Cycle gear ratio's

[Doug.]

In addition to my racer I have a Hybrid.
Namely a Gitane 300,.
Please can any one help re. the follwing....
The 1st. (bottom gear) is o.k as I ride up some very steep hills,however the top gear is to low as I can peddle faster than the gear chain can provide me with extra speed.
That is it feel that the rear cog ratchet is not engaging (over/under ?)geared
Do I need lower or higher gears ?
Wishing for a higher top speed.
The bike has 21 gears and would be happy to change the back wheel 7 sprocket set.
I appreciate the above is some what confused and hard to under stand.
Shall be most grateful for advice,and tolerance of the above rambling message.
Regards
Doug.

 

[Arch]

It's probably helpful if you tell us what gears you have now - that is, how many teeth are there on each of your sprockets (that's the back cogs) and how many teeth on each of the chainrings (the front cogs)...

You can probably get a higher top gear somehow if you need it - I'm not a techy type but someone else will be along soon I'm sure...

 

[marinyork]

Put your info in Sheldon Brown's gear calculator

Without any information whatsoever it seems unlikely you haven't got a fast enough top gear. Fairly unlikely.

 

[I am Spartacus]

Don't take this the wrong way.. but you live in a gorgeous part of France.. dream bike country..you can't be short of a bob or 2... what pile of doo have you got yourself .. (eugghh hybrid) ??
(the last time I referred to a racer btw was when I was 12... it's a road bike now)

go treat yourself summat according to status, bud.. and enjoy..

maybe something starting DE Ros...

...what do I know...

 

[Hont]

As others have said, need the ratios to be sure, but my MTB was very similar - I could only get 22mph on the flat in top gear.

 

[Banjo]

As others have said, need the ratios to be sure, but my MTB was very similar - I could only get 22mph on the flat in top gear.

my Apollo hybrid is similar.Great on steep hills but can only pedal up to about 25 mph. Suits me at the moment,Im not really interested in top speed but dont want to over stress my knees etc.

 

[willem]

In my experience having a sufficiently low gear is what really counts with touring. And really, that means the lowest gear you can get with current technology, i.e. 34 rear and 22 or 24 front. Since derailleurs sytems have a finite range, the top is the something like 44 or 46 by 11. To be honest, that is good for pretty fast riding. I don't think you will often outrun this, unless on a long but not very steep descent. But then, who cares that you are only going 45 km rather than 50. Usually, this is rather time for the brakes. If you want higher gearing, the only wau to do this is by having bigger chainwheels at the front. 26/36/48 will work fine, but that is your limit with mtb gear systems.
Shimano long cage mtb rear derailleurs have a 45 teeth capacity. 11-34 at the rear takes 23 of those teeth, leaving 22. That is precisely the capacity of their mtb front derailleurs, and what you use with 22/32/44 or 24/34/46 or 26/36/48. The step between the middle and the largest front chainwheel should be 12 teeth for the front derailleur to work best.
Willem

 

[jimboalee]

Here comes another gem from the annals of cycling mysticism.

Highest gear you are likely to use on the flat.

At what speed do you cruise? Go to your Roadload curve and look up what power this represents.

[A 'Roadload' curve is a curve which is Power (Watts) vs velocity (kmh). It can be plotted when you have a figure for CdA ( Cd x Xsection area ).]

Multiply the power for cruising by 3. Xreference back to speed.

Using the cadence for your 'comfortable cruise', calc what length gear this represents. Hey presto.

Some weekend research ahead for you.

 

[MacB]

Masterful Jim, masterful

alternatively plug in your current set up to Sheldons calculator and have a play. I have the outputs for each of my bikes in excel, showing the gear inches and also the expected mph at the various cadence(pedalling speed) levels.

Go Jims route if you plan on serious competitive racing, go Sheldons tables if you just want to have fun but also understand enough to set your bikes up for best returns.

 

[jimboalee]

Use any 'Gear calculator' you wish. Install a 125" gear because the 'Gear calculator' says you can ride at 35 mph.

But , and it’s a BIG BUT, can your legs pull that gear round? 35 mph requires about 900 Watts.

Incidentally, I exchanged a 12 – 23 cassette for a 13 – 25 because quite honestly, 52 x 12 was never used. At my natural cadence of 78, that would be 27 mph. A whopping 480 Watts. What do I need this gear for?

I fitted a 13 – 25 to give me a 'step change' lower. Considering 3 x 140 Watts ( my cruising output at 17 mph ) = 420, the 13 tooth sprocket gives me 25 mph at 78 cadence.

I still DON'T use this gear.

I am considering utilising a 22/32/44 chainset with the 12 – 23 cassette to give me 86 cadence at 25 mph.
I haven't bothered yet cus I would need to shift the front mech. Anyway, 42 big ring on a roadbike looks definitely WIMP.

 

[MacB]

Jim, not a million miles away from my conclusions to date, though I accept that I may yet improve output wise, but certainly stamina wise.

I have a 12-26 30/42/52 triple setup on my hybrid, I've done a couple of thousand miles on this bike and haven't yet used the 52 ring. In fact I think I've only gone bigger than 42x14 a couple of times. Admittedly it's my courage that fails going down hill. I spend most of my time in the 50 t0 80 inch range.

On the commuter, 9 speed hub gear, 48/21, I spend nearly all my time within the central 5 gears. These range from 45 to 85 inches, the top 2 gears are 100 and 115 inches. I'm considering changing the chainring to a 42, when this one wears out. This would reduce the upper range and increase the lower. I can't imagine needing the upper end but could appreciate a bit more at the bottom.

 

[Ant]

When I was deciding what gearing to put on my new road bike I went for a standard 53/39 double with a 13-29 on the back.

This gives me 110" at the top, which is more than enough for me, and 36 at the bottom...which got me up Ditchling Beacon (the steepest climb I'm likely to do) no problem. It also gives me plenty of useful ratios in between without needing to change on the front too often.

I decided on this going by 'feel' and what I'd been riding on for the previous couple of years. Not a calculator or gear chart in sight

 

[Hont]

At my natural cadence of 78, that would be 27 mph. What do I need this gear for?

Pedalling during long downhill stretches. No?

 

[marinyork]

Pedalling during long downhill stretches. No?

Downhill is not at equilibrium

 

[willem]

Personally I think on a road bike for someone who is not a top athlete an ultracompact double like 44/30 with a 12-27 cassette is about right, or perhaps still just a little bit too high.
Willem