I currently have a 50/39/30 triple 10 spd and would like to go just a little lower gearing and currently have a 11/28 cassette w/105 deraileurs can i go to a 26 or 28 inner chainring with this combo

Your chain rings are most likely 130MM BCD. Those rings are too small.

Maybe a cassette change to a 13?-xx?

Where'd you get an 11-28 10 speed cassette?

EDIT:
OOPS, I was thinking middle ring.
I belive the granny ring is 74MM BCD, so yes.
https://sheldonbrown.com/harris/chainrings/74.html

Re-EDIT
Right now you are at the maximum chain wrap capacity for your RDER. Going to a smaller granny ring will exceed that.

No big deal, though... the chainwill be too slack in the small-small combo, but you don't want to use that combination anyway.

You would never normally use the little ring with the last 3 cogs, so 2T of extra wrap should be no problem, if the chain length is adjusted properly. The 26T cog creates a situation where you would have almost no overlap with middle ring ratios and the chain might hang loose in 1-2 more cogs.

I believe it's Hillrider who has posted numerous times about switching out the 30T ring on a triple to a 28 or 26. According to him, or whoever it was, shifting from the little ring to the middle ring is a little more touchy but still perfectly acceptable. And IIRC, a chain watcher is a necessity for this setup due to the long drop the chain must make from the middle to the little ring.

SRAM makes 11-28 10 speed casette. (OG-1070)
Cogs are: 11-12-13-14-15-17-19-22-25-28

You've got it exactly right. A 26T works fine with minor degredation of the granny-middle upshift. And the chainwatcher is a highly recommended addition to any triple but this one in particular. It's is very cheap way to get significantly lower gearing.

It might not be so easy, some of the modern triples, especially those for ten speeds don't use the 74 bcd granny, instead they use a 92 bcd, which doesn't allow for the tiny granny gears of a 74. The smallest commonly available chainring for 92 bcd is a 30.

I'm not saying yours is one of these, but you have to check.

AFAIK, Dura Ace was the only one that did this and only for the 7800 series. The new 7900 series doesn't list a triple at all. Ultegra and 105 triples were and are 130/74.

I have triples with a 130/74 spider on all of my and my wife's bikes. Not one of them still has the 30 tooth inner ring still on it, they all have a 26 (tourers and commuters) or 28 (racers) tooth inner ring instead. They also all have some sort of chain retention device. If anyone needs a 30 tooth ring, I have a stack of about five barely-used ones!

The big advantage I find with this setup is that you can still have a really small lowest gear with a cassette that goes up to 25 or 26 teeth, but you don't have the big jumps between lower gears that you do with a cassette that goes up to 27 or 28 teeth.

BTW, the smallest ring you can get on the 74mm BCD is a 24 tooth, but I've never needed to try one of those. If you want that, then you should get yourself a crankset with a 110/74 spider, or a MTB crankset, so that the middle ring can be a bit smaller.

For 9 or 10 speed Shimano cassettes, the only difference between the 12x25 and 12x27 cassettes is with the two biggest cogs. They are 23,25 or 24,27. The 7 or 8 smaller cogs are identical.

My stock RSX triple is 28/38/48, as far as I can recall, with normal BCDs.

The RSX triple I have experience with was 26/36/46 with 110/74 bolt circles. This was on a 7-speed Trek 1220 from 1996.

well damn, I just revealed how much I know about high end bike parts...I suppose I'll have to go into hiding until someone has a question about a helicomatic...

I thought all RSX cranks that Shimano made were with a 110mm bolt circle, and 74mm for the granny on the triple cranks. While a 130mm bolt-circle can handle a 48/38 combo (38t is the smallest possible ring for 130mm BCD), I think every triple I've seen with 48/38 as the two large rings has been a 110mm bolt-circle.

As an aside, one thing that interests me is why the compact double didn't catch on when Shimano introduced it with RSX in the 1990's. Maybe because they marketed the double with a 46/36 chainring combination, which doesn't have the wide-gear-range benefits that makes the compact double so desirable. Or maybe just because they introduced it in a low-end component group (RSX was replaced by Sora in Shimano's road-components lineup).
My dad's mid-90's Trek is equipped with RSX with a 46/36 double crank.

According to Sheldon RXS was built in 110 BCD and 130 BCD, doubles and triples. The triples are either 110/74 or 130/74. https://www.sheldonbrown.com/bbsize.html
A friend of mine has an RXS 110 triple. I'm impressed by how well it shifts, better than my wife's Ultegra triple.

Al

And if that is not low enough, you can get down to 17 or 16 on your 74 bcd with the Mountain Tamer Quad or Triple adapters.


https://www.abundantadventures.com/quads.html

This is exactly my point. The spacing on the biggest cogs of a 9- or 10-speed cassette is 21-24-27 vs. 21-23-25 on Shimano cassettes. I hate the 21-24 jump, so I find the best compromise is one of SRAM's cassettes that have 21-23-26 as the biggest three cogs, then I use an inner chainring that is either 26 or 28 teeth to get some nice low and closely spaced gears. When climbing Swiss mountain passes for an hour or more, I pretty much just stick in the bottom three of four gears, so I want nice tight spacing so that I can grab a faster gear whenever possible without my cadence sinking too low.

All that is for my single bike. On our tandem bike, we really need one more lower gear than that even. The tandem came with a SRAM 11-28 cassette, and paired with a 28 tooth chainring that gives a decent low gear (we recently made it up a 17% climb ). However, the biggest 4 cogs on that are 19-22-25-28, which means that there are two jumps that are too big for my liking: 19-22 and 22-25. I'm therefore about to take a 12-25 10-speed cassette and will add a 28 tooth single cog from an old 9-speed MTB 11-32 cassette (but still using the 10-speed spacer), and I'll remove the 16 tooth cog in exchange. Compared to the old 11-28, we'll lose the 11 tooth cog, but we won't miss that, but we'll gain a gear in the low end to make the spacing tighter - the spacing will now be 19-21-23-25-28: perfect! (the 11-28 also doesn't have a 16 tooth, so there's no actual loss there). As far as I know, there are no cassettes that come stock with this combination. Alternatively, to get the same low-gear spacing using a stock cassette I could change the inner chainring for a 26 tooth instead of the 28; I could then use a stock 11-26 or 12-26 (depending on whether we decided the 11-tooth or 16-tooth cog was more important). However, the cadence change and the rougher shifting when moving between the middle and inner chainrings would be a bit too much with a 26-tooth chainring to allow two people to keep pedaling smoothly on a tandem, so I'd like to keep the 28 tooth chainring and not go any lower there.

My wife says that I think about all of this way too much, but it keeps me happy.

I agree.

Actually, losing the 16T cog and have the resulting jump from 15 to 17, a 12% change, would bother me far more than the difference between 21 and 23T (9%) compared to 21 to 24 which is also about 12%.

How about a difference tack?

Change your road RD for a mountain RD, then you can move to a 11x32 cassette?
I'm not sure about a 10 speed cassette in that range, but I separate (saw apart) my 9 speed cassette's and swap sprockets to create idealized cassettes.
If serious low gearing is desired, this might be an answer.

I agree, not having a 16T cog does bother me. On my single bike with the 11-26 cassette, I have occasionally removed the 13T and put a 16T in instead. This seems counter-intuitive because the 12-14 jump is a bigger percentage difference than the 15-17 jump, but it makes sense to me because the 16T cog is right in the middle of the cassette where I spend a lot of time, while the region where the 13T cog has disappeared from I spend a very little amount of time, and so I miss the 13T much less than I do the 16T. No matter what, I still want to keep the tight spacing on the low end and have a decent top gear, so one of these has to go.

Everyone keeps saying that the new Campy gear going to 11-speed cassettes is pointless, but I would certainly appreciate being able to have one more cog in there, because then I wouldn't have to make these difficult decisions. However, I'm probably never going to use Campy because then I can't interchange parts between manufacturers (Shimano and SRAM mostly) and between mountain and road components very easily, and the cassettes won't fit on my current hubs. I've heard that FSA should be coming out with a full groupset soon-ish, and it will probably be 11-speed, so I'll take a long look at that once more details are available.

I expect Shimano will also make the jump to 11-speed and certainly they will if SRAM does.

BTW, seen the prices on Campy's 11-speed stuff? WOW!

I've got no real need for anything higher than a 52 or 53 x 13 so for my riding, Campy's 13x29 10-speed cassette is the ideal. It's a straight block from 13 through 17 and has small jumps the rest of the way. If you really want tight gearing Campy also makes a 13x26 10-speed which is straight from 13 through 19.

I've converted a couple of Shimano 12x27 9-speed cassettes to 13x27 by dropping the 12T, and adding a 16T which gives the same small steps. Shimano's 12x27 10-speed will be similar but require no changes. All of these include the "essential" 16T cog.

I didn't mention the most unusual part of the gearing on my single bike - I'm running a "super-compact" double crankset with 28T and 46T chainrings. Because of the 46 tooth big ring, I need an 11 tooth cog to achieve a similar gear as your 52-13, which I agree, you really don't need anything more than that (I can still pedal up to about 55 kph / 35 mph, which is plenty).

You may wonder why I'm using such an unusual chainring combo. Well, I did have a triple, but decided there was too much overlap and not much need for the biggest gears, so I replaced the 39 and 52 tooth rings with one 46 toother. I saved about 80 grams in doing so and simplified my front shifting tremendously. Now I can cruise around on the 46 tooth ring all the time until I find a significant climb. It has similar advantages to a regular compact double, but allows a good range of gears at a high cadence for someone who is not insanely fit (I've tried a standard compact double, but I really didn't like the gear options that you end up with). It's hard to find an appropriate crankset to mount the 28-46 tooth combo onto. I've done it using the inner and middle positions of a triple crankset, this would normally cause some chainline issues, but its OK because I have a Jtek jumpstop installed inside the drive-side BB cup, which also prevents me from losing the chain when making the jump from outer to inner ring. I originally got inspired by some discussion on the Long Distance Cycling part of this forum to give this a try, and I love it so far (except for needing one more cog on the cassette). I've done a similar thing on my touring bike, where I've gone with 26-42 chainrings, but I won't do it on the tandem, because as I said above, we need to keep the pedal cadence somewhat smooth when doing front shifts.