Teeth

[Phil H]

I gather that it's possible to purchase 59/39 tooth chainrings for a compact (110mm BCD) Shimano chainset.

Has anyone done this? Is there any reason why it's a bad idea - for instance if you are massively powerful? Also, who stocks them?

I was following a car down a hill on Saturday afternoon and it was getting very spinny on 50/11.

[Dan_K]

What is your current setup Phil? 50/34 11-25?

As I understand, the limiting factors are the length of the rear derailleur and chain length.

[George]

I wouldn't worry about it Phill you've to to have massive power first

[Phil H]

At first it was 50/34 and 12-27

Now it's 50/34 and 11-25 (needed the 11 for TTs).

Wanting 53/39 and 11-25. So the chain length and rear mech should be OK (if not, I have a spare chain). I realise I'll probably need to move the front mech up a notch.

That way, for stupid sportives I can put the original gearing back on.

[Phil H]

George: with my weight, I need massive power to move at all.

[Dan_K]

I've got a similar situation where i'm running a 50/34 12-27 and am spinning out so i've just ordered the SRAM 11-28 and will see how I get on with it.
Still need the 27 for when I go up north to the in-laws but shimano want over £100 as they don't do a 11-27 in 105 yet and the SRAM was only £35.
The 28 may come in handy for when i'm feeling really lazy

As i'm only running one bike at the moment, i need it to be able to cope with everything.

Phil, when you say spinny, what kind of cadence were you doing?

[Phil H]

I think I paid £54 for the 11-25 Ultegra. It only takes a couple of minutes to swap to the 12-27 for stuff like the Black Mountains. Swapping chainrings should be fairly quick too.

Not sure on the exact cadence as I wasn't recording and I was watching the car in front carefully. I saw about 116rpm at 40mph though. Maybe I should convert the steel bike to fixed and get spinning.

[Dan_K]

How much faster do you need to go

Doesn't there come the point when you think, "that'll do"?

I can understand the 11 tooth as on the CG I feel i've got more to give but am limited with a 12-27 but I think when I get the situation when i'm drafting a car at 40mph, i'll just enjoy the moment and let gravity do it's thing.

I suppose it'll only be a matter of time before i'm riding behind you one minute and the next there's just a burning tyre mark like in Back to the Future.....

[Phil H]

The reason I put the 11 tooth on is that on the TT's, it was getting a bit spinny on the downhills over 35mph. Even with the 11, on the SCCU 25, I was hitting 38mph with a cadence well over 100. A bit more would be useful there.

Of course what I really need is a TT bike, but that comes with a (non-free) divorce.

[Antloony]

I run a 50/34 compact with an 11/23. I occasionally spin out, usually when sprinting, but don't feel like its a major problem as I rarely need a bigger gear as I'm not very fast

[Marek]

I moved to a compact at the end of last year for my racing bike as I was doing a lot of sportive type riding. With the 11 on the back I don't think I need too much, although can imagine that on time trials with a fast dual carriageway it may be more comfy to ride a slightly slower cadence. From what I have seen it might be cheaper for you to actually just buy a spare chainset than buy the rings separately as they seem to be about the same price. Look out for bargains on some of the usual suspect sites like Ribble, Parkers or even GB's (I got a great deal on a Centaur compact from them). Much easier to just swap over the chainset and make the change to the chain size and then move the mech about a bit.

Cheers

Marek.....

[Andrew G]

No reason why you can't swap chainrings around although you'd have to change chains too for one with the correct length, however I'd go the route Marek suggests. Scout around the sales for a spare chainset to switch on and off which will be easier. You'll also want to keep chains running with the chainrings/cassette(s) so you may have to swap chains more regularly.

I think on Shimano you can run up to a 27 sprocket on the shorter cage and a 39/27 is a pretty low gear so you may find that apart from very hilly rides like sportives you'd prefer to stick with standard rings (53/39) and vary cassettes from a close ratio for TTs to a wider spaced for everyday riding. Cassette swaps take minutes.

What's your preferred gearing? I don't like compacts, the gears or their spacing so only tend to use a compact for very hilly/mountain rides but different folk like different things.

A final option is to fit a triple with a 53 big ring and a 40 or 39 middle and a 32 inner and just run a 11-23 cassette. More weight and bigger Q factor, I don't like them, but again you may find it works for you.

[Phil H]

Well, I reckon n if the chain fits 50/27 it'll fit 53/25. Probably. If not - spare chain.

I don't like the massive jump from 50 to 34 either really but it's handy for hilly sportives. In normal use, I don't use the 34 much these days. When I do, the 11-25 cassette is sufficient for all but the maddest mountains.

I have the tools (allen keys) to switch chainrings and a cassette tool. I don't have the gear to switch whole chainsets though. I figure if I have two cassettes and four chainrings, I'll be able to set the bike up for anything from the ToBM to an evening 10 in a few minutes.

So, back to the original question: 53/39 chainrings on a 110mm BCD spider. Sensible thing or not?

[Andrew G]

You really want to fit a chain based on small ring small sprocket and then when run through the cage you'll have a small gap between chain running under top jockey wheel and chain returning to the chainrings. This should give a cage angle of about 45 degrees when in big ring big sprocket combo, although you don't really want to run big ring big sprocket when riding as you're stretching out the chain and cage to their limit.

Original question, I don't see why you can't as Contador ran a ridiculous 53/34 chainring set up in the Vuelta stage which finished on the really steep mountain, the name of which escapes me at the moment, which has 25 percent sections and a lot of it above 18-ish degrees.

[Dombo]

On a 53/11 at 120rpm you'll be doing 47 mph, on 50/11 the speed drops to just under 45 mph. I don't know at what point one would consider the cadence to have spun out, maybe 130?