Condensed Answer: In theory, a 700c frame can accept 26-inch wheels. However, the conversion will cause the following issues:
- Failure of the brake calipers to catch the rim (in the case of rim brakes)
- Ultra-low bottom bracket when using skinny tires causing annoying pedal strikes
In the end, it may be cheaper and wiser to avoid the conversion and follow a different path to your goals.
Rim Brakes = Incompatibility
A 700c frame is designed for 700c wheels. Those use a rim with a 622mm diameter.
Meanwhile, 26″ wheels have 559m rims – a 63mm difference in diameter.
Therefore, if the frame operates with rim brakes, they will be located about 3.2cm (63mm/2) higher than where the 26″ wheel will require them to be. As a result, the caliper won’t be able to grab the rim, and the bike will have no brakes.
There are several ways to fight this problem:
Case A: Calipers
- Caliper Extender
If the bike uses caliper brakes and has braze-ons for a rear rack, one can install a caliper extender adapter like the one in the picture below to lower the brake and allow it to reach the rim of a 26″ wheel.
You can purchase those from online platforms such as eBay.
- BMX Caliper Brakes
Another option is to install BMX caliper brakes such as Odyssey 1999 or Dia-Compe Bulldog.
Those models have a long reach in comparison to standard road calipers. An added benefit is that you will be able to run wider tires.
Having said that, one cannot know with certainty whether the brakes will work with every set-up.
It will be wiser to measure the original calipers’ reach and the distance between them and the new rim.
Then, add the discrepancy to the reach of the original calipers and see if the new brakes can make up for it.
- Welding or Brazing a Seat Stay Bridge
Another option would be to weld or braze on a second seatstay bridge lower than the original one and attach the brake to it.
This procedure is more complex than one may think for the following reasons:
- It works only on steel bikes.
- The welder must have experience with bike tubing. (Bike tubes are very thin and it’s easy to burn through them and damage them.)
- The builder also needs to machine the seat stay bridge and heat treat it.
- The area has to be repainted.
When you get the bill, you may feel like buying a new frame would’ve been cheaper.
V-brakes or Cantilever Brakes
If the bike uses V-brakes or cantilever brakes, the options are:
- Clamp-on V-brake mounts
You can buy aftermarket V-brake mounts and attach them anywhere you want on the seat stays or fork.
The downside of this approach is that the mounts aren’t cheap, especially if you have to buy two sets – one for the fork and one for the seat stays.
If the bike uses disc brakes, you won’t experience this problem because the disc rotor is always at the same place (the hub) regardless of the wheel size. Thus, the frame and fork will accept the new wheels without problems.
Alternatively, you could also consider the following combinations:
- Front Disc Brake + Fixie Rear Brake
You can replace the fork with one that supports a disc brake and couple it with a fixed-gear drivetrain which will allow you to slow down the rear wheel by fighting the pedals.
This is an unusual combo but provides a lot of braking power and eliminates the issue that rim brakes create when installing 26″ wheels on a 700c frame.
Note: If you don’t like fixed-gear braking, you can install a coaster brake.
26″ wheels have a smaller circumference and will lower the bottom bracket. The change will decrease the bike’s clearance, and the frame will hit the ground when riding on off-road terrain.
Also, the rider may experience what’s called a pedal strike – the pedal hits the ground when riding on technical terrain and cornering. Thе problem will be even worse if the rider uses long cranks (175mm).
(The chances of a pedal strike can be lowered by using very short cranks – 140mm or so. This change, however, will affect the bike fit, and the rider’s body may not agree with it.)
In some situations, a pedal strike could result in a fall that could lead to serious injuries or even a lethal end. This is a strong argument against the conversion.
The bottom bracket drop can be offset by installing a fat tire which will make the overall circumference of the wheel closer to that of a 700c wheel with a slimmer tire.
However, the frame and fork may not have clearance for a tire of that width.
That said, a bottom bracket closer to the ground has a benefit too – it makes the bike more stable by lowering the center of gravity. As a result, the bike will corner more aggressively.
The Pros of Converting to 26″ Wheels
The benefits of converting to 26″ wheels are:
- A Stronger Wheel
All things being equal, a smaller wheel is a stronger wheel. A quality 26″ inch wheel built well will need less truing than a 700c one and can take a lot more abuse before spoke failure.
Thus, a conversion to 26″ wheels could be a legit option for people who have “adventure bikes” with disc brakes and lots of fork and frame clearance.
The lowered bottom bracket issue can be resolved by using a fat tire. For example, a 26″ wheel with a 2″ tire will have a diameter closer to that of a 700c wheel with a 38mm tire.
- Parts Availability When Touring
Components (spokes, tubes, tires) for 700c wheels could be harder to find at some remote locations whereas 26″ parts are readily available.
If the rider uses fairly skinny tires for the conversion, it will be easier to fit racks on the bike.
That said, the skinny tires may lower the bottom bracket to the point where pedal strikes become an issue.
Another “in the middle” solution is to go for 27.5″ rather than 26″ wheels. A 27.5″ wheel uses a rim with a 584mm diameter – only 38mm less than that of a 700c wheel.
As a result, the user will have the option to install long-reach road brake calipers to compensate for the new rim position on top of all the other solutions listed above.
27.5″ wheels won’t lower the bottom bracket nearly as much as 26″ would. If the tire is wide enough, the bottom bracket height will stay the same or even increase.
Ultimately, 650b conversion is more common, and people know a lot of tricks and tips to make it smoother.
Summary: What You Need To Know
- 26″ wheels can be installed on a 700c frame but create some notable issues.
- If the bike is made for rim brakes, the rim of the new wheel will be too low. As a result, the rider will have to use brakes with ultra-long calipers or install drop bolt adapters. The process is finicky and there are no guarantees that the outcome will be satisfactory.
- If the bike uses disc brakes, the brakes won’t create an issue.
- 26″ wheels will lower the bottom bracket to the point where pedal strikes become an issue.
- The bottom bracket drop can be compensated by using fatter tires. The frame and fork, however, may not have clearance for fatter tires.
- The main benefits of 26″ wheels are faster acceleration, extra strength and a greater number of available parts when traveling to little-known locations.
- A conversion to 27.5″/650b wheels seems more feasible.