CykelFlicka

Hey all-
Apologies in advance - I don't know if I trust my math according to the magic cog # formula, and it'd help to have some reassurance.

Setup I'm trying to achieve: 9 speed, 50/34T compact up front, 11-28+ behind. Would prefer 30 if I could find it, but I don't think it exists - it's either max 28T road or 32T if you use a MTB cassette. (FrankenBike?)

Max chainring difference: 50-34 = 16
Max cassette cog difference: 32-11 = 21
Total drivetrain capacity: 37

According to the Shimano manual, it looks like it should work... right?

I haven't yet bought the bike - it's a 9 speed with Ultegra all around, short cage and 53/39 up front. Someone I know is selling a 6500 GS (9 spd "triple"/medium cage Ultegra) rear derailleur in great condition for a song, so it'd theoretically work if I swapped them out.

I guess the real question is, would a MTB cassette with 32T behind with a compact up front be too weird? [Side note: doing a triple is out of the budget.]

Thanks!

-KC

Eggman84

Per the Shimano specification sheet, (available at https://si.shimano.com/pdfs/si/SI-53Z0D-000-00-ENG.pdf ) the RD-6500 GS is rated for 27T largest cog, and 37 tooth maximum capacity. If you want to run a 32 tooth large cassette and have index shifting, then you can use a Shimano 9 speed MTB rear derailleur like the RD-M591 or RD-M592 (I like the M591 better because it has an adjusting barrel). Shimano changed the cable pull with the 10 speed MTB RDs so can't use them (or higher).

Camilo

[edit]
I wrote this as the above was being posted. I was too lazy to actually look upt the spec for the OP (teach a man to fish, etc.) But since we agree 100%, and I expended a lot of electrons typing it, I'll post it anyway....

Couple of comments. First, its not a magic formula, it's two specifications that will be in the technical sheet for that derailleur. Look on the Shimano website, or just do a web search for your derailleurs maximum sprocket and wrap. The spec will give you a maximum cassette sprocket size (e.g. 25, 28, 30.... whatever). It will also give you a maximum wrap capacity spec which is the difference between the large chain ring and the small chain ring (regardless of double or triple) + the difference between the largest sprocket and the smallest . OK, that's a formula, but it's not the formula that will answer your question, it's the formula applied to the spec for that derailleur.

So, look up up the specs and compare to what you're trying to do.

That said, I've used 6500 GS derailleurs (as well as the 105 and Dura Ace 9 speed equivalents equivalents) for years on my Shimano Ultegra, 105 and Tiagra road triple bikes. The triple crank is 52...42?...30 which is a 22 tooth difference between largest and smallest. Yours will be 16. I KNOW I used a 11- 26 tooth cassette, but I'm not sure if I put a 28 on there. I know I didn't put a 30 on there (I switched to a Deore XT RD when I went up to 34). So I know I've used it with a 15 tooth difference in the back. Front + back = 37. So I know for sure mine wrapped 37 teeth and had at least a 26t maximum sprocket capacity. Since your crank only has a 14 t difference you can have much greater span in your cassette as far as wrap goes. The bad news is that I believe you will be limited not by the GS derailleur cage length/wrap, but by the maximum sprocket size - which is the same whether the 6500 RD is short or long cage since they have the same RD body and differ only in the cage length. My guess 26 or 28 max.

But, just look up the published spec for the 6500 GS and compare it to what you want to do.

If for some reason you want a 30 or higher in back (I'm pretty sure the 6500 GS won't accommodate 30), just get a 8 or 9 speed Shimano MTB RD. It will work perfectly with the 6500 shifters. I'm not sure about Shimano 10 speed MTB RDs and higher. It's easy to find the various levels Shimano 8 and 9 speed MTB RDs on eBay. I've outfitted three triple bikes in my family that way.

CykelFlicka

Cool cool. I had read a couple places that Shimano tended to be conservative with their max cog estimates, but I didn't want to challenge that theory without consulting the gurus first. Granted, I am posting on a forum, which means I'll get 5 different opinions.

The other bike I'm looking at (same brand, similar frame, just a couple years older and RSX components instead of Ultegra) has a long cage as it originally came with a triple up front. The LBS apparently "couldn't source the parts" for the front crank, so they basically forced the guy to change to a double up front and I'm not sure if he kept the original shifters. Right now I'm waffling between the two because the first (Ultegra one) is a couple years newer, is cheaper, has a better frame/fork, but needs a new crank up front and will need a new derailleur to make it work with a compact. Second one is an older 8 speed w/ an alum fork but may not require as much overhaul to fit my needs. Hopefully one I see them in person it'll be clear which one's the better deal.

Matt Gaunt

Stop teasing us - what frames are they?

I love a retro bike project. Let us know how you go on.

CykelFlicka

One is a 1996 Giant CFR 3 (originally 7 speed RSX), the other a 1999 Giant CFR "Pro" (9 speed Ultegra). Giants are reaaaaally popular down here, I guess they did a good job with direct marketing to the Ozzies. I'm after these because I need something that's inexpensive, not super flashy but also not a clunker. Basically something that a bike thief will look at and thing, "Hmm, it has more than 22 spokes on the front wheel and isn't very shiny... Pass." My issue is that I absolutely need a compact or triple up front. Triples are becoming exceedingly rare, and I've resigned myself to the fact that I likely won't be able to pick up one used.

Camilo

The lowest you can get with the new crank and the GS will probably be 34 in front and 28 in back.

But if you really want the low gear to be lower than that, like 34t in front and 30t in back, you will need to use a MTB derailleur.

Given that, the cheapest and excellent option is not to change the crank, but just do the rear end. A 34 in front with a 30 in back is approximately the same as a 39 in front with a 34 in back.

Importantly, either way you go with the cassette - 30t with a new crank or 34t with the existing crank -, you'll need to go with a MTB rear derailleur, Like I mentioned, basic Deore 8 or 9 speed RDs are common and cheap on ebay. XTs are a little lighter and a little more expensive.

My guess is that your derailleur cost will be a wash whether you stick with the Ultegra GS (and are limited to 28t) or go with the MTB derailleur which will give you either 30 or 34t. And either way, you're buying a new casssette, so those options are pretty much a wash as well.

Just a thought.

tFUnK

Was able to squeeze in a 32t cassette using 6700 short cage. Maybe the 6500 has similar tolerance?

Camilo

Maybe... https://www.cyclecycle.info/bicycle-...ar-derailleurs

cpach

https://www.amazon.com/Shimano-HG50-.../dp/B00MVS39EI 9 speed 11-30 is a thing. Official max cog is 27t, 30t will usually work, 32t is a stretch. If you want low gears the best solution is to buy a 9 speed MTB derailleur and use a 11-34. Won't feel weird with a 50/34. Only you can decide whether the jumps are too big. I could live with it, though I would notice them.

bwilli88 

This Zunow of mine is running a 9 speed 105 with a 48x45 with a 11x36 9 speed rear.


My 10 speed Fuji running a 46x34 with a 10 speed 11x36 and an Ultegra 10 speed RD and both work extremely well.

CykelFlicka

Update: Bailed on the Giants and bought a 2003 Cannondale R2000 that already has a compact on front. It originally came with 9 speed Ultegra but the guy swapped out for 10 speed Dura Ace (not sure if it's 7800 or 7900). I've heard the DA can be really finicky when you get to 28T, but I'll put one on and see how badly my knees hurt after the ride.

I can feel the judgey eyes of my Bianchis back home glaring at me for buying oversized aluminum...

davidad

I know you can run a 30 on the back. Harris cyclery makes a cassette for you. https://www.harriscyclery.net/produc...ssette-702.htm You can make your own using a 30 individual 8sp cog an a first position 13. you use the spacer between the 12 -14 and replace the 12 with the first position 13.

CykelFlicka

Thanks! I was going to get a Sunrace 11-28 (ten speed) as they don't offer that one that size w/ a 30T. I'm in Australia right now so my options are limited...

davidad

If you have a shop there they may be able to get the 8sp first position 13 and the 30. 8speed cogs will work.

Camilo

Excellent choice! That's an ageless frameset, imho.

I had a baby blue R2000 triple (stock was full 9 speed 6503 Ultegra w/ DuraAce long cage RD, Mavic Ksyrium wheels) it was a great bike. With the Ultegra road triple (which is now on it's third or fourth bike in my garage, still going strong), I had no problem staying within the capacity of the DuraAce derailleur. With a compact double, I'm pretty sure I would have been happy with a 28 in back, since that's what I have on my three other compact doubles. And I'm an old coot with chicken legs.

I think mine was a year or two older than yours, it was badged R2000 and also badged CAAD7 frame, with a matching paint Slice Ultra fork (CF+aluminum) - which was a terrific and lightweight frame. The fork was very nice if not a little heavy, but some of the CAAD frames back then came with the Slice Premium (all CF) forks which were as light as almost anything available. I think the Premiums might have come in black CF weave instead of painted. Not sure about that, but a friend had a CAAD8 frameset from a year or two later (newer) than mine and his had a Premium fork that was black. I don't know if his came built up with the DuraAce he had on it, I think he bought the frame and fork and built it up himeslf.

Note: wouldn't you think "ultra" > "premium"? Not so 8-)

What CAAD# is yours?

If you need lower gears, do not hesitate to put a larger cassette on the back with an 8 or 9 speed MTB rear derailleur. It will work great. In keeping with DuraAce/ Ultegra, don't settle for anything less than an XT RD 8-)

Nice bike, show pictures!

bldegle2

48/33 up front, 11-36 on the rear, 4700 GS cage, road bike...works like a charm, can be used as a gravel bike with tire swappage....

CykelFlicka

I have the CAAD7 with the carbon fork, it might be the same as yours - it"s light blue (which was the inaugural WSD model, I believe). The guy I bought it from was a bike mechanic and swapped the 9 speed Ultegra with a 10 speed Dura Ace of another bike as apparently finding new brake hood covers for the Ultegra was impossible down here. No idea if he's right, but I'm not going to complain about an upgrade!

Will post photos soon.

HillRider

I've read that the 9-speed GS Shimano rear derailleurs, despite the spec of 27T max, will easily take a 28T cog, almost always take a 30T cog and will sometimes take a 32T cog. I hope this is correct since I have an Ultegra RD-6500GS on one bike currently using a 12x27 10-speed cassette but for it's next rebuild I plan to install a 12x30 cassette as 12x27 is nowhere to be found. If it refuses to work I have a new RD-5700GS in my parts box that will accept up to a 32T cog but I'd rather not have to use it.

noobinsf 

No mods needed for a 36-tooth big cog? Did you have to fiddle with the chain length to get it to work? I ask because I have a 6500 GS, but have been reluctant to use it due to the perceived limit to 27-30ish large rear cog, and I like a 32 if I have a wide range derailleur..

bwilli88 

Nope, it went on no problem, runs like a champ. I did run the wheels toward the rear of the dropouts but not far. I did the Shimano Fit; Big and Big + 2 links

Camilo

Yeah, finding brake hoods for the 9 speed 6500 series brake levers is nearly impossible. Sometimes you can find trashed levers "for parts" on eBay and get decent covers off of them. Many years ago, I searched high and low and finally found a set for my 6500 levers, but I kept the old ones since they're not trashed, just very used looking. Actually the "new" one are about in the same condition now.

Looking forward to seeing the pictures

CykelFlicka

Right after I bought it - had to take the train an hour south to try it out, but it was worth it! Need to get some shoes as my cleats are back home in the US, hence the flat pedals.

Dumb question - can I cobble together a 30T ten speed cassette? I read in another thread that you have to do some wizardry with the rivets, though.

tFUnK

12-30t 10 speed cassettes should be easily available. If you were to cobble up a custom one you would still need to source the low end (larger cogs) cluster at the bottom.

CykelFlicka

Good call, for some reason I was only searching 11-30. [Dopeslap.]