Saturday, July 26, 2014

25mm Tires Beat 23mm - Report on

The skinnier and higher pressure the tires, the faster the bike, right? Well, no, actually. Speed comes down to a variety of factors, and even many pro road riders these days are choosing wider rubber for training and racing.

So what should you be considering when you're weighing your tire width options? First up is, well, weight. A 20mm or 23mm tire is just plain less rubber than a 25mm tire -- so it will weigh less than the wider tire, resulting in lower rotational weight, which means you'll be able to spin your wheels up to speed that much quicker.

But weight isn't the only thing to consider. Rolling resistance, aerodynamics, grip, and ride quality all play an important role in how fast you ride. 23mm tires still have 25mm tires beat in terms of aerodynamics, but with the newest aero rims, which tend to be wider than previous incarnations, that advantage is negligible, and 25mm tires perform better in pretty much every other way.

You mean 25mm tires actually offer less rolling resistance than 23mm tires? How does that work? Yes, it's true! A 25mm tire at slightly lower pressure has a wider contact patch that actually allows the tire to conform to imperfections in the road surface much more effectively than a hard, bouncy 23mm tire, resulting in lower frictional forces and, yup, a faster roll. That greater contact patch also gives 25mm tires better grip through corners, meaning you can roll through them at higher speeds with greater confidence. And, of course, wider tires provide a softer, more comfortable ride -- which doesn't seem related to speed until you consider that the better you feel, the harder you can push.

So consider widening the gap between you and the competition by widening your tires. Our favorite racing and training tires are all available in 700c x 25mm sizes. 


Caledonia said...

Substantiating the above is this link to a summary of Jan Heine's several tire tests:
Much food for thought!

Miley said...

Another consideration for us Fat Old Guys is rider weight. To adequately support our load, either the air pressure or volume has to be increased, compared to lighter riders. Increasing pressure to the max allowed by a tire worsens the ride and performance characteristics noted above.

Go with a wider tire's increased volume, lower the pressure and enjoy the improved speed, handling and comfort. For loads around 250# and higher, try 28mm.

Two cautions: A high quality, supple tire is required to realize the benefits, and be sure your bike will accommodate the tire width: chain stay clearance near the bottom bracket and brake adjustment.

Tango Bravo said...

I agree with most of this with the caveat that the short articles quoted oversimplify things. In-depth analysis of the pros and cons of different tire sizes could easily fill a book. For example, the statement that wider tires have a greater contact patch is only true if you run it at a lower pressure. (The contact patch area is proportional to tire pressure and the weight supported.) The wider tire enables you to run a lower pressure with less potential for a pinch flat.

I personally notice more difference in ride comfort between tire brands and construction than between different widths. Miley's comments were spot on.

Caledonia said...

I agree with all of the above.
The optimizers among us might find this article and chart of interest: