29-inch MTBs already use 700c wheels. 26 and 27.5-inch MTBs have enough clearance to accommodate 700c rims combined with a tire of an appropriate size.
If the bike and the new wheels are disc brake ready, the conversion will be easier.
Unfortunately, rim brakes will create compatibility issues because the pads and the rims will not align and will require special adapters. The rear hub’s width can also create problems.
Fitting 700c Wheels on 29-Inch MTBs
The rim diameter of 700c wheels and 29-inch MTB wheels is identical – 622mm. Therefore, 29-inch MTB wheels are 700c wheels themselves.
A 29-inch MTB bike does not have to be converted to 700c wheels because it’s already a 700c machine.
This is basic information but somewhat specialized too. Hence why sometimes even bike shop guys don’t know that 700c tires can be installed on 29-inch MTBs right away as long as the tire width is supported by the rim. If the tire is too narrow for the rim, it won’t be secure and may blow out.
You won’t be able to run a road racing tire on a 29-inch MTB rim, but it’s possible to install fairly slim city tires.
Fitting 700c Wheels On 26 and 27.5-inch MTBs
MTBs designed for 26-inch wheels offer the smallest clearance, but even they can accept a 700c wheel as long as the tire isn’t very big.
The chainstay bridge and the fork’s arch will be the areas with the poorest clearance.
One of the ways to minimize potential issues is to match the circumferences of the new and old wheels.
For example, a 26-inch MTB wheel combined with a 2.2-inch tire has a circumference of 2107.25mm or 210.725cm.
To get close to this circumference, a 700c wheel will have to be equipped with 23-25mm wide tires which is the classic size for road bike tires. (700c23mm tires have a circumference of about 2098.58mm whereas that of 25mm models is 2111.15mm.)
Naturally, a mountain bike designed for 27.5-inch tires will provide even more space to work with. The circumference of a 27.5-inch wheel with a 2.2 tire is 2185.79.
Therefore, a 27.5-inch MTB fork and frame should at least theoretically accept 700c35mm or even slightly bigger tires.
Note: The data is gathered from this useful chart containing the circumference of various wheels. Chances are you will find yours there.
Of course, you also have to take into consideration that there are size differences between manufacturers.
In some cases, you may be able to fit a bigger tire than what the chart says, especially if you don’t plan to use full fenders.
Rim Brakes = Trouble?
700c wheels have larger rims. In consequence, the braking surface of the rim will end up above the pads of standard MTB V-brakes and cantilevers. The new position of the rim will render the default brakes useless.
There are a few workarounds that may solve the problem, but they are more of a patch than a routine procedure.
The possible fixes are:
1. 700c V-Brake Adaptors
There are 700c V-brake adaptors which elevate the V-brakes’ position by mounting to the original bosses and providing a new pair of higher attachment points.
Mavic Horseshoe Brake Adaptors
One of the options is Mavic’s V-brakes adaptors. They’re shaped like a horseshoe and allow you to attach the brakes a bit higher while also acting as brake boosters stiffening the seat stays.
Unfortunately, they are no longer in production. Online stores for second-hand goods are the only way to find them.
V-Brake Boss Extenders
V-brake extenders are another possibility. Unlike the Mavic ones, those come as two separate pieces that mount to the original brake bosses via a single bolt and provide new mounting holes above.
The benefits of those adaptors are their lightweight and availability. I easily found numerous options on eBay. The body is usually made of aluminum whereas the studs are steel.
Those adaptors may be lighter than the Mavics but they are less capable of dealing with braking force due to the lack of stiffness.
Note: The Mavic adaptors can be installed even if the original V-brake studs aren’t removable. The V-brake boss extenders, however, require you to unscrew the original studs. If the studs aren’t detachable, you can’t use the extenders.
There are also 700c brake adaptors that keep the brakes on the same mounts but elevate the pads instead. Those models look a lot cleaner than the other options but reduce the original mechanical advantage of the brakes because the pad sits higher on the brake arm.
As a result, the brakes will not perform as expected and may even have insufficient stopping power.
Clamp-on V-brakes Bosses
Another way to get the brakes closer to the rim is to use V-brake clamp-on bosses and install them a bit higher than the original ones.
V-Brakes with Adjustable Pads
V-brakes that allow you adjust the height of the pad work too. Paul Motolite and LitePro V-brakes were the only models with those parameters that I could find.
Weld a New Set of V-Brake Braze-ons
If you know an experienced steel frame builder, you could pay him to cut the old V-brake bosses and weld a set of new ones a bit higher. Make sure that the person in question has the necessary experience to complete the task. Otherwise, your safety will be compromised.
Long Reach Caliper Brakes
In some situations, it may also be possible to install caliper (road) brakes. This can only be done if the fork is rigid and has a hole for a fender. The frame needs to have a mounting hole for a fender or a reflector too.
This set-up is likely to have poor reach because the mounting holes on the fork and the frame are often too far above the wheels. In consequence, the calipers’ arms don’t extend to the rim.
Long-reach caliper brakes are the only solution. Since this is a very custom job, it’s difficult to know to what extent the plan will work.
Disc Brakes = Easy Mode?
Disc brakes make the conversion to 700c wheel a lot easier as they don’t come with the compatibility issues that rim brakes “politely” provide.
As long as the new wheels have rotors designed for the calipers that you have, the installation process should be fairly straightforward.
Of course, some adjustments may have to be made in some custom scenarios, but you wouldn’t have to restructure nearly as much.
In some cases, people even store two sets of wheels and swap them according to the ride ahead.
Different Hub Spacing
The Over-Locknut Dimension (O.L.D.) of the new wheels could also be a source of frustration.
The term O.L.D. refers to the usable part of the rear hub and is essentially the distance between the outer sides of the hub’s locknuts.
The O.L.D. of front MTB and road hubs is usually 100mm, but the rear hubs are different. Standard road bikes with caliper brakes have a rear O.L.D. of 130mm whereas rear MTB wheels have a rear O.L.D. of 135mm. New rear road bike wheels designed for disc brakes tend to have 135mm O.L.D. as well.
If your rear wheel has 130mm O.L.D., but the dropouts are designed for 135mm O.L.D., the wheel won’t install as expected.
Installing a 130mm O.L.D. Hub on a 135mm Frame
When the O.L.D. of the hub does not match the frame’s spacing, we have a problem. In this case, the hub is a bit (5mm) shorter than the requirement.
What are the possible solutions?
Note: None of the options below are guaranteed to work 100% as there many factors involved. Proceed at your own risk.
1. Spacers/Washers on Each Side
A common advice is to put two 2.5mm spacers on each side of the hub. The job of the spacers is to “eat up” the free space and center the wheel.
The washers may center the hub, but they don’t change the position of the cassette. In consequence, the cassette ends up behind in relation to where it would be if the hub had 135mm O.L.D. This has a negative effect on the chain line.
2. Spacers/Washers on the Non-drive Side
Another option is to put a 5mm spacer on the non-drive side of the wheel. This method ensures a straight chain line because the cassette will assume its appropriate place.
However, this method comes with issues too. First, the entire wheel gets closer to the chainstay of the drive side and may even rub against the frame depending on how big the tire is.
To fix this issue, the wheel will have to be re-dished (re-centered). If you don’t have the skills and the equipment to do the above, the conversion becomes even more expensive.
Note: Another downside of this method is that the axle protrusion on the non-drive side will be reduced by 5mm. Most quick release axles are designed to leave 5.5-6mm on each side. When you add the spacers, the non-drive side will be left with just 0.5-1mm of protrusion.
3. Do nothing
Since 5mm of difference aren’t all that much, some people just squeeze the axle with the dropouts and call it a day. The problem with this approach is the stress on the frame.
If the frame is made of steel, this is less of an issue due to the elasticity of the alloy. However, if the frame is made of any other material (e.g., aluminum) the stress could be catastrophic.
The axle will also be under extra pressure because the squeezing of the frame will result in uneven dropouts.
The Shortcomings of Converting a 26-inch and 27.5-inch MTB to 700c
A conversion to 700c wheels has many downsides that have to be known before the start.
Here they are:
1. Low financial sense
If the bike uses rim brakes, the conversion will require the following parts:
- New wheels;
- New tires;
- New inner tubes;
- V-brake extenders;
The expenses may climb so high that you may be better off buying a second-hand road or gravel bike.
If the O.L.D. of the hub doesn’t match the frame’s spacing, you will have to play with that adjustment too. The extra labor will cost you money and/or time.
If disc brakes are available, fewer parts will be needed, namely:
- New wheels
- New tires
- New inner tubes
2. Unnaturally High bottom bracket
MTBs have higher bottom brackets than road bikes for extra clearance. When you max out the fork and frame’s spacing by putting larger wheels, the bottom bracket will go up even more. The end result is an unstable bike due to an elevated center of gravity.
In some cases, the bike will get so high that you won’t be able to put your foot on the ground when stopping without getting out of the saddle.
3. Toe Overlap
If the MTB frame is small, putting 700c wheels on it will greatly increase the chances of hitting your toes with the tire during tight turns.
4. Poor Aesthetics
The shenanigans required to make rim brakes work will leave you with a non-aesthetic brake area. Some cycling enthusiasts will consider this a major problem.
5. Limiting Tire Options
Unless your MTB is a 29-er, the number of tires that will fit will be highly limited.
6. Too Much Work
The conversion will require quite a bit of tinkering. If you are a bike mechanic by profession or hobby, you may like the experience, but newbies may not share your enthusiasm.
FAQ: Will 700c Wheels Make My Bike Faster?
If two bikes have the same gearing, then the one with the bigger wheels will technically be faster.
When ridden at identical cadence/rpm (revolutions of the cranks per minute) and in the same gear, both bicycles will have rear wheels spinning the same number of times per minute.
However, the bike with the larger wheels has a greater circumference and will therefore be faster and cover more distance.
I’ll throw some numbers to illustrate this point more vividly.
The distance that a bike travels per 1 rotation of the rear wheel is equal to the circumference of the wheel.
If bike A (big wheels) has 700c25mm wheels, then it will move forward 2111.15mm/211cm.
If bike B (small wheels) has 26×2.2 wheels, it will travel 2107.25mm/210cm per revolution.
The difference is about 10mm or 1 cm.
If the highest gear of both bikes is 44/11 [44 chainring + 11 rear cog], the highest gear ratio is 44:11 = 4:1.
This information reveals that for every rotation of the large chainring, the smallest cog and subsequently the rear wheel spins 4 times.
If we multiply the circumference of the wheel by four, we will find out the bike’s travel per 1 revolution of the cranks at that gear.
Here are the results:
Bike A: 211cm x 4 = 844cm/332.28inches
Bike B: 210cm x 4 = 840cm/330.7inches
Conclusion 1: For each revolution of the cranks, bike A (700c wheels) will move 4cm/1.57 inches more than bike B (26-inch wheels).
Conclusion 2: If the cadence of the rider is 90rpm, and the bike is in the highest gear (44/11), the cranks will make 90 revolutions per minute which will result in 90×4=360 rotations of the rear wheel.
In the case of bike A, 360 rotations equal 211×360=75960cm or 759.6 meters of travel.
In the case of bike B, 360 rotations amount to 210×360=75600cm or 756 meters of travel.
In short, bike А would cover 3.6 meters more than Bike B.
To find out the speeds in both situations, we have to divide the traveled distanced by the elapsed time.
Bike A: The speed of bike A is 759.6m/60s = 12.66 m/s = 45.5km/h = 28.27mph
Bike B: The speed of bike B is 756m/60s = 12.6 m/s = 45.36km/h = 28.18mph
Conclusion 3: Bike A is 0.47% faster than bike B.
Doesn’t sound like a lot, does it?
The difference between the two tires may be less than 1% in terms of speed, but that’s the case only if the cadence is identical.
We also have to take into consideration the rolling resistance of the tires because cyclists aren’t robots.
If the 700c tires are slick and narrow, they will make it easier to maintain a higher cadence and will therefore be faster because the rider will have an easier time spinning the wheels.
However, if you switch your MTB tires to narrow slicks, then you would get closer to the result discussed above.
You Can’t Turn an MTB into A Road Bike
Even if you put road wheels on an MTB, you won’t get a road bike experience because the two types of bicycles have a different geometry.
Mountain bikes put the rider in an upright stance whereas road bikes are more aerodynamic and fight headwinds better.
Just put slicks on?
The fastest and the most efficient way to increase the speed of a mountain bike on the road is to simply put slick tires on your existing wheels. This strategy is the most economical and saves you the trouble of dealing with mismatching rim brakes.