mjohn

Being very new to Tandems I thought I would get some opinions on this.

For road Tandem, I was under the assumption that one would want a 700c tire as like you would on a road single ( with maybe a beefier rim ). But looking at several, even higher end road Tandems I am seeing some with 26 in wheels.

I even read one article about a custom Tandem maker that only uses 26in wheels on its wheels because of the following
• 26” wheels are stronger than 700c wheels. Since tandems carry more weight than single bikes, they are ideal for running 26” wheels.
• 26” wheels have less inertia and weigh less than a comparably designed 700c wheel. Therefore, they accelerate more quickly, climb better and are fast.
• 26” wheels offer a versatile tire selection, from narrow road tires to aggressive mountain bike tires.
I know TandemGeek should have some insight on this, what about the rest. Stay with 26 or move to 700c??

jgg3

It is all marketing and personal bias. Figure out what your personal bias is, and go with it.

72andsunny

an old bill mccready article on the subject:
https://www.gtgtandems.com/tech/700-26.html

mjohn

Great article! Thanks

jgg3

I had not seen this article, and it is interesting. I question some of his results, like 26 inch rims being almost 20% less effective braking surfaces; but at least the bias in the article (700c is better) matches my own...

One important factor he does not discuss, and that is response to road hazards like potholes. Larger wheels are much better than smaller ones there. Try riding a folding bike with 20 inch wheels on bad pavement and you will get the message. But don't say I told you to.

Another thing he doesn't address. If 700c is better than 650, then why not 800? 1000? These are in fact superior in many ways. But bike geometry would have to change, and we have sort of ended up near the ideal size -- somewhere in the 700 range -- for all of the compromises that have to be made. And it sure is easier finding 700c things these days. It really is nice to have standards.

SDS

Looking at Bill's article, a 26" tire will be of 2.5" less diameter than an equal width 700C tire. Multiplying the difference by pi, and given an 83.75" loaded rollout diameter for a 700 X 28, that works out to slightly more than the difference between a 12T cog and an 11T cog. Given a partner who is not too keen on higher cadences, it seems to me that the difference is sufficiently great to be a solely decisive factor.

Nominal front derailleur capacity is quoted in teeth of difference between the large ring and the small ring, so as you increase the ring size you are decreasing the difference in ratio. The Shimano STI-type front derailleurs are adapted to work best with particular sizes of chainring, though close produces performance sufficiently good for some people. I prefer to use 53-39-28 rings with my STI Ultegra (FD) systems to copy road bike systems and improve upon them at the bottom end. This helps keep the cog sizes from getting too large, and keeps the ratio difference between consecutive cog choices close. A 39T ring in the middle can prevent a shift to the small ring that you would have had to make with a 42T.

Given that the chainring gearing is relatively fixed, if you are going to ride a road tandem like a road bike, for example, in a pack of road tandems or road singles, it is likely that you are best served by 700C wheels and tires.

zonatandem

If the larger rim (700c) is faster than 26", why did the larger 27" rims go into disfavor?
As for braking, Bill was obsiously talking about rim brakes . . . not discs.
So now that he is pushing discs on tandem, why not go to smaller wheels?
Marketing?!

masiman

My impression of the 27" demise was because tubulars did/were not going to change from 700c. Being as there were both 27" and 700c clincher offerings, the riders that wanted compatibility opted for 700c spec'd bikes.

Xanti Andia

We went to 26" due to tire availability in wider sizes in Argentina, on a Mocha Co-Pilot. Found an advantage of 26" when fitting the bike into the cases, gives you a little more space.

I have the impression that we could squeeze out a slightly higher top cruising speed on the 700c tandem, but have no scientific basis to prove it.

We went for a 54t x11t top gear, thinking that if we were infrequently using 54x12 on our old 700c tandem, we would need 54x11 on a 26". However in hindsight, I think we should have ordered it with 52x11, by the time we get to 54x11 we are going down a hill fast enough that we will be coasting. Some day I'll try the bike with two very strong riders to see what we can do.