SRAM 1x - Shift in Logic SRAM 1x - Shift in Logic

SRAM 1x - Shift in Logic

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Wednesday, July 1, 2015

My first real test of SRAM’s Force 1 group came at the Ironman 70.3® North American Championships in St. George, Utah. I went into the race feeling nervous about my single-ring drivetrain choice and even found myself gazing longingly at the front derailleurs of my competitors prior to the start. St. George is a course where people run big cassettes and big chain rings. Steep hills and fast descents require you to time trial at 10 mph, 45 mph, and everything in between. If ever there was a course to test the paradigm of double chain ring necessity, this was it.

Two things gave me the guts to break front derailleur paradigm and commit to 1x at St. George. First, was the week I was in San Luis Obispo for the SRAM 1x™ product launch where we rode hard in the mountains. Gravel riding in a group is much different from time trialing, but it showed me the wide range of gearing possible with an 11-36 cassette.

The second experience was completely data-driven (I’m a self-confessed analytics nerd). I collected Garmin files from several past races and used BestBikeSplit.com to project my race speed and gearing needs throughout the course at St. George. I’ve expanded on that process below, but my conclusion was that I would have sufficient range to never spin out or grind, and in exchange for my small ring I would lose two gear ratios in the middle of the cassette (the 14 and 16-toothcogs). The key takeaway: the gearing on my 1x setup was going to be just fine, at least on paper. Yet I still wondered about the missing 14 and 16-tooth cogs.

Shift Ahead to Race Day

By the first climb at St. George my gear choice was no longer in question. At the base of the climb I was in third with of a small group that exited the water close together. The guys in front of me shifted to their small rings, and almost instantly I was propelled into the 12-meter draft-zone and forced to make the pass to the front of the pack. They soft pedaled and shifted front and rear derailleurs. I clicked straight to the next gear and kept the pressure on. That small difference – it might only take two pedal strokes to shift to the small ring and adjust the rear derailleur – turned out to be a crucial moment. Over that first hill and onto the descent I went. Looking back I saw the pack of 10-15 riders was gone – just two rivals remained.

Every time we approached a hill I found myself gaining one to two bike lengths on those around me as they soft pedaled and shifted front derailleurs and I was able to click quickly to the next cog. On the flats I never noticed the missing 14 and 16-tooth cogs that my data analysis had me worried about. The bike was quiet and felt fast. I rolled into T2 with the second-fastest bike split. Would I have done as well on a 2x? Perhaps. Would I have done better? No.

I had a great race at Saint George, finishing 10th in the Pro Men’s division. I did eventually bonk on the run – I have a history of suffering in the heat. But I was really happy with how I rode, and how fresh I felt starting the run. In the course of 2 hours I went from a willing field tester to a 1x convert. Is 1x for everyone? Maybe not, but if it works at St George, it’ll work at any triathlon. For me, the risk of dropping a chain while shifting the front derailleur, the added noise and extra thought that goes into shifting between chain rings and the extra maintenance is not worth those two extra cogs.

Deep Data Dive

Below is a deeper analysis of how I selected my gearing: an X-SYNC™ 54 tooth front ring with an 11-36 rear cassette.

I first created my own Excel model, looking at the gaps between gears. There is one 17 percent jump in gear ratio on the PowerGlide 1170 11-36 Cassette – when shifting from the 13 tooth to the 15 tooth cogs (an 11-26 never exceeds jumps of 15 percent). I studied the speeds where I would be between gears, given my preference for 95rpm cadence, and what my cadence variance would be in order to maintain that speed. Without knowing exactly how much of the race I would be at any of those speeds I really didn’t know if it would be a problem that at 28.5mph, for example, I would have to choose between 88rpm or 102 rpm. (Based on my training data, 102 was within my normal range, but 88 wasn’t.)

To figure out specifically what ratios I would need for this race I turned to BestBikeSplit.com. This site takes time trial analytics to a new level. It uses your FTP testing data, plus a course profile to create a specific race plan for you to set the best possible time on the course. The staff at BestBikeSplit.com jumped at the chance to play with the numbers and help me out. I sent them a bunch of Garmin files from past races so they could get an idea of my race power abilities, as well as my drag coefficient. They built a race plan for me at St. George and from that drew a frequency chart to show the percent of time during the race that I would be in any given gear, given 95rpm cadence as a target.

 

What’s important here is that this is what I would use if I had every gear from 11 up to 36. The 11-36 Cassette, however, has 11,12,13,15,17,19,22,25,28,32, and 36 teeth cogs. The majority of the missing cogs are barely used and aren’t much different from their closest peer (35 and 36 are less than 3 percent apart). I worried about the missing 14t cog, which accounts for almost 12 percent of my target race, and the 15 is (15-14)/14*100 = 7 percent away – meaning about 6rpm over my “ideal.”

During the actual race, I never felt like I needed a gear that I didn’t have, and I had as much range as I needed. The times I noticed I didn’t have a front derailleur were when a rider was in front of me and I would almost surge toward him as he slowed while shifting into the small ring for a hill. (Actually, it’s three shifts because he had to shift the front, then shift the rear a couple of times to get to the next ratio). During his multiple shifts, I was one click away from my next gear, and it seemed to save me more than I expected.

I’m already thinking ahead about the possibilities for Force 1 in upcoming races. Perhaps a smaller front ring? Also, St. George’s hilly course made the 11-36 cassette the best choice, but on many flatter more typical triathlon courses the super light XG-1190 cassette with a tighter 11-32 or 11-30 gear ranges open up all sorts of possibilities...

Photos ©Nils Nilsen N2PHOTOservices

Read more My 1x stories from: Grinduro!, Open the Road Gloucester, Gloucester GP CX Race, riding and racing in Indiana, The JAM Fund Grand Fundo, German National TIme Trial Champs, and the Dirty Kanza 200.

Learn more about SRAM 1x Force 1 and Rival 1 groups in the video below.

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