how many teeth to get on a chainring ?

mr_sj

i have a 2nd hand orbea roadbike and upon close inspection the chainrings are quite worn and the teeth are rounded over and i want to replace them. im still new to biking but after doing some research i know my chainring is 130bcd and currently is 52teeth and 42 teeth.

so my question is, do i just replace like for like and get the same number of teeth or change and what is the difference with having less/more teeth on either the outer or inner ring ?

asi say im new to this and eager to learn so any advice appreciated, thanksa lot

Nigel Bennett

What's your rear cassette? If the largest rear sprocket is only a 23, then a 42 tooth front chainring may be a tad large for steeper hills. Depending on the age of the chainset, it may be possible to fit a 38T sprocket, but you should certainly consider a 39T. 53/39 is a very popular set-up, which I have on my summer road bike (13-23 cassette). I did Rosedale Chimney on that!

My winter bike has 46/38 with 11-23. It's a heavy thing with all the lights and such on, and I find that gives me all the gears I need - I can't get it much above 40mph downhill anyway because of the drag of the huge mudflaps!

If your smallest rear sprocket is 11T, then you don't need much more than 48 or 50T unless you're keen on breaking the 50mph barrier downhill.

Having said that, you'll probably find that you can easily source 39/42/53 & 53 rings, and others are more hard and expensive to come by. Stronglight do pretty well any size cheaply, as do TA (more expensive).

moonshine

a standard road setup is something like a 53/39 , but you can get a 52/39 as well.
a compact setup is normally a 50/34, which many people who ride recreationally or do sportives prefer, as it gives access to a lower range of gears for steeper hills. (at the expense of a couple of higher gears that can be hndy in a bunch with a tailwind.

If you are strong and into doing time trials, many use a 53/42, a 54/42 or a 55/42 (or even greater) as the need for high gears outweighs the need for low gears.

if you decide to try and emulate a compact range i.e a 50/34 with a 130 BCD chainset, you might run into issues with the 34T chain ring, as the 130 BDC might be too big for a 34T chainring. I think you might manage with a TA chainring, but a regular shimano 34T chainring might have problems fitting on a standard (i.e. noncompact) chainset

mr_sj

rear cassette is 8 speed and largest is a 23 and smallest a 12.

as i say im still new to road biking and at the moment its just an alternative to running but future plans are to do sportives and in the long term duathlons.

moonshine

mr_sj wrote:

rear cassette is 8 speed and largest is a 23 and smallest a 12.

as i say im still new to road biking and at the moment its just an alternative to running but future plans are to do sportives and in the long term duathlons.

in that case, i would probably recommenda a compact setup - a 50 / 34 a 23 isn't a really big gear at the back - I run a 10 speed, with a 12-25 normally on a standard 53/39, but i'm quite a strong rider and will pull that up a 1 in 4. you woild probably get more enjoyment out of a compact - that will give you a lower gearing of 34/23 which is ok for a lot of things.

Bear in mind that if you go down the route of changing chainrings, they are not particularly cheap - typically £25 - £35 each. You may well be better off trawling the net shope, e.g CRC / Parkers / Wiggle / planet X / ebay etc for an old model 105 (or equiv) compact chainset - it will be almost as cheap as bying new rings.

Thats what i did when i was building up a winter bike - I could buy a slightlt cosmetically marked chainset plys new rings for less than the replacement rings would have cost induvidually. If you go down this route, you will need to be sure the Bottom bracket is compatable with whatever chainset you get - it may mean a new BB, but that should be no more than £20

mr_sj

my initial thought was to look at changing the chainset but i got kind of scared off when i asked that question before and people started talking about bottom bracket compatibility !!

Rodrego Hernandez

Most chainrings these days have profiled teeth that can look worn or rounded - check that yours are really worn out before buying a new one. If the teeth are really pointed with the valley between getting V shaped then it is worn but best to get someone experienced to check for you.

moonshine

mr_sj wrote:

my initial thought was to look at changing the chainset but i got kind of scared off when i asked that question before and people started talking about bottom bracket compatibility !!

working out BB compatability isn't too hard to be honest - there are a few types, but once you know what chainset you have, then choosing the right BB is east enough.

e.g. if you get a new shimano chainset that is "hollowtech" then the BB axle is part of the chainset, therefore all you need are external BB cups, that screw into the BB in the frame. There are a couple of variations on this e.g FSA chainsets may / may not fit a shimano BB ets, but as a general rule - if you stick with the same manufacturer, you should be OK.

There older style of BB & chainsets had an axle attached to the bearings - the axel could be either a square taper type laterly or a couple of splined axle types, called Octalink and ISIS- again, if your chainset is one of these, then choose the according BB style.

The final questions are shell width, axle width & thread. almost all road BB are 68mm and English thread.however some italian frames are "italian" thread, which if i recall correctly is 70mm wide and one of the cups is threaded the opposite way from the "english" thread. Again, pretty straightforward.
BB width only really an issue if you get a chainset that requires the older style axle & bearings style BB - not an issue with the newer style chainsets with an integrated axle.

BB30 / BB80... don't worry about it - a new standard on very new frames...

sent to confuse us all!

A

moonshine

Rodrego Hernandez wrote:

Most chainrings these days have profiled teeth that can look worn or rounded - check that yours are really worn out before buying a new one. If the teeth are really pointed with the valley between getting V shaped then it is worn but best to get someone experienced to check for you.

echo that....

I have only had to change 2 chainrings in my life - one on my winter commuter that i have no idea how old it is - many years!!! and another on a 10 year old 9sp 7700 Octalink Dura-ace chainset that had done about 40,000 miles - both were obviously shagges - as the teeth were very thin & pointy - almost shark toothed in profile -

Newer chainrings are aysmmetric and change profile around the chain ring to help shifting.

moonshine

for example -

this http://cgi.ebay.co.uk/Shimano-105-Compa ... 2eb2a3148f
and
http://www.wiggle.co.uk/shimano-105-550 ... m-bracket/
and
http://cgi.ebay.co.uk/Shimano-Octalink- ... 5191222ee6

choose the right bb axle length - IIRc the short length of 109mm is for the double chainset and the longer one - 118mm is for the triple chainset. - 68mm refers to the BB shell width - 68mm on the English frame - (70mm is italian)

mr_sj

ok, going by info i got on another thread i asked about this before.

my bike uses shimano sora and the crank arms are stamped with '98, ofmega, italy, 170c', i was told that ofmega uses a european/iso taper.

moonshine

the best place to look would probably be sheldon brown for more cartrage BB info - all you will ever need

http://sheldonbrown.com/tooltips/cartridge.html

If it is a ISO square taper, then your choices of replacement cranks using the existing BB are becoming limited, as most new cranks use external BB now. and the cost of replacing the hainrings on the Sora kit is probably greater than the cost of new kit.
ISO taper means a square taper BB axle of ISO dimesdions - See Shelfon Brown for more info - 170 may well bethe crank length

You may bell be better replacing the BB at the same time as the cranks..

I'm afraid i cant be of more help

mr_sj

thanks a lot you've given loads of useful info ! will takea look at that link later tonight and ive also emailed orbea to see if tehy can give me some more info re the bottom bracket

fleshtuxedo

No one's asked where you live and what sort of terrain you have locally.

Where do you live and what sort of terrain do you have locally?

I think that's a key part of deciding what gearing you need.

Buckled_Rims

If it's Sora just look for a whole new chainset. This is just an example, not sure if it'll fit your bike, someone might advise - note this is a standard, not compact, but it's a good price.

http://www.edinburghbicycle.com/ebwPNLqrymode.a4p?f_ProductID=11040&f_SupersetQRY=C424&f_SortOrderID=1&f_bct=c008921c014619

Buy it and take the rings off!

Buckled_Rims

Buckled_Rims wrote:

If it's Sora just look for a whole new chainset. This is just an example, not sure if it'll fit your bike, someone might advise - note this is a standard, not compact, but it's a good price.

http://www.edinburghbicycle.com/ebwPNLqrymode.a4p?f_ProductID=11040&f_SupersetQRY=C424&f_SortOrderID=1&f_bct=c008921c014619

Buy it and take the rings off!

And I should say, after you take the chainrings off, flog the cranks in ebay and you have an almost free set of chainrings...how wonderful life is if my ideas actually work out

mr_sj

i live in the north east on the coast and its pretty flat, a few inclines but mostly flat.

thanks for that link buckled rims, that looks very tempting