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Swapping in a larger cassette

Old 11-30-14, 12:01 AM
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Swapping in a larger cassette

Contemplating buying a bike online. It'll ship with a full 105 drive train, including a 11-25T cassette. Seeing that I suck on the climbs I'm thinking of swapping out the 11-25 cassette for a Tiagra 12-30 (both 10 speed). Will I need to get a new chain as well? My intuition says yes because I'll need more links for the bigger sprockets.
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Old 11-30-14, 01:25 AM
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Could need a new rear derailleur too.
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Old 11-30-14, 04:13 AM
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If you shift intelligently, you may not need to replace the derailleur or add links to the chain. If you have extra links for the chain, I'd probably add them because it easy and cheap, but you should get your distinct gears even with the original chain.

The real question will be the capacity of the rear derailleur -

Bicycle Rear Derailleurs from Harris Cyclery
How to calculate the capacity of a rear derailleur - Bicycles Stack Exchange
Sheldon Brown's Bicycle Glossary Ca--Ce

It looks like Shimano will rate the rear derailleur to 27Tmax because they don't make larger road sprockets, but Sheldon Brown's comments that the derailleurs actually exceed the capacity make sense.

Try the 30T freewheel; you may not need need to replace the derailleur (or chain).

If you don't use the large chainwheel and large sprocket (bad chain line) and choose to shift intelligently, you shouldn't need to replace the chain. If you don't use the small chainwheel and small sprocket (another bad chain line), you may not need to replace the derailleur either.

You'll lose a few redundant gears you won't miss, and shouldn't use to avoid bad chain lines.
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Old 11-30-14, 06:28 AM
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Originally Posted by English3Speed
If you shift intelligently, you may not need to replace the derailleur or add links to the chain. ...
While true, I'd bet that there are darn few cyclists that haven't cross chained in either extreme at one time or another. Buy a longer chain to prevent pulling the RD into the wheel accidentally. If the current RD can clear the 30T a very annoying chain on chain rubbing noise will warn you of a small-small cross chain.

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Old 11-30-14, 06:48 AM
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It worked OK on my 10 speed...No other changes needed.

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Old 11-30-14, 07:05 AM
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Originally Posted by English3Speed
If you shift intelligently, you may not need to replace the derailleur or add links to the chain.....
If you don't use the large chainwheel and large sprocket (bad chain line) and choose to shift intelligently, you shouldn't need to replace the chain.
BAD ADVICE

If your chain is not long enough to comfortably shift into the big-big combo and you forget (and you WILL forget) and shift into that combo, you WILL severely damage your derailleur and possibly wheel and/or frame before you know what has happened.
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Old 11-30-14, 08:42 AM
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+1 - and...
Originally Posted by 10 Wheels
It worked OK on my 10 speed...No other changes needed.
It does not matter what worked on someone else's bike. Get the bike in hand and then check the chain length. Plenty of guidance online as to how to size a bike chain.
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Old 11-30-14, 08:54 AM
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Switch the cassette and then try (carefully) to shift into big-big. If it goes without binding, your chain is fine. If it gets too tight before going into that gear (don't force it), you need a longer chain. I agree that the bike MUST be able to safely shift into big-big.
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Old 11-30-14, 09:15 AM
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Theoretically, you need an 1-1/4" longer chain.
IF your chain was sized a little long, you might be OK.

What I'd do-
With the factory cassette, shift to the Big:Big combination.
Take 2 skinny screw drivers or similar.
Where you have a long, straight run of chain, insert the screw drivers into links and then try to "pull" them together, keeping them parallel to each other.
See how much slack you can generate.
5 half links would be ideal. <4, new chain. 4 is on the "snuggish" side, but you won't damage parts if shifted into the Big:Big.
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Old 11-30-14, 09:38 AM
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I see. So I should factor in the cost of a new rear mech as well as a new chain/links (worst case scenario). Assuming the stock mech isn't compatible, should I buy a Tiagra mech? If so I'd basically be downgrading my drivetrain
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Old 11-30-14, 09:49 AM
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Originally Posted by yankeefan
I see. So I should factor in the cost of a new rear mech as well as a new chain/links (worst case scenario). Assuming the stock mech isn't compatible, should I buy a Tiagra mech? If so I'd basically be downgrading my drivetrain
That's jumping the gum. (auto censor is stupid)
Is it a GS or SS RDER?
Both have a 30T max cog, so you are good there.
The chain wrap capacity is different. What ring sizes do you have?
IF a double, the current RDER will work. IF a triple, it might be able to made to work with a saggy chain in the low:low combo.
I'd wait until you actually have the bike and do the test I mentioned.
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Old 11-30-14, 09:50 AM
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Depending on which version you have the 105 rd is rated for a maximum of a 27 or 28T largest cog. However, much experience says you can exceed this by a modest amount and it is likely (not certain) the 30T cog will work. You may have to screw in the B-screw all the way or even reverse it to get the derailleur to miss the biggest cog.

A new Tiagra rear derailleur should certainly work and "downgrading" your drive train is a non-issue. Tiagra components are very good and, except for bragging rights, you will never notice any difference.
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Old 11-30-14, 09:58 AM
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Originally Posted by Bill Kapaun
That's jumping the gum. (auto censor is stupid)
Is it a GS or SS RDER?
Both have a 30T max cog, so you are good there.
The chain wrap capacity is different. What ring sizes do you have?
IF a double, the current RDER will work. IF a triple, it might be able to made to work with a saggy chain in the low:low combo.
I'd wait until you actually have the bike and do the test I mentioned.
Compact double crankset, SS rear mech
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Old 11-30-14, 09:59 AM
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Originally Posted by HillRider
Depending on which version you have the 105 rd is rated for a maximum of a 27 or 28T largest cog. However, much experience says you can exceed this by a modest amount and it is likely (not certain) the 30T cog will work. You may have to screw in the B-screw all the way or even reverse it to get the derailleur to miss the biggest cog.

A new Tiagra rear derailleur should certainly work and "downgrading" your drive train is a non-issue. Tiagra components are very good and, except for bragging rights, you will never notice any difference.
NEW 105 (5701) is listed with a 30T max cog.
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Old 11-30-14, 10:02 AM
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Originally Posted by yankeefan
Compact double crankset, SS rear mech
Your RDER should barely work.
Correct chain sizing is IMPORTANT!
Too long and it'll be saggy in Low:Low, which shouldn't be used anyway, but won't break anything.
It might even be "slightly saggy" with a correctly sized chain if your double has a 16T difference instead of 14.
Too short and you have a potential for damage if you end up in High:High.

This is assuming it's the SS model. If GS, you have more leeway..

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Old 11-30-14, 10:23 AM
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Originally Posted by HillRider
Depending on which version you have the 105 rd is rated for a maximum of a 27 or 28T largest cog. However, much experience says you can exceed this by a modest amount and it is likely (not certain) the 30T cog will work. You may have to screw in the B-screw all the way or even reverse it to get the derailleur to miss the biggest cog.

A new Tiagra rear derailleur should certainly work and "downgrading" your drive train is a non-issue. Tiagra components are very good and, except for bragging rights, you will never notice any difference.
Thanks. I guess my main concern is that the [potential] cost of additional modifications are starting to negate the upfront savings in buying the bike online. I suppose I could sell the stock cassette & mech to recoup some cash.

Kinda a bit of a tangent, but at what price difference do you guys think purchasing a bike online is no longer a good deal? For example, lets say that buying on-line saves approximately $300 dollars compared to buying an equivalent bike at your LBS, is it worth it? Of course that extra $300 can be invested in clipless pedals & shoes, but at the cost of the free fitting and tuneups that you'd get from a brick and mortar store.
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Old 11-30-14, 10:52 AM
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There's really no way to set an amount. One has to factor in several variables that are either unpredictable or subject to personal preference, some of which you've already noted:
  • Ease of warranty claims and whether labor is included
  • The value of the time you will require to assemble and tweak the bike or take it to a shop to have done.
  • The cost of professional assembly or adjustment of a boxed bike.
  • The ability of a shop to swap out components for the difference in price vs. needing to pay for duplicate parts with an online purchase. Includes the ability of a shop to fit you to the bike by changing stem/bars, etc. during assembly
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Old 11-30-14, 11:09 AM
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As mentioned, you will likely need just a cassette & chain. If the original ones are new, you should be able to sell them as new "take-offs" get close to the price of the replacements. Or hang on to them and as you get stronger, you may find the 25 is good enough for you in a year.

I NEVER cross chain big-big, so I don't need a longer chain .... except for those couple of times when I accidentally did, so it was good that my chain was long enough .....
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Old 11-30-14, 12:14 PM
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Need more details --- specific gearing front and rear, and specific rear derailleur part number. Yes, you will probably need a new chain, or the ability to add a couple links to it.
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Old 11-30-14, 03:30 PM
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Originally Posted by yankeefan
Kinda a bit of a tangent, but at what price difference do you guys think purchasing a bike online is no longer a good deal? For example, lets say that buying on-line saves approximately $300 dollars compared to buying an equivalent bike at your LBS, is it worth it? Of course that extra $300 can be invested in clipless pedals & shoes, but at the cost of the free fitting and tuneups that you'd get from a brick and mortar store.
As stated brick and mortar stores are very valuable. When I purchased my Litespeed (many years ago from a B&M) they fitted me (specing all the components defining crank length, stem length, ETC.), upgraded the tires and installed Cinelli cork handle bar tape all without my asking. The salesman noted I had made a comment that I didn't like the stock tape shown in the catalogue! The bike worked perfectly when I picked it up!

In about four months or so the Mavic Reflex rim on the rear cracked a couple of the eyelets. They warranted it and replaced it no charge to me with an Open Pro Mavic rim...still have that wheel and have been ridding it this last season.

Another of my hobbies is Radio Control gliders. Many of the B&M hobby shops I remember and frequented have come and gone. Some claim that the online seller and people using their dollar to vote have voted those shops into oblivion. Be that as it may, one needs to ask themselves where will I go when I need that one little item or I don't have the knowledge or tool to fix that problem for my ride tomorrow?
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Old 11-30-14, 03:51 PM
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Originally Posted by Bill Kapaun
NEW 105 (5701) is listed with a 30T max cog.
Interesting. I knew the 5700/5703 were just rated for 27T max although they would generally tolerate more.

To the OP: The savings from buying on-line can be quickly absorbed if you need professional help with component changes and adjustments. If you are capable of doing the work your self and have the needed tools, the savings can be real. That's a big IF.
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Old 11-30-14, 04:40 PM
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[QUOTE=HillRider;17351050]Interesting. I knew the 5700/5703 were just rated for 27T max although they would generally tolerate more............QUOTE]

It's in the new dealer manual-
SHIMANO Dealer's Manual / User's Manual

Interestingly, they claim a different amount of chain wrap if used for a double or triple**********??
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Old 11-30-14, 06:01 PM
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Thanks, you guys have been tremendous. After careful consideration I am leaning against getting the bike. The prospective level of aftermarket modifications makes the bike less financially viable. I do have a basic bike repair kit (Chain whip, chain tool, lock ring remover, spoke wrench and an assortment of allen keys) and I was able to assemble and fine-tune a mail order bike from BD (with tons of help from youtube), but the I suspect that I did at best an okay job. The bike I'm currently contemplating (Kestral Legend 105) will be used mainly for Gran Fondos/Centuries next spring/fall and I think I'd benefit from a professional fit and service since this bike will be more performance oriented than my commuter. The problem is with my budget ($1500 bike + $500 accessories -- pedals, shoes, garmin, etc ) I'd be lucky to afford a Trek 2.1 in a NYC bike shop.
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Old 11-30-14, 08:24 PM
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Originally Posted by dsbrantjr
BAD ADVICE

If your chain is not long enough to comfortably shift into the big-big combo and you forget (and you WILL forget) and shift into that combo, you WILL severely damage your derailleur and possibly wheel and/or frame before you know what has happened.
+1 I destroyed a SRAM Red RD like this. Fortunately I was a few blocks from home. If you leave landmines laying around, you'll eventually step on one.
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Old 11-30-14, 09:58 PM
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Originally Posted by yankeefan
The problem is with my budget ($1500 bike + $500 accessories -- pedals, shoes, garmin, etc ) I'd be lucky to afford a Trek 2.1 in a NYC bike shop.
Seems like the perfect time to get a leftover model on sale.
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