I've posted this in Road Cycling but have gotten few responses. Just wondering if folks in the 50+ forum might be more inclined to be using something like this cassette with a 50x34 crankset. I'm currently running a 10-spd 12x25 cassette with my SRAM Red 50x34 crankset. A typical club B ride was like yesterday's. We did 52 miles with 3800 ft. of climbing at 14.2 mph. I don't have much use for my 50x12 and a 34x27 would help with climbing. So, a couple questions.....does anyone make a 13x 27? Will a Shimano cassette work with my SRAM setup?

This sort of inquiry does best in the "Mechanics" sub-forum if one can past the guff of some who post there.

Here's how, but it takes two 10 spd Shimano cassettes, a CS6600 "Junior" & a 5700.

13-14-15-16-17-18-19-21-23-25
12-13-14-15-16-17-19-21-24-27

Use the "bottom" 3-cog 21-24-27 on the Junior cassette which was designed to shift to a 21 8th position anyway.
Use the lockring from the CS6600, custom 13-27 Done. SRAM/Shimano are compatible.

edit: And you get a 12-25 as a bonus!

-Bandera

I think you are out of luck for Shimano or Sram. (edit--that's interesting to combine the two cassettes. And you would get the 18 cog!)

I think it's a marketing decision to not offer 13-28 or 13-29 on Shimano. It would be very useful for a lot of riders. And the new wide range cassettes are often 11-30 or 11-32. The 11 is totally useless, and there's big speed gaps between shifts.

I have a Campagnolo 10-speed drive train. So I can get a 13-29 cog set. It's not supposed to work with a short cage derailleur, but it's fine on many bikes.
The only time I miss having a 50-12 high gear is on medium grade downhills, where I want to pedal to increase my speed past 32-33 mph. I start spinning out the 50-13 at about that speed. That's very rare--coasting downhill is fine for me at that speed.

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I was using a 13-26 cassette. It has an 18 cog, which I liked a lot. I'm pushing hard if I'm at 18-20 mph, so it was great to have 1 mph jumps between shifts. I could get the exact cadence I wanted.

At 90 rpm:
50-19 is 18.5 mph
50-18 is 19.5 mph
50-17 is 20.6 mph.

But I've kept the 13-29 on the bike, since I use the 34-29 low gear a lot on hills over 7-8%. And I'll even use it on 4-5% grades to spin up at 95 rpm.

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The Shimano 12-25 10 speed is:
12 13 14 15 16 17 19 21 23 25
Shimano 12-27 10 speed. The same except the two lowest gears.
12 13 14 15 16 17 19 21 24 27

Campagnolo 13-26 10 speed:
13 14 15 16 17 18 19 21 23 26
Campagnolo 13-29 10 speed. It drops the 18 cog and adds a 29 cog.
13 14 15 16 17 19 21 23 26 29

Shimano cassettes should work with SRAM. Is 50x43 a typo?

Here is a source for the Shimano Junior cassette: Shimano CS-6600 Wide 10 Speed Cassette - Normal Shipping Ground

If you're mostly interested in the 27 or 28 tooth sprocket, you can easily find a 12-27 or 12-28 cassette. Just don't use the 12. If you really want a 13-27, there are companies that make cassettes that allow you to customize each cog, but they cost more.

yes. Thanks.

Might have to take one of those suggestions. Thanks.

As noted in prior posts, there are numerous options for cassettes with a low cog of 27 or more. However, you need to check the capacity of you current RD. If you go from 25 to 27,or more, you may need a different RD. Since you have SRAM, I recomment their WiFLi (https://www.sram.com/sram/road/technologies/wifli) RD. This will give you more than enough capacity. You will also need to replace the chain since the larger cog will require a longer chain.

Another suggestion is to switch out cassettes as needed. You need a chain whip and a cassette removal tool, but the job takes 10 minutes and you don't need to adjust the derailleur if switching within brands. I use corncob cogsets (11-23) when in Illinois and use a 12-27 or 12-30 for hilly century rides.

There ya go. And that's how to do that.

I don't think that SRAM has made a road RD that won't handle a 27t cog.

As an aside, you and I have probably the only two Look 585s (mine's an Optimum) in a 500 mile radius.

For the OP or others trying to come up with an unavailable or unlikely cassette, Universal Cycles has individual cogs to customize gearing. Universal Cycles -- Cassettes & Cogs

Their amazing selection of Shimano 10spd cassette cogs is Two, a 12T or an 11T.
Can't get there w/ that.

It's a far cry from "back when" one could peruse the cog board & build a 14-18, 13-32 or whatever as a matter of course.
Still I can live w/ 10 gears out back and a couple of chainrings or three instead of a total of 10.

-Bandera