compact Crankset - Bigger Big Blade

[levett]

From what I can see, compact cranksets seem to come in 34/50 i.e. 34T small blade and 50T big blade.

 

Is it possible to swap the big blade for a 52T or 53T or, looking at it the other way round,it it possible to swap the small blade on a 'normal' crankset' for a 34T (usually its 39T or 42T I think).

 

So, having a crankset with 52T/34T, would the 'gap' (difference in diameter) be too big for the front derailleur to handle?

 

I suspect also that you would need a 'GS' rear derailleur (depending on the 'ratio' of the the cassette.

[NickD]

Compact cranksets use a BCD of 110mm as opposed to 130mm (Shimano) and 135mm (Campy), in order to accomodate the small 34 blade. The biggest blade for a 110mm BCD is a 52, made by FSA, Sram and some others. Hope this helps.

Regards,

Nick 

[Mudsimus]

BBB makes a 53t 110bcd

[The_Break]

From what I can see' date=' compact cranksets seem to come in 34/50 i.e. 34T small blade and 50T big blade.

 

Is it possible to swap the big blade for a 52T or 53T or, looking at it the other way round,it it possible to swap the small blade on a 'normal' crankset' for a 34T (usually its 39T or 42T I think).

 

So, having a crankset with 52T/34T, would the 'gap' (difference in diameter) be too big for the front derailleur to handle?

 

I suspect also that you would need a 'GS' rear derailleur (depending on the 'ratio' of the the cassette.

[/quote']

 

No, as posted BCD (Bolt Centre Diameter) of the bolts used to secure the blades differe between nearly all of the cranksets makes and therefore you will need to buy a second crankset.

 

Zipp however were very clever in that they developed the 1st crankset that allows you to change between compact and normal blades. Costs close to 10k, but if you buy 2 DA cranks or Record cranks I would imagine that is pretty close to 10K. I have a Zipp crank and can verify, it is worth every penny. It is super stiff as marketed (Stiffer than the closest competitor by 14%) and also the lightest crank (including BB) on the market. If you are thinking of going compact and are nearing an upgrade on your existing normal crankset then Zipp would be the way to go.

 

P.S. I do not work for Zipp, other than all the marketing I do for them.

[techguy]

The Gap between a 34t and a 52/53T blade would be too great, the average ratio is 1.5x, meaning that if you have a 34T small blade then the no of teeth on the big blade must be 1.5x that of the small blade. so ideally the max no of teeth on the big blade (using a 34 small blade) is a 51 without the FD Struggling to shift...

[levett]

(using a 34 small blade) is a 51 without the FD Struggling to shift...

Thanks TechGuy - is that 'will struggle' as in be a bit 'sluggish' or will not 'shift correctly?

i.e. it it pushing the envelope? or smashing it to pieces?

It looks like, with FSA, you can get a Compact Crankset, and then a 52T Blade with the 110 BCD.

 

levett2010-02-11 05:07:57

[Eldron]

If memory serves (on normal cranksets) the max difference in teeth is 14 (the common 53x39 is at max).

 

Your compact crank with 50x34 seems to prove me wrong though...

 

I do think anything over 14 will cause the chain to rub at extremes.

[greatwhite]

As Eldron said, the difference between the 2 rings would be too large for a double front deraileur

Not to be rude, but you have 3 options:

1. get a bit fitter and fit a 53/39 combo up front

2. get a triple crank set and front deraileur (and gear changer....)

3. go for a wider spread on the cassette

 

both option 2 and 3 might require a GS (or SGS) rear mech - in all cases you might need a longer chain

[techguy]

@Levett, the FD won't "smash to peices" it'll be sluggish...The FSA 52T blade is supposed to be used with the recommended 38T ring also in 110mm BCD...

[levett]

the difference between the 2 rings would be too large for a double front deraileur

3 options:

1. get a bit fitter and fit a 53/39 combo up front

2. get a triple crank set and front deraileur (and gear changer....)

3. go for a wider spread on the cassette

Your right - I'm rather unfit, and more of a MTB'er than a Roadie, but, even more so, I have a lot of weight to drag up hills (currently 115kg )

 

This was more of a 'thought process' than anything else - I currently have a 'triple' on my roadbike and didn't want to go less than the 52T big blade (52 - 11 is good on the flats) when the going gets steep, I use the small 30T front blade but, really I use the one gear on the lowest chainring and then, when the going gets less steep, I go straight back to the middle ring without working my way through the cassette on the smaller blade.

 

As you say - best stick with the triple until I loose around 30kg

[Guest Agteros]

the difference between the 2 rings would be too large for a double front deraileur

3 options:

1. get a bit fitter and fit a 53/39 combo up front

2. get a triple crank set and front deraileur (and gear changer....)

3. go for a wider spread on the cassette

Your right - I'm rather unfit' date=' and more of a MTB'er than a Roadie, but, even more so, I have a lot of weight to drag up hills (currently 115kg )

 

This was more of a 'thought process' than anything else - I currently have a 'triple' on my roadbike and didn't want to go less than the 52T big blade (52 - 11 is good on the flats) when the going gets steep, I use the small 30T front blade but, really I use the one gear on the lowest chainring and then, when the going gets less steep, I go straight back to the middle ring without working my way through the cassette on the smaller blade.

 

As you say - best stick with the triple until I loose around 30kg

[/quote']

I weight 80kg, and I have a triple up front 52/42/something smaller..

 

Works a charm for me

[Ox_Wagon]

38t is the smallest you can go on a 130 BCD. <?: prefix = o ns = "urn:schemas-microsoft-com:office:office" />

 

Compact are usually 50/36 or 50/34.  Campy front derailers have a 16 t capacity so a 52/36 should work.  I used a normal FD with out problems on a compact.  <?: prefix = o ns = "urn:schemas-microsoft-com:office:office" />

 

You don't need the 52 as you can make up the speed by dropping one tooth on the smallest sprocket.  See pic.

 

 

Here is a nice tool to see what difference the gearing makes:

http://sheldonbrown.com/gears/index.html

Ox_Wagon2010-02-11 10:32:49

[Tankman]

 

 

 

 

No' date=' as posted BCD (Bolt Centre Diameter) of the bolts used to secure the blades differe between nearly all of the cranksets makes and therefore you will need to buy a second crankset.

[/quote']

 

That is not true Break... just buy different chainrings if you have compact.

you cant do much if you have a standard crank.

 

there seems to be quite a lot of different answers here.

 

The basics:

A standard crank has a BCD of 130mm and normally comes with 53/39

A compact crank has a BCD of 110mm and normally comes with 50/34

 

Crampy is the only weird one with a 135mm BCD on some of their older standard cranks. Not sure if they still do it like that.

 

Compact is more versatile as there are much more chainrings available 30/34/36/39/50/52/53 (FSA manufactures these)

 

I have been using 52/36 without having to do anything the front or rear derailleur and have never experienced the sluggish shifting that someone mentioned here.

 

In fact I was running 52/34 for almost 6 months while waiting on my 36 blade without any issues.  The "bigger" blades are not that easy to come by and normally needs to be ordered.

 

You can then change a compact crank to a standard crank by replacing the chainrings 50/34 with 53/39.

 

The smallest blade I have seen for a standard crank (130mm BCD) was a 38.

 

So dont worry about your FD it will cope (i have long cage)

and it doesnt effect your RD at all so you are good to go compact!

 

 

Tankman2010-02-11 12:43:42

[Minion]

 

Crampy is the only weird one with a 135mm BCD on some of their older standard cranks. Not sure if they still do it like that.

They still do. Their compact cranks are 110mm, though.

 

Using a 53 chainring on a compact crank will cause it to flex more than a 53 chainring on a normal crank, unless the chainring is stiffened (heavier) to prevent this. It is, however, debatable whether this will make any significant or noticeable difference for most of us.

 

[Yang]

For those who have done the Panorama, would you recommend a change to compact if you're doing the event? I can choose to modify a bike that has the conventional Campag Chorus 11, or a bike with Record 10.