compact or triple

[515mm]

Have to say that Mrs515 has a triple on her Giant Defy Thing and she struggles like hell with it. Yes, it's got a big spread of gears but there are so many gear combinations and she has to trim the front mech so often it pisses her off no end. I'm tempted to convert her iron to a compact for simplicity's sake.............

 

[GrasB]

If you have a triple with a smallest gear of 30/25 and you need smaller, it's easy to replace the cassette or even the chainrings without drastic modification to the bike.

If you're running a compact with 34/28 and you need smaller, you don't have anywhere much to go other than a long reach rear mech or swapping your compact for a triple.

Unfortunately due to some brain-dead decisions by SRAM & Shimano going triple or compact has more to do with what group set you use than gearing layout reasons when you're pushing the limits of gearing ranges. Both Shimano & SRAM offer a rear mechs with +39t capacity (which equates to 455% gearing range on standard road platforms) & at the end of the day the limiting factor on gearing range is the rear derailleur capacity. SRAM don't have shifters which support triple chainrings but have high sprocket capacity mechs means you're tied to compacts & wide ratio cassettes. Shimano don't offer road rear derailleurs with high sprocket capacity but support triples up front.

If you start to reduce the bottom chainring of a normal 64/130bdc (30/39/50) triple you quickly find that you have a compact like setup with an extra gear on the top chainring & so your chainring spiders becomes a limiting factor to sensible gearing. The same thing goes for a compact, you're just a little closer to that lower limit. In both cases you're faced with needing to swap cranksets. Thankfully if you look off the beaten track you can find cranks which support replaceable spiders to give you all kinds of weird & wonderful gearing combinations; how about a 64/104 double that gives you 20-54t chainring options. Or you could have a 58/94 triple giving 20-50t chainrings Both can be setup with MTB or road chain lines depending on what combination of BB & spider spacer you use.

 

[Hacienda71]

Why do the vast majority of tourers and mountain bikes have triples?

 

[lulubel]

Unfortunately due to some brain-dead decisions by SRAM & Shimano going triple or compact has more to do with what group set you use than gearing layout reasons when you're pushing the limits of gearing ranges. Both Shimano & SRAM offer a rear mechs with +39t capacity (which equates to 455% gearing range on standard road platforms) & at the end of the day the limiting factor on gearing range is the rear derailleur capacity. SRAM don't have shifters which support triple chainrings but have high sprocket capacity mechs means you're tied to compacts & wide ratio cassettes. Shimano don't offer road rear derailleurs with high sprocket capacity but support triples up front.

Your post is quite technical for me, but I think I understand most of this. My question is, how compatible are Shimano and SRAM when it comes to mixing and matching to get the desired gearing? I understand there's some compatibility between those 2, but Campag is a different matter.

If you start to reduce the bottom chainring of a normal 64/130bdc (30/39/50) triple you quickly find that you have a compact like setup with an extra gear on the top chainring & so your chainring spiders becomes a limiting factor to sensible gearing.

This is where you lose me (64/130bdc and chainring spiders are foreign terms to me). I have a 30/42/52 triple - the middle ring may only be 40, but the other 2 are definitely correct. It sounds like you're saying it's difficult to change just the small chainring. But what about changing all of them? My understanding from having asked about this on another forum when I was living in a very mountainous area (but didn't do it in the end), is that I could change this for a 26/??/48 triple without making any alterations other than lowering the cage. Swapping my 12-25 cassette for something with an 11 tooth small sprocket would then give me the same biggest gear, and I'd still have a bit of leeway if I wanted it to have more teeth on the large sprocket for smaller gears.

 

[GrasB]

This is where you lose me (64/130bdc and chainring spiders are foreign terms to me).

Okay the spider is what the chainrings are bolted to, for most chainsets this is an integral part of the crank.
BDC... to quote oracle that was Sheldon Brown:

Bolt Circle Diameter (B.C.D.)

On a crankset, the diameter of the circle formed by the stack bolts.
Common double-chainwheel sets use 130 mm or 110 mm diameters.

Modern triple chainwheel sets have two diameters, a large one for the two outer chainrings, and a smaller diameter, with a separate set of bolts, for the granny ring.

Full-size triples usually use 110 mm/74 mm, or 130 mm/74 mm for newer "road triples." Campagnolo uses 135 mm/74 mm. Compact triples commonly use 94 mm/58 mm.

The BDC defines the smallest chainring you can use; 130mm has a lower limit of 38t, for 110mm it's 33t & 104mm (typical on MTB triples) is 32t. 74mm has limit of 24t. 64mm & 58mm are 22t & 20t respectively.

Note: I made a mistake with the small ring BDC it should have been 74mm not 64mm

I have a 30/42/52 triple - the middle ring may only be 40, but the other 2 are definitely correct. It sounds like you're saying it's difficult to change just the small chainring. But what about changing all of them? My understanding from having asked about this on another forum when I was living in a very mountainous area (but didn't do it in the end), is that I could change this for a 26/??/48 triple without making any alterations other than lowering the cage. Swapping my 12-25 cassette for something with an 11 tooth small sprocket would then give me the same biggest gear, and I'd still have a bit of leeway if I wanted it to have more teeth on the large sprocket for smaller gears.

If you put a 26t chainring on the bottom & kept your 42t chainring (it probably is a 30/42/52 as that's a common chainring setup) you've got a huge 62% gearing jump from the bottom to the middle chainring: you can see that setup here. This may well make the change between the bottom & middle chainring a bit hit & miss. If you wanted to use a 24t chainring you have even more problems & you may find that even going for a 38t middle chainring makes it feel like a very big drop to the bottom chainring & a small jump to the top chainring - shown here.

If you understand what I've said You might want to play with Mike Sherman's gear calculator

 

[zexel]

Have to say that Mrs515 has a triple on her Giant Defy Thing and she struggles like hell with it. Yes, it's got a big spread of gears but there are so many gear combinations and she has to trim the front mech so often it pisses her off no end. I'm tempted to convert her iron to a compact for simplicity's sake.............

Innit.

 

[aberal]

Why do the vast majority of tourers and mountain bikes have triples?

Tourers because they are carrying big loads and MTB's because they are climbing very steep often slippery hills through mud, streams and over boulders.

 

[Hacienda71]

Tourers because they are carrying big loads and MTB's because they are climbing very steep often slippery hills through mud, streams and over boulders.

So basically they are better at lugging heavy things or going up steep hills, or you would see lots of tourers and MTB's with compact doubles on. So the triple works best at the extreme, or am I missing something.

 

[GrasB]

So basically they are better at lugging heavy things or going up steep hills, or you would see lots of tourers and MTB's with compact doubles on. So the triple works best at the extreme, or am I missing something.

Kind of... to get the gearing range required in MTBing & touring without huge holes that means triples to get 15 or so non-overlapping gears. This on a 9 speed setup means a double chainring setup would have 1-2 gears overlap on the chainrings & that's a lot of double shifting, even for people who don't mind doing it. With 10 speed you have 2-3 gears overlap, which while requires some double shifting is much more reasonable. So while with 9 speed you could just about cover the required gearing range with a double & not have the gaps it wasn't great (there is 2x9 but it tends to sacrifice the higher gears). With the advent of 10 speed cassettes in MTBs you can much more comfortably cover the gear range without holes & reasonable amounts of chainring overlap.

if we move onto touring bikes you want the same sort of gearing range as an MTB but you also need proven robust technology so they tend to lag 1 or 2 generations behind MTB tech. This means 3x8 & 3x9 speed technology rather than latest & greatest 2x10. It wouldn't surprise me if in 3 or 4 years you start to see a migration to 2x10 on touring.

 

[aberal]

So basically they are better at lugging heavy things or going up steep hills, or you would see lots of tourers and MTB's with compact doubles on. So the triple works best at the extreme, or am I missing something.

The gearing is basically much lower. Typically 46-36-26 or even lower, with maybe 32 or 36 on the rear large cog.

 

[zacklaws]

Have to say that Mrs515 has a triple on her Giant Defy Thing and she struggles like hell with it. Yes, it's got a big spread of gears but there are so many gear combinations and she has to trim the front mech so often it pisses her off no end. I'm tempted to convert her iron to a compact for simplicity's sake.............

Perhaps Mrs515 is using the wrong gear combinations and getting a chain line that catches the front mech, I use a triple most of the time and rarely have to trim. I only use the small chain ring when I need too on the steepest hills, and in conjunction with it, only use the four biggest sprockets, likewise, when on the big ring, I avoid the four biggest sprockets, and when in the middle ring, avoid the two largest and two smallest sprockets, this keeps my chain line inside the front mech.

Another possibility is the front mech could be out of alignment with the chain.

 

[Fab Foodie]

Wades-in with both big feet.

Mostly I'd say Triple

And the only reason I'd say that is for 515mm's comment, compact doubles are very slightly (but not greatly) simpler to use.

I chose the Boardman Hybrid for Mrs FF and one of the reasons is that it has a very sensible and simple SRAM compact set-up with a big dinner plate rear cog, long cage mech and not overgeared at the top end. She finds it simple enough to use and the botttom gear is almost the same as my own 30x25 triple. I'm not a fan of compacts per-se because they tend to require a lot of double shifting, whereas my 52/42/30 set-up makes for much more gentle and useable gaps between chainsets and very litttle double shifting, I find it more flexible.
Shimano mechs will take a 27T rear cog AFAIK and most triples already have long-cage mechs so a 28T inner ring could be fitted, 28 x 27 would get the average road-bike up the side of a house.
Tourers need a wider spread of very low gears in smaller intervals between gears for obvious reasons, but less speed on the top end. Also when going-up hill at full load you don't need any complicated shifting to screw-up progress.

At the end it depends how and where you ride, no worries if you only encounter a big hill once in a blue moon so pushing would be OK, but if you're up hill and down dale for hours on end a good spread of low end cogs might be more appropriate.

However, on balance I'd go Triple every-time.

 

[yello]

However, on balance I'd go Triple every-time.

It's certainly the advice I'd give someone who is unsure, or I'm not familiar with. It's safe advice. Like having you hair cut innit? Can't get it stuck back on once it's gone. Having a safe bail option of the granny gear doesn't mean you have to use it but, by god, you might just be thankful you've got it one day!

But clearly it all depends on the bike, the rider, where they ride and the type of riding they do.

I've just converted my alu framed (i.e. light) bike to a compact... and I'm really pleased I did it. I don't miss anything about the triple. For me, it's been a positive change. Like having another bike.

BUT... it isn't my only bike, it is my lightest bike (the others are steel), I ride fixed around here too so I knew what I was in for, I don't ride huge distances on it so muscle fatigue is less of an issue and, most importantly, I was conservative in my selection and opted for a 48/34 compact.

I do think it's a horses for courses thing and would never categorically state one or the other for everyone's needs. That said, the safe option is a triple!