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Just say, I wanted to fit compact front chainrings.....?

JimmyKJimmyK Posts: 712
edited November 2009 in Workshop
Bike is a Trek 1000 , double front chainrings 53/39 and rear cassete is 8 speed shimano 12-25, shifters are sora type. Ive mentioned before that I have MS, but some of the climbs on runs I do are real tough and Ive got to be so careful that I dont push myself into a MS relapse. If I ride on my granny gear 39/25 , it will take me up steep hills ok, but my body does get quite warm and so I am thinking maybe compact double front chainrings are what I should be considering.

LBS would be doing the job . but.........

is removing 53/39 front rings and replacing with compacts a big job ?
is there any particular compact chainrings you would recommend for me ?
would my speed take a big hit with compacts ?
would the steep hill climbs be made a bit easier for me ?
would i need to buy any other components for the bike if compacts were to be fitted ?

hope you dont mind answering these questions, id appreciate all the advice I can get on this one :)

Jimmy

Posts

  • Compact chainring won't fit. You need a Compact chainset mate.

    Std double = 130mm bcd and Compact = 110mm BCD

    Climbing is easier with a compact double. All the bits you currently have should be fine with a compact.
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  • JimmyKJimmyK Posts: 712
    Compact chainring won't fit. You need a Compact chainset mate.

    Std double = 130mm bcd and Compact = 110mm BCD

    Climbing is easier with a compact double. All the bits you currently have should be fine with a compact.


    what does BCD mean ? could you provide a link as to what I should be buying ?

    thanks a lot :)
  • http://www.chainreactioncycles.com/Mode ... elID=35734

    Comes with BB. Fit that and jobs a good 'un.

    BCD = The diameter of an imaginary circle that intersects the center of each chainring bolt on the crankset. The standard is 130 millimeters; Campagnolo uses 135 millimeters. 110 BCD is typical for compact cranksets.
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  • JimmyKJimmyK Posts: 712
    is BB bottom bracket ?

    how would I know which size of chainset I need ?
  • John.TJohn.T Posts: 3,698
    BB is bottom bracket.
    Most compacts come as 50/34. Make sure you get the same crank length. If you use 175mm ones then that one at £29.99 is a bargain. You may need to use a 9sp chain to help prevent the chain rubbing on the outer ring when using the small ring and smaller cogs. It will work fine on your 8sp cassette. You will probably get some rub on the small / small gear but you should not normally use this one.
  • JimmyKJimmyK Posts: 712
    how would i know if its 170mm, 172mm,175mm ?

    would getting a 9sp chain mean the need for a new rear cassette ?

    would there ever be a need to change deraillure(s) or cage ?

    yeah small front ring / small rear cog is never a combination id use.
  • John.TJohn.T Posts: 3,698
    how would i know if its 170mm, 172mm,175mm ?
    It will be stamped on the back. It is best to stick with the size you are used too but you would be hard pressed to notice the difference between say 172.5 and 175. If I used 172.5 but could save money like the cranks above I would change to 175. I use 175s but have used 180 with no trouble. When on the track I use 165 and never notice the difference after a 10 minute warm up.
    would getting a 9sp chain mean the need for a new rear cassette ?
    No.
    would there ever be a need to change deraillure(s) or cage ?
    Not if you did not exceed 50/34 and 12/27.
  • Jimmy Read this fella's site:

    http://www.sheldonbrown.com/

    It has near enough you need to know about bike bits.
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  • rakerake Posts: 3,204
    edited March 2010
  • John.TJohn.T Posts: 3,698
    no need to swap to 9 speed chain
    Most after market chainsets are now 9/10sp and the rings are slightly closer together. It may still be OK with a 8sp chain or you may need to change if rub is a problem.
  • i ride a 10 speed 50 /34 road bike in the winter and a 9 speed 48/39 flat bar scott cr1 in the summer,i find this works well for me,----ps can i put a 39 tooth chainring on my compact,50/34
    going downhill slowly
  • John.TJohn.T Posts: 3,698
    can i put a 39 tooth chainring on my compact,50/34
    Yes you can. I am running 52/38 on one of my bikes on compact cranks. It is cheaper to get a compact and move bigger if you want. Various options here.
    http://www.spacycles.co.uk/products.php?plid=m2b0s149p0
  • John.T wrote:
    can i put a 39 tooth chainring on my compact,50/34
    Yes you can. I am running 52/38 on one of my bikes on compact cranks. It is cheaper to get a compact and move bigger if you want. Various options here.
    http://www.spacycles.co.uk/products.php?plid=m2b0s149p0

    +1 to Spa Cycles. They've got the best collection of chainrings I've seen.
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  • rakerake Posts: 3,204
    edited March 2010
  • k2riderk2rider Posts: 575
    why not stick a mtb cassette on with a 32 tooth or 34 tooth biggest cog with a cheap mtb mech? might be cheaper than a chainset and bb.
    who cares?
  • JimmyKJimmyK Posts: 712
    my bike is going to LBS on thursday morning, I may get it back after teatime on same day. im having a compact fitted 50/34 and a new bottom bracket fitted , the only size available is a 175mm crank which the shop tech tells me is a negligible difference to a 172.5mm crank.

    i asked the tech if he had to choose one bike only , would he go for 53/39 or compact 50/34 ...............he said compact........without hesitation. with me doing a lot of coastal cycling , he said also that the compact would make a big difference as pedalling into headwinds can be demoralising and energy sapping , he also said that there is no reason why i should worry about speed and my MS will be better taken care of as I will have lower gearing when I really need it.

    i am so hoping that this will be the correct course of action for me, ive been up church road in holywood, county down and man..........that is one tough tough climb, im hoping the compact will take a lot less out of me on climbs like that bad boy, I appreciate the help you guys have given me by chipping in on this one :)

    Jimmy
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