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Discussion Starter · #1 ·
I am newly returned to the mountain bike community, so I apologize if this is a stupid question but here we go. I just purchased a 29 full suspension and was curious if you could change out a 29" wheel for a 27.5? eventually i plan on setting up this bike for more freeride/downhill. would like to eventually have a fox 40 fork. but until then can the tires inter change?
 

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Forks and frames are designed around specific wheel sizes. There are a couple of 26/27.5 compatible frames out there, but I don't know of any 27.5/29 compatible. There are outlying cases of modding and running smaller wheels on bigger frames, but in general, it's not such a great idea.
 

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R.I.P. DogFriend
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I am newly returned to the mountain bike community, so I apologize if this is a stupid question but here we go. I just purchased a 29 full suspension and was curious if you could change out a 29" wheel for a 27.5? eventually i plan on setting up this bike for more freeride/downhill. would like to eventually have a fox 40 fork. but until then can the tires inter change?
There is a term for what you are proposing: 'Frankenbike'

It's not a stupid question at all because you don't know until you know, and it's far better to find out by asking a question rather than by spending money on a Fox 40 only to find out what you would eventually have found out when you went from plan to action. Strapping a cannon to the hood of a Corolla doesn't make it a suitable battle tank. If you want a riding experience that is worthy of throwing down for a Fox 40, then I would advise getting a frame (and the other components) or a complete bike, that is designed with that in mind. Get the right tool for the job.

I wouldn't put a Fox 40 on the front of my 29 full suspension bike if someone gave it to me (and it is a relatively 'long travel' 29er).

The wheel exchange from 29" to 650b is not something I would advise either. The chainstay length (relative to other 650b bikes) and bottom bracket drop would likely be the biggest negative issues. The only swap of that sort that would make sense is if you had a 26" wheel bike and wanted to swap in 650b. That might work OK, or even be better (if they fit, and many times they do).
 

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Discussion Starter · #7 ·
Thanks for the responses I think I will keep rolling 29 for now. Just had some ideas rolling around in my head. I am 6'1" 235 so I am a little nervous about my front end suspension. My current forks are a set of rock shox recon silver. I am sure they are on the low end of their line and with my size there is some concern. I am by no means a downhiller but I will hit 4' to 5' drops on occasion. thought perhaps a down hill fork would be advantageous and with the limited suppliers and reviews for a 29 thought 27.5 might be the ticket. Time will tell all I guess
Thanks
 

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ballbuster
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Short answer is YES. Be prepared for a different ride....
... but why would you want to? Seems to me if the OP bought an XC bike but wants to freeride, he got the wrong bike. Changing the wheels won't help much if the frame isn't up to it.

That said, I find most folks who want 'Freeride' bikes are only riding XC level stuff anyway. Heck, I ride the same stuff the local Freerider wannabes (6"+ travel, full face helmets, body armor, can't pedal up the hill) around here ride on a 100mm front travel hardtail 29er... and I am not a svelte guy... and I ride it just about as fast... and I'm not that fast.

Putting a Fox 40 on an XC bike won't make it a freeride bike. It's only going to make it handle badly, and potentially shear off the headtube on a big hit. You're not going to turn your Subaru WRX into a rock crawling Land Cruiser by putting big tires on it.

Like others have said; You'll have none of the benefits of 29ers (big tires rolling over everything, keeping momentum), and none of the benefits of a 27.5er (tighter geometry, more flickable) either. You'll just be dropping the BB a bit, basically... which is what you don't want in a freerider anyway.

Also, don't believe the hype so much. 27.5 is the new buzzword, but personally I'm not sold. I love my wagon wheels, and the downsides everybody keeps talking about just aren't there for me. I don't see it, so I have little motivation to change.

If you're just starting out, I say ride a lot more until you have a better idea of what you want, and then get that.
 

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What are the BB calculations and will it result in impeding doom to put a 650b wheel on the back of a 29er?

First, consider that many bikes now have 'slack' chips. Such as the new Evil Following, Banshee 29ers, Rocky Mountain Altitude, and others.

Furthermore, some people like the small drop in the BB.

As for chainstays being longer, some 29ers now have shorter chainstays than some 650b-ers!

I say try it. Cheap wheels can be found on the PB or craigslist.

=== What is the real BB drop ? ===

The real drop will be 1/2 the difference in wheel diameter * the (wheelbase/chainstay distance ratio).

In other words, mathematically:

29er (622mm) - 650b (584mm) = 38mm
Divided by two is 19mm of drop.

However, since the back chainstay is less than half the wheelbase, the BB will drop more than half the 2cm, ie. a bit more than 1cm!

Now that's huge right, 1.0 cm to 1.5 cm is so so huge right? :)

Of course, if it is 650b front and back, then it will be 2cm *unless* you add a bigger fork to the front.

Why not? Add an inch of travel out front then. Solved.

As for that 2 cm. Again, some people add/minus a good fraction of that by running low psi and tubeless. Try it, 35psi vs 20 psi. With a rider it can be that amount of drop.

Based on the math, switching to a 650b at the back seems no big deal. if changing front and back, a few details need looking at:

1) How high was the current BB?

If it was a bike with a high BB, then problem solved.

2) How steep is the head angle?

If it was a steep headangle, then problem solved.

:)

=== Looking at Kona's offerings ===

Kona Process 111 (29er)
fork 120
bb drop 35mm
estimated BB height: 335mm (assuming installed tire is 29.15")
wheelbase 1173
chainstay 430
ht angle 68

Kona Process 153 (650b)
fork 160
bb drop 10
estimated BB height = 339mm (assuming installed tire is 27.5")
wheelbase 1190
chainstay 425
ht angle 66.5

The BB of the 650b bike is higher than the 29er by 4mm. The Process 111 with a 650b rear wheel would have ~1cm drop and be at about 325mm. But with an increase in front fork, say 140mm travel, then it comes to a nice midpoint.

A Kona Process 111, with a 140 Revelation fork, and big tires, runs at 349mm BB height (fact :) ). With a 650b tire it would be close to 329mm. Which is *higher* than the new Evil Following in low/slack mode.

The new Evil Following BB height is adjustable from 326mm to 334mm. So, a Process 111 with a 650b rear wheel would have the same BB as an Evil Following in low BB mode.

I'm not saying it is geometry ideal, just saying that the BB height is not such a big deal unless you change back and front and leave the fork the same. Even the shock sag will make for an impact and some people that sagalot (tm) will already have low BB by 2cm.

== Verdict ===

If you buy all that, then I have some swampland to sell you.

I'm not sure you should take any of those calculations tooooo seriously!

It's just some bad math and bike geometry fun.

You will never know unless you try.

Cause it's probably not as bad as they say :)

Someone has the balls:

Canfield Yelli Screamy - 160mm 650B fork and 650B wheels

View attachment 887298
The real answer, we need to ask him:

How does it ride?
 

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SNGLSPD
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Devinci Atlas

The Devinci. Atlas has short very chainstays and a high bottom bracket, your results might very, It has actually worked for this bike but it was built for my wife to make it more manageable with better standover. shown here 29"

AS far as how it rides, pretty awesome, arguably better than 29 and i love 29ers
 

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Just converted a stumpjumper from 29 to 650b. Took all the parts off of my beloved mondraker vantage hardtail to see if it would work. ( had pondered over the idea for a while ). .. it works out that the spesh has +1cm bottom bracket height compared to the raker... (with my 650 140mm revelations) with a bit of sag I am sitting roughly where I was to the floor as I was on my raker.. comfortable so far.. however if i start scraping or smashing pedals i will buy some 29 forks and go 27.5+ on that ****... 170mm crank set is also an option if clearance is a problem.. just have to go ahead.. see if it works..
 

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I am soooo close to pulling the trigger on a new 27.5 rear wheel for my Trance X 29er. But being unable to locate a wheel to test, the only option left for me is to buy one.
I can´t see any downsides.
I want the lower bb height, I´d also like it to be more slack, and as a bonus it should even be lighter. :)
/Allan
 

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The problem, as pipmbot already said, isn't if it'll fit. It's the fact that it'll still be a poorly handling XC bike that's not meant for big hits or DH. (scroll back up - he put it well already)
 

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Results from the Trance thus far are good.
The slight lowering of the bottom bracket is much welcomed on the Trance.
Turning seems to be easier than before.
Rear end is a bit lighter now, enough that I had to make some adjustments in the front to get back the front/rear balance I want.
So far, no downsides. I guess I won´t be able to figure it out for real until I switch back to the 29er rear wheel.

/Allan
 

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09' Rockhopper comp 29er to 27.5+

For me, it has worked out well. I converted my old hardtail rockhopper to a 27.5 plus and it rides great, it made it a new bike. Running a 2.80 WTB trailblazer rear and 3.0 WTB Bridger out front. Slightly clearanced the fork "horseshoe" with a deburring tool and the 3.0 fits fine. I also went to a 1x8 instead of the triple it came with. 32t oval chainring. 760mm bars.. Rode it yesterday and I'm still smiling!
 

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