Welcome to our Ask a Mechanic column where our expert mechanic Daniel Slusser answers your bike maintenance questions. If you have a question for Daniel, please post it on our Facebook Wall or e-mail Daniel directly at firstname.lastname@example.org. In today’s entry Daniel reviews how to do a conversion from a mountain triple to a mountain double; and yes, even MORE bottom bracket questions.
I have a 3×9 9-speed MTB with Shimano SLX crank 44/32/22 and I want to convert to 2×9 36/24 using the same crank with new rings and bash guard. What exactly do I need to do? From: Isaac
It’s true that when it comes to chainrings, two is company and three is a crowd. I answered a very similar question to this one about 3 months ago but I have put together another answer just for you Isaac. There are two routes you can go with this. You can either put together a standard 2×9 system, or build a hybrid 2×10 system up front mated to a 9-speed setup in back that gets you half way to a new complete 2×10 system upgrade.
For the standard 2×9 all you need are chainrings, a bash guard, chainring bolts, and a front derailleur. Truvativ makes some great affordable and reliable chainrings that fit the bill for you in both 36t and 24t. Gamut makes the best bash guard on the market at the moment in my opinion because it is light and has the durability of a thermoplastic. You will also need longer chainring bolts to go with the bash guard which are also available from Gamut. Shimano makes an M665 9-speed front derailleur that is optimized to work with the 36/24 chainring combo that not only shifts great but keeps your chain on better than a triple derailleur. If you are on a tight budget however, you can get by with your current triple front derailleur, it just won’t shift as well and as mentioned earlier, you run a higher risk of dropping chains.
For the 2×10 hybrid you need all the same things plus a chain and front shifter. But in this scenario you’ll use a 2×10 ring set such as this one from Race Face that is available in 36/26 which is not quite the gearing you are looking for, but it will shift better and last longer. For shifting, use a Shimano Dynasys 2×10 front derailleur of your choice mated to any Shimano Dynasys 10-speed front shifter. The Gamut bash guard and chainring bolts will be the same as the previous option. The last thing you need is a 10-speed chain. This is required because of the narrower spacing of the 10-speed chainrings and front derailleur. While the 10-speed chain will not shift quite as good on your 9-speed cassette as a 9-speed chain will, you will be hard pressed to notice the difference. I have been using 10-speed chains on 9-speed cassettes for a while now and find the difference to be very subtle.
I am sure that you will enjoy your new 2x system Isaac. If you run into any problems during installation just give me a holler or consult a trusted mechanic in your area.
I just got a new frame with a pressfit30 bottom bracket shell. My old bike was BB30. I took all my crank parts from the old bike and transferred them to the new bike except for the bottom bracket bearings since they are different. After putting all the old crank parts on with a new pressfit30 bottom bracket I am getting a lot of noticeable drag when spinning the cranks. Will this go away after the bearings break in, or did I do something wrong?
You too have discovered that these new bottom bracket standards can sometimes be a real drag. What likely went wrong is that you used the wrong bearing shields. Pressfit230 bottom brackets use shields that sit a little farther off of the bearing in order to clear the seal that is between the plastic cup and the bearing. A BB30 shield will drag on this seal unless the seal is pried out and removed. This is a common problem because people are often tempted to use the higher quality alloy shields from a BB30 bottom bracket in place of the OEM plastic shields that sometimes come with an OEM pressfit30 bottom bracket. Just stick with the shields that come with your BB and you will be fine.
The only other possibility for the cause of the drag is that you have a crank that uses shims to preload the bearings and you just have too many in there. Remove 1 or 2 and see if that doesn’t improve things.
Daniel Slusser is a professional bicycle mechanic with over ten years of experience. He holds a bachelor’s degree in business administration from HSU and a master’s degree in history from Cal Poly University. When he is not riding, wrenching, or writing he enjoys spending time with his wife and two children.