derailleurs but not 10-speed MTB derailleurs). I set it up with single-side drive, which means I'm only using 2 of the front shift positions, but I have the option to use a triple in the future. The reasons for single side drive were keeping cost down (I already had one of the cranks I needed) and size options. I am using a 180 mm front crank and 165 mm rear. When the kids get a bit taller, I will probably eventually go to 170 rear and 175 front with regular tandem cranks.

The rear crank is made by Origin8. It's inexpensive and also comes in even shorter lengths, an ideal option for someone setting up a single-side drive tandem for a short stoker. I used 39 tooth chainrings for the timing chain because I already had one in that size. The inner two rings pictured here are 48 and 32 tooth rings, which have been paired with a 11-32 10 speed cassette. This gives a gearing range just slightly lower than a 50/34 compact road crankset with similar cassette. The 1:1 ratio of the low gear should be enough for moderate climbs and the high end is more than enough for how I anticipate using the bike.

The finished bike comes in at 38 pounds as pictured, a full 12 pounds lighter than the Bike Friday. I don't have an exact cost total, but it came in somewhere between $1600 and $1700. It is probably possible to build one of these in a similar way with true tandem cranks (such as Sugino XD) for under $1800.

The frame has a few quirks that I didn't expect. None of them are serious flaws, but things that might have been helpful to know about in advance:
  • shift cables are routed for a top-pull front derailleur. As far as I know, this means most road derailleurs won't work.
  • only 2 water bottle cage mounts.
  • no guide for brake cables on the fork, as would be expected on a disc brake fork.
  • There are double threaded eyelets on the rear dropouts, but no rack eyelets at the top of the seatstays. There is, however, a threaded hole underneath the seatstay bridge and chainstay bridge, which is presumably for mounting a fender. I'm working on a custom bracket for attching a rack I have that uses this hole.