Charles.Plager
Recumbent Quant
I would expect that this would work better for most people who have one leg shorter than the other.
V20 finding that fit
- Thread starter ratz
- Start date
I would expect that this would work better for most people who have one leg shorter than the other.
Charles.Plager
Recumbent Quant
Do you compensate? If so, how?
PeteClark
Active Member
I have not used any shims for cycling or walking, but left it to my body to compensate. Used to give me back pain when I ran. No apparent trouble from cycling or walking.
I expected to find that I'd set my boom a bit short of the recommended position in order to favor the shorter leg, but in fact I've been very comfortable with +0.5 cm. Pretty clear that my toes are not vertical at full extension, but pointed forward. That seems to help pull down (equivalent to "scraping mud off your shoe" on a DF).
Charles.Plager
Recumbent Quant
I'm a little hesitant to suggest this (because you seem to have found what works for you), but have you considered a shim? It might take a bit to get used to, but it might give you a better experience in the long run. (And, it might not.
)
PeteClark
Active Member
I appreciate the suggestion Charles. I've thought about this before (back in the DF era) and decided I didn't want to increase the distance between the ball of my foot and the pedal spindle.I'm a little hesitant to suggest this (because you seem to have found what works for you), but have you considered a shim? It might take a bit to get used to, but it might give you a better experience in the long run. (And, it might not.
Now I'm 60, feeling no pain (at least related to this issue), so not inclined to experiment.
Here are my numbers:
Inseam = 32.5" = 82.5cm
lll = 22" = 55.9cm
v20 with standard boom, slider, seat pan, and standard Ventist pad
estimated bb to seat pan = 82.5 - ((16.5/2) + 1.75) = 72.5cm
actual bb to seat pan = 72.4cm
My knees start talking to me (in a bad way) if my leg extension deviates more than about 0.5cm from this setting so I know this is correct for me.
Inseam = 32.5" = 82.5cm
lll = 22" = 55.9cm
v20 with standard boom, slider, seat pan, and standard Ventist pad
estimated bb to seat pan = 82.5 - ((16.5/2) + 1.75) = 72.5cm
actual bb to seat pan = 72.4cm
My knees start talking to me (in a bad way) if my leg extension deviates more than about 0.5cm from this setting so I know this is correct for me.
ratz
Wielder of the Rubber Mallet
Well definitely interesting so far for those that have measured.
Since it's hard to measure to the dead center of the BB
seeing +- 5 mm accuracy was better than I had hoped for.
I was orginally looking for a "beginners" recommendation
I'm now a week in; and I have noticed 4 things:
1) I'm spinning a faster cadence
2) My calves are carrying more of the workload
3) The typical bikers muscles directly above the knee are not happy as they suddenly have to do work
4) Load on the gluts is less
My full 1" correction was definitely a lot . At this point I might also be 5mm too close now but I was definitely too far out; not sure if that was from boom slip or just a side effect of how many times I wind up adjusting my bike so other people can try it. Going to at least finish the week before I try the 5mm adjust. This also begs to have an FTP test which I really don't have time todo right now.
Since it's hard to measure to the dead center of the BB
seeing +- 5 mm accuracy was better than I had hoped for.
I was orginally looking for a "beginners" recommendation
I'm now a week in; and I have noticed 4 things:
1) I'm spinning a faster cadence
2) My calves are carrying more of the workload
3) The typical bikers muscles directly above the knee are not happy as they suddenly have to do work
4) Load on the gluts is less
My full 1" correction was definitely a lot . At this point I might also be 5mm too close now but I was definitely too far out; not sure if that was from boom slip or just a side effect of how many times I wind up adjusting my bike so other people can try it. Going to at least finish the week before I try the 5mm adjust. This also begs to have an FTP test which I really don't have time todo right now.
Barefoot Biker
Active Member
inseam=34"=86.36cm
crank axel to seat pan=29"=73.66cm
crank axel to where bars attach to boom = 34.5"=87.63cm - is that "boom length" ?
height of thigh = 24"=60.96cm
crank length = 170mm=17cm
classic / original / stock pad = x = 1.75cm
Boom Length = LLL + Crank Length + 8 cm
87.63 = 60.96 + 17.0 + 8
87.63 = 85.96
BB distance from front of Seat Pan = Inseam - ((CrankLength /2) + X))
73.66 = 86.36 - (17/2) + 1.75
73.66 = 77.86 + 1.75
73.66 = 79.61
what does this mean?
crank axel to seat pan=29"=73.66cm
crank axel to where bars attach to boom = 34.5"=87.63cm - is that "boom length" ?
height of thigh = 24"=60.96cm
crank length = 170mm=17cm
classic / original / stock pad = x = 1.75cm
Boom Length = LLL + Crank Length + 8 cm
87.63 = 60.96 + 17.0 + 8
87.63 = 85.96
BB distance from front of Seat Pan = Inseam - ((CrankLength /2) + X))
73.66 = 86.36 - (17/2) + 1.75
73.66 = 77.86 + 1.75
73.66 = 79.61
what does this mean?
ratz
Wielder of the Rubber Mallet
In theory if you make the boom 86cm long and set the BB center 79.5cm from the front of the carbon seat pan; you should be able jump on the bike and have it fit with only small adjusts to your liking. That's the theory we are testing.
It means your BB is closer than the formula predicts
which in turn means you may be riding with more knee bend that you need to
and you might be loosing power at the bottom of your pedal stroke.
You have 6cm to play with that's a lot you can test by making it 5mm longer at a time, test repeat and see if it's comfortable.
Your total boom length might be able to be shorter IF you want your hand further forward for a straighter arm position; it's probably "longer" than predicted but I would play with first adjustment first
Charles.Plager
Recumbent Quant
Can you post the same picture with your heal on the pedal? I always start by setting my boom up so that my knee is straight with the heal on the pedal and then tweak it from there. I'm curious how close to ideal your fit is to that starting point.
ratz
Wielder of the Rubber Mallet
Yep infact that's how I use to do it then tweak from there; but I don't recall where that puts me now; this weekend I will get some help to do that.
trapdoor2
Zen MBB Master
I've finally gotten around to doing this.
Measured BB distance from Seat Pan = 29.75" (75.565cm)
81.28-((16.5/2)+2.25) = 81.28-10.5 =70.78
Looks like my numbers are off by 4.79cm. Nearly 2" (1.886")
Hmmmm. I'm very comfy at the current setting. My cleats are at nearly mid-sole, so even if I am an ankler it shouldn't make much difference. I set my knee extension by the old 'flat on the heel' method...but I would say my angle is a good bit flatter than 'optimum'. However, I experience no knee pain at all.
Well, I'll be riding about 30 mi tomorrow morning on my breakfast run. I'll do 20 mi, stop for 2hrs and drink coffee/gab with my 70yr old brother (who will be riding a Honda Blackbird named "Habu") at "Panera Bread Co"'. Then it is 10 mi back to my house. I'll try to pay more attention to the nuances of my riding style during the trip. If I have any gumption afterwards, I'll try setting up at the shorter number and try it out.
Measured BB distance from Seat Pan = 29.75" (75.565cm)
81.28-((16.5/2)+2.25) = 81.28-10.5 =70.78
Looks like my numbers are off by 4.79cm. Nearly 2" (1.886")
Hmmmm. I'm very comfy at the current setting. My cleats are at nearly mid-sole, so even if I am an ankler it shouldn't make much difference. I set my knee extension by the old 'flat on the heel' method...but I would say my angle is a good bit flatter than 'optimum'. However, I experience no knee pain at all.
Well, I'll be riding about 30 mi tomorrow morning on my breakfast run. I'll do 20 mi, stop for 2hrs and drink coffee/gab with my 70yr old brother (who will be riding a Honda Blackbird named "Habu") at "Panera Bread Co"'. Then it is 10 mi back to my house. I'll try to pay more attention to the nuances of my riding style during the trip. If I have any gumption afterwards, I'll try setting up at the shorter number and try it out.
trapdoor2
Zen MBB Master
Well...I ran out of time to do any testing at a shorter length. Very windy yesterday: strong base wind @ 15mph with strong gusts therein. That 10 mi back to my house was right in the teeth of the wind and once I got onto the main road there was no protection. My normal speed on that road is 18-20mph...yesterday I struggled to make 14 and keep my HR below 150. By the time I got home, I was whipped!
Again, no knee issues. If I get a chance, I'm going to measure my static knee angles and see what I can see.
Again, no knee issues. If I get a chance, I'm going to measure my static knee angles and see what I can see.
ratz
Wielder of the Rubber Mallet
Intersting here is it sound like you have your cleat mounted mid shoe correct? Is that stock or custom? I would expect that would make your boom even shorter. Now that said this forumla is meant to be a starting point as a way to get a better first attempt fit for people; that's why it's interesting to see how many people are close and how many are far off. Being the first person to be way off, isn't necessary bad; it just means the fit for your is different... Why that is becomes the interesting part.
trapdoor2
Zen MBB Master
My cleats (SPD) are simply mounted as far towards the middle of the shoe as the original slots allow. Size 12-1/2 shoes.
I don't mind being 'off', but I would like to better understand what's going on. I am well-known for my adaptability for fitment...and tend to do well by selecting "average" . IOW, I may very well be riding in a 'less than optimum' configuration and not know it. I suspect my extension angle is closer to 170. My off knee is very close to 90 degrees. Of course, I'm just guessing. I'll measure as soon as I can.
Phantomrider
Active Member
great info for half of the equation, is there a standard for the upper body? yep, I'm a newbie and trying to figure all this out. I have been working just based on feel so I wonder, is there a better way...
