Can 29er MTB frame assembled with 27.5er wheels?

[ibike]

Hello,everyone:
Can 29er MTB frame assembled with 27.5er wheels?Are there any insecurity factors?

[PeterXu]

Yes, sure.

See attached pictures, N-SS HR740C 40mm width 27.5er wheels on CS-256 SL 29er frame, 2.8'' front and rear tires mounted on the 27.5er wheels

This bike was built by one customer from the US.

[Oolak]

I actually didn't realize you could do this, or perhaps I just never thought about it. Seems like it'd be an easy way to try out the wheel size and/or bigger tyres.

[RS VR6]

Would you really want to do it? It would bring the bottom bracket that much closer to the ground. 

[Oolak]

Would you really want to do it? It would bring the bottom bracket that much closer to the ground. 

Yeah good point. I guess it depends on the the geometry of the frame. You're probably right tho, bad idea, in general.

[bxcc]

That 256 frame with 27.5+ tires seems like an awesome idea to me. Standard 27.5 tires would mostly likely change it for the worse though.

[Oolak]

That 256 frame with 27.5+ tires seems like an awesome idea to me. Standard 27.5 tires would mostly likely change it for the worse though.

So with the 27.5 wheels and 3 inch tyres does anybody know if the bottom bracket height would be about the same as if the frame was outfitted with 29er wheels with standard sized tyres? If so, that's something I'd seriously consider and bet a lot of other guys would too. Peter?

[JohnnyNT]

Difference in rim Radius between 650B and 29er is 19mm , you'd have to measure how much higher is 3" tire over standard one, probably around 10mm difference, the rest will be BB height change so around 1cm of it.

[Jerryno]

Difference in rim Radius between 650B and 29er is 19mm , you'd have to measure how much higher is 3" tire over standard one, probably around 10mm difference, the rest will be BB height change so around 1cm of it.

The BB height from wheel centers on 29er is usually 15mm lower than on 650B. All the other height measurements would be the same if both frames are equipped with same 650B wheels. So you get the number from frame geometries only, don't need to bring wheels into it.

That means 650B frame with 650B wheels has BB 15mm higher than 29er with 650B wheels. I bet you can get 3 inch tires on both.

[JohnnyNT]

From what I understood the actual issue is the real BB height over ground, which is the equal to the radius of wheel with tire minus bb offset. When the rim size is decreased, the way for the BB to stay on the same height over the ground is either to change frame to a one with smaller offset or have tires with higher profile. Obviously, sticking to the same frame makes only latter viable. As mentioned earlier, change of less than 2cm coming form the wheels shouldn't be a big deal and fat tires should alleviate for at least half of the difference .

[bxcc]

Wheels and specifically tires definitely need to be factored in when determining actual BB height over the ground. Here is some reading material on the topic.

http://forums.mtbr.com/27-5-29/27-5-frame-compatibility-thread-post-your-setup-957906.html

[kingchickenstrip]

Length of the front fork will change BB height.

[Sitar_Ned]

So with the 27.5 wheels and 3 inch tyres does anybody know if the bottom bracket height would be about the same as if the frame was outfitted with 29er wheels with standard sized tyres? If so, that's something I'd seriously consider and bet a lot of other guys would too. Peter?

It's been in the plans to upgrade to a carbon wheelset for a while now, and I'd definitely consider going with the 27.5 rim and 27.5+ tires option; So long as BB height difference was negligible. 

[RS VR6]

I would just start with a frame made for whatever wheel size you plan to run. Even if you can get a 650+ into your 29er frame...the tolerance in the rear would be so tight that any debris caught on the tire will go right into the frame. Imagine the rear tire getting packed with mud and only a couple MM's of room between the tire and the frame. 

[PeterXu]

Sorry, the tires are 2.8'', not 3.0''

Here is the original email record from that guy:

"Hi Peter, here is a couple pictures of
The CS-256 with the 27.5x40mm wheelset
Mounted with WTB trailblazer 2.8 in the rear
And Vee trax fatty 2.8 in the front.
The WTB is slightly slimmer than the Vee tire
And fits the rear nicely, the Vee is to wide for the
Rear but fits nicely in the rockshox SID 29er 100mm fork."