Cassette for aero wheels

Triathlon Forum
1

I have an 04 Carbon Trek Team TT bike and an 03 Specialized Allez Comp road bike. My TT bike has a Zipp full carbon disc on the rear with a 9spd 11-21 Dura Ace cassette and a HED H3 carbon on the front. I have a 53/39 10 spd Dura Ace Crankset, but I also have a 54 tooth Dura Ace TT big sprocket I could put on. My road bike has Shimano R-540 wheels with an Ultegra 12-25 cassette and standard Ultegra crankset.

I just got some new HED 50mm Alps aero wheels and haven’t bought a cassette yet. My goal is to make all of these wheels compatible with both bikes (except the disc to road bike which I wouldn’t ever need to do) without having to do derailleur or other adjustments (I know I’ll have to change brake pads on the TT bike between the carbon disc wheel and the aluminum braking surfaces. In other words, I want to be able to use my training wheels on either bike, my aero wheels on either bike and my H3 on front of my road bike.

My idea is to get a 12-25 Dura Ace cassette for the Alps rear on the theory that if I’m using the Alps on either bike it is either a windy or hilly TT, or a windy or hilly triathlon, or a road race without much wind. Will the 12-25 cassette on the aero wheels and the 12-25 cassette on the road bike easily transfer to the TT bike that is set up for an 11-21 cassette without having to adjust anything. I want to have to do as little adjustment as possible because I have screwed this up before and cost myself a better finish in a race when the chain came off. I thought I might take the whole setup for both bikes to a shop and ask them to set it up (with spacers, etc., whatever else is necessary) to make them all perfectly interchangeable, but I don’t want to buy the cassette from a shop because I can get a much better deal elsewhere, so I am looking for advice on what cassette to buy for the Alps. Thanks for your consideration and assistance.

2

Not knocking you man, but go to your LBS and have them show you how to adjust your derailler. There is no reason you should need spacers or anything, I trained on a 12-25 and raced on an 11-21 and switching wasn’t a big deal and I am no wrench. Get the casettes you really want for each wheel and learn how to adjust the derailler.

3

I’m no technical wizard, but I believe a DA or Ultegra rear derailleur can accept up to a 27t cog on the rear cassette … so going with a 25 shouldn’t be any problem there. My TT bike has very short chainstays. That means a shorter chain than on my road bike. That means it’s more critical that I not cross-gear the bike (ride on the big ring up front, and on the larger cogs on the back). Just keep that in mind if you run the alps on your TT bike. It’s never good to cross-gear like that, anyway. It’s especially bad to do it on a bike with shorter chainstays (which many Tri bikes have because of the steep seat tube and the rear wheel cutout). It will wear the chain rapidly, at the very least. You should test the setup in a workstand to make sure it doesn’t jam the drivetrain completely. I don’t think it will, but you don’t want to find out by mistake out on the road.

Bob C.