powerglide

Actually posted over at road forum but was hoping input from mechs here...to make sure there aren't any issues I may have overlooked.

I need more lower gears for climbing (I'm a clyde yes)...running a short cage campy derailleur.
Official campy stance: medium cage needed for 13-29 (rather not do that) but some say they run it just fine...

I don't like the idea of losing that much tall gearing so leaning towards the IRD 12-28 (120 bucks) or the Miche 12-27 (60 bucks)

Anyone have experience with these cassettes? Any recomendations very welcome.

Thanks always!

Evoracer

Your current rd will run the Campy 13-29 just fine. You'll have chain length issues to deal with probably. It seems cost is a factor in your descision. Miche makes individual cogs so you can mix and match. Pull the 13t or 14t from your current cassette and add a 27t to the backside with the appropriate spacer. About $7 plus shipping. It's worth a try to see if it is low enough for you before dropping the dough on a cassette.

2 cents out.

San Rensho 

What you are running now and what you want to change to is not appreciably different. You will be getting about 5 gear inches lower, which is likely to be unnoticeable.

Theres more of a jump in gear inches from a 52/13 to a 52/14 than what you will achieve by changing to another cassette.

powerglide

Thank you Evoracer! Thats a good idea, I have a Campy Veloce casstte right now, can I break that down, remove the 13t and add a 27t or 28t to it?


Is it that unnoticeable? 5 gear inches sounds to me like a noticeable difference...especially since I can feel the less than 2 g.i. difference resulting from latest crank swap.
I lost you with this 52/13, 52/14...

Evoracer

Yes you can change it out. Now, trying to find the cog you want may take a little effort. Jensonusa.com used to carry them, but appears they do no longer.

San Rensho 

To calculate gear inches, you divide the number of teeth on the chainring, by the number of teeth on the cog and multiply by 27 inches. Most people think, "Oh, I'm going from a 25 tooth cog all the way to a 29 tooth cog, so there must be a huge difference in gearing." Well, if you do the math, its about 6 gear inches difference which is not that much. Its less of a jump in gearing (do the math) than from a 52/13 to a 52/14.

If you can feel 2 gear inches, you are a better man than I.

Al1943

I think 6 gear inches is a huge difference when it's the lowest gear on the bike and you're climbing a steep hill. And a difference of 2 gear inches does also makes a significant difference when climbing.

HillRider

6 gear-inches is a large percentage change in the low gear range and should be a very noticable improvement. Going from a 25 to a 27T cog is an 8% reduction and 25 to 29T is a 16% improvement. 8% is noticable and 16% is really noticable.

San Rensho 

Why would 6 gear inches be any different in lower gears than it would in higher gears? 6 gear inches is 6 gear inches, no?

HillRider

No, not really. What you "feel" on gear changes is the % reduction or increase, not the pure number.

Sort of like price changes. If a new car increases from $20,000 to $20,005 it's not the same impact as if a can of coffee increases from $10 to $15. Same $5 change but not perceived the same.

powerglide

What he vvv said.

My friends on the track are uber sensitive about gear ratios...gear inches was explained to me like this:
If my bike has a 6 gear inch difference compared to your bike, then our bikes will be 6 inches apart every revolution fo the crank. Consider track cyclists spinning at 150-180 rpms, races are won and lost by a gear inch or less...from what I understand.

operator

No they are lost because the other guy put out more power than you did or used superior race tactics when it mattered. That being said. 2 gear inches is definitley noticeable.

Sorry I disagree. 6 gear inches is 6 gear inches, anywhere you go. The reason why we talk in gear inches is that they are comparable.

powerglide

that too

San Rensho 

Ok, that makes sense, so from your post above, going from a 36/25-27 (8%) is about the same % change as going from a 52/13 -14, (7.7%) which is definitely noticeable, and from 36/25-29 is double that, or close to the difference between a 52/13 -15 (16%), which is a big difference in percieved gearing.

So is it safe to say that the rule of thumb in lower gears is that a 2 tooth difference is about the same as a one tooth difference in higher gears, in terms of how a cyclist perceives the change?

55-11

I think you're all missing the forest through the trees. Gear inches refers specifically, as stated previously, to distance traveled. At no point have I seen anyone account for effort (which is also not evident in converting to percentage change). If we apply the percentage change to any factor, it must be the distance traveled in one revolution at different gear ratios, which may APPEAR to be effort but clearly is not.

there ... I said it ...

powerglide

Yup I hear you....that's why gear inches is not that main stream anymore I guess.
For instance, like I mentioned in the OP I changed my crank arm length from 172.5 to 175. So I'm laying down more torque hence it should feel easier climbing. This isn't reflected in GI charts, but if you use gain ratios, you get a picture of the effort. (old schoolers still prefer gi though)

Al1943

It doesn't quite work that way. "Gear inches" are not the distance travelled for each crank rotation. Gear "development" is the distance travelled. For development you need to multiply gear inches by pi (3.1416). The gear inch number is only good for comparing gear combinations. If one rider has a 110 gear inches and another rider has 116 gear inches and they are riding at the same cadence then the rider with the 116 is going 18.9 inches farther with each rotation of the crank.
110 X 3.1416 = 345.5 inches
116 X 3.1416 = 364.4 inches

364.4 - 345.5 = 18.9 inches

55-11

EXACTLY.... that's what I meant (y'know with all the other "important"information being assumed, but yeah, we're on the same page... eloquently spoken.

Camilo

A lot of good discussion after you asked this question, and it's been answered in various ways. I've enjoyed reading it.

To me, a simple rider with only high school physics (but college math!), small changes in the low (climbing) gears are more noticeable than similar changes in the high gears, whether they be in some absolute number such as gear inches or relative number like percentage change. Not only more noticeable, but more important.... for me anyway.

Why? Because I'm not only just a simple rider, I'm old and weak. To me, I really notice and appreciate any small difference that makes difficult hills more ridable within the "zone" of effort I try to maintain on normal, "base-building" rides. I don't notice the same small change on the other end, because I don't really care, or notice what it takes to go 40 MPH downhill or whether my top speed is 44 or 41 mph. The change from my 11-23 cassette to 12-26 was a very little change on either end, but it is noticeable and important on the low (30 front-26 rear) end and virtually invisible at the high (52-12) end.

DMF 

And you're going through all this why? Because you don't want to run a medium cage dérailleur. Would you care to tell us why not?

powerglide

Oh yeah..the PI! Thank you for clarifying this for me.


why should I go spend money on a rd if I don't need one

DMF 

According to Campagnolo, you do need one.

Al1943

On another forum I've heard people say that they have run a 13-29 with a short cage Campy RD and with a 53/39 ring set (plus evoracer above). You could always try it, just be careful. If we assume that the short cage RD can handle the size of the 29t then, as you know, the issues are chain wrap, and chain length. If your chain is at the normal ideal length and if you accidentally shift into the 39-13 combination the chain will probably go slack and you'll have chain on chain in the rear derailleur area, not good. If you shorten the chain and accidentally shift into the 53-29 the rear derailleur may reach its forward limit and destroy itself and possibly damage the frame. If the chain is long enough to handle the 53-29 and if you stay out of the small ring small cogs combinations you should be OK.
I guess you could try it very carefully on the workstand and then decide about a medium cage.
Personally I would buy the medium cage or go with a 50/36 Campy compact. I've got Record carbon 53/39, 13-26 and in the future may need to make the same expensive decision. That 26 isn't low enough for some of these 15% hills around here.

operator

And since when does noticeable make 6 gear inches not 6 gear inches. If I am wrong please enlighten me. The whole point in talking gear inches is that we don't need to say stuff like the following.

If you want to compare gear inches to gear inches. Pretend you're on a fixed gear or single speed. and change out the cog or the front chainring to get whatever the heck gear inches you want. So long as the difference is 6.

I still don't see how you can claim, everything else on the bike being equal that, +6 gear inches at 30 gear inches total on the drivetrain is different than +6 gear inches at 60.

bigbossman 

Yeah - the compact with a 13/29 would make the most sense and difference in your case, if you're looking for more climbing gears.

Or, you could go whole hog and get a standard triple crank with the 13/29 cassette - but you'd also need a long cage RD.