It’s a lot easier if everyone uses the same system to compare one bike with another.

Which is a higher gear, 32×19 or 34×20 ?
32×16 on a 26er or 32×18 on a 29er ?
It’s not immediately obvious is it ?

Convert it to inches and you get 48.8″ or 49.3″
52″ or 51.6″
What could be simpler ?
For those who don’t know, it’s the distance travelled for each crank revolution. The higher the number, the further travelled, the higher the gear.

http://sheldonbrown.com/gears/

singlespeed in gear ratios
fixed wheel in inches

always. don’t know why though?

Because not everyone is an Internet dwelling bike geek.

I don’t know.

I was trying to explain to someone who had a compact (50/34) chainset and 12-25 cassette that they would get more bang for their buck on a £40 11-25 cassette than spending £150 on a double 53/39.

They didn’t want to buy both, and “A double has got bigger gears than a compact…”

Singlespeeders are too lazy to calculate their gear inches, so they just tell you what ratio they have because they can read that off the packaging of the chainring/cassette.

Some people live in the real world, not in a 1930’s shed dreaming up new gear combinations.

but then there are gain ratios, which include crank length and being dimensionless are superior.

If you told a noob how many inches they would still have to work something out. If I say 32 :16 they go thanks if I tell them inches I still need to explain a lot of stuff.
32:16 is much easier though I get your point

I thought someone would have spotted the mistake in my first post where I got gear inches and metres development mixed up. 😳
Gear inches is the equivalent wheel size with direct drive and dates from Penny farthing days.
Metres development is the distance travelled per crank revolution.

So, 32×16 on a 26er is a 52″ gear, which means one revolution of the cranks will move the bike the same distance as one revolution of a 52″ diameter wheel.
32×16 is also a 4.1m gear, meaning the bike will travel 4.1 metres for each revolution of the cranks.

“Singlespeeders are too lazy to calculate their gear inches…”

“…if I tell them inches I still need to explain a lot of stuff.”

I think that’s about it, although people who can’t be bothered to learn are missing out.
Apart from the confusion of different wheel sizes affecting gearing, there’s the option to fine tune your gears by understanding the numbers.

32×18 a bit high, but 32×19 a bit low ?
Once you know that 32×18 is 51.5″ on a 29er and 32×19 is 48.8″, you can see that 34×20, which is 49.3″, is an option.

Got to love the way the bike industry combines metric and imperial measures at random…

If you’re being a real bike geek don’t you have to correct it for tyre size?

i.e. a 2.5 width tyre will give you a larger inches measurement than a 1.8 for the same gear ratio because it is taller

Got to love the way the bike industry combines metric and imperial measures at random…

most industries to be fair. oil and gas (pipes) seems to be the worst. decimal inches! wtf.

If you’re being a real bike geek don’t you have to correct it for tyre size?

i can feel the difference between tyres.

For those who don’t know, it’s the distance travelled for each crank revolution

That’s not how I understand it. I thought it was the equivalent diameter of the wheel, i.e. 32×16 on a 26″ wheel is the equivalent of a 52″ diameter wheel.

Edit: Doh, just spotted your post further into the thread correcting yourself

igm, that’s the only reason I got into the whole gear inches thing: my ratio’s 76-odd with 28c tyres, nearly 84 with not quite-2-inchers

It’s not just the bike industry, cars use 185R13 tyres for example.
A lot of bike measurements seem to be left over from the old imperial days, 7/8″ ‘bars or 1 3/8″ BB threads.
ISO caliper mounts are a fairly recent idea though, and yet they went for 51mm rather than 50mm. Could it be that they are actually 50.8mm (2.0″) with 0.1mm clearance on the bolt holes ?

If you look at the drop down box for tyre size on http://sheldonbrown.com/gears/ it gives various tyre widths as well as diameters.

Well one of the issues you have is that a 29er actually has a 28.5″ tyre (if you’re using a standard 2″ tyre which makes for a 26″ tyre on a 26er).

Hence in reality your measurements should be 48.0″, 48.5″, 52.0″ and 50.7″ (ie your 29er 32/18 isn’t as near to 32/16 on a 26er as you think).

Also what igm says.

ISO caliper mounts are a fairly recent idea though, and yet they went for 51mm rather than 50mm. Could it be that they are actually 50.8mm (2.0″) with 0.1mm clearance on the bolt holes ?

Something designed by the septics – they don’t do metric (or make a mess of it if they try)

If you’re being a real bike geek don’t you have to correct it for tyre size?

I was wondering when the whole issue of tyre sizes was going to crop up! It makes much more of a difference than people would think…

Because not everyone is an Internet dwelling bike geek.

True… But some of us sadly are! 😳

Anyway, for ANYBODY who wants a FREE copy of my gearing calculator (I created it for all the various popular Internal Geared Hubs but you can bastardise it to your hearts content) that is actually much easier to use than Sheldon Brown’s (mainly cos it’s actually an Excel file), then please drop me an email (in my profile)… I’ve not messed with it in over a year, so any feedback and recommendations welcome.

MTG, I know you use a Rohloff, did you ever get my IGH calculator in the first place?

Yes, I remember you sending me that gear calculator a while ago.
It’s on my old dead PC now, so I haven’t currently got a copy, but I’ve pretty much settled on 34×13 for the Rohloff.

No worries Graham

Saw you briefly whizzing past at bikefest last weekend, I was spectating rather than riding though… Assume the bike held up?

Yes, the Kona seems to be lasting OK. I haven’t broken it yet.
Rode it singlespeed with a 48.8″ gear. 😉