Real life Max Shimano Derailer is spread of ___ teeth? 30 work?
 

I had been so focused on a triple, I overlooked a potential double combo: 24 && 54 chainrings with 12-25 cassette gives nice transitions and only two gears to change up front. Instead of the normal 16 to 18 effective gears for a triple, it gives 20 effective gears with only one shift of greater than 11% change. Very nice, BUT questions

-- will a long cage derailer handle the gears. {yes Shimano will say no, but if careful shifting rings will it work?**

-- will any double handle the 24 and 54 tooth 10 speed rings?

thanks

BTW, triple with spread of 26t from low to high, 28t to 54t works fine

Is the chainring combo you mention available? You are saying a big 54 tooth combined with a small 24 tooth? Who is the maker of this?

If we are talking 110 BCD here I have never seen anything smaller than a 33

I'm curious myself. The largest road ring I've seen is a 53T,and road BCD's only go down to 30T. MTB BCD's max out at 48T I believe.

It's not stock. You replace the 52t upper with a 54t upper. For 9 speed systems, salsa makes a chainring. See sheldonbrown or nashbar. You also replace the low end. Last time I replaced a 30t with 28t, but now need to go lower. I wan thinking of a new drive train of 24-39-54 x 11..28. However, in reviewing the gearing, nothing is gained by the 39t middle, and if can get 24-54 x 11..28 to work, I can change from a triple to a double.

A 110mm is only available with 33t, but a 74mm will go down to 24t. Don't know if there is a 110mm to 74mm adaptor. I seem to recall someone mentioning this was available, but I have lost the reference.

You don't need an adapter,run the 54 on the center and 24 on the inner.Make the outer a bash/chainguard if you like.

I've never seen a double crank that will take 110 outer and a 74 inner,doesn't mean that there isn't one.

I have seen 110 rings,drilled for bolt-on 74 rings,used as a triple.Somebody used to make those rings,I can't remember who it was.I don't think they came in 54.

You could buy a 54 ring and drill it yourself,easy to do,if you do that kind of stuff.

Good luck shifting from 54 to 24.

Well the consensus of the other forum is forget the double, just go with a triple. So back to the original plan.

I've found the max tooth spread for a triple seems to be about 26-28 teeth. The exact capacity is dependent on the seat tube angle; more relaxed angles are more likely capable of the 28-tooth spread. I've personally run a 30/44/58 and it worked for me (barely.) That was on a recumbent, so the reality of an upright might be different. I don't think you'll get a 30-tooth spread to work without dragging the chain on the bottom of the front derailleur cage, no matter what. Either a 105 or Ultegra front derailleur would be equally capable of wringing the max out of your bike's geometry.

The rear is a little more forgiving, because the worst that happens is the return chain is a little slack in your small/small combination. On my above 30/44/58, I was running a 11-32 cassette, which makes 48 teeth of chain wrap. Your proposed 24/??/54 and 11-25 would only be 45 teeth.

Edit: I just re-read your first post. A 24-54 DOUBLE? I don't think any derailleur on the market will shift that.

Sheldon had a 50-28 double on his Hetchins: http://sheldonbrown.org/hetchins/source/3.html

Those who have tried this end up going back to more "normal" gearing. You have to shift through the whole cassette, then downshift all the way, upshift the front derailleur, and then work your way through the cassette again. Since the big double-shift is right in the middle of the range, you'll end up hitting this a lot when you're tired and sore and wanting to finish the ride. Not pleasant.

FWIW: I have 24-42-52 chainrings and a 11-34 cassette. It works fine, and I've used all of those gears.

IRD Tripleizer: http://www.interlocracing.com/triplizer.html

When he downshifts,that chain is going to yell GERONIMO!

Seriously,I think the OP would do better running a standard front triple with a wide range rear cassette. Shimano and SRAM are both coming out with 11-34 and 11-36 10sp.

Yeah, that one's gonna shift like crap.

I think you need the middle chainring to help the chain get up to the big ring from the small one.

Right now, I have a 48-40-24 on my Crosscheck. It works pretty well, but shifting from the 24 to the 40 is a little rough.