Technical FAQ: Shim-SRAM brakes, descending, rolling resistance

Dear Lennard,
I am considering upgrading from my current Shimano 9-speed system to SRAM eTap 11-speed. So far, I am sure both my current Mavic wheelset and my Campy 10-speed crank will work OK.

My question: Will my current Shimano 7700 brake calipers work correctly with SRAM eTap brake levers?
— Jerry

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Dear Jerry,
This question of whether you can pair a SRAM brake lever with a Shimano brake caliper is a recurring theme for my column, but finally I get to answer one of these in the affirmative. Yes, your Shimano Dura-Ace 7700 brake calipers will work as intended with SRAM levers! This is because your calipers are so old.

Dura-Ace 7700 STI levers have the shift cable coming out of the side of the lever, out into space in front of the head tube; this is the cue to let you know that your calipers will work with SRAM levers. This goes for all Shimano STI levers with the shift cable sticking out of the side. At the time those levers were made, Shimano was using the same leverage ratio on its road brakes as other major manufacturers.

When Shimano went to levers with shift cables hidden under the handlebar tape (Dura-Ace numbers switched from 7700 9-speed to 7900 10-speed), it changed the leverage ratios of its levers and calipers. This leverage design change carries forward to Dura-Ace 9000, Ultegra, and 105 11-speed STI levers and brakes. Current Shimano brake calipers for 11-speed groups are built with higher leverage (they have longer brake arms above the pivot and shorter below) and are paired with a low-leverage lever that pulls more cable.

SRAM and Campagnolo levers still maintain the leverage ratio of the generation of Shimano brakes that you have. Hence, your 7700 brakes will work fine with eTap levers, and, as you said, 10-speed chainrings work fine with SRAM eTap, and Mavic wheels that were originally set up for 9-speed (or 10-speed) Shimano cogs with a spacer behind the cassette work perfectly for an 11-speed SRAM or Shimano cassette. You obviously also know that eTap’s wireless system allows you to install electronic shifting on your old frame that has no drilling for electronic shift wires. You’ll have a cool setup.
― Lennard

Dear Lennard,
I have two unrelated questions.

1.) I’ve been working on my aero descending skills and have added 2-3MPH on my fastest hills. My question, is it better to shift weight forward or back (which I tend towards) or is this irrelevant given the benefits of good aero position?

2.) In the past you have discussed tire drop as well as handling, which tends to suggest lower PSI is best. But then recently on some testing it was suggested that a Pro Race 4 should be run at a high pressure, seeming conflicting with the tire drop advice, while a Vittoria EVO 320TPI open clincher seemed best at lower PSI, which is consistent with the tire-drop advice.

Do you now suggest to follow the tire-specific findings or do you think the handling and tire drop guidance should take precedence?
— Jeff

Dear Jeff,
1.) The steeper the downhill corner, the more your weight has to shift back, because applying the brakes throws your weight forward onto the front wheel, as does the hill’s pitch. You want to maintain as much rear tire traction as possible.

For straight-tucking downhill without braking, it’s fastest to sit on the top tube, as long as you have a “compact-geometry” frame (i.e., sloping top tube). This will, of course, move your weight forward. But then when you have to brake hard and corner sharply, you’re better off getting back up onto the saddle and pushing your weight back.

2.) If you have tire-specific rolling-resistance vs. tire-inflation data, I recommend going by that. The Michelin Pro Race is a vulcanized tire, which will have a stiffer carcass than that of a non-vulcanized, “open tubular” clincher, and the stiffer tire will not benefit as much from reducing tire pressure as a more supple tire will.
― Lennard

Dear Lennard,
I recently had a tire pressure issue while riding my hardtail 29er. My rear tire lost some pressure for whatever reason so I decided to use a little CO2 to complete the ride and get home. I’m currently using Stan’s NoTubes on a standard Giant wheelset with a tubeless-ready Specialized Captain tire.

Once I got home, I noticed that my rear tire was bleeding air excessively through the sidewalls. The bleeding was significant and completely even around the sidewalls, both sides — and only on the tire that got the CO2. I did a little research and found your article on this and the quote from Stan’s. “Do what you have to get home, but there might be issues using CO2 …” or something like that. There are issues.

The bleeding was so significant that the tire was completely wet and dripping clear liquid onto the floor. It was obvious that there was some sort of chemical (or other) reaction with the Stan’s from the CO2, so I decided to clean everything out and install new Stan’s to see if I could fix the issue. When I opened the tire, it was now completely dry with latex unevenly stuck to the tire and the rim. All of the liquidity of the Stan’s was gone. The shot of CO2 separated the Stan’s, and the liquid portion seeped out of my sidewalls and onto my garage floor while the latex portion stayed behind. After cleaning out everything from the tire and the rim, I installed new Stan’s and rode the same day with no issues. Everything seems back to normal now. So, “do what you have to get home” but know that you’re signing up to re-Stan’s your wheel if you use CO2.
— Kelsey

Dear Kelsey,
Yes, that’s absolutely correct. Thanks for the clear description of the consequences.
― Lennard

Feedback on last week’s column:

Dear Lennard,
I thought you may like to know that I’ve been running 10 speed U-Di2 for three years and have experienced this same dropped chain issue intermittently, although I have never been able to work out why it occurs. Thank god for K-Edge chain catchers I say.

I’m running a PF30 (Chris King) BB with Shimano cranks. Rear cluster is a 11-28. The chain stay length is 410mm. The frame is a custom Guru Praemio R. The firmware on the Di2 is up to date on all pieces as well. I’m going to try out the suggested rapid shifting to see if I can force it to drop. I would note that I have the rear mech programmed on “fast” mode presently.
— Rich

Dear Lennard,
It was interesting to read about UDi2 chain derailments with non-Shimano rings. I haven’t experienced anything like that with either my Specialized (50T) or FSA (46T) rings, but my Roubaix does have long stays.

However, I did have that issue with my 9-Speed Dura-Ace triple, with the 39T middle ring. It always occurred, as Pete noted, when the chain was slack, never under load. I found two things that improved my issue. One was when I put on a new MB derailleur. I think it had a stronger jockey spring, so the chain never got as slack. But in fairness, I also put on new rings and a new chain at the same time, so that may be correlation, not causation. My guess is that the freehub makes a difference a well. Any stickiness would cause momentary chain slack.

But the one thing I noticed for sure was that the problem suddenly returned when I put on a new chain (no new rings). This kind of fits in with your chainsuck theory. The problem went away again once the chain had accumulated about 2,000 miles of wear.
— Steve

Dear Lennard,
Wanted to weigh in on this week’s question about the 11-speed SRAM Yaw front derailleur paired with 10-Speed SRAM drivetrain. Running 11-speed Force Yaw front derailleur on mine and my wife’s 10-speed Force drivetrain for about nine months now and it works way better than the original 10-speed Force derailleur.
— Doug

Dear Doug,
Very nice. Thanks.
― Lennard

Dear Lennard,
Re: your comments about gearing combination for bike storage, Nick Legan wrote a VN column in which he said it’s PRO (and possibly beneficial) to always leave the bike in small-small. I’ve done it ever since reading it in 2012.
— Don

Dear Don,
As Nick wrote, it can’t hurt!
― Lennard