The timeless appeal of 7-speed gearing

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brynpoeth
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Re: The timeless appeal of 7-speed gearing

Postby brynpoeth » 9 Feb 2018, 7:49pm

Tyre pressure might be relevant to freewheeling speed
Cycling-of course, but it is far better on a Gillott
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The utility cyclist
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Re: The timeless appeal of 7-speed gearing

Postby The utility cyclist » 9 Feb 2018, 8:47pm

Samuel D wrote:
The utility cyclist wrote:
Samuel D wrote:So why not? If I put my figures into Bike Calculator (using “Tubulars” because their tubular is closer to my tyre’s rolling resistance, and “Aerobar” for the position although my full tuck is assuredly better than any pedalling position with aerobars), I get a freewheeling (zero watts) speed of 45 miles per hour for a −8% gradient. And heavier riders should be faster than I am.

Do you have some data to back up that statement, because not just I but others will say that's not accurate.

Name these others.

I have no data, but it’s a safe guess that a full tuck is more aerodynamic than a pedalling position. If not, why would you go to the full tuck? My downhill posture is a bit like Obree’s egg position, except a bit lower, with a straighter back (because I don’t need to pedal), and knees in.

https://www.youtube.com/watch?v=-FNtR77x-XU fast forward to about 2 minutes
I pedal downhill until I max out, usually hill type/length and even road condition dependant as to when I might stop pedalling but I can reach top speed quicker pedalling than I could ever do freewheeling in a tuck. You and others might not do that but at the speeds you are talking about your full tuck is not better than "ANY" - your words, pedalling position with or without aerobars.

is it more energy efficient, probably, but you said better and didn't quantify that, it certainly isn't better as being quicker/fastest, but do what you want to do, but making statements without data when there is plenty of evidence that pedalling at high rpm/top gear at certain speeds/gradients in the range you mentioned is more effective at getting you to x point quicker.

cc1085
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Re: The timeless appeal of 7-speed gearing

Postby cc1085 » 9 Feb 2018, 9:44pm

Just as I was thinking of changing my 8sp for something new and fancy you come along with this post and destroy all my excuses. Thank you very much. You have saved me from fashion and a sizable wad that I will now spend on a cycle tour.
Thom

JakobW
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Re: The timeless appeal of 7-speed gearing

Postby JakobW » 9 Feb 2018, 10:10pm

If you can put out 400-600W whilst hunkered down on your top tube, then it might be worth your while to pedal in that position; but then I suspect most of us will get more of a gravity assist than Froome! (and pushing 60 mph is way outside my comfort zone...)

Samuel D
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Re: The timeless appeal of 7-speed gearing

Postby Samuel D » 9 Feb 2018, 11:06pm

Hold on! There’s been a misunderstanding.

The context was using Bike Calculator to estimate freewheeling speed. I said my full tuck was “better” than Bike Calculator’s “Aerobar” position, but I only meant aerodynamically better. Someone in the pedalling aerobars position might go faster than me despite that.

I’m only saying I can coast at least as fast as Bike Calculator’s fastest estimate for my weight, because Bike Calculator doesn’t have a full tuck option.

I don’t believe the YouTuber’s comment that Froome was putting out 400–600 watts on his top tube. His FTP in an optimum position is barely 400 W. I’d be amazed if he exceeded 200 W while visibly struggling to carry his feet over the top, and that at an aerodynamic cost compared to a pure, knees-in, top-tube tuck. What gained him more time was the initial sprint over the crest while the others slept, followed by skilful, motivated cornering of the kind he’s often demonstrated in the last couple of years. The top-tube pedalling was good for the show but not the reason he gained 13 seconds on that stage.

When riding fast (and often just for fun), I descend like most of you, sprinting up to speed and then tucking hard. This is both fast and efficient, not to mention fun.

Pedalling downhill is for the fixed-gear crowd.

Brucey
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Re: The timeless appeal of 7-speed gearing

Postby Brucey » 9 Feb 2018, 11:10pm

just to put some numbers to it, if you plus the bike weigh about 100kg and are doing about 30mph down a ~7.5% slope, you have a ~1kW 'gravity engine' pushing you along.

A racing cyclist on the drops typically needs about 500W to do about 30mph on the flat. If when tucked you don't manage 40mph or so down a hill like that, there must be a very strong headwind or your tuck position is not very aerodynamic. Pedalling at those speeds needs a gear of about 130" if your cadence is to be kept sensible and adding 200 or 300W (if you can do that when tucked) won't increase your speed much anyway.

cheers
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[XAP]Bob
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Re: The timeless appeal of 7-speed gearing

Postby [XAP]Bob » 10 Feb 2018, 5:52pm

Not sure I can reasonably tuck... I’ll pedal 130+ rpm into a 75 chainset, 11 tooth ring, 20” wheel...

Then again you lot on uncomfortable bikes won’t get it ;) ;P
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Cugel
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Re: The timeless appeal of 7-speed gearing

Postby Cugel » 11 Feb 2018, 8:57am

Brucey wrote:just to put some numbers to it, if you plus the bike weigh about 100kg and are doing about 30mph down a ~7.5% slope, you have a ~1kW 'gravity engine' pushing you along.

A racing cyclist on the drops typically needs about 500W to do about 30mph on the flat. If when tucked you don't manage 40mph or so down a hill like that, there must be a very strong headwind or your tuck position is not very aerodynamic. Pedalling at those speeds needs a gear of about 130" if your cadence is to be kept sensible and adding 200 or 300W (if you can do that when tucked) won't increase your speed much anyway.

cheers


Aha - some data. It meshes with my experience-based knowledge that tucking in properly when going down a significant hill will gain much speed if the gravity-watts are not wasted by air-tugs at one's person.

So, the other side of the equation here is: how much is gained/lost in the way of gravity-generated watts by the air dragging effects of various positions upon the bike? In particular, what is the difference in these losses of watts to the air between a fine knees & elbows-in crouch and the churning perch of a frantic pedaller on the same hill?

My experience tells me that I can outdistance any such pedaller on a significant downward slope except for those who really are Froomish so can output an enormous number of watts in a very crouched (aero) position. I know few such, bordering on none.

These elusive downhill super-pedallers are, of course, the same fellows who need an 11 sprocket or even a 12. We ordinaries will find a 13 or 14 more than sufficient and also supportive of the close ratio cassette, which adds further efficiency & speed to our cycling, upon the less downhill roads.

Cugel

Brucey
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Re: The timeless appeal of 7-speed gearing

Postby Brucey » 11 Feb 2018, 9:14am

lets put it this way; even with pretty poor Crr touring tyres @ 40mph (on a smooth road) you would be hard pushed to get the rolling resistance losses much above about 120W. The rest of your ~1kW or so (varying with speed, weight and gradient) is dissipated against air resistance. So if you top out in speed, then you can be assured that the rest of the power is spent against air resistance.

Yes, it can take ~900W to push some riders/bikes through the air at ~35mph!

cheers
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fausto99
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Re: The timeless appeal of 7-speed gearing

Postby fausto99 » 11 Feb 2018, 11:57am

Brucey wrote:Yes, it can take ~900W to push some riders/bikes through the air at ~35mph!

No wonder I struggle on the flat, with or without a head wind - according to Strava, the most I generate on a good day going uphill is <200W! :lol:

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bigjim
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Re: The timeless appeal of 7-speed gearing

Postby bigjim » 13 Apr 2018, 6:35pm

Interesting thread that I have only just noticed. Let me tell you a story. Try to stay awake at the back!
Last Sunday, I cocked up the meeting point for the B ride. I usually ride this because it is easy going with plenty of stops. I'm big, heavy and ancient and don't reard myself as a fast rider. Nobody at the meeting point! Then an A rider turned up. Saying he was going to meet the A ride some 15 miles away at the coffee stop. I should come with him. Said I would be fine. Well ok. We set off at a hundred miles an hour [or thereabouts]. I motored through the Cheshire lanes, up and down hill, breathing hard, at the side of the Froome lookalike on his carbon steed.
After coffee, unbeknown to me, I was in the fast pack for the ride to the lunch stop. Jeez... :o
Crazy, to me, pace. But I stuck it out all day even having conversations. Must admit my thighs were on fire. The day finished with some 70 miles under the belt and an average speed of 17/18Mph. And I was still there, but a wreck! I sometimes think we don't realise what we are capable of. I changed gears without noticing and stayed with the TDF minded guys. My bike? A 1980s Dawes Super Galaxy with heavy standard wheels and Marathon thick treaded tyres. I was supposed to be doing some Off road with the B's. I was on a 7speed triple, don't even know the size but it's a standard bike with DT shifters. Where am I going with this? I think it's the heart, lungs and legs we should look after.
Took Monday off though. :D
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horizon
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Re: The timeless appeal of 7-speed gearing

Postby horizon » 13 Apr 2018, 6:38pm

Seriously lurrvely bike (and well done!).
It's autumn in England with the trees turning golden. So we say leaves mean leaves.

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bigjim
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Re: The timeless appeal of 7-speed gearing

Postby bigjim » 13 Apr 2018, 7:50pm

horizon wrote:Seriously lurrvely bike (and well done!).

Thanks. It's a reliable old tank. Took me from Switzerland to the Med a couple of years ago. I must add the rest of the Mob were probably cruising and a couple took off from the front a few times. Something I could not emulate. Oh for young legs. :)
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Samuel D
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Re: The timeless appeal of 7-speed gearing

Postby Samuel D » 13 Apr 2018, 9:14pm

That was good going with those tyres and all the rest. You must be a strong rider yet, bigjim!

Your bicycle is no road bike and that will have made you work appreciably harder. But the 7-speed gears, assuming adequate range, give up nothing to the latest 12-speed Campagnolo and will even be fractionally more efficient in the cruising gears for the reasons discussed in this thread.

Marathon tyres, on the other hand, would be a serious handicap on a fast ride.

Annoying Twit
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Re: The timeless appeal of 7-speed gearing

Postby Annoying Twit » 14 Apr 2018, 12:27pm

I have actually wondered if Shimano Tourney 7-speeds, for an example, are probably ample for the needs of most cycle journeys taken in the UK.

My geared bike is 2x8-speed Claris, and I feel no need to have more gears. I did ride a 2x10 105 for a bit, and the range was narrower than the Claris. I have seen discussions on the touring forum where wider range and more gears are extremely useful, but for the trips I do, I don't feel the need.

In hindsight, I think that the main advantage of the Claris is that it has proper brifters. The A070 brifters that work with Tourney have that small side button like the old Claris. Not that I'm ever likely to buy any bike with them on, but out of curiosity how well do the A070s work? How good is the 'user interface'?