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Advice on compact double crankset

Old 03-15-17, 05:52 AM
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jimmie65
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Advice on compact double crankset

I picked up a used Giant Revel 2, unsure of year.
The previous owner switched out the the stock triple crankset with a double. I believe it's a 24T/38T. Original was most likely a 24/34/42. The shifter wasn't changed so should still work with a triple.

I'd like a little faster gearing for when I'm on the road or flat trails, and I don't do a lot of climbing. Can I change the large chainring to a 42 (so a 24-42) or would it better to just put a triple back on the bike?
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Old 03-15-17, 06:25 AM
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You need to know the BCD of the chainrings in order to find one that fits. Yes you can probably find a 42 that will fit, but then the drop from the 42 to the 24 will be inordinately large and will shift like crap. You could just put the 42 back on the outer. With that said, a 38/11 gives you 25mph at 90 rpm in the 11t cog in the back . . . do you really need larger gearing?
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Old 03-15-17, 06:28 AM
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they didn't put a double on there, they took the outer ring off and possibly replaced the middle ring with something larger. they might not have even done that. if you leave a double on there, either way, make sure you adjust the front derailleur cage, it is much to far away from the top of the chainring, and make sure the stops are adjusted so you don't shift the thing right off the chainring
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Old 03-15-17, 06:37 AM
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Originally Posted by ypsetihw View Post
You need to know the BCD of the chainrings in order to find one that fits. Yes you can probably find a 42 that will fit, but then the drop from the 42 to the 24 will be inordinately large and will shift like crap. You could just put the 42 back on the outer. With that said, a 38/11 gives you 25mph at 90 rpm in the 11t cog in the back . . . do you really need larger gearing?
I spin out going downhill, at least on paved surfaces.


Originally Posted by ypsetihw View Post
they didn't put a double on there, they took the outer ring off and possibly replaced the middle ring with something larger. they might not have even done that. if you leave a double on there, either way, make sure you adjust the front derailleur cage, it is much to far away from the top of the chainring, and make sure the stops are adjusted so you don't shift the thing right off the chainring
Stops are good; I thought I would drop the chain when I test rode it because of the derailleur but it never did fall off (tried so I could talk him down a little more...)

Appreciate the help; I will just add the 3rd ring back.
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Old 03-15-17, 07:04 AM
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jimmie65, You may also need to order a smaller middle ring to provide clearance for the back side of the FD cage. A 32/34T and a 42/44T would be good options. I suggest a minimum of 10 teeth between the middle and outer chain rings.

Brad
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Old 03-15-17, 07:23 AM
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If you don't want to change the current "large" chainring, add a 48T (10T difference) chainring to the outside as your new large chainring. That will give you the higher high gear you want and restore the triple. As noted, no matter what you do, even if it's nothing, reposition the front derailleur so it's outer cage is only 2-3 mm above the largest chainring. The way it is now I'm surprised shifting is at all acceptable.
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Old 03-15-17, 09:34 AM
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Originally Posted by HillRider View Post
... reposition the front derailleur so it's outer cage is only 2-3 mm above the largest chainring. The way it is now I'm surprised shifting is at all acceptable.
+1. Amazed that this even works.
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Old 03-15-17, 03:15 PM
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Originally Posted by WizardOfBoz View Post
+1. Amazed that this even works.
Actually I run a 24/34 on my mountain bikes and 22/32 on my wife's mtb with a high position derailleur. You do realize that the FD is a triple and the large chainring is really a middle ring. The OP's setup doesn't have a large chainring. You need to setup the FD as if there was a large chainring so the shifting from the small to middle utilizes the derailleur the way it was designed. In my experience, dropping the FD to 2/3mm above the middle ring results in terrible shifting.

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Old 03-15-17, 03:24 PM
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For the OP... Do you really use that 24t? If not bump it up to a 28t or 30t and the run your 42t. I have an urban flatbar with a 30/42 and have no issues.

Also, if you are at all concerned, you can also add a bash/chainring guard on the outside position as a failsafe against over shifting and dropping the chain on the crank arm. Same thing as having a large chainring without the teeth.

John
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Old 03-15-17, 03:34 PM
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Originally Posted by 70sSanO View Post
Actually I run a 24/34 on my mountain bikes and 22/32 on my wife's mtb with a high position derailleur. You do realize that the FD is a triple and the large chainring is really a middle ring. The OP's setup doesn't have a large chainring. You need to setup the FD as if there was a large chainring so the shifting from the small to middle utilizes the derailleur the way it was designed. In my experience, dropping the FD to 2/3mm above the middle ring results in terrible shifting.

John
Ah, so the idea is that the setup is just about exactly what you'd have if you had the large chainring, huh? I guess that makes sense. It's just that I was checking the adjustment of my road dura ace FD and was applying the tool that tells you the optimal position of the nub on the cable clamp screw (something to do with "compensated" or "noncompensated") and the the manual specifies 2mm clearance (+/-1mm). On on and on with details.

Since this works, it works, and I stand corrected. Thanks for pointing this out.

On another topic the OP's current setup confuses me. I can make no sense of someone pulling the outboard chainring off and adjusting the limit screw. It seems to me that you lose a lot of function, with very little (the weight of chainring? C'mon, man!)to gain from the change. Going from 3 rings to 1 might make sense (less complicated, more reliable, more weight reduction). But I can't grok 3 to 2.
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Old 03-15-17, 04:16 PM
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Originally Posted by WizardOfBoz View Post
Ah, so the idea is that the setup is just about exactly what you'd have if you had the large chainring, huh? I guess that makes sense. It's just that I was checking the adjustment of my road dura ace FD and was applying the tool that tells you the optimal position of the nub on the cable clamp screw (something to do with "compensated" or "noncompensated") and the the manual specifies 2mm clearance (+/-1mm). On on and on with details.

Since this works, it works, and I stand corrected. Thanks for pointing this out.

On another topic the OP's current setup confuses me. I can make no sense of someone pulling the outboard chainring off and adjusting the limit screw. It seems to me that you lose a lot of function, with very little (the weight of chainring? C'mon, man!)to gain from the change. Going from 3 rings to 1 might make sense (less complicated, more reliable, more weight reduction). But I can't grok 3 to 2.
Not necessary corrected, I just figured this out when I made the switch from triple to middle/small double and the shifting wasn't very good. I ended up just going by trial and error. At first I thought... that sure doesn't look right, but it seemed to work.

I have a similar issue running a 46t with a Dura Ace FD-7703 triple. Running it slightly higher results in better shifting for me with non-ramped chain rings.

You are correct for normal setups, although I tend to fiddle with any setup until I feel I get the best shifting.

John
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Old 03-15-17, 06:12 PM
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I have no idea why the high derailleur setup is working, but it does.
After reading this discussion, I am also confused as to why the original owner took off the outer ring. Perhaps he scavenged it for another bike.

I'm going to get an outer ring put on; considering I wasn't savvy enough to recognize that this wasn't a compact double, I think I will let the LBS do it for me. A 48T might be overkill, but I will probably go for the largest they can fit anyway.
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Old 03-15-17, 06:19 PM
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Originally Posted by jimmie65 View Post
Original was most likely a 24/34/42....Can I change the large chainring to a 42 (so a 24-42) or would it better to just put a triple back on the bike?
I think that the original was 42-32-22. Adding a 42 seems like the best path. Or replacing the whole thing, as these cranks don't get the best reviews. If I could find a good 22-32-42 crankset for cheaper than the chainring, I'd do that.
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Old 03-15-17, 06:24 PM
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Originally Posted by jimmie65 View Post
I have no idea why the high derailleur setup is working, but it does.
After reading this discussion, I am also confused as to why the original owner took off the outer ring. Perhaps he scavenged it for another bike.
I'm not the original owner, but I'll venture a guess... it is a mountain bike. Might be entry level and people do use it on paved paths/roads. But, this model usually comes with a suspension fork.

As a mountain bike, most people don't need a large 42/44/46 chainring when riding in the dirt. There are tons of 1x setups that only run a 32t or so. I took off my large chainrings because I never used them. It is either 24t or 34t. When my wife was first getting used to trigger shifters, I blocked out her 42t so she would inadvertantly shift up instead of down. Removing the large chainring also eliminates those nasty teeth that somehow have a way of finding your calf in a crash. Not to say my 34t won't bite me anyway.

John
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Old 03-16-17, 07:47 AM
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I'm getting wishy-washy on this. I think now I'm going to switch to a 1x in the front and just put a bigger granny gear in the back. Rode on the bike over 20 miles yesterday on dirt, gravel, paths and streets. I didn't miss the big chainring too much and never switched to the smaller ring.
I need to recount the teeth - if it's a 38, probably put on a 42. If it's just a 34, then I'll get a 38 or so.

Found another interesting issue with the bike as well. The original owner upgraded to an 8 speed, but left the original shifter. That's causing me a little bit of issue with skipping in the top gear, so going to switch out the shifter as well.
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Old 03-16-17, 08:55 AM
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Originally Posted by jimmie65 View Post
I have no idea why the high derailleur setup is working, but it does.
The set-up works because they simply removed the outer ring.

Originally Posted by jimmie65 View Post
considering I wasn't savvy enough to recognize that this wasn't a compact double, I think I will let the LBS do it for me.
Well, it is a "double" now. And it is "compact". So you're not really wrong...
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Old 03-16-17, 09:44 AM
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Originally Posted by jimmie65 View Post
Found another interesting issue with the bike as well. The original owner upgraded to an 8 speed, but left the original shifter. That's causing me a little bit of issue with skipping in the top gear, so going to switch out the shifter as well.
The Revel 2 is a 21 speed (7 speed cassette or freewheel?) If you have a 7 speed shifter, you can't get all 8 speeds. Are you getting all 8 speeds? If you are then you have an 8 speed shifter that is having issues or needs adjustment. Or maybe he used a 9 speed shifter. Might even be a little play with the top gear of the cassette because the lock ring isn't tight.

As for a 1x, you might want to think about that first. Typically the front derailleur is removed and a special chainring is installed. May even a chain guide. You may not need to do this, but if you ride off-road, you don't want to throw a chain. If you keep the front derailleur on the bike, you might as well keep a small ring on the bike, maybe go a little bigger.

John
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Old 03-16-17, 09:47 AM
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LBS talked me out of the 1x. We're going to install a 44, switching the middle ring to something smaller if needed.

Shifter was still the stock 7 speed, so it's being changed.
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