jockstick

I'm looking to swap out my 13-23 7 speed rear cassette for something with a 11-30 or 12-28 cassette.

I believe everything on this bike is stock Shimano 105 from the 90's, "105-SC" - the derailleurs are "FD-1055" and "FR-1055". The front downtube shifter uses friction shifting; the rear shifter is indexed.

As far as I can tell, there's 2 potential pitfalls:

1. The rear derailleur won't accept a 30T cassette - I can't post links yet, but googling "RD-1055" links to a velobase.com page with a comment on the bottom that says that the derailleur can take 30T.
2. The front derailleur won't shift properly with the larger cassette. I'm hoping friction shifting will alleviate this, but I haven't found any info online to confirm or deny.

Thoughts? Would 11-30 be ok, or should I try the 12-28? Or neither? Thanks!

HTupolev

Your front derailleur will probably be fine. If it turns out that it doesn't have enough cage height to deal with the more extreme vertical chain angles rub-free, this won't cause anything to explode, and you'll probably be able to find a suitable replacement on the cheap.

Your rear derailleur might be problematic. The RD-1055 rear derailleur is rated to handle a maximum cog size of 28T, and its tension cage is rated to wrap up to 28 teeth of chain. A 30-tooth cog is two teeth larger than the max cog size. And (53-39)+(30-11) is 33 teeth of wrap, so you're significantly exceeding that rating. Shimano is a bit conservative with their derailleur capacity ratings, but you might be pushing things here.
The 12-28 cassette would be within the cog size rating, and would only exceed the wrap rating by two teeth... you might be able to get away with it.
Shimano did use the same pull ratio for nearly all of their 7/8/9-speed road and mountain derailleurs, so another option would be to replace the 105SC derailleur with something that has more capacity, like any of Shimano's cheap 7/8/9-speed MTB derailleurs.

jockstick

That's very insightful, thanks.. I hadn't considered chain wrap. I think I'll go with a 13-30 cassette, since I definitely don't need 11, and this has a more reasonable chain wrap.

colnago62

stevoo

The Sora road rear derailleur works perfectly for this application. Inexpensive, has plenty of chain wrap so you can run ALL the gear combinations if you like with even a 32 tooth cog in back. Converted couple of older 7-speed bikes with 39 x 53 front using up to 32 cog in back. Worked excellent. Rode all over Colorado with that set up.
Great way to get a bit lower gears on older stuff cheaply.
Good luck.

jockstick

After a lot of deliberation, I think I'll go with the following for extra low gearing as I want to take this bike touring (I wish I could post links below):

• 50-34 compact crankset
• 13-28 cassette

It's about the same price as swapping out the rear derailleur (sjscycles has a really good price on the crankset) but this way I also get a fresh set of chainrings and won't risk getting a dud used derailleur or have to replace my chain to a 9 speed (just replaced it).

jeffreythree

I did it in the past and it worked OK, though it was a close call whether to flip the b screw around. I swapped to 50/38 chainrings when it wore out since I needed those as well, and went back to an 11-28 cassette. Those Sugino rings (only current 38 130 bcd ring maker i think) cost about as much as a compact crank. Probably a good call you made going with a compact.

Dean V

I can't follow what you are trying to do.
The bike has a 7 speed cassette or freewheel?
You are looking at putting how many gears on the back?
If it is more than 7 there are other issues that haven't been mentioned.

Second Mouse

Not sure how applicable this is, but I've got a 50-34 crank and put a 12-30 cassette on an older Cannondale CAAD 8, with an Ultegra 10-speed short cage rear derailleur. While it's outside of the specs, it does work, but just barely. It's an effort to get into the 30-tooth cog, makes a slight grinding noise and I need to be very careful not to get into the big ring/cog. If doing it again, I'd go with the 12-28, like you're planning to do and I'll probably replace the cassette with a 12-28, as it's fine when in the 28.

rm -rf

That 34-28 low gear will be a lot lower than your current 39-23. 40% lower! That's about 3-4 rear shifts, depending on tooth counts.

But the 34F-28R still just the same as many new 11-speed road bikes. But even my triple's approximately 1:1 low gearing, 30F-29R, isn't low enough for steep climbs on rough roads or a big load. My triple is great for all-day rides carrying the day's supplies -- the middle 39 chainring is perfect for flat to rolling terrain, and the 30 small chainring is pretty good on climbs. I'd like even smaller, though, a 28 or 26 small chainring.

For touring, carrying a fairly heavy load up a moderate to steep grade will be hard work with a 34-28. It should work okay for lightweight loads.

Lower gearing
Can you switch to a triple crankset? That would really help.
Or some riders are getting small cranksets, like a 30-46. They tend to be expensive, though.

EDIT--
I don't know much about square taper cranksets or 7-speed compatibility, but this one from sjscycles is 110 / 74 sized. It should fit 30 & 46 chainrings.
Thorn crankset

Dean V

A modern 34/50 compact will not work with a 7 sp chain.
A 7sp wheel will not take more gears without modification and possibly replacement.
Your frame will be too narrow to take more than 7sp without modification.
For 8sp and more they went to 130mm rear spacing, prior to this it was narrower, 126 I think for 7sp?
I would keep the 7sp, and get a suitable triple crankset and change derailleurs if required.

jockstick

Wow, thanks for all the responses.

It's a 7 speed cassette - I'm generally just trying to get lower gearing for taking the bike on a short tour. I originally planned to just get a bigger cassette, but I've also ended up ordering a compact crankset.
-----
​​​​​​​Yeah, I ended up deciding to stay within the recommended max because I'm the type of person to lose sleep over a slight grinding noise.
-----
I considered a triple crankset, but given the age of the bike and the many different standards at play for a change like that (chainline, BB crank/length, etc), some research made it sound like a difficult thing to get right, esp on a reasonable budget. I didn't want to also chance having to replace the BB.

The crankset I ended up ordering from SJSCycles was only $32 and should fit my current 7 speed cassette + square taper JIS BB. The only slight concern is that it's designed for a 110mm BB whereas I believe mine is 113 or 115 - some of the comments on the site suggest that should be ok.

I want to start with a few really easy and short tours to see how I like bike touring - and more importantly, to see if the wife will put up with it. The first couple will probably just be staying at hotels/airbnbs and eating at restaurants, so the load should definitely be pretty light. The plan is to probably upgrade to a dedicated touring bike if we decide we're dedicated to the activity (I've learned not to splurge on hobbies until I'm certain I'll stick with them).
-----
Still don't have enough post count to share links, but if you Google "SJSCycles Alloy Compact Double Square Taper Chainset - 50/34T" it should be the first result. It's designed for 7/8 speed. Only concern is the BB length it's designed for is about 3-5mm diff than what I think I have.

HTupolev

New parts still get made for 7-speed drivetrains (including compact cranks), and most cranksets will work fine across a huge variety of chains. Some are even spec'd by the manufacturer as being compatible with a pretty wide range... I've seen as broad as 5-10 speed.

I don't think the OP is trying to add more speeds.

Dean V

He was talking 11-30 and 12-28. Are they even available in a 7sp?
OP really needs to give a bit more detail.

jockstick

I wrote a long response replying to everyone, but it's still pending approval for some reason

It's a 7 speed cassette, not freewheel. Goal was basically to get lower gearing so I can take the bike on short tours. I initially just wanted to get a bigger cassette, but ended up also getting a 50/34 crankset and a more reasonable 13/28 cassette.

If you Google "SJSCycles Alloy Compact Double Square Taper Chainset - 50/34T", it's the first result. I think everything should fit (7speed compatible, JIS square taper), with the only risk being that my BB is slightly longer (it's either 113mm or 115mm, whereas the crankset was designed for 110mm). According to comments on the product page, that should be ok.

I also toyed with the triple crankset idea but it seemed much harder to get right, with a high chance of having to change the BB and/or front derailleur. I don't plan on doing long tours or using heavy loads, so I think this should be a good starting point. I think the next step if this isn't sufficient is to go with an old MTB rear derailleur and a larger cassette.