Wheel Comparison: 650B vs 700c
In the gravel cycling scene, 700c sized wheels have been dominant. Sure, we see the occasional 26 inch wheel out there, but by and large the traditional road wheel size of the last 30 plus years has been the size most often used for gravel road riding. However; as with mountain biking, we are seeing some 650B wheels and tires being used now. Obviously, we are testing a set of these wheels and tires, (seen HERE), and we have seen a question arise about the differences between the wheel sizes themselves. So, this post will aim to compare 650B and 700c wheels and give you, the reader, some information with which you can use to decide which might be better or interesting to try for yourself.
In a traditional 650B conversion, where the 650B tires are swapped into a 700C road bike, most authorities agree that a fat, 42mm-47mm 650B tire will approximate a 700 X 28-30mm wheel and tire’s diameter. This means that a swap between wheels on a bicycle that fits both would result in a very similar bottom bracket height, gear inch figures, and trail geometry. You might gain a more comfortable ride using 650B wheels and tires, since the increased volume in the tires might allow you to use a lower pressure than with the 700X 28mm-30mm tires. Traction is another area where this swap might make sense for the rider, as a bigger, wider contact patch results when a lower pressure 650B tire is used over that of the 700c X 28-30mm tire.
However; most gravel going bikes are using tires much wider and with much more volume than a 700c X 28-30mm tire. What are the differences between these 700c X 35-40mm wheels and tires and 650B X 47mm wheels and tires? Wheel diameter is a very noticeable difference, but there are other factors to consider when thinking about making the swap from 700c to 650B on your gravel machine. So, following are a few things that may help you sort through the benefits and negatives in your specific case when looking at the switch.
Comparison: What you are looking at above are two wheels on a board which has been leveled using a liquid filled level and on which are the two wheel sizes in question. I chose to use two tires more closely related in volume and width rather than diameter, so keep this in mind. The Panaracer Gravel King 40, as we tested here, was found to be more of a 42-43mm tire based on user feedback and our own testing. This compares most favorably with the 47mm Horizon, which is right at 47mm on the Velocity Aileron rim. Both tires are set up tubeless in this demonstration and both set to the same air pressures. Following are the measurements for diameter.
- Gravel King/HED Ardennes+ Wheel: 28 1/16th” or 70.27cm diameter
- WTB Horizon/Velocity Aileron Wheel: 26 7/8th” or 68.26cm diameter
Note: 1 inch = 2.54cm
We can see then that the overall diameter difference is a bit more than 3/4’s of an inch, or 2.01cm. Considering that a rider can use a lower pressure with the wider 650B tires, that difference could be larger by a small amount, however, we will assume similar differences for this comparison. Diameter has an affect upon your trail figure. That is a definition of how far your steering axis is ahead of your front axle. For reference, please review the information at this link and try to understand the concept. Many believe this can help determine how a bicycle will handle. I am merely trying to show that the differences in diameter do have an affect upon this trail figure, and subsequently may take the handling of a certain bicycle in one direction or the other. Either more stable or more unstable. It will be up to you to decide what is desirable.
In the case of the Raleigh Tamland Two, we can see that by using the stock spec figures given by Raleigh, the Tamland Two should have a trail figure of 66mm. If we use the Panaracer Gravel King size in this formula we get a number of 67mm. Now if we plug in the numbers using the Horizon wheel we get a figure of 62mm. The difference in trail between the Panaracer Gravel King 40mm tire and 700c wheel versus the 650B Aileron/Horizon 47mm wheel is therefore approximately 5mm. This should mean that the Horizon/Velocity wheel is slightly less stable than the Panaracer/HED wheel on the same bicycle. NOTE- A bicycle with the lower number will be less stable than the same bicycle with a front end geometry that results in a larger figure which is typically understood to be more stable.
So, does this play out or matter at all in the real world of riding? In a word: yes. However; there is a lot more to it than a simple “yes” answer. I have a long and varied background in using several different trail figure set ups on several different types of bicycles. I ran a test in 2008 using eight different forks on a single bicycle, trying to keep all the other variables the same, to see, amongst other things, what trail did to the way that bicycle handled. In short, the results showed that a human being is an amazingly adaptable creature, and trail figure differences, while greatly affecting how a bicycle rides, can be adapted to, for the most part, by most humans. What that means is, you can tune your handling to your tastes.
In this instance, using the Raleigh, I was aware immediately that the 650B set up was more nervous, twitchy, and required a bit of acclimation. However; that sensation went away after about five miles, and only has occasionally reared its head since then. Unless you are looking to load the front end of your bike with a rack, or some other means of carrying stuff, this probably is of little import to this discussion, but it is something to consider in the overall concept of switching from 700c to 650B for gravel roads.
With the switch from the 700c wheels to the 650B wheels on the Tamland, I found a few other things that were notable, or that may be something you should make note of if you are considering a swap to 650B wheels and tires.
- Clearances: The big benefit of going to 650B is for the width and volume of that wheel size and tire size. Unless your bike has room for 40mm tires or slightly bigger now, you may want to make a special note of this and carefully measure the space in your frame for big tires. The wider, more voluminous tires, like the WTB Horizon, will require more room, but affect your geometry the least. You can use a radius measurement based on my diameter measurements above to start out with, but some research may be required on your part to ultimately figure this out.
- Momentum: The experiences I have had with 650B mountain and road wheels seems to point to characteristics that are different than I have experienced with 700c based wheels. My experiences seem to line up with many others. In short, the 650B wheel seems to spin up faster, but it also loses momentum faster than a 700c wheel that weighs similar and with a similar tire mounted. This can be seen as a benefit for some, but others will see it as a negative. It is up to you to decide which it is for you.
- Gearing: Smaller wheels will result in a slight lowering of your gearing range overall than it was with larger diameter wheels. Again, this can be compensated for with changes in chain rings, or you might want to stick with what results in your specific case.
- Computers: The old style of computers that do not rely on GPS, but on an impulse from a magnet on your wheel, will not read the same with a switch from 700c to 650B. This will only be a hassle for those who want to switch from one wheel size to the other on a regular basis.
- Tire Selection: While there are a lot of 700c sized, gravel class tires available now, there are not a lot of suitable 650B models out now. Not only is the selection of gravel road suitable 650B tires slim, but getting a tire replaced in the wilds may prove to be an issue for some folks.
- Bottom Bracket Height: With the slight decrease in diameter of 650B wheels, bottom bracket height will be lowered if you swap from 700c gravel wheels to 650B wheels. You may want to check out your current bottom bracket height and make sure that you do not end up with pedal strikes due to a lowered bottom bracket.
- Weight: In the case of the swap I performed, there was a slight decrease in weight with the 650B wheels versus the 700c set that came off the bike, but this may not be the case in every instance. The differences are close enough that one may actually gain weight going to a 650B wheel set depending upon where you are coming from with your 700c set.
I found that the 650B wheels had some attractive characteristics. One of them was that I can run ridiculously low air pressures. Think low as in mountain biking low. I have gone down as low as 22psi front/27psi rear, and have ridden two hours of rough, loose gravel with no ill effects. The reason for testing the depths of low pressure is that I am thinking that the same benefits mountain bikers enjoy with wide tubeless tires can be enjoyed by 650B wheeled gravel cyclists as well. Those would be comfort, increased traction, and some amount of flotation in looser road conditions. All this with little to no penalty in rolling resistance or perceived effort at the pedals. On harder roads and chip seal, these wheels are like cheating, the ride is that smooth and comfortable. I would tour on a set of these wheels in a heartbeat.
On the other hand, I could always feel that I was pedaling more with the 650B wheels versus a set of 700c X 38-40mm wheels and tires. Momentum can be an important thing on looser gravel, or softer terrain, and in these cases, I feel a 700c wheel set has a bit of an upper hand. That said, it is hard to argue that a 650B and fat tire set up tubeless does not have a better ride feel than anything 700c X 40mm or so.
Besides those things, I feel a smaller diameter wheel is a bit less stable in terms of getting knocked off line, or in terms of lateral stability on loose gravel, than a 700c wheel and fat gravel tire. This may have more to do with the Horizon tire’s smooth file tread and round carcass profile than it does with its diameter. Still, there is that lingering feeling at times that you are on a slightly more skittish wheel. I suspect I would completely become immune to this after several weeks of riding 650B exclusively.
Now it will be up to you to decide whether or not this wheel size deserves more of your attention. Look for more specific comments on the Velocity wheels and WTB Horizon 47mm tires coming up soon here.
Note: The component parts of these wheels were sent to Riding Gravel by the various brands/manufacturers for test/review at no charge. We are not being bribed, nor paid, for this review and we will strive to give our honest thoughts and opinions throughout.