Sheldon Brown's gear calculator - question

[ny biker]

I'm trying to compare the gears on my current road bike and a new one that I might buy, and although I used to be good at math, for some reason Sheldon Brown's gear calculator is challenging my brain. So, am I interpreting this correctly? Here are the details:

Old road bike:
- triple chain ring, 52/42/30.
- 9-speed cassette, 12/25.

New bike:
- compact double, 50/34.
- 10-speed cassette, 11/28.

Using Sheldon's calculator, I get the following numbers:

Old bike with triple:
- top gear (52-12): 8.5 gain ratio, 113.9 gear inches.
- lowest gear (30-25): 2.4 gain ratio, 31.5 gear inches.

New bike with compact double:
- top gear (50-11): 8.9 gain ratio, 119.5 gear inches.
- lowest gear (34-28): 2.4 gain ratio, 31.9 gear inches.

So if I'm doing this right, the lowest gears are virtually the same for both bikes -- gain ratio of 2.4 and gear inches of 31.5 vs 31.9. Is this correct?

Also it looks like the top gears are not too different, with the new bike having an advantage. Yes?

My biggest concern is losing the granny gear if I switch from the triple to a compact double. Currently I do most of my riding in the middle chain ring, but I use the small ring often for steep hills (of which there are plenty around here). I don't use the large ring very often. But if I'm understanding this right, both bikes are the same when I'm in the lowest gear.

FWIW, the old bike is aluminum, and the new one is carbon.

Thanks!!!

[Cataboo]

Yeah, both bikes are pretty much the same in the lowest gear. For what it's worth, compact doubles shift better for me, less issues.

There's only a few hills that I struggle with on a compact double with an 11-28

[HillSlugger]

I know you are considering a Madone. The calculations show that you won't lose a thing.

I've also been planning on a new Madone so I've been considering the the same thing. In my case I already have a 12-27 on the old bike with the triple, so I'd definitely be losing on the low end. It's exactly this that has me deciding on the 5.5 that comes with SRAM Force. My thinking is that if I can't hack it with the stock gearing I'll be able to switch out the RD to a mid cage Rival and switch the cassette to 11-32 and get my low back.

[Cataboo]

Doesn't shimano have an 11-32 or 11-34 10 speed cassette now?

[HillSlugger]

Doesn't shimano have an 11-32 or 11-34 10 speed cassette now?

Probably, but I was told that I would need an MTB RD and STI shifters are not compatible with an MTB RD. Do you know if this is correct?

[7rider]

I don't understand your concern.
You'd get nearly identical gearing in a lighter, less complicated package. What's not to like here?

Your concern over losing the granny gear is a crutch - as you've already shown yourself that you will still have the low gearing you desire.

There will be some adjustment as you learn to shift the new gearing, but it's all there.

[Cataboo]

Probably, but I was told that I would need an MTB RD and STI shifters are not compatible with an MTB RD. Do you know if this is correct?

I'm pretty certain that's not correct. The push pull distances between road & mountain bike shifters are the same - derailleurs don't really care, they just do what the shifters tell them to do as long as they're big enough to cover the tooth range.

http://www.sheldonbrown.com/harris/k7.html

Scroll down to the 10 speed section and they go over using the shimano 10 speed with road shifters & a mountain bike cassette. People have been using shimano road shifters with IRD cassettes (11-32 & 34) with mountain bike rear derailleurs for years - SRAM cassettes are also fully compatible - so you can use shimano road shifters with the 10 speed large cassettes from SRAM (you should check into whether you'd have to use a shimano rear derailleur though, I know for a while the amount of push pull needed for a shimano rear derailleur was different than for an sram - so you had to keep the shifters & rear derailleur the same, but could interchange the cassette without a problem)

So you don't have to go to SRAM to get the bigger gear range - Alot of people seem to like the doubletap system though, I hadn't tried it