Fit Recovery

Home » 2013 » July » 09

Daily Archives: July 9, 2013

A Cycling Noob’s Guide to Choosing Shifting Ratios…

I’ve often contemplated the best gearing for my road bike.  I’ve currently got a triple on my 5200 that I love in the mountains but hate on my normal Tuesday club ride.

So, in the next year I’ll be either trading my 5200 in and buying a Specialized Venge, Roubaix, Trek Domane or rebuilding my 5200 – including a new paint job and new 10 sp. Ultegra components (everything, shifters to derailleurs to crank).  Either way I decide to go, I want to have as much reasonable versatility built into a double drivetrain as I’ve currently got in my triple.

The one thing (and there is only one) that I hate about my triple is that it cross-chains like a bear in the big ring once I pass the middle gears on the cassette. I can get into the 23t and 25t cogs but the chain will skip on both so I often end up riding in the 42t middle ring because I can hit all of the cassette gears and many of the easier gears in the big ring are close to the same ratios as the middle to smaller gears when I’m on the middle ring.

So here’s the conundrum… I love riding in the mountains.  We’re vacationing in northern Georgia again this year and the climb to the house we stay in is north of a 20% grade. I wasn’t strong enough to climb it in the granny/granny gear last year (my goal is to crush it this year)… With the new drivetrain I’ll want to be as close to that 30/25 ratio as possible.

There are a few options here but the one that gives me the best of both worlds is a double – the only question is do I go compact or standard and which cassette do I choose… This gets tricky.

First, I check my current setup on Sheldon Brown’s gear ratio page (selecting my current triple (52/42/30) and cassette range (12-25), 172.5 crank and mph@90 rpm cadence – to keep it simple).

I’ve got a top speed of 30.5 mph and a low end speed of 8.4 mph in the granny/granny gear. The surprising thing is just how many gear ratios in there are duplicates, or close to it – there’s a lot of overlap.

Now, I can go with a classic/modified double (52/39) and if I choose an 11-34 10 sp. cassette, my top speed jumps to 33+mph and my low end speed drops to 8.1 – this appears to be the best option right off the bat – but hold the phone… I like to ride at or near 21 mph (give or take) for my regular training rides. With this setup, I’ve got one gear that gives me 21.4 but each cassette cog has to jump by two teeth per gear to make the 11-34 spread. Going with an 11-32 is no benefit either because the only cog that changes is the granny gear. Still, this is an appealing option.

If I look at a compact double (50/34) with that same cassette, the top speed only drops to 32 mph but the bottom drops to 7.1 – which I like for the mountains. Unfortunately the hole at 21 mph, where I normally like to ride, is huge! I’d have an 18.4, a 20.7 and a 23 mph gear. I don’t like that one bit. If I go to a 12-25 cassette, my large hole in the 18.5-23 mph range closes up tightly but my low end speed raises to over 9 mph… Possibly too tough for the steepest climbs I’ll see. A 12-27 cassette with a compact double though, now that raises my low end to 8.9 and lowers my high end to 29.3 mph but the 20 mph hole is fixed.

So let’s try a classic modified double (52/39) and a 13/29 cassette – low end is too high (9.5 mph) and the high end is too low (28.1 mph). That definitely won’t do…

In the end, if I want an overall setup that does everything my current triple does, only with a greater range, the logical choice is a 52/39 double with an 11-34t cassette.

If, however, I want to be clever, I could get the compact double 50/34 and two cassettes, one for home (11-23t) and one for the mountains (11-34t). The home cassette would give me almost any gear I could need to climb hills around here (I’ve never used the 30t small chain ring in Michigan – only the 42t middle ring) while giving me the perfect stretch of speed gears for my club ride… and the 11-34 cassette would be excellent for the mountains, giving me a granny gear that I could use to climb almost anything but a sheer face.

Now all I have to do is run that by Matt at the shop to make sure I didn’t make any stupid assumptions or mistakes.

So why the consternation over the crank and cassette? My current setup, 52/42/30 crank and 12-25 cassette is great but I really hate that cross-chaining triple. Back when all we had was seven and eight speeds they were great and even necessary. A triple on my ’90 Cannondale seven speed would be great because with a racing double (52/42) and the largest cassette cog at 23t, that bike is rough on the climbs. If that bike had a triple, I could take it just about anywhere. With the newer 10 and 11 speed cassettes there are enough gears available that the triple chainring is all but obsolete for road cycling.  However, when it comes right down to it, going with a double, compact or not, still leaves a few holes – and thus the reason for this post…

I’ve got enough experience now that I can walk into my local bike shop and say, “okay here’s what I want…  I need a normal flat Michigan cassette that gets me a few decent climbing gears but better options right around 20 mph (preferably 1 tooth increments on the cassette), then I’ll need a cassette that I can take to the mountains.”  When we’re noobs, the tendency is to take what we’re given until we get that experience and can narrow down exactly what we need.  I don’t have an easy answer to this, I don’t think there is one.  For me, I found my favorite speeds (around 19-23 mph and I’m going to get the gears to match that so I can keep an easy 90 rpm cadence in the big ring for my next bike – and then add an option to switch cassettes when I head down south.