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Larger cassette for a Trek 1800C

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Larger cassette for a Trek 1800C

Old 07-23-21, 09:10 PM
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JustinDemoude
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Larger cassette for a Trek 1800C

Yes, I still have my original. But now that I'm getting older I can't run with the 12-25T cassette like I used to and I want to add a larger one. The crankset is a triple Ultegra 52-42-30 and the RD is an Ultegra GS 6500/6510 GS Long Cage. I want to add a 34T cassette and believe a Deore CS-M770-9 (five hanger) will work with the Ultegra derailleur. My question of course is, will it work? I know a 27T/28T would and I think a 32T will too, but doing the research online is akin to neuroscience! Now I do have a Deore 9-speed RD-M592-SGS that maybe I could swap out for the Ultegra if I had to and run the M770 that way. Does anyone out there have a similar re-build experience? And no, I do not have the money for a Cannondale CAADX!

Any rational, constructive and measured comments are welcome...and thanks for taking the time.

Last edited by JustinDemoude; 07-23-21 at 09:11 PM. Reason: punctuation
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Old 07-23-21, 10:30 PM
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I wouldn’t run your 6501GS with that setup. I’ve pushed max cog 2 for road RD and 4 for mtb RD, if the stock hanger is generous enough.

The other issue is capacity. Ideally you want a 45t capacity. 11-34 = 23 and 52-30 = 22 for a 45t capacity. I’ve pushed it some, but the 6501 GS has a capacity of 37 and 8t is a bit much.

Your 592 would work. I’m more partial to an older 9 speed XT as I think you get a bit better shifting. But finding one usually means eBay and being very careful to find a really good one.

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Old 07-24-21, 05:48 AM
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Justin, welcome to C&V. Believe it or not, 9 speed is not quite vintage, yet, but we are a friendly bunch, and we'd never make some snarky comment like, "Why don't you just mount the latest DuraAce Di group?"

In fact, most of us ride a wide range of different bikes so you did come to a place that is helpful. I'm running a Deore RD (don't remember which model but I believe it was for a 9 speed cassette) on an 8 speed HG/UG hybrid cassette and my largest sprocket is 34T with no issues. I am using friction bar-end shifters and not index ones.

Don't forget you will need a longer chain, so purchase a new one at the same time. The chain will need to be shortened to the correct length, which can be critical when riding a wide range cassette with a triple crankset. If you don't have a chain breaker tool, buy one as well. A SRAM or KMC 9 speed chain with the quick link would be my choice.

Let us know how you progress. Again, welcome to our friendly little spot on the internet.
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Old 07-24-21, 10:30 AM
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Originally Posted by 70sSanO View Post
The other issue is capacity. Ideally you want a 45t capacity. 11-34 = 23 and 52-30 = 22 for a 45t capacity. I’ve pushed it some, but the 6501 GS has a capacity of 37 and 8t is a bit much
That's what I was afraid of. I could not find the specs for the Ultegra GS so I was hoping to push it to 45 and you are saying it is much less. That means I'll have to use the Deore RD I have, or look around for an older one..or just use a 28T cog and live with it. The shifters are Ultegra ST-6510 and I hope they'll handle any mod I may add as well. But outside of changing everything over I don't know what else to do...maybe Sora is the only option. For it's age this bike still handles beautifully and I just hate the thought of having to "redesign" it.

Thanks for your response, I really appreciate it!

Last edited by JustinDemoude; 07-24-21 at 10:32 AM. Reason: grammar
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Old 07-24-21, 10:40 AM
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For Pastor Bob:

My 1800C was built in 2004 and Trek considers it "vintage". I felt this would be the place to start. I'm not sure how the forum feels about double-posts, so here I am.

Yes I bought a longer chain and a new cable set too. I even have a new FD (Sora) if I need it. Now I need a mechanic to try and make it work. I want to get the cassette right or try to find out if I can even do it and that's why I posted here. I'm glad to hear your setup works, good for you.

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Old 07-24-21, 03:18 PM
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Your shifters will work with any 9 speed Shimano road or mountain rear derailleur.

There “might” be a very slight tweak to the low limit setting on the front derailleur. Probably be fine, but it all depends on the inner cage shape and where the chain is positioned on the 34t.

If you eventually look for an older mtb rear derailleur, you’ll want an SGS long cage.

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Old 07-25-21, 10:01 AM
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[color=#222222]Your shifters will work with any 9 speed Shimano road or mountain rear derailleur. There “might” be a very slight tweak to the low limit setting on the front derailleur. Probably be fine, but it all depends on the inner cage shape and where the chain is positioned on the 34t. If you eventually look for an older mtb rear derailleur, you’ll want an SGS long cage.]
All very good to hear! I did not think I would have any problem with the shifters but I believe the cable pull will change and need to make sure these old Ultegra "brifters" can handle it! Also VERY good to hear the M592 I have now will work and the 11-34T cassette I ordered will max out it's capacity. But what do you mean by "a tweak"...is that a mod to the derailleur itself or just an adjustment? For an older deraileur I could order a M591, which is another GSG long-cage and a "pre-Shadow" design almost identical to the 592. I can see why an older RD design would work better with older shifters, so I will remember that.

Thank you for all your help, it is much appreciated! I feel confident now my setup with the new cog and derailleur will work.
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Old 07-26-21, 01:22 PM
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I agree the Deore is the better way to go, to much for the Ultegra.

I dont think you will ever hear anyone in Classic-Vintage group ever tell you to just go buy a CAADX.. lol
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