# 26" tyre & on 27.5 frame, any effect?



## yayahoo (Nov 17, 2014)

Hi guys,

Stupidity of me, ordered a Hardtail 2014 Giant XTC 27.5 frame and to fit a 26" tyre & fork. Now I learned my lesson. Any effect of riding?

I am still searching the model for bottom bracket before the frame arrive. I checked on web, it is a pressfit which has extended 86mm or something. I cant get more info on the bottom bracket dimension and the length except for FS (they got drawings).



Need help guys.


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## keen (Jan 13, 2004)

Sell the wheels and fork and get the correct sizes. Using 26" wheels will result in a low BB height. The geometry is based on 27.5" wheels.


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## Impetus (Aug 10, 2014)

The frame was designed for a wheel with a larger radius. The big get effect will be the bottom bracket being closer to the ground by the same distrance as the decrease in wheel radius which is not a huge amount. Pedals will hit more stuff if you're not careful.

I can't help with the bb size. That sh!t's a black art as far as I'm concorned. I'll take a good old 68/73 English threaded shell, thank you.


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## Jerrad (Oct 23, 2014)

at least put a 27.5 on the front. it'll roll over rocks better, but you'll still have the torque of the 26" in the back.


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## Wisconsinite762 (May 24, 2014)

It would be best to use 27.5 inch wheels and fork, that is what the bike is designed for. If you already have the 26 inch wheels and fork I would sell them and get 27.5 inch versions.

Using 26 inch components on a 27.5 frame will cause the BB height to be lower and possible the HA to be slightly steeper.

For your question on the bottom bracket I recommend checking with the Giant sub-forum on this site if you haven't already.


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## noapathy (Jun 24, 2008)

I'd agree with the above - correct wheel size is always the best option, but if you're short on cash and have some 2.4"+ tires that would probably get you by till you could save the cash for a new fork/wheelset. Happy riding!


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## Guest (Dec 28, 2014)

1 option you have is 26+ tires which depending on brand will effectively equate to 650b. The surly DW is one such tire.
Wheels | Parts and Accessories | Surly Bikes


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## gotdurt (Jul 3, 2008)

I'm interested in hearing how this went; thinking about ordering a 27.5 frame to replace my 26, with the intent of eventually moving to 27.5 wheels. Bottom bracket height will be affected by 1/2" +/-, depending on what frame I go with (There is almost 1" different just between my two 26" bikes). My fork is a long-ish 130, so it shouldn't hurt anything (most of the frames I'm looking at are designed for 100-140mm).


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## Goran13 (Jun 26, 2012)

The wheelsize difference will be minimal, but take it into consideration. That frame is a different geometry and bb height will depend on the fork used along with wheel size. 

The BB on the other hand... I just replaced a pressfit 86/92mm on my Fuel EX8. What I found is that you can pretty much put any BB that is in the 86mm to 92mm range and it will work. The BB you should not use is a BB30, that's a different animal and is found on road bikes mainly. 
What you have to pay attention to is the axle outter diameter of the crank you're using. Mine was a Shimano and it was 24mm. You can mess with spacing rings and such to adjust chain line but really just stuff one in there. I got one from Wheels Manufacturing and it has a nice aluminium shell with angular contact bearings. They offer a few different bearings in different price ranges. Take a look at their site. There are many other companies that offer the same thing for different prices. KCNC, Chris King, SRAM GXP to name a few. 

Do the reading and understand what you have before purchasing as it could quickly become a headache if you order the wrong axle size in a bottom bracket. That's just my experience, anyone else have some other helpful tips?


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## 70sSanO (Nov 20, 2013)

Just a couple of thoughts.

The cleanest route is to sell the 26" stuff and get 27.5" stuff as everyone has already said.

You may, and I am somewhat doubtful, find a headset with a tall lower stack that may add 3-5mm. This won't make up for all the height you are losing but you will pick up a little. I have also heard of people putting a spacer in between the crown and the lower race to keep the crown from hitting the down tube. The only issue here is that it has to be short enough to keep the larger diameter to seat the lower crown race.

It is possible to have a press fit base plate fabricated to compensate the crown to axle geometry differences, and keep the press fit lower race, but that is probably pushing the cost beyond what you want especially since you will still end up with a somewhat odd looking final product, but you will be able to compensate for the geometry, at least on the front.

You will still have a 26" in the rear. Having a 26/27.5 (equivalent) setup isn't as bad as there will be less bb height issues. Then again taller tires may help as noted above but may negate using lower tire pressures.

If you want to go with a 26/27.5, you can swap out the fork and front wheel but that is probably not worth the slight savings over a full 27.5. But, if "you" are able rebuild the front wheel, you can keep the hubs and buy a new rim and the correct length spokes and build a 27.5 front wheel and just replace the fork. you can also build a 27.5 rear too. If you have something like CK hubs it may be a better route.

If you go with 27.5 wheels, you could try to combine both of the above if you can stuff them into that 26" fork.

All of this takes a lot of research and working a lot of numbers so you don't end up with an expensive piece of garbage. If that is not something you can do then sell the 26 stuff and buy 27.5 stuff.

John


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## gotdurt (Jul 3, 2008)

I have run a 27.5 front wheel on one of my 26" bikes (140 Fox), and it felt great, with little difference in handling. I didn't really feel any distinct advantage either though.

If you compare geometry between a random selection of various 27.5" frames to a selection of 26" frames you'll find that there is a great deal of overlap, and in fact most 27.5" frames that I've looked at are comprised of geometry that is 100% available on 26" frames, unlike 29ers that are a totally different beast. My 26" Yeti and my 26" Giant differ more from each other than some of the 27.5 frames do from them... in fact, their bottom bracket heights differ by an inch; 1/2" fits well within that margin alone. In fact, the range of fork lengths that a frame is designed for (On-One 456 is designed for 100-150mm) will almost make that much variance on one given frame... So, running a 130 fork with 26" wheels will still keep the BB height near the intended height with a 100mm fork and 27.5 wheels, and it will rail in the twisties! Also, I know of several people who are running 26" forks on 27.5 frames and wheels with no issues at all; the crowns come nowhere near down tubes, visibly no closer than they do on the 26"s (these are all Fox forks; can't vouch for others yet). On Paper, the numbers say that 26" wheels will work fine (if not well) in a 27.5 frame, especially for a temporary scenario, but I'd just like to find someone who has actually done it.


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## bob13bob (Jun 22, 2009)

it's gonna cost a bunch of money and time to do that to swap over. Personally, i'd just ride the 26er parts o the 27.5" frame. The bike will be slightly steeper, but we're talking a very small difference in actual wheel size.

of course lawyers from companies will tell you to ride as designed or your bike will explode.


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