Powered by Outside

Geometry Change from 27.5 to 29

PB Forum :: Mechanics' Lounge
Geometry Change from 27.5 to 29

 Post Message | Latest Comment
Author Message
flag mmarkey21
O+ FL
Posted: Feb 17, 2020 at 11:20 Quote
Hey all, I tried searching but didn't find much in the way of my specific question. I'm toying with the idea of putting some 29 wheels on my 27.5 frame. I've already checked and a 29 clears in the rear no problem. I know in general the bb height will increase 19mm. However, I was also going to reduce the fork travel by 10mm and flip the switch to "low" which reduces bb height by around 5mm and also slackens the hta.
I found this calculation for change in fork travel online - (20 x sin(head angle) x chainstay length)/wheelbase
Using this I'm at (20xsin(66.1) x 434/1231 = ~6mm . Adding the additional 5mm drop in using the switch to lower my bb height it looks like 19mm (increased wheel diameter) minus 11mm (reduced travel/"low setting") I'm at a total of 8mm increased bb height?

Any geometry experts have any thoughts? This would put me at 353mm bb height. Do you think it'd be noticeable from a handling perspective? Mainly looking for some gains in pedaling on the climbs but also don't want to alter everything so much as to lose much traction/control on the descents.
flag cmcrawfo
Posted: Feb 17, 2020 at 16:31 Quote
27.5+ wheels with plus size tires generally have a similar diameter to standard 29" wheels/tires.

You are thinking too hard.
flag mmarkey21
O+ FL
Posted: Feb 18, 2020 at 19:42 Quote
cmcrawfo wrote:
27.5+ wheels with plus size tires generally have a similar diameter to standard 29" wheels/tires.

You are thinking too hard.

Ha! Edited due to a stupid typo. Currently it's set up as a 27.5 and I'm looking to toss a 29" fork and dropping the travel to 140mm. A 29" rear wheel clears no problem when fully compressed.
flag eshew
Posted: Feb 19, 2020 at 23:19 Quote
I'd guess that unless you need a higher bb on your trails you'll be losing a bit of manuverabilty and cornering precision with a 19mm increase in bb height. 29's do give you a bit better rollover and traction but I think that would be offset by the higher bb.

You'll obviously get a bit more traction for climbs but a different tire could help as well without going through the trouble. 353mm bb height isn't insanely tall about 7-12mm above some 29's. But those have 150ish rear and 160 up front. Chances are with the shorter suspension you'll be riding higher so real world average bb height might be even taller than static geometry.

**I'm not a geometry expert, be warned.
flag cmcrawfo
Posted: Feb 19, 2020 at 23:22 Quote
Honestly....The most effective way to get climbing gains is through personal training.

The bikes not broken, so dont try and fix it.
flag jurassicrider
Posted: Feb 20, 2020 at 0:13 Quote
I don't want to disapoint...but you will not climb better with 29" wheels unfortunately.
flag cmcrawfo
Posted: Feb 20, 2020 at 7:51 Quote
gotohe11carolina wrote:
go mullet!

Totally.


.... I mean, if you want change just for the sake of change, you may as well go with the trends.
flag mmarkey21
O+ FL
Posted: Feb 20, 2020 at 8:06 Quote
jurassicrider wrote:
I don't want to disapoint...but you will not climb better with 29" wheels unfortunately.

That’s not what all the bike reviewers say...

You all are right, might try just lowering the travel up front from 160-150...maybe even 140. Just steepen the HA a little more for those steep, punchy climbs.
flag eshew
Posted: Feb 20, 2020 at 8:09 Quote
Or you could just slam your stem.or go lower rise bars.
flag doxey91
Posted: Feb 21, 2020 at 1:28 Quote
Seat tube angle is probably going to affect climbing more than wheel size. Maybe try put your seat all the way forward before wasting loads of money.
flag mmarkey21
O+ FL
Posted: Feb 21, 2020 at 8:31 Quote
Thanks fellas. I think I might just take 10mm of travel out and lower the stem slightly to see what that does. My seat is already slammed forward.
flag gotohe11carolina
Posted: Feb 21, 2020 at 10:29 Quote
what kind of climbing problems are you having exactly? Standing climbing is more technique driven. Seated climbing can benefit more from tweaking your platform.
  • Previous Page
  • Next Page

 


Copyright © 2000 - 2026. Pinkbike.com. All rights reserved.
dv65 0.008806
Mobile Version of Website