By Jim Weaver, Service Manager, Fit Werx, Waitsfield VT
At the Fit Werx located in the Mad River Valley of Vermont, we see many clients looking for ways to get ever lower gearing to help them conquer the gaps more comfortably. For those looking for a road bike with ultra-low gearing, SRAM components are one of the very best options. Unlike Shimano, SRAM’s road shifters work just fine with SRAM mountain bike rear derailleurs. I have built many bikes equipped with SRAM road shifters, brakes, and front derailleur, paired with a SRAM mountain bike rear derailleur and a 12/36 cassette. With a compact chainset, you can get gearing that is less than 1:1, making the local climbs easier and doable by any rider who is feeling like their power is not quite what it needs to be with standard road bike gearing.
However, what if you have a compact crankset, and a 12/36 cassette, but still need a lower gear? Here in New England we have some of the steepest long climbs in the United States. For example, part of Lincoln Gap, just down the road from our Waitsfield shop, has been purported to be the “steepest 1 mile paved section of road in the country” by some. Wolf Tooth Components recently released two new very big cassette cogs for 10 speed SRAM drivetrains, one with 40 teeth and the other with 42 teeth, to answer that need. The basics of how it works is that you remove mid-range cog and then mount the Wolf Tooth cog on the inside of the existing 36 tooth cog.
In some cases, people will find that just pulling a cog from the cassette creates too big a gap when shifting. Wolf has a solution to this as well. They recommend that both the 15 and 17 tooth cogs be removed from either an 11/36 or 12/36 cassette, and replaced by a new 16 tooth cog. This would make the cassette gears 11 or 12, 13, 16, 19, 22, 25, 28, 32, 36, and 42. This conversion will work on SRAM 1030, 1050 and 1070 10 speed cassettes. Sorry, no 11 speed choice is available at this time. Also of note, due to the design of SRAM’s mountain rear derailleurs, this conversion does not work with 2011 or earlier SRAM rear derailleurs. SRAM redesigned their rear derailleurs in 2012, and Wolf says that these new cogs work fine on 2012 and newer SRAM 10 speed mountain bike rear derailleurs.
So does this really work as well as Wolf says, without having to do anything tricky with the rear derailleur? Trying to get a rear derailleur to work with a cassette cog that is too big can be a dicey proposition. Bad shifting is the least undesirable result, and in worst cases the rear derailleur can be either torn apart or actually ripped off of the bike, to the detriment of both the derailleur and the bike frame. How to tell if it will work? Well, rear derailleurs have a “chain wrap” specification. To calculate this, subtract the number of teeth on the small front chainring from the large outer ring. For a compact crankset, that difference is 16. Next, subtract the number of teeth on the smallest rear cog from the largest. For a 12/42 cassette, that difference is 30. Add these two results together and you get a chain wrap of 46. So long as that total is less than the number specified by the derailleur manufacturer, you are fine. SRAM’s specification for their 10 speed mountain bike long cage rear derailleurs is 47, so this combination (or even an 11-42 rear cassette) will work well, and safely.
I doubt Wolf had the road bike market in mind when they designed and released these new cassette cogs; how many areas of the U.S. have people interested in such low gearing? Wolf was simply looking to give mountain bikers the option of lower gearing. However, as SRAM mountain bike rear derailleurs can be used with their road shifters, this immediately became an option for those riders looking for truly low gearing on their road bike.
There is now a way for you to get extremely low gearing on your road bike that will allow you climb roads like Lincoln Gap, or maybe even climb that nearby vertical brick wall… A little is good, so a lot must be better. That usually is not true, but in this case, it is.
With bike shop and bike fit studio locations outside of New York City in Ridgefield Park, NJ; in Peabody and Lexington, MA; and near Burlington and Stowe, VT in Waitsfield, Fit Werx technicians have helped people find the gearing they want for years. Contact us if we can supply parts, give advice or be of service.