Noob Advice- New Buildout - 27.5 wheels on 29er frame?

PB Forum :: All Mountain, Enduro & Cross-Country

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gman00910

Posted: Jul 26, 2020 at 20:57

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Hey All! I've checked around a ton and haven't seen much on this topic.

The frame I'm interested in is the S-works Stumpjumper, not sure what year, possibly 17 or 18'. Anyways, I'm in love with the geometry of the stumpjumper, color of this version, and also the internal space you can put CO2 and tubes in(I do much better without a pack on me)....The only problem is that its a 29er.

youtu.be/8PDGXSpswZA --> Here's a video of a trials guy that does it, but this isn't really my style. Apparently he does jumps too so maybe it'll be okay? Yes it will lower the BB and maybe skew the angles by a few degrees, but I'm sure It wont negatively impact me....thoughts?

*background*
I just started last year jumping around at Valmont park here in Boulder, Co with my roomates old 07 santa cruz blur. A month ago, I went to Deer Valley and Park City and stayed at a friends. First bike trip, and man, was it a f*cking blast. I have now found my second passion, behind snowboarding of course

The birms, the tabletops, the ripping feel you get while skiin', ahh! I now found a summer action sport and so beyond happy about it, as Corona has really took a tole on my stoke meter recently...So I bought a crappy $300 dirtjumper to get me by until I have a buildout, and even took it to Trestles(Winter Park) and although all the snickering I got from my friends, I crushed it!

Anyways, so I'm looking for a all around ripper, one that can do Enduro if I need to(ugh), jumping at valmont(learning the large boys soon hopefully!), and overall trail/tech riding.

If you have any other frame recommendations it would be much appreciated! I'm a recent grad in a first job so money is still tight for me, trying to keep it to around 3k.

Thanks,
Garrett

Danzzz88

Posted: Jul 26, 2020 at 21:09	Quote
Don't even entertain the idea putting 27.5 wheels on a 29er frame, the bottom bracket will be so low and you will always be hitting your pedals. In some cases you might even hit the chainring on the floor before bottom out.

gman00910

Posted: Jul 26, 2020 at 21:21

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Danzzz88 wrote:

Don't even entertain the idea putting 27.5 wheels on a 29er frame, the bottom bracket will be so low and you will always be hitting your pedals. In some cases you might even hit the chainring on the floor before bottom out.

Appreciate it mate. I wouldn't think a 1.25" drop would be detrimental but I'll trust ya. I suppose I should drop the love goggles and keep looking.

ski-n-bike-da-east

Posted: Jul 27, 2020 at 5:00	Quote
By only outing 27.5 wheels on a 29er frame, the bottom bracket with be super low. However, you could try bumping up your fork travel, and using offset bushings in the rear to regain some bb height. I have never tried this or heard about it being done with 2 27.5 wheels, but i know people who have put a 27.5 back wheel on a 29er and used offset bushings to regain some bb height and steepen angles

ski-n-bike-da-east

Posted: Jul 27, 2020 at 5:03	Quote
Have you checked out the santa cruz bronson frame?

skerby

Posted: Jul 28, 2020 at 9:38	Quote
It would be sick if you could find a 29er with super high BB, you need to run the 29 fork though, as you have 20mm of extra fork length with 29, so if you did 27 fork and wheel you would have a really steep HA

gman00910

Posted: Jul 28, 2020 at 11:47

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skerby wrote:

It would be sick if you could find a 29er with super high BB, you need to run the 29 fork though, as you have 20mm of extra fork length with 29, so if you did 27 fork and wheel you would have a really steep HA

Hmm okay that makes sense...thanks man! So in your humble opinion, you think its worth putting on 27 wheels and see how it rides? I mean, 1.5"/2 is just .75"(I was wrong before lol), so not even an inch of BB drop. I really don't think that would be critical considering I'm also 6 foot/160lbs. But I may be wrong. Hmmm... this is hard man. That pro does it apparently but hes more of a trials rider, I'm sure it would still rip though.

gman00910

Posted: Jul 28, 2020 at 11:55

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ski-n-bike-da-east wrote:

By only outing 27.5 wheels on a 29er frame, the bottom bracket with be super low. However, you could try bumping up your fork travel, and using offset bushings in the rear to regain some bb height. I have never tried this or heard about it being done with 2 27.5 wheels, but i know people who have put a 27.5 back wheel on a 29er and used offset bushings to regain some bb height and steepen angles

I have but a little over the budget for what I'm looking for.

So the BB height is 338mm, and 27 wheels would drop it by .75" or 20mm. Really doesn't seem like it would be an issue but I'm not sure. Hmmm..

bcpblurker

Posted: Jul 28, 2020 at 12:03

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I put a 650b rear wheel in my Yeti 5.5c. 2.35 Magic Mary.

It cornered like a banshee, and I didn't get any pedal strikes, but have thin pedals and 170mm cranks.It felt pretty good.

It did not climb well at all on technical trail, it felt like the lower back end affected the way the linkage worked. When popping and pedaling over a small branch or rock it would dive into its travel in an unsettling way.

I switched back to 29er because I do have a lot of technical trail to climb.

If you can fit like a 2.6 or larger rear tire on the 650b rear wheel, I would recommend that to find a middle ground.

ricochetrabbit

Posted: Jul 29, 2020 at 1:43	Quote
Why not just get a 27.5 frame?

R-M-R

Posted: Feb 28, 2021 at 17:42

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gman00910 wrote:

Appreciate it mate. I wouldn't think a 1.25" drop would be detrimental but I'll trust ya. I suppose I should drop the love goggles and keep looking.

Appreciate you being willing to take advice.

• In the video you linked, the stock geometry of Fabio Wibmer's Enduro is about 0.5 cm higher than the Stumpjumper (accounting for dynamic geometry, rather than static geometry).
• Urban huckers do most of their pedaling on flat ground or with the front wheel off the ground, so pedal strikes aren't much of a concern.
• 27.5" wheels have a radius of 19 mm less than 29" wheels. Combined with the difference in frame geometry, that's over an inch lower.
• Pedal strikes usually occur when the suspension is significantly compressed. When your crank is at 6 o'clock and the suspension is compressed, the end of your crank or bottom of your pedal may be 10 cm or less above flat ground. Add a chunky rock or edge of a bench-cut trail to cut down on your clearance and you can see how an inch is a huge difference in your clearance. It's not the inch of difference to the BB height, it's the inch less pedal-to-rock clearance when you only had an inch in the first place.

There are bikes with geometry similar to the Stumpjumper and there are many ways to store tools on the bike. You can get brackets like these for a few dollars on AliExpress.

AdinK

Posted: Feb 28, 2021 at 18:30

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gman00910 wrote:

It really would not work your bottom bracket would hang way too low and u might even be able to put a crank or pedal to the ground just by bouncing on the suspension. On trails you will be pedal striking all the time and it just won’t be fun. I would just look for a regular 27.5 frame.

janderson

Posted: May 24, 2022 at 22:35	Quote
https://m.pinkbike.com/news/sea-otter-classic-2021-cody-kelleys-dual-slalom-bike.html

Gravelben

Posted: May 24, 2022 at 23:22

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ricochetrabbit wrote:

Why not just get a 27.5 frame?

Or just ride it as a 29er?

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