It's my understanding that one's knee should line up over the ball of your foot, or where your cleat makes contact with your pedal for optimum pedaling performance/power.
I'm 6'1" and trying out a large TB. With the seat at the proper height, I cannot get my knee plum with the pedal. My knee sits behind where it should be. I'm wondering if this is occurring because the saddle is too high and therefore placing me too far back from the cranks? BTW...I'm running a straight Thomson post. The post height is about = or just slightly higher than handlebar....120 5 degree stem flipped.
I notice that the curve in the seat tube does angle back and wonder if this might be the reason it places me back further when there is more post showing.
I also wonder if an XL frame with less seat post exposed and say a 100mm stem might be better. But, the longer TT has thinking I will be placed even further back from the cranks.
I feel a bit slower on climbs, and using more energy than I should. This is the real reason for my questions.
leg extension feels about right. I've not tried lowering the seat yet. On all of my other bikes the measurement from the center of the crankarm to the top of the seat is about the same...31".
I upped the air pressure to my body weight plus 5lbs for gear and this does feel better when climbing with the shock open. In fact, I don't feel the bob anymore....just smooth pedaling over the bumps, rocks roots, etc. I 'm faster in the flats and rolling sections, however, here in CO we've got some long climbs and this is where I start to get worked.
Oh, forgot to mention, its not easy to do this correctly by yourself, enlist a helper. And try 2-3 times each leg. Make sure to get the ankle in same position as when pedaling. Many riders unintentionally drop their knee the moment they stop pedaling and this changes the relationship of the knee over the pedal.
Great link GRFSR. The comment about the exposure to the hamstring was interesting. I did feel more sore than normal in my hamstring just above the knee, especially when I tried the bike with a set back post.
I notice that the curve in the seat tube does angle back and wonder if this might be the reason it places me back further when there is more post showing.
This is true, and can be a problem for a lot of riders who are shooting for knee over the pedal spindle.
Originally Posted by rianclay
I also wonder if an XL frame with less seat post exposed and say a 100mm stem might be better. But, the longer TT has thinking I will be placed even further back from the cranks.
Top tube length doesn't put you further back. If the XL has a similar seat tube angle you should go for it. The XL will allow you to bring the saddle down, and forward, to get the correct fit. I am more comfortable on Large niner frames vs Mediums for this same reason.
A shorter stem on a larger frame will also likely feel far more confident when you are pointed down without any sacrifice on the climbs.
im 6'1 and im riding a large with 90mm stem bontrager xxx stem on no risers, and it fits perfectly, I am using a kindshock ks900 seatpost with the saddle a few mm from all the way forwards in the clamp, and the seat about 4 inches above my bars, knees line up just fine. The seat feels a little higher and further forwards than I used to run it on my old xc bike, but this bike is much more comfortable and I am faster on it. An XL would have been a mistake for me, but fit can be a very personal thing, from differences in physical build to comfort preferences, it might be the right one for you.
KOPS for me has been more about balance for me. I need to be slightly behind KOPS (10mm or so) to keep from having too much pressure on my hands and shoulders. Especially on my road bike when there is not as much on the bike movement.
G
You can't depend on honest answers from dependant hands...
lot's of valid points here. I will apply several of the recommended adjustments before going to the XL. I do think overall the SC measurements seem to run small compared to other bikes.
I also plan on jumping back on my Yeti asr SL to see where and how things line up. That bike just seems to feel like I'm exerting less effort on the extended climbs. Overall weight and wheel weight are very similar, so this is not the issue. The one easy thing I notice is the frame dimensions. Yeti is 21" ST, 24.75" TT vs. 19.5 & 24 =SC - L.
lot's of valid points here. I will apply several of the recommended adjustments before going to the XL. I do think overall the SC measurements seem to run small compared to other bikes.
I also plan on jumping back on my Yeti asr SL to see where and how things line up. That bike just seems to feel like I'm exerting less effort on the extended climbs. Overall weight and wheel weight are very similar, so this is not the issue. The one easy thing I notice is the frame dimensions. Yeti is 21" ST, 24.75" TT vs. 19.5 & 24 =SC - L.
Perhaps the XL will be the right size.
Drop a plumb line from the nose of your saddle on your Yeti, measure how far the nose is behind the center of the BB and see if you can replicate this dimension on your Tallboy. Note that this only works if you have the same kind of saddle on both bikes. The sweet spot varies greatly between different saddles.
On the bike fit, iIt all depends on how you like a bike to fit, me I like a long reach so @ 6'2.25" with a 35.25" inseam I go for a ETT of 25"+ i.e. XL frames. On the KOPS (knee over pedal spindle) thing, as some said, it's a starting point and then you work form there depending on your pedaling style - if you like to spin, KOPS is good. If you like bigger gears then slightly back of KOPS is better and allows more power. As far as I have learned, you can move as far back as 60-75mm from KOPS and still be good, just as said, what works and is comfortable for you. I like bigger gears, so I run about 2-3cm behind.
[edit] yeah Spoon, you got me, been using Illustrator too much and used the wrong function key to hold verticle, was off by a bit, so uploaded another one - made sure it was straight.
Last edited by LyNx; 08-17-2010 at 05:28 AM.
Originally Posted by Harold
You're doing mtbr wrong, you're supposed to get increasingly offended by the implications that you're doing ANYTHING wrong.
I don't see how getting larger frame will make any difference. The seat tube angle is the same, presumably he will set his seat height to be the same distance from crank to saddle. So his position from ass to crank won't change, he'll just have more seat tube and less seat post.
Also, I don't know if it's an optical illusion, but that line does not look plumb at all
To - JMH: You are on to something with the plumb line @ the saddle nose. I also measured from the center of the top of seat post. Interesting results - On the SC, the plumb line dropped further back behind the cranks at the 3/9 position by about 3/4-1" vs. the Yeti when measuring from the center of the post. Same held true when measured from the tip of the seat.
So...then I tested what happened if the seat was lowered within the frame to see if the plumb line ended closer to where the Yeti lined up.
Answer: Yes, and, in fact it was nearly exactly the same as the yeti when equal amounts of post were exposed from the frame. The curved seat tube does in fact change where the plumb line drops in relation to where the cranks are.
Based on this the XL will fit much closer to that of the Yeti. The real test will come when I have the shop build up the XL. I will post results ASAP.
I am enjoying the discussion as I am trying to optimize fit and bio-mechanics to get mine dialed in. It's tough as there are MANY opinions and as noted, everyone has a different concept of what works for them. My previous bike was fitted using the Bio-Racer system and right or wrong, I've kind of taken it for 'gospel'.
I'm still soaking it all in but am slightly overwhelmed as I chase the elusive 'perfect fit setup'...
Tallboy
Salsa El Mariachi SS
Salsa Vaya
Salsa Mukluk
Surly Big Dummy
So...then I tested what happened if the seat was lowered within the frame to see if the plumb line ended closer to where the Yeti lined up.
Your seat won't be lower on the XL! It will just have less seatpost exposed. The seat tube angle is the same, so the front to rear position will be the same. I'm not saying an XL is right or wrong, just don't expect your knee to pedal position to change.
spsoon is right. A bigger size does not mean that your knee position change according to your pedal.
What fork length are you running? If you bring it for example down from 120 to 100 mm your seatpost angle would put you more forwards above the cranks.
I just skimmed much of this, but did anyone mention moving the saddle on the rails? Or do Tallboy frames somehow prevent the most obvious solution to position of femur/knee relative to spindle??
Your seat won't be lower on the XL! It will just have less seatpost exposed. The seat tube angle is the same, so the front to rear position will be the same. I'm not saying an XL is right or wrong, just don't expect your knee to pedal position to change.
You and fatboy66 would be correct if you weren't missing the primary point mentioned early... there is a bend in the seat tube so the seat angle is very likely "virtual". If it's like most other bent seat tube bikes, the lower portion of the tube is steeper than 73º, and the upper portion of the seat tube is slacker than 73º. It's probably only "virtually" 73º inside a very small "sweet spot", perhaps if the saddle is roughly level with the stem or something like that. So raising the saddle IS going to make a much bigger difference in fore/aft saddle position than it would on a bike with a straight seat tube, and buying a larger frame will put your saddle back in the "virtual" seat angle sweet spot.
And then there is some bikes geometry does not fit some people. A guy that works for me has really long femurs and there are very few bikes he can ride comfortably. Just how it is. You can also run a laid back Thomson post reverse.
I agree spinning lizzard that not every bike suits somebody but according the figures from the santa cruz website the 73 degree seat angle with a 100 mm fork should be fine.
I think that one of the problems is the longer fork. So you can say the seat angle goes to 72 degrees. This could lead to a problem if you need a lot of seatpost.
KOPS is only a starting point, I wind up pretty forward of KOPS when I'm balanced right, other people wind up in back.
I'm not sure if going to a different frame size would help, it would only help if they put the seat tube bend in a different place on different size frames.
This is written towards roadies but the same principles apply:
spsoon is right. A bigger size does not mean that your knee position change according to your pedal.
What fork length are you running? If you bring it for example down from 120 to 100 mm your seatpost angle would put you more forwards above the cranks.
Good luck.
You raise another good point to consider. One degree slacker HA caused by a taller fork (20mm is not quite one degree, but it's close) will move your saddle about 1cm back.
I'm 6'2" with 34" inseam running a Large with KS 900r Seatpost - makes all the difference in the world. XL is huge IMO. I think it really depends what kind of rider you are. You want a flickable bike always go smaller, you like to just sit back and peddle go bigger. At 6'1" i think a large should be perfect unless you have some out of norm inseam or torso.
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Originally Posted by rianclay
