Confusion re gearing

FAT_ROB

Good day one and all

I have had a search through the forum but can't find anything that fits.

Im confused about all this talk of compacts and gearings, being fairly new to road biking and never really having to swop my mountain bike gears im completly lost.

I currently ride a Specialized tarmac comp which is superb for my normal rides However as I start doing more and more distance and start to combat steeper and steeper hills I have found that I tend to be running out of gears.

Do I need a triple?
What is a compact?

How are gear rations worked out

Thanks in advance

FAT_ROB
NEVER KNOWINGLY PAST A PIE SHOP

willbevan

Expect your tarmac has what is called a double , so 53/39 typically. (Sorry if thats patronising)

Compact gives a smalerl set of rings, say a 50/34 (48/34, 50/36 or 38 etc etc), which gives you a lower and wider set of gearing, and unless your uber fit or like going incredibly fast down hill you wont run out of gears on a compact top end wise, mind you i do like hammering it down hills (i run a compact) and will sping out, but really at that speed i should be thinking of slowing down not worrying about gears!

I expect your tarmac already has something like a 11-27 on the back (correct me if im wrong), so changing the rear cassette wouldnt do much as you could change to a sram 11-28, so changing to a compact would be easier (and wouldnt require you to change your left shifter for a triple)

I did wish i had a triple yesterday, just a bit under 80 miles with 6500ft climbing (lot for me you know), and i had a full set of panniers on that were laiden, going up some of the steep parts...

Really depends on your riding etc, a lot of people see a triple as unfashionable, but honestly i think i will get a triple on my summer bike (when i buy one) thats Ultegra or DA i think, why you say? Well i can have a nice close gearing, say a 11-23 and stll have some lower gears by droping into the granny ring, but then im unfit.

Good gear calculator here

http://www.sheldonbrown.com/gears/

Lots to read on that site to

Bronzie

Triple = like mtb chainset - 3 chainrings typically 52/42/30
Standard double = normal road bike chainset typically 53/39
Compact = smaller geared version of standard typically 50/34

The gearing is the number of teeth on the front chainring divided by teeth on the rear cassette. Commonly this is multiplied by the wheel diameter in inches to give you an equivalent wheel diameter or "gear inches".

Example:
53/39 standard with 12/23 rear cassette => smallest gear 39/23*27 = 46 inches
50/34 compact with 12/23 rear cassette => smallest gear 34/23*27 = 40 inches
50/34 compact with 12/27 rear cassette => smallest gear 34/27*27 = 34 inches
52/42/30 triple with 12/27 rear cassette => smallest gear 30/27*27 = 30 inches

You don't say what gears your Spec has fitted as standard, but you can easily swap a standard double for a compact to give lower gearing, or swap the rear cassette for one with a larger sprocket (eg swap 12/23 for 12/27).

To convert to triple will cost more as you'll also need new front mech, front shifter, rear mech and chain. The advantage of triples is you have more gears spaced closer together.

Peasoup

... if you change to a triple, I think you'd probably also need a new (wider) bottom bracket to cope with the 3 rings.

Bronzie

Peasoup wrote:

... if you change to a triple, I think you'd probably also need a new (wider) bottom bracket to cope with the 3 rings.

Depends on the groupset - the Shimano Hollowtech II chainsets (with bottom bracket bearings mounted outside of the bb shell) use the same bb for compact, double or triple.

The older style "Octalink" Shimano bb's needed a different wider bb for a triple than the compact / double.

dennisn

Here's another way to look at it. Assume your bike has a 27" diameter wheel. 27" times
pi(3.14) gives you a tire circuimference of 84.8 inches. Now, divide 53 by 12(or any front and rear gear that you choose). This equals 4.416. Now multply 4.416 by 84.8" and you get 374.47 inches. This is the distance your bike, in a 53-12 gear, with a 27" dia. tire, will
travel in one revolution of the crank. Same math with a 50-11 compact gear and the same rear tire will move the bike 385.45 inches in one crank revolution. At a cadence of 90
rpm this 50-11 will move you about 33 MPH give or take a bit. Your fear of running out of
gears is somewhat unfounded. On most big hills or mountains you can coast down fast
enough to scare the hell out of yourself. Especially when you come flying into a curve
and see gravel on the road, a car ahead, a cow, or just about anything else in your way.

Dennis Noward

willbevan

dennisn wrote:

On most big hills or mountains you can coast down fast
enough to scare the hell out of yourself. Especially when you come flying into a curve
and see gravel on the road, a car ahead, a cow, or just about anything else in your way.

Dennis Noward

Dennis got to say, loved that bit, did make me smile

FAT_ROB

Cheers for that think I have a bit of an understanding of this now.

That said have been working down in London this week so have not been off the big chain ring all week.

feel

dennisn wrote:

Your fear of running out of
gears is somewhat unfounded. On most big hills or mountains you ...

Dennis Noward

I suspect if he is anything like me it is going up the hills that is the problem not coming down them

dennisn

feel wrote:

dennisn wrote:

Your fear of running out of
gears is somewhat unfounded. On most big hills or mountains you ...

Dennis Noward

I suspect if he is anything like me it is going up the hills that is the problem not coming down them

You suspect right. It's not a pretty thing watching me climb. Then again not many people get to see it because they are all up ahead. However, on the downhills it is a proven
fact that fatter is faster.

Dennis Noward