You are hereForums / By Discipline / Mountain (off road) / MTB Gear / 27.5" outside diameter cf. to 26"?

27.5" outside diameter cf. to 26"?


By Marvin - Posted on 22 July 2015

NB: Originally posted elsewhere on the Global Riders Network and appears via syndication.

I am interested in perhaps putting a 27.5" wheel in the back of my 2011 Trance, but am confused about whether it would fit. Reason is to get the rolling advantage, and also to slacken the head angle a bit for racing.

Logic says it might not fit, given the difference between the two should be about 3/4" (or 20mm).

However, this website says a 27.5 with a Pacenti Neo-Moto 2.1 is 702mm (27.6") wide, which would fit easily:

http://forums.mtbr.com/27-5/26-vs-27-5-vs-29-tir...

For comparison, looking at the existing 26" wheel on the Trance (which is a Crossmax rim with a 2.25 Crossmark tyre) the diameter (including knobs) appears to be around 700mm (27.5")...

That doesn't seem to be quite consistent/believable?

As it stands, I have about 8-9 mm clearance currently in the triangle on the existing tyre.

Therefore the Pacenti above, while fitting quite easily (if the specs are true) would seem to offer little advantage in attack angle. Maybe a bigger tyre would offer gain? Maybe I am just better off putting on a 2.4 or something on the 26"?

Confused!

I don't have access to a 27.5 wheel to test it, so any advice appreciated.

Cheers

Tags

I can't see any positives in this? Of the wheels you would swap to a bigger one you'd do the front every time. It would ride really strangely as different size wheels create a different arc when you turn and lean in. I am still running the opposite of what you want to do and it has it's merits and drawbacks.

Has to be the other way around for sure

Fairy, what arev the positives and negatives you find?

Slackens the HA, always a positive.
Back wheel turns on a tighter arc making the bike slightly more nimble than a same same bike, rear tyre also hooks up a bit better, lower BB, all positives.

The bike is a pig to drift as each wheel wants to do different things and doesn't feel balanced, front is more likely to push, both negatives plus I guess the rollover would be a bit worse but that's more important at the front.

Back tyres are cheap too Smiling

It always intrigues me why you would put the longer radius turner on the front - wouldn't that give the front more understeer? I really notice the relative understeer when I switch to my 29er (and that has a sharper head angle).

Also, isn't the rollover benefit greatest on the back, where there is more weight (I note we run significantly more tyre pressure to compensate for that extra weight up back)? I'm always happy to mogul the front wheel off a rock, as given the lower weight on it, I get less forward momentum check. On the other hand, I always track for the back wheel to avoid the bumps - which can really check momentum.

I know putting the wagon wheel on the front is the standard practice, but, for the above reasons, it doesn't make sense to me. Also, I am looking to sharpen up the head angle, and raise the BB a tad, given that the Trance is a bit slack for racing (by the wife, improving).

I'd like to get the rolling benefit on the back, while keeping the front a nimble, playful 26er. Maybe pie in the sky?

Perhaps I could try a tyres option, to see if there is any noticeable difference (e.g. something like 2.4" on the back, 2.1" on the front)?

Correct me if I am wrong but wouldn't putting a 27.5 wheel in the back of a 26inch frame while leaving the front as 26 actually steepen the head angle???

That's correct. Will also (in theory) make it marginally harder to loft the front as the distance between the BB and the contact patch becomes longer in comparison as the front wheel comes up.

Correct Marvin, but you only really have problems with the front pushing when you are cornering while seated. With modern geometry this is becoming less of a problem but if you want your bike more nimble a bigger rear wheel may work for you.

I ride a hardtail and really couldn't care about rollover, slackening the HA was more important as my bike sat far too steep at 68deg. If I didn't hate the frame so much I would have bought a straight steerer fork and an angled headset but I didn't see the point in wasting money.

As above manualling will be tricky, you may need to raise the bar height.

Can someone clarify please

bigger wheel up front
= SLACKER head angle and LOWER BB

And are the results the same using a bigger wheel only as opposed to a 650b fork and wheel
But more (slacker and lower) with a 650 fork as well

A bigger rear wheel will 'sharpen' the head angle. For XC type riding this sharper steering can liven the bike up a little. For faster more aggressive riding it will start to feel too twitchy and sketchy.
To combat that, you could use an Angleset headset to slacken it off, but once you start messing with a bike so much, you might ruin it's balance.
To slacken the HA, an easy fix is to use a bigger front tire.

More to the point, I doubt it will fit your bike. Just by looking at the photos, the tire diameter is very close to that suspension brace. The crossmark is also a small tire for its size rating. Using an aggressive 2.4 tire you might run into issues anyway. From there, I don't see the point of using a 27.5 wheel with a skinny 1.9ish tire.

I know the mojo can take a 27.5 rear wheel, and many people have done so, but always with a front. They also offer to sell you a new rear from their 27.5 bike.

this really isn't rocket science.

Can you all go and get your bike, with its wheels still attached and "something" about 1/2 an inch thick, that's about 12.5mm in our speak.

Rest your bike, wheels on the ground, against a wall, try and have the bike as upright as possible.

Measure your bb height and get a good "sight" of the head angle, measure it if you have the tools. Now shove your "something" under the front wheel. What has happened to both the bb height and the head angle compared to the positions without the "something". If you can't visually see a change in head angle, get "something" thicker to help show you what is happening.

Take the "something" out from under the front wheel and stick it under the back wheel. Now what has happened?

Fairly simple really.

Bloot, re the 'b wheel and 'b fork, it's just like using a thicker "something" than you just did. Most a-c measurements on a 'b forks are taller than 26" forks to allow for more clearance. If you are worried about it being too much just use a fox 26" fork, they never use full travel so you are unlikely to have issues of rubber on crown contact.

Marvin, you are over thinking things, just get on your bike and have fun. Every change you make will have both good and bad consequences to the way your bike rides. If that wasn't true there would be one perfect bike by now and all other manufacturers would be broke.

jeez kit
You know I'm not a technically minded bloke
Who else do you know who cable tied their spokes to their fork
Might have to use my head as a something and get my missus to do the measurements Sticking out tongue

I would have thought you could use one head as something and use other head to sight the angles. My eyes are getting old but I believe I see two heads in your profile pic.

Yes Andy, bigger wheel on front slackens head angle, smaller wheel on front steepens head angle. A bigger wheel than what came on your bike will raise BB height regardless of which end of the bike it is fitted to, a smaller wheel than what came on your bike will lower bb height regardless of which end you fit it to. Questions answered now leave your better half alone, she has suffered enough.

liteville have now made their bikes size specific and their wheels size specific, ie for large or xl riders doing xc n trail they have a 29 up front n 27.5 out the back, medium sized riders get a 27.5 up front n 26 out back n small riders get 26 n 26, im not sure if it goes into their gravity bikes, they give a good explanation for this , ive seen a test of their long travel trail bike, 27.5f 26 r and after a few rides couldn't tell the difference, apparently it handled really well, although this bike was designed like this.....as for "something " I suppose you could use " anything "

I think the main truths came out here.

Apologies if this thread is so 2009/2010 - looking around the web that seems to be the time when all this 69er and 96er stuff was the rage on the forums.

I guess now you just takes your pick with your new bike - with most average size people opting for 27.5 as the best compromise. None of this retrofitting stuff.

Realistically, I could/should just build the wifi a hardtail in 27.5 of appropriate geometry, and be done with it.

But really, we can't justify the cash, particularly with a perfectly nice bike sitting there that is of seemingly little value to anyone else second hand. And its not that far off being right - the slack head angle is very forgiving given that she doesn't hit rock gardens at speed (and we all know what that means for stability).

Anyway, I'll go the tyre route, just for fun, and see if I can notice any perceptible difference compared to the current setup.

Ah remember way back in the crazy days of 2002 when 26" up front 24" on back was so cool specialised designed their big hit around the concept.

Putting the Bigger wheel on back makes no sense at all unless you like feeling as though you have a head start on your next over the bars experience.

Maybe its the suspension gettin you all hooked up, time for a new shock.?

"Putting the Bigger wheel on back makes no sense at all unless you like feeling as though you have a head start on your next over the bars experience."

Yikes, don't even think about it.

I'll measure the head angle change and report back. I think you are exaggerating.

(And shock is great thanks - is is an after market TF Tuned adjusted for weight - best investment in a FS bike you can make IMHO if you are not the standard 75 kgs).

Some interesting concepts but I think one important factor has been overlooked.

You are talking about changing the size of a wheel to make a static difference of lets say 1".

Remember that while riding the suspension travels up and down by more than 1" which based on the theories being suggested has a greater impact on the fork angle than changing the wheel size.

But the suspension will act almost the same meaning the bike will sit ~1" higher at all times.
A 1" increase in BB height is massive unless you are on something super slack and long.

The OP's bike is already pretty steep and tall with a bigger rear wheel the HA would be beyond 70 degrees which is nuts, it would be good for stupid tight switchbacks...................annnnd, nothing else.

Liteville's reasoning on running wonky wheels- http://www.liteville.com/t/25_579.html

I have a Liteville 301 with 26'' all around and have a decision to make at some stage
Bike has a tapered tube but runs a straight steerer fork - A RS revo 32
It's a great fork, but would like something with 34 stanchions and a tapered steerer
A 650b wheel will not fit in the revo fork, so no idea how a 650 wheel would feel in a 26'' fork

My decision is do I get a 26'' or a 650b fork
I went riding with a mate (a far better rider than me) who stuck a 650b wheel in his Fox 26'' forks
And was so impressed with the results he is now on the lookout for a 650b front wheel

The other thing is, Liteville's are quite slack (66.3) but with a relatively high BB (354mm @ 26'')
I would like to 'future proof' myself with a 650b fork, but slacker with a higher BB doesn't sound like what I need for the riding I do

I've read all the blurb on Liteville's running the different wheel sizes and haven't read a lot of negatives (recent AMB is probably the most neg thing I've read)

So I'm still in 2 minds
Do i get a 26'' Fox and try a 650 wheel with the option of running a 26''
Or do I bite the bullet and just go for a 650b fork and hope I like it better
Note that my 26'' 819's are 8 years old and need replacing as well

I'm thinking there may be some confusion over the terms used.
Slacken the head angle is to give it more rake, this tends to equal slow steering and move the riders centre of gravity back which makes it more stable (to a point) when descending the steep stuff.

You can achieve this with a bigger wheel on the front or running longer fork

Steepen the head angle means to get the rake closer to verticle. This will result in more responsive steering but can make things very twitchy when taken too far. And it places the ride weight further over the front wheel meaning OTB antics could be more prevalent on steep stuff

This could be achieved by putting a bigger wheel on the back.
Both options will result in a slightly raise bb height

As for how much effect it will have Google Sheldon Brown fork length for s pretty thorough explaination.

But basically 300 years of bicycle engineering design shows a head angle of around 73* (off the horizontal) is spot on for nice handling on flattish terrain. The more DH orientated the lower you want the number to make it more slack, down to mid to lower 60s for some DH sled

My bike descends well enough for what I do
I would actually like it to 'rail' turns better (adjusted for ability limitations)
So it would seem, apart from some rollover improvement
A 650 fork and wheel would be getting away from what I want
As it would slacken the head angle and raise the BB

I'm thinking a 26'' fox 34 now

Andy.

You could go to a shorter travel fork and possibly even find some offset bushes or have the shock modded, a slight change shouldn't mess around with pedalling performance too much.
You may find that with the bigger wheel you don't use/need quite as much travel, I run a ~5" fork on my hardtail that was designed for a 6" fork so running the 650 front kept my HA about right.

There is something awry with all that Liteville stuff (and that finger bike video).

I don't care what they say, my experience is that the front wheel rolls over obstacles more easily than the rear.

As noted above, I always ride a line for the rear wheel for that reason.

Really? I'd give a kidney or two and someone else's for a Liteville.

Meh, the back wheel is just a passenger which is why I like my hadtails, on moderately rough XC trails I seem to roll through stuff as quickly as the guys on dual suspension bikes. There is however a lot more chance of a foot flying off or the bike going off line which is what makes riding fun.

Every few years there is a Rampage event to watch. The events predate the whole debate.

My wheel size isn't the limiting factor.

26" bikes have gotten really cheap. Enjoy the benefits.

Some racers may claim an edge. If you're recreational wheel size may not be worth worrying about as other factors may be at play.

I personally find the benefits of travel adjust forks are more about the head angle change than the travel. With bottom out limiting even 100mm can take a decent drop. Bike can change from snappy XC, AM to sled at flick of a switch. Some standard forks you can mod to shorten travel. Beats changing wheel size combos.

Ride.

For me the benefit of a bigger front wheel is that the bike doesn't get hung up on stuff as much and this is most useful when descending steep stuff - less proclivity for going over the front.

It's good for climbing too but stalling on something is less likely to result in hurting yourself than a trip over the front. So if it's only one wheel then I'd go on the front.

My preference though would be to do both. It's a roughly 12-15mm increase in BB height. Noticeable but not a deal breaker. A slight loss in cornering stability that you'll quickly learn to adjust for, compensated for by less pedal strike on rough stuff.

*face palm*

:|

maybe you were actually on to something.

http://i.dailymail.co.uk/i/pix/2015/07/30/10/2AF...

Just getting back to the original question posed. Will a 650b wheel and tyre fit on the rear of a 2011 Giant Trance. I have been toying of the idea to try
650b wheels front and rear of my Trance, as I need to upgrade my wheels anyway?

If someone has a pic or info that would be great.

Thanks

Comment viewing options

Select your preferred way to display the comments and click "Save settings" to activate your changes.

Best Mountain Bike