Converting MTB Wheel Sizes (26 to 27.5)

b1

This is my carbon Merida. I hate to retire this so I decided to update it by changing the wheelsize from 26 to 27.5. I made measurements first and borrowed a friends 27.5 wheel before I spent anything on the conversion.

There are voluminous discussions on what is the best wheel size- a 26’er, a 29’ner or an in-between 27.5. This is not another article on that subject matter but this is about how to convert an existing MTB with a different wheel size. Most of the assumptions when one chooses a new wheel size is that a new entire bike will be bought. But one question is- what if I would just like to change the wheel size of my bike assuming that the frame can accommodate the change?

b3

There is just enough space. This is a 2.10 tire. I think it will be better to have a 1.95 tire.

In general this is not advised by manufacturers with the claim that the design or geometry of the bike will be severely affected. This pretty much says that you should not convert at all and just buy a new bike if you need a new wheel size. Fair enough, but what if its possible? What are its implications? What are the do’s and don’ts? What if due to financial restrictions, sentimental reasons, etc., you want to keep most of your bike and only replace the wheels to gain the supposed benefits of the new wheel size? Or maybe you can only afford a gradual upgrade of the entire bike as limited budget permits. Would this be possible?

b4

Same case as the space in the seat stay.

In reality, the bike frame from a bigger wheel sized bike can obviously accommodate a smaller wheel size i.e. a 29ner frame can be fitted with a 27.5 or 26 inches wheel diameter.  But according to most articles I have read- this is not the best conversion since the bigger frame’s geometry will have the biggest impact if it will be fitted with a smaller wheel size. In particular- the bottom bracket base will be lower that pedals might hit the ground. So I guess defacto rules will be:

  • frames with smaller wheel size can be converted to bigger wheel size only and not the other way around- frames with bigger wheel size to change with smaller wheel size.
  • convert to the next increment only and don’t jump two sizes ahead- i.e. if its a 26er- then convert to a 27.5 and not a 29. If its a 27.5 then you can do a 29.
  • Check if your feet on the pedals will not touch the front wheel when turning if you convert to a bigger wheel size.

I would think this conversion scenario is only feasible for the current people who owns a 26er bike which is a majority of us. I don’t see any reason why one with a 27.5 would convert to a 29ner. And of course I don’t think somebody will go from bigger to smaller. So given the points above, we can further simplify that this is only applicable for 26er converting to a 27.5. Or that is the only valid reason. Period.

b2

Just got lucky the fork also fit since the actual difference between a 26 to a 27.5 is only 3/4 inches.

Besides the foot hitting the wheel rule, another thing of course which is obvious is to see if the frame can accommodate the bigger wheel. If the frame cant, then its not possible. If the frame can and the fork cannot, then there is still hope of buying a 27.5 specific fork which is cheaper than replacing the frame. Note that there should be ample space between the frame and the tire. Sometimes this clearance can be further improved by choosing  a tire with a smaller casing like a 1.95 than a 2.10 tire size. In the end- even if all the criteria is possible, you still need to try the bike and see its effect to your handling, comfort and safety before you certify that the conversion is a success. As mentioned earlier, this is not advised by manufacturers and these are my opinion based on other articles so in the end, I also advise that you also do your own research before going this path.

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