[jonKranked]

so i have a 2010 xprezo furax with a fox 40. 26" wheels. a former teammate had mentioned that he was able to fit 275 wheels in his so that got me curious about trying it. should also add, aside from the wheelsize and overall length/reach (wheelbase is 46.75"), the geometry of the bike has aged pretty well by modern standards.

a local buddy let me borrow his 275 dh wheels to do a test fitment. and sure enough, there was plenty of clearance in both the fork and the frame. i did measure the BB height with it, and woof. it was a bit over 14.5". with the 26" wheels it's about 13.5" as it stands. so it increased the bb height by just over an inch, which is more than just the wheel size change itself. his tires were a fair bit bigger than mine. bontrager g5 2.5. i've got michelin dh34 in 2.4 on my 26" wheels, but those are a small 2.4 and not a very big casing. so i'm kind of assuming that the roughly extra quarter inch of height was just due to tire size (based on 275 rims having 0.75" larger radius / BSD).

the other thing i remembered is i was messing around with head angle at the end of the season, and had the stanchions of my 40 pushed as low as possible, and the head angle was something silly - about 61°. so i pushed the stanchions back up until the head angle was a more reasonable ~63° and that dropped the bb to about 13 3/8".

so with that correction, and assuming i'd be using the same tire if i built up 275 wheels, the bb height would still be a hair over 14" (i'd guess about 14.125"). would that still be worth it? at what point is it just too high? i'm not racing anymore and aren't going as fast as possible, but i don't want it to ride like crap because of the extra bb height.

 

[6thElement]

It might be my tired brain, but wouldn't steepening the HA by raising the fork increase the BBH?

 

[jonKranked]

It might be my tired brain, but wouldn't steepening the HA by raising the fork increase the BBH?

tired brain, or maybe i described it poorly. to steepen the head angle i lowered the crowns down the stanchions (so there is more sticking about the top crown).

 

[StiHacka]

tired brain, or maybe i described it poorly. to steepen the head angle i lowered the crowns down the stanchions (so there is more sticking about the top crown).

Which should also lower the BB.

As someone who rode 27.5 wheels on 26 frames for years, I would not recommend. You'll never stop looking for ways to get the sky high BB lower. Cornering sucks, standover sucks, going down steep isht sucks, tire options may be very limited. Would not recommend.

 

[jonKranked]

Which should also lower the BB.

As someone who rode 27.5 wheels on 26 frames for years, I would not recommend. You'll never stop looking for ways to get the sky high BB lower. Cornering sucks, standover sucks, going down steep isht sucks, tire options may be very limited. Would not recommend.

fair enough. maybe i'll try a run or two once the season starts to see how it rides. swap the wheels out for a run or two. were you running the larger wheels in a trail / enduro bike or a dh bike?

re: tire options due to clearance, that's not what i'm concerned about.

 

[StiHacka]

fair enough. maybe i'll try a run or two once the season starts to see how it rides. swap the wheels out for a run or two. were you running the larger wheels in a trail / enduro bike or a dh bike?

re: tire options due to clearance, that's not what i'm concerned about.

Trail/enduro.

 

[Westy]

Roughly speaking with the forks in the same position your BB should rise 1/3 of the increased wheel radius (don't know your chain length). So if you use the same tire that should be about .25". Sounds like you can compensate for that a bit with fork height. Some people are a lot more sensitive to this shit than I am but .25" is in the range where I am not sure I would even notice. Give the fork an extra click of rebound or drop your preload a bit and dynamically things may be the same. Like you said, easy to go back if you don't like it.

 

[jonKranked]

Roughly speaking with the forks in the same position your BB should rise 1/3 of the increased wheel radius (don't know your chain length). So if you use the same tire that should be about .25". Sounds like you can compensate for that a bit with fork height. Some people are a lot more sensitive to this shit than I am but .25" is in the range where I am not sure I would even notice. Give the fork an extra click of rebound or drop your preload a bit and dynamically things may be the same. Like you said, easy to go back if you don't like it.

if i made the change, it would be from 26/26 to 27.5/27.5, so my assumption is that the front and rear axles would increase by the same amount - which would be the radius difference between 26 and 27.5 (about 0.75"). and that this would also equate to the same amount of increase to the BB.

 

[Westy]

if i made the change, it would be from 26/26 to 27.5/27.5, so my assumption is that the front and rear axles would increase by the same amount - which would be the radius difference between 26 and 27.5 (about 0.75"). and that this would also equate to the same amount of increase to the BB.

Sorry, for some reason though you bwere considering mullet

 

[jonKranked]

Sorry, for some reason though you bwere considering mullet

that's not necessarily off the table, but would result in a bike that's too slack, especially when i'm pushing the limit of slackness with 26" wheels on it.

 

[jonKranked]

i found the MY manual for my fork and reset the crowns to the factory height. this got the BBH down to right about 13.3" (HA was spot on 64°). i also remembered that I had started messing around with the fork not to make it slacker, but to actually slightly increase the BB height to get better ground clearance because the frame has 8.5" of travel, not the standard 8" that most dh bikes have.

 

[Sandwich]

i'm not racing anymore and aren't going as fast as possible

so why are you messing around with kind-of-big wheels?

I'm all in favor of experimentation and doing dumb shit with your bike (have you seen my rolling trashheaps) so I say go for it if you want to give it a shot, but at the same time- you have a bike that presumably rides well but just has slightly worse rollover than 650b. I'd say try higher volume or better/newer tires before messing with the wheels, but only because I'm largely in the same boat.

 

[jonKranked]

so why are you messing around with kind-of-big wheels?

I'm all in favor of experimentation and doing dumb shit with your bike (have you seen my rolling trashheaps) so I say go for it if you want to give it a shot, but at the same time- you have a bike that presumably rides well but just has slightly worse rollover than 650b. I'd say try higher volume or better/newer tires before messing with the wheels, but only because I'm largely in the same boat.

a couple factors:

part of it is actually tire selection. while there's still plenty of 26" dh tires to be found, the only ones i can find that are tubeless ready are michelin DH34. i tried a good condition set of DHFs, but they didn't work. maxxis never made a tubeless ready 26" DHF (or any of the DH tires) in a DH casing. i went through this last year, and the DH34 was the only TR 26" dh tire i could find that was worth trying. its a really nice tire, but they only released it in their race casing so it wears quickly as race tires are apt to do.

and why tubeless? because cushcore (which has been discontinued for 26") . i started messing around with inserts on my trail/enduro bikes and liked it. and opted for the cushcore on the DH bike. the park i ride (blue) is pretty rocky, and I'm pretty hefty. and i've found i like it an awful lot. speaking of rocky, the slightly larger wheels should make a slight improvement in terms of rollover (and maybe also carrying a little more speed, despite not racing, i still like going fast, i'm just not pushing myself the way I would if racing).

also just to future proof it a bit I guess, as this is the DH bike i'm gonna have for the foreseeable future. next new bike purchase will be a trail bike.

and speaking of dumb ideas i'm considering

Reach Adjust EC49-EC49 - To Suit 1 1/8" Steerer - 7mm

Specifications This headset will allow you to alter your top-tube length by /- 7mm. Fits headtube internal diameter Upper - 49.61mm EC49 Fits

www.workscomponents.co.uk

 

[jonKranked]

i'm also considering new brakes, my m800s are north of 15 years old.

 

[Sandwich]

My bontrager G5s are set up tubeless on stans flows. The rear loses air after several months of disuse, but holds up perfect for a full day. Haven't looked into inserts, but that makes some sense.

 

[iRider]

a couple factors:

part of it is actually tire selection. while there's still plenty of 26" dh tires to be found, the only ones i can find that are tubeless ready are michelin DH34. i tried a good condition set of DHFs, but they didn't work. maxxis never made a tubeless ready 26" DHF (or any of the DH tires) in a DH casing. i went through this last year, and the DH34 was the only TR 26" dh tire i could find that was worth trying. its a really nice tire, but they only released it in their race casing so it wears quickly as race tires are apt to do.

and why tubeless? because cushcore (which has been discontinued for 26") . i started messing around with inserts on my trail/enduro bikes and liked it. and opted for the cushcore on the DH bike. the park i ride (blue) is pretty rocky, and I'm pretty hefty. and i've found i like it an awful lot. speaking of rocky, the slightly larger wheels should make a slight improvement in terms of rollover (and maybe also carrying a little more speed, despite not racing, i still like going fast, i'm just not pushing myself the way I would if racing).

also just to future proof it a bit I guess, as this is the DH bike i'm gonna have for the foreseeable future. next new bike purchase will be a trail bike.

and speaking of dumb ideas i'm considering

Reach Adjust EC49-EC49 - To Suit 1 1/8" Steerer - 7mm

Specifications This headset will allow you to alter your top-tube length by /- 7mm. Fits headtube internal diameter Upper - 49.61mm EC49 Fits

www.workscomponents.co.uk

Never had issues with getting Maxxis DH casing tires sealing tubeless (disclaimer: only tried on hooked rims). Maxxis HP lists 26x2.5 UST Dual as well, not sure if really available though.

 

[jonKranked]

Never had issues with getting Maxxis DH casing tires sealing tubeless (disclaimer: only tried on hooked rims). Maxxis HP lists 26x2.5 UST Dual as well, not sure if really available though.

i tried 3 or 4 of the DHFs i had sitting around. none of them held air, they all leaked at the tire bead the entire way around. mavic 823s.

 

[iRider]

i tried 3 or 4 of the DHFs i had sitting around. none of them held air, they all leaked at the tire bead the entire way around. mavic 823s.

Strange, especially on that rim they work well for me. Only issues I have seen is if they were dirty.
Did you inflate them with a tube in it over night? That is what I do with a new tire.

 

[jonKranked]

Strange, especially on that rim they work well for me. Only issues I have seen is if they were dirty.
Did you inflate them with a tube in it over night? That is what I do with a new tire.

i was using old DHFs, which may have been the issue. point is still that i'd probably have better tire selection at 27.5

 

[jonKranked]

also, i maybe also have a second frame of the same model that i want to start collecting parts for

 

[jonKranked]

Reach headset might be out. There's an internal taper to the headtube that's in the 2-3mm range, the jaws on my calipers aren't long enough to accurately measure (I would estimate probably closer to 3mm). And with 7mm offset that would likely not give enough clearance between the headtube and the steerer.