Ratio Query - Sorry don't undertand it all so any help greatly appreciated!

[Fab Foodie]

You're point is completely valid but, again, way over my head! Apologies for being so dumb!

Was just after the difference between a compact 50/34/ 28 and a 53/39/32 as an example.

Wish I was fit and strong enough to be smashing out the miles at 25MPH - but I'm not!

Well, yeah I could do a mile at that - -then would be knackered haha! The pros average 28 MPH + on the Paris Robaix. Over 120 miles....

Short answer is, there is bugger-all difference in the hill climbing but the 53/39 gives better top end and useability.

For you and @migrantwing I will try and explain ....

The gear inches is an archaic term really, From Sheldon Brown: http://www.sheldonbrown.com/gear-calc.html

Gear Inches
One of the three comprehensive systems for numbering the gear values for bicycle gears. It is the equivalent diameter of the drive wheel on a high-wheel bicycle. When chain-drive "safety" bikes came in, the same system was used, multiplying the drive wheel diameter by the sprocket ratio. It is very easy to calculate: the diameter of the drive wheel, times the size of the front sprocket divided by the size of the rear sprocket. This gives a convenient two- or three-digit number. The lowest gear on most mountain bikes is around 22-26 inches. The highest gear on road racing bikes is usually around 108-110 inches

Using the gear calculator I linked to: http://www.bikecalc.com/gear_inches
If you had the same size chainring and rear sprocket the resulting gear in inches = approx 27" the diameter of the old 27" wheels and for sake of argument the 700c wheel as well. So at 27" one 360 degree turn of the crank turns the rear wheel once through 360 degrees. In other words a gear ratio of 1:1. Using Sheldon's example, the lowest MTB gearing has gear inches below 27" and so for one turn of the crank, the rear wheel completes less than one revolution, and at the high gear end for a road bike if we take his 110" we can see that for each turn of the crank we will get more than 1 turn of the rear wheel. In fact, if we divide 110" by 27" we get approximately 4 revolutions of the rear wheel for 1 turn of the crank a ratio of 1:4.

Fortunately, the gear calculator I linked to not only gives gear inches for us old farts but also calculates gear ratios AND meters travelled for any given combination of Chainring teeth and Sprocket size ... choose which works best for you or helps you visualise the difference and you'll be able to see that the bottom-end gear ranges for @Alltalk examples are approximately the same in both cases, but the top end is bigger with the 53/39 x 32 set-up.

Hope that helps!!
:

 

[e-rider]

Currently on a 50/34 - 28 - absolutely go anywhere. Comfortable with this!

Am looking to change to a 53 / 39 - 32 - simply because I have a good deal on it.

Can alternatively swap for the semi 52/ 36 - 32 or 28

Are any of these worth doing and I apologise for being completely useless at Maths but it just hurts my brain! Sorry.

Any help or advice that you think I may be able to understand received with major thanks.

changing will give similar gears so not worth it. Do you have a short or medium rear cage length?
More importantly riding a 39/53 with a 11-32 cassette will make you look like an idiot. riding 34/50 with a 11-28T will make you look normal.
Stay away from the 11-32 cassette unless you need lower gears and pair it to a compact 34/50T chainset with med cage mech

 

[Fab Foodie]

changing will give similar gears so not worth it. Do you have a short or medium rear cage length?
More importantly riding a 39/53 with a 11-32 cassette will make you look like an idiot. riding 34/50 with a 11-28T will make you look normal.
Stay away from the 11-32 cassette unless you need lower gears and pair it to a compact 34/50T chainset with med cage mech

Why will 11-32 make you look like an idiot? One of the dumbest things I've ever seen posted on CC.

 

[e-rider]

Why will 11-32 make you look like an idiot? One of the dumbest things I've ever seen posted on CC.

why would anyone go out and buy a standard 39/53 chainset and pair it with a 11-32 cassette with med cage mech, when they already have the same ratios made up in the more conventional way of 34/50 11-28T? You would be an idiot! Also you'd need a longer than normal chain to run 53-32T with med cage mech - 116 links might do it but if you have a longish wheelbase bike you'd need 118 links which means joining two chains - again you'd be an idiot to take that route!

 

[Fab Foodie]

why would anyone go out and buy a standard 39/53 chainset and pair it with a 11-32 cassette with med cage mech, when they already have the same ratios made up in the more conventional way of 34/50 11-28T? You would be an idiot! Also you'd need a longer than normal chain to run 53-32T with med cage mech - 116 links might do it but if you have a longish wheelbase bike you'd need 118 links which means joining two chains - again you'd be an idiot to take that route!

That's better, explaination helps ....
First the OP was offered a deal and only wanted confirmation that he'd have the same low end gears (which he does) plus some bigger ones to boot.
Secondly I'd assumed a new chain anyhow and having run 52/42 with 34T many moons ago, it ran just fine with a single chain (unless they're shorter these days).
I do agree a long cage mech might be required, we don't know what he currently has.

Compacts are not the be-all and end-all of gearing, just the recent fashion. I may be a heretic, but 53/39 and a 32 rear would do quite nicely thanks.

 

[Markymark]

I know very little compared to these gurus but I'd say the best thing would be a bigger 'engine'.

 

[Aravis]

why would anyone go out and buy a standard 39/53 chainset and pair it with a 11-32 cassette with med cage mech, when they already have the same ratios made up in the more conventional way of 34/50 11-28T? You would be an idiot! Also you'd need a longer than normal chain to run 53-32T with med cage mech - 116 links might do it but if you have a longish wheelbase bike you'd need 118 links which means joining two chains - again you'd be an idiot to take that route!

The switch would give the same bottom and a slightly higher top - reason enough to consider it if that's what you think you need. You need to look carefully at what happens in mid-range to see if there's any benefit there. Then, clearly, you have to think about the issues you mention. You probably come to the conclusion that the benefits aren't sufficient to justify going to the trouble, but it's perfectly sensible to think about it.

 

[e-rider]

That's better, explaination helps ....
First the OP was offered a deal and only wanted confirmation that he'd have the same low end gears (which he does) plus some bigger ones to boot.
Secondly I'd assumed a new chain anyhow and having run 52/42 with 34T many moons ago, it ran just fine with a single chain (unless they're shorter these days).
I do agree a long cage mech might be required, we don't know what he currently has.

Compacts are not the be-all and end-all of gearing, just the recent fashion. I may be a heretic, but 53/39 and a 32 rear would do quite nicely thanks.

I'm personally not a fan of compact chainsets. I ride 36/52 and 39/53 both with 11-28T cassettes but I have no need for a lower gear.
If a lower gear is needed, I would run 34/50 11-28 and if that was still not low enough I'd run 34/50 11-32T - what I wouldn't do if put a 11-32T on a standard chainset, and I'd also avoid it with a semi-compact too. That said, changing the cassette is a cheaper option than changing the chainset (or rings)

 

[2IT]

Currently on a 50/34 - 28 - absolutely go anywhere. Comfortable with this!

Am looking to change to a 53 / 39 - 32 - simply because I have a good deal on it.

Can alternatively swap for the semi 52/ 36 - 32 or 28

Are any of these worth doing and I apologise for being completely useless at Maths but it just hurts my brain! Sorry.

Any help or advice that you think I may be able to understand received with major thanks.

Any clearer now?

Crank length also plays a part. The longer the crank, the shorter the gear. From Sheldon Brown -
What About Crank Length?
All of these systems share a common inadequacy: none of them takes crank length into account! The fact is that a mountain bike with a 46/16 has the same gear as a road bike with a 53/19 only if they have the same length cranks. If the mountain bike has 175's and the road bike 170's, the gear on the mountain bike is really about 3% lower!

Made a similar change to yours and I did notice it on the roads that I regularly rode. Made some changes using the smaller chain ring more often or sooner and it's been fine.

 

[MiK1138]

i have just changed from a 53/39 11/26 to a 50/34 11/28 the reason for this was i was useless on hills and always felt i was working to hard in the big ring, i would never use the 11, 13 and 15 rear sprockets unless i was on a decent descent. unfortunately i have been off the bike since i did the change so haven't been able to test the difference

 

[migrantwing]

why would anyone go out and buy a standard 39/53 chainset and pair it with a 11-32 cassette with med cage mech, when they already have the same ratios made up in the more conventional way of 34/50 11-28T? You would be an idiot! Also you'd need a longer than normal chain to run 53-32T with med cage mech - 116 links might do it but if you have a longish wheelbase bike you'd need 118 links which means joining two chains - again you'd be an idiot to take that route!

Ah, but people make mistakes. It doesn't mean they are idiots, maybe just that they have no bike related knowledge, or don't understand gearing ratios, like the OP.

 

[migrantwing]

I'm running 50/34 11-28 but am awaiting delivery of an Ultegra 12-30t. I don't think I've ever used the 11t successfully, so opted to lose one higher sprocket to gain one lower sprocket. North and East Staffordshire and the surrounding areas have some very annoying and unforgiving hills, and a 15 mile commute in below 5 degree, wet weather at 7am is no fun...and that's before I've even started work. Damn you, lactic acid

 

[nickyboy]

All this talk of gear inches....makes my head hurt. Seems so archaic a system

I'm relatively new to cycling. All I work out in my head is the Teeth on Front Ring / Teeth on Back Sprocket as a ratio. This ratio accurately identifies how many times my back wheel rotates per turn of the cranks, no?

So 50/25 is the same as 34/17 for example.

 

[Crackle]

So 50/25 is the same as 34/17 for example

I don't think you're accounting for wheel size in that. For the same wheel size, then yes it's a rough comparison but you can't compare different bikes and wheel and tyre sizes that way.

Wheel diameter(inches)x(chainwheel/cog) is gear inches.

 

[deptfordmarmoset]

All this talk of gear inches....makes my head hurt. Seems so archaic a system

I'm relatively new to cycling. All I work out in my head is the Teeth on Front Ring / Teeth on Back Sprocket as a ratio. This ratio accurately identifies how many times my back wheel rotates per turn of the cranks, no?

So 50/25 is the same as 34/17 for example.

Me too but we're outnumbered by a ratio of 2:quite a lot....