MtbVfr: Bike Fit / Stem Length, Saddle Position, Handlebar Height
06-07-17, 04:57 PM
#1
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MtbVfr: Bike Fit / Stem Length, Saddle Position, Handlebar Height
Hi Folks,
I want to be as scientific as possible to determine the Stems I need to get so as to not waste time and money on buying something that won't solve the Fit issues that I have.
I was buying stems with a shorter reach but now it appears I should have first been looking at just going higher and then maybe some more reach to solve the problem of always pushing my butt backwards. I don't think the saddle shape helps neither as it's a little concave. I have a flat saddle (Prologo Zero II 141 T2.0) to try but the instructions are adamant about not installing the saddle close to the limits of the rails as you can see in the first image attached.
I have attached 4 images.
The first shows the distances for the Handlebar/Saddle relationships. There is 10mm of rail in front of the clamp and 35mm of rail behind the clamp. So, to centre the rails, the the saddle needs to be moved 12.5mm forward. The Red and Blue measurements start from the centre of the bar in the handlebar clamp.
The 2nd shows an overall view of my position which shows that my back is not flat, because the handlebar is too close to the saddle I think.
The 3rd zooms in on the Knee/Pedal relationship.
The 4th shows the leg extension.
Diamond Back (DB) Details
The Top Tube has a length of 22.5" from the centre of the Seat Tube to the centre of the Head Tube. It's 21" from the back of the Head Tube to the front of the Seat Tube. Let me know if you want any other measurments.
Biomechanical Details
In 1994, in Denver, Andrew Pruitt determined, via X-rays, that my right leg is 8mm longer than the left with the right femur being 5mm longer than the left one and the Tibia and Fibula 3mm longer than the left. I also have long femurs for my leg length/height. A few years back, I changed from 175mm cranks with a 4mm shim on the left cleat to flat pedals with a 177.5mm left crank arm and a 180mm right crank arm. I found this newer setup more comfortable but still not perfect (I probably needed better orthotics to better cater for the pronation in my right foot). I am now using a 175mm left crank arm and a 180mm right crank arm which seems to provide a pretty smooth action and better feeling with the right knee but I still have a tendency to want to bring my left forefoot closer to the crank arm and backwards a little. I have some NC-17 Trekking Pro pedals coming that will allow my feet to be 5mm closer to the cranks. I dropped the saddle 3mm yesterday but have yet to take a ride to see what effect it has on what I am feeling with the left foot at the bottom of the stroke. Maybe having the saddle so far back in relation to the BB is also a contributing factor to what I am feeling with the left foot?
My right arm is effectively 2cm shorter than the left due to a compound fracture (1999) above the right elbow and hence the right elbow tends to "flap in the breeze". The muscles of the right side of my neck and top of the right suffer the most tightness.
The following are the measurements taken in 1994.
Current Stem and Handlebar (DB)
The current stem is a Profile Design BOA 120mm x 40°. If I changed that to a Dimension 135mm x 35°, it would puts my hands 18mm forward and 6.4mm higher (14.9mm higher with 9mm of Spacers, Dimension stem has a stack height of 41mm and the Dimension Quill/Aheadset adaptor extension has a 50mm clamp height). If the saddle was centred over the clamp, though, my hands would only be 5.5mm further forward from the saddle.
The Handlebar has a 30mm Rise and a 16° Backsweep.
Based on the suggested corrections for the old DB I can then extrapolate on those to calculate what would be best for my Haro V4 (18") which has a longer effective Top Tube than the DB. The handlebar I will be using on this has a 23mm Rise and a 25° Backsweep.
For a custom frame for me, I am thinking that a bike with a longer Effective Top Tube, taller Head Tube and a lower Bottom Bracket (so my feet can more easily touch the ground) maybe the way to go eventually.
Let me know if more details are required.
Thanks, mtbvfr.
I want to be as scientific as possible to determine the Stems I need to get so as to not waste time and money on buying something that won't solve the Fit issues that I have.
I was buying stems with a shorter reach but now it appears I should have first been looking at just going higher and then maybe some more reach to solve the problem of always pushing my butt backwards. I don't think the saddle shape helps neither as it's a little concave. I have a flat saddle (Prologo Zero II 141 T2.0) to try but the instructions are adamant about not installing the saddle close to the limits of the rails as you can see in the first image attached.
I have attached 4 images.
The first shows the distances for the Handlebar/Saddle relationships. There is 10mm of rail in front of the clamp and 35mm of rail behind the clamp. So, to centre the rails, the the saddle needs to be moved 12.5mm forward. The Red and Blue measurements start from the centre of the bar in the handlebar clamp.
The 2nd shows an overall view of my position which shows that my back is not flat, because the handlebar is too close to the saddle I think.
The 3rd zooms in on the Knee/Pedal relationship.
The 4th shows the leg extension.
Diamond Back (DB) Details
The Top Tube has a length of 22.5" from the centre of the Seat Tube to the centre of the Head Tube. It's 21" from the back of the Head Tube to the front of the Seat Tube. Let me know if you want any other measurments.
Biomechanical Details
In 1994, in Denver, Andrew Pruitt determined, via X-rays, that my right leg is 8mm longer than the left with the right femur being 5mm longer than the left one and the Tibia and Fibula 3mm longer than the left. I also have long femurs for my leg length/height. A few years back, I changed from 175mm cranks with a 4mm shim on the left cleat to flat pedals with a 177.5mm left crank arm and a 180mm right crank arm. I found this newer setup more comfortable but still not perfect (I probably needed better orthotics to better cater for the pronation in my right foot). I am now using a 175mm left crank arm and a 180mm right crank arm which seems to provide a pretty smooth action and better feeling with the right knee but I still have a tendency to want to bring my left forefoot closer to the crank arm and backwards a little. I have some NC-17 Trekking Pro pedals coming that will allow my feet to be 5mm closer to the cranks. I dropped the saddle 3mm yesterday but have yet to take a ride to see what effect it has on what I am feeling with the left foot at the bottom of the stroke. Maybe having the saddle so far back in relation to the BB is also a contributing factor to what I am feeling with the left foot?
My right arm is effectively 2cm shorter than the left due to a compound fracture (1999) above the right elbow and hence the right elbow tends to "flap in the breeze". The muscles of the right side of my neck and top of the right suffer the most tightness.
The following are the measurements taken in 1994.
Code:
INSEAM 84.5cm THIGH 41.0cm Foot Length 261.0mm "Q" Factor 48.52% Arm Length 610.0mm Torso Length 605.0mm UBM(sum of arm & torso) 1215.0mm
Current Stem and Handlebar (DB)
The current stem is a Profile Design BOA 120mm x 40°. If I changed that to a Dimension 135mm x 35°, it would puts my hands 18mm forward and 6.4mm higher (14.9mm higher with 9mm of Spacers, Dimension stem has a stack height of 41mm and the Dimension Quill/Aheadset adaptor extension has a 50mm clamp height). If the saddle was centred over the clamp, though, my hands would only be 5.5mm further forward from the saddle.
The Handlebar has a 30mm Rise and a 16° Backsweep.
Based on the suggested corrections for the old DB I can then extrapolate on those to calculate what would be best for my Haro V4 (18") which has a longer effective Top Tube than the DB. The handlebar I will be using on this has a 23mm Rise and a 25° Backsweep.
For a custom frame for me, I am thinking that a bike with a longer Effective Top Tube, taller Head Tube and a lower Bottom Bracket (so my feet can more easily touch the ground) maybe the way to go eventually.
Let me know if more details are required.
Thanks, mtbvfr.
06-24-17, 08:31 AM
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Knee appears to be quite a bit behind KOP, but that's because your heel is dropped down. (It's supposed to be done with a level foot, I believe.) If level, probably would be about KOP. Leg extension looks about right
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