jackbucz

It’s a dumb question but I have been wondering (with no intention of actually doing it) why oh cannot put a 27.5 wheel in a frame ment for a 29. I was just thinking that since the bike can take a bigger wheel, it should be able to take a smaller wheel too. Explain this to me, thanks, Jack

Steve B.

A lot of them can and are designed for this.

Obviously lowers the bottom bracket and with a trend towards lower b-brackets in general, subsequently going to a 27.5 means pedal strikes. Also and if not designed for it, the front handling gets wonky.

Usually the 29/27.5 capable bikes I see are designed for 27.5 plus, so a 3” tire, which puts height closer to a 29.

Wildwood 

First you need to understand marketing terms from wheel sizes?

someone will link a chart with wheel sizes.

Darth Lefty 

If you have rim brakes, the pads won't line up with the rim.

If you have disk brakes, you can. The bike will sit about 3/4 in lower with the same width tires.

There are two styles of bike right now, mountain bikes and gravel bikes, that are using this to advantage. For example, the Salsa Timberjack is available with 29er wheels or with 27.5+ (extra wide) wheels. On the road/gravel side, Salsa Warroad is available with skinny 700c x 30mm or wider 650b x 47mm wheels - the road bike equivalent sizes.

Cyclist0108

yew cud. as long as it has disk breaks.

hillyman

Because 29er sounds cooler.

Elvo

Yes you can. I run 27.5 and 29 on my bike and it works perfectly.

Caliper

Remember to account for not only the width of the tire, but also the location of the widest part. If you run a wider 27.5 to make up the same diameter as a 29, then the widest part of the tire will be not only wider than on the 29er but also closer to the axle. Depending on how your frame is shaped this may or may not be a problem.

If you run the same width tire and just a smaller diameter then the bike handling will change. It could be bad or it could be just different. Obviously the BB gets lower but also the trail shrinks as you put on a smaller diameter tire. This would generally make the bike a bit less stable. How much depends on the rest of the bikes geometry. You may like it or you may not. Considering road bikes are usually made with much more aggressive front end geometry than MTB's, it is not likely to be unrideable but may not be great for a MTB trail. Give it an easy test ride before diving into anything aggressive.

autonomy

You can, but it all depends. As mentioned already, if you have rim brakes, forget about it.
I've experimented with 26" MTB wheels on my 700x40mm stock bike. It made the bike more nimble but also more prone to pedal strikes (it also comes with 180mm cranks, that doesn't help)

Noctilux.95

29 is bigger than 27. Bigger is better. I go with 700c on mine. 700 is bigger than 29

PickleRick

... Guffaw!! ... coffee out nose....on keyboard.

MikeyMK

Some aggressive frames may not clear the same tyre on a smaller rim. I have a GT STS-1 with 2in wide rims and 2.35 tyres, and the chainstay fork fully wraps around the tyre and rim, it's keyhole shaped - the same rim and tyre combo cannot be closer to the hub because then they'd foul the fork's stays.

This isn't a common issue, just something to bear in mind and look out for.

JohnDThompson 

Who says you can't? 29er is the same bead seat diameter as 700C (622mm) and 27.5 is the same bead seat diameter as 650B (584mm), and 700C to 650B conversions are quite common. The issues to be aware of are brakes (assuming a frame designed for 700C/29er wheels, 650B rims will need a longer reach caliper than 700C -- not an issue if the frame uses disk brakes), tire clearance, and possibly ground clearance for crank arms (mostly an issue with fixed gears).