In these two photos you can see from the fender clearance, how much space is gained by going to 650b; the fenders were set up for the stock 700c wheels.
Another change we experienced after swapping wheels was lower gearing. Although this was not our primary goal in this project, we were pleasantly surprised to find that the lowest, climbing gear of this particular bike went from about 21" to about 19 or 20" (depending on tire size). By the way, to understand what this means, take a look at our article on tandem gearing.
This shift to lower gearing was welcome. So welcome in fact, that we began to think about shifting the climbing gear down even further. We are not getting any younger or stronger and the hills are not getting any flatter. So lower climbing gears are welcome.
To make a long story short, in addition to the wheel change, we also changed the front chain ring from 55t to 50t. This required a change in the drive belt size from 118t to 115t. The resulting primary gear ratio of 2.5 is still within Rohloff guidelines for a tandem and yielded a low, climbing gear of about 18", a gear that feels much better to us on the steeper local hills.
You can see there is ok tire clearance with the fork, but going much bigger, tire-wise, would be limiting. We were able to cram in a 700x35c tire, with fenders, but that's as far as we could go.
TANDEM Diversity
The bike is a medium Co-Motion Carrera Rohloff. The above photo illustrates the bike as it came equipped from Co-Motion, specifically with 700c wheels, built on Velocity Dyad rims. Here, it is fitted with Panaracer Pasela PT 700x32c tires.
In the above photo you can see what the bike looks like with the 650b wheels mounted. These are built on Velocity Cliffhanger rims and at the moment have Panaracer Pasela PT 650x42b tires mounted. I left the fenders set where they were for the 700c wheels, so you can see how much more room was made available by the wheel size swap.
Here we are with the 42 mm tires and a fender. Good clearance. We could go with a bit bigger tire, but we are liking the ride of the 42's. We also tested some Rene Herse 650x38b and they felt great as well.
Refining the concept of adventure tandem?
Our good friend Andy Speier, a frequent touring companion, an expert and experienced mechanic, and a tandem captain with many years under his belt, has for years now been extolling the virtues of 650b wheels on tandems (well, on bikes in general, actually). Much of the time his comments went in one ear and out the other, in my case. However, a few years ago his fervor for 650b wheels was heeded by a couple, mutual friends, who had purchased a Co-Motion Primera from us and wanted to be able to use higher volume, lower pressure tires. The Primera is pretty limited when it comes to using significantly larger tires than the 700x28c tires that come standard.
Anyway, when this couple tried out 650b wheels on their Primera, they reported back to us that the ride was great and the project was a success, using 650x42b tires; they have stuck with that arrangement on a permanent basis.
Next, another couple, in this instance having purchased a Co-Motion Carrera from us, reported a desire to have the ability to do more loaded touring, even with the chance of the occasional gravel stretch. These folks, also mutual friends with Andy and his stoker, acquired a pair of 650b wheels and installed them on their Carrera. They've never looked back, reporting that the ride is good, the world of loaded touring on their otherwise light touring engineered tandem is more open to them, and they can use the larger volume, lower pressure tires that afford them a more diverse riding experience. When I say loaded touring, keep in mind they are heeding the advice of Co-Motion to limit the weight placed on the carbon fork with a front cargo load; they place most of the weight on a rear rack, with only a few pounds on the front. They tell us the handling still remains good and they feel more confident on the sturdier wheels (they had possibly damaged their original Rolf wheels by overloading them). They do keep their Rolf wheels for recreational riding between tours.
Well, about this time we decided to start paying attention to the experiences reported by these couples. We thought, what if we could put 650b wheels on a Co-Motion Carrera Rohloff Co-Pilot? Would the result be a truly versatile adventure tandem capable of serving well no matter the terrain and road surface?
We've done just that and we think we've hit the jackpot when it comes to tandem diversity (get it?)! Let me tell you the story.....
So, we've been riding this new setup for a few hundred miles now, on a variety of surfaces, mostly paved roads but also some gravel trails. I think it's fair to take a step back for assessment: what exactly were we out to do and what exactly has been achieved?
First let me say: we like this so much we may never go back. Now, for some details...
Our basic intent was to be able to ride higher volume, lower pressure tires than we could with the stock Carrera wheels. Check. We're doing fine with 42 mm tires, running at 75 psi. The ride is good on the trails and road surfaces in our area. And like much of the world, our infrastructure as concerns roads is degrading over time and not seeing much improvement from any infrastructure spending, as in none. Most of our local roads are chip sealed, badly in need of repair, rough, and full of pot holes. Our trails range from very packed limestone to stretches of fresh gravel. The 42 mm tires are doing well at giving us a smooth and comfortable ride on these surfaces - better than the 700x35c tires at 90 psi we usually rode up to now. Furthermore, there is great clearance for fenders with the 42s.
At first I was skeptical about 650b being a wheel size that was too odd, with parts hard to get. Not so, apparently. It has become a main stream wheel size and tires and tubes and spokes, etc are easy to find (you can use 700c tubes in a 650b tire).
Next, we were skeptical about the smaller wheel size based on prior experience with 20" and 26" wheels on tandems. Our experience with these smaller wheels was that they were lighter and climbed ok, but required higher energy input on flats to maintain speed, compared to full sized wheels. We worried we'd feel the same impediment with 650b. Didn't happen. In fact, our average speed on our daily ride has actually gone up about 1 mph since the switch. We assume this is because of the lower rolling resistance of the high volume, low pressure tires. And at the recent NW Tandem Rally we felt we could keep up with other riders just fine, even with the smaller wheels, bigger tires, and lower psi.
As an aside, I was amused by how many captains stopped by our booth at the rally, where we had this tandem on display, to assure me that skinny, high pressure tires roll better than fatter, lower pressure ones, even though this fallacy has been debunked by good scientific methods.
We also were concerned about the bike being lower to the ground and therefore risking pedal strikes on corners. We have not hit a pedal, though I admit we are being consciously aware of the need to keep the inside pedals up on tight corners. However, the lower to the ground thing (by almost an inch!), has been a real boon when it comes to getting on and off the tandem. Remember back to that part about we're not getting any younger? Well, part of that aging has been an increase in the challenge of mounting and dismounting the bike. Moving the top tube closer to the ground has been great! And one could argue it has made a safer bike. I broke my back in 2017, falling after catching my heel while dismounting. Much less likely to happen with these smaller wheels.
So, it seems we worried about things that turned out to be non-issues, or perhaps even points in favor.
Have we made a road bike that is gravel capable, or have we made a gravel bike that is road capable? We think both. We think we have further refined what was already a good all-rounder adventure tandem.
We can't wait to try it out on our next travel adventure to Albania this fall, a hilly ride on often rough roads where these modifications would seem to be made to order.
Thanks for reading. Enjoy your own special adventures!