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Tech FAQ: Tubular tires and rolling resistance

Dear Lennard,
I just read a great article entitled, “Where The Rubber Meets The Road.” Unfortunately, none of the tires used were full tubulars. Do you know where I can get a reliable comparison of tubular tires with information on friction and power loss?

I just bought a new set of carbon tubular wheels, and I want to educate myself a little more before I buy tires.
Matthew

Dear Matthew,
I do not know of a similar test that has been done on tubulars. The closest thing that I know of that is in the public domain is an article I did in Velo in 2012 (“Resistance is Futile”) comparing rolling resistance of different widths of the same tubular models entitled.
― Lennard

Dear Lennard,
I’m a cold-weather rider in Cincinnati, and this is to provide additional input on disc brake performance. In September, I bought a Trek Domane with TRP HY/RD cable-actuated hydraulic disc brakes. Last week I rode it for the first time in below-freezing weather (25 F). The brakes were fine until I stopped at a traffic light after riding about 10 minutes. When the light turned, I could barely get the rear wheel to turn. The calipers would not release the rotor.

At this point, I began walking home with the bike on my shoulder. After a couple of minutes, I decided to check the rear wheel and noticed that it rotated with less resistance but was still not free. After another 10 minutes of walking I tried it again and the wheel was free.

When I took it to the Trek dealer, it was about 15 F, and it did the same thing. The brakes have been returned to TRP for inspection, and they are sending a free replacement.

A couple of additional observations:

1. The week before, I’d done a 30-mile ride with the temperature in the mid 30s with no problems. I was wondering if 10 F would make that much of a difference in seal behavior or the fact that it was below freezing might indicate that the issue was in the mineral-oil hydraulic fluid.

2. My front brake is the same as my rear brake and did not experience the same issue.

Additional investigation determined that the hydraulic fluid/o-ring was NOT causing the problem. The problem was too much friction in the brake cable. My fingers were strong enough to overcome the friction when applying the brakes, but the elasticity of the o-ring and the little spring on the cable attachment were not enough to overcome the friction when trying to open the calipers. A new brake cable with low-temperature-tolerant lubricant has solved the problem. Apparently, the fact that the front brake cable is so short prevented the development of such a large amount of friction there.

Dave

Dear Dave,
Great research there! Yes, that has been my experience—that a full-hydraulic system, while more sluggish in cold weather due to thickened hydraulic fluid, won’t freeze up completely like a cable can. I’ve ridden a lot this winter in single-digit and low teens temperatures with my two disc ’cross bikes, mainly with one equipped with SRAM Force1 hydraulic, and a lesser amount with one equipped with Shimano R785 hydraulic. Both of them have braked absolutely perfectly, no matter the temperature.

This subject of cable freezing came up here a year ago in Magura’s answer (http://velonews.competitor.com/2015/01/bikes-and-tech/technical-faq/technical-faq-disc-brakes-extreme-cold_358757).

That said, I managed for many years to keep my brakes working on cantilever-equipped ’cross bikes during many cold winters, so, while the cable run is longer with a disc, it still should be doable to keep it unfrozen — unless you bring the bike inside into a warm, moist environment and then head out in the cold right afterward.

In temperatures a lot lower than the ones you were writing about, this article (http://velonews.competitor.com/2015/01/bikes-and-tech/technical-faq/technical-faq-disc-brakes-cold-weather_358172) mentions a consensus toward cables for increased reliability. With the TRP HyRd, I suppose one could be getting either the cold-weather benefits or detriments of both hydraulics and cables.
― Lennard

Dear Lennard,
I recently upgraded my winter bike, an old and trustworthy Ultegra-clad Dale R1000 from 2001, with a pair of Shimano 105 shifters with under-the-bar-tape routing. Looks really neat and tidy, but it turns out that the spring that pulls the rear mech towards the small cogs isn’t strong enough to pick up the slack in the cable caused by shifting to a higher gear. I often have to shift two up and one down to get into the desired higher gear. Do you know of a known “spring upgrade” for the rear mech, or does it look like I need to upgrade there to a newer model with stronger spring action as well?

— Maxim

Dear Maxim,
Since it’s your winter bike and you’re riding it in moist Amsterdam and may be taking it in and out of warm, moist buildings, you could be experiencing some of the cable-freezing problems discussed above in the prior question and answer.

Besides avoiding the above moisture issues as best you can, I am sure that you could also reduce that cable friction significantly by, first, using low-friction coated cables (these are becoming standard on high-end component groups nowadays) coupled with better, low-friction cable housings, and, secondly, being careful with housing length so that the cable runs are as straight as possible and the housing curves have longer radii.

As for the “mech” spring, the parallelogram linkage on Shimano rear derailleurs can not be disassembled and reassembled, so you can’t replace that return spring. However, if you remove the derailleur, put a washer on the mounting bolt, and screw it back into the derailleur hanger, you will effectively increase the return-spring tension throughout its motion, and this will be particularly noticeable when shifting over the smallest cogs. The thicker the washer, the greater the spring tension, but make sure that it is not so thick that the b-screw can no longer hit the tab on the derailleur hanger. Also, lubricate the return spring inside the derailleur parallelogram with a light lubricant that won’t stiffen up much in the cold.

Lennard