My friend Nikki tapped me up for some gear advice this week. She’s ordered her first gravel bike and currently owns a road bike and MTB and asked if the gears on her gravel bike were going to be low enough as she likes to spin them out on climbs? Hold my beer. Let’s do some gear math.
I thought I’d share my thoughts.
So to work out gear ratios, simply divide your chainring teeth with your sprocket teeth. So taking a road bike with compact gears (50/34T Chainrings + 11-34 Cassette) lets look at the highest gear first.
A 50×11 gear will be 50 divided by 11 = 4.55 meaning 1 crank revolution will turn the rear wheel 4.55 times. Nice and big.
Now the lowest gear. 34 divided by 34 = 1 so 1 crank revolution will turn the rear wheel once. It’s low but we need lower for offroad riding.
Remember those numbers and let’s look at MTB gears now. Here we’d expect to see the lowest gears so riders can tackle the steepest and most technical inclines.
Nikki has 1x setup with a 30T chainring and 10-51 Cassette. So the lowest gear will be 30 divided by 51 = 0.59. So 1 crank revolution will turn the back wheel 0.59 times or 59% or in another way nearly 2 crank revs per rear wheel turn. A very, very small gear as we’d expect to see right?
So now for gravel gears. I’d expect to see them lower than road and higher than MTB. So the lowest gravel gear should be somewhere between 1 and 0.59. Let’s have a look.
Nikki’s new gravel bike comes with a stock 40T Chainring and 10-46 Cassette. So the lowest gear will be 40 divided by 46 = 0.87. In the range we expected. However, as with road bikes, the industry, in my opinion, tends to overgear riders so a better setup for gravel, given the offroad nature of the bike would be to offer a lower gear rather than a higher so a 38T chainring would get the ratio down to 0.83 where I think the gravel sweetspot is. In comparison, my Dolan GXA 1x has a 38×42 low gear which is 0.90 and my Dolan GXC 2x has a 30×34 lowest gear which is 0.88. All in the same ball park. 30×34 is really low and I can get up anything on that fully-loaded for touring so I think my assertion the 38×46 on Nikki’s bike at 0.83 will be plenty low-enough for her is correct.
What are your lowest gear ratios on your bikes?
Prediction
You read it here first.
My prediction is you’ll begin to see 1x setups on road bikes soon. The industry got it wrong with compact. For most riders a 50T chainring is too big. They ‘think’ they need the biggest gears but, the truth is they don’t, they need lower, and spend a very small amount of time in the biggest. I’ve argued a 46T chainring instead is better before but with 13 speed cassettes beginning to drop and SRAM moving to 48T rings and 10 tooth sprockets, there has been a shift and it will continue. Riders will have enough gears to ditch one of the front chainrings and maintain a range of gears high and low enough for the riding they do now.
40×11 is bigger than 50×14 and 40×46 is lower than 34×36. It just seems a no-brainer to me. The pro’s are beginning to dabble with it and that will begin to trickle down.
One of the strongest, most experienced riders in our Club (just turned 79!) has built his own setup from scratch. He has a single oval front ring and a massive cassette. I don’t know the ratios at the back but his rear cassette looks like a MTB! Riders half his age can’t stay with him, he’s an engine!
Oops typo – he’s just turned 70 🤣
sounds like a mullet setup. MTB gears on road/gravel shifters. It’s a good idea as you can achieve quite high and very low gears on 1 chainring. At the moment my straightfoward, straight out the box 38×42 works fine for me though but it does intrigue me to have a tinker
it’s a good point however I’m not a SRAM fan (burnt by too many warranties when I had my bike shop and never got over it) so I’d have to fit a GOAT Link and probably go 11-50 on my GRX setup. Might try it though and see.
Completely agree with the industry over gearing on stock bikes, given that a lot of the market is driven by middle age to older potentially less fit riders.. IMHO go mullet if you do most of your riding off road, it’s easy and cheap to change chainrings as your fitness/ strength changes or if you have insanely steep climbs, and a 52 will get you up virtually anything! I’m currently on sram 10-52 cassette with a 44T chainring.
Thanks Paul. Just had to work yours out for my peace of mind lol. 44×52 = 0.85, so bang on the money!
Yes it gets you up the hills but just as important for me is that the 44T gives really good top speed so no spinning out which can be a real problem on say a 10-46 with a 38/40T ring.. but so much depends on riding style, fitness and terrain..
GRX 400 is one of cheapest options and its lowest gear ratio 30 X36 = 0.83 got me up all the hills of the Marcher Castles Way and KAW, with 46X11 = 4.2 for the faster bits.
Perfect!