tkatzir

Hi,

I'd like to have a double with a large range of chainrings, something like 52/30.

I saw Specialites TA's Vega or Carmina cranksets,
they can have a 94 BCD double spider, and matching chainrings from them as well.

Do you believe it's feasable?
Does anyone here have a similar setting?

Can you recommend a derailleur that could handle such a crankset?

Thanks in Advance, Tal.

HillRider

I suppose it can be done but why? A triple crank with 52/42/30 rings would give the same overall gearing range without sacrificing all of the middle steps. There is nothing difficult or tricky about a triple and STI or Ergo shifters handle them very well.

The current trendy set-up is a 110 mm BCD compact with 50/34 rings (aka "the proud man's triple") which is the widest range most front derailleurs are happy with. That gives a smaller overall range than you want.

MichaelW

I have doubts about whether any mech could handle 52-30 in one jump. I would expect it to derail to the BB shell on the downshift. If you want a wider range, fit a wider rear cogset or go with the triple.

tkatzir

Triple is an option, but I'd like to pursue Double first.

It CAN be done. e.g.: https://www.sheldonbrown.com/harris/french-cranks.html shows a 50/28 crankset.

Tal.

Retro Grouch 

So why'd you ask? What are you planning to use for a shifter?

tkatzir

I wrote in my original post.

I saw this one pic in Sheldon's site, and wanted to know whether it's done today, with the modern cranksets from Specialites TA (or any other manufecturer.)


The reason is similar to Sheldon's -
I'll use the larger chainring almost exlusively, but would love to have bail out gears, for the climbs I'm having trouble with the Shimano Compact FC-R700 I currently have, or when I'm really tired in long rides.

I have a flat handlebar, and plan to use a friction shifter, so I hope it could handle anything.

Tal.

Phoible

Why don't you just run a mountain bike cassette in the back? That would give you a good range of gears and then a bail-out gear of 34. You should be able to get it to work, especially if you use a mountain derailleur in the back. 34/34 is lower than 25/28 or 27/28 (if you aren't running a 12-27 in the back, you might go for that first).

tkatzir

I'm aware of this, but I'd prefer exploring the crankset option first.

Tal.

DMF 

The big issue is the BCD. A 52T ring typically lives on a 130mm BCD and a 30T on a 110. You'd have to find a 52T that can live on a 110.

Do that and you'll still have the shifting problem. You might be able to coax a shift with a light foot and a friction shifter, but don't be surprised if it just doesn't work reliably.

tkatzir

The smallest 110 BCD is 33T.
I'm talking about both being 94 BCD.

What's "light foot"?

It doesn't have to shift as crisp as modern gears.
If anything - I'll shift down at the begining of some hard section, and shift back up.
I assume I'll spend around 90% of the time on the large chainring.

Tal.

DMF 

Then try to find a 52T with a 94 BCD. My point is that if they make them at all, they're not common.

Not trying to shift under load.

ggg300

https://www.bikeusa.com/components/chainrings.html

see above...if you cant find it then custom rings, but $$$

best bet is to get a triple....take off the 42 ring and move over the 53 to the middle...keep the 30 on...get a smaller bb and enjoy...use triple drl and friction and light foot...

Gonzo Bob

I have something similar but not quite as wide range. I bought a used 5-arm 94/58 BCD triple crank on eBay and put Ritchey 2x9 44/29 chain rings on it. I have no granny ring on it. I run an 11-28 7-speed cassette so I have a 4:1 high gear and nearly 1:1 low gear. Front derailer is Deore LX and rear is 600 short cage.

As others have said, the 52/30 combo will shift slowly/poorly, if at all. You'd probably need a road front derailer since most MTB are designed for big ring of 44-48. And I'd probably go with road double FD rather than triple but that's based on gut feel and not on any testing.

tkatzir

Thanks for the link, there are some interesting items there.

I thought about this option, but it means I'll need a larger BB (123 vs. 118 with a double crankset.)
BTW, With your idea, there's room for a chainguard on the outer.

Tal.