Category Archives: fat

Is bigger better? 29er vs 26er and wide vs skinny tyres

Are bigger wheels and tyres better? In this post I’ll share some thoughts and experiences of testing different wheel sizes and different tyre sizes.

I’m at least a decade late to the wheel size wars, but I wanted to test for myself whether the recent bandwagons of larger wheels and fatter tyres are the real deal or just industry hype designed to sell more bikes.

I’ve tested four different set ups:

  1. A 90s Raleigh Dynatech MT4 with a Girvin Flexstem and rigid fork and 26×1.8 Panaracer XC Fire tyres (~23 lb)
  2. The above bike with 2.35 Maxxis Larsen TT rear and 2.35 Maxxis Ignitor front (~24 lb)
  3. A 2017 KTM Aera Pro carbon 29er hardtail, with 2.4 Schwalbe Rocket Rons, and 2×11 Deore gearing (~25 lb)
  4. A rigid steel Salsa El Mariachi with 29×2.35 Maxxis Ikon rear and 29×3.0 Maxxis Chronicle up front (~28 lb)

The test course consisted of a ~10 km off-road loop with ~200 m of ascent, broken into 4 individual climbs, some flatter sections and some downhills. Being Portugal, the conditions were bone dry with a mixture of weathered bedrock, a kind of gravel made of fist-sized stones, and dusty hard-pack. Basically, these are fire roads but built without bothering to condition the surface for vehicles.

The climbs are somewhat technical in places to due rocks, and their average gradients range from 6% to 13%, and the downhill sections are similar in character.

Before discussing the results — a word about the wheel sizes. Set up #1 (26×1.8) used the smallest wheels, with the 26×1.8 tyres resulting in an outside diameter of just 25.6 inches. In setup #2, the 26×2.35 tyres gave a diameter of 26.7 inches, more than a whole inch larger. To put this into context, the difference between 26×2.1 (22.2 inches) and 650b x 2.1 (27.2) is slightly less than 1 inch. This means that, in effect, my comparison between #1 and #2 is also a test of whether the size difference between 650b and 26 results in a noticeable difference in speed, even if it isn’t actually a test of 650b itself.

Setup #3 is fairly standard in that it used 29×2.4 (29.3 inches) on both wheels, and setup #4 used an unorthodox combination of 29*2.35 on the rear and a 29*3.0 on the front. The 29+ front wheel has an outside diameter of 30.5 inches, which is 1.2 inches larger than the other 29er wheels used in this test.

The results are very straight-forward: the bigger the wheels, the faster I climbed. My 26×1.8 setup was the slowest, but felt the fastest. Next was my 26×2.35 setup, which climbed about 10% faster. The carbon 29×2.4 hardtail was approximately another 10% faster still, and my 29×2.35 / 29×3.0 bike was 4% faster than that, but felt the slowest. All in all, the fastest setup was about 26% quicker than the slowest.

In general terms, these results aren’t too much of a surprise, as it’s been claimed (perhaps even known) for years that larger wheels are generally faster for XC type riding, even if the industry has been strangely unable (or unwilling) to prove it with transparent testing.

There were two big surprises in this data. The first surprise is that just by opting for widers tyres, I was able to get an extra 10% of climbing speed from my 26er. In the more realistic case of a 26er with 2.1 tyres, switching them to 2.35 ones should still mean a climbing speed increase of ~5%.

The second surprise is that the heaviest bike of all was the fastest climber. Naively, I expected that it’s steel frame and forks, together with its heavy 29+ front wheel, would result in a bike that’s a bit slow for a 29er, but still loads of fun. The best explanation I have is that the 30.5 diameter front wheel rolled over obstacles and bumps even better than  a “normal” 29 inch wheel – the same “science” behind 29ers being faster than 26ers, but with a bigger wheel.

Another interesting point is as far as I am aware, this is the first test to compare a 29+ front with a 29er rear against a normal 29er. Some magazines have tested proper plus bikes against “skinny XC” equivalents, usually concluding that the plus bike is fun but slower. This might be because the rear wheel suffers more rolling resistance because it’s this wheel that the riders applied torque to when they pedal, resulting in greater losses due to tyre deformation. By combining a fast rolling real wheel with a 29+ front wheel, maybe I got low rolling resistance where it counts more, and a large diameter wheel for rolling through obstacles where that counts more.

And it certainly does feel like the 29+ wheel can roll over anything in its path. In fact, during a recent marathon race I found I was able to pass riders on the climbs by taking the slightly rougher, outside line to overtake, thanks to the amazing rolling capabilities of that wheel.

On a more general note, the results show that bike weight is not such a big deal as long as you have the right technology on your bike. In the tests described here, it is clear that any time penalty from running a 29+ front wheel is outweighed by the speed increase provided by this wheel. Likewise, the extra weight of setup #3 (normal 29er) over #1 (26×1.8) is outweighed by the benefits of the 29er wheels.

Some technicalities:

I started each session well hydrated and with a good breakfast (identical on each day) 2 h behind me, and an energy bar eaten a few minutes before starting. During the climbs I maintained a 95% level of effort, determined using a heart rate monitor. I rested for 5 minutes between each climb.

When doing this kind of test it’s important to be honest and state that it’s next to impossible to run a side by side test of two different bikes or components in a completely controlled manner. Variables like the weather conditions, trail conditions, nutrition, hydration level, tiredness etc. are likely to differ between runs, and as a rule of thumb I’d say the uncertainty in speed differences are likely to be around 2% or more. It must be frustrating being a pro racer trying to figure out which tyres or bike set up makes them faster, because  even a few tenths of a per cent is enough to make the difference between winning or coming second, yet detecting a 1% difference over a test course is technically very challenging.

Nevertheless, in this case it is clear that my results are statistically meaningful, not only because the difference in times are quite large, but also because these differences were consistent across all four climbs. What’s more, my times consistently decreased each time I tried larger wheels and/or wider tyres.

Megamo Tank fat bike review

Behold the Megamo Fat Tank. I’ve been riding this one for 6 months now, I thought I’d write up some thoughts after testing the bike under various conditions and different off road routes. My usual ride covers about 80 km, mostly off-road, with an elevation gain upward of 2000 m.

Although I own the 2016 model, this review should also apply to the 2017 version as it appears to have identical specifications.

The drivetrain components are as basic as one would expect at this price-point (RRP 500), with a mix of no-frills Shimano Altus and Acera components which get the job done reliably. The Shimano M315 hydraulic disc brakes work surprisingly well.

I like very much the look of the bike, which strikes a good balance between the brash paint jobs of yesteryear and the understatement of modern bikes. The bike itself attracts a lot of attention and is always a talking point.

To make sure I get the most out of it, I immediately looked for cost-effective upgrades to make to my new bike.

Although the 3×8 transmission works well, the gearing isn’t quite low enough to deal with the kind of steep, low traction climbs that the fat tyres would otherwise let you ride up. Swapping out the Tourney HG400 12-32 cassette for my spare HG41 11-34 one helped a lot, but after a few months I still feel I need even lower gearing, so I’ll be fitting a 9 speed Deore 12:36 cassette and the corresponding rear shifter and chain. I’d say a 2×11 with an 11-45 cassette would be ideal, but upgrading to 11 speed is too costly to justify on this bike for the time being.

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The stock tyres were extremely heavy, weighing in at more than 2 kg a piece, so I changed them for a pair of 120 TPI folding Floaters from On One, saving about a kilo per wheel in weight, and making a very noticeable improvement in rolling resistance.

I also fitted a pair of lighter inner tubes, saving an additional few hundred grams per wheel. Thus, merely by changing the tyres and tubes I was able to remove a good 3 kg of rotating mass, and just as importantly, get a reduction in rolling resistance.

In collaboration with my local bike shop, I tried to do a tubeless set up to get a further reduction in rolling resistance, but the current rim and tyre combination doesn’t appear to allow a tubeless configuration. Which is a shame, because I think this bike would turn out to be almost as fast as my XC hardtail if it could be set up tubeless.

One minor issue is that even on the size L bike, the stock seat post is too short at 350 mm to accommodate very tall riders like myself, and the unusual seat post diameter (30.4) limits your choice of replacement post. I went with a 400 mm Kalloy SP248 alloy seat post, in black and without decals.

There are many other upgrades that could be done to shave off a few hundred grams here or there, but at a rather poor cost to benefit ratio compared to the performance gains that could be made by improving the wheels and tyres.

How fast is my Megamo Tank? Based on my Strava times, on a typical off-road climb I am about 15 per cent slower on the Tank than on my lightweight steel hard tail. Although it is a little heavy, the extra weight of the Tank is nowhere near enough to explain why it climbs so slowly. The extra rolling resistance from the fat tyres is to blame, and going tubeless should reduce the climbing handicap to something like 7 per cent.

However, on steep, loose or technical climbs my times are quite a lot faster, just as they are much faster on all off-road downhill sections. How much faster is hard to quantify, because it depends on the terrain. Sometimes the slower climbing is negated by being much quicker on the subsequent descent, sometimes not. On some climbs I am actually faster on the fat bike than on my hardtail!

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A better way to assess the speed gain / loss from using a particular bike or set-up is to look at the overall time taken to ride a climb and the following descent, or several ups and downs rolled added together.

I’m still collecting data on this, but on one of my most traveled Strava segments, a 6 km route with a 250m climb, my best time on the fat bike is only 2 per cent slower than my all time personal best. On another climb+descent segment, my current personal best was obtained riding the Tank, and was 4 percent quicker than my best times set on any of my other MTBs.

The verdict: A entry level yet capable fat bike that would benefit from a few inexpensive upgrades.

Full catalogue specs of the 2017 Megamo Tank can be found here.

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