enter image description hereThe bike I wanna buy has a 42/34/24 crankset and TX-50 FD, now I was wondering if I could install a 48t(or bigger if possible, do tell) ring upfront while keeping the rest (i.e transforming it to 48/34/24..). Is this possible ? What do I need to adjust ?


  • Dumb question ---> why are slicks more expensive (in my country) than knobbies (2x almost) ?? I'm looking to make my bike a speed machine and thats quite a problem............
    – reaper
    Oct 10, 2014 at 12:50
  • The title is crank. Even 110 BCD you can get a 48 so the crank is not a problem. FD is the question? 24 to 48 is a longer stretch.
    – paparazzo
    Oct 10, 2014 at 13:11
  • In a comment state 48t is the max supported by the FD. Then why did you not put that in the question?
    – paparazzo
    Oct 10, 2014 at 15:07
  • sorry bout that, but will the FD have any probs shifting? Thats my question.
    – reaper
    Oct 10, 2014 at 15:13
  • If the specifications say the FD should support 48T then it should. You will need to move the derailleur up and adjust. Be sure you have room the FD up. You can gauge how much up as it will be a little less than the difference between you 42/32. You also my need to add some chain or just never cross chain big to big.
    – paparazzo
    Oct 10, 2014 at 15:17

3 Answers 3


The TX-50 is a tourney level part (bottom of the barrel). If the bike is spec'd with a Tourney derailleur, it is most likely spec'd with a crankset which does not have replaceable chainrings, and you'd need to put on a new crank.

As for chainring size, I'm not sure a TX-50 can take a 48t chainring (likely not - you'd have to look at the data sheet, which I also can't find), but most bikes which such a part would be mounted on would have problems with either chainline or actually getting the front derailleur up high enough to clear the chainrings for a 48t.

Your options for increasing speed generally on mountain bikes (or bikes with mountain-type groups on them) are:

1) Slick tires

2) Locking out your fork/rigid fork

3) possibly a smaller cassette

4) (Most importantly) Bring up your cadence.

If you really want to go faster on roads, look at a different (road) bike (possibly on the used market).

  • The TX-50 FD can support a maximum of 48t upfront -- that I know. I am a newbie, so I dont completely understand how a front dera actually works - therefore I dont know if that combination will mess up the FD for the "teeth increment" or something. I am looking for speed, but roadies within my price range have plastic components, crappy brakes and no real brands-> unsafe for city riding (Dhaka has disgusting roads). I CAN get pretty decent MTB's for the same. Sheldon Browns calculator say I will get a maximum theoretical speed of 30 mph with 48/11 gear(with slicks and other mods ofcourse)
    – reaper
    Oct 10, 2014 at 14:32
  • I've included the specs and photos on the link.Batman pls see if you can recognize that crank --> are the rings replaceable ? The fork isnt lockable, but it does have a preload. link
    – reaper
    Oct 10, 2014 at 14:37
  • I don't know what model it is, but its a low end Shimano crankset which can't have the chainrings replaced anyway.
    – Batman
    Oct 11, 2014 at 12:33

You will probably not be able to just exchange the big ring, as that will probably require a new front derailleur.

There are quite some people around, complaining for too small front chainrings, when in reality the problem is their low cadence (<70). However, a 42t big chainring could indeed be a problem for road riding.

I am familiar only with Schwalbe pricing, and they have Active compound (about 20BGN), performance compound(40BGN+) and evolution compound (60BGN+). Point is, different rubber in the same tire can change the price several-fold.

Bottom line: find a bike that is suitable for the way you ware going to be riding it. Replacing new components is more expensive, than buying the bike with those components in the first place.

  • I am not able to locate any documentation on that FD, here the closest I came across. That's why in my first paragraph, I say probably.
    – Vorac
    Oct 10, 2014 at 13:00
  • 48t is the max supported by the FD. Thats why I said 48 not 50 or 53t. FYI thats the only (and the best) bike I could find at my price point - the frame is great, components I can change.
    – reaper
    Oct 10, 2014 at 14:59

A bigger gear is useful only if you can actually use it. With the 42t & the smallest cog, pedaling at 90rpm, speed will be, approximately, between 24 & 26.5mph depending on the size of the cog. Can you spin the bigger gear, the 48t? You need to know the specs for the front derailleur. The maximum chain-ring size the FD can handle will need to be at least 48t. A FD has a max range of teeth over which it can operate. This is the difference between the small chain-ring and the large chain-ring. Assuming the chain is currently the correct length, you would need a longer chain. Otherwise, shifting to the large cog & large chain-ring could cause the chain to become stuck on this gear, damage, or even destroy the rear derailleur.

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