adlai

I'm contemplating an advent build. They have really wide cassettes that go down to 42t.

On a double, you could have a front crank that is smaller in diameter than the rear. Like 30-42 ratio.

Is that useful? Or below a certain point is it pointless to have?

BoraxKid

The only limitations for what you can build are the capacities of the derailleurs involved. If you have 46-30t chaingrings in the front, and 11-42t x 10 speed cassette in the rear, you would need a derailleur system with 47 tooth capacity. My touring bike has a rear derailleur that can handle this, but 47 tooth capacity is the largest I have seen for sale. Of course, there will also be a limit to what size large cog a derailleur can handle, as going too big will cause interference with the derailleur pulley wheel.

For the front gears, you need to make sure the derailleur can reliably handle whatever jump is between the chainrings. Usually the manufacturer will tell you the limits, but I've never seen one that can reliably handle more than a 16t change. Here's a calculator where you can play with your planned setup:

Bicycle Gear Calculator

One more item: your low gear (30x42) would give you about 20 gear-inches, which is very useful for exceptionally steep climbs and/or climbing with a load.

mstateglfr 

Advent has just 1 fd option, i think. So that better fit whatever your setup is.

As for the general question, yes a sub 1:1 ratio can be useful. Its standard on mountain bikes and standard on almost all gravel bikes.
My gravel bike is 48/32 mated to 11-36 and while I don't spend much time in the 32/36 combo, it does get used on some of the punchy 12-16% grade climbs I ride.

Maelochs

I have an old Cannondale touring bike with a 48-38-28 triple and a 14-34 cassette. When the load is large, the day is long, and the hills are seemingly endless, all that matters is not falling over as you creep along.

If I were doing serious mountain touring fully loaded, I'd consider a 42-32-22 triple.

HTupolev

Depends on your legs and the hills you're riding.

I have sub-1:1 gears on my gravel bike and my touring bike, and they definitely get used.

martianone

I use 30/36 often on my mtn/pasture bike. Often difficult to avoid "organic bumps" on pasture paths, need low ratio to not spin on them.

Chuckles1

Never had a gear too low to use at some point. 700c tire bike below 0.8 gear ratio might be too slow to stay upright without spinning mightily... 3mph gets a little shaky.

Elvo

Definitely useful to have options

phughes

Extremely useful, if you need it. I have a triple and the lowest I have is 24 to 34. Of course mine is a touring bike, and is often loaded, and I live in a very hilly area with hills near my house with 20% or greater grades.

When I commuted in the Ozarks, I would go downhill at 40-45mph, and up at around 3-4mph. I was happy to have the 24-34.

HTupolev

A 25mm 700c tire on a .8 gear ratio is about 4.5mph even when you're down around 70rpm. You wouldn't drop below 3mph until your cadence drops below 50rpm, which is low enough that most people would be wanting an even lower gear.

CAT7RDR

I admit to using a 24-34 combo riding up to the Ski Lifts on Mt Baldy Rd on my MTB. So yes, 15% grades makes a triple come in handy.

pdlamb

Somewhere below 20 gear inches it's better to walk -- easier than trying to stay balanced, and uses different muscles.

Less that 1:1? Oh heck yeah. What you don't have in your legs you need to have in your gears.

Phil_gretz

Touring.

cyccommute 

I have a 0.56 (20/36) on my touring bike (15.1”) and on a couple of mountain bikes (14.6”). Riding at 3 mph isn’t that difficult. If you know how to track stand, it’s easier but it’s still not that hard to ride very slow.

LV2TNDM

This question depends on your riding. Are you really fit? Do you live in a hilly location? Do you prefer to spin higher cadence? If you're regularly on really steep terrain, then going lower than 1:1 on a road bike is definitely in order.

I'm just about to modify my road gearing. When I was racing, going from a 42T small ring to 39T was such a luxury. I did fine in the hilly east bay area with a 39-23. Well, let's just say things have changed! My current 39-25 is fine for the flats and mellow climbs, but not what I need to get over the real hills encountered regularly. Plus, spending so much time on 3 X 8 or 9 means my cadence has increased since the 39-23 days. So I'm hoping the spare parts I have can accommodate my needs of getting my old 8-speed setup more ideal. Hoping a 39-32 will be enough. (It won't for the really steep stuff, but I'm not planning on climbing walls on this bike a the moment. That's what the bikes with triples are for!)

But switching the rear 8-spd to a 12-32 will mean fewer ideal gear ratios when I'm on the flats. I know I'll miss some of the gears I currently appreciate now. But if I want to climb more comfortably on my old road bike, this is the compromise I'll have to accept. I am NOT going to 10 or 11 speed. Nope, my '89 SLX road bike is a treasure and I'm not "Frankenbiking" it. Just a little optimization, gearing-wise.

rydabent

Not a problem on a trike.

Really low gears on a loaded touring trike ensure that you will never have to get off and walk. Walking a trike sucks, or a bike for that matter.

rydabent

What you lowest gear inches are is pretty much dictated by your terrain. While my riding is pretty much not very hilly, my lowest is a 28 front 34 rear. As the Boy Scouts say----------be prepared.

Pop N Wood

I use my gravel bike for touring. It doesn't go below 1:1 so I am seriously considering dropping $150 or so on a new crank to make it do that.

Have to agree with the others below a certain range you are better off walking.

Canker

Better off walking BAH!!!!! Maybe it is because I'm mostly a mountain biker but the whole point is making up the hill on the bike.

Maelochs

On walking---trying to balance a heavily laden touring bike while pushing it up a steep slope is a Very annoying exercise. Balance is automatic while riding---and the faster one goes the more centripetal acceleration and/or gyroscopic effect help keep it upright.

Standing beside it, trying to to get hit by the pedal or the pannier while pushing a big load up a steep hill .... the slightest deviatio0n from pure vertical demands attention, and the slightest overcorrection leads to an oscillating feedback situation which forces the pusher to grab the brakes to catch the bike.

Better to ride up at 4 mph than to push up at a quarter that speed.

pdlamb

Oookay. Did I mention I know from experience the speed at which my cyclometer stops registering movement while slowly climbing? When I'm going that slow, getting off and walking a few hundred yards lets me use different muscles, and I'm not losing any speed by doing so. I've still got another 50 to 150 miles that day to enjoy riding.

phughes

No it isn't. Many of us use a combination that results in sub 20 gear inches very successfully. I am much happier climbing a hill at 3.5 mph than I am trying to push a loaded bike uphill. My lowest gives me 17.6 gear inches, and I have used it a lot, and wouldn't even want to go back to the 26 I swapped for the 24.

Trust me, it is easier to stay balanced on the bike while riding it, than it is to balance the fully loaded bike pushing it uphill.

pdlamb

Maybe a few dozen can ride more than a quarter mile at less than 2.5 mph. Or can you name even 100?

Maelochs

Back when people still gathered, I rode sweep for a 5K charity walk/run, which meant I had to ride slower than the slowest walkers. It got challenging at times, but the speeds were down around or below the speeds being discussed here and never had to unclip (nor did I fall over while clipped in.)

If someone can devise the rules and testing methods .... start a "Sub-3 mph quarter-mile challenge." it would be the only race I could ever win. Make the purse big please .... a good way would be offering all the people who say it is impossible, 2-to-1 returns on their donations if no one won. It's a safe bet.

HTupolev

If the "winner" was whoever completed the quarter-mile in the longest time without going backwards, it could still end up being a very challenging endurance event with a strong field. Some folks are obnoxiously good at trackstands.