Going Compact
622
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515 days
Iron Dan posted 15 weeks ago.
Typical compact cranks have a 110mm bolt circle while standard chainrings have a 130mm bolt circle. You might be able to get smaller chainrings for a standard size of 130mm but if you want to switch to a true compact set, you will likely need to get new cranks that have the 110mm bolt circle.
Depending on how many miles you have on your current bottom bracket, you should be able to switch the cranks out without switching out the bottom bracket. You just have to make sure that the cranks you buy are compatible with your bottom bracket. There are a few different styles and you need to make sure what you get will work, so it might just be easier to change everything out at once.
727
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486 days
theShiba posted 15 weeks ago.
It looks like FSA makes a 130mm 50T Outer ring, and 39T Inner Ring... Anyone have experience with the FSA Pro Chainrings? Info here.
Also, looks like Salsa makes them as well... http://www.salsacycles.com/chainrings.html
Any experience with this stuff would be most helpful!
5
Member
957 days
h-bomb posted 15 weeks ago.
Questions:
1. Do you want just a smaller big ring, the smaller inner ring, or both? If it's inner or both, you need a new crankset, not just new rings. Most 130 cranksets do not accomodate anything smaller than a 39 tooth inner ring, so if you want a smaller ring for the tough climbs, like a 36 or a 34, then you need to go to the 110 compact.
2. What type of BB do you have now? Octalink (slightly older with internal bearings), Hollotech (external bearings), or something else? If you're set on keeping your current BB, you need to figure out which compacts are compatible with it. If it is an older one, eBay may be your best bet.
3. Are you on a double or triple crank now? Keep in mind that triple crank BBs cannot be used with doubles because the bottom bracket is wider.
4. What type of front derailleur are you using? Not all regular FDs work well with compacts, so you may need to swap that out too depending on your setup.
I've found FSA's chainrings to be perfectly serviceable. As far as their cranksets--you do hear bad things about the SL-K loosening. However, I have ridden one of those and never had a problem that loctite couldn't solve. Make sure that the bolts FSA is using are compatible with your crank spindle if you are going this route.
42
Member
265 days
gshuldes posted 15 weeks ago.
To determine if you have 110mm or 130mm bolt circle, measure the distance between two of the chainring bolts and multiply by 1.7
The distance between two bolts on 110mm rings is 64.7mm (about 2.5") ... on 130mm rings it is 76.4mm (about 3").
4339
Member
1594 days
kylie posted 15 weeks ago.
or just look on the rings as one side often says ;)
Kylie Donia's Miles of Life --- Powered by MarkyV
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727
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theShiba posted 15 weeks ago.
h-bomb wrote:
Questions:1. Do you want just a smaller big ring, the smaller inner ring, or both? If it's inner or both, you need a new crankset, not just new rings. Most 130 cranksets do not accomodate anything smaller than a 39 tooth inner ring, so if you want a smaller ring for the tough climbs, like a 36 or a 34, then you need to go to the 110 compact.
What makes you say that I would need a new crank to change both rings if I can find them both in 130mm? I have, by the way, determined that they are 130mm, but forgot to post that last night.
Right now I have a 53/42, which is standard for the Shimano FC-7400 cranks that I have. I'd like to go to 50/39. I don't think that I really need to go any smaller than a 39 on the inner ring, if that's the case, do you think I would still need to get a whole new crank to change both?
h-bomb wrote:
3. Are you on a double or triple crank now? Keep in mind that triple crank BBs cannot be used with doubles because the bottom bracket is wider.
I'm on a double, so we're straight there...
h-bomb wrote:
4. What type of front derailleur are you using? Not all regular FDs work well with compacts, so you may need to swap that out too depending on your setup.
I have an older Shimano 600 (Ultegra) FD. It's a clamp-on, so I think that if there were alignment issues with the bottom of the cage, I could just slide the whole bracket down a few mm's, no?
Thanks for the help!
987
Member
1153 days
PJT posted 15 weeks ago.
theShiba wrote:
h-bomb wrote:Questions:1. Do you want just a smaller big ring, the smaller inner ring, or both? If it's inner or both, you need a new crankset, not just new rings. Most 130 cranksets do not accomodate anything smaller than a 39 tooth inner ring, so if you want a smaller ring for the tough climbs, like a 36 or a 34, then you need to go to the 110 compact.
What makes you say that I would need a new crank to change both rings if I can find them both in 130mm? I have, by the way, determined that they are 130mm, but forgot to post that last night.
Right now I have a 53/42, which is standard for the Shimano FC-7400 cranks that I have. I'd like to go to 50/39. I don't think that I really need to go any smaller than a 39 on the inner ring, if that's the case, do you think I would still need to get a whole new crank to change both?
h-bomb wrote:3. Are you on a double or triple crank now? Keep in mind that triple crank BBs cannot be used with doubles because the bottom bracket is wider.I'm on a double, so we're straight there...
h-bomb wrote:4. What type of front derailleur are you using? Not all regular FDs work well with compacts, so you may need to swap that out too depending on your setup.I have an older Shimano 600 (Ultegra) FD. It's a clamp-on, so I think that if there were alignment issues with the bottom of the cage, I could just slide the whole bracket down a few mm's, no?
Thanks for the help!
Oops--that was me in that earlier message from h-bomb-- Mrs. PJT was logging her workouts and I didn't check to see who was logged into trifuel on the home PC when I posted the reply.
Anyway, to answer your questions:
1. If you are OK with a 39T inner, then you can keep your regular crank and switch the outer chainring. It's only when you go smaller than that on the inside that you typically need a compact crank because most manufacturers do not make chainrings smaller than a 39 (maybe a 38?) in the 130BCD size.
2. Should be OK with the same FD. The problem typically comes when people try to use a 50/34 combo. Some Shimano FDs can't handle the 16-tooth "jump" between rings, they do better with the 14 tooth jump of a 53/39. Just make sure you are able to slide the FD down. That's not a problem if your FD is a clamp-on, but if you have a bracket-mounted derailleur make sure there is still room to drop a bit.
727
Member
486 days
theShiba posted 15 weeks ago.
PJT wrote:
Oops--that was me in that earlier message from h-bomb-- Mrs. PJT was logging her workouts and I didn't check to see who was logged into trifuel on the home PC when I posted the reply.Anyway, to answer your questions:
1. If you are OK with a 39T inner, then you can keep your regular crank and switch the outer chainring. It's only when you go smaller than that on the inside that you typically need a compact crank because most manufacturers do not make chainrings smaller than a 39 (maybe a 38?) in the 130BCD size.
2. Should be OK with the same FD. The problem typically comes when people try to use a 50/34 combo. Some Shimano FDs can't handle the 16-tooth "jump" between rings, they do better with the 14 tooth jump of a 53/39. Just make sure you are able to slide the FD down. That's not a problem if your FD is a clamp-on, but if you have a bracket-mounted derailleur make sure there is still room to drop a bit.
OK... thanks for the clarification. I figured that you assumed I was wanting to go smaller than 39T for the inner... I mean... I'm wimpy, but I think in can handle a 39 ;) Just need that extra little drop instead of the 42.
Ok, so after my race yesterday, I decided that I really need to go compact...
Here's the deal: I have an older Shimano 600 Crank. Do I need a whole new BB, or would a new Ultegra crank fit into the same BB? Do I even want to go this route, or is it better to just replace the crank and the BB at the same time?
Finally, and I think we have touched on this before, is it at all possible to put different chainrings on my existing crank? I know there is something with the alignment of the holes on the ring, but I don't know how they are measured...
Any help appreciated. Of course, if you need me to measure something, or look for model number specifics, please let me know.
Thanks everyone!