gear ratio's

[sarahm]

Hi everyone,
I was on a cycle ride yesterday, going down hill, peddling as fast as I can in my highest gear and was passed by another person not peddling as fast as I was but who disappeared into the distance. My gears are 11-32 and 26-36-48, I never go down into the granny ring, which one of these would I have to change not to have to peddle as fast.

[gaz]

Traditionally gears are calculated in inches. The formula is Number of teeth on chainring x rear wheel diameter in inches / number of teeth on sprocket. The resulting gear in inches is comparable to riding a penny farthing with a wheel of that diameter. A bigger wheel goes further for a single pedal revolution.

Assuming a 700c rear wheel then 48 x 27 / 11 = 118 inch gear. IMO that's a very high gear.

Sprockets smaller than 11T are extremely specialist items. Increasing the size of your front chainrings is the simplest way to a higher gear. Not that simple though as you may need a different front derailleur, longer chain and possibly new sprockets (if the old ones are too worn).

If you are already pedalling as fast as you can in a 118 inch gear it may be time to learn to pedal faster .

[Mark1978]

It's easier than that really if you aren't comparing between bikes.

For the biggest / fastest gear 48 / 11 = 4.36

It's possible the person passing you had a 52 or 53 teeth on the front which would give 53 / 11 = 4.81

You need to also think about technique. He may have been pedalling for harder and longer than you and didn't look like he was putting effort in because he had a lot of momentum. Also he would have had better aerodynamics which would make him faster for the same effort.

[thirdcrank]

A heavier rider will also tend to descend more quickly than a lighter one and if the difference is in the order of three or four stones, they'll descend a lot more quickly.

[MikeF]

Hi everyone,
I was on a cycle ride yesterday, going down hill, peddling as fast as I can in my highest gear and was passed by another person not peddling as fast as I was but who disappeared into the distance. My gears are 11-32 and 26-36-48, I never go down into the granny ring, which one of these would I have to change not to have to peddle as fast.

Using the chainring with 48 teeth and the rear 11 tooth cog will give you your highest gear ie the slowest pedalling rate. If you are pedalling too fast using this combination then you need a larger chainring ie change the 48 tooth ring for one with more teeth.

[Moodyman1]

The 48-11 combo that Sarah has can easily hit 40mph, so I doubt she was outgeared. At that speed, it about gravity and aerodynamics

I think the other rider was more tucked in or heavier - or both.

[NATURAL ANKLING]

Hi,
48 x 11 on a 700c will be 115 cadence at 40 MPH, most cyclist can manage that for a short time, especially down hill.
The trick is to get into top gear as soon as you can power that gear on the hill and accelerate as quick as you can up to your max cadence, then drop into an aero position, remembering to stop pedaling.
If you try to speed up your cadence when you are already at a comfortable max you will have already used up your omph.
If your light say 65 kgs then you will find it hard to stay with a not so athletic 80 kg lump.

[niggle]

You 48-11 top gear is actually marginally higher than my 50-12 top gear. As others have said its probably down to something else, and anyway the big question is did you catch him when climbing the next hill

[Mick F]

My top gear is 53/12 and that gives 117" with my tyres.

I "spin out" regularly descending hills round here, and often wish for a higher gear, but it would put the whole gearing system into a different ball-game, so I'll put up with it. Spinning out in top gear gives me 40mph ish and a cadence of about 115rpm. I can't keep that up for long!

[niggle]

My top gear is 53/12 and that gives 117" with my tyres.

I "spin out" regularly descending hills round here, and often wish for a higher gear, but it would put the whole gearing system into a different ball-game, so I'll put up with it. Spinning out in top gear gives me 40mph ish and a cadence of about 115rpm. I can't keep that up for long!

I make that 116" with 23mm tyres, or 116.5" with 25mm but thought you ran 23s? Anyway besides quibbling over an inch if the OP has 23mm tyres they have 115" so not a lot in it and with 26x1.9" tyres (with that set of gears it sounds like an MTB) 112" so still not drastically different. Not sure how much bigger rings could be used with the MTB type chainset and front mech, possibly 50 but an increase to 38T for the middle ring may be needed as well? Then the rear mech capacity may be out of spec unless willing to increase the bottom ratio with a 28T granny as well (from 21 to 22.5" with 26x1.9" tyre).

I run 50-39-28 on a road triple with 12-27 9 speed cassette and its just within spec for the Tiagra GS rear mech and OK on all gradients unloaded in Cornwall on a road/audax bike. I don't often spin out in my 111.5" top gear, I usually don't bother trying that hard down hill, and I have not got off and walked with a 28" bottom gear for three years apart from a few yards up Dartmeet hill near the end of the 2012 Dartmoor Devil when totally done for

[Mick F]

My (latest) rear wheel circumference as calculated by my Garmin 705 today is 2083mm. I had a hilly 38mile ride today with a really steep climb complete with zig zags up to Higher Larrick.
https://maps.google.co.uk/maps?q=congdo ... 3,,0,14.35

This circumference figure varies a tad from ride to ride due to rear tyre pressure and how hilly the ride is. It actually varies throughout a ride too. Hills make the effective circumference smaller as the rear wheel digs in. Road surface alters the figure a tad too - rough tarmac vs smooth tarmac. A flat ride on good tarmac will give a bigger figure for the same tyre pressure.

Today's 2083mm circumference is 663.04mm diameter.
This is 24.92"
This makes my 53/12 top gear only 110.06"

However, sometimes my rear circumference is as high as 2,150mm making a 119" top gear.

[niggle]

My (latest) rear wheel circumference as calculated by my Garmin 705 today is 2083mm. I had a hilly 38mile ride today with a really steep climb complete with zig zags up to Higher Larrick.
https://maps.google.co.uk/maps?q=congdo ... 3,,0,14.35

This circumference figure varies a tad from ride to ride due to rear tyre pressure and how hilly the ride is. It actually varies throughout a ride too. Hills make the effective circumference smaller as the rear wheel digs in. Road surface alters the figure a tad too - rough tarmac vs smooth tarmac. A flat ride on good tarmac will give a bigger figure for the same tyre pressure.

Today's 2083mm circumference is 663.04mm diameter.
This is 24.92"
This makes my 53/12 top gear only 110.06"

However, sometimes my rear circumference is as high as 2,150mm making a 119" top gear.

Ahh but when going down hill the effects will be different to climbing, where 'digging in' occurs, so you may even get an enlarged wheel circumference due to effects like centrifugal force and heat (from the brakes) and this will be when you are in top gear I assume

[Mick F]

Yeah. Possibly!

Basically, what I'm saying, is that you cannot know your gear ratio exactly. You can do a roll-out test and believe that figure; you can look at the Garmin screen and believe that figure too. Take your pick, but I tend to believe the dynamic readings from my Garmin. Pity it doesn't show the gear ratio considering it knows my GPS speed/position and my cadence!
(I wonder if they'll ever get round to doing that. All the info is there, all it needs is a software patch)

I picked 117" because it varies a bit. 117" sounds like it's in the middle of the range. If you said that 700c was the same as 27", it would make my top gear as nearly 120"

[honesty]

To be pedantic you can know your gear ratio exactly (its a ratio of the front gear to the back) you can't know your gear inches exactly though

[Mick F]