2012 Giant Trance 26er with 27.5 fork?

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2012 Giant Trance 26er with 27.5 fork?
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Posted: May 10, 2021 at 9:53 Quote
Hey so I have an older 26" Giant Trance X3 that I'm tempted to throw a 27.5" wheel fork on with the same travel as stock.

Would this adversely affect the geometry of the whole bike?

Posted: May 10, 2021 at 14:48 Quote
bbarlow wrote:
Hey so I have an older 26" Giant Trance X3 that I'm tempted to throw a 27.5" wheel fork on with the same travel as stock.

Would this adversely affect the geometry of the whole bike?
It would change it. It’ll raise the front end by 0.75” at least (wheel radius difference between the two). Plus the axle to crown length difference of the fork. This will slacken the head angle, slacken the seat tube angle, and decrease reach. High chance it ends up riding really awkwardly.

Plus there’d be different fixes against the head tube that it might not be able to handle.

Seems risky to me.

Posted: May 11, 2021 at 2:41 Quote
I think 0.75" is over estimating... 26"and 27.5" are closer than many think

27.5" is actually a rim diameter of 584mm and 26" is 559mm , which makes a diameter difference of 25mm and a radius difference of 12.5mm ( 0.49") using like tyres...

So if you pay attention to fork axle to crown lengths.. ( i.e get a 27,5 fork with a relatively shorter A2C ) , you'll be fine.. just ride a tiny little more sag..

H..

Posted: May 11, 2021 at 9:56 Quote
hermichut wrote:
I think 0.75" is over estimating... 26"and 27.5" are closer than many think

27.5" is actually a rim diameter of 584mm and 26" is 559mm , which makes a diameter difference of 25mm and a radius difference of 12.5mm ( 0.49") using like tyres...

So if you pay attention to fork axle to crown lengths.. ( i.e get a 27,5 fork with a relatively shorter A2C ) , you'll be fine.. just ride a tiny little more sag..

H..

Fair enough, I’ll admit I expected 27.5” wheels to be 1.5” larger, as advertised.

So then, you’ve got about 12.5mm higher front triangle, with resulting slackening of the head angle just from the wheel change. Then you must consider any offset differences between the old and new fork. And then axle to crown length difference.

I still think there’s a high likelihood the new parts make the bike ride like shit.

Posted: May 11, 2021 at 10:17 Quote
Dr-YTMTB wrote:
hermichut wrote:
I think 0.75" is over estimating... 26"and 27.5" are closer than many think

27.5" is actually a rim diameter of 584mm and 26" is 559mm , which makes a diameter difference of 25mm and a radius difference of 12.5mm ( 0.49") using like tyres...

So if you pay attention to fork axle to crown lengths.. ( i.e get a 27,5 fork with a relatively shorter A2C ) , you'll be fine.. just ride a tiny little more sag..

H..

Fair enough, I’ll admit I expected 27.5” wheels to be 1.5” larger, as advertised.

So then, you’ve got about 12.5mm higher front triangle, with resulting slackening of the head angle just from the wheel change. Then you must consider any offset differences between the old and new fork. And then axle to crown length difference.

I still think there’s a high likelihood the new parts make the bike ride like shit.

Ground contact is made by the tire contact patch and not the rim, so actual tire diameter is more relevant than any other measurement.
I admit I don't know much about actual tire diameters but if 27.5" and 26" are close enough representations of tire diameters .75" is closer than .49".

Posted: May 11, 2021 at 10:25 Quote
You could of course run your old 26” wheel in the 27.5” fork….

Posted: May 11, 2021 at 17:28 Quote
I want the lower angle of attack of the 27.5". The slacker head tube would be welcome. Doesn't seem worth it in the end from what you all are saying

Posted: May 11, 2021 at 17:31 Quote
You could run a thinner front tire to drop the height a little bit.

Posted: May 16, 2021 at 21:36 Quote
You can use a bike geometry calculator to enter the data of your current setup and then with a 27.5 fork and front wheel to compare the two.

Not done the math, but given that overforking by 10mm is usually fine, you can get the bigger wheel and fork, just go 10mm less on travel so it all evens out.

Despite what most people say I found a significant difference going from 26 to 27.5. If you're buying used and don't spend too much money on this it could be a fun experiment. Maybe add an angleset into the mix while you're at it?

The other option is to ditch the project and just get a new bike. Apart from the wheels geo will be better overall. But if that's not happening and you can test a 27.5 for little money then go ahead.

Posted: May 17, 2021 at 5:53 Quote
Real world experience:

I just put on a new fork yesterday, went from 150mm 27.5” pike rct3 to a 160mm fox factory 38. My bike came specc’d in 160mm fox gear as an option when I bought it.

New fork has 10mm more travel but is a total of about 14mm longer axle to crown length (150mm pike is 542mm per SRAM chart, and the 160mm 38 is 555.7mm per Fox’s spec chart). Comparing the two I’d say that’s a close estimate.

Source:
SRAM: https://www.servicearchive.sram.com/sites/default/files/techdocs/gen.0000000005176_2017_fs_oil_air_coil_spring_spec_rev_d_english.pdf

Fox:
https://www.ridefox.com/fox17/help.php?m=bike&id=1089

I put 10mm’s of spacers under the stem, just as I had it with the Pike. But I lost some height replacing the crappy Acros headset with a Chris King Dropset. The Chris King dust cover has a significantly lower profile than the acros (probably half).

All in all I estimate I’m probably 10mm higher up at the handlebars with this new setup compared to previous. I’m going to ride a bit, and decide if I’m going to take those spacers out from under the stem or not, or magnesium get a longer stem to get some reach back, but it’s a very very noticeable change.

The difference in feel is startling with just those few mm increase in front end lift. I can’t imagine what going from 26” to 27.5” fork and wheel would do, all else being equal.

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