Gearing, maximum cadence and maximum speed?

[I like Skol]

I went out yesterday to ride very fast down a hill. As it turns out conditions were near optimal and I didn't just go fast, I went extremely fast, 55mph fast and the fastest I have ever been on a bicycle.

I have been doing some sums because I felt I could have gone faster if I had the gearing or could have pedalled quicker.

With a 700x23c tyre that has a rolling circumference of 2100mm my wheels were turning at about 703rpm
My 50x11 gearing then gives me a cadence of just under 155rpm and I don't doubt this as I felt I couldn't pedal any quicker without risking an accident while trying.

When I stopped pedalling and tucked in my speed stabilised at about 52mph for a long time, possibly as much as a mile, which leads me to my conclusion if the hill and tailwind allowed 52mph surely I could have gone faster with the right gears?

So, theoretically only (because I am not about to change my bike set-up just to chase a top speed on the odd day of perfect conditions that happens once a decade), would bigger gears be the answer or do I need to learn to pedal faster than 155rpm? My maths suggests I would hit the same 155rpm barrier at only 58mph if I swapped to a non-compact 53T chainring. Is it feasible to pedal faster than 155rpm?
In my ideal dream world, I would like to be able to pedal to 60mph and still feel in control, so a cadence of 135-140rpm but this would need a chainring of 60T or bigger

 

[Dave Davenport]

This is handy for this sort of thing; http://cycleseven.org/bicycle-gear-inch-calculator
I hit 40mph on a 72" fixed gear last week (down Blissford hill) which is around 186rpm, so yes it's perfectly feasible to pedal faster than 155rpm, how much control you've got is an entirely different matter.

 

[Jason.T]

There is a app called bike gear calculator on the android play store which is very good, not sure if it's in the apple app store

 

[Citius]

At those speeds, your biggest barrier is wind resistance, not gearing. It's the reason why you see some of these absurd and frankly dangerous looking aero-tucks adopted by the pros on mountain descents.

 

[jefmcg]

http://www.cnet.com/uk/news/fast-fixie-bicycle-with-giant-chainring-aims-for-100-mph/

 

[helston90]

Just stick a 53 on the front- although don't expect to use it in conjunction with the 11 rear very often.

 

[Tim Hall]

<hand waving>
I read somewhere that at those sort of speeds, losses due to turbulence as you pedal become significant. So tucking as @Citius says, combined with not pedalling should be faster.

 

[raleighnut]

Good fun innit.

 

[ColinJ]

I hit 56 mph early in my adult cycling 'career', freewheeling down Rossendale Rd from the Manchester Rd lights on the fringes of Burnley. I too was aiming to hit 60 mph, but what I actually hit (due to staring at the computer rather than the road ahead) was a raised manhole cover! While I was in the air with my bike I decided that if I survived, I would be a bit more careful in the future!

The bike somehow touched down without the tyres puncturing, bounced back into the air, landed again, slewed in front of oncoming traffic, and then I regained control ...

Other descending madness included accidentally taking off on the abrupt transition to 25% at the top of the descent of Fleet Moss towards Hawes. That one almost ended in tears too. Years later, I was watching 'Helicopter Heroes' on the BBC and 'Helimed One' was called out to the very same spot to tend to a cyclist who had crashed doing what I had done, only I had got away with it.

I often hit 50 mph freewheeling on the descent of the A58 from Blackstone Edge to Littleborough.

I reset the maximum speed log on my GPS recently. It had been showing 83 kph which is ~52 mph. I think that was going back down Snake Pass towards Glossop too when I went out recently to enjoy the closed road, and that was with a bit of a headwind. I would have hit 60 mph if I had still been the weight I used to be, but my freewheeling speeds are much lower since I lost a lot of weight.

I agree with the posters above - the most significant factor in high-speed descending is aerodynamics, not pedalling big gears. My top gear on Snake Pass was only 48/13.

 

[ColinJ]

I agree with the posters above - the most significant factor in high-speed descending is aerodynamics ...

Actually, that is the second most significant factor. Number one is switching your mind off so you don't get distracted by thoughts of what would happen to you if you were to crash at that speed ...

 

[ColinJ]

Actually, that is the second most significant factor. Number one is switching your mind off so you don't get distracted by thoughts of what would happen to you if you were to crash at that speed ...

I was quite impressed that a friend was able to do that recently on a rapid descent through Cragg Vale, only 10 minutes after replacing this exploded front wheel inner tube!

 

[ColinJ]

[QUOTE 3775531, member: 9609"]
I find you cadence of 155 to be astonishing - In relation to another thread I recently tried to work out what my typical cadence was and found that typically it is just under 60 and on long big hills I raise it to 65 I doubt I ever go above 65rpm - I worked out my max cad at just under 100 but felt as though I was about to do myself an injury - 155 is just amazing.[/QUOTE]
I remember watching footage of Eddy Merckx spinning away on a set of rollers. I reckon he was doing well over 155 rpm.

Ah, I found it on YouTube - fast forward to 12:20!



155 rpm is very high. I can do 125-130 rpm but I prefer to limit myself to 120 and am more comfortable at 90-100.

 

[Ian H]

I once managed about 212rpm on a fixed descent. I was younger then. I reckon my maximum nowadays is around 185. I'm comfortable up to about 130. Years of riding fixed-wheel.

 

[dan_bo]

If I'm doing 55MPH I ain't pedalling anymore.

 

[Citius]

If I'm doing 55MPH I ain't pedalling anymore.

Amen.