best compact gear ratios?

billholding

I am currently building my first bike, and am about to order a Campagnolo 2007 Mirage 10 Speed double compact groupset, which requires me to make a few decisions. As far as the crank arm length goes i am going to go for 172.5, and with Mirage Ultra-Torque double chainset 34/50 10 speed chainrings. I need to now choose the rear 10 speed cassette, and my choices are:
12/23, 12/25 or 13/26 sprockets.
I could do with some advise on which to go for, so any help would be much appreciated.
The end result is going to be a hybrid for use (primarily) commuting in London, so mainly flat, but with the need to take on hills when i head up to North London.

gavintc

Sadly, it is extremely difficult to provide accurate advice on gear ratios on a forum. Gears are a function of fitness and strength. If you have spent the last 10 yrs with the most strenous activity as lifting a glass of Guiness, you will need some seriously low gears. Equally, if you are reasonably fit and have played a modicum of sports throughout your life a ratio of 12/25 with a 34-50 will suffice.

billholding

Thanks for the reply, and i appreciate what a mine-field such a request could be! I think i will play it safe and go middle of the road with the 12/25, as i have been cycling in around London for years, and it is my main mode of transport, so i'm not too couch potato, but at the same time, i'm certainly no Lance Armstrong! I guess if i feel they aren't right changing the rear cassette isn't going to break the bank! My main concern isn't so much the up hill, but running out of gears down hill, which i found when i first started cycling around London on my mountain bike! As i am building one from scratch i just want to try and get it as right as possible from the off.

gavintc

From your description of your experience, I reckon that the 12-25 will provide you with a reasonable range. Remember, many people do not appreciate that an effective cycling cadence (the speed that the pedals go round) is actually quite high and you should aim to be spinning at 80-90 rpm. If you are achieving this, the 50-12 ratio will allow a reasonable top speed. You may find in time, and as you get fitter, that you would want to replace the compact with a normal chainset, but having a 34-25 is a useful insurance policy for the occasional steep stretches that we all come across.

nun

<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by billholding</i>

I am currently building my first bike, and am about to order a Campagnolo 2007 Mirage 10 Speed double compact groupset, which requires me to make a few decisions. As far as the crank arm length goes i am going to go for 172.5, and with Mirage Ultra-Torque double chainset 34/50 10 speed chainrings. I need to now choose the rear 10 speed cassette, and my choices are:
12/23, 12/25 or 13/26 sprockets.
I could do with some advise on which to go for, so any help would be much appreciated.
The end result is going to be a hybrid for use (primarily) commuting in London, so mainly flat, but with the need to take on hills when i head up to North London.
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">

The difference in gear inches you are talking about is pretty small, and for most of your riding I bet you'll be in the middle of the range anyway. I'd go with the 12/25 see how it feels and its an easy change if you need to adjust stuff.

I've always liked messing about with different ratios on my bikes, but after riding single speed for the past few years I find that
I'm much less inclined to worry about what's on my geared bike as I
ride 80% of the time between 65 and 75 gear inches which is a good range for travelling between 15 and 20 mph

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<i>42x16 works for everything</i>

billholding

thanks for all the advice, can't wait to get it all sorted so i can ditch the mountain bike, which isn't ideal for central London!

Cheers

monty_dogcp

12-25 is ideal compromise - it would get a reasonably fit rider round the Surrey Hills and beyond and yet is plenty fast enough to race on. I was over in Belgium riding a sportive in the Ardennes and we were lining-them-out at 55kph on some flat stretches riding 50x12. I doubt there's many downhills in the smoke that you could safely ride that fast without encoutering traffic or lights.