julian_s

Hi I purchased a used Kona Blast. It is an 8 speed with 3 at the front for a total of 24 gears. The original deraileur was a Shimano STX-RC which i believe was long cage. Original bike specs , 30T , 11T rear and 42T, 22T on the front, max capacity of 39. I changed the rear wheel only and the back cassette so the new specs are 32T,11T on the rear giving a max capacity of 41. I am looking for a replacement deraileur, I just want to confirm that this one would be suitable:

Shimano Claris RD-R2000 Rear Derailleur GS

Min cog size : 11T
Max cog size : 32T (SS), 34T (GS)
Max front difference : 16T (SS), GS 20T
Capacity : 37T (SS), 43T (GS)
Specifications:
GS Cage:
Cage: GS
Max Front Difference: 20T
Maximum Cog: 34T
Minimum Cog: 11T
Primary Color: Grey
RD Capacity: 43T
Speed: 8

Thanks for your help.
Julian

Crankycrank

Yes, that will work. Here is a chart that will show some others that will also work if you're interested. Bicycle Cassettes & Drivetrains - Google Sheets To eliminate any that won't work, check the pull ratios first. (Look right on the top column for "pull ratio".) You need a 1.7 ratio derailleur. STX-RC is listed in row 286 for reference.

Barry2 

Julian,
Are you looking to change the existing rear derailleur due to the Total Capacity being 2T too low?
Shimano is quite conservative with their Max rear cog limit and their Total Capacity limit.

Look this one up
RD8050 with 50/34 front and 11-36 rear. Many have gone as far as 11-40 rear.
Yep.... way over spec for both Cog and Capacity. I've got 4-5000 miles on that 11-36 setup.

For the sake of being 2T over the capacity, I'd give test it on the bench and see how it changes.
DO BE SURE your chain is the correct length. If it was cut short to begin with, the 2T could aggravate the problem.

Welcome to Bike Forums

Barry

Bill Kapaun

IF you existing RDER works, keep it.
Size the chain for BIG:BIG.
Worst case is you have a tiny bit of chain sag when using the smallest ring:cog.
That's a really dumb combination to use.

julian_s

Thanks for the feedback.

The original derailleur on the bike is the Deore RD-M510. In the spreadsheet it is listed as 9 speed. However the original cassette is an 8 speed, so that is somewhat confusing to me. Why is this? I am new to this, first bike rebuild. I am okay keeping the original derailleur, it is just that i have some newer rims with a cassette already on it that has and extra 2T on the largest rear cog compared to the original cassette. Both original and new cassettes are 8 speed. I guess I could move the cassette from the original rim, to the new rim. It seems the original Deore RD-M510 could handle the extra 2T according to the specs ? Also I thought having a newer derailleur would be better for performance ? The Claris seemed to fit well.

julian_s

Bill what combination did you mean is really dumb? Sorry I am a newbie.

veganbikes

Deore is way way better than Claris which is one small notch up from the absolute bottom Tourney. It is also road vs mountain which in your case doesn't matter (but go to 10-11-12 speed and it does) I run 7 and 8 speed derailleurs (XT) with 9 speed shifters and it works great. If yours is working fine no need to change and if you want to change get a new 9 speed shifter and a chain and cassette and enjoy that extra gear and if everything is fine and un-worn than keep it as is.

A new derailleur especially a downgraded one is not always better, my 94ish M737 rear derailleur will probably outlast the bike it is on and like I said it is running 9 speed. If they made it for 11 speed I would be all over it in a heartbeat. It is a very well built derailleur that I think looks decent but some people disliked the looks but in the end the performance is flawless and it is hard to kill one. I have tried certainly and I got it used and it just keeps going and going. Deore can also last quite a while. I have seen some old deer head stuff that is still going strong after almost 40 years.

Basically you are using your smallest ring at the front and your smallest cog at the rear which would be a very easy gear at the front and a very hard gear at the back it is called cross chaining when the chain is at the extremes in either direction but in that case it is quite an odd combination to be in.

Bill Kapaun

Put the chain on the smallest ring (front) & smallest cog (back)
Now stand 5-8 feet or so behind the bike and "sight" down the chain like a rifle. (it helps if you can have someone hold the bike vertical)
You'll see it runs at a very extreme angle. Bad enough that even a newbie would realize "it can't be good" for longevity of the chain.

SpedFast

Thank you for the link. Great information to have handy.

PromptCritical 

This is awesome - great work!

Gonna be a HUGE help in keeping a couple of vintage bikes running!

julian_s

Thanks now I understand. So essentially the original design was a bad combination ?

Crankycrank

There are a few details left out from some items on the chart but in this case 8 and 9 speed are irrelevant for your old derailleur and the Claris. They can be used for both. Many Shimano derailleurs can be used for various numbers of speed combos and groupsets. It can get a little confusing but just ask here when in doubt.

Barry2 

No, the original combination of parts is good.

If the “pull ratio” matches on both shifter and derailleur, an 8 speed shifter can be used with a 9 speed derailleur and an 8 speed cassette.

The “bad combination” comment earlier did not refer to your parts, but referred to the way you might use them.
it was referring to cross chaining. << clickable link.

Hope that helps

Barry

bboy314

Seems like the original setup was fine, and you probably don’t need a new derailleur. You may need a new chain if you’re installing a new cassette, and the chain is worn. As for using the small/small gear combo, that is called cross chaining and should be avoided on any bike.

dedhed

that Deore will index &shift 6-9 speed mountain and 6-10 road (except 4700 Tiagra & some older DuraAce) shifters. Better unit than the Claris

PromptCritical 

You didn’t mention why you are looking for a new derailleur. If it doesn’t shift well, don’t forget to check the derailleur alignment. Misalignment can cause shifting problems. You’ll ned a Park DAG-2.2 (or 3) or have a bike shop check it.

PromptCritical 

I've converted both of our tandems (one now retired) to flat bars due to my arthritis. Switching to a trigger shifter for the rear derailleur was easy. However, I've never found a derailleur/shifter combination for the front (triple crankset) that works.

It's not a problem, as I converted to a friction shifter using a Paul Comp thumbie and Campy lever, but I'm curious as to what I'm missing.

Crankycrank

I would just keep the friction shifter. It works for you, lasts forever, front shifting/trimming is not complicated so not much advantage in an indexed setup.

PromptCritical 

I'm going to keep it, but I'm still curious........(I'm a recovering engineer, but my friends say the recovering isn't going well).

bboy314

Shimano has made plenty of flat bar road shifters including Sora R3000, Tiagra 4600, etc. I think Microshift has options as well.

PromptCritical 

Yeah, and I have a box full of them (for the front DR - the rear was easy) that didn't work. No idea why. Free to a good home (or a bad one).

bboy314

I’ll bet there is a reason why. Are you pairing them with appropriate derailleurs? What sort of issues are you having?

I’ll take them off your hands if you must get rid of them though!

PromptCritical 

I sure thought I was, but buying individual parts instead of a groupset, is problematic since there are so many variations.