26" wheel in 27.5" fork

PB Forum :: 27.5/650b
26" wheel in 27.5" fork
Author Message
flag nealy578
Posted: Jan 24, 2015 at 2:42 Quote
Im looking to do this with my covert carbon, I've just ordered the 15 36 160mm in 26" but wondering if i should go for the 27.5 version to future proof things, frame could then follow then wheels. Going to run a -1.5 degree angleset too so this is in the equation, This will drop the head angle to 65 degrees, and keep everything else the same barring the wheelbase which i will gain 20mm. If i go for the 26" one i will get a 65.6 degree head angle, drop the bb 4.2mm and gain a further 6mm reach. Now I'm a little undecided on what to go for!

Will the 650b fork not look silly with a 26" wheel? like 2" mud clearance at the arch?

The fork rake is 37mm for 26 and 44mm for 650b, how will this further affect the geometry?
flag singulardroid
Posted: Mar 5, 2015 at 3:20 Quote
so finally, would you recommend use 27.5 fork on gambler with 26 wheels? as i undestood it will change geometry and I will lose 2 degrees in headtube angle (it will become stiffer lets say). what about handling? Does it differ that much? I know I will feel 2 degrees loss, but overall handling, would it be a big issue?
flag Singletrackmac
Posted: Mar 11, 2015 at 21:54 Quote
nealy578 wrote:
Im looking to do this with my covert carbon, I've just ordered the 15 36 160mm in 26" but wondering if i should go for the 27.5 version to future proof things, frame could then follow then wheels. Going to run a -1.5 degree angleset too so this is in the equation, This will drop the head angle to 65 degrees, and keep everything else the same barring the wheelbase which i will gain 20mm. If i go for the 26" one i will get a 65.6 degree head angle, drop the bb 4.2mm and gain a further 6mm reach. Now I'm a little undecided on what to go for!

Will the 650b fork not look silly with a 26" wheel? like 2" mud clearance at the arch?

The fork rake is 37mm for 26 and 44mm for 650b, how will this further affect the geometry?

Don't think you'll really be able to tell that it's a 26" wheel on a 27.5" fork. If you ran some 26" 2.1" or 2.2" tires than you would have about an extra 1/2" of clearance at the arch vs a 27.5" wheel. Remember, 27.5" is 1" larger diameter than a 26" so that means only a 1/2" difference in radious, which is what matters for clearance. I would just run some large volume 26" tires like some 2.5" wides. I am running these on my AM bike and their diameter is 27.4".

As for the fork rake, that will not matter if you run high volume 26' tires since the diameter will end up being a few 16ths of an inch under 27.5". The idea behind having the longer rake on the 27.5" fork is to account for the extra 1/2" the 27.5" wheel lifts the axle off the ground. This extra rake keeps the bikes handling characteristics close to as if it where a 26". All it does is help prevent the handling from becoming too sluggish since the wheel base, chainstay, stack and bb drop all increase as you increase the size of the wheel. 26" is the standard for performance so things like the rake need to be adjusted in order to try and get the feel that we are all accustom to with the 26".
flag DerkGort
Posted: Apr 27, 2015 at 4:02 Quote
Hi, does the handling/geometry/BB hight change a lot if I would get a 27.5" frame but fit 26" fork and wheels on them?
flag crashrobinson
Posted: Apr 27, 2015 at 18:44 Quote
I'm looking fo a good trail to,ride long distance in Ontario Canada with a backpack and a tent like three days around 60 km per day ..does anyone know of such a trail
flag deeeight
O+
Posted: Jul 15, 2015 at 21:02 Quote
While the diameter is nominally 1.5 inches difference, in practical terms its usually not that big and more importantly to geometry of the bike concerns, its the difference in RADIUS of the wheel/tire that matters to the math. A 650B x 41 tire is 26.5 inches in diameter, a 650B x 60 is nearly 28 inches. There are certainly 26er tires that break into the 27 inch territory (afterall, Fox provided maximum tire diameter numbers for their forks more than tire width maximums, and for the 32s it was 27.0 inches and the 36/40 platform it was 27.3 inches, and those numbers didn't include the extra clearance leftover for mud/debris on the tire). More important to a bike's geometry is the fork offset, with 650B and 29er models typically having increased offset numbers to improve the steering on today's bikes with ever slackening head angles. If you put a new 650B with increased offset on an older 26er frame, with 26" tires, the extra fork height that slackens the frame angle slightly will still steer better thanks to the offset boost than simply putting an equal length 26er fork on that frame. If your 26er frame is designed say, around a 120 to 160mm travel range fork, its quite possible to find a 650B fork in 140mm that's the same length as a 26er would be at 160mm. Then you'd still be in the geometry compatibility range for your frame.
flag dufoz
Posted: Jul 19, 2015 at 13:47 Quote
And if you take the problem the other way around? Meaning a 27"5 wheel in a 26" fork... does it change the geo?
flag adwamski
Posted: Jul 21, 2015 at 4:19 Quote
My bike has a 120mm 493/39 mm QR offset fork. I am looking to upgrade to 15mm axle & 130 - 140mm fork. I am looking at 650b Revs with 130mm and a 42mm offset. Will this mess the bike up?
flag DerkGort
Posted: Jul 21, 2015 at 4:31 Quote
I am looking for a frame, now everything is it the 27,5" weels... any body knows for sure if I can put a 27,5" weel In a dorado pro fork? its a 2012.
flag deeeight
O+
Posted: Jul 21, 2015 at 6:53 Quote
"And if you take the problem the other way around? Meaning a 27"5 wheel in a 26" fork... does it change the geo? "

Assuming the 26" fork can safely take the 650B wheel/tire (not all can, it depends on the specific tire used and the specific fork without bottoming into the crown underside at full travel) then at most it changes the geo by 1 degree if its just in the front (and not the rear wheel going 650B also) and a quarter inch of BB height increase. If you do both wheels then you get 3/4 inch of BB height increase and no other changes in geometry. That's why so many early adopters did conversions.

"My bike has a 120mm 493/39 mm QR offset fork. I am looking to upgrade to 15mm axle & 130 - 140mm fork. I am looking at 650b Revs with 130mm and a 42mm offset. Will this mess the bike up? "

Well the number I found for that 650B Revelation 130 is 501mm length, so only 8mm higher than your existing fork. That's at most maybe going to be a third of a degree difference slacker and a couple mm higher BB height.

"I am looking for a frame, now everything is it the 27,5" weels... any body knows for sure if I can put a 27,5" weel In a dorado pro fork? its a 2012. "

Any 26er fork that could safely clear a 26 x 2.7 tire can take a 650B x 2.35 tire instead. That's why for example, Rockshox Psylo's were a popular fork for early adopters doing conversions. Out of the box they took the tires straight away without any internal mods needed. Fox forks prior to them offering 650B specific models could all clear them in the brace area fine and could take the shorter tread height 650Bs under the crown (like Racing Ralph 2.25s and Rocket Ron 2.1, Slant Six 2.1, Quasimoto 2.0s, Karma 2.0s, etc) of the 32 stanchion models without any internal changes. Larger/deeper tread tires you might have to add a bit of oil to limit the travel a bit for crown clearance. 36s and 40s could take the bigger tires from the start as the Fox tire diameter maximums include extra space for mud over and above the limits of 27.0 (for 32s) and 27.3 (for 36/40s). All X-fusion forks were the same, some simply needed a 10mm bottom out reducer if you ran a bigger example of a 650B then available. As to the Dorado Pro's... like Cannondale Lefty's, they can take 650Bs and even 29ers simply by making some internals adjustments to limit the
maximum travel. I've even seen people set them up with fat bike tires.
flag ryan198232
O+
Posted: Jul 22, 2015 at 15:00 Quote
Why is everyone saying the head angle is going to change going from 27.5 to 26? Yes it'll change if you leave a 27.5 out back but if youre changing both front and back to 26"(would only assume this is the case) the only thing that is going to change is bb height
flag DerkGort
Posted: Jul 22, 2015 at 15:11 Quote
ryan198232 wrote:
Why is everyone saying the head angle is going to change going from 27.5 to 26? Yes it'll change if you leave a 27.5 out back but if youre changing both front and back to 26"(would only assume this is the case) the only thing that is going to change is bb height
Yes, that is what I think too. Will the bb hight be that diferent/lower than 26?
flag ryan198232
O+
Posted: Jul 22, 2015 at 15:13 Quote
DerkGort wrote:
ryan198232 wrote:
Why is everyone saying the head angle is going to change going from 27.5 to 26? Yes it'll change if you leave a 27.5 out back but if youre changing both front and back to 26"(would only assume this is the case) the only thing that is going to change is bb height
Yes, that is what I think too. Will the bb hight be that diferent/lower than 26?

Realistically it should drop about 1/2".
flag nealy578
Posted: Jul 22, 2015 at 15:16 Quote
Bb raised about 12-15mm when I put 650b wheels in the covert
flag c4mtb
Posted: Sep 3, 2015 at 17:19 Quote
so whats the general consensus on this, yes no maybe? Razz

 


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