STA & Cranks

I've done some reading on these two aspects of geometry, but need some more feedback...

Seat Tube Angle (STA):

The fitter has noted for me 74degrees is a good STA. I've read stock average is between 73-75degrees. My femurs are probably shorter than average in comparison to the rest of my body proportions.

In reading here, some of you with long femurs do well with a 73 STA to get enough set back. In searching geos in smaller frames, the STA seems to be steeper for most brands...

I realize my position could be moved back (with a steeper STA), but it increases reach. Which I have that problem now with my frame that's too big for me...

So, I'm almost thinking I'm better off going with a 73 STA and being moved forward. Which I assume then would shorten my reach, and could be addressed with a longer stem if needed from my ideal TT size...

BUT... what does this moving forward do to your knee position? :confused:

Crank Arm Length:

I found a link to an article on bike fit from an old thread that gave an equation regarding crank arm length...

According to that, 165 would seem ideal for me. That's what's on my "overall non-fitting bike" right now as stock. The fitter wrote down 170. It seems like most smaller frames come normally with smaller cranks.

If my legs are average/shorter, would a 165 be better? Or are there other reasons?

The fitter comes very well recommended, so I'd try it... but just looking for some answers from others if there is a reason a longer crank could be a better fit.


TYIA :)

My guy insisted I get a 170 when I got my Kuota. I had only had 165s on my other bikes. One ride on the 170s told me no way. I felt like I was mashing the whole time. He thought it would give me power. I said, "You have to have power to get power."
Seriously, I am barely 5' 1" and have a 28.5 inseam. There is a reason small bikes come with small cranks.

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Originally Posted by Crankin

My guy insisted I get a 170 when I got my Kuota. I had only had 165s on my other bikes. One ride on the 170s told me no way. I felt like I was mashing the whole time. He thought it would give me power. I said, "You have to have power to get power."
Seriously, I am barely 5' 1" and have a 28.5 inseam. There is a reason small bikes come with small cranks.

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Thx for that post. I read in the fit link I posted about the arguments for diff crank sizes... being what you are saying from your fit guy. The longer crank will give you more power 'supposedly'... but, I agree with you (and that is what this article was saying). There are things about my body that are not designed to 'mash'. My heart muscle can take more effort to spin. I didn't really think/ask about it at the time to the fitter. Too many other things swirling around my head. But, I will. Appreciate the input:).

While I think it's very good that you are delving in so deep into the geometry, eventually you will need to just ride a bunch of different bikes and see which ones are comfy and which are not (and try to note what is different about each). At the very least, you will be able to translate all that geometry into real bikefeel, which in the end is all that matters.

For me, crankarm length has to do with the angle of my knee at the top of the pedal stroke. Too far flexed and I get kneecap tracking problems. If I'm going to be able to reach the pedal at the bottom of the stroke, then I need 165s. Your fitter should be able to measure your knee angle at the top of your pedal stroke and give you an idea of whether it might cause trouble, and if so, whether it can be remedied by setback or a different STA, or whether you need shorter cranks. That's how I'd discuss it with the fitter if it was me, in any case.

My 50 cm bike came with 170s and I swapped the cranks. I have short femurs.

Quote:

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Originally Posted by tulip

While I think it's very good that you are delving in so deep into the geometry, eventually you will need to just ride a bunch of different bikes and see which ones are comfy and which are not (and try to note what is different about each). At the very least, you will be able to translate all that geometry into real bikefeel, which in the end is all that matters.

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That is problem #1... Finding something remotely close to what I want in my size at a shop. I have started calling some out of town shops too. Even one in a larger city for sure I thought would carry my size did not. It's not just low winter stock either. They said they do not stock it standardly *ever*. Of course any shop is happy to order it for you... with the idea that you are going to buy it. Mail order bride deal. Tulip, as I read your story of finding your Luna you wrote about in Ana's thread, I sat at my computer shaking my head thinking... "man, GF, you got lucky!". It's like your Luna found you... it was destiny;). Me, on the other hand, hasn't gotten there yet *sigh*.

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Originally Posted by OakLeaf

For me, crankarm length has to do with the angle of my knee at the top of the pedal stroke. Too far flexed and I get kneecap tracking problems. If I'm going to be able to reach the pedal at the bottom of the stroke, then I need 165s. Your fitter should be able to measure your knee angle at the top of your pedal stroke and give you an idea of whether it might cause trouble, and if so, whether it can be remedied by setback or a different STA, or whether you need shorter cranks. That's how I'd discuss it with the fitter if it was me, in any case.

My 50 cm bike came with 170s and I swapped the cranks. I have short femurs.

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Oakleaf... that is good to know. I had knee pain before when my stroke was too far forward. I do know what that feels like. Plus, it gives me some things to discuss with the fitter. Thx.

I would not have bought that particular pre-built Luna without riding it. I just happened to be in the same place as the bike, so it worked out. I would (and eventually will) order another Luna from Margo from afar. This one will be custom made for me. Don't start yet, Margo, I have a kitchen to finish paying for!

I don't know what to tell you about trying bikes. If you get to the point of knowing all the geometry, you can really narrow it down. But I would still want to ride a few before I spent money on a bike.

In any case, you are really gaining alot of knowledge so that when you DO find bikes to ride, you will be armed with great information, maybe even more than the salesperson!

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Originally Posted by tulip

I would not have bought that particular pre-built Luna without riding it. I just happened to be in the same place as the bike, so it worked out. I would (and eventually will) order another Luna from Margo from afar. This one will be custom made for me. Don't start yet, Margo, I have a kitchen to finish paying for!

I don't know what to tell you about trying bikes. If you get to the point of knowing all the geometry, you can really narrow it down. But I would still want to ride a few before I spent money on a bike.

In any case, you are really gaining alot of knowledge so that when you DO find bikes to ride, you will be armed with great information, maybe even more than the salesperson!

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Thx Tulip:). Unfortunately I bought my current road bike before finding TE. Since the TE discovery, my brain has been like a bike info sponge:o.

Before this post, I actually spent some time on Margo's site reading all the 411. Even though I'm fit-able to a stock, I have started to see why later some peeps go custom. One bike has maybe 2 out of 3 things you really need, but not them all... or the like. That's where components/etc. switching out make the fit by judge of the fitter/rider.

Part of my issue now is lack of knowledge--to my own true preference. While I know part of the things I want my future ride to have (or not), I don't know them all. Like... would I truly prefer my frame to be more stiff and responsive... or stable, plush. That I have to sort out still.

What Margo says about going back for adjustments, in comparison to the frame being built specifically to you square one, makes sense to me now.

I'm going to keep searching for my test rides. Actually, I think I will try contacting someone at the manufacturer level and see what they would suggest. Mine can not be a unique problem.

I'm 5'1, with a 29 or so inch inseam? I never thought I had long arms, but my top tube lengths are around 540, which seems to be longer than most of you guy's ... And I ride fairly upright...


Summary - I like 165 cranks, my knees hate 170 cranks, and I prefer 73 degree seat angles to 73.5 or 74... and I'm still usually using setback seatposts and my seats all the way back. If I don't put my seat all the way back with a 74 or 73.5 seat angle, my knee seems to have to go above the horizontal to pedal, and I end up sitting off the back end of my seat to try to get to a comfortable knee position.

I have 3 road bikes - the 43 cm surly pacer has a 74 degree seat angle... I currently have the seat all the way back with a set back seatpost & 170 mm cranks on it. I hate the 170's... I can ride them, but I definitely feel it in my knees when I'm geared to high. I just bought it 165 mm cranks. I think I have a 120 cm stem on that because it's got a short top tube.

I've got a carbon park pre frame that has about a 45 cm seatpost (it's supposed to be a virtual 53 cm, but I definitely don't ride it like that), with a 73 degree seat angle, that I love... I like having the 73, and I've got 165 mm cranks on it. I still have a setback on the seatpost, but I don't think I've got the seat all the way back.

I've got a marin vernoa that's about 49 cm frame (probably a 45 cm seatpost actually) with a 73.5 cm seat angle - again, 165 cm cranks & seatpost all the way back on a setback seatpost ... My bf has the same frame (he rides it with the seatpost way up, i have mine way down)... and 170 cm cranks. I definitely do not like the 170's... my knees feel it very quickly.

Hi Miranda -

You sound similiar to me. I have short femurs (short legs, actually) and had some issues with finding the right geometry bike. I would walk into bike shops and they would take one look at me and put me on a 52cm bike which was WAY too big for me. I've got short legs, a long torso BUT, short arms...so while the geometry of the men's bikes were probably close for me...they were all too big and I couldn't even find one to test ride.

Anyway, I did what you are doing - tons of research based on what I could learn here at TE, what the geometry of my first two bikes were (I tried two - a 49cm men's Fuji and a 44cm WSD Specialized), and what I was reading everywhere. I was determined to get the best possible bike for me because I was tired of 'almost' fititng bikes. I ended up ordering a 19" Terry Isis (the 2005 model that is TI) from the website. I figured I was 'safe' giving it a shot since she gives 30 days to try it out. My STA is 74 and I still need a zero set back seat post to get my short femurs over the crank correctly. My saddle is just forward of center on the seat post, too. BUT, my longer torso leaves me a bit too cramped in this position, so I needed a longer stem (110) AND a shallow reach handlebar (to accomodate the short arms). I had my fancy fitting about 6 months after I got the bike and I was just terrified that she was going to tell me that my bike was all wrong (and I'd fallen in love with it by then). Turns out, she gave me a gold star for getting the best possible stock frame for me.

My fitter did mention that while I clearly had the strength/power to kick it with 170mm cranks, my leg dimensions would not allow it. Thankfully actually, since my bike came stock with 165's. I've since set up my commuter bike to the exact same dimensions (it's also a Terry) and they both fit extremely well.

Of course, then I read Margo's site and now I cannot wait until I've got the cash to go full custom. :D I'll still keep my TI Isis until the end of time though - I love it so much. :o

Two dimensions I left out: I'm 5'4" and a 19" Terry is about a 48cm...

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Originally Posted by Catriona

I'm 5'1, with a 29 or so inch inseam? I never thought I had long arms, but my top tube lengths are around 540, which seems to be longer than most of you guy's ... And I ride fairly upright...


Summary - I like 165 cranks, my knees hate 170 cranks, and I prefer 73 degree seat angles to 73.5 or 74... and I'm still usually using setback seatposts and my seats all the way back. If I don't put my seat all the way back with a 74 or 73.5 seat angle, my knee seems to have to go above the horizontal to pedal, and I end up sitting off the back end of my seat to try to get to a comfortable knee position.

I have 3 road bikes - the 43 cm surly pacer has a 74 degree seat angle... I currently have the seat all the way back with a set back seatpost & 170 mm cranks on it. I hate the 170's... I can ride them, but I definitely feel it in my knees when I'm geared to high. I just bought it 165 mm cranks. I think I have a 120 cm stem on that because it's got a short top tube.

I've got a carbon park pre frame that has about a 45 cm seatpost (it's supposed to be a virtual 53 cm, but I definitely don't ride it like that), with a 73 degree seat angle, that I love... I like having the 73, and I've got 165 mm cranks on it. I still have a setback on the seatpost, but I don't think I've got the seat all the way back.

I've got a marin vernoa that's about 49 cm frame (probably a 45 cm seatpost actually) with a 73.5 cm seat angle - again, 165 cm cranks & seatpost all the way back on a setback seatpost ... My bf has the same frame (he rides it with the seatpost way up, i have mine way down)... and 170 cm cranks. I definitely do not like the 170's... my knees feel it very quickly.

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Thanks... that is really good to know. I kinda thought the higher gears might be the place to feel the crank length being good or bad. It gives me a good ref point to think about.

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Originally Posted by GLC1968

Hi Miranda -

You sound similiar to me. I have short femurs (short legs, actually) and had some issues with finding the right geometry bike. I would walk into bike shops and they would take one look at me and put me on a 52cm bike which was WAY too big for me. I've got short legs, a long torso BUT, short arms...so while the geometry of the men's bikes were probably close for me...they were all too big and I couldn't even find one to test ride.

Anyway, I did what you are doing - tons of research based on what I could learn here at TE, what the geometry of my first two bikes were (I tried two - a 49cm men's Fuji and a 44cm WSD Specialized), and what I was reading everywhere. I was determined to get the best possible bike for me because I was tired of 'almost' fititng bikes. I ended up ordering a 19" Terry Isis (the 2005 model that is TI) from the website. I figured I was 'safe' giving it a shot since she gives 30 days to try it out. My STA is 74 and I still need a zero set back seat post to get my short femurs over the crank correctly. My saddle is just forward of center on the seat post, too. BUT, my longer torso leaves me a bit too cramped in this position, so I needed a longer stem (110) AND a shallow reach handlebar (to accomodate the short arms). I had my fancy fitting about 6 months after I got the bike and I was just terrified that she was going to tell me that my bike was all wrong (and I'd fallen in love with it by then). Turns out, she gave me a gold star for getting the best possible stock frame for me.

My fitter did mention that while I clearly had the strength/power to kick it with 170mm cranks, my leg dimensions would not allow it. Thankfully actually, since my bike came stock with 165's. I've since set up my commuter bike to the exact same dimensions (it's also a Terry) and they both fit extremely well.

Of course, then I read Margo's site and now I cannot wait until I've got the cash to go full custom. :D I'll still keep my TI Isis until the end of time though - I love it so much. :o

Two dimensions I left out: I'm 5'4" and a 19" Terry is about a 48cm...

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Yea... looking at Margo's web site made me want to take an airplane road trip... but I don't think that wold get a stamp of approval atm. Terry... we do not have any dealers close. I have not called yet, but I was planning a trip if they had something just to feel the ride of modern steele. I figure I'm limping along on my bike the way it is now, anything close should be ok for a test ride (for frame material feel). That is interesting what you say about the lbs guessing you at a 52cm. I'm only 1/2 taller at 5 4 1/2"... they usually spout off the same thing to me (except for the current fitter of course).

I addressed STA in your other thread. I need 73 or shallower to get my KOP set up right with commercially available seatposts.

Regarding crank arm length, I am a 165 all the way. I tried a 170 at a previous fitters recommendation, and it made my knees come too high at the top of the pedal stroke, applying too much shear force across my knee cap and causing horrible pain. I am 5'4" tall, 30.5" cycling inseam.

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Originally Posted by Triskeliongirl

I addressed STA in your other thread. I need 73 or shallower to get my KOP set up right with commercially available seatposts.

Regarding crank arm length, I am a 165 all the way. I tried a 170 at a previous fitters recommendation, and it made my knees come too high at the top of the pedal stroke, applying too much shear force across my knee cap and causing horrible pain. I am 5'4" tall, 30.5" cycling inseam.

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Thx:)... I remember that we are pretty close except my legs are a bit shorter in the inseam... and I seem to make up for it in the torso. I'm still thinking the RS would come pretty close to fitting me. I need just a wee bit steeper STA in the 74. I know you had to shorten your reach up by switching out the bars. That might be ok for me as is. The TT length of 51.5 is what the fitter suggested as well--same as the RS. I'm just thinking if I need my seat moved forward to get the knee over the spindle... then that puts my seat going up??? That part gets my brain confused. Maybe that's where he's thinking the 170 cranks could work. But, my legs just seem too short. Plus, I assume being a smaller 48cm bike it comes stock with 165s. Hmmm...

erm. If you're ever in the DC area, I have 3 bikes you can ride to see how they fit!

But definitely, it's getting started from high gears or going up a hill that I really feel it in my knees on 170's... I do have patellofemoral syndrome or whatever in my right knee - so it has a tendency to track wrong because the muscles on the inside of my thigh aren't as strong as the muscles on my outer thigh, so they pull my knee cap off track. On 165 cranks... I don't feel my knees till maybe 40 or more miles? Depending on how hilly it is... If I'm on 170's... I feel my knees fairly instantly.

And yes, I need to do my knee exercises more often.