Commuting - gear ratios

I have a Giant TCR 2. I love it. I also live in Nova Scotia with many hills. I even live at the top of a 1 km straight up hill which I have to climb at the end of every ride.

I have noticed in various reviews and forums that some have altered the bike to make it a bit more hill friendly. Replacing the large rear "cog" with a larger one.

I cannot find anywhere on the net the gear ratios for Giant bikes. They do not list them. The bike has 39/52T at the front and 12-25 at the rear.

Is it easy (advisable) to replace the rear 25 for somethinglarger and would it really make a noticable difference? Can a 3rd be added to the front or does that go away from the design of the bike etc. Maybe changing the front 39 to something slightly smaller? Maybe if I knew how to calculate the gear ratio chart i could answer a few of these question.

All help welcome, thanks.

Most bikes in your category have 52/39 or 53/39 and 12-25.
These are good al-around gears that handle 90% of rides, but it sounds like you are in the other 10%. Looks like the bike has 105 components. You could go to a triple crankset, but then, you would also have to get the triple front derailer, triple rear derailer, and triple levers. See http://bike.shimano.com/road/105/index.asp

You could maybe get an upgrade kit from someone like http://www.branfordbike.com/gruppos/gruppo7.html#item3 , but then again, the whole triple gruppo is only $499.

It would probably be cheaper to change the 39 on the crankset to a 30. The Ultegra 30 tooth is $19.88 from Branford and I assume that it would fit on a 105 - http://www.branfordbike.com/chains/chains2.html

PS, I did not know if you saw this, but it is important you check it out IMMEDIATELY - Giant TCR2 fork recall - http://www.cpsc.gov/cpscpub/prerel/prhtml01/01160b.html

Thanks for your suggestions.

My fork is OK since my bike is a 2002, recall seems to be 2001.

The smallest ring you can fit on your double would be a 38 tooth.
At the rear you could fit a 12 to 28t cogset. Shimano ones are bought as a set.
Comparing the lowest gear using gear inches using a 27" wheel.
(39/25)X27= 42"

(38/28)x27 = 36"

That is a significant reduction on gear, and your rear mech should cover it.

To get lower, you could fit a low ratio double (36/48) with a different chainset, or a triple (30/40/50) but that would need different chainset, bottom bracket. shifter and mechs.

MichaelW, you are correct.
The 30T Y-16X-3000 is the FC-5504 and uses a Bolt Circle of 74mm which requires the triple. The 39T Y-16V-39100 is the FC-5501 (B-type) and is the smallest offered by Shimano for the 105.
I also read somewhere that for smoothest shifting performance try not to get more than a 12 tooth difference between the big pizza and the small pizza. What is your experience?

12 t difference is recomended, but this difference is more critical on triples. You may get a few teeth more, depending, but its probaby its better to go for a 38/50 combo. That way you can lower the front mech to give correct clearance to the big ring

. If Shimano dont make the rings, Specialities-TA do (See Peter White Cycles).

How critical is it on a double?
What tooth difference can you go to?

It depends on the design of the front mech.

TA do a double with a 14t difference.

If Shimano dont make the 38 rings, Specialities-TA do
You are right MichaelW. I use a 53-38 on my bike. it seems few people are aware that the 38t is available and fits Shimano. Mines unmarked but I believe it is a Stronglight TA
I also use a 11-23 cassette and that gives me a very good spread
I think the 38 from memory gives the equivalent of a cassette with an extra 2-3 teeth on each sprocket. ?
Geno should check the gear tables on Sheldon Browns page

I keep lots of spare sprockets and a spare cassette body and love to work out different combos for various events Just bolt on and go.

EarlyBird,
I just ran this off Excel,
here you go....................

Listening to what you guys have been saying...
Present: TCR2 39/52;12-25
Option: 38/50;12-28
XT: using XT Hub 39/52;12-34

where RED are stay away from gears, ORANGE are most used range.

The XT options seems like less work, less cost, and easy to change back? What are the other pros and cons?

Excel spreadsheet: the chart (http://www.sdsoftwaregroup.com/wwwMisc/BikeGears.xls)

SpongeBob, don't know why forum would not let me attach my table (tried .bmp and .jpg).

nice one knifun :thumbup: :thumbup:

I just love playing around with the ratios and testing them out.
I hate the embarassment of having to use a 78t sprocket on the back to get my bulk up the hills. It marks you out straight away as an unfit fat bloke so the 38t chain ring saves a couple of teeth on the rear

Thanks earlybird, glad I could help. Are there any other gears you would like me to add? Give me a list of the gears (50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60 then 30, .....)

Please note: this table assumes a 700c wheel.

geno - I too had difficulty attaching a file from a website (http://www.......), I couldn't get it to work either. The only way I got the "Attach file:" to work is clicking 'Browse" and point to the file located on my own hard drive. Its not you, its the forums software - maybe a bug?
SB

My local bike shop guys looked into this for me and found a 3rd party hub with 13,14,15,16,17,19,22,25,28 which should not effect gears or chains or anything else.

So I looked at the math. 39 front and 25 read = 41.5
The OCR3 which I could climb everst with has at the lowest gear a 30 front and 25 rear = 31.9

With this new propsed hub, I would have a 39 front and 28 rear = 37.0

I took the heavier OCR3 up some big hills today in 3rd gear which was 30 front and 21 rear = 38.0 and had no problems.

So I figure 37 with a lighter bike is the answer. Bike shop is just double checking the math and ensuring there are no additional changes to the equipment required (gears, chain).

Thanks All!