Gear inch/ratio question

Is it just me or has no one mentioned Shedon yet...he always has the answers...

http://www.sheldonbrown.com/gears/

He also discusses skid spots, building fixed gear conversion etc...

Sady missed is sheldon but he lives on in cyberspace...

Based on some quick calcs, 27" is 700x32c, the gear with a 23c tyre should be about 2.5% smaller. (700c = 622mm ETRTO, not sure on the average proportion between tyre width vs height from rim edge).

Seems like a small difference but into a headwind or going downhill that difference will haunt you...

(says me running 32x21 on 26x1.35...)

Jumping in here

I'm strange as I use my Pompino singlespeed for normal road riding, no in town stuff as I live out in the sticks, so while my friends on on their roadie bikes me I'm riding singlespeed with them on a 42 / 16 - 167.5mm setup, yesterday ride for instance was 87km

I'm going to change the whole drive setup and was thinking about buying a Miche Primato Advanced Track Chainset as they seem a good price, but the smallest chainring size is 48T so down to my question : should I fit a 18T cog which is about the same ratio as my 42/16 (which is just fine) or should I fit a 17T

PS : I've seen the chart above and have the app rabbit for the ratios, just wondering if I run a 17 would it be to hard for instance,
I've just noticed that the miche primato on Wiggle only comes in a 165mm /48T or a 170mm /50T so can I replace my 167.5 cranks with 170mm ? 2.5mm shouldn't make any difference, right ? and a 50/19 is exactly the same as a 42/16

many thanks

You want an 18t.

The answer is in the chart up there ^

There's a good (and pleasingly simple) gear inch calculator here too: http://www.fixiestudio.com

Look, I'm a newb and I've just built a ss out of my old Raleigh by removing the gears. It's got a 7 speed cassette on the back and the big chainring from my old mountain bike on the front - giving me 42 / 17 (on 700 x 23c) which by the standards of everyone on here is pathetic (66" or so). However ... I love it. Given my hilly commute I can just about grind up the steepest section although I'm well out of spinning range at a few points on the way home. Best thing is I'm developing power on the slighter inclines and declines. I think I run out of power at about 20mph? Certainly can't spin beyond 25mph.

So do you find your legs strengthening over time? Am I going to want a taller gear in a year or so?

As I've got better at spinning I'm using lower and lower gears. I used to run 74", then 70" but am now hovering around 66-68" (48/19 on my commuter, 49/19 on my long ride fixed wheel).

I find that I can hold a decent pace if needs be, but I've also got up the odd sizeable hill with those gears so it works out nicely for me.

I'm not great shakes at climbing however so prefer to miss out on high top speeds in order to get over any bumps in the road. Plus, if I'm on a long ride I'm invariably not in a hurry!

66" is not pathetic at all, a great gear for long rides with some climbs. <this coming from someone that can't climb for toffee.

I wouldn't change it. You could maybe try low 70s" for a flattish ride like out to cambridge or southend, but I wouldn't be tempted to risk mashing your knees to bits with a big gear. Save the massive gears for riding on a track.

this coming from someone that can't climb for toffee

Tish and pish sir!

Look, I'm a newb and I've just built a ss out of my old Raleigh by removing the gears. It's got a 7 speed cassette on the back and the big chainring from my old mountain bike on the front - giving me 42 / 17 (on 700 x 23c) which by the standards of everyone on here is pathetic (66" or so). However ... I love it. Given my hilly commute I can just about grind up the steepest section although I'm well out of spinning range at a few points on the way home. Best thing is I'm developing power on the slighter inclines and declines. I think I run out of power at about 20mph? Certainly can't spin beyond 25mph.

So do you find your legs strengthening over time? Am I going to want a taller gear in a year or so?

As I've got better at spinning I'm using lower and lower gears. I used to run 74", then 70" but am now hovering around 66-68" (48/19 on my commuter, 49/19 on my long ride fixed wheel).

I find that I can hold a decent pace if needs be, but I've also got up the odd sizeable hill with those gears so it works out nicely for me.

I'm not great shakes at climbing however so prefer to miss out on high top speeds in order to get over any bumps in the road. Plus, if I'm on a long ride I'm invariably not in a hurry!

66" is not pathetic at all, a great gear for long rides with some climbs. <this coming from someone that can't climb for toffee.

I wouldn't change it. You could maybe try low 70s" for a flattish ride like out to cambridge or southend, but I wouldn't be tempted to risk mashing your knees to bits with a big gear. Save the massive gears for riding on a track.

My favourite rides fixed are 30-40 mile climb-fests with 2000ft of climbing or more. I try and avoid routes that take me over ascents that are much steeper than 8 percent though as it's possible I won't get up them. For these rides I ride my normal 48x18 which is the magic 70 gear inches. I know two guys you've each done the Paris-Brest-Paris... on 70 gear inches. They both ride that gear pretty much all the time, and both do pretty epic annual millages on audax rides and stuff.

I take it really easy on the descents but can spin up to 45mph on some days. I didn't used to be able to hold over 25mph for long, but it's fine now so long as the knees feel alright.

If your new to fixed it's certainly beneficial to develop your spinning. Forget about grinding a big gear it's wasting time whilst you could be getting fitter. Keeping a cadence above 80 rpm is good for fitness and suplesse, and you still get a bit of over-gear training on the climbs when that cadence drops a bit.

To develop speed there is some merit in doing shortening bursts in a heavy gear. This is only worth doing when your already pretty fit, and why I've got a smaller cog on the other side of the wheel.

Sticking your tongue out as you crest a climb is always good too.

:P

Sticking your tongue out as you crest a climb is always good too.

:P

That's to catch the toffee on...

I ride my normal 48x18 which is the magic 70 gear inches.

I take it really easy on the descents but can spin up to 45mph on some days. I didn't used to be able to hold over 25mph for long, but it's fine now so long as the knees feel alright.

Jeez. I hit 30 once on that gearing and thought I was spinning fast.

What cadence would you be doing at 45mph (72km/h) on 70 gear inches? Fuck me. You must have bionic knees.

Just over 200 rpm I think. I've seen 200 rpm whilst on one of those horrible gym bikes with wide pedals and cranks.

Should I try roller racing?

I'm currently riding 44/16 my hurt my knees recently doc told me to leave off the cycling for a bit. Now I'm plan on changing my back sprocket to ease my way back into cycling.
Now I've been looking at what to change it to. I want to ease the gearing without spinning madly on flat. My question is will I noticed much of a difference should I switch to a 17t sprocket or would I be better going for one with 19 teeth to really notice any difference?

1 tooth makes a MASSSIIIIIIVVVVVEEEEE difference

(just ask middleofnowhere)

try playing with this:

http://sheldonbrown.com/gears/

lower numbers in gear inches are easier to spin.
around 66.4 is good.

..and have a read of this, now slightly larger, thread on the matter.

I'm buying a bike with 52 - 16, I'm quiet a noob at all this technical stuff but the higher the ratio, the easier it is? I want to be able to climb up hills with ease, will a 16 make it hard for me?

Higher the ration the harder it is, 52-16 is 87.8 gear inches, so the inverse of spinny. Look at the sheldon brown links and maybe consider a different chainring or cog.

lower numbers in gear inches are easier to spin.
around 66.4 is good.

I've been on 66.4 (48x19) for month now and it's good for 30-60 mile hilly rides. I can get more miles into the week with less risk of exploding knees too.

Quicker rides averaging 18mph are a bit spinny but it's probably good for technique and the heart so I'm sticking with it FTW.

just setting up hack fixed for spring spinning to get me back in the mood.

crappy hack road chainset was 56/42t and chrome, urgh, flexible even as a geared rig and throws the chain when S/S
Just found a low end but not badly made (shimano altus) MTB crank with 44t top ring. and with a 20t & 18t on a double fixed hub on 27" wheels.. .sheldon gives me 59.4" and 66.0" which sounds OK to me.
I live in lakes so its hilly as hell, 66" is great for spinny spring rides, and 59.4" for the mountain passes/ more hilly areas.

Just need to find a 39t NOS ring for road bike now, current inner ring is 42 or 44t which is just murder on the hills