I want a smaller front cog - not sure what I have

I want a smaller front cog - not sure what I have

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tobinen

Original Poster:

9,184 posts

144 months

Sunday 21st September 2014
quotequote all
Hello, I want a smaller front cog as I think my 42 is hindering me and I'm not a good climber. I think it's an old Campagnolo (the rear mech says Campagnolo Veloce 9 speed).

Would I still be able to buy such a thing and what do I ask for please?


16simon

53 posts

131 months

Sunday 21st September 2014
quotequote all
You need to measure the bolt circle diameter (BCD): details here http://www.sheldonbrown.com/gloss_bo-z.html

You can then look for rings in that size. IIRC the BCD on older cranks may not allow much smaller than a 42t chainring so you may be better off changing the rear cogs for a larger range.

Barchettaman

6,283 posts

131 months

Sunday 21st September 2014
quotequote all
Hi Tobinen,
That looks like a 135 BCD so you're stuck with a 42 tooth inner ring with that crankset.

Now, there are plenty of ways to get a compact crankset on that bike but I'm pretty sure you're going to have to put a new bottom bracket on as well, to get a JIS square taper spindle.

I think you have ISO on there now which vastly reduces your options as far as compact crankets are concerned - they will sit too inboard on the spindle and the bolt will bottom out.

I had this exact situation on my Olmo. I swapped out the Campy 53/42 crankset and BB for an FSA Vero 50/34 and a Shimano ST BB. Make sure you order the BB with correct threading! Mine was Italian threaded. You'll know by checking the BB you remove, it'll have thread dimensions on it and Italian is righty tighty on both sides!

http://www.bikeforums.net/classic-vintage/773449-o...

tobinen

Original Poster:

9,184 posts

144 months

Sunday 21st September 2014
quotequote all
OK thanks chaps. I'm not too surprised then given its age. It's soon to become the winter/bad weather bike so I'll make do.

gazza285

9,780 posts

207 months

Sunday 21st September 2014
quotequote all
Barchettaman said:
Hi Tobinen,
That looks like a 135 BCD so you're stuck with a 42 tooth inner ring with that crankset.
You can get 39t sprockets in 135BCD, I've got one on my Campagnolo chainset. If it is a Campagnolo rear derailleur you might be limited to how big a sprocket you can use on the rear as well.

TheLemming

4,319 posts

264 months

Monday 22nd September 2014
quotequote all
42t inner ring?

Respect smile

tobinen

Original Poster:

9,184 posts

144 months

Monday 22nd September 2014
quotequote all
Ha! With my little legs, 10% gradients are bloody hard work (rule 5 I know!)

What about this? http://www.ebay.co.uk/itm/NOS-Vintage-Campagnolo-3...


Barchettaman

6,283 posts

131 months

Monday 22nd September 2014
quotequote all
gazza285 said:
You can get 39t sprockets in 135BCD, I've got one on my Campagnolo chainset. If it is a Campagnolo rear derailleur you might be limited to how big a sprocket you can use on the rear as well.
Every day's a school day! Thanks.

tobinen

Original Poster:

9,184 posts

144 months

Saturday 29th November 2014
quotequote all
Ordered a 39T / 135 BCD, ready to change it this morning and it turns out I have 144 BCD. Balls banghead

Next job, changing the chain and cassette. What could possibly go wrong?