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Changing 50/34 to 50/38

GGBikerGGBiker Posts: 450
edited November 2013 in Workshop
Does anyone know if it is ok to swap a 34t chainring for a 38t on a compact chainset ? Is there a problem with shifting due to ramps/pins etc?

It is a FSA gossamer 50/34 at present, I find the 34t a nuisance on rolling terrain with racing and club runs as riding in a window between 18-22mph mostly means frequent front shifts and upset cadence in this terrain. I notice others using 53/39 do not seem to have this problem, the 39t suffices for most terrain and front shifts are infrequent.

My bike has a band on front derailleur which I don't really want to move for fear of damaging the carbon frame, otherwise I would just get a 53/39 standard.

Posts

  • gozzygozzy Posts: 640
    You'll not damage the frame if you move the FD and use the same torque setting to fit it again. If you're really worried then ask your LBS to do it.
    The main issue of changing the inner ring to a 38t is whether the BCD is the same, otherwise I can't see there being anything else to worry about other than chain length, and you might want a cassette with a lower gear, depending on how you get on with climbing on the bigger ring.
  • StillGoingStillGoing Posts: 5,207
    As long as you can find a 38 tooth ring to fit your cranks then there is nothing to do. You don't need to adjust the chain length as you aren't going any bigger than your 50 tooth ring and obviously the FD doesn't need to be raised either.
    I ride a bike. Doesn't make me green or a tree hugger. I drive a car too.
  • smidsysmidsy Posts: 5,273
    It does not matter what you fit you will simply fall into what is comfortable. The only way to overcome the issue you describe is to work on your cadence.

    You can easily ride at 20mph on a 34 front chainring as long as your cadence is right.

    Even If you could change to a 38 you will still have the same issue - just in different rear sprockets.

    What cadence do you tend to run in and how does that compare to those around you who you say do not seem to have an issue?
    Yellow is the new Black.
  • GGBikerGGBiker Posts: 450
    My cadence is on the higher side, typically 90-105 is where I am most comfortable.

    Somebody could be doing 24-25mph on a 38/39t inner ring while I would have to increase cadence to 115 to avoid shifting to the big ring, this results in a lot of shuffling between rings if you are riding at a speed that pushes you above a comfortable cadence. For me frequently riding along at a cadence of 120 is too high, can't say I know anyone who rides at that sort of cadence except when sprinting.

    I expect I will be able to do the vast majority of riding in the small ring with a 38t because it gives me a more usable spread of gears for the speed I will ride at mostly. Having to change rings frequently really interrupts the flow especially when riding with a group who are all on 39t.
  • smidsysmidsy Posts: 5,273
    Ok you originally said 18 - 22 mph. At 24/25mph surely you would opt for the large front chainring anyway?

    Can you not ride the front ring and adjust with the casstte instead. Most ratios overlap.
    Yellow is the new Black.
  • keef66keef66 Posts: 13,123
    On my winter bike I have a triple so spend 95% of my time in the middle, 39 chainring, and use all of the 12-25 cassette. The rolling terrain round here means I rarely use the 30 tooth inner or the 50 tooth outer chainring.

    So I can see why the OP might fancy a 38t chainring

    On my dry weather bike I have a standard double, and also seem to spend most of the time on the inner 39 tooth chainring.

    I've always thought that a compact double would involve too much front shifting for me, but I confess I've not actually tried one.
  • deswellerdesweller Posts: 5,175
    If you can find a chainring with the right PCD then happy days. Stronglight probably do something; take a look at Spa Cycles.
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  • GGBikerGGBiker Posts: 450
    Thanks for input all, I have ordered an FSA 38t so I'll see how it goes.

    Also looking for a 38t for a Campagnolo Centaur power torque chainset, very confusing trying to find something compatible, TA and Stronglight have some but it isn't really clear if they are compatible with a power torque chainset. I may just have to buy one and see if it fits.
  • imposter2.0imposter2.0 Posts: 11,365
    There is no issue whatsoever with using 50/38. I ride the same setup. Shouldn't be a problem on Campag either, provided the BCD is the same.
  • The smaller the drop between the chainrings the better the shifting, but if it's too small (say less than 8 teeth) it makes no sense to have two chainrings.
    If you can find both rings with the same BCD there is nothing wrong with using 50/38.... I use a 49/39, just to give you an idea.
    Stronglight makes a wide range of chainrings of all sorts of sizes... look at Ribble or SPA cycles
  • John.TJohn.T Posts: 3,698
    I use 50/36 on the Gossamer cranks on my winter bike. Perfect with the 12/27 cassette. Rings are Stronglight. The 36/13 sits in the hole between the 50/19 and 50/17 so the overlap is better than with the 34.
  • smidsysmidsy Posts: 5,273
    How do you get 36/13 with a 12/27 cassette ???
    Yellow is the new Black.
  • imposter2.0imposter2.0 Posts: 11,365
    smidsy wrote:
    How do you get 36/13 with a 12/27 cassette ???

    think about it...
  • smidsysmidsy Posts: 5,273
    Imposter wrote:
    smidsy wrote:
    How do you get 36/13 with a 12/27 cassette ???

    think about it...

    :mrgreen:
    Yellow is the new Black.
  • GGBikerGGBiker Posts: 450
    So Stronglight ring arrived from Ribble, got the torque wrench out to do a quick change, hmm, not coming out, just turning round. Need a special chainring tool to hold the nut on the back.

    Is there no f**king end to the money needed to be spent on a bike?
  • DeVlaeminckDeVlaeminck Posts: 7,226
    Flat bladed screwdriver should work
    [Castle Donington Ladies FC - going up in '22]
  • keef66keef66 Posts: 13,123
    Before I bought a chainring bolt tool I used to use the end of a steel ruler to hold them. Much easier with the chainset off the bike and clamped in the workmate.
  • GGBikerGGBiker Posts: 450
    Screwdriver no use due to the bolt protruding, special tool required !
  • GGBiker wrote:
    Screwdriver no use due to the bolt protruding, special tool required !

    Get the tool
  • GGBiker wrote:
    So Stronglight ring arrived from Ribble, got the torque wrench out to do a quick change, hmm, not coming out, just turning round. Need a special chainring tool to hold the nut on the back.

    Is there no f**king end to the money needed to be spent on a bike?

    Could just go to the LBS you know..... I know people on here think that the only bikeshops in the world are Wiggle and CRC but there are real life ones that have workshops and stuff.
  • GGBikerGGBiker Posts: 450
    All sorted, tool was £3, took about 1/2 hr and is shifting nicely (not the usual big "thunk" that going from 50 to 34 gave).

    LBS? I would be waiting a week and probably £30 worse off, and they would likely have broken something while they were at it.
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