elston1999

I have a Shimano rx100 52/42/30 crank. Many of the teeth in the middle ring are worn down and some even gone. I'd like to replace it. Finding that specific crank is a bit challenging. The crank is on an old Cannondale r500 3x7. What size cranks can go on it? Would a 48/38/28 crank work? Thank you.

nlerner

You can likely just replace worn chainrings rather than the whole crankset.

dddd

One important thing to know about "modern" front derailers is that the inner cage plate is shaped for a specific tooth-count difference between the big and middle rings.

So as long as the new crank and rings have a ten-tooth difference between the middle and big ring, and if the derailer height is set properly above the big ring's teeth, the shifting will likely be as good as the particular new crank's chainrings were designed to perform, using a good chain (such as Shimano's, since they literally invented most of the performance features of modern chain).

elston1999

not a modern front derailleur. Old suntour.

verktyg 

Shimano RX100 cranks take 130mm BCD chainrings. The triples used a smaller 74mm BCD inner chainring. They used "SG" chainrings which were slightly narrower than older models.

The easiest, cheapest solution is to just replace the 42T inner chainring. An eBay search for "Shimano 42t SG 130mm BCD chainring" turns up a bunch of them for $30 bucks and up.

Velobase RX100 Triple:

https://velobase.com/ViewComponent.a...5-2358d9f4fa99

There are several complete RX100 triple cranks listed on eBay right now:
https://www.ebay.com/itm/26577281282...IAAOSwe3JiyXu2
https://www.ebay.com/itm/18505058068...oAAOSwkcNhQNb4

If you switch cranks, you don't know what you're going to get with a used set. Also as dddd mentioned, you might run into a FD problem shifting if you go to a smaller big chainring???

I'm running 49T or 48T x 39T or 38T chainrings on most of my 130mm BCD Shimano cranks. Switched from 52T x 42T... No problems.





Personal opinion on chains: they're 3000+ mile consumable wear items. Most of the Shimano chains are CRAZY over priced!!! All of the better brands like SRAM and KMC will give the same life and... performance as Shimano chains for less money!

verktyg

The Golden Boy 

Hi @elston1999!

I included your post from your other thread, since I think you're asking about the same setup.

Since you have a RX100 crank and a Suntour derailleur with Microshift shifters on a Cannondale- you've got the proverbial "dog's breakfast" of parts on there- so there's a whole world of options.

I think your 2 immediate solutions are- pick out any pre 1995-ish front derailleur (I'd get one to match your rear derailleur just because) and you'll be fine and pick up a 130 BCD chain ring in that 42 range.

For the most part- friction front derailleurs will work on triples in friction- irrespective of being "triple" or "ATB" or "mountain bike" derailleurs. Ask anyone who has a Suntour Cyclone pulling a triple or any Schwinn Voyageur that's running a FD-204 or 206... Once you start getting into indexed front shifting- then the derailleur and tooth count start to really matter.

As far as the crank goes- it looks like the RX100 triple was a 130/74 BCD triple. ATBs and MTBs generally used a 110/74 BCD for their triples. (BCD is Bolt Circle Diameter- where your chainring mounting holes are located.) The smaller BCD meant they could fit a smaller ring- (I think 110 goes down to 34 and the 74 inner ring goes down to 26 or 24)- but you see a lot of ATBs and MTBs with 48-38-28- Which I think is a good range.

If you're comfy with the gearing- just replace the chain ring. If you think it's geared a little tall- get a 48-38-28- But keep in mind the crank length (a lot of ATB/MTB cranks are 175 and a lot of road bikes are 170/172) and that you may need a different length bottom bracket spindle. (it's a lot easier to just change the chainring)

​​​​​​​Good luck!!!

Ross200

Many Shimano chainrings of this vintage have(had?) several teeth that are cut down and shaped to facilitate shifting-super glide. Many not familiar with this feature have been tricked into thinking teeth are worn/missing from the rings. Check the face of the teeth where the chain rollers mesh to verify the wear.

TA and Stronglight both make very nice ramped/pinned middle rings that work great and last much longer than OE if you indeed require new rings.

pastorbobnlnh 

elston1999 , only two more posts and you can include pictures with your posts! We like pictures. Just add two more here with basic comments.

Refreshing your existing drive train is the best way to help renew your bike. What year is your Cannondale? My guess would be mid to late 1990s.

clubman 

I've got an rx100 50/40/30 in the basement. I'll take a close look with some pics.

dddd

My preference for Shimano chain is particularly with their 10-speed chain, but also with their 9s chain.

I've observed first-hand, many times, that using a SRAM 10s chain on a 10s Shimano road drivetrain caused very poor shifting quality, which immediately corrected itself with the installation of a similarly-new Shimano 10s chain.
It's also quite noticeable on 9s drivetrains, to a somewhat lesser degree.

I do usually use KMC X-series chain on my own bikes having 7s or 8s cassettes or freewheels, with no difference observed as compared to using Shimano's 7-8s chain.

I've taken a digital caliper to all of the popular 9s chains, and observed that Shimano's 9s chain does have a greater ratio of inside width (at the outer plate) to overall/outside width, this as compared to SRAM, Campag and KMC 9s chain. This may explain the Shimano 9s chain's more-aggressive tooth-grabbing qualities during shifting (which makes for less need of fine adjustment of the cable to insure robust shifting).

Again though, it's with 10s Shimano road drivetrains where Shimano's 10s chain shows the biggest advantage over SRAM 10s chain, and where Shimano's later-issue asymmetric chains (6701, 7801, etc.) clearly offer the best shifting possible. This can be critical when larger 10s road cassettes are used, as the tighter B-tension screw adjustment leaves the guide pulley further away from the smallest cogs in the "convex" part of the cassette's outer profile (usually 3-4 cogs in from the small end of the cassette).
So it's at the 10s level where, to me, Shimano chain actually seems like the best bargain (and where the prices are also closer between brands).

dddd

How old, i.e. which model FD?

Generally it was during the mid-90's that shaping of the front derailer's inner cage plate for specific middle-big chainring count differences took over, but such shaping did develop, to some degree, years earlier.

I've been brought several bikes where a well-intended shop mechanic's chainring size changes rendered a customer's triple-drivetrain practically unusable, even after the customer had brought it back to get it's shifting problems corrected!

elston1999

Think this would work? Stronglight Type S-5083 130 BCD Chainring

verktyg 

Almost all 130mm BCD chainrings will fit on your crank. Is there a ratio that you would like to use: 52T-42T, 52T-44T and so on?

That 44T Stonglight should work well. It will give you and intermediate choice rather than the smaller 42T ring.

verktyg

elston1999

My existing setup is 52\42\30 so I was just trying to keep it simple.

verktyg 

That should work... You might find that you will be riding on the 44T CR a lot more...

verktyg

elston1999

Last question, that stronglite says 9 speed. Reading conflicting opinions but will it work on my speed setup? Thanks!

elston1999

Will that stronglite work on 7 speed? Says it’s a 9 speed ring but reading conflicting opinions. Thank you

verktyg 

All of the Shimano cranks that I pictured in my previous post are running 9 speed or 10 speed chainrings with 6-7-8 speed SRAM chains and 7 speed or 8 speed FWs or cassettes. No problems with them.

verktyg