RMoudatir

I have a custom single speed track bike, the frame is aluminum and it uses an FSA Carbon Track crankset with a 49 tooth Pro Track chainring with the ISIS bottom bracket. I thought this set up would be beyond stiff for my needs but I've noticed when I climb and sprint, there is a lot of flex involved, my bike feels as if it were a noodle. I only weigh 60kg, I am a light rider so It can't be my weight.

JeremyLC

More details would help. More information on the frame, maybe a geometry chart. What stem, bars, and seatpost do you have? Where are you feeling flex? What kind of wheels do you have? Have they been trued and tensioned recently?

RMoudatir

It's a 6KU Track bike but the frame is pretty much an Aventon Cordoba, they make the same frame in the factory it's just with a different paint job and cheaper components that I have swapped out for better components. I use the stock 100mm 6KU stem, it's pretty decent with 400mm alloy compact drop bars that I got from China, and the stock 6KU seat post which is pretty good as well, I still have the stock wheels which are about 30-35mm deep 28H front, 32H back with 16 tooth free wheel with 25mm Conti Gator Skins. I have trued the wheel but not professionally. I feel the flex mainly betweem the crank arms and the bottom bracket feeling as if it were being twisted from one side to the other when pushing power on it.

Altimis

Did you assemble it by yourself or you have LBS do it?

Maybe they not properly torque it, who know, maybe there "gap" you can't see from outside, a little hair gap that allow movement inside when you do it without "proper tools"

I guess though, better take to the shop before you damage it, otherwise, live with it

TimothyH

Check the frame for cracks.

Have someone stand next to the bike, put the front wheel against a wall and press one of the pedals with their foot, hard. Look at the bike while it is stressed, especially around the bottom bracket and where the seat stays attach to the downtube.

Also, what kind of wheels?

Trakhak

I'd try riding a couple of other bikes that are as similar as possible to see whether they feel stiffer.

A long shot: did you recently change frame sizes, or is the bike different in some significant way from the bike or bikes that you're used to? When I used to test-ride customers' bikes when I worked in bike stores, I often noticed that larger frames seemed stiffer and smaller frames seemed more flexible, which were illusory perceptions stemming from how I fit on those bikes.

TejanoTrackie 

Sounds like lateral frame flex, although no frame is 100% rigid.

Scrodzilla

You're really wondering why your cheap 6KU frame is flexing?

Yes, they are made in the same factory but aside from having an "aero" down tube, it's a different frame than a Cordoba. The tubing on the Cordoba is double butted, where on the 6KU it is straight-gauge. That alone would make a considerable difference in rigidity.

JeremyLC

Well...



FRAME
6061 Double Butted Alloy w/ Smooth
Welding

Scrodzilla

Either way, it's a cheapo 6000-series aluminum frame. Of course it's going to flex like a soggy potato chip.

Putting a stiff track drivetrain setup on it will only make the frame flex that more noticeable, as opposed to increasing performance.

TimothyH

My money says the frame is on crack.

Altimis

I still on positive side, maybe his bike not properly installed BB and parts, not proper torque etc.

Human sense could be deceptive, he thought frame, BB and crank is flex but its may not the case. Wheels may have play so its felt "noodle" on bottom, its all possible.

He is not heavy at all, he said weight 60kg. I have no idea how he even possibly damaged the frame with just 60kg weight.

Scrodzilla

Nobody is saying he damaged the frame.

I'm saying it's a cheap aluminum frame, which commonly aren't the stiffest. I could probably flex a 6KU Track by giving it a dirty enough look.

seau grateau

Have we ruled out psychosomatic flex?

hairnet

x1000

RMoudatir

I forgot to say that for every revolution of the crank, it makes a cracking, creaking sound in the same exact position it turns. It seems to be more obvious when I torque up.

TejanoTrackie 

Remove the cranks and tighten the bottom bracket. Then reinstall and tighten the cranks.

franswa

Diagnosis 101:

Make mention of all related issues/concerns at the time of diagnosis.

Scrodzilla

Pretty common issue for FSA ISIS Drive track cranks.

Let me guess, you bought them used?

Kindaslow

I stop by this sub forum to see if anyone is talking about SS MTBs and to read threads like this. There isn't anything this good in the old folks sub forum and the MTB sub forum is kind of on life support. Keep up the good work!

veganbikes

Since when did 6KU start doing custom bikes? Did you get to choose from a wide array of colors for the frame and low grade colored components and thought that when it said CUSTOM online frame creator they meant it? Oy Vey!!!

I have a Custom Thruster, I put a sticker on it!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! NYAH!

RMoudatir

Lol! no way am I falling for those custom color fixies that cost $200 more than they should! I meant custom as in I bought the 6KU track stock and replaced everything with components I chose except for the the frame, wheels and stem lol

RMoudatir

6KU Track https://imgur.com/gallery/VOuBm

This is a pic of my bike currently, ignore the awkward drop bar angle lol

veganbikes

So you added a few non-custom components to a cheap online fixed gear bike and that is custom? When did this happen? The 6KUs are maybe a notch above the colored fixed gears but really not by much if any. Both are lumps of low grade metals shaped like bikes one says Bigshot and one says 6KU.

bikerdude69

i have the same frame with stock parts don't feel a thing