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I am looking for some higher cog front gears for an old bike I am considering. I've been away from it for some time and don't know the current number of cogs on the front ring, but I am looking to maybe put a really large ring on it. I just find that there are times I need one or two more gears to shift up to. I don't always ride in the highest gear, but I have way too much in the lower range.

Is it possible to switch to a larger front ring to boost my higher end range?

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It may be more practical (and cheaper) to replace your rear gear cluster. A good bike shop will be able to give you guidance -- there are a lot of variables. –  Daniel R Hicks Apr 16 '13 at 10:57
    
Could you find out how many cogs, and how many teeth each one, you have in the rear, the same for the back, end include this information in your question? Then we will be able to give you much better advice! :o) –  heltonbiker Apr 16 '13 at 12:50

3 Answers 3

Some background on the front chainrings:

  • Lots of bikes have a front derailleur, allowing more than one chainring. Some bikes have a single front chainring and no derailleur.
  • They're called chainrings rather than cogs (which are at the back).
  • There are typically either 3 or 2 chainrings on the front crankset.
  • If there are 2 chainrings, there are two 'flavours': Compact (with smaller rings, eg: 50 tooth and 34 tooth) or Standard (with larger rings eg: 53 tooth and 39 tooth)
  • Another important stat is the BCD (Bolt Circle Diameter). This is the diameter of the circle described by the bolts attaching the chainring to the crankset. A common figure is 130mm.

So you have a few factors to consider, and there's more information we need.

  • Do you have a front derailleur?
  • How many chainrings are in the front?
  • What make and model do you currently have?
  • How many teeth are on each chainring?
  • How many cogs are you your rear cassette?
  • How many teeth are on the smallest and the largest cog on the cassette?

With this information we can give you some advice. Just as an alternative, you can also replace the cassette at the back to change your gear ratios.

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He said its an old bike so it might be that he has and old style standard 53/42. –  robthewolf Apr 17 '13 at 8:14

The simplest way is to take the bike to your LBS and ask them what the options are. The answer may be limited by what they have in stock and might cost more than buying parts on the Internet, but they'll do the work for you and you'll be sure that the parts they supply will work together or they'll be obliged to fix it.

To do it yourself, start by counting the number of teeth on the chainrings at the front and the cogs at the back (aka the cassette). Then you can plug the numbers into a gear calculator. That gives you a table of either gain ratios or gear inches which can easily be compared to other cobinations of rings/cogs you might consider.

Bear in mind that not all drivechain parts are compatible and it's safest to stick within the same brand/model. Also, if you significantly change the size of the cogs/rings, your existing deraileur and chain may not have enough scope to take up the slack.

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Ok, Thank you all for the given information. Sorry about the confusion of terms (cogs vs chainrings, etc) Im currently at college, so I can't get the number of teeth on either the chain rings or the cogs. I will start at the top, and answer the questions going down as best I can. Mac: Yes, I have a front derailleur. 2 Chain rings. I believe it is a Schwinn, madel, I really have no idea. This bike is easily 30 to 40 years old, It is a good bike, it just is way past due for some TLC. Again, I don't know the current number of teeth, but there are five cogs, 2 chain rings. –  Bryce Apr 16 '13 at 18:13
    
Sorry to make this so long. As for the next two, The bike is really old, I plan on replacing almost everything, and I have access to a fairly large range of tools, so I want to do the work, and can, it is to be my summer project. I had found the 53 tooth chain rings, I was hoping for the option to go larger, which may not exist. Thats why I came to those who know. If it doesn't exist, I will just go that far and ride. It may be a huge step up from what I have. Again, Thank you for all the information, I do plan on visiting several LBS I just want to know basically what I wanted before I went. –  Bryce Apr 16 '13 at 18:17
    
@Bryce: Please edit your question to include this information! –  Jahaziel Apr 16 '13 at 20:57
    
I'm not sure you can get larger than 53 on the front... can you? Certainly you can go down to an 11-tooth cog on the back which would make for a very high gear ratio (9.7 gain ratio, or 130.1 inches) - realistically more than any normal person needs. –  James Bradbury Apr 17 '13 at 7:40

Usually there are three types of road gearing

  • Compact Double (50 / 34)
  • Traditional Double (53 / 39)
  • Triple

Where the numbers is the number of teeth on each ring. Very old racers (pre-90s) tended to be very different, so it depends on what you mean by old.

Most modern road bikes come with a Compact Double chainset these days, older bikes normally have closer groupings because the derailleurs at the time couldn't deal with the range. If you largest chainring on the front is larger than 53, I doubt you would need larger gearing and maybe you might think about riding at a higher cadence instead.

Most rear cassettes have 12-26 teeth on the back for systems that 7 speed or higher in my experience.

If you feel you need to change the front chainrings, you need to know the number of arms the crank arm has and the BCD. It usually says on the chainring, or as others had said ask your local bike shop.

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Welcome to Bicycles.SE. –  amcnabb Apr 16 '13 at 17:11

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