Results 1 to 15 of 15
  1. #1
    Rep Power: Infinity
    Reputation: NateHawk's Avatar
    Join Date
    Dec 2003
    Posts
    12,063

    gear ratio for urban commuter ss?

    I'm working on a SS road bike for commuting, and I need to decide on a gear ratio to use.

    I'm starting out with this:

    Trek 420 project bike

    A late 80's Trek 420. I'll be sending it off to a builder soon to have it modified to accept disc brakes and a Gates Carbon Drive. The builder is going to build me a 1" threadless fork with a disc tab to go with it (I can't track down the 1" steerer road fork with disc tabs that Dimension used to make - nobody has any).

    I've bought a used LX crankset (newer one with external bearing bb) from the classifieds here to build off of.

    I am thinking of using a 2.5:1 gear ratio. The biggest hill on my commute is about 80ft of vertical over around 1000'. Town's not terribly hilly, but there are a couple of hills with 200ft+ of elevation gain with a similar sort of grade I'd like to get.

    Too small of a ratio? Too big? Looking for thoughts on this one.

  2. #2
    .......
    Reputation:
    Join Date
    Apr 2007
    Posts
    3,707
    I'd start with 70-ish gear inches. On a 700x23, that's about 48x18 or 42x16. I'd also use the stock cranks on there, as it will look better, IMO.

  3. #3
    Rep Power: Infinity
    Reputation: NateHawk's Avatar
    Join Date
    Dec 2003
    Posts
    12,063
    Quote Originally Posted by p nut View Post
    I'd start with 70-ish gear inches. On a 700x23, that's about 48x18 or 42x16. I'd also use the stock cranks on there, as it will look better, IMO.
    A had a buyer for the whole gruppo on this bike, so the stock cranks went with it all. The LX cranks weren't my first choice, but I went with them b/c they were cheap. Gates makes bigger rings I can put on 104mm bcd cranks to achieve most combos (up to 55t)

    The whole gear inches concept is new to me. if by 700x23, you mean the tires, the pictured tires were trashed. they were 700x25, anyway (flat and dryrotted to hell). I'd like to use 700x30 or 32's on this bike being that my commute has an option for a dirt MUP.

  4. #4
    Bro Mountainbiker
    Reputation: Sheepo5669's Avatar
    Join Date
    May 2010
    Posts
    3,537
    49x18 would be a good starting place. Maybe get a 17 if you are undergeared. Its gonna be a sweet bike. Definitely update the thread with some pics as it progresses!
    Raised in a Chicken-Coop by Chickens

  5. #5
    mtbr member
    Reputation:
    Join Date
    Oct 2009
    Posts
    6,535
    52/11 or HTFU.

  6. #6
    Rep Power: Infinity
    Reputation: NateHawk's Avatar
    Join Date
    Dec 2003
    Posts
    12,063
    Quote Originally Posted by Sheepo5669 View Post
    49x18 would be a good starting place. Maybe get a 17 if you are undergeared. Its gonna be a sweet bike. Definitely update the thread with some pics as it progresses!
    With the Carbon Drive system, the parts are quite expensive ($100-ish to replace one part, and replacing the pulley/sprocket also means replacing the belt, which runs close to $100, too). What I plan to do is get a short list of ratios to try out on my commute and other local roads, and find what works for me before I buy the super expensive Carbon Drive parts and am stuck with a ratio for quite some time.

    I absolutely will post progress pics. I've got the bike stripped down to just the frame in the garage right now. I'll get a pic of it this evening. I'm awaiting the estimate for the frame mods by the builder, and working to remove the remnants of a stuck rack mount bolt that I had to drill out (without mangling the threads on the frame).

    I'm currently into the frame $45, so I've got a good bit of room in the budget for frame mods.

  7. #7
    Ovaries on the Outside
    Reputation: umarth's Avatar
    Join Date
    Dec 2007
    Posts
    4,361
    **** man, 70 gear inches. I do 39x15 cause I like the smaller chainrings.

  8. #8
    .......
    Reputation:
    Join Date
    Apr 2007
    Posts
    3,707
    Quote Originally Posted by NateHawk View Post
    A had a buyer for the whole gruppo on this bike, so the stock cranks went with it all. The LX cranks weren't my first choice, but I went with them b/c they were cheap. Gates makes bigger rings I can put on 104mm bcd cranks to achieve most combos (up to 55t)

    The whole gear inches concept is new to me. if by 700x23, you mean the tires, the pictured tires were trashed. they were 700x25, anyway (flat and dryrotted to hell). I'd like to use 700x30 or 32's on this bike being that my commute has an option for a dirt MUP.
    Not sure why you bought MTB cranks for your road bike? Whatever. Anyway, I'd go 42x16, as 42T 104 can be found for dirt cheap an you may even have it in your parts box. It's a way to try out the gearing for cheap. Also, make sure 700x30 will fit the frame/fork. Most road bikes have tight tire clearances.

  9. #9
    Rep Power: Infinity
    Reputation: NateHawk's Avatar
    Join Date
    Dec 2003
    Posts
    12,063
    Quote Originally Posted by p nut View Post
    Not sure why you bought MTB cranks for your road bike? Whatever. Anyway, I'd go 42x16, as 42T 104 can be found for dirt cheap an you may even have it in your parts box. It's a way to try out the gearing for cheap. Also, make sure 700x30 will fit the frame/fork. Most road bikes have tight tire clearances.
    Not sure it really makes a difference whether the cranks are labeled for "mtb" or "road" use, to be honest. As long as I can get a suitable gear ratio for what I want to do with the bike (I can), I'm not sure what it matters. It's going to be somewhat of a Frankenstein bike, anyway.

    I don't have to worry about the current fork because it won't be part of the final build. As for the rear end, if a 30 or 32cm tire won't fit, I'll use the biggest that will. It is a touring frame, though, so I expect a bit more clearance for tire choices than some.

  10. #10
    .......
    Reputation:
    Join Date
    Apr 2007
    Posts
    3,707
    I guess it's just personal preference. Usually road cranks have a narrower profile, as less chainstay clearance is required vs MTB frames. Also, and most importantly (IMO), 5-bolt 130bcd vs 4-bolt 104bcd to handle the bigger chainring. Just less chance of bending the ring. But this may not be an issue for you.

    Not knocking your build. I'm sure it will turn out pretty cool. Just confused why you'd use mtb parts on a road bike. Good luck with the build.

  11. #11
    mtbr member
    Reputation:
    Join Date
    Feb 2010
    Posts
    390
    op - i don't know if you are aware, but obviously with some of their suggestions your other respondents are not, but gates drive "spockets" both front & back are only available in somewhat limited sizes compared to ordinary chainrings & cogs.

    i researched these things awhile back when i had a bug up my ass to get a belt drive bike & finally dropped the idea partly because of this.

    iirc smallest rear is 20t & goes up in irregular increments & smallest front is 39t & also goes up in weird jumps & not every size is available in the both bcd's.

    do you know for sure that your cranks will fit either of the gates front sprocket configs?

    good luck...i think you're gonna need it

  12. #12
    Rep Power: Infinity
    Reputation: NateHawk's Avatar
    Join Date
    Dec 2003
    Posts
    12,063
    Quote Originally Posted by markaitch View Post
    op - i don't know if you are aware, but obviously with some of their suggestions your other respondents are not, but gates drive "spockets" both front & back are only available in somewhat limited sizes compared to ordinary chainrings & cogs.

    i researched these things awhile back when i had a bug up my ass to get a belt drive bike & finally dropped the idea partly because of this.

    iirc smallest rear is 20t & goes up in irregular increments & smallest front is 39t & also goes up in weird jumps & not every size is available in the both bcd's.

    do you know for sure that your cranks will fit either of the gates front sprocket configs?

    good luck...i think you're gonna need it
    yes. I posted a link to the Gates product catalog in an earlier post, which shows the available combinations. I may not be able to get EXACTLY the ratio that works for me in chain drive, but I will be able to get close enough to find something that will work. There is an overlap for the front sprockets. I won't be pushing a huge gear on a commuter, so I'm not so concerned about the fact that I will not be able to use a 60t sprocket on my 104mm bcd crankset. 55/20 (the biggest range I can run) is probably big enough for me, and seems to be at the upper range of what folks are suggesting, anyway. I will play with gear ratios from a bit under 2.5:1 up to 2.75:1 and see what I like. If possible, I'd go with a smaller ring up front.

    Just confused why you'd use mtb parts on a road bike
    cost. I am somewhat limited on what I can spend for this build, so I am trying to get what I want for as little as possible. I was not having good fortune finding a road crankset at a price anywhere comparable to what I found the mtb crankset for. that said, I did get a good enough of a deal on the LX crankset that I might be able to resell it for a profit and work my way into a suitable road crankset.

  13. #13
    transmitter~receiver
    Reputation: meltingfeather's Avatar
    Join Date
    May 2007
    Posts
    7,994
    sounds like an interesting project. i'd go 2.75.
    Quote Originally Posted by NateHawk View Post
    I did get a good enough of a deal on the LX crankset that I might be able to resell it for a profit and work my way into a suitable road crankset.
    lol... sure.
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
    29er Tire Weight Database

  14. #14
    mtbr member
    Reputation: sasquatch rides a SS's Avatar
    Join Date
    Dec 2010
    Posts
    4,738
    I run 48x17 fixed around town..seems like a good gear but on the straights I could use a 16 in the back.

  15. #15
    Rep Power: Infinity
    Reputation: NateHawk's Avatar
    Join Date
    Dec 2003
    Posts
    12,063
    Quote Originally Posted by meltingfeather View Post
    sounds like an interesting project. i'd go 2.75.

    lol... sure.
    well, I guess I wasn't looking hard enough. Found a decent price on a suitable road crankset w/bb. It's a 30-39-50, but it'll give me the option of going higher than the 2.75:1 max ratio the mtn crankset will give.

Similar Threads

  1. Gear ratio
    By Jwind in forum Utah
    Replies: 0
    Last Post: 06-09-2011, 01:44 PM
  2. Which Gear Ratio?
    By jt29 in forum Drivetrain - shifters, derailleurs, cranks
    Replies: 5
    Last Post: 09-29-2010, 10:18 AM
  3. Gear ratio help please...36 x ???
    By igotbanned in forum Singlespeed
    Replies: 16
    Last Post: 07-21-2008, 02:25 PM
  4. gear ratio/ gear inch. Really confused!!!!
    By cummings in forum Urban/DJ/Park
    Replies: 5
    Last Post: 11-18-2006, 07:06 PM
  5. Replies: 15
    Last Post: 05-16-2006, 09:06 PM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •