FSA K-Force Compact cranks

[Saul]

I'm a bit technically challenged so bear with me.

I currently have a pair of FSA K Force Compact cranks that came with my new bike. I persisted with them for a while (chain rings 50/34 and cassette of 12-25) but found i couldn't quite get the the speed/power i needed for races/sprint finishes. So after trying an 11-21 cassette which didn't help i changed the chain rings over to a standard 53-39.

This is better than before, but i still feel i can't quite get that "get up and go" when i need it. I also notice quite a lot of flexing down around the bottom bracket when i'm trying to power along. Could this be because compact cranks use a 110 bolt diameter compared to normals cranksets which use 130 and i'm loosing a bit of power tansfer maybe?

Hope that all makes sense.

 

[alfeng]

I'm a bit technically challenged so bear with me.

I currently have a pair of FSA K Force Compact cranks that came with my new bike. I persisted with them for a while (chain rings 50/34 and cassette of 12-25) but found i couldn't quite get the the speed/power i needed for races/sprint finishes. So after trying an 11-21 cassette which didn't help i changed the chain rings over to a standard 53-39.

This is better than before, but i still feel i can't quite get that "get up and go" when i need it. I also notice quite a lot of flexing down around the bottom bracket when i'm trying to power along. Could this be because compact cranks use a 110 bolt diameter compared to normals cranksets which use 130 and i'm loosing a bit of power tansfer maybe?

Hope that all makes sense.

Unless you are in a velodrome & only have one gear ratio, you will find that you will PROBABLY accelerate faster if you learn to use your gears REGARDLESS of whether or not your are using a compact crank with 110BCD or a "regular" road crank (135BCD or 130BCD) -- in that last 200-to-400 meters, your chain should probably be on the THIRD (better) or SECOND (okay, I guess) smallest gear when you begin to accelerate ... accelerate, upshift ... accelerate, upshift.

As far as the flexing goes, I (or, others) can't "help" you without knowing what is your bike's frame made of AND what kind of BB does your new/old crank have?

 

[alfeng]

BTW. If your compact crank doesn't have an ISIS BB (heck, even if it does), you can send it to me ... I don't generate enough power where it would make a difference if there is any flex in the crank's spider & rings, or not.

 

[LeDomestique]

I didn't know you could have the "standard" 53/39 combo on a compact crank (110 BCD). I though the tops was 52/38.

You learn something new every day....

 

[Powerful Pete]

Tell us more about your entire setup, as well as your weight and riding style.

Then we might be able to help.

In any event, seriously consider a Campagnolo UT and/or Shimano stuff (don't know much about the latter ). Most of what I hear about FSA is not wonderful...

 

[daveryanwyoming]

..... i still feel i can't quite get that "get up and go" when i need it. I also notice quite a lot of flexing down around the bottom bracket when i'm trying to power along....

+1 on Alfeng's posts. It sure sounds like you're trying to power big gears with a lot of force instead of developing the leg speed to use more reasonable gears. You may or may not have a flexy bottom bracket in terms of your attempts to "power along" but "get up and go" is all about leg speed not big gears. It takes practice to get used to winding up a moderate gear instead of just mashing the biggest gears on your bike but it's the key to quick acellerations and the key to closing gaps, getting on a wheel, attacking or jumping in a sprint. The real big gear combos like 53:12 or 50:11 are fine for long steady downhills, time trialing with a stout tailwind or going real fast when the going is steady but there are very few riders that can quickly acellerate those kind of gears on the flats from a reasonable pace.

Take the time to develop leg speed and a quick high tempo cadence and you should have all the get up and go you need with either a compact or standard set of rings. The real reason to go to a compact crank is to climb steeper hills at a reasonably high cadence, if that's not a problem where you live and ride then stick with the standard cranks, but if you're having trouble developing speed with a 53:12 then you need to work on leg speed.

-Dave

 

[Saul]

Tell us more about your entire setup, as well as your weight and riding style.

Then we might be able to help.

In any event, seriously consider a Campagnolo UT and/or Shimano stuff (don't know much about the latter ). Most of what I hear about FSA is not wonderful...

It's a BMC SLT01 and i'm 75kg/175cm tall and i admit i do ride in big gears. I guess when i say i don't get the power i want i mean in comparrison to my Giant TCR which just goes when i stomp on those pedals. I can really jump when i want too with that bike.

 

[alfeng]

It's a BMC SLT01 and i'm 75kg/175cm tall and i admit i do ride in big gears. I guess when i say i don't get the power i want i mean in comparrison to my Giant TCR which just goes when i stomp on those pedals. I can really jump when i want too with that bike.

How many QUALITY training miles have you managed since the beginning of the year? AND, are you ALSO comparing your performance at the end of last season with the beginning of this?

Same shoes? Same pedal system?

Is the orientation of the saddle to the crank the same?

Same width bars? Same reach?

It could be the wheels ... obviously, the majority think that a laterally soft wheel doesn't matter, but it can if you are trying to sprint ... so, some high-zoot wheels OR wheels laced with double-butted spokes will be energy sappers -- at least, IMO.

WORST CASE SCENARIO -- you pay me (especially, if it is green & yellow) to take your bike off your hands ... kidding!

 

[artemidorus]

It's a BMC SLT01 and i'm 75kg/175cm tall and i admit i do ride in big gears. I guess when i say i don't get the power i want i mean in comparrison to my Giant TCR which just goes when i stomp on those pedals. I can really jump when i want too with that bike.

I think you're wrong about the cranks; as bobbyOCR would agree, no BMC could ever keep up with a TCR!

 

[Saul]

It's like you say below. It could be this and could be that. There's countless reasons why but i thought it couldnt hurt to ask the crank question!.

I think your wheel theory is interesting.

How many QUALITY training miles have you managed since the beginning of the year? AND, are you ALSO comparing your performance at the end of last season with the beginning of this?

Same shoes? Same pedal system?

Is the orientation of the saddle to the crank the same?

Same width bars? Same reach?

It could be the wheels ... obviously, the majority think that a laterally soft wheel doesn't matter, but it can if you are trying to sprint ... so, some high-zoot wheels OR wheels laced with double-butted spokes will be energy sappers -- at least, IMO.

WORST CASE SCENARIO -- you pay me (especially, if it is green & yellow) to take your bike off your hands ... kidding!

 

[AussieRider]

It's a BMC SLT01 and i'm 75kg/175cm tall and i admit i do ride in big gears. I guess when i say i don't get the power i want i mean in comparrison to my Giant TCR which just goes when i stomp on those pedals. I can really jump when i want too with that bike.

I also ride a BMC SLT01, originaly with the FSA K-Force Cranks, after about 1000 Kms a small crack appeared and they were replaced under warranty.
By choice I replaced them with the FSA SL-K cranks which are the next model down and slightly heavier.
I've found the SL-K cranks noticably stiffer which has improved that 'stomp & jump' feel to the bike