29ers....Why?

WisePranker

Pretty simple question really, why are 29 inch wheel MTB's becoming more popular?

What's the benefits of the 29 over a 26 inch wheel?

What's the disadvantages?

ravey1981

disadvantage number 1: They look bloody awful

WisePranker

ravey1981 wrote:

disadvantage number 1: They look bloody awful

There is a bit of a Tonka toy/Hot Wheels look to them

supersonic

Been many a thread on this, and the only thing I can say for definite is:

- they will roll better over bumps, as the angle when they hit them is shallower
- the wheels are usually heavier, like for like, and take a little longer to get up to speed
- they require different geometry and usually fork offsets than standard mtbs

But like 26ers they vary a lot. So rather than viewing them as a seperate platform, I would just view them as part of the scene and something to try, just like we have diferent amounts of travel etc.

sherbert19

supersonic wrote:

Rather than viewing them as a seperate platform, I would just view them as part of the scene and something to try, just like we have diferent amounts of travel etc.

Got to agree with that, each to their own..

John Moore

WisePranker wrote:

What's the disadvantages?

None

I've 3 and one more on order.

The only 26er I've left is my local trip to the shops and dog running bike

Magpie9

There's a decent article about this argument in the latest MBUK.

supersonic

Every set up has pros and cone ;-) 'None' is a bit optimistic lol.maybe for you, but I have yet to find one that does everything better than a 26er set up to my liking.

Shaggy_Dog

Well, the other question is 26" wheels, why?

26" wheels were not designed for mountain bikes, in fact they were the wheels fitted to the converted beach cruisers - bikes designed for 12 year olds - that Gary Fisher & co used to ride the trails in Marin county in the founding days of the sport. 26" wheels were not there by design, they were there by default. I think it's highly unlikely that the wheel size they tried out first time is the "perfect" formula, since just about everything else on those bikes have been superceded. Suspension, disc brakes, carbon fibre and aluminium, threadless headsets, the list goes on...

I'll go through the science first

Because the wheels are bigger you sit lower down in relation to the wheel axles. This gives you more stability and you're less likely to go over the bars, it also make the bike harder to manual. The extra length in the chain stays compounds this, but then the extra length of the fork increases the front to centre measurement (distance from BB to front wheel axle), reducing the chance of going over the bars even further. It does all of this while keeping the pedals quite clear of the ground

Because the wheels are bigger the contact patch is long and thin, this is a double edged sword. A long contact patch has more rolling resistance, but on the other hand it increases grip on uneven ground, take this as an example. If you are climbing up a grippy slope and encounter a slippy root, more of the tyre is in contact with the grippier ground than would be on a smaller wheel, in turn decreasing the chance of the tyre breaking traction. The tyres also have a much greater air volume so you can get away with much lower pressures because the chance of a pinch flat is reduced, the shallower angle of attack as mentioned by Supersonic also helps in this respect.

Because the wheel is bigger it increases the trail (the distance between a point where an imaginary line drawn from the steering axis intersects the ground, and the centre of the tyre's contact patch, as shown below) A larger trail figure equates to slower feeling steering. The trail is affected by 3 factors; head angle (slacker = slower), wheel/tyre size (bigger = slower) and fork offset (less = slower). Since a 29er has a larger wheel it slows down the steering, this has meant most early frame designs had very steep head angles, reducing the inherent stability of the big wheels. Recently, most fork manufacturers have switched to a 45mm offset to counteract this, Trek and Gary Fisher bikes use a 51mm offset.

The bigger wheels have a greater moment of inertia, again a double edged sword. More inertia means a greater resistance to change of direction, slower acceleration and slower braking. On the other hand the wheel is less likely to slow down when attacking rough lines since the wheel resists deceleration more than a small one would do, it is also less likely to be deflected off course. When combined with the shallower angle of attack it means you can basically blat (technical term) through nearly anything with reckless abandon.

The big wheels mean compromises in the frame and fork structure. Since the fork has to be longer from axle to crown (assuming the same travel) it has to be stronger, in turn it increases leverage on the head tube so that has to be stronger too. The chain stays and seat stays are longer so are heavier and more flexible - good for comfort, not so good for frame stiffness. Longer + stronger = heavier, so it's not just the wheels that increase in weight. The wheels have longer spokes so aren't as stiff or as strong, conversely, they don't take as much impact due to their shallower angle of attack

Bigger wheels make your gears taller and have a greater mechanical advantage over the disc brake rotors. Testers have noted that gears shift more smoothly due to the bikes rolling momentum and 36 tooth cassettes are now available. To maintain braking power you need a larger rotor = more weight.


Great, so what does all this mean?

Positives

+The bike is inherently stable and can corner faster.

+The bike has more traction, cornering grip and braking grip.

+The bike rolls over rough terrain easier, like having "free" suspension.

+The bike maintains it's speed on draggy terrain because the wheel doesn't sink into deep mud, snow or sand

+The wheel can steer out of ruts easier

+Because the bikes have less suspension travel, they bob less and don't pitch fore and aft as much during braking and climbing

Negatives

-The wheels are heavier and take more energy to accelerate. The bike is heavier in general

-There is more rolling resistance in the tyres

-The frame and wheels can be flexier

-The bike is harder to make rapid direction changes

-The brakes are less powerful

-Big wheels may compensate for less suspension against rough ground but for drops, there ain't no substitute for lots of travel

-Riding a big wheeled bike requires a different approach to riding that some riders struggle to adjust to.

-The availability of parts can be difficult, UST tyres are widely available for 26" wheels but only Bontrager make tubeless ready 29" tyres.

-Shorter riders can find it difficult to fit due to high handlebars and toe overlap

A lot of these negatives are counteracted by the positives, yes, the brakes aren't as powerful and the acceleration is slower but because you carry more speed through corners, you brake less and don't have to pedal as hard after. The bike is harder to change direction on rapidly but because the bike can plough through rough terrain and there's so much grip you pick your line and stick to it, carving a smooth arc, rather than skipping around from one smooth patch of trail to the next.

Essentially, a 29" wheel is just another aspect of the bike's geometry, just like top tube length and handlebar width. As Supersonic mentioned, try not to paint them all with the same brush, some are great, others are awful. But I will say this, the best mountain bike I have ever ridden had 29" wheels...

supersonic

Good post.

Shaggy_Dog

Cheers

wobbem

Bloody hell mate.
See we are cleverer as well

Northwind

They make giants look less silly. And they make small riders look even sillier. What's not to like?