Gear Ratios - Help Me Understand

[MacB]

Ok, I joined another thread recently, received some great info, and have also read all I can find on this subject, though not understood all of it. So I've been analysing my current gear ratio and considering future options(already sizing up my next bike and not even finished tinkering with current one).

Current bike - 30/42/52 & 12-26 9 speed, 175mm cranks, this gives me a range, in inches, from 31.4 to 117.7, totalling 27 gears. Now I discount 4 of these gears, the 52-26&23 and the 30-12&13, removing 54.3, 61.4, 62.7 & 67.9 inches from the range. This reduces me to 23 gears, of these there are 2 that are both 54.3 inches and another 2 where the gap is only 0.2 inches. This reduces my effective range of gears to 21, across this range the gaps between gears go from 0.9 to 9 inches. If I then ignore the top 2 gears(hardest ones) which, at 109 and 118 inches, I'm unlikely to get to, then this reduces again to 19 useable gears. Range now 31.4 to 100.9 inches and gaps variance from 0.9 to 7.3 inches. A smooth progression would be increments of 3.66 inches.

Right, that's the boring bumph out of the way and would appreciate it if someone, maybe Rando, could verify if the above is a correct assessment. If it is then I get to the conclusion that I actually have nothing like 27 gears. If I smooth out the progression and only look at changes where the impact is greater than 2 inches(they're all either <2 or >3), then I get a final number of 13 gears.

Question, am I just stating the blindingly obvious by feeling that all of my extra teeth and cogs do nothing but give me more to maintain and more to go wrong? At least I think I now understand why my shifters allow me to move multiple cogs at a time. Messing about with SB's calculator I seem to be able to meet all my needs with a double 34/42 and a rear 7 speed 13-30 or 12-32, assuming all 14 gears would be available without the chain rubbing on the derailer.

Are 7 speed cassettes going to be discontinued, do I need to devote my future musings to 10 speed and upwards? Any thoughts on all this appreciated, if you're not asleep already

 

[Crackle]

Aha! The great gear musings conundrum. You seem to have it right but you also have to consider where the gears are. It's quite acceptable to have repeat gears but on different chainrings. What people try to do is avoid double shifting, so having your favourite gear in two or three places is no great shakes. For instance I have my bike set up to use a different ring for different terrain. Most of my riding is on the middle ring and I prefer a 10 speed in the 11-25 range to give me smaller increments between gears: Why? Well because flicking a gear is easy and doing so helps maintain my cadence which is more important than my speed. Start to factor in cadence to your gears and you will put the final puzzle pieces in place.

 

[jimboalee]

Keep the set-up you have. Here is a diagram of my Dawes Giro 500.

The greyed-out combinations are never used.
The progression is 4 -5" at the low end and 8 -9" at the top end. That's how it works.
The middle ring is used most. 'Granny' ring is only for steep climbs, and 'Big ring' is for cruising with a strong wind following, or drafting a group.

This set-up gives me 7 'everyday' gears, with extras for exceptional conditions. A far cry from the 27 on offer.

I worked it out once. A 5 block 14 - 18 with a 53/39 will give 10 smooth gears; 59" up to 102".
Is this the only way it can be done?

 

[MacB]

OMG, I wish I'd never started this, I'm now finding myself deeply attracted to the Cannondale Bad Boy Rohloff 2009, a mere snip at £2250 Looked at Thorn as well, I can see an expensive new bike on the horizon, the temptation of the Rohloff hub is becoming irresistable......must find some bad reviews.......

 

[MacB]

Have been looking at the Thorn Raven Sport Tour and the Fahrrad T900 from Bikefix, both with the Rohloff hub. Barring haveing a custom build any other bikes recommended with the Rohloff?

 

[bonj2]

just don't try and apply too much maths to it, just change up for faster and down for easier, and don't have the chain crossing over. simple as that.

 

[Cranky]

Have been looking at the Thorn Raven Sport Tour and the Fahrrad T900 from Bikefix, both with the Rohloff hub. Barring haveing a custom build any other bikes recommended with the Rohloff?

Van Nicholas do an Amazon Rohloff if you're feeling flush. It's knocking on for £3k.

I've been looking at Rohloff-equipped bikes for a while but just can't justify the expense to myself. The Thorns look to be the best value but I don't like their appearance and all those spacers.

 

[MacB]

Have sent off to Thorn for info and I think I can see the future:-

Thorn Sport Tour for all my commuting, poodling, yucky weather stuff.

Fancy Road Bike for the nice weather fun rides

Extremely fancy foot(mouth)work to my wife to justify the expense

 

[peanut]

ahhhhh the holy grail. the perfect gear ratios .

I have been mentally swopping sprockets for years and have yet to find the perfect cassette.I spend endless happy hours on the PC constructing gear tables

Thats half the fun of course. If it was easy there wouldn't be such a vast array of gear options available.

I like your appraisal of redundant gears... you're quite right of course but there is no avoiding it without going the Rohloff route.

I think the key is to do a few test rides on your fav loops making notes as you go of which sprockets you use most. Which you rarely use and which are essential and build a cassette from that.

I now have two identical rear wheels each with its own unique cassette ratio so I simply swop wheels for different rides. If I'm doing a hilly Audax I'll stuff on a 12-28 and if I'm doing a flat training ride or TT or Tri then I'll swop for 12-23

I have recently bought two 50x36 compacts and I'm hoping to reduce the huge jumps I have with my current 53x38 chainsets. I hate double changes

 

[jimboalee]

Can you imagine what it was like back in the sixties when a 5 sprocket screw-on with a two ring chainset was all one could fit.

The sprockets were two teeth apart from top to bottom and the chainset step was 'single'. ie one sprockets apart.

There was never a perfect gear. Either just too short or just too long.

I had a 53/39 with a 14,16,18,21 & 24

This gave 44 - 50 - 60 - 68 - 80 - 89 & 102 inches.

60 to 102 were all 5 sprockets on the 53 ring. 68 was cruising, but 80 was used when out with the club riders, and was a tad too high.
The bike weighed the same as my Dawes Giro 500 does now ( 23 lb ).

For fast stuff today, I have a Spesh SWorks at 16.5 lb.
On the Spesh, I have more gears than I know what to do with. There is an 81" gear - close to the stiff gear on my Carlton, but PERFICK on the spesh; and the next is 92", which I can roll round quite easily due to the weight and streamlining of the bike.

All this fuss about gearing on bikes,,,, You don't know you're born

 

[tyred]

Singlespeed anyone...

 

[MacB]

All this fuss about gearing on bikes,,,, You don't know you're born

I know, I really wish that they'd just bin all gears and SS or fixed all round Nope, hang on, it's called progress and I'll take advantage Grandad I just feel a bit of a fool from starting out believing I really had 27 gears to the realisation that it's a lot of smoke and mirrors

 

[PpPete]

This set-up gives me 7 'everyday' gears, with extras for exceptional conditions. A far cry from the 27 on offer.

I think this is the big point here...Jimbo has 7 gears which covers most situations and then extra 4 lower and 4 higher for special occasions... so in effect he has only 15 gears ...but those 7 are accessible WITHOUT DOUBLE SHIFTING. To those of us who grew up with 2 x 5 on down tube shifters only those easily accessible "middle 7" are sheer luxury

My "best bike" (still with down-tube shifters !) is now a triple for exactly that reason.

 

[peanut]

oops

Can you imagine what it was like back in the sixties when a 5 sprocket screw-on with a two ring chainset was all one could fit.

The sprockets were two teeth apart from top to bottom and the chainset step was 'single'. ie one sprockets apart.

There was never a perfect gear. Either just too short or just too long.

I had a 53/39 with a 14,16,18,21 & 24


This gave 44 - 50 - 60 - 68 - 80 - 89 & 102 inches.

60 to 102 were all 5 sprockets on the 53 ring. 68 was cruising, but 80 was used when out with the club riders, and was a tad too high.
The bike weighed the same as my Dawes Giro 500 does now ( 23 lb ).

For fast stuff today, I have a Spesh SWorks at 16.5 lb.
On the Spesh, I have more gears than I know what to do with. There is an 81" gear - close to the stiff gear on my Carlton, but PERFICK on the spesh; and the next is 92", which I can roll round quite easily due to the weight and streamlining of the bike.

All this fuss about gearing on bikes,,,, You don't know you're born

 

[jimboalee]

Cheers peanut.

My Mum had a Sturmey 3 speed 531 Hurcules Mixtie.

Going back a bit further, my Uncle had a 3 speed 'kick change' Claude Butler 531 in 1937.

McBludgeoan - I KNOW its PROGRESS, that's why I have a tripple with Tiagra, and a double with Ultegra.
Brake and gear levers in one unit - sheer luxury.

But --- I can still flick those friction levers, Sonny, young lad

If you notice, when you shift to a larger sprocket, the gear changer takes the chain a tad further and then when you release the lever, the mechanism drops back to the optimum position ( if you have the system adjusted correctly ).
On a friction ( Grandad's bike ), THE RIDER had to move the lever over distance, wait for the chain to engage and then shift the lever back to an optimum position below the sprocket.

Thank the Lord I don't have to do that any more. That would be TOO much bother while watching my Garmin and checking my HRM, signalling and swerving away from the young whippersnappers who are getting confused with their STI.