Double Chain Ring...yikes

[aicabsolut]

Originally posted by Oakleaf:
I might change out the chainrings before replacing the cassette - five teeth in front will make MUCH more difference than two in back.

Does anyone know what's the maximum differential in a compact? Can she do 53/34, or would that result in poor shifting and/or a lot of cross-chaining?


Whether or not you can go down to a super-small inner ring depends on the Bolt Circle Diameter of your crankset.

I believe standard road doubles (53/39) have 130mm BCD's -- if this is the case with your cranks, you are limited to a 38 small ring.

Most compact doubles have a 110mm BCD; if somehow you ended up with a 110 mm BCD, you can go down to like a 33.

Sheldon Brown has a little information about this on his website, and you will get more if you google some combination of "BCD" and "chainrings".

Correct. She probably cannot change her rings without changing the entire crankset, which will cost mega $$. It would be much much cheaper to go with a cassette change if the rear derailleur can handle it (she needs to look at what's on there now). A good Ultegra cassette costs under $100. A new crankset can run well over $300.

Plus, even if she could change the rings, she's going to have to change both of them to get a compact inner ring, because the front derailleur won't be able to handle more than about a 16T difference.

Also, don't underestimate how big of a difference the rear cassette can make. Example: a 50/11 is a bigger gear than a 53/12. So say she's only got a 12-25 on there now. Moving to a 27 or 28 will be a big jump. She'll sacrifice some of the range towards the top end with such a large spread, but that's not necessarily a bad thing. It could get a little annoying on flat roads or in groups, but I think that's a better trade off than having gears that are too hard all the time.

[ginny]

Hi guys - okay, so this is the first thread I have read here that is pretty much greek to me. Can you provide me with a web site with a good tutorial on gearing ratios? Or maybe if I provide you with the specs from my bike you can explain the math to me? Alrighty... my bike hs a sugino crankset (triple) 30.42.52 and the cassette is campy 13/26 9 spd. So, how are you arriving at inches from teeth? Somewhere on the internet it looked like you need tire ratios too to calculate gearing ratios, but aren't all road tires the same unless you are a really small framed woman with smaller tires. For what it's worth, my tires are 700x23c (does the c mean cm?)

Thanks!

[Chile Pepper]

Can you provide me with a web site with a good tutorial on gearing ratios?

Sheldon Brown is always good: http://www.sheldonbrown.com/gloss_g.html#gearinch

use his online gear calculator to figure out your gear inches.

[violette]

Well, I went on a 60km practice run on the weekend. I had such a hard time with my bike, that when I got home, I threw-up. I know I pushed myself too hard, but I've done this ride all last year with absolutly no problem, the hills were almost impossible to climb ( or I should say inclines) I was soo discouraged, I had tears in my eyes, and my legs were burning so bad, I had to stop at every km. I called my LBS and they told me I could change the rings and would make a difference. I'm just wondering if it's worth it?? Will it make a BIG difference or will it be just barely noticeable? I went from a $1200 bike to an almost $3000; you'd think it would be better.

[violette]

Now is the casette the one on the back? I would have thought that the crank would be a lot cheaper to just add 1 chainring that taking the casette appart and adding just one chainring.

[Andrea]

The chainrings are on the front and the cassette is on the back. Just in case youre getting a little confused- here's a quick rundown...

What you have now is a "standard" chainring/crankset. It's got a 39 tooth small ring and a 53 tooth big ring. The diameter of the circle of bolts (AKA bolt circle diameter or BCD) that hold the rings together with the crank arm is 130mm.

A "compact" is a set of rings that is smaller. Usually the small ring will be 34 or 36 teeth (sometimes less, but 34 or 36 are most common). The big ring is almost always 50 teeth. The reason why you can't just change the rings from standard size to compact is the BCD- on a compact set of cranks, it's 110mm instead of 130mm. This is why it will be expensive for you to change to a compact- you have to get a whole new set of cranks with a 110mm BCD.

The cassette, on the other hand, is that group of gears in the back. Though they look complicated, they are relatively easy to remove and replace. Usually, you replace the whole cassette at once rather than just replacing the individual gears. It's a much cheaper endeavor than replacing your crankset.

[OakLeaf]

The first question is what was your gearing on your old bike? If you want a low gear that's nearly as low as your old one, you need to know what it was.

Sheldon Brown's gearing chart is pretty limited, but it's easy enough to do your own spreadsheet, or someone probably has a more detailed one online. Figure out what your old gearing was. Ask your LBS what range of chainrings and cassettes you can put on without changing your cranks or derailleur(s). Figure out what gear ranges you'd get from different combinations of chainrings and cassettes.

(Nowadays you don't normally swap single cogs in the rear, that's why it's called a "cassette.")

[violette]

I checked the specs of the OCR3; 30/42/52, 12-26.

[alpinerabbit]

Now is the casette the one on the back? I would have thought that the crank would be a lot cheaper to just add 1 chainring that taking the casette appart and adding just one chainring.

What Andrea said, and of course you can't add a chainring to a double crank. You can exchange, but the minimum small chain ring in the front can be 38 teeth.

How much will this cost...
A cassette sets you back maybe 60$.
A Compact crank will be around 150$?
I assume you have Shimano 105 for that pricing.

Do change to a compact - you are obviously overtaxed by the regular. You can almost do your tour but it's too much for you. You'll do much better on the compact, talk to your LBS what they can do for you (do they need to replace the front derailleur?) and pricing instead of torturing yourself.

Wrong gearing has little to do with the price of the bike... do treat yourself, stop being frustrated and then enjoy your ride.

[OakLeaf]

If her low gear now is a 39x25, but the gear she found comfortable was a 30x26, then she's going to need to swap crank and cassette to even get close. A 34x28 is almost as short as her old low. But anything over 27T rear would probably require an alpine RD, yes?

OTOH, a 30x25 is even slightly lower.

So it doesn't look like there are any cheap solutions unfortunately. It might be just as simple to get the triple and keep the cassette and RD? Especially if her lever is triple-compatible?

[alpinerabbit]

The shimano rear derailler *could* handle a tad more than 34x27 (official capacity) - 28 for sure, say the sources. This or going to triple is all a matter of what the LBS quotes for the remodel.

[violette]

Ok but would this make it a lot easier to go uphill?

[Andrea]

It depends on your definition of "easier"- with lower gears, you will feel less resistance on the pedals, but you'll either have to turn them faster to maintain the same speed, or just slow down, meaning that you will be going uphill for a longer time. It's a trade-off, and you just have to decide which one you'd rather have. Most women opt for the lower/slower route.

[alpinerabbit]

It will make it closer to what it used to be like on the triple-chainring Giant you had before. Not identical but closer.

[sundial]

Ok but would this make it a lot easier to go uphill?

Yes and no. You will be spinning like the dickens while traveling a shorter distance with a granny gear. Your heart rate will go up because you are spinning faster because of less resistance. However, because of less resistance, your legs won't poop out as fast in the long run and you may finish your ride feeling strong.

I'm curious, have you had any time off the bike to recuperate? Sometimes overtraining will sneak up on you and zap you when it's least convenient.

By the way, I keep reading Double Chin Ring, lol!