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How wheel sizes, rim and tire widths influence riding performance

Friso Lorscheider is a marketing specialist at DTSwiss and intensively observed wheel development on the manufacturer side. We wanted to know more about the actual industry trends in this specific area and met with him for an interview.

At the beginning, let’s have a look back: How did it happen that new developments didn’t take in account the 26” size but only concentrated on the 27.5” and 29” formats?

In order to understand the development we have to look back at the mountain bike history. Mountain bikes where developed due to customer needs, when a group of people wanted to ride their bikes off-road. Since road bikes with 28” wheels were absolutely unsuited for this task city bikes with smaller wheel sizes and with thicker tires were used. These bikes were the kick off to develop mountain bikes and the 26” wheel size was never questioned.

Wheels with a smaller size are more stable, correct?

Yes, that was an issue at the beginning of mountain biking. Until a couple of years ago material development wasn’t that advanced and it wasn’t possible to build functional and firm wheels for mountain bikes with bigger sizes. But this has changed. From a technical point of view for most customers a bigger wheel size is the better product.

How so?

Bigger wheels rol better. That is simple physics. Furthermore they are firmer, don’t get nervy  that fast and due to the bigger foot print do have a better grip. This knowledge lead to the 29” wheel size, which basically is a 28” wheel with wider tires and bigger outer diameter. The rim size already existed. As a complement there are 27.5” wheels. 26” are being used nowadays on kid bikes only.

What criteria should I consider when choosing the wheel size?

That depends a lot on individual needs. Unless you are a very small person I would recommend a bigger wheel sizes to the mountain bike beginner. A smaller wheel size would make more sense to the ambitious mountain biker who prefer an agile driving style since the smaller wheel size is more playful.

Should my body hight influence the wheels size selection?

Only under extreme circumstances. I would always recommend a 29er to people with an average body hight starting at 1,65m.

Can a selection of either 27.5” or 29” be made independently from the bike geometry?

The longer the bike the better the driving stability and the sooner a small driver can drive 29” wheels. But if you prefer an agile bike and a short top tube you have to consider that big wheel sizes at a short distance between axles won’t work anymore. Ultimately at the point when my feet touches the wheel when turning. 

Does it make sense to adapt wheel diameter using different tire widths to use in different conditions?

Yes, it can make sense. Therefor you can find bikes with 27.5+” on the market. These are nothing else than 27.5” wheels with wider rims and wider tires. Normal mountain bike tires do have an average width between 2.1” and 2.3” inches. The outer diameter changes very little. This is different with 27.5+” wheels, which can be mounted with tire widths of 2.8” or 3.0”. In this terms a 3.0” tire on a 27.5+” rim has the same outer diameter as a 2.1” tire on a 29” rim. 

What advantages do I have using such a wider and bigger 27.5+ wheel?

The tire roles better, similar to a 29er. Additionally my bike’s driving stability improves significantly. A reduced tire pressure adds more comfort and the wider rim avoids that the tire flexes too much. The easy handling has a lot of benefits for the mountain bike beginner.

How exactly does a wider rim influence the driving performance?

Wider tires and rims can take off the fear from loose soil downhill tracks from beginners. I  suggest to each mountain biker to try a wider rim. It isn’t mandatory that you drive a wider tire at the same time. A 30 mm rim gives you the feeling to ride a totally different bike. Even myself I wouldn’t change my wider rims anymore!

Tipp:

The new R.C1 FS is a wheel size optimized full suspension bike for Cross-Country use. Two geometries for different preferences make it the perfect allrounder for bike marathon and Alpine Cross. The S and M sizes are designed for 27.5” use meanwhile the M, L and Xl sizes for 29” use. 

Learn more about the 2017 ROTWILD C-Series here.

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