double / triple gear ratio Q

Dr M

I'm currently thinking of getting a triple for steep hils like Honister pass / Hardknott, but then i started thinking of a Compact with a different cassette.

If i had a triple fitted it would be 50/39/30 with 12-25 on the rear. This gives a gear ratio of 2.4 according to Sheldon Browns cacluulator (700c x 23 wheels)

If i use a compact 50/34 and a 12-27 cassette i'd get a ratio of 2.5

Now these numbers seem close, but to be honest dont actually mean that much to me on a road bike :? I'm used to mountain bike gearing, but obviously a mountain bike has heavier wheels / general weight and more rolling resistance.

Would there be much noticeable difference between the lowest gears of 2.4 and 2.5?

(triple would go 2.4, 2.6, 2.8 in lowest chain ring for 3 easiest gears, compact would be 2.5, 2.8, 3.2 so obviously more gaps in the compacts range, but i'm just looking for an easy 'escape gear' for when gets really tough)

Thanks

John C.

The thing that the shops don't tell you is that on a compact 34-27 is the lowest you can go, full stop. How ever on a triple you can change cassettes and granny ring so you will be as low as a mountain bike on 9 speed. As I've said before, if in doubt go for a triple, I can ride Boltby, Chimney and Wrynose on the middle ring when I just start out but after 100 miles I'll need every gear I've got.
So for example you can have a normal use set up of 52/42/30 with a 12-25 rear and then for long sportive rides swop your granny for a 26 or 28. You may have to shorten your chain a bit and check what the limits are on your mech, but it's possible to do this. Or, for a very hilly sportive you could fit a cassette with a 30 tooth ring.
These are not options with compacts, what you get is what you're stuck with, choose wisely.

deal

Dr M wrote:

I'm currently thinking of getting a triple for steep hils like Honister pass / Hardknott, but then i started thinking of a Compact with a different cassette.

If i had a triple fitted it would be 50/39/30 with 12-25 on the rear. This gives a gear ratio of 2.4 according to Sheldon Browns cacluulator (700c x 23 wheels)

If i use a compact 50/34 and a 12-27 cassette i'd get a ratio of 2.5

Now these numbers seem close, but to be honest dont actually mean that much to me on a road bike :? I'm used to mountain bike gearing, but obviously a mountain bike has heavier wheels / general weight and more rolling resistance.

Would there be much noticeable difference between the lowest gears of 2.4 and 2.5?

(triple would go 2.4, 2.6, 2.8 in lowest chain ring for 3 easiest gears, compact would be 2.5, 2.8, 3.2 so obviously more gaps in the compacts range, but i'm just looking for an easy 'escape gear' for when gets really tough)

Thanks

you might find the comparison more useful if you use MPH (KPH)@ 90 rpm or whatever cadence you tend to climb at rather than using gear ratios

30 chainring, 25 cassette, at 90rpm you would be doing 8.4mph, or 5.6mph at 60rpm
34 chainring, 27 cassette, at 90rpm you would be doing 8.9mph or 5.9mph at 60rpm

alot more meaningful than the ratios

suze

I have ridden a compact for a couple of years now, with a bottom gear of 34x28. I can get up most climbs when I'm fresh, but later in the day with a few miles in my legs its a different story.
I'm planning for next years sportives, so I'm now looking towards a triple for my road bike this will give me 30x28 if I use the same cassette. It should get me up most things.

I could even put a mountain bike triple on my road bike....It would make the gears even lower...enabling me to "ride up the wall".... I rode Bealach na ba last year on my mountain bike, had lunch at Applecross hotel (great langustines) and rode back over... no problems with the lower gears. Bottom gear was 22x28 mega low, but the Mtb is not the lightest, so I feel a 30x28 on a lightweight road bike will be ok for me.

If in doubt about getting up climbs say on the Fred W then go for a triple, I am.

CrookedCucumber

I just don't see what advantages a two-ring unit (compact or standard) has over a triple other than that it's easier to clean and perhaps slightly easier to keep in proper adjustment.

Anybody who tells you that you `don't need a triple' unless you're fat and unfit blah blah yawn blah blah is a snob and can safely be ignored

Having said all that, I doubt you'd notice the difference between 2.5 and 2.4 ratios if that's all the difference amounts to.

At the end of the day it's your bike and your legs and your money. A triple will give you more flexibility and more options, and has very few disadvantages (so long as you don't neglect the adjustment).

musto_skiff

deal wrote:

you might find the comparison more useful if you use MPH (KPH)@ 90 rpm or whatever cadence you tend to climb at rather than using gear ratios

30 chainring, 25 cassette, at 90rpm you would be doing 8.4mph, or 5.6mph at 60rpm
34 chainring, 27 cassette, at 90rpm you would be doing 8.9mph or 5.9mph at 60rpm

So is 0.3mph a big deal? Not the speed but the ability of push it if you are on your feeling the gradient wear you down?

roger_merriman

looking at the gear inches, in terms of getting the lowest gear, road triple gives you a lower gear but only one, ie your about one gear down from where you'd be on the compact.

this said if your climbing a 30% or more hill that might well be the gear you wanted...

redddraggon

John C. wrote:

The thing that the shops don't tell you is that on a compact 34-27 is the lowest you can go, full stop.

They shouldn't tell you that anyway because it's wrong.

If you've got a compact and run 8 or 9 speed Shimano, you can fit a MTB rear mech and run a 11-32 or 11-34t giving pretty tiny gears.

If you run shimano 10 speed the 11-32/11-34 cassettes do exist but are rarer and cost far more.

If you run Campag you can run a 13-29 cassette with the compact.

W5454

Dr M wrote:

I'm
(triple would go 2.4, 2.6, 2.8 in lowest chain ring for 3 easiest gears, compact would be 2.5, 2.8, 3.2 so obviously more gaps in the compacts range.........

????????? What happened to gear ratios in inches?

Dr M

W5454 wrote:

Dr M wrote:

I'm
(triple would go 2.4, 2.6, 2.8 in lowest chain ring for 3 easiest gears, compact would be 2.5, 2.8, 3.2 so obviously more gaps in the compacts range.........

????????? What happened to gear ratios in inches?

haha um yeah i wasnt sure what units to select on the sheldon brown gear calculator, so i figured as long as i did all my calculation in the same on it would be ok. Those numbers are 'gain ratios' but not exactly sure what that is....

willbevan

i run a compact at the moment on my road bike

50/34 and a Mountain bike cassette at the back, 11-32 (XT rear mech as well), 8 speed sora shifters etc

Now i wish i had gone to a triple.

Mainly becuase after now ridding a bike with close gears (my TT bike has 11-21 on it at the moment) i am really disliking the large jumps between gears!

Now if i had a triple, i could be using a smaller rear casstte, getting the same range but have the gears closer together for cruising, or worst case, change out the 30 ring for something smaller on the triple, or change (if its 8 or 9 speed) to a larger mountain bike cassette

As people have said, if in doubt triple! i wish i had heard that first lol

musto_skiff

If you change a double to a triple how many new bits do you need?

I assume;

- Left break/shifter
- Front mech
- New triple crank

Any other issues?

redddraggon

musto_skiff wrote:

If you change a double to a triple how many new bits do you need?

I assume;

- Left break/shifter

If you run Campag the left shifter is always both triple and double compatible.

willbevan

musto_skiff wrote:

If you change a double to a triple how many new bits do you need?

I assume;

- Left break/shifter
- Front mech
- New triple crank

Any other issues?

Proably need a new bottom bracket as well, so the chain line is correct for a triple after changing from a double..

musto_skiff

willbevan wrote:

musto_skiff wrote:

If you change a double to a triple how many new bits do you need?

I assume;

- Left break/shifter
- Front mech
- New triple crank

Any other issues?

Proably need a new bottom bracket as well, so the chain line is correct for a triple after changing from a double..

I run shimano; so it's pretty expensive to switch a double toa triple then ,,,

dennisn

I'm 60 and overweight(a bit) and I use a 50-33 with a 12-27 for The Bike Tour of Colorado
and do pretty good with it.

Dennis Noward

Dr M

musto_skiff wrote:

If you change a double to a triple how many new bits do you need?

I assume;

- Left break/shifter
- Front mech
- New triple crank

Any other issues?

i was told might need a new rear mech as well - long cage one - as a normal one wont be able to cope with the size differences.

Gary D

musto_skiff wrote:

willbevan wrote:

musto_skiff wrote:

If you change a double to a triple how many new bits do you need?

I assume;

- Left break/shifter
- Front mech
- New triple crank

Any other issues?

Proably need a new bottom bracket as well, so the chain line is correct for a triple after changing from a double..

I run shimano; so it's pretty expensive to switch a double toa triple then ,,,

You might be lucky

9sp Tiagra and 9sp & 10sp 105 LH Sti's are double or triple compatible. These are the major cost item if you are upgrading.

Gary.

bilbo.baggins

I run a Shimano (Ultegra) 10 speed groupset with 53-39 and 12-27. Suits me pretty well for most sportives although 25% plus gradients can be 'a bit of a challenge' and I'm toying with a cheap and easy way to get that extra gear.

I really don't want to incur the expense and hassle of moving to a compact or a triple and was wondering if I can move up to something just slightly bigger than a 27 (28 or 29) on the rear without having to alter my rear mech and where I'd source such a cassette. I notice SRAM offer a 11-28 (OG1070) but can't find anyone with it in stock and not sure of the relative quality.

richa

Believe it is about £100.

jezcc

I recently had to choose gear ratios on my new bike (first road bike)

I went for a campag compact 50-34 at the front and an 11-25 cassette at the back.

So my easiest gear is going to be 34x25. I'm hoping it's easy enough!!

It's easy to change the cassette though if I don't like it.... just make sure that you get a small enough ring at the front.

jedster

I've got a triple and have experimented with

50/39/30 and 12-25
52/42/30 and 12-27
50/39/30 and 12-23

I'm likeing the last set up now. I use the big ring a lot, the middle on hills and stiff headwinds and the granny only rarely when it gets really tough. I really like the close gears and the smooth changes (minimal double shifting) between the 50 and 39.

I had thought that I would get a compact when I buy a nice bike but I think in comparison I'll find myself using nasty chain lines on the big ring quite often. A 34 ring is really too small to be used very much (I find myself using 39-12 or 13 quite a lot in rolling terrain).
I could go for a standard double and a 12-27 but I dont have much use for 52-12 and 39-27 wouldn't leave me with an emergency exit on tough climbs.