Thanks for the insights. I'm hoping one tooth doesn't make a difference. I'll report back in a couple of weeks when I try installing the new cassette and new chain. I plan to use a KMC X8. I'm pretty sure that will be OK for 7 speed?
I plan to keep my current chain and cassette in case the above doesn't work out (each are still good) ... but I expect to be able to make the 12/28 work ... what's 1t on the rear small/high side? ... (I don't know what I'm talking about) ...
Not to mention 7 speed cassettes in this configuration are not that easy to come by and are expensive. I believe Shimano still make one in a not so quality, but probably just fine model, the MF-TZ500.
The 12/28 I found is an HG70 that looks contemporary with my bike.
I always use the big / big plus 1.5 link (or something like that) method when fitting a new chain, but will have my mechanic friend do it since I don't have a chain whip or much experience with cassettes.
Originally Posted by
dsbrantjr
You cannot necessarily have the max front difference AND the smallest rear cog AND the largest rear cog all at once and still not exceed the max capacity.
Why not!
I found the quote interesting ... it seems to align with what the seller said when I asked a similar question:
I believe I have come across some instances where the max difference on the front and rear adds up to more than the max total difference per shop catalogs. I've always taken that to mean the manufacturer is telling us you cannot have the max difference on the front and back at the same time. So for example, if running the max difference on the rear sprocket, then the front chainring difference has to be something less. Then there is your comment that probably makes all this moot...and that is manufacturers have a tendency to be overly conservative with their capacity limits...and you can usually squeeze out a few more teeth with sensible shifting habits.
Does this mean that if my front was under max by let's say 4, or a 53/44, I could have a smaller high gear (like 11t or 12t) in the rear with a 28t for low? Does that extend to being able to have a larger lower gear (like 30t) in the back as well, assuming the capacity wasn't exceeded? For some reason I thought max rear cog was a hard limit for the RD. This is kind of confusing.
Are you also saying the Shimano document is not wrong, because it's expected that not all variables can be at max?
Originally Posted by
dsbrantjr
If this combination does not work you can replace the derailleur with a Shimano mountain derailleur up to 9-speed (or road up to 10-speed) which has sufficient chain wrap and large cog capacities.
Noted.
I'd like to keep the bike as original as possible, since as far as I can tell it's pretty much entirely original ('93 Bridgestone RB-1).
I'm familiar with the Deore RD-MT60 and use them on 2 other road bikes, it's one of my favorite derailleurs, and I have at least one spare.
I'm willing however to sacrifice some originality for more gear choices (I do not want to be seen walking my bike
). 13/23 seemed a bit high but then again I'm getting more comfortable using the 40 up front. I'd been in the large-front-(at almost all times)-is-better camp for a while. I will also appreciate a higher 12t in back for downhill speed.