This article will open your eyes to the problems/solutions for switching/selecting 650C Road Bike Wheels & Tires vs 559mm 26" Mountain Bicycle Wheels & Tires.
In the world of Rode Bikes you'll find dozens of opinion based articles around the issue of Road Bike 700C vs 650C wheels. These articles primarily focus on the benefits of one over the other in relation to rider size and aerodynamics. In the world of Recumbent Bicycles the issue has more to do with rider comfort and what comes specified on most pre-built high racers.
I'm less interested here in the aerodynamic argument of 650C vs 26" and more interested in rider comfort and tire availability.
Before I get started it's important to note that a 650C has a rim diameter of 571mm and a 26" Wheel for our purposes has a rim diameter of 559mm. Thus for practical purposes the size of these two wheels rim diameter is only 12mm different. Thus they are very close to the same size. However they are NOT interchangeable. You'll encounter some problems when you need to match your Brakes to the rims and try to source tires to meet your own cycling needs.
I am not about to get involved in the most minute technical issues here, I'm only going to cover the "surface" issues... should you desire to really dig into the "Problem" I'd suggest your first do some reading at Sheldon Brown's site (Harris Cyclery). This information is very easily found by searching for Sheldon Brown in Google. Sadly Sheldon passed a short time ago so the status of his material being updated forward is unknown to me.
Back on point. There is another issue that comes into play with Recumbent Bicycle configurations and that is rim width. Many Recumbent Bikes feature a mix of Road and Mountain Bike components. Many road forks are not wide enough to comfortably accommodate wider 26" rims (The brakes might not line up properly and may be too narrow to work with some 26" Rims). So braking is definitely an issue.
Another factor is the ERD - Effective Rim Diameter. If a wheel is too tall it might rub on the Brake Housing or the Fork itself. This depends on the design of the Fork and Brake that is on your bicycle.
This information from Bikeman.com should shed some light on the ERD issue.
ERD, Center to Flange, Over Lock Nut.... All terms - measurements that help wheelbuilders determine the correct spoke length for a particular wheel. Many of the on-line spoke calculators still require you to enter your own measurements, especially if you have an older hub / rim combination. Ever wonder how to calculate these number on your own? Here is a little info to get you started.
The measurement you aquire in the process can be used in conjunction with the DT-Swiss spoke calculator and the spoke calculator provided by Damon Rinard. The other option is to take these measurements and email them to Bikeman with the following information. We will need to know the number of holes your hub has and the lacing or number of crosses you would like the spokes to have.
We recommend using a few tools to help you with this process. A set of metric calipers will be enough to take the measurements from your hub. Precise measurement of ERD (Effective Rim Diameter) requires a rim measuring kit, like one from Wheelsmith . Bikeman offers both for sale. The DT kit is a bit more cumbersome to use but is much cheaper and comes with a set of calipers. Click on the Products below to get details. Damon Rinards spoke calculations web site offers some alternatives to the rim measuring kits. Follow the instructions carefully if you go that route.
This doesn't exactly make me want to jump in and build my own wheel set that's for sure.
Back on point. Rim width, Rim Height, Spoke length, Spoke Count - all issues with selecting the correct size wheels that need to be addressed BEFORE you can select your tires.
650C seems to be a bit of a dying breed for a very small niche of small roadies and Triathalon Competitors. Even in the World of Triathlon competitors newer road geometry has taken a bite out of the 650C crowd. With 650C wheels you may be limited to 23mm tires at high pressure. I know there is the Terry Tellis 28mm that is mentioned in some Recumbent Forums but it's not exactly the best option for many recumbent riders.
So this brings us back to 26" - 559 Wheels which are readily available, but not always an easy task to select either.
With 559" we have a whole new problem in the selection and purchase of Wheels/Rims. Road bikes have 100mm front fork spacing... and so do mountain bikes and recumbent bikes. Easy so far! But when you get to the back wheel, the drop out on a Mountain bike is 135mm and a road bike is 130mm. My recumbent is 130mm rear drop out, I'm not sure on most recumbents but if you check your own you are more likely to have a 130mm rear drop out than a 135mm rear.
So most recumbent bike riders who want to run 559" will need to have them custom built because stock hubs for the rear wheel in the 559mm size will be 135mm. In addition Mountain Bike hubs should have extra seals and "Beefier" axles adding weight to the equation - weight that is of no benefit to the Recumbent Rider who isn't taking their bike off the pavement.
So what is the solution?
The solution is to talk to your Manufacturer to see what size wheels and which brakes will work with your Recumbent Bicycle. In some cases all that is needed is a switch to side-pull brakes. In others you may have the flexibility to adjust a V-Brake the 6mm up or down to accommodate either size assuming the wheel clearance is available between the drop out/forks.
You'll save weight with 650C as most tires in this size are 190-250 grams vs 250-500 grams in the 559 size. You'll also need to run 650C tubes (Because they are much thinner (material thickness and width) thus saving more weight. But you had better like the high pressure and road vibration which comes along with the light weight high pressure tires.
For me the solution is to have a custom built wheelset based on 17mm 559 rims and road hubs. This will allow me to get a lightweight wheel, run 559" tires from 1" to 1.5" (25mm to 32mm - yes I know not exact sizing but close enough) and run at a little lower pressure (Good speed and more comfort).
Light weight wheels will absolutely improve the "feel" of your bicycle. Less rotational mass allows you to start up quicker and climb better. At speed wheel weight makes little difference, but getting up to your cruising speed or if you ride on city streets and start and stop a lot a light wheel will really matter.
I like the Velocity Rims and the Mavic Rims and the DT Swiss rims - brands you may want to consider. DT Swiss spokes or Sapim Spokes. Hubs? I just can't really decide yet. Velocity hubs are Formula OEM very lightweight (80 grams front) but cartridge based so not very serviceable. I'm considering Ultregra Hubs... but there are so many choices.
For my rear wheel I'm seriously considering an Off Center design to compensate for the "Dish" (Spoke tension of drive side vs non-drive side) of the rear wheel.
And for me I'll probably stick with a 32 spoke design as I'm not very keen on breaking a spoke when I'm out on the road. I dread even having to change a flat (Not easy to flip my bike upside down and get it to balance). My tire preference is the Durano folding tire at 250 grams. I may give the Kojak a shot as well, but I understand they are not nearly as puncture proof. My Schwalbe Duranos now have 900 miles on them and look almost brand new. My Specialized "Fatboys" with the same mileage were coming apart at the seams and had small chunks missing in the tread!
So what has been accomplished in this article? Well hopefully you now understand that there are many issues involved with Wheel/Tire/Hub/Spoke selection for the 650C vs 26" debate.
Bottom line is if you have a high racer with 650C you'll probably be able to run 26" and vice versa but you need to make sure you've done your homework first.
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