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Old 08-30-13, 09:45 AM   #1
darraghm
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Changing the gearing on bike

Hi,

I currently have a bike with full Tiagra groupset with a compact 34/50 at the front and 12-28 on the back.
Next year I will be using the bike for racing and I was looking at changing either the chain ring from the 34 to 39, and maybe even the 50 to 53. Or else I have the other option of changing the 12-28 to maybe 11-25 or 11-23.

Which would you recommend me doing? The races wouldn't feature huge hills, many of them will probably be flat circuits in suburbs of a city.

Changing the rear cassette would give me the option of being able to change it to the 12-28 if it was a real hilly race, but I would like to leave it alone once I make the initial change if I can.

Would I need to make any adjustments to the bike as it is - standard from shop- if I change the chainrings, or if I change the rear cassette?
Thanks.
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Old 08-30-13, 11:03 AM   #2
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I wouldn't change much unless or until you know that it's holding you back. 50/12 is a healthy top gear, and you should be able to spin it up to 35+ MPH if you consider yourself racing material.

Be advised that "standard" cranks (usually 53/39) and "compact" cranks (usually 50/34) use different bolt patterns for the chainrings -- most people will swap the whole crankset when switching from one to the other.

BTW, it's redundant to say "rear cassette" as there's only one.
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Old 08-30-13, 11:09 AM   #3
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Save your money. 50x12 is plenty of top gear for the 5's. Heck, it's plenty for the 3's.
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Old 08-30-13, 01:51 PM   #4
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Hi,

New gearing won't make you faster, unless it will .....

I've hit my maximum top speed on the flat hammering 5th of my 7 gears. 6th
is used on the flat and 7th is strictly downhill. Higher gears wont help me at all.

A close ratio cassette is best for fairly flat racing, and you don't want redundant gears
at the top or bottom. I could see someone having 3 options on the rear for racing.

A hilly course must go down as well as up and an 11t top makes
a lot more sense with a 28t bottom than it does with with a 23t.

rgds, sreten.

I'm of the opinion many have too high gears they can't use.

Last edited by sreten; 08-30-13 at 01:57 PM.
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Old 08-30-13, 02:08 PM   #5
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Quote:
Originally Posted by sreten View Post
Hi,

New gearing won't make you faster, unless it will .....

I've hit my maximum top speed on the flat hammering 5th of my 7 gears. 6th
is used on the flat and 7th is strictly downhill. Higher gears wont help me at all.

A close ratio cassette is best for fairly flat racing, and you don't want redundant gears
at the top or bottom. I could see someone having 3 options on the rear for racing.

A hilly course must go down as well as up and an 11t top makes
a lot more sense with a 28t bottom than it does with with a 23t.

rgds, sreten.

I'm of the opinion many have too high gears they can't use.
True.

Recently I raced on a velodrome for the first time and discovered that my sprint on the track bike (50x15) was only 1.5 mph slower than my typical sprint speed on my road bike (53x12). Which was a good reminder for me to focus on pedal turnover rather than mashing a giant gear.
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Old 08-30-13, 02:49 PM   #6
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Quote:
Originally Posted by caloso View Post
True.

Recently I raced on a velodrome for the first time and discovered that my sprint on the track bike (50x15) was only 1.5 mph slower than my typical sprint speed on my road bike (53x12). Which was a good reminder for me to focus on pedal turnover rather than mashing a giant gear.
Hi,

So see if you can go faster dropping a gear or two on the road bike.
If you can't, that would indicate your best gearing is higher *.

And FWIW if your used to mashing the road bike for speed you
really don't have the best preparation for spinning a track bike.

I'm 50+ and normal cadence is about 80 rpm. I hit top speed
doing about 120 rpm, x 1.5 faster than I normally go in that
gear (wind behind helped) and a good push not a sprint.

My folder is good for spinning. In top 100 rpm flat wind behind.

rgds, sreten.

* might sound like I'm contradicting myself about high gearing
but not really, the most simply cannot go fastest in top gear.

Last edited by sreten; 08-30-13 at 03:27 PM.
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Old 08-30-13, 03:10 PM   #7
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Air is the resistance to going faster , not the gear size, above a certain point.

Fat guy on a Motorbike right in front of you will help you go faster.. if you can keep in his wind shadow..

It's Called Motor Pacing ..
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Old 08-30-13, 10:01 PM   #8
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Quote:
Originally Posted by sreten View Post
Hi,

New gearing won't make you faster, unless it will .....
I'm of the opinion many have too high gears they can't use.
Agree. I've been arguing this point for years. At every group ride and nearly every low- and mid-level race I've ever done or seen, a majority of people never use their highest gears--but hardly anyone will gear down, because That's Not What Racers Use.
When you're spinning out in your highest gear, regularly turning 130rpm and wishing you had more, then it's time to install higher gearing. Until you need it, you don't need it.
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Old 08-31-13, 07:15 AM   #9
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You'll find that one of the biggest differences going from a wide range cassette to a more narrow range is a smoother transition between gears when shifting meaning be able to maintain a higher cadence between shifts while not having to increase power output by a lot...it is important especially during fast speed changes in a race.
I'd go for a 11-23 and a 52/42 chainring group for crits and flatter road races, using the wide range cassette for hillier races.
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Old 08-31-13, 02:20 PM   #10
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Hi,

An 11-23 and 12-28 is not the way to do it. If you don't need a big low
gear for hills you don't need a small top gear for non-existent downhills.

rgds, sreten.
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Old 08-31-13, 05:41 PM   #11
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Quote:
Originally Posted by darraghm View Post
Hi,

I currently have a bike with full Tiagra groupset with a compact 34/50 at the front and 12-28 on the back.
Next year I will be using the bike for racing and I was looking at changing either the chain ring from the 34 to 39, and maybe even the 50 to 53. Or else I have the other option of changing the 12-28 to maybe 11-25 or 11-23.

Which would you recommend me doing? The races wouldn't feature huge hills, many of them will probably be flat circuits in suburbs of a city.

Changing the rear cassette would give me the option of being able to change it to the 12-28 if it was a real hilly race, but I would like to leave it alone once I make the initial change if I can.

Would I need to make any adjustments to the bike as it is - standard from shop- if I change the chainrings, or if I change the rear cassette?
Thanks.


What kind of racing? TT, road or Crit? It makes a difference in the answers you get.
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