Road Bike Gearing

rflynnr

Apologies for possibly restarting an ancient thread but...

I'm switching from my beloved but (as it turns out) one frame size too big Kinesis roadbike to a Trek 1500. The Kinesis ran 52/42 front cranks and a 12/25 rear cassette. The new bike has a 53/39 front crank and a 12/27 cassette (originally a 12/25 but I asked for the other to be swapped out). I raise this to ask whether I can expect to feel like I've effectively got two extra lower gears as a result of the combination of the smaller front crank and the larger rear sprocket. (The bikes are both aluminium and approximately equal in weight so I don't expect to gain much there.)

I ask because although I try and get out once a week on the road bike I'm perhaps not the strongest cyclist. (Most of my cycling is commuting.) I can go up Howth Head (north face) and Sally Gap without pausing but there are moments on both climbs where I'm gagging for an at least one additional low gear.

I'm reluctant to go the compact route because the standard 34/50 setup is probably going to leave my legs spinning uselessly on real descents and the triple option - assuming I can find one with a 53 big cog - will add significantly to the purchase price. That said I have ambitions in the direction of the Wicklow 200 next year and I'm wondering whether I'm simply storing up trouble by not going the compact/triple route from the off.

Any thoughts or experience would be welcomed.

Morgan

rflynnr wrote: »

ask whether I can expect to feel like I've effectively got two extra lower gears as a result of the combination of the smaller front crank and the larger rear sprocket.

You've got several lower gears by the sound of it, 39/27 is a way lower gear than 42/25. You can work out all your ratios here:
http://www.sheldonbrown.com/gears/

You shouldn't need a triple/compact for Wicklow - 39/27 is a comfortable climbing gear. You have about 10 months to train for the Wicklow 200 so I expect you'll be fine.

doozerie

There are several ways of calculating gear ratios, but I still rely on the old "gear inch" method. You multiply the diameter of the wheel (about 28.5" for a 700c wheel) by the number of teeth in the front chainring and divide by the number of teeth in the rear cog. It just gives you a means of comparing different gear ratios between gears and between bikes.

On your "old" bike your highest gear was 123.5 and your lowest gear was about 47.9. On your new bike the top gear, assuming the same size wheels, is 125.9 and your lowest gear is 41.2. Basically your new bike has a significantly lower gear - if you have a 23-tooth cog on your new rear block then that is about the equivalent of 1st gear on your old bike. If you could get up Sally Gap on your old bike, then the gearing on your new bike is likely to be more than adequate for you.

blorg

You may well not need a compact but I certainly wouldn't rule it out on the grounds that you will be spinning out on long descents, it really doesn't make that much difference. I have a 50 front ring on one of my bikes; hit 89km/h coming down Lugalla on this year's Wicklow 200 and don't think if only I had a 52/53 I would have been going any faster. Bear in mind also with a compact that 50-11 is a bigger gear than 53-12 so you always have the option of an 11t cassette if you really feel you need it (but you do not, take it from me ) There are other benefits to a standard double but this is not really one of them.

Howth means nothing as an ascent if training for the W200, it is simply too short. Sally Gap is a better test but it is still only the first climb. Ideally, given the length of the W200 to come after, you want something that will get you up Sally Gap comfortably. You may not "need" a compact for Sally but you might appreciate it on Slieve Maan!

I have a triple and while I may not "need" it I don't feel it diminishes my masculinity in any way and while I don't use it that often any more there certainly have been times that I have been glad of the granny ring! There is no particular glory in being able to mash big gears if you are overtaken by someone spinning. Will probably go compact on my next bike myself; I could go for a standard double but it would not have compelling advantages for me over the compact.

EDIT: Having said all of that above 39-27 should be an OK gear to climb most stuff you will encounter if you do go for the standard double.

niceonetom

sheldon compares. actually i've attached a word .doc that i made for like for like comparisons when i was making a similar decision to yours...

there's a fair amount of posturing that goes on around here whenever compacts and doubles are raised. personally, i don't really think that anyone needs a full race double unless they are a competitive club cyclist. i have a compact and with an 11 tooth cog if you're "spinning uselessly" with that you're probably going over 70kph. stop pedalling and concentrate on your tuck :P. as for climbing, well i think i'm better of with the 34 ring and a 23 or 25 cassette than a 39 ring with a 27. why you ask? well i've found that with a big cassette the jumps between gears at the climbing end a are so far apart that you loose an awful lot of momentum with each gear change.

as blorg points out, you get no bonus points for mashing a big gear, indeed i've passed many a man grinding away at his race double, especially at the w200.

doozerie

There seems to be a perception that people avoid tripe and compact chainset because they are seen as less manly. That may be the view of some, but I think they are the minority. Personally, I see no advantage to a triple on my road bike (wouldn't be without it on my mountain bike though), and in fact I would find that it made finding the "right" gear more awkward - due to the fact that I avoid crossing my chain excessively, I don't use the inner half of the rear cogs while on the big ring, the outer half of the rear cogs while in granny ring, and the 2x innermost and 2x outermost rear cogs while in middle ring.

When I compared the figures for usable gears on a triple versus a double, in the past, my usage of a triple left me with the same number of gears but with more changes on the front chainset to reach some of them than I would have to do on a double (and therefore more awkward). I would have gained a lower first gear with a triple but with my style of riding my existing double provides a low enough first gear anyway and with a small and consistent jump between gears.

As with most things, which option is most suitable depends on personal taste amongst other things, but for me there are technical benefits to a double too (whether a standard or a compact).

cantalach

Seeing as you're aiming at the sportif scene rather than racing, I'd wholly endorse what blorg and niceonetom have said. Go compact with a 12-25 on the back and it'll get you up virtually anything you'll encounter in Ireland. If you are worried about not being able to power down a decent go for an 11-25 (but this isn't an issue very often in Ireland as most of our decents are too narrow, too twisty and too bumpy).

rflynnr

Phew! There's a fair bit to take in there and thanks to all for their advice and in particular the details on gear ratios which puts the differences between cogs in a more comprehensible light. I don't think my preference for the double was informed by posturing (although this may demand a moment for introspection) but rather that I've been offered what I think is a pretty good deal on an existing bike (full ultegra groupset - bar the hubs - on a 2007 Trek) and switching cranks (and therefore derailleur and shifter) would be expensive. On the other hand I ruled out the W 200 this year on the grounds that I knew I wasn't capable of doing all three of the big climbs on my existing setup and there was little point in moving to a bike that left me still unable to take them on. In truth I realise I wanted to hear that the double standard ring with the 12/27 was fine but I'm hearing that it may not be. Given this I think I'll revisit the triple option.

I stick by the spinning out thing though - as it stands even coming down the south face of Howth in the highest gear (my most common cycle) I'm hard pressed to keep up with the pedals (which suggests the tuck isn't a problem?) and I seem to be maxing out at about 65-70kph. Indeed the fastest time I've ever recorded (76kph) was on a heavily laiden hybrid whilst touring where weight and gradient did all the work.

Thanks again gents.

rflynnr

Actually on reflection - if I did go the compact route is it likely I could retain the existing front derailleur and shifter?

niceonetom

rflynnr wrote: »

Actually on reflection - if I did go the compact route is it likely I could retain the existing front derailleur and shifter?

almost certainly - and you raise a very good point. what's the groupset your starting with?

it's much easier to switch between doubles than to go from double to triple (or vice versa). some shifters are agnostic (ie double or triple compatible) some are double specific. samw goes for dérailleurs.

unless you're talking camag, in which case i'll let someone else deal with this as i haven't a clue about that italian stuff.

cantalach

niceonetom wrote: »

unless you're talking camag, in which case i'll let someone else deal with this as i haven't a clue about that italian stuff.

He was talking about going to Ultegra so it's most likely some other Shimano already on it. But in case he's not...the older Campag (before Ultra-Torque) used to have different front mechs for traditional and compact. They've dropped this distinction from the new range though.

Raam

OP, I used to be in your boat, as I bought my bike with a 53/39. I thought long and hard about going for a triple or a compact because initially I found the hills tough. In the end I was advised just to swap my 12/25 for a 12/27, which I did. I'm glad I took that advice, because it gives plenty of range.

rflynnr

Yeah, it's Ultegra brakes and front and rear derailleur so it sounds as if that does make a switch to a compact relatively painless. I'll ring the bike shop again...