You will be giving yourself one lower gear in the granny range than what you had. With your old setup your 3 lowest gears were 28.8, 24.7, 21.6 gear inch. Gear inch is best described as what the tire size would feel like given a 1 to 1 gearing or direct drive like on a unicycle or kids trike etc. , so picture yourself riding a bike with a 21.6” tire. With your new setup your 4 lowest will be 27.9, 24.4, 20.9, 18.3 gear inch. You can see how it all will be shifted over one place the difference of 3.3 GI will be quite noticeable.

Your center gears were in the range between 30 and 87 GI and now will be 27 and 77 GI so you will be losing 10 GI off the tallest ratio when on your center ring. That’s what djb was referring to in his last sentence in the above post and what I didn’t care for also when I tried a mountain crank. Like he mentioned I also use my touring bike a lot as a commuter and all around road bike and I liked having my center ring have all my normal range I liked for both loaded and unloaded riding, and I missed the couple gear I lost quite a bit.

Your old big ring gave you a range between 40 and 116 GI and your new ring it will be 37 and 106 GI. As mentioned the 116 is ridiculously large, picture trying to ride a bike with a 116” tire even if your legs were long enough. But on the other hand the next gear over on your old set up was 106 so you didn’t gain any gears on the big ring.

Let’s say you are riding along on fairly level roads and you are on your center ring and you get to the end of the range on the cassette 32-11 combo 77 GI. Your next shift up will be to down shift twice on the cassette and move over to the big ring in the front to get 44-14 and 84 GI. Then you will have just two more gears to use on the big ring 98 and 106 GI and in all likely hood you won’t use the 106 very much except maybe down hills. So for practical purposes the big ring still won’t be used much.

No one can really tell you where your sweet spot is on the center ring but you can test it out ahead of time because your old center has the gears you will be moving to the large ring and you can ride around and think about what will be your new point you will have to make that front shift. Pretty much your 36-12 and your 36-11 gear ranges will be moved to the big ring. If those don’t feel like gear you will using a lot or jumping between. Then it will be good to lower all your gears with the mountain crank.

For me I absolutely hated running out of gear on the center ring and absolutely loved the low gear on the granny. So I took a different approach to get both. I think you could just change your granny ring to a 24t as an option to get a bit lower with the crank you are taking off if you find the mountain crank isn’t your thing. A 24t would lower your granny to a 20 GI. That’s what I did and I also switched to a 12-36 cassette lowering it even more to a 17.7 GI. With doing that that you only loose a smidgen between the 11t and 12t when you keep your larger center ring and the 11 to 12 helps a bit lowering the big ring top number.

Now that I have you completely confused I bet. I just wanted to point out both the upside and the down side to the mountain crank per my experience. Hope this helps not confuses you more.


PS: Just for the record my final gearing front is 45,42,24 with 12-36 (9 speed) in the back. 42 is my magic number and I suggest people start off looking at their center ring and find their magic number as that ring is where you spend most of your time.


PSS: The suggestions above for 11-28 cassette to smooth out the jumps between shifts is a good one for doing that but will take you back to almost the same low gear you have now old granny gear is 21.6 GI and with an 11-28 you will be at 21GI. It will seem to be the same low gear you have now.