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cyclocross 42x38 chainring Thorne/Blackspire

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cyclocross 42x38 chainring Thorne/Blackspire

Old 08-15-12, 05:33 PM
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skeem
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cyclocross 42x38 chainring Thorne/Blackspire

To start off Im a very good bike mechanic, but I have not dabbled with weird CX ring choices before, so Im experimenting on my own bike.
I decided to get fancy and order some Blackspire 38x41 130bcd chainrings, the 41 being the outer. I thought it'd be cool to experiment with ring sizes, but I was wrong (and should have stuck with a standard size range). My sexy rings came today and after much fussing, and tweaking, I was wholly unable to get the chain to shift. the 38x41 range is too close and the chain cant hit the ramps to shift up- it only get caught between the 2 rings. why they make the 41 as an outer is beyond me and the unhelpful man at Blackspire could only tell me that the europeans love the 41 ring, bt he did not know what would work with a 38. I was wondering if anyone knows if a 42 will work in the stead of the 41. by work I mean actually shift properly- Im running Campy record so I want my first geared cross bike to work well. A man at cxworld said the 42x38 thorne combo they have will work, according to his mechanic. Does anyone know if a 42 blackspire will work the same, or, what it the smallest outer ring one can run with a 38 inner? Anyone use the thorne stuff- Blackspire will refund me and Id buy thorne. 44 is the biggest I could go though. I have ridden ss for a few years and just like a low gear combo. Thanks in advance for all of your knowledge.
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Old 08-15-12, 05:42 PM
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What are the cranks? I've had issues with 130bcd crank spiders being too large for 38t rings so the chain can't fully engage with the ring. Might be some weirdness there that's keeping the chain from wobbling on the ring to let it get to the 41.

My truvativ rolleur cranks had too much metal on the end of the spider out past the chainring bolt hole to let me run a 38t. I filed them down, but still hadn't been brave enough, so I went with a 39.
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Old 08-15-12, 06:22 PM
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tried a half step before 43 - 47, since I have an assortment of 144 chainrings.
had no problems.. regular old period <C> FD..

Afraid I cannot type my way to making you set-up work.
pick one and take the other off? shift with greasy fingers approach?
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Old 08-15-12, 08:42 PM
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39x42? I have ultegra 6600 cranks.

by shifting with greasy fingers I assume you mean use my hands to move the chain. I would but I will be racing... and its Campy Record.

Last edited by skeem; 08-15-12 at 08:45 PM.
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Old 08-15-12, 09:10 PM
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no, the chainring spider might be acting as a physical barrier to the chain sitting properly on a 38t chainring.
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Old 08-15-12, 09:55 PM
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nah. it looks like the chain can sit just fine on the 38 ring. 38 is made because it is the smallest ring which can fit on a standard (shimano/sram etc) 130 crank.
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Old 08-16-12, 07:45 AM
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Three tooth difference? Why not run a single 42 T up front?
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Old 08-16-12, 07:54 AM
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well, the main reason for no single up front is that i have been doing it but feel I could utilize more gears. Also, I have (got for $200) a record 10 groupset and I rebuilt the shifters and have a front derailleur, so I kinda want to use them. its lame. I know. But I just need to.

Also, would a 38/44 shift better than a 38/42?
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Old 08-16-12, 07:56 AM
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3 teeth wont matter... loose the 38/9. use a single ring. the 42,
if you cant climb the uphill sections of the course, on the bike,
get off, shoulder the bike and Run.

Also, would a 38/44 shift better than a 38/42?
theoretically the push plate of the FD has a better setting up
situation.. when it can clear the inner chainring
without being sky high above both..

Last edited by fietsbob; 08-16-12 at 08:02 AM.
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Old 08-16-12, 01:13 PM
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I'd use a single 40T ring myself, with some kind of chain catcher to keep it from bouncing off.
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Old 08-16-12, 01:48 PM
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Are these plain rings? If not, I think the issue here is the shifting gates and ramps not being intended for the size ring they're next to. The way to do it is with rings designed to be next to each other, or plain rings.
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Old 08-16-12, 02:02 PM
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I have an old bike with a 38/42. It shifts great with my down tube friction shifter. Although you might not need two rings this close they do help with keeping the chain line better. My rings are the old type with no ramps or pins.
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Old 08-16-12, 03:00 PM
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Originally Posted by skeem View Post
well, the main reason for no single up front is that i have been doing it but feel I could utilize more gears. Also, I have (got for $200) a record 10 groupset and I rebuilt the shifters and have a front derailleur, so I kinda want to use them. its lame. I know. But I just need to.

Also, would a 38/44 shift better than a 38/42?
you don't believe me ... that's cool good luck everybody is telling you to run single ...
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Old 08-16-12, 09:54 PM
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dont take offense Im not going to run a 1x10. I am fully committed to front shifting until I decide I dont need it. why is single so great (not to hold my own post hostage)? yes plenty of great riders ride 1x, but plenty of pro riders also ride 2x10. I want to run rings because I think the added ratios will be of assistance to me. I only started this to ask other people if a 38x42 would work with thorne or blackspire rings, or if 38x44 might shift better, because my 38x41 was a failed experiment on my part.

anyway, Kimmo, youre spot on. The blackspire site called the 41 in question an outer ring that was ramped and pinned (which it is), but it seems its not meant for anything but a single front ring; to sorta paraphrase the blackspire guy on the phone: "yeah, uhh, I dont now what the 41 is for or, uh, why it doesnt work if its supposed to, but I do know the europeans buy them up by the bucketload". And thats where Im at now.
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Old 08-17-12, 04:26 AM
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Try mounting it arse-about and see if that sorts it any.
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Old 08-17-12, 10:27 AM
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Originally Posted by skeem View Post
dont take offense Im not going to run a 1x10. I am fully committed to front shifting until I decide I dont need it. why is single so great (not to hold my own post hostage)? yes plenty of great riders ride 1x, but plenty of pro riders also ride 2x10. I want to run rings because I think the added ratios will be of assistance to me. I only started this to ask other people if a 38x42 would work with thorne or blackspire rings, or if 38x44 might shift better, because my 38x41 was a failed experiment on my part.

anyway, Kimmo, youre spot on. The blackspire site called the 41 in question an outer ring that was ramped and pinned (which it is), but it seems its not meant for anything but a single front ring; to sorta paraphrase the blackspire guy on the phone: "yeah, uhh, I dont now what the 41 is for or, uh, why it doesnt work if its supposed to, but I do know the europeans buy them up by the bucketload". And thats where Im at now.

I was joking ... but seriously give the 44 a shot or maybe consider adding some variety out back.
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Old 08-17-12, 11:21 AM
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Most current front derailleurs are designed for a 10T or more chainring difference and will have to be mounted way too high over the big ring to clear an inner ring with a smaller tooth difference. The people referring to half-step front gearing are remembering older style front drrailleurs with very shallow inner cage plates.
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Old 08-17-12, 11:37 AM
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38-46 is a common chainring setup on the cross race circuits..

Kludge tuning: If you go with a band to braze on adapter
and a braze-on FD.
wedge shims between the 2 let you rotate the angle
relationship of the FD to the seat tube..

Last edited by fietsbob; 08-17-12 at 11:41 AM.
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Old 08-17-12, 11:48 AM
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Originally Posted by skeem View Post
why is single so great (not to hold my own post hostage)? yes plenty of great riders ride 1x, but plenty of pro riders also ride 2x10.
Because then you won't have to worry about shifting the front at all, and modern cassettes have all the range you'd need for CX.
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Old 08-17-12, 11:57 AM
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+ the people who will beat you probably worked on technique,
and run up the hill faster, shouldering the bike, than you can in your lowest gear.
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Old 08-17-12, 05:34 PM
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It should work I ran a 39 42 for a while the 42 was an inner turned around. Try turning both chainrings around this will tell you if the ramps and pins are the problem.
 
Old 08-18-12, 07:49 PM
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ill turn them around and probably get some 38x44 rings. i just want the gear. I have raced plenty of 1x mtb setups and just am stubborn and want the gears... for the future when I can runup as fast as anyone and mount and dismount really well.
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