Converting to compact chainset when buying a new bike?

Stevo_666
Stevo_666 Posts: 62,022
edited May 2010 in Road buying advice
Some advice needed here folks.

I am starting to weigh up a few options for a road bike. I know from the gearing on my commuter and the hilliness of where I'm likely to ride that I will want a compact chainset; however there are quite a few good bikes out there that do not come with a compact as standard and are not of the 'spec it yourself' (Ribble, PX) variety.

Clearly I'd get a bike with a compact if possible but if I settle on which I feel is right for me apart from the above point, what is the easiest way to convert to a compact? Is it generally easier to just buy new chainrings and swap them over, or buy a whole chainset and change that. I would make life as easy as possible by keeping the same make and model (e.g. SRAM Force double replaced by SRAM Force compact).

Changing the cassette is also an option but I don't want to have a particularly wide spread of gears on the back cog and a 34t small ring would mean I could probably live with the most common cassette options i.e. the ones with 25 or 27 teeth on the largest ring.

Hopefully this is a generic question as I haven't pinned down my choices yet - there is a lot of kit out there that appeals and I need to do a fair bit more research first. But if this is a realatively easy job it will make my choice of bike that much wider :)

Any words of wisdom much appreciated!
"I spent most of my money on birds, booze and fast cars: the rest of it I just squandered." [George Best]

Comments

  • hopper1
    hopper1 Posts: 4,389
    You'll have to buy a new chainset, I'm afraid, as the chainrings will have different BDC's...
    Have you actually mentioned this in a LBS, I'd have thought that chainging of a chainset would be a bargaining point at least.
    Start with a budget, finish with a mortgage!
  • Stevo_666
    Stevo_666 Posts: 62,022
    hopper1 wrote:
    You'll have to buy a new chainset, I'm afraid, as the chainrings will have different BDC's...
    Have you actually mentioned this in a LBS, I'd have thought that chainging of a chainset would be a bargaining point at least.
    Thanks - that's clear now. I haven't mentioned it yet as I need to pin down my bike choice before seeing which LBS can supply and getting into negotiations.

    I probably shouldn't have to ask but what is BDC? Ive seen it mentioned a few times in posts but it has never been explained :?
    "I spent most of my money on birds, booze and fast cars: the rest of it I just squandered." [George Best]
  • nmcgann
    nmcgann Posts: 1,780
    Stevo 666 wrote:
    ....

    I probably shouldn't have to ask but what is BDC? Ive seen it mentioned a few times in posts but it has never been explained :?

    It's actually BCD - bolt circle diameter. The chainring bolts are on a 130mm diameter circle on a standard Shimano-compatible double chainset, 135mm on Campag and 110mm on most compact chainsets.
    --
    "Because the cycling is pain. The cycling is soul crushing pain."
  • Stevo_666
    Stevo_666 Posts: 62,022
    Ta very much - that one has been puzzling me for a while !
    "I spent most of my money on birds, booze and fast cars: the rest of it I just squandered." [George Best]
  • hopper1
    hopper1 Posts: 4,389
    nmcgann wrote:
    Stevo 666 wrote:
    ....

    I probably shouldn't have to ask but what is BDC? Ive seen it mentioned a few times in posts but it has never been explained :?

    It's actually BCD - bolt circle diameter. The chainring bolts are on a 130mm diameter circle on a standard Shimano-compatible double chainset, 135mm on Campag and 110mm on most compact chainsets.

    Doh!! My bad... :oops:
    Start with a budget, finish with a mortgage!
  • gsk82
    gsk82 Posts: 3,622
    i changed my compact (34/50) to 36/52 a couple of weeks ago, all i did was buy bigger rings and lift the front mech slightly. i'm by no means a bike mechanic, its actually the first thing i've done really, but it was really simple. i don't see why you couldn't just bash some smaller rings on it, but, as i said, i'm no expert.
    "Unfortunately these days a lot of people don’t understand the real quality of a bike" Ernesto Colnago
  • The Spiderman
    The Spiderman Posts: 5,625
    Smaller BCD on a compact so you can down to smaller rings,to get your lower gearing.
    2006 Giant XTC
    2010 Giant Defy Advanced
    2016 Boardman Pro 29er
    2016 Pinnacle Lithium 4
    2017 Canondale Supersix Evo
  • Mettan
    Mettan Posts: 2,103
    Stevo 666 wrote:
    Some advice needed here folks.

    I am starting to weigh up a few options for a road bike. I know from the gearing on my commuter and the hilliness of where I'm likely to ride that I will want a compact chainset; however there are quite a few good bikes out there that do not come with a compact as standard and are not of the 'spec it yourself' (Ribble, PX) variety.

    Clearly I'd get a bike with a compact if possible but if I settle on which I feel is right for me apart from the above point, what is the easiest way to convert to a compact? Is it generally easier to just buy new chainrings and swap them over, or buy a whole chainset and change that. I would make life as easy as possible by keeping the same make and model (e.g. SRAM Force double replaced by SRAM Force compact).

    Changing the cassette is also an option but I don't want to have a particularly wide spread of gears on the back cog and a 34t small ring would mean I could probably live with the most common cassette options i.e. the ones with 25 or 27 teeth on the largest ring.

    Hopefully this is a generic question as I haven't pinned down my choices yet - there is a lot of kit out there that appeals and I need to do a fair bit more research first. But if this is a realatively easy job it will make my choice of bike that much wider :)

    Any words of wisdom much appreciated!

    If for example you buy a "budget Double bike" - you'd then just buy a Compact chain-set and the corresponding BB Cups - (make sure you get the correct cups etc to go with your chosen chain-set) - you can always sell your original Double on Ebay as "as new" - your LBS can fit all of this for a small fee (probably ~ £15) or you can do it yourself if you're mechanically minded.
  • passout
    passout Posts: 4,425
    I'd try the double first. I went from compact to double recently and don't miss it. I do some really hilly rides too (Pennines etc).
    'Happiness serves hardly any other purpose than to make unhappiness possible' Marcel Proust.
  • Stevo_666
    Stevo_666 Posts: 62,022
    passout wrote:
    I'd try the double first. I went from compact to double recently and don't miss it. I do some really hilly rides too (Pennines etc).
    The masochistic streak in me might just do that; does no harm to give it a go and could save some money if my instincts are wrong. Also gives me an incentive to MTFU :)
    "I spent most of my money on birds, booze and fast cars: the rest of it I just squandered." [George Best]
  • cw42
    cw42 Posts: 205
    I bought a specialized allez double last august. It came with a 52x39 chainset and 12x25 cassette. It has been a real struggle on the hills, but I've managed to increase my climbing power over the 1600 miles I've done on it. However, I've recently taken to riding more in the hills and been put off by the hard gears, so have just today fitted a new tiagra compact chainset. This cost a total of £55 from wiggle, inc bb. I've just tried it and unfortunately the rear cassette is slipping due to the new chain and the last 1600 miles I've done :( So we're off to Decathlon in a while to pick up a new cassette 13x26 which will make my gears even lower! I should be able to cyclocross with that range now :)
    Will let you know after my first hilly ride tomorrow :D
    live long, eat biscuit

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