Monday, November 12, 2018

700c vs 650B For Gravel Travel

700c Wheel on the Tamland
With all the new gravel bikes coming down the pike these days, I've noticed that several of them have a certain feature. That is that they are capable of being set up with 650B or 700c wheels and tires. This post will seek to convey my take on the attributes of each wheel size and why I think one or the other is good, or why one or the other may not be so much.

Let me say right up front that neither is terrible, bad, or a wheel size that you shouldn't try. Each has their merits. That said, I have a favorite and I won't be shy about telling you about it. Now, on with the show......

I suppose I should give my background for these opinions. First of all, I have 650B experience going back over a decade. I have ridden mountain bikes, road bikes, and gravel bikes set up with 650B wheels and tires of various tread patterns and on various bicycles. Of course, I have a LOT of 700c experience going back, waaaaay back, and along with this I have ridden a lot of on road and off road 26" wheel and tire combinations. All of this is being drawn upon to formulate these opinions. Basically, I have had enough time on all of these wheels that I feel that my opinion is not lacking in experience based observations.

Despite the latest "Ride The Supple Life", or whatever the slogan is, marketing, and despite the efforts of marketing wonks, the simple truth is that 650B is basically going to end up being your "mtb-ish" wheel for gravel bikes going forward. This is for good reason. Taking into account the limitations of "gravel bikes", the 650B option allows riders to put the biggest footprint on the trail possible. Add in aggressive tread and you have, what I call, "mini-mtb" wheels. They are about 1.8" wide, and essentially turn a gravel going bike into a late 80's XC mtb bike with drop bars. This is cool, fun, and useful, if you want that sort of deal. Obviously, it is a flavor not everyone will desire, or even understand.

The Tamland with 650B tires and wheels
Smoother, more "gravel" oriented treads, are certainly out there for 650B. Basically, the only time I'm opting fr the 650B gravel type tires is when things are really loose, wetter, or when the course is going to present a lot of looser dirt and gravel. Basically anytime I want more flotation. I might also opt for 650B if there are a lot of quick accelerations or short sight lines between turns- basically single track. This would be because these wheels and tires accelerate a bit easier than 700c, generally speaking, that is. Obviously a 700c X 35 tire might actually accelerate easier than a 650B X 50mm wheel and tire just due to weight differences. But all else being the same, I would say 650B accelerates a bit easier. Especially so at 47+mm widths.

The other way I would use 650B and smoother tires is for loaded touring on roads. The wheels would be stronger, the tires fitted could be wider, more comfort might be eeked out, and again, looser gravel and dirt would't present an issue. Not that you couldn't do a wider 700c tire, but keep in mind, some of these "dual wheel size" gravel rigs are limited to 42mm-45mm tires. That may not be big enough for some. There could be an argument made that says it doesn't matter with the wheel strength thing too, but I'm giving the nod here to smaller wheels.

In fact, you could make a really stout case for 26" wheels and loaded touring. Especially "world touring", but I won't get into all the why and why nots about that. Just know that 26" isn't dead in that area of cycling. Almost all my loaded touring experiences were on 26" wheels.

650B gravel rigs are very reminiscent of this 80's era Ibis. Image courtesy of VintageMTBworkshop.com
My predilections run toward 700c for gravel travel because of the way a 700c wheel tackles the loose gravel, dirt roads, and rolling hills I encounter most often. 650B is okay, but 700c is definitely better in ride quality and in terms of performance. This is my experience talking, but you may have a different take on it. My 700c set ups carry momentum just a bit better too. It just is a better tool for the job I am doing.

As far as ride quality goes, a thing many 650B enthusiasts like to hang their hat on, I'm not pickin' up what they are layin' down. 700c is every bit as smooth if you have quality tires and wheels as 650B is. All things relatively equal, that is. Of course, a 700c X 28 at 100psi is not going to feel as smooth and pillowy as a 650B X 47mm tire. However, I have a 700c X 42 set of tires on some wheels here I'd put up against anything 650B for smoothness. So, "supple life" can be had in bigger diameters.

So, which wheels should you get? My advice would be that if you are going to ride wide open gravel roads, maybe some pavement, and if you'd never consider loaded touring, single track drop bar bike action, and would never ride in adverse, softer conditions, stick with 700c. Otherwise, get both sizes. My ideal set up is going to be a 650B tire with some tooth to it for single track/dirt/looser stuff and 700c the rest of the time. Almost every inch of in-town trail here could be easily tackled, when it is dry, with a drop bar mtb bike. Slapping on some "mini-mtb" 650B wheels and tires would be great for doing that activity here. I might do smoother tread 650B in Spring around here when things are softer and 700c tires tend to push into the softer road ways. But that kind of condition is only about two weeks out of the year, so........maybe not so much. I will say that 650B X 47mm was a boon when it was like that last Spring around here. So, it is a viable option when things are wetter and/or looser and deep.

But yeah, I'm primarily going to opt for 700c most of the time for gravel travel.


5 comments:

bostonbybike said...

This is how I built my latest "gravel" bike. It was designed around 650b wheel with 2.2" tires, with an option to run 700c wheels and 38mm tires as well. It just happens that both of these combinations have the same diameter so geometry should be largely unaffected. I haven't tried riding on 700c wheels yet though. I'm enjoying my "MTB" too much to switch to narrower tires.

Guitar Ted said...

@bostonbybike: That's a good set up, I am sure. However; most of the stock bikes coming out won't have that sort of clearance, (V4 Warbird is one that does), and therefore you are going to have results that vary from yours. Also add in that many "Road Plus" tires are not anywhere near the diameter of 700c X 42-45mm and you can also see why I have the comments I do. The diameters are quite different normally due to either lack of clearances or choice of tires. This can lead to issues which I did not address in my piece, the most significant of which is the effects smaller diameter wheels have on geometry.

bostonbybike said...

@Guitar Ted: Yes, that's my point too. My bike is custom so I consciously decided to have it built for two different wheel sizes but of the same overall diameter. Most production bikes have the problem you mention - they come with e.g. 700cx45mm tires but then have an option to run 650bx2.0" tires as well (like the Warbird you mentioned). The diameter of these two wheels will be quite different so you end up with two different BB heights, etc.

I think it comes from the conservative approach of many manufacturers who still try to fit a road compact crankset on gravel bikes, hence limiting tire clearance (see Warbird again). My bike can't take chainrings larger than 44T but that's all I need anyway (and it's not a racing bike to begin with).

Guitar Ted said...

@bostonbybike- Understood. Thanks for the clarification. And I agree with your points on the conservative manufacturing and design choices brands make.

Bob said...

GT, my experience with road plus was less than desirable for my style of riding drop bar including a mixture of pavé, gravé and trailé.

What has gotten me to the supple ride I desire has led me to believe that rim width/ tire aspect ratio and the ability to run as low as possible psi at all times, which seems to be around 35psi using i25 rims and 40-45c tires, is my personal magic number. At this psi the road plus performed well in the latter two categories but for the pavé part, especially at dh speeds while cornering, I felt the higher profile casing 650b was causing squirm from the rear end that is not exhibited with my 700c setups lower profile at my desired psi which I found was the same with both setups.

If you factor in your comments on "mini mtb" tires, as bitd of my early mtb experience it was impossible to get away with much under 40psi without threat of pinch flatting/rim strikes, but that was in the days of tire tech, narrow rims and tubes. The advent of 29"ers and their higher volume lowered that number to 30psi for me but still with tubes and the narrow rims available for conversion to 700c it still had potential, although exhibited much less frequently, the same issues.

Today with a wide selection of sealant systems, rim widths and tires mixed in with some creative marketing from the manufacturers the right combination for ones personal requirements and the road to that perfect combo can be trial and error at some considerable expense. But once you are there you will know as you have discovered for your personal requirements. And it is a very happy place.