Chris Porter claims that the good traits of 29ers could have been done with 26in wheels if bike designers had done their job properly in the first place

Video: Pole Evolink 140 29 TR (2016) review

By Chris Porter

The off-road Bicycle industry is a funny old place.

Riding styles change, components change, trails change and in response to all of this the industry brings in rafts of new standards. No backwardly compatible, incremental improvements for the MTBer.

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No sir, if the rider wants access to the new stuff then he/she has to accept the complete obsolescence of their current steed. The rider will even have to get a new multi-tool with new tools on it because 4, 5 and 6mm Allen keys aren’t new enough for bike designers!

Go back to school

The clearest illustration of this ‘Primary School’ approach to design comes not with the 100s of different headset, BB, transmission and axle standards but with the whole wheel size debacle.

We were sold bigger wheels on a performance basis; 29er wheels were simply better for getting about off road in a spritely manner.

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Apparently 29er wheels roll over bumps better. Er, isn’t the problem here a suspension problem?

A 29er, yesterday.

A 29er, yesterday.

Apparently 29er wheels have calmer steering characteristics. Er, the problem here isn’t the size of the wheels but the shape of the bike.

Apparently 29er wheels are better for bigger guys. Er, can’t we just make bigger bikes for the bigger guys with the exisiting size wheels?

Apparenlty 29er wheels have more grip. Er, that would be a weight distribution issue then?

29er wheels were introduced in a blaze of glory and a load of poor saps believed the hype and bought into it.

Remember 26 inch wheels?

At a time when we had reasonably light but tough 26 inch wheels and tyres, in came the 29ers and a lot of people walked a long way home with bent wheels and torn, paper thin tyres. But whilst they walked we all had to listen to them witter on about how awesome that bike was (before it broke).

I, along with many others, spent some time addressing the actual performance issues of suspension, geometry, weight distribution and rider space instead of focussing on wheel size.

I made sure my fork seals were as well lubricated as possible.

I changed a few other seals in my shock and fork to get less stiction.

I changed the size and shape of the air springs and coil negative springs to get a better feel at the start of the stroke.

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I re-valved the dampers to get a nice balance in the corners.

I optimised my riding position to accommodate better weight distribution in the corners.

I fitted Angleset headsets and offset bushings to get a better head angle and BB height.

I didn’t have to make any new standards. Well, until development pretty much stopped on 26” tyres and 27.5” took over the industry. I was backed into a corner and forced to accept new standards.

What we’ve ended up with

So anyway… Back to the initial reasons for going to 29ers. Let’s work though what the designers did, what they do now and what we’ve ended up with.

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The designers decided to try a bigger wheel size to see if it brought any benefits over a raft of 26 inch bikes (which were too small, too steep, too tall and too short). Unsurprisingly they did have some benefits… Accidentally.

Can you spell serendipity?

Even though wheelbases didn’t really extend, the rider space did extend. It extended upwards because of the longer forks and bigger rims. They even extended a few mm in top tube lengths.

We got accidentally bigger frames. Instead of just building bigger frames for 26” wheels.

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In most cases this higher bar position would have meant a lack of weight over the front wheel but – accidentally – the bigger rear wheel meant a longer chainstay which means more weight transferred to the front wheel albeit by the feet rather the hands.

We know this was accidental because the designers have been reducing bar heights and chainstay lengths on 29ers ever since!

A thousand subtle changes

By using a bigger wheel and keeping the BB height roughly the same a thousand subtle geometry changes were introduced and some of them improved some parts of the bike’s handling.

In order to change direction on a bicycle the rider’s weight must move to the side to allow the vehicle to lean and stabilise in the corner. The increased BB drop (the distance the BB sits below the wheel axles) makes it much more stable but slower to turn and it also limits the speed of direction change, requiring more room to change direction.

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In the same way a slacker head angle would make the bike more stable and a lower BB height would make the bike more stable. Geometry improvement by accident again!

The first raft of 29ers had very XC focussed wheels and tyres which flattered the rolling speed of the vehicle because of the compliant carcass. rims and light weight. They felt grippy because of the flex in the tyre and wheel. They turned okay because they were light weight too.

But there were loads of tyre and wheel failures

One of the reasons for these failures is the larger diameter of the wheel. The tyre carcass construction is cross-ply. The carcass is laid at an angle from one side of the tyre to the other and then laid across at the opposite angle going back across. A smaller diameter tyre will give more stability because the plys wrap further around the wheel.

High volume, lightweight tyres with narrow rims on a large diameter wheel will flatter you… until they roll off the rim! Which they did.

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Nail the Strava segment and then walk home later when the wheel or tyre fails. When riders got tired of the tyres they started to add heavier DH style tyres for more stability. To offset this extra weight, riders started to add £2000 carbon wide-rim wheelsets.

You can’t get away from physics

We are back to physics again. A bigger wheel will be heavier than the equivalent strength smaller wheel. In order to make a 29er wheelset tough enough we have to run 1kg tyres and spend £2k on wheels?!

We’ve lost any acceleration once inherent. Rolling speed is compromised by the carcass strength and tyre pressures needed for lively riding.

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We are also back to trying to make the sprung/unsprung weight ratio feel nice over the bumps again. Back to the root of it all and it was a suspension problem after all.

The bigger, heavier tyres also resist turning even more! A whole load of straight lines started to appear on the mountains as ‘accidental KOMs’ were had by people who couldn’t get their vehicle round the corners at speed!

What happened next

To summarise, the initial lightweight XC focussed 29ers had some benefits because of their paper thin tyres. We’ve now lost these benefits as riders demand more tyre (and wheel) stability.

With that in mind, can anyone guess what new wheel standards the industry comes out with next? 27.5+ and Boost.

That’s right. Stiffer, wider wheels with better spoke angle that might have helped the 29ers five years ago. Bigger, softer tyres with less stability. Genius!

My genius plan

I’m going to approach Honda with a plan to finally beat KTM to the Dakar win by going big on the wheels and tyres.

I reckon a set of 12% bigger wheels with 30% bigger, fatter balloons on there should really improve the handling! They’ll p*ss it for the win.

I can’t see any problems with un-resolved rebound issues from the balloon tyres.

I can’t see how it would require more energy to spin a heavier, larger circle.

I can’t see any issues in gently changing the geometry of the bike simply to fit in larger wheels?

Should all be good. I wonder why they never tried it? Maybe they aren’t as clever as the designers in the bicycle industry.

I’m off to fit my Vivax assist for my next enduro. Don’t want to get beaten by a 29er!

  • AlexXSmith

    I was good for a bit, but then the anecdotal evidence and analogies overwhelmed me.