Stupid Q - 22mm saddle ht difference.

[novetan]

I experimented on saddle ht using 155 and 145 degree between thigh and leg. It seems any angle between these 2 values are the most adopted angle and I just hv to find one that is suitable in time to come. I used a home made cardboard cut to these angles for my trial testing. I found there is a 22mm in height difference between these 2 angles. Can anyone testify is this ht difference about right? I may be asking a stupid question as you may said why not just find one suitable angle that suit me. Why bother to know the diff. Its because I'm still searching for a right ht and I like to do it within these 2 recommended angle. Or it varied from person to person.

 

[alienator]

First, it's pretty damned hard--essentially impossible--to measure the angle between your femur and tibia by yourself. Even with a cardboard cutout it would be difficult to hold it to the correct landmarks: the greater trochanter at the hip, the lateral condyle at the knee, and the lateral malleolus at the ankle. Further, foot position is difficult to maintain, even with someone else helping. Changing foot position--heel down, heel up, etc--also changes the angle of interest. With all that said, it's difficult to say how much your seat height should change between your stated angles (assuming their correct). It all depends on your femur length, tibia length, and your natural foot position at the bottom of your pedal stroke. You should also note that you also need to maintain the proper knee position with respect to the BB. That position will change as you raise or lower the saddle. To what landmarks did you cut and do you set your cardboard cut-outs?

 

[novetan]

Originally Posted by alienator .

First, it's pretty damned hard--essentially impossible--to measure the angle between your femur and tibia by yourself. Even with a cardboard cutout it would be difficult to hold it to the correct landmarks: the greater trochanter at the hip, the lateral condyle at the knee, and the lateral malleolus at the ankle. Further, foot position is difficult to maintain, even with someone else helping. Changing foot position--heel down, heel up, etc--also changes the angle of interest. With all that said, it's difficult to say how much your seat height should change between your stated angles (assuming their correct). It all depends on your femur length, tibia length, and your natural foot position at the bottom of your pedal stroke. You should also note that you also need to maintain the proper knee position with respect to the BB. That position will change as you raise or lower the saddle.
To what landmarks did you cut and do you set your cardboard cut-outs?

Tks for info,

I'm not a pro, not even can be considered a serious cyclist. But just want to do the right way as close as possible to established std. without having to pay money for a bike fit. I hv a helper which although none of us knows abt those biological terms u mentioned, we are running the cardboard along the middle of thigh to middle of leg. I think it will still get us some ballpark markers.

 

[daveryanwyoming]

If you really want to measure bike fit angles:

- Mount your bike on a trainer

- Shoot video from a tripod mounted camera set level to your bike with the camera square to your position from the side (not tilted down towards the floor, up towards the ceiling, or skewed towards the front or rear of the bike) and about a meter off the floor so you're shooting roughly straight into your hip

- Mark the anatomic landmarks mentioned above with something that stays put and is easy to spot in the final video. A magic marker dot on the lateral condyle and malleolus works nicely but something that contrasts with your shorts should be attached to your shorts and make sure this doesn't move relative to your GT as you pedal. BTW, palpating your own GT can be difficult but this gets you close: http://pinnaclept.files.wordpress.com/2010/03/greatertroch.jpg?w=600

- Shoot video while you're riding the trainer and at representative intensity and cadences.

- Download this free software to analyze the angles:
http://www.kinovea.org/en/

- Pay attention to more than just max knee angle at full extension. Also look at Min hip angle, min knee angle at top of stroke, torso angle, etc. some good guidance on what you might expect to see here: http://bikedynamics.co.uk/guidelines.htm

And in the end remember that there's a lot of art and not just hard numbers in terms of achieving a good bike fit, deal with specific concerns like limited flexibility, leg length discrepancies, varus/valgus issues in the feet, etc. And be willing to make tweaks to your positions based on things like feel for instance if the angles look great on paper but your hips are rocking as you pedal or your hamstrings get tight on longer rides. Those are clues that not everything is dialed in even if the numbers look good.

Also be aware that static angle measurements often differ from loaded dynamic measurements as most folks change things when they pose. For instance it's pretty typical for riders to pedal with at least some toe down style throughout the pedal stroke but then ask them to stop and hold their legs at the bottom of the stroke and they tend to flatten their feet out to horizontal. This has a big impact on max knee angle and would lead to a lower than ideal saddle position if you took that to be their normal pedaling style.

Good luck,
-Dave

 

[novetan]

Originally Posted by daveryanwyoming .

If you really want to measure bike fit angles:

- Mount your bike on a trainer

- Shoot video from a tripod mounted camera set level to your bike with the camera square to your position from the side (not tilted down towards the floor, up towards the ceiling, or skewed towards the front or rear of the bike) and about a meter off the floor so you're shooting roughly straight into your hip

- Mark the anatomic landmarks mentioned above with something that stays put and is easy to spot in the final video. A magic marker dot on the lateral condyle and malleolus works nicely but something that contrasts with your shorts should be attached to your shorts and make sure this doesn't move relative to your GT as you pedal. BTW, palpating your own GT can be difficult but this gets you close: http://pinnaclept.files.wordpress.com/2010/03/greatertroch.jpg?w=600

- Shoot video while you're riding the trainer and at representative intensity and cadences.

- Download this free software to analyze the angles:
http://www.kinovea.org/en/

- Pay attention to more than just max knee angle at full extension. Also look at Min hip angle, min knee angle at top of stroke, torso angle, etc. some good guidance on what you might expect to see here: http://bikedynamics.co.uk/guidelines.htm

And in the end remember that there's a lot of art and not just hard numbers in terms of achieving a good bike fit, deal with specific concerns like limited flexibility, leg length discrepancies, varus/valgus issues in the feet, etc. And be willing to make tweaks to your positions based on things like feel for instance if the angles look great on paper but your hips are rocking as you pedal or your hamstrings get tight on longer rides. Those are clues that not everything is dialed in even if the numbers look good.

Also be aware that static angle measurements often differ from loaded dynamic measurements as most folks change things when they pose. For instance it's pretty typical for riders to pedal with at least some toe down style throughout the pedal stroke but then ask them to stop and hold their legs at the bottom of the stroke and they tend to flatten their feet out to horizontal. This has a big impact on max knee angle and would lead to a lower than ideal saddle position if you took that to be their normal pedaling style.

Good luck,
-Dave

Thks so much Dave. Let me digest it. Quite a load full of info.

 

[daveryanwyoming]

Getting back to your original question about establishing a good range of acceptable saddle height:

You might consider using total saddle to pedal height as a function of Greater Trochanter height as your basis instead of leg angles. In the end they tend to work out about the same but the former is much easier to implement and to check. Basically cycling VO2 Uptake, power, and efficiency studies have looked at cyclists output and O2 utilization as a function of total saddle height vs greater trochanter height. Based on these studies cyclists perform well with a saddle height between 96% and 100% of GT height measured while wearing cycling shoes (yeah, that makes a lot of assumptions about cleat/pedal system and sole/insole thickness but that's how the studies were performed).

Using this method:

- Find and mark your GT (again a bit tough to do on yourself but start with your thumb on the highpoint of your Iliac crest with your hand pointed down and your middle two fingers should be feel the rounded bump of your GT. Double check that this bump moves back as you lift your knee.

- Stand straight upright while wearing your cycling shoes and have someone measure the distance from the floor to the center of your GT or transfer this measurement to a wall and measure it yourself.

- Set the total height from the center of your pedal spindle to top of seat at the place you'll actually ride (typically measure straight up the seat tube for road bike saddles, but it can change for things like TT/Tri saddles where the rider tends to ride far forward). This should be in a range of 96% to 100% of GT height.

Only the most flexible folks will be able to run at 100% without hip rocking or hamstring tightness issues but most folks can ride higher than 96%. Higher is good until you go too far at which point the rider either struggles with flexibility issues and discomfort or their O2 uptake and HR for the same moderate power output climbs dramatically which is what happened to the test subjects when they raised their saddles above 100% of GT height. Performance falls off fast when you go too high so err on the side of lower and FWIW a lot of folks seem happy around 98% of GT height.

Also FWIW for riders around 5'10" to maybe 6' tall it's not unusual to see GT heights around 93-97 cm, so for folks around this tall with typical body proportions that 4% range from 96-100% is about 2.5 to almost 4 cm of total seat height working range. This also tends to agree well with a range of maximum knee angles in the 145 to 155 degree range but it's a bit different way of getting to similar results and is less dependent on things like whether you stretch with your toes to reach the pedals at high seat heights (IOW, you could be running say 102% of GT height which isn't recommended but stretching a lot with your feet and down pointed toes and still come up with say 150 degree max knee angle but you're basically compensating with excessive toe down to get that angle and are actually riding a bit high).

BTW, all of this stuff assumes a nominal cleat position under the ball of your foot and typical foot sizes, long feet or far forward cleat placement will typically require a higher seat position and smaller feet and especially aft cleat position or mid foot 'arch' cleats require a lower saddle height as almost everyone toes down a bit in the pedal stroke and the length of that down pointed foot adds to leg reach. Of course if the rider is truly a flat footed or heel dropping rider (and not just because their seat is low and they're compensating) then shoe size is less relevant.

-Dave

 

[novetan]

Originally Posted by daveryanwyoming .

Getting back to your original question about establishing a good range of acceptable saddle height:

You might consider using total saddle to pedal height as a function of Greater Trochanter height as your basis instead of leg angles. In the end they tend to work out about the same but the former is much easier to implement and to check. Basically cycling VO2 Uptake, power, and efficiency studies have looked at cyclists output and O2 utilization as a function of total saddle height vs greater trochanter height. Based on these studies cyclists perform well with a saddle height between 96% and 100% of GT height measured while wearing cycling shoes (yeah, that makes a lot of assumptions about cleat/pedal system and sole/insole thickness but that's how the studies were performed).

Using this method:

- Find and mark your GT (again a bit tough to do on yourself but start with your thumb on the highpoint of your Iliac crest with your hand pointed down and your middle two fingers should be feel the rounded bump of your GT. Double check that this bump moves back as you lift your knee.

- Stand straight upright while wearing your cycling shoes and have someone measure the distance from the floor to the center of your GT or transfer this measurement to a wall and measure it yourself.

- Set the total height from the center of your pedal spindle to top of seat at the place you'll actually ride (typically measure straight up the seat tube for road bike saddles, but it can change for things like TT/Tri saddles where the rider tends to ride far forward). This should be in a range of 96% to 100% of GT height.

Only the most flexible folks will be able to run at 100% without hip rocking or hamstring tightness issues but most folks can ride higher than 96%. Higher is good until you go too far at which point the rider either struggles with flexibility issues and discomfort or their O2 uptake and HR for the same moderate power output climbs dramatically which is what happened to the test subjects when they raised their saddles above 100% of GT height. Performance falls off fast when you go too high so err on the side of lower and FWIW a lot of folks seem happy around 98% of GT height.

Also FWIW for riders around 5'10" to maybe 6' tall it's not unusual to see GT heights around 93-97 cm, so for folks around this tall with typical body proportions that 4% range from 96-100% is about 2.5 to almost 4 cm of total seat height working range. This also tends to agree well with a range of maximum knee angles in the 145 to 155 degree range but it's a bit different way of getting to similar results and is less dependent on things like whether you stretch with your toes to reach the pedals at high seat heights (IOW, you could be running say 102% of GT height which isn't recommended but stretching a lot with your feet and down pointed toes and still come up with say 150 degree max knee angle but you're basically compensating with excessive toe down to get that angle and are actually riding a bit high).

BTW, all of this stuff assumes a nominal cleat position under the ball of your foot and typical foot sizes, long feet or far forward cleat placement will typically require a higher seat position and smaller feet and especially aft cleat position or mid foot 'arch' cleats require a lower saddle height as almost everyone toes down a bit in the pedal stroke and the length of that down pointed foot adds to leg reach. Of course if the rider is truly a flat footed or heel dropping rider (and not just because their seat is low and they're compensating) then shoe size is less relevant.

-Dave

Tks so much once again. I find the last link you send me is really useful and I'm trying out in accordance to the instruction. I supposed the conclusion cannot be that fast. Need a few rides to fine tune.