1x gear ratios for new bike - bigger chainrings?

dirtyflyer

Hey folks. I've been doing what any biker who's hoping to soon be in a position to splash some cash does, dream and make spreadsheets!

I've been perusing the specs of new bikes as mine is now considered retro and isn't at all versatile. Rapid as hell on my local XC rides but take it anywhere challenging and it's, well, challenging (XC race geometry, 70° head, 100mm travel full suss, fixed seat post, 26" wheels).

The problem I'm seeing with all the trail bike offerings I'm keen on (Jeffsy, Spectral etc) is the gearing, it all seems too low. So I crunched some numbers to see how they stack up against my bike, and to see if I'd want to size up the chainring. Does the following logic stack up (assuming the same size cranks)?

Current drivetrain 3x9.
42/32/22 (the 42 is reduced from the standard 44 cos it's far more usable)
11/12/14/16/18/21/24/28/32
Top ratio 42/11 = 3.818
The lowest ratio I probably ever need is about 1, that equivalent to 32T chainring + 32T sprocket or granny + 21T sprocket. (demonstrating that 3 chainrings are pointless!)

If I look at the Spectral CF8 27.5 that is a 1x12 (10-51) with a 32T chainring.
If you factor up the ratios by the wheel size 27.5/26 you get default range of 0.664 - 3.385.
0.664 compared with the minimal of 1 that I need is crazy low, you'd never need it.
If I size up to the biggest XT single available which is 36 I get 0.747 to 3.808 (pretty much same top gear as I have now and would probably never use the biggest sprocket. Having a 11sp ranging from 10-40 would probably be nicer, finer steps.

Anyone done similar and changed the spec when ordering?

billycool

I've sort of done what you've done but split over 2 bikes.

My 2006 Stumpy HT was is the same boat as your FS. Quick XC bike but challenged on more techy stuff (XC race geometry, 70° head, 90mm forks, fixed seat post, 26" wheels). Also 3x9.

I bought a Brand X 650B HT frame for £80 and moved most stuff over (inc the 3x9). The 26" wheels rock! Just got some lovely 140mm Fox Factory forks to tweak the geomtetry and a dropper post. It's awesome.

As for the gearing. My FS is 1x11 and runs a 34T 11-42 (XT cassette). With that balance, I get the hill climbing gears that I need (did Afan this year) and also some sensible downhill pace. It will never have the top end that my 3x9 has and that is partly why I'm happy to leave the 3x9 on the HT as it does more road/path/track winter riding. The big ring is a great help in that respect.

If you can run a 36T and get much the same top and bottom ratios then go for it. I don't have the range in my rear cassette to do that, so a 34T works for me. I don't think a 32T isn't enough on any 1x setup. With 3x9 a lot of the gears overlap anyway and mine is really a 2x9 (don't use Granny).

I don't know what terrain you ride, but I would ensure that I had enough climbing gears and not worry so much about the top end.

From what you are saying, you should have a decent balance.

Steve Sordy loves his gear ratios - he'll be on soon to prove/disprove your theory. I just go with what works for me!

steve_sordy

Billy Cool knows me too well!

I'm not going to check your maths, but your approach is exactly what I would do. Your view about what is "crazy low" is interesting and entertaining at the same time!
You are correct to take into account wheel diameter, but don't forget crank length. By the way, wheel diameter is not as massive a difference as basic gearing maths would have you believe, as you will discover. The reason is that bigger wheels roll better and have a reduced torque requirement benefit just from that. It's not a simple calculation, but the benefit is about 3% per wheel size increase if my memory serves me.

I had an Eagle 12-speed on one bike and even the standard 34T ring driving a 50T rear on a 27.5" wheel wasn't crazy low enough for me. I had to put a 30T ring on (the smallest) before I could climb out of some of the bomb holes on my local trail. (ie 0.6 ratio). But for me it wasn't an issue of leg strength, I had that (or used to), it was about reducing pain in my knees to what was bearable (osteo-arthritis, better known as wear and tear). Once I found a better way of dealing with the pain I could get out of the same bomb holes with a 28 or a 32, close enough to your 1.0 ratio. Despite that, I didn't go back to a larger chain ring, just in case. I was right to be conservative because I had bad days now and then.

My advice would be to go for a 1x for the benefits it gives you: simplicity of shifting, less bar clutter, better location for your dropper remote, weight reduction, lower maintenance costs.... Just make sure that you have the biggest range you can get on the cassette, then choose a size of front ring that puts the ends of that range where you want them.

PS: It's nice to know that its not just me that looks at this stuff!

The Rookie

You do need to factor the wheel size, gear ratio isn't relevant, gear inches are.

A 27.5 (27" if a 26 is a 26") will lengthen the gearing by circa 3% for the exact same numerical gear ratios (and same width tyre), if it also has a bigger (wider and so taller as well) tyre (the Spectral is on 2.4) that could well go to 4-5% difference.

If you only need a 32:32 on a 26" then a 30F 32R or 32F 34R would be pretty much the same when you factor in the 27.5 wheel. However don't forget that with a longer travel and heavier bike you'll likely want to 'sit and spin' more than monstering climbs so may need to tend towards a slightly lower first gear.

While a narrower range cassette would seem logical, you can't do than as easily on a 12speed as you'll need to find a cassette that fits the new 12 speed freehub pattern, the only alternative I think is the 10-45T 'rhythm' cassette combined with maybe a size larger chainring.

You could go 11 speed with it's wider range of cassette options but would need a new rear wheel or freehub, mech and shifter but then that's a lot of money and you may be better off finding an 11sp bike as a starter.

robertpb

If you are looking at a jeffsy or spectral and you think the gears are too low for you then you are looking at the wrong bikes.
The pro riders of these bikes ride much the same gearing, a 38T is the biggest I've seen with a 10-50 but most ride on 30T to 34T.
I'm also sure that these riders have more power under the bonnet than you or I, the 38T is on Nino Schurter's bike and that's an XC bike not enduro.

thecycleclinic

Yes go with a bigger ring. I ha e the same issue with a 29er and a 34t ring is tok low on the XC race bike.

Witha 26" wheeled bike I'd go 11-40t cassette and a 38t ring. Garbaruk do rings that big.

dirtyflyer

robertpb said:

If you are looking at a jeffsy or spectral and you think the gears are too low for you then you are looking at the wrong bikes.
The pro riders of these bikes ride much the same gearing, a 38T is the biggest I've seen with a 10-50 but most ride on 30T to 34T.
I'm also sure that these riders have more power under the bonnet than you or I, the 38T is on Nino Schurter's bike and that's an XC bike not enduro.

Yeah but taking the 29" wheels into account that's a bloody high top gear, relative ratio 4.24, even higher than my old 44T big ring. So it's not apples with apples, I'm not that keen on a 29er and I'm only suggesting 36T on a 27.5.

robertpb

dirtyflyer said:

robertpb said:

If you are looking at a jeffsy or spectral and you think the gears are too low for you then you are looking at the wrong bikes.
The pro riders of these bikes ride much the same gearing, a 38T is the biggest I've seen with a 10-50 but most ride on 30T to 34T.
I'm also sure that these riders have more power under the bonnet than you or I, the 38T is on Nino Schurter's bike and that's an XC bike not enduro.

Yeah but taking the 29" wheels into account that's a bloody high top gear, relative ratio 4.24, even higher than my old 44T big ring. So it's not apples with apples, I'm not that keen on a 29er and I'm only suggesting 36T on a 27.5.

So I answer your post about too lower gears and you've come back about too higher gears. The bikes you have quoted come with those chainrings because for the intended purpose those are the gears you'd use. If you put a 36T on a Spectral it means you would not use it to its full potential as it tells me that it would be used on more flatter trails, unless you are pushing out watts like a pro.

larkim

You're either superhuman fit or not riding challenging enough uphills if 32x32 is the lowest gearing you'd need on terrain that is MTB relevant!