Compact

PO Paul

Could someone explain the term "compact" please?

I've heard/seen it used as a description in at least two areas, frames and groupsets (or was that chain rings).
What's the difference between a compact frame and a "normal" frame?
Apparently a compact groupset (chain rings?) give you a wider selection of gears. How?

Thanks in anticipation.

il_principe

http://www.terrybicycles.com/weblog/200 ... nsets.html

And from Shelodon Brown:

Compact Frame
Traditional "road" frames have been built with level top tubes since the early 1900s. The influence of mountain and BMX bike design has led to the increasing popularity of frames with sloping top tubes, higher at the front.

"Compact" road frames have sloping top tubes, and are intended to be used with a long seatpost. Compact frames are a little bit lighter than traditional ones, but this is partially offset by the weight of the longer seatppost. Some riders believe they are stiffer.

Manufacturers like them because they are more versatile in terms of fit. Usually 3 or 4 sizes are enough to fit 98% of customers. This saves a lot of money for a manufacturer who doesn't need to deal with so many SKUs.

maddog 2

compact frame has a non-horizontal top tube

compact chainset has smaller chainrings, usually 34/50

PO Paul

Thank you both very much

Garybee

jashburnham wrote:

Compact Frame

Manufacturers like them because they are more versatile in terms of fit. Usually 3 or 4 sizes are enough to fit 98% of customers. This saves a lot of money for a manufacturer who doesn't need to deal with so many SKUs.

I don't understand where this idea, that compact frames are more versatile for fit, comes from. If you set your saddle at the correct height for your leg length, your saddle will be in the same place regardless of the slope of the top tube.

maddog 2

maybe it's something to do with standover height?

as you say, the only thing that matters is the effective top tube length.

andyp

PO Paul wrote:

Apparently a compact groupset (chain rings?) give you a wider selection of gears. How?

This isn't quite true - what a compact gives you is a lower selection of gears. Most road bikes are sold with a 53/39 set up which is what your average professional rider uses. For most of us the higher gears are too big and the lower gears too small, i.e. a top gear of 53x12 and a low gear of 39x25. A compact means you have a better range of middle to low gears which is more usable for those who don't race.

normanp

Is there any disadvantage in using 48/34 chainset? Sounds ideal for the mid-level sportive rider where the 48 would be good over a range of terrain (where 50 would be too hard). I worry about being dropped on downhills though... The 34 would be fine if combined with a few cassettes for different rides eg 13-29, 11-25 etc. A 50/34 has a huge drop and would often involve multiple changes at the rear to compensate... and if the 50 is too hard there will be a lot of changes...

maddog 2

that's what I run

34/48 with either 12-25, 12-27 or 12-34 (mtb mech, fro Fred Whitton)

Don't miss the top end but can stay on the 48 for most underlating roads only dropping to the 34 for a proper hill. Shifts better than a 34/50 too.

normanp

Thanks maddog. Looks like my preferred Campag Record or Chorus 07/08 172.5 34/48 might be hard to find though! Maybe there is an alternative...

maddog 2

Chorus

http://www.ribblecycles.co.uk/details.a ... MPCHAR1520

Record

http://www.ribblecycles.co.uk/details.a ... MPCHAR1510

normanp

Thanks again maddog. Interesting how £100 extra produces a weight drop of 30g! Maybe Record is better in some other respects!

SteveR_100Milers

andyp wrote:

PO Paul wrote:

Apparently a compact groupset (chain rings?) give you a wider selection of gears. How?

This isn't quite true - what a compact gives you is a lower selection of gears. Most road bikes are sold with a 53/39 set up which is what your average professional rider uses. For most of us the higher gears are too big and the lower gears too small, i.e. a top gear of 53x12 and a low gear of 39x25. A compact means you have a better range of middle to low gears which is more usable for those who don't race.

not quite true Andy - there is a bigger gap in the front chainrings on a compact (50-34) compared to a traditional 53-39. This means there is actually more useable ratios than a 53-39 set up, i.e. less overlap at the extremes. I know this because I have made up a gear inch chart showing the gear inch ratios of both my compact and 53-39 chainsets coupled with either the 11-23 and the 12-27 rear cassettes that I use. The idea of a compact is to replace a triple by offering the same spread of ratios but with only 2 front chain rings. The downside is you have to shift up and down the rear more as you flip the front rings in order to access these ratios.

maddog 2

SteveR_100Milers wrote:

The idea of a compact is to replace a triple by offering the same spread of ratios but with only 2 front chain rings.

Thta's one interpretation of a compact.

another is that standard double gears are simply too high, so you decrease the size of the front rings to bring the overall gearing down. Forget about triples/doubles. Just ask the question "what two rings would I like at the front?"

The downside is you have to shift up and down the rear more as you flip the front rings in order to access these ratios.

Again, depends on how you ride. If find I do much less front shifting on my compact than I ever did on a standard double. As I said above, the big ring handles pretty much everything except proper hills. On a standard double I'm always in between the rings. 53 is to0 big and 39 too small.

DavidBelcher

maddog 2 wrote:

SteveR_100Milers wrote:

The idea of a compact is to replace a triple by offering the same spread of ratios but with only 2 front chain rings.

Thta's one interpretation of a compact.

another is that standard double gears are simply too high, so you decrease the size of the front rings to bring the overall gearing down. Forget about triples/doubles. Just ask the question "what two rings would I like at the front?"

Stronglight made such chainsets (such as the Model 80 or the Escapade, with a 48-36 combo) well before the "compact" concept became fashionable with marketing people. Away from road riding, they're just the ticket for cyclo-cross where ordinary double ratios can be too high for manageable off-road pedalling. I made my own compact chainset - which I still use for 'cross - 6 years ago by losing the granny ring from a Middleburn triple and fitting 46-36 for the remaining pair; a Stronglight like those above would've done the job but only 170mm cranks seem to be available in the UK for such chainsets (still the case I think, the Impact being their latest incarnation), which wasn't much use for taller riders like me who prefer 175mm crank arms.

David

andyp

I agree with maddog2 on this. I don't think 50/34 is a useful set up for a compact because, as you say yourself Steve, it's too big a gap between the two rings. More sensible ratios are 50/36 or 48/34.

I don't see a compact as replacement for a triple though, it's to give me a spread of gears that is more suited to the riding I do than a 53/39 set up.

wildmoustache

i am with maddog and andyp again. 50-36 is great for a reasonably fit amateur for pretty much everything ... i can TT and sprint on 50-11, which is a bigger gear than 53-12. 36-25 is a nice climbing gear, and you can go out to 26 or 27 with a short cage deraileur depending on whether you have campag or shimano.

50-36 and 11-25 /26 is the ultimate combo for me riding around the uk and riding mountainous sportifs, but it does depend on fitness.

agree on the shifting ... it's very nice to be able to leave the front in the 50 for everything but the tough stuff. for example, boxhill in surrey is easily manageable on a 50, whereas I wouldn't do it on a 53 as the chainline would be bollox.

Burghley

Hi

Most of my bikes run a Stronglight 34 - 44 compact chainset with 170 cranks, because I like to spin the pedals. It's down to personal preference really.

My latest bike has a 34 - 48 Campag setup (because I couldn't get a smaller outer ring). It works OK but I don't like the large difference when changing chainrings - you have to move the rear mech a couple of cogs as well and this can lead to a loss of speed whilst climbing.

Rgds

Pete