Why only 2

[Xiorell]

I've noticed alot of race/road bikes only have 2 chainrings, even expensive ones.

Why is this when many MTBs etc have 3?

 

[Mikeoupe]

I'm new to this road bike thing but as I understand it, two chainrings are lighter than three, it's known as a compact, mine's like it.
Being pretty flat where I live it's all I need but if you live in the peak district you might be better of with three chainrings (a triple) to get you up the steepest climbs.

 

[cyberknight]

You can get bikes with both double and triples.

Most road bikes sold do tend to come with a compact that is a bike with 2 chainrings with a big gap between them eg a 50-34 to give you a very good spread of gear ratios from fast to uphill.The only issue with them is that becuse of the big difference on the front chainrings you find that when you drop from the big to small chainring you might need to use a faster speed at the back as you can find it a bit too easy unless you plan ahead and know you will need that gear soon.

A flat out racing bike will be a lot lighter than a typical MTB and is designed for that , speed .It will typically have a 53-39 front ring combo to be linked with a rear block of maybe 12-25 , 11- XX. 13 -XX. The new sram set has a long cage rear mech that allows you to use a really easy gear at the back , up to 30 odd teeth i believe so you would be looking at a very similar lower gear to a MTB.

For loaded touring i would be looking at a triple to give a wide range of gears with a really low gear for those hills.
for normal cycling /commuting i find the compact double works great
If i was going to race then you need the fitness and the speed for a "normal" front chain ring set up.

 

[Muddy Ground]

Mountain bikes are moving towards two rings, and quite a few only have the one. Lots of change out there ;¬)

www.muddyground.blogspot.com

 

[Xiorell]

I have to admit I've only gone to the smallest chain ring on my hybrid once I think, more out of "play with all the levers" than actually needing it.

I was just curious about this, in my limited knowledge I'd have thought race type bikes want more gears. I stand corrected

 

[jig-sore]

I'm new to this road bike thing but as I understand it, two chainrings are lighter than three, it's known as a compact,

to correct that... two chainrings are known as a double, three a triple. the term compact refers to a double that has a smaller lower ring giving an unusually large jump between the two rings and therefore giving a larger range of gears.

the only down side to a double is that changing rings at the front can force you to do a bit of skipping around at the rear to avoid a bit of spinning or grinding due to the large "jump" between the two gear ranges.

very easy to get used to actually

 

[exbfb]

In my limited experience, I initially found the jump between the small and the large chainrings to be fairly massive, but I think I was using it wrong. That's because I was restricting the big ring to only getting used once I had ran out of gears on the little ring and ended up making a big jump between the chainrings.
What I'm doing now is setting off and pretty much getting into the big ring as soon as possible but in conjunction with a fairly short gear on the back.
I then have the opportunity to make inceremental upshifts all the way up without that big jump coming in.

On a flat bit of road I may be somewhere about 4 or 5 out of 8 on the back whilst on the big ring.
This is maybe doing say 18mph or thereabouts ?

If I need a very marginally shorter gear for an incline, what I can do is move onto the little ring but step up one at the back, it's almost like a half gear shorter.
Once I'm ready to step back up, it's onto the big ring again, but down one at the back. I then have the opportunity to add a little at a time and keep the legs in the very narrow zone where mine actually work

I'm making this sound more complicated than it actually is, but it works for me and means that I'm not ignoring the big ring or feeling like it's a big step up. Helps get over that big gap on a compact setup like my road bike has.

 

[cyberknight]

I was just curious about this, in my limited knowledge I'd have thought race type bikes want more gears. I stand corrected

The latest road bikes have an 11 speed rear gear block , matched with a double on the front that's 22 gears , though probably less in real life as some gears will have the same speed ratio as another one by using different front/rear combinations.
As long as you have enough of a gear range and enough gears to keep up a reasonable/effective rpm of your legs then the extra gears are not really a necessity .I get along fine with 16 speed although i only really use 11 of them with any regularity.
When actually racing then a close ratio block on the back ( eg 12,13,14 ,1516, 17 etc teeth is more important to keep you legs in that effective rpm band, think like a car that gives the most power in a certain engine rev band and give the ability to react and attack

 

[Deleted member 1258]

My Verenti came with a compact chainset, 50/34, and 12-27 10 speed on the back, I changed the front chain rings to 48/42 to give me a set of gears that suited my legs better, and give me a chance of staying with the group on hills, using a 34 tooth front ring on a hill would have shot me straight out the back. Traditionally its been triple on the front for touring and double on the front for fast club rides and racing.

 

[cyberknight]

My Verenti came with a compact chainset, 50/34, and 12-27 10 speed on the back, I changed the front chain rings to 48/42 to give me a set of gears that suited my legs better, and give me a chance of staying with the group on hills, using a 34 tooth front ring on a hill would have shot me straight out the back. Traditionally its been triple on the front for touring and double on the front for fast club rides and racing.

interesting i was considering changing my rings to a 50-38 as i find the 34 to small for weekend riding .On my commuter with panniers on a hilly route i find 50-34 with a 12-25 block gives me plenty of leeway.

 

[jig-sore]

In my limited experience, I initially found the jump between the small and the large chainrings to be fairly massive, but I think I was using it wrong. That's because I was restricting the big ring to only getting used once I had ran out of gears on the little ring and ended up making a big jump between the chainrings.
What I'm doing now is setting off and pretty much getting into the big ring as soon as possible but in conjunction with a fairly short gear on the back.
I then have the opportunity to make inceremental upshifts all the way up without that big jump coming in.

On a flat bit of road I may be somewhere about 4 or 5 out of 8 on the back whilst on the big ring.
This is maybe doing say 18mph or thereabouts ?

If I need a very marginally shorter gear for an incline, what I can do is move onto the little ring but step up one at the back, it's almost like a half gear shorter.
Once I'm ready to step back up, it's onto the big ring again, but down one at the back. I then have the opportunity to add a little at a time and keep the legs in the very narrow zone where mine actually work

I'm making this sound more complicated than it actually is, but it works for me and means that I'm not ignoring the big ring or feeling like it's a big step up. Helps get over that big gap on a compact setup like my road bike has.

nope, that makes perfect sense

 

[Downward]

Compacts cheaper.

 

[exbfb]

nope, that makes perfect sense

Cool, glad I got that bit sort of right(ish)

 

[BrumJim]

On a road bike you run out of grip on the road before you run out of gears on the bike. So no point in having a really, really low bottom gear.