Technical FAQ: Winter commuter tires and 29er downsizing

In Technical FAQ, Lennard Zinn explores a reader's custom winter rubber and responds to another's desire to user 26-inch wheels on a 29er

The holiday season has passed and I hope you had a merry and white Christmas, and a happy New Year. If you had a white one, or a black ice one, as many in the Northeast experienced, here’s a studded-tire tip a reader sent me that seemed appropriate for the season:

We have icy roads in Minnesota, and grip is an issue on a bike, even with studded tires.

I take an old road tire, 700×25, and cut off the bead. I put the tire, less the bead, inside a studded tire as a tire liner, which prevents flats. It also allows low pressures without the risk of a pinch flat.

I commuted in December in -6 Fahrenheit temp with 42 psi (measured inside the house) in a 240-stud, 700×42 front tire. It was 36 psi after my hour-long commute home. I store the bike inside at work. I measured 34 psi in the 108-stud, 700×35 rear tire. I run the more aggressive tire in front for better control and braking. As you might imagine, there is massive rolling resistance; just sit up and the bike rolls to a stop.

Road conditions this week were really bad after a wet snow and then a big drop in temperature. Road salt does not work in colder temps; even high traffic roads are severely rutted, and these relatively narrow (compared to 26-inch sizes) studded tires worked far better at lower pressures.

Since I don’t use studded tires, I ran this by my friend Mike Prendergast, who rides practically every day no matter the conditions. He created a movie about commuting through the winter, and he said:

I’m not sure what tip Ted is trying to pass along (flat protection, low pressure traction n…). I have never had a problem with studded tires getting flats. My route to work was so goathead infested that liners were mandatory on regular tires for a trail section in Old Stapleton, but studded tires never flatted over 10-plus years riding to work. And the only grip issues I’ve had were with low stud count tires (approx. 100) on ruts. A 240-stud tire is really good on small ruts as there are studs on the edge and middle.

Enjoy riding on ice, and stay safe!

Can I use 26-inch wheels on a 29er?

Dear Lennard,
I’ve been using your videos to fix problems with my bike and have really learned a lot and just wondered what your thoughts are on using 26-inch mountain bike wheels on a 29er frame. I have 29er wheels and find it too much effort using it for commuting to work and thought about using 26-inch wheels with slick or commuter tires when commuting to save hassle in changing the tires each time.

Dear Samuel,
Assuming that you have disc brakes and the rotors are the same size on both wheelsets, you certainly can do it. You will need to deal with a large change in ground clearance. In going from a 29er tire to a slick for 26-inch mountain bike wheel, you’ll have a radius difference on the order of 45mm. In other words, your pedal at the bottom of the stroke will be around 45mm (1-3/4”) closer to the ground. If you are okay with this, go for it. For commuting, it may be fine. You might have a bottom bracket height as low as 250mm, or it could end up being closer to the road bike standard of 265mm, depending on the bottom bracket drop of your frame.

How quickly does carbon fatigue?

Dear Lennard,
Tom Ambrose (p. 174), in his book, The History of Cycling in Fifty Bikes: From the Velocipede to the Pinarello: The Bicycles that Have Shaped the World, makes a comment about carbon fatigue in that they can lose rigidity in a few years.

I’ve seen lots on fatigue on other materials (steel, aluminum, titanium), but this is the first mention I’ve seen on carbon. (I can imagine it’s hard to figure because not all carbon is created equal.)

But anyways, what is your take both on his statement and carbon fatigue? (I’ve never been able to get even a crooked, let alone straight, answer to this.)

I asked Phil White at Cervélo for his thoughts on your question:

When properly designed and manufactured, there should be no loss in stiffness or strength over the life of a carbon bike frame.

Cervélo carbon frames are lasting 10 times longer on the fatigue machine than aluminumn frames. And our aluminum frames lasted 2-10 times longer than competitors’ alloy frames.
—Phil White
Co-founder, Cervélo Cycles