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Gear Combinations and Mtn Derailleur help.

Old 04-21-05, 08:35 AM
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Gear Combinations and Mtn Derailleur help.

This is kind of mechanical/touring/commuting related, so I posted in Touring since you guys mix and match mtn & road components frequently. Sorry if it seems too off topic.

Can you run a mtn cassette with road chainrings? I ask because I'm buying a new bike (Jamis Nova) that will be my light touring/pull the munchkin trailer/commuter/group ride bike. The bike comes with 105 rear & tiagra front triple derailleurs with 12-25, 30/42/52 combo for gearing. I'm certain I cannot pull my daughter up some of the hills around here with 30-25 and I think this might be too tall a gear to spin properly on some of the steep hills around here with 40 lbs of clothing/food etc. I think I could "survive" with 30-32 so I only want to change the rear derailleur and cassette to avoid additional expense of changing the cranks. So, can I run a mtn cassette with road gearing chainrings?

Also, I'm pretty sure I can use the 105 shifters with a deore or LX rear derailleur, but I want to make sure I get the right kind of derailluer so it isn't "backwards." LX seems to come as M580 or as M570. M580 is described as "rapid rise" which is the one I think I do NOT want. Is that correct? I have also seen a derailleur described as "low normal" without the model numbers (online). Is "low normal" the 570? Is there any benefit to getting XT/LX over standard deore in terms of longevity? Deore = $26, LX = $50 and XT = $65. Weight is not a big deal to me, but surviving road grit (winter salt/sand) is a concern. Can I go with Deore and not worry about it, or should I go with LX at double the cost? If its only weight, I don't think 12 grams are worth $25.

I basically want to run a standard road cassette (12-25) for commuting/club riding but the wider gearing for touring/munchkin pulling/winter commuting. I have a spare wheelset already, so I was thinking put the mtn geared cassette on my fat tire (32-35) wheels and the road cassette on the wheels it comes with and a (25) tires. When I want to swap, change the chain & wheels and be on my way. Is this a reasonable approach to getting 2 bikes for the price of 1+?
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Old 04-21-05, 11:11 AM
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Originally Posted by DogBoy
This is kind of mechanical/touring/commuting related, so I posted in Touring since you guys mix and match mtn & road components frequently. Sorry if it seems too off topic.

Can you run a mtn cassette with road chainrings? I ask because I'm buying a new bike (Jamis Nova) that will be my light touring/pull the munchkin trailer/commuter/group ride bike. The bike comes with 105 rear & tiagra front triple derailleurs with 12-25, 30/42/52 combo for gearing. I'm certain I cannot pull my daughter up some of the hills around here with 30-25 and I think this might be too tall a gear to spin properly on some of the steep hills around here with 40 lbs of clothing/food etc. I think I could "survive" with 30-32 so I only want to change the rear derailleur and cassette to avoid additional expense of changing the cranks. So, can I run a mtn cassette with road gearing chainrings?

Also, I'm pretty sure I can use the 105 shifters with a deore or LX rear derailleur, but I want to make sure I get the right kind of derailluer so it isn't "backwards." LX seems to come as M580 or as M570. M580 is described as "rapid rise" which is the one I think I do NOT want. Is that correct? I have also seen a derailleur described as "low normal" without the model numbers (online). Is "low normal" the 570? Is there any benefit to getting XT/LX over standard deore in terms of longevity? Deore = $26, LX = $50 and XT = $65. Weight is not a big deal to me, but surviving road grit (winter salt/sand) is a concern. Can I go with Deore and not worry about it, or should I go with LX at double the cost? If its only weight, I don't think 12 grams are worth $25.

I basically want to run a standard road cassette (12-25) for commuting/club riding but the wider gearing for touring/munchkin pulling/winter commuting. I have a spare wheelset already, so I was thinking put the mtn geared cassette on my fat tire (32-35) wheels and the road cassette on the wheels it comes with and a (25) tires. When I want to swap, change the chain & wheels and be on my way. Is this a reasonable approach to getting 2 bikes for the price of 1+?
Yes, you can run a "mountain" cassette with a road crank. The cassettes and the cranks don't really care what the size is on either. The limiting factor are the derailuers. The rear derailuer must have a long enough arm to take up the chain slack as you shift from the large cog to the small one. The front derailer must be wide enough and low enough to accept moving the chain from the large chainwheel to the small one. Since your bike already has a triple the front derailer is not an issue.

The rear may be but look at if first. If it has a long arm (roughly 3" to 3.5") instead of a short arm (1" to 1.5") it may be able to take up the chain slack. I would suspect that it is a long arm derailer since the bike comes with a triple. Get a cassette in a 12-32 range and put it on your current wheel. If you can shift, on a work stand, into the low gear you should be okay.

If you need to replace the rear derailer, you want to avoid "rapidrise" or "low normal". They are the same thing and they are about the dumbest idea Shimano has ever come up with. Suntour used to make a "low normal" front derailer which was an excellent idea since you pulled the chain onto the smaller chainwheel with the cable. Under high torque, which happens when you are trying to shift to lower gears, pulling the chain onto the smaller chainwheel makes sense. Shimano's Rapidrise rear derailuer is using the return spring to push the chain onto lower gears in the rear under high torque situations - exactly the opposite of what you need! It's just plain dumb! And made worse when you get dirt and grit into the system.

Dumb. Dumb. Dumb.

Okay, rant mode off.

P.S. You can just change the cog set on the wheel and don't have to change the wheel. Unless you have the same width (and usually brand) of wheel for the wide tire wheelset, you may have to readjust the brakes every time you change the wheels. It easier to just change the cassette.
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Old 04-21-05, 01:09 PM
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Well, I found a trekking crankset that won't require swapping cranks for ~60 after the promotional discount. They are nashbar trekking cranks and are 28-38-48. I figure this is ideal for me and is about 1/3 the cost of the shimano trekking crankset that was what I was previously aware of ($150). So I think I'll just go whole hog and change the cranks ($60), the rear derailleur (105 can only handle up to a 27t cog) to Deore ($30), the rear cassette to an HG-50 (105 I think) 11-34 ($30). This means I get touring gearing for $120. I was thinking of getting an axis instead of a nova because of the gearing, but it was $400 more. This is definately a better deal.
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Old 04-21-05, 03:43 PM
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Originally Posted by DogBoy
Well, I found a trekking crankset that won't require swapping cranks for ~60 after the promotional discount. They are nashbar trekking cranks and are 28-38-48. I figure this is ideal for me and is about 1/3 the cost of the shimano trekking crankset that was what I was previously aware of ($150). So I think I'll just go whole hog and change the cranks ($60), the rear derailleur (105 can only handle up to a 27t cog) to Deore ($30), the rear cassette to an HG-50 (105 I think) 11-34 ($30). This means I get touring gearing for $120. I was thinking of getting an axis instead of a nova because of the gearing, but it was $400 more. This is definately a better deal.
One thing to be aware of is that the Nashbar crank is an ISIS bottom bracket. If your other crank is a square taper or if it is a Shimano brand Octalink crankset, you will have to change the bottom bracket. That will add another $30 or so to the cost.

Instead of replacing the entire crankset, you could just replace the chainrings. Your existing one is probably a 130mm bolt center diameter (BCD). The Third Hand or Lickton Bicycles (google it) has replacement rings. You can replace the outer rings with a 48/38 in a 130mm BCD and the inner ring you can go as small as a 24 tooth in a 74 mm BCD (also at Third Hand). It a wash as to which is more or less expensive but changing rings is easier than changing the crank especially if you have to change the bottom bracket too.
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Old 04-21-05, 06:32 PM
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bottom bracket is 68-118 mm ISIS, same as what nashbar cranks require. Thanks for the heads up though.
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