Changing gears on the chain ring

musto_skiff

After a few months it has become clear to me that I never use my biiggest gears (well not often).

I have a 53/39 and think I'd be better served with a 50/34 compact.

I notice on my bike which has Ultegra groupset that the chainrings are attached to the crank casting with allen keys.

Is it possible just to buy two chain rings and fit them or do I need to buy a whole new chain set like this?

http://www.wiggle.co.uk/ProductDetail.a ... 20chainset

If I do have to buy a new chainset I get the option to specify crank length; I currently have 175's but have no idea if I should change this.

Any help would be much appreciated.

Monty Dog

I'm afraid it's a new chainset - the rings on your chainset are bolted on with a pitch circle diameter (PCD) of 130mm which means the smallest ring you can fit is 38teeth - a compact chainset uses a PCD of 110mm to allow you to fit the smaller inner chainring.

redddraggon

You'll need a new chainset.

The BCD is too big for 34t chainrings. Smallest you could get with your current setup is 50/38 by swapping the chainrings.

How tall are you? How long are your legs? Are you comfortable with 175mm cranks?

geoff_ss

That's why I put an MTB chainset 44/32/22 on my new road bike. I actually use all the gears. When I had a 50/40/30 Mirage chainset I realised the 50 ring just wasn't getting any use.

Geoff

musto_skiff

I am 5'11" and have an 850mm inseam.

I am comfortable with the 175's but I don't really know any different.

On the cranks it says Shimano Ultegra and the part number is FC-6600-A and it's silver.

On the bottom bracket it says "DO NOT DISASSEMBLE" :?

Is anyone able to point me at the exact part(s) I need to order?

Also; are any special tools required as it specifies on the sticker at torque for the bolts?

Is this a job I can do (I like to tinker) or should I ask the LBS to do this?

Final question for now - will I have to remove and chain links and if so how many?

John.T

Any of the Shimano Hollowtech 2 Compact chainsets will fit. They are available from Tiagra up to the R700 which is listed as Ultegra/ Dura-ace. You need the tool to set the preload on the bearings and also you should use a torque wrench on the crank bolts. You did not hear this from me but I have had no problems not using one with care.

musto_skiff

Isn't there an actual Ultegra Compact Chainset?

John.T

Yes. Pt No FC-6650-S. Also for 10sp are the R700 and FC-5650 (105). Tiagra FC-4550 is 9sp. Check the Shimano web site for details.

musto_skiff

Thanks JOhn. I think I will ask my LBS how much to supply & fit ...

The only open issue is what crank length?

alfablue

Generally speaking people of average height tend to go for 170mm cranks for the road (higher cadence) and 175mm for mtb (more torque). You probably won't notice much if any difference between the two.

musto_skiff

Is there a decent detailed book that will show me how to change the chainset; I'm thinking I'd rather learn how to do it myself than keep depending on the LBS ...

redddraggon

musto_skiff wrote:

Is there a decent detailed book that will show me how to change the chainset; I'm thinking I'd rather learn how to do it myself than keep depending on the LBS ...

Zinn and the Art of Road Bike Maintenance

John.T

If you have no trouble with the 175 cranks stick with them. I have used 170, 175 and 180 in the past and don't really notice the difference. It just makes setting saddle height more complicated so now use 175s on all my bikes except the one I use on the track which has 165s. I only notice them for a short while.
Re changing the crank set the instruction sheet that comes with the cranks or downloaded from the Shimano site is quite good. Otherwise check out Park Tools site.

musto_skiff

When you order the bits does it include the bottom bracket?

Which parts in this diagram are the bottom bracket?

http://techdocs.shimano.com/media/techd ... 621039.pdf

John.T

The BB consists of 6,7,8 & 9. It may or may not come with the crankset. Check with the supplier. As you are already running this type of crankset you do not need to change the BB.

musto_skiff

John.T wrote:

The BB consists of 6,7,8 & 9. It may or may not come with the crankset. Check with the supplier. As you are already running this type of crankset you do not need to change the BB.

Thanks - that is what I though so all I need to do to change this is just undo and redo items 1 & 3.

Is that the case?

John.T

Undo both3. Remove the outer one to free off 4. Remove 1 and slide the crank off. Slide the RH crank assy out and grease and fit the new one. Fit the LH crank and tighten 1 to the correct torque (about finger tight with the correct tool) and tighten both 3 evenly to the correct torque. Job done.

musto_skiff

Nice one - I'll order the bits.

Thanks for you help; will I need to remove any chain links?

John.T

No more than one. Try it first, if the mech will take up all the slack when on small ring and small cog I would not bother. I have found that Shimano works best with the chain as long as possible.

musto_skiff

I got the LBS to do it in the end; having had a look at the parts they gave me of the old chainset seems a pretty easy job if you have the torque wrench.

I wonder if I will get out this weekend with the weather or perhaps I'll be stesting it out on the Turbo :-(