JCox3370

What is the best size wheel for a gravel tandem used mainly on roads, not trails?

bikeinxs

I guess that depends on the tires you want to run. Most of the time we run 700c wheels with 38 mm tires on our tandem. That's fine on good quality gravel roads. When we are going to hit serious gravel we switch to 650B wheels with 48 mm tires. We are a 300 pound team.

The big advantages of 650B are:

1. The smaller wheel is inherently stronger, all else being equal (although it never is - our carbon 700c wheels are definitely stronger than our aluminum 650B wheels)
2. Larger tires allow you to run lower pressure while still avoiding pinch flats or rim impact. On rough roads that will be more comfortable and faster.
3. Even with the larger tire you will probably have a smaller wheel circumference, which gives you lower effective gearing for climbing.

The only disadvantage is that the big tires will be a bit slower on the road.

If I only had one set of wheels for our tandem they would be 650B. Although 80% of our riding is straight road we do love the gravel and ATV trails.

For touring with an extra 80 pounds of gear we will run 650B.

CaptainHaddock

I'd argue that 650b x 43mm to 50mm are the sweet spot for tandems. you don't want to go much smaller for a couple of reasons: You'll be loosing the volume and so having to run higher PSI/Bar, and so a much less supple / vibration dampening. The other reason that comes to mind is bottom bracket drop.

bikeinxs

BTW we've been experimenting with tire pressures. I was running 45 psi in the 700x38 tires. Control was good and we didn't have problems with flats but I have been edging the pressure up a bit as I think I was well below the optimum pressure for lowest rolling resistance. I think 55 psi is perfect. 60 psi gets a bit rough.

I have been running the 640x48's at 40 psi tubeless. I haven't ridden them as much so I haven't experimented with anything lower yet. Once I put them back on the bike I will definitely be experimenting with lower pressures.

124Spider

I won't argue at all.

Our experience: There are a lot of nice crushed-gravel rail-trails in our area (Seattle/east side), and we didn't feel comfortable with the slick 32mm tires above about 12mph. So we bought 700x42, and knobby tires to fit. It solved our problem. I'm still not willing to ride much faster than 15mph on gravel, but it's perfectly stable at 15mph.

We mostly keep the 700x32 wheels/tires on the bike, and switch over (along with appropriate tubes) to the fatter wheels/tires when we want to ride on gravel.

Mark

torger

On modern single gravel bikes 650B is typically only used for very wide tires, 47mm or more. If the gravel is not too rough most satisfy with 700c 40mm, and I'd say that is the most common for single gravel bikes today. However tandem frames are still quite rarely designed for the recent gravel trend which means that they often do not fit 40mm with 700c. One could also argue that it's preferable to have a bit wider tires on a tandem as you hit stuff harder than on a single bike when you can pull on the handlebars to lift over a hard edge etc.

This leads to 650B being a more popular gravel wheel size on tandems. We run 650B with 47mm tires, which maxes out our Cannondale frame. We could only run about 35mm in 700c, and we prefer the smaller diameter so we can fit 47mm tires, we thought 35mm was a bit narrow, it works great on fine gravel but we wanted to be able to take on a bit rougher gravel too, get more comfort and have lower risk of punctures. If we could fit 47 in 700c we would probably run that size though to get a bit more bottom bracket height to reduce risk of pedal strikes on uneven ground. Pedal strikes is more common on tandem than on a single bike due to the long frame.

With 47mm tires the 650B diameter is about the same diameter as a 28mm 700c road wheel though, so bottom bracket height is not really a problem, it just would be nice to have even more.

dstke

Timely discussion. We're looking at switching from our 650 x 47 wheelset (Spank Oozy Trail 395+ rims, White Industry hubs, Teravail Cannonball tires) to 700 x 44 wheels (WTB Raddler and haven't decided on rims or hubs - any suggestions?) Our 'road' wheelset is 700 x 38 (Velocity Blunt 35 rims, White Industry hubs and Vittoria Terreno Zero tires).

The reason for switching is pedal strikes. On single track trails where maneuverability is limited the cranks frequently hit rocks. On gravel roads I can usually maneuver around obstacles. I'm hoping that the 1/2 - 3/4" additional clearance will be enough for the 3-4" high rocks and roots. That said, we're fairly new to gravel riding and haven't found many smooth trails in the Lake Tahoe region. We did a little forest service dirt road ride in the SF Bay Area last week and had no problem with our 700 x 38 wheelset.

Doug

rocknrollin

i don't have experience with them, but if we were to get a new all-purpose/ touring tandem, I would probably go for the DT Swiss HX 491 or HX 531 rims. It is their new e-MTB line, and they claim a weight limit of 150kg and ASTM4 classification, so they should be able to take some abuse.
I would be curious to hear if anybody has some tandem experience with them.

rocknrollin

I forgot to mention it, but they have 25 mm and 30 mm internal rim width respectively. so they are optimized for a tubeless setup of wider tires at lower pressure.

merlinextraligh

Our new Calfee, which we intend to use for fast road rides, gravel, and some bike packing is being spec’d with two sets of wheels, one 700c, one 650b. The diameter of a 25mm tire on the 700c will be virtually the same as a 45mm tire on the 650b’s, which will keep geometry, bb drop and handling neutral between the wheel changes.