The place for fixies and other rides without gears
My favourite gear ratio? Hmmm, lemme think about that...
Ah yes, 1:1giving me 24 gear inches. No cogs, fixed wheel with cranks attached direct to the wheel hub.
Sounds a bit like a baby's trike actually.
Unchain yourself - Ride a unicycle .
Soooooo.... your wheel diameter is only about 7.6 inches?
your wheel diameter is 24 inches which will give you about 75.5 gear inches (give or take depending on what size your tire is....)
(edit, because you have direct drive, your gear inches is the roll out of the wheel, i.e. it's circumference...)
he's talking about a unicycle with a 24" wheel, hence the 24GI calculation. GI doesn't incorporate Pi, it is a simple Chainwheel divided by Sprocket times the wheel dimaeter in inches. So 1:1 drivetrain (cranks directly on wheel) yields 24GI.
No it does not, GI calculations specifically exclude Pi from the calculation to keep it simple. As Pi is a constant, there is no point including it and clouding a very simple calculation. And GI calculations pre dated chain drive (ie like a unicycle drivetrain) and was the standard for knowing the gearing of a bike.
That's rollout. How else do you think people are getting GIs of around 70 with common street gearing like 48:18?
27 * 48 / 18= 72 That's the lazy GI formula that assumes 27" diameter.
Gear Inches is a throw-back to the high-wheeler "Ordinary Bicycle" (Penny-Farthing) days. The Gear-Inch measure is an equivalent to the diameter of the drive wheel on an "ordinary". Back in the day, 60 Inches was pretty much the standard bicycle "gear", as it was approaching the limits of what a man's leg length could accomodate.
At the moment I'm looking at gear ratios again... I'm building up a single-speed roadster style bicycle for my personal use at college. A simple machine with minimal maintenance. In fact I would get a coaster-hub, but I already have a set of wheels which are ready for a screw-on freewheel. I'll be using north-road handlebars, steel frame, steel stem & bar, steel seat-post, steel mudguards... (lots of lovely steel)
Anyway, it's going to have 700 x 38c wheels and tyres, and a 44/18 chainring/freewheel, which gives a gear of approximately 66.8 gear inches. If I get a smaller 42-tooth chainring it'll be 63.7 gear inches. What do you think?
At the moment I'm going with 44/18 (67 gear inches) because that is what my current collection of components will allow me to do. I had thought about doing a 5-speed freewheel, but I find that around here I rarely shift gears anyway. I suppose I'll just try it and see how it works out.
P.S. Remember that just about everything on this bicycle will be gaspipe steel, except for the alloy rims.
On a lovely, big 62cm x 56cm (st x tt) frame:
Depends on the terrain you ride and how strong your legs are. I ride a all steel except alloy guards roadster to the train station regularly. 400m (AT) 4% on brick paving or 300m (AT) 5% are the finish sections depending on direction and I am happy with 42/16 71GI on that.
On the other hand on Sunday did a 60km belt up the freeway with a few thousand other people, this time with CrMoframe and alloy components. I needed the 52/16 85GI to be able to ride at pace aka almost 40kmh. Even managed the solo return trip into 20kmh gusting to 30kmh headwinds with out problems. The 8% grades early on the return trip where a different matter.
Terrain is mostly flat, but would also be used for cruising rather than getting anywhere fast. I'm also going to be "Sit up and beg" seated. The idea being it is a comfy bicycle I use for short trips.
Your explanation of what a gear inch and it's heritage is, afaik, pretty well perfect. It's all about the rider's inside leg measurement.
However 60" is little on the long side unless going to exotic variants. Even with the excessively tall youths of today it would be impossible for all except maybe Manute Bole. They tend to be around 50 ,maybe, 52". Though I have seen a pic of bloke with an excessive wheel size and blocks ridiculously attached to the top of the pedals. And there is also the far more practical variation where the pedals are a fair way above the axis and linked to the axis through a pair of rods. With those the rider can go to whatever GI he wants regardless o f his inside leg measurement.
btw newly built retro penny farthings built to the old spec will become harder to come by. The solid rubber that they clad the wheel with, termed pram chord (remember the old sprung base prams of yesteryear with 1" solid rubber cladding?) is no longer manufactured I believe.
Unchain yourself - Ride a unicycle .
i'm a softie - 16x46
I'm more of a softie... at the moment It looks like I'll be trying out 42/18 single-speed.
I'm running 44 x 18 on my Raleigh super course fixed. That's 65GI with 700x28c tyres. I find this gives a relaxed cruising speed on the flat of about 30km/h, not too bad up hills but I find it spins too fast down hills and I really need to brake a bit to stop my legs from exploding... Might try a 17t cog next on the other side of the hub which is 69GI
Hopefully my favourite will be 46x16, which is what i'm building my new SS with. Current SS is 42x16 which is just TOO short on the flat, i'm uncomfortable above 32kmh. Lots of steep hills on my commute so a really big gear is out (i did try 52x16 for a while but it hurt like hell).
When man invented the bicycle he reached the peak of his attainments- Elizabeth West.
It was that day with a 20kmh tailwind & a bunch of 50 people, until I moved out of the inside of the bunch because they where all moving around, worrying me and outside into the wind.
Last Sunday slogged 30km into a 30kmh gusting to 40kmh headwind, wanted a 52x19 or 20. it was all 60rpm. Then I got to ride home with tailwind and close to 100rpm.
This is going to sound pretentious and I wasn't going to post because I will sound like I'm just making stuff up, but in the interests of adding something different to the mix, I ride a 60 x 17 SS on an old malvern star revenge 80's road bike, 700c 23 wheels.
This means I grind up the hills, there are places on the 1 in 20 where I am doing less than 15 cadence. The computer goes to zero under 15. It does mean I can fly down though, I can pedal through to over 70 kmh,up over 160 cadence cooming down. On the flat I can hold 48 with 53 flat out.
This is my daily commuter, 48 km round trip, eastern burbs to hawthorn.
This isn't for everyone and has taken a while to work up to. I started with a 48x 18 and worked my way up. Changing the cog then the ring to 52x16 then 54, 58 and now 60. I did have 60x16 but this is too hard in the hills.
I have hand cut and filed bigger rings than this for my recumbent and for a raleigh twenty. For the record my knees are still ok.
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