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How to determine if I am better off steep of shallow STA(15 posts)

How to determine if I am better off steep of shallow STAkilimanjaro
Jan 7, 2003 11:47 AM
I have been convinced (nay accepted that) it is the engine and not the equipment. Therefore I am going to improve my conditioning/riding on my late 80s Peugeot 6spd for the next few years while dreaming/saving for the next bike.

My question concerns how to determine if I am better suited for a steep or shallow STA. Since I am 5'6", just about any bikes I can try at the LBS that might fit will have a steep seat tube angle. Therefore I cannot realistically test shallow STA bikes.

A little more background. I am a former masher who is trying to learn how to spin due to a recent knee surgery. I think my current ride has a steep STA though I have not had it measured. When I am on the bike I often want to strech out more even with the saddle all the way back and I end up sticking my tush beyond the end of the saddle.

I think for the next bike I would like to get a custom cyclo-cross/tourer for all around riding.

I have heard/read that the effects of STA can be adjusted by changing effective TT length via stem length, moving seat back an forth etc. I would love to hear comments on how effective such an approach is.

I don't mind paying for something like a Serotta fit sesstion at the LBS but I don't see what I can gain much if I don't know whether I want steep or shallow STA.

Thanks in advance,
re: How to determine if I am better off steep of shallow STAMike-Wisc
Jan 7, 2003 12:04 PM
Size is relative, and frame geometry is a function of many variables: your proportions, use of bike, handling preferences, top tube length, seat tube length, seat tube angle, crank arm length, handlebar width and configuration, handlebar height, seat height, pedal width, ....

It sounds like you might prefer a longer top tube relative to seat tube length. The LeMonds tend to have longer seat tubes, you might try sitting on different brands in your "regular" frame size. You can also adjust the stem length by quite a bit to make up for top tube sizes. There are also various seat posts that will allow you to position your seat/saddle farther back.

Lots of variables and options.
FitNessism
Jan 7, 2003 1:10 PM
The first thing to do when fitting a bike is determine saddle height and setback. Height is easily determined with an equation but setback is more difficult. A good starting place is KOP (knee over pedal). Fine tune from there based on your ability to spin the cranks in a nice round circle. Spinning round circles is of MAJOR importance for someone trying to develop power and make their knees last! Just slide the saddle forward or back to give the best position. If you run out of adjustment, think about a different seatpost first and then a different frame as need be.

Only after you have your "up and back" position finalized should you start to mess with reach to the bars. Many people adjust their seat forward or back to benifit bar reach. I think this is the wrong way to make a bike fit.

Good luck.

Ed
What I understand about STA...Cima Coppi
Jan 7, 2003 1:12 PM
From having a custom fit performed for one of my bikes, here is the explanation of the importance of STA from the builder. The STA should be set up correctly relative the the length of your femur. If you have a long femur relative to the rest of your inseam length, you will need a more relaxed STA to correctly obtain KOP fit. This is my problem, and therefore the STA on my bikes are all 72.5 degrees. If you have the opposite problem, then a steeper STA is required to get your knee over the pedal correctly.

Another thing, STA really has nothing to do with increased or decreased ability to spin. This must be developed by other manners, and one of the best is getting a set of rollers.

Good luck,

CC
What I understand about STA...Fez
Jan 7, 2003 1:34 PM
So, is your saddle mounted on the center of the rails?

What seatpost are you using (straight or setback)?

What saddle are you using?

What you said makes sense, but absent some extreme conditions, there is an awful lot of adjustment available to compensate for pretty much any STA. There must be 2 cm fore/aft from the saddle rails and 2cm from switching from straight to setback.
More information...Cima Coppi
Jan 7, 2003 3:02 PM
Yes indeed there is a lot of adjustability in this with the saddle and the setback on the seatpost. Some of this is personal preference. Personally, I like to sit back a bit further from the center of the BB, so I have my saddle adjusted back on the rails as far as it can go. I use a Flite saddle and Campy seatposts. Also understand that I have long legs relative to my total height.

CC
FitNessism
Jan 7, 2003 1:12 PM
The first thing to do when fitting a bike is determine saddle height and setback. Height is easily determined with an equation but setback is more difficult. A good starting place is KOP (knee over pedal). Fine tune from there based on your ability to spin the cranks in a nice round circle. Spinning round circles is of MAJOR importance for someone trying to develop power and make their knees last! Just slide the saddle forward or back to give the best position. If you run out of adjustment, think about a different seatpost first and then a different frame as need be.

Only after you have your "up and back" position finalized should you start to mess with reach to the bars. Many people adjust their seat forward or back to benifit bar reach. I think this is the wrong way to make a bike fit.

Good luck.

Ed
I picture a triangle between seat, hands and feet.dzrider
Jan 7, 2003 1:51 PM
Since your feet move around while pedalling, make one point of the triangle the bottom bracket. If you arrive at triangle with a top leg that's the right length between your seat and hands and a leg that's the right length between your seat and feet, the seat tube angle pivots that triangle on the bottom bracket. Go all the way steep you get a tri bike with aero bars over the front wheel. Go all the way shallow you get a recumbant. There's a point between the extremes that will fit most comfortably for you.

You can experiment by sliding the seat forward and back on a bike that you have. Remember that if you slide the seat forward you should also raise it a little to keep the distance from seat to feet constant. If possible, lengthen the stem to keep the distance from seat to hands the same. Adjustable stems are great for this process. Ultimately the answer is where you are most comfortable in terms of the ability to sit and the ablility to handle the bike.
generally people with longer femurcyclopathic
Jan 7, 2003 3:02 PM
are the ones who like shallow STA. At 5'6" you're looking at 50-53cm frame, and unfortunately most frames in that range have steeper STA. Fortunately you can fix it with offset seatpost, (1 deg is ~ 1/2" offset) and there's enough saddle rails for most.

what is your inseam? if it is ~30-32, you're a candidate for shallow STA, if 29" or less you'd better off with steeper STA.

start with KOPS (rotating point in knee above pedal axle); then mashers tend to move saddle back ~2cm (some as much as 6cm), spinners usually prefer to move saddle forward. Try and see what you like.

If you find that you need shellow STA, look for frames with longer chainstays they make more stable ride good luck.
Re: generally people with longer femurkilimanjaro
Jan 7, 2003 4:02 PM
Does that mean that if I wan to promote spinning I should consider steeper STA? Why is it then touring bikes, which I assume are specked for more spin the mash) tend to have shallow STA? I am just curious to the rational.

Thanks again,
tourersFez
Jan 7, 2003 4:08 PM
have a longer wheelbase. that may explain the slacker STA.

spinning vs. mashing is a personal preference. within a range, STA won't matter since the seatpost and saddle rails provide enough fore/aft saddle positioning.
re: rationalecyclopathic
Jan 8, 2003 7:30 AM
moving seat back utilizes more hamstrings and moving forward more quads. Quads are stronger (~150% of hamstrings), however they have much higher % of fast twitching fiber which fatigues faster and recovers longer. Hamstrings have more slowtwitch and can maintain power output for much longer time and recover fast. Why? because as species we evolve for several million years walking (uses hamstrings) and jumping (usus quads); not riding bikes or climbing stairs.

Since riding touring bike is not all out effort (like time trials or sprints) and requires sustained effort for long time, shallow STA are preferable. Second, on long rides comfort is much more important then speed and shellow STA give your more comfortable position.

btw you can spin in any position even in horisontal like on recumbants; steeper STA just allows to sprint faster.
Yes..Fredrico
Jan 9, 2003 4:04 PM
Getting the saddle up over the crank promotes a good circular pealing action--a good spin. The reason racers move their saddles all the way back is because it is slightly easier to mash from furthur back. You get better lever action out of the femurs, but the cadence tends to slow, the mashing increases and your knees get sore.

That is a logical inconsistency with touring bikes having shallow seat tube angles. I've always thought, it was because it's easier to push, and you can slog along all day at low cadence on a bigger gear. But spinning at around 90 rpm from up over the crank on a 74 degree seatube, once your body gets used to it, is by far the most efficient and lesss injurious way to go all day, whether touring by yourself at low speeds or racing all-out in the Tour de France.
Fore/aft positioning and spinKerry
Jan 7, 2003 5:36 PM
As a general rule, a more forward position (knee relative to pedal spindle) is for spinning, and a more aft position is for mashing. This is why you tend to slide back when climbing, which means a lower cadence. KOPS is just a starting point, with most people ranging from +1 to -2 cm of that. If your bike angles are such that you're at KOPS with the saddle in its "mid" position on the seat post, then you're probably covered. The reason to change STA is if you can't get to the desired knee position relative to the PS (saddle all the way forward or back on the seat post). If you're worried about your knees and want to spin more, you should be moving forward relative to your old position, whatever that old position was. STA and TT length interact, since the combination of the two determines where the head tube is relative to the seat tube. IOW, if you steepen the STA one degree while keeping your position constant relative to the BB, then your head tube will move forward about 1 cm. All these things need to factor together to get the right fit.
re: How to determine if I am better off steep of shallow STAgtx
Jan 7, 2003 8:27 PM
This is the first thing I set up on a bike, and it's the same on all my bikes--cross, road, mtb. I think it's basically where my butt wants to be when I'm riding no hands, slightly behind KOPS. Everyone has their own position, it develops with time. I don't think you can pay someone to find it for you. In general, as others have pointed out, spinners tend to prefer a slightly forward position--pulling through the bottom of the pedal stroke. People who push bigger gears tend to sit farther back and push over the top of the pedal stroke.