1x Retrofit for the Road

Even among staff at Bike Hugger, there is an ongoing debate about road & gravel bikes equipped with “1x” drivetrains, which employ a single chainring with a rear derailleur. If you want a really detailed comparison of 1x vs double chainring drivetrains, you should read here, but in this post I will give you an example of an older road bike retrofitted with 1×11 drivetrain that earned praise from the customer.

 

Dura Ace 7703 triple crankset, stock rings replaced with a Wolf Tooth Components Drop Stop 38T x 130mm 1x chainring

 

 

 

SRAM PG-1130 11sp cassette, 11-42T range. Unlike 11-speed cassettes 11-36 and smaller, this cassette will fit older 8/9/10sp Hyperglide freehub bodies. Here, this PG-1130 is fitted to a Dura Ace FB-7700 hub, first introduced in 1997.

The bike is a Davidson custom titanium, originally built around 2003 with Dura Ace 7703, a 9sp triple drivetrain. With a 53/39/30 chainring set, the bike was also equipped to give a 12-32 cassette serviced by a 9sp XTR rear derailleur. The customer has used the bike for fitness and leisure, frequenting the often steep, hilling neighborhoods surrounding Seattle.

Recently he purchased a new production steel Davidson that could accept large-volume 700C tyres to supplement his riding options. Since triple drivetrains are quickly disappearing from distribution, we talked at length about whether a 1×11 or 2×11 drivetrain would suit him best. We looked at how he rode his existing titanium road bike, specifically the gearing combinations he used most frequently vs the lowest gear necessary to ride where he desired. We chose a SRAM Rival 1x gruppo with a 38tooth chainring and 11-42 cassette.

In the end, the customer liked the 1×11 setup on his new steel bike so much he asked if his old titanium road bike could be similarly converted without costing too much.

Going into this retrofit, one advantage we had in trying to meet the cost target is that we could reuse his wheelset. Still in great condition, the original wheelset had Mavic Open Pro rims laced around Dura Ace 7700 hubs, hubs that were originally designed to fit 9sp cassettes. Although they also fit 10sp cassettes, the freehub body will not accept the wider 11sp road cassettes. However, SRAM 11-42 cassettes (as well as 11-40 and 11-42 cassettes from Shimano) were designed to be able to fit existing 8/9/10sp mountainbike hubs; when the cassette is mounted, the largest cog cups toward the spokes so it squeezes 11 cogs onto the narrow freehub body. The big cassette would give the wide range of gearing needed to make a single chainring practical on a bike that once had three rings.

The choice of single chainring did present a little bit of an issue. We had already reached the conclusion that a 38 tooth ring suited the customer’s usage, but we were hoping to retain his existing Dura Ace triple crankset. The DA crankset has a 130mm bolt-circle-diameter, and SRAM doesn’t make offer 38T x 130bcd rings in the narrow-wide tooth profile that allows 1x drivetrains to run reliably without a chain keeper. Fortunately Wolf Tooth Components makes such a thing in their Drop-Stop chainrings. We simply removed the old chainrings and bolted the new Wolf Tooth ring in the middle position of the crankset.

The result was total satisfaction from the customer. Keep in mind that wide-range 1x drivetrains frequently require some careful and realistic evaluation of rider usage. The customer and I realized that we could give away some of the high-end gearing of his previous triple drivetrain in order to assure that he had the low-end climbing options on the 1×11 setup.

 

Why go through the trouble and expense of retrofit?  The customer liked the ergonomics of the SRAM DoubleTap shifting and the simplicity of the single derailleur. There might have also been a marginal reduction in weight, but that wasn’t really a consideration here. In the end, it was just more fun to ride with the SRAM Rival 1x.

 

 

Stock Dura Ace 7703 chainrings, 53/39/30. The innermost ring has a unique 92mm bolt-circle-diameter and bolts to the proprietary DA 7703 middle chainring. This system allowed Shimano to offer a Dura Ace triple crankset that used the same crankarm forging as the standard double crankset. Unfortunately, replacement rings are scarce in 2016, and there is little inter-compatibity amongst the other Shimano road triple chainrings.