Login required to started new threads

Login required to post replies

90 degree hip angle fit question
Quote | Reply
In a fit article on Slowtwitch, I understand the article to say there should be a 90 degree angle formed by the torso, hip joint, and pedal spindle. On the newer FIST articles and photos on Mr. Demmerly's site, the 90 degree angle is formed by the torso, hip joint, and knee joint.

Am I reading this incorrectly? Or, has the recommendation changed somewhat?

Thanks!



Quid quid latine dictum sit altum videtur
(That which is said in Latin sounds profound)
Quote Reply
Re: 90 degree hip angle fit question [ktalon] [ In reply to ]
Quote | Reply
Hmmm, good question, although I'm not 100% sure I understand the question. One difference between how we've been measuring saddle height and how Dan and Fiona of Endurosport (Canada's finest tri shop) are doing it is that they take the measurement in line with the seat tube, whereas we take at the bottom dead center. We get the same or similar results in total leg extension but do use a different method. Is that what you mean?

Tom Demerly
The Tri Shop.com
Quote Reply
Re: 90 degree hip angle fit question [Tom Demerly] [ In reply to ]
Quote | Reply
Thanks for responding, Tom!

It's not a matter of seat height that I'm asking about, it's the angle between the torso and the extended knee vs. the angle between torso and the pedal spindle at the bottom of the stroke. Both sites say this angle should be 90 degrees, but you can't have it both ways...which one is considered to be "correct". (Or, am I just reading it wrong...ALWAYS a possibility!)

Thanks again...



Quid quid latine dictum sit altum videtur
(That which is said in Latin sounds profound)
Quote Reply
Re: 90 degree hip angle fit question [ktalon] [ In reply to ]
Quote | Reply
my own view is it's the pedal axle, or the BB, either/or of fine, because the functional difference is slight. hip to knee makes the angle too acute for my taste or, to put it another way, in order to get the 90-degree angle you'd move the bars up higher, which would cause the rider to be a little high in front.

Dan Empfield
aka Slowman
Quote Reply
Re: 90 degree hip angle fit question [Slowman] [ In reply to ]
Quote | Reply
Thanks millions! Where else in the world can you get clarification responses like this, and so quickly!?!

FWIW, I'm setting up my new Yaqui Carbo tomorrow, provided UPS delivers as scheduled. I've got my helper, T-square, plumb-bob, mirror, measuring tape, etc. all ready, and don't have a lot of time to mess around too much trying to get it right. I'd like to race it Saturday morning, if I can get situated on it well and have time to practice a bit.

I really appreciate the help!



Quid quid latine dictum sit altum videtur
(That which is said in Latin sounds profound)
Quote Reply
Re: 90 degree hip angle fit question [Tom Demerly] [ In reply to ]
Quote | Reply
Tom, you raise an interesting point. I have always measured for myself and customers with the pedal in line with the seat tube, as that is the furthest the foot will ever be away from the hip, i.e. that is the longest that the leg could be extended, with the heel touching the pedal spindle. Why do you measure from BDC, are you measuring with the ball of the foot on the pedal?

tommy
Quote Reply
Re: 90 degree hip angle fit question [Slowman] [ In reply to ]
Quote | Reply
ahhh, what Dan says.... Geez, now I'm totally confused...

Tom Demerly
The Tri Shop.com
Quote Reply
Re: 90 degree hip angle fit question [Tom Demerly] [ In reply to ]
Quote | Reply
i seriously doubt you're totally confused, maybe just temporarily and slightly bemused. in practice i'm sure your fits and mine would come out looking pretty similar.

Dan Empfield
aka Slowman
Quote Reply
Re: 90 degree hip angle fit question [Tom Demerly] [ In reply to ]
Quote | Reply
I am glad someone is paying attention. I certainly wasn't. We were all asking why Tom Briggs' position is up so high. I didn't even notice that the hip angle is measured to the knee rather than the pedal spindle at the bottom of the cycle. The result is that his hip is much more open than 90 degrees and he is higher in front as a result. Duh. His angle is probably more like 100 degrees measured normally.

If I were a big guy like that, I would want a more open position too. In fact, I do have too much around my middle, so I do have a higher position than I might like compared to the skinny kids I envy.

I hate it when I overlook the obvious that way.

Clueless in Florida,
Quote Reply
Re: 90 degree hip angle fit question [Slowman] [ In reply to ]
Quote | Reply
Do you use a _long_ goniometer to try to measure the shoulder socket/hip socket/pedal spindle at bdc combination? It seems that in practice small differences in measurement from finding the exact socket positions would result in variations of a couple of degrees, making most of these positions functionally equivalent.

A couple of other fit questions I've had rolling around in my head and which I came back to when I saw the fit at Tom Demerly's site:

1. Why is the saddle to armest drop recommended by Dan's formulas so much higher than what you see in road biking time trials? With the basic idea of tri bikes being to be rotated more forward around the bb to get lower than on a road bike, it would seem that you would have larger saddle to bar top drops on a tri bike than on a road TT bike since you don't have the UCI restrictions to work around. The only reason I can think of is the longer nature of the bike TTs in triathlon.

2. I can understand the importance of an open hip angle to achieve optimum power. Buy why is the torso-upper arm angle of 90 degrees so important? For relaxation, it would seem that you would want a more acute angle so your upper arms would be perpendicular to the ground, allowing your skeletal system to fully support your body weight. There might be a bit more shock absorption with the elbows further foward, but that also forces your muscles (posterior deltoids, upper lats, lower back?) to work to maintain the body/upper arm relationship. Is this rule all about knee clearance? Maybe people with shorter femurs can ride with a more acute upper arm/torso angle.
Quote Reply
Re: 90 degree hip angle fit question [goathead] [ In reply to ]
Quote | Reply
"Why is the saddle to armest drop recommended by Dan's formulas so much higher than what you see in road biking time trials?"

i don't think the drop formula DOES result in a lesser amount of drop vs. road bike time trials, except if you consider certain exceptions, such as chris boardman (but then you'd have to consider triathlon's exceptions, like joe bonness). i think the positions in the two sports track fairly well.

"Buy why is the torso-upper arm angle of 90 degrees so important?"

i guess i should say that "no more than 90 degrees, or at most 95 degrees" is optimal. i wouldn't mind a smaller angle, except:

1. yes, you've hit on it, it's knee clearance, both in and especially out of the saddle, and...

2. the other positions, descending, cornering, etc.

Dan Empfield
aka Slowman
Quote Reply
Re: 90 degree hip angle fit question [Slowman] [ In reply to ]
Quote | Reply
Dan-

What do you use to measure the angles when you fit someone? I don't feel like I could say with any confidence if I was + or - a couple of degrees.

Re. the saddle to bar drop, I haven't run many numbers through your formula so maybe the difference isn't as much as I thought. Still, I see lots of pictures of triathletes sitting relatively high, while many road TTers appear to have nearly flat backs. Seems to contradict what one would expect if the tri folks are going to be placing their saddles further forward.

Here's a related conversation over at Cycling Forum:

http://www.cyclingforum.com/forums/Thread.cfm?CFApp=2&Thread_ID=4650&mc=52

They also have threads on aerodynamics and on wind tunnel testing which may be of interest.
Quote Reply
Re: 90 degree hip angle fit question [goathead] [ In reply to ]
Quote | Reply
"What do you use to measure the angles when you fit someone?"

i have a big plastic angle thingy, like a goniometer. but i use it for show. after fitting 500 or a thousand people you get to where you know what 90 degrees looks like.

"I see lots of pictures of triathletes sitting relatively high, while many road TTers appear to have nearly flat backs."

that's probably because the triathletes AREN'T fit according to my formula for armrest drop, and the roadies ARE.

Dan Empfield
aka Slowman
Quote Reply
Re: 90 degree hip angle fit question [Slowman] [ In reply to ]
Quote | Reply
Dan-

When you do a fitting, do you change the formula results much for differences among people with the same saddle height? Differently stated-- do you find that differences between individuals such as long/short torso, leg and arm length, flexibility, etc. all fall within the + or - 1.5 cm factor?

Also, have you found a similar formula which would work with riders on standard road bikes, e.g. no drop bars and slacker seat tube/hip angles?
Quote Reply
Re: 90 degree hip angle fit question [goathead] [ In reply to ]
Quote | Reply
the formula works pretty well for everybody, tho like coca cola i've found that there's value in my original formula: .2d instead of .22d. therefore, i'm going back.

i have nothing of value to say to the road race community about bike fit that hasn't already been said or written. i'll just keep to tri bike fit.

Dan Empfield
aka Slowman
Quote Reply
Re: 90 degree hip angle fit question [ktalon] [ In reply to ]
Quote | Reply
I've been reading the forum a little since attending the FIST camp last month. I figured this is as good a time as any to chip in with my two bits.

First, thanks to Tom and Dan for their positive comments on our work on bike fit. Second, Dan is the one who taught me how to fit triathletes in the first place when I opened Enduro Sport eight years ago. Third, Dan and I now speak slightly different "dialects" when it comes to fitting. This may be where the confusion of the original poster comes in.

The Slowtwitch method involves measuring the angle between the torso and a line from the ball socket of the hip through the pedal spindle at the "bottom of the pedal stroke" (which is open to some interpretation). Ideally this angle would be about 90 degrees.

The Enduro Sport method measures the angle between the torso and femur at maximum leg extension, when the crank is inline with the seat tube (i.e. not quite at 6 o'clock, more like 5:30). We look for a minimum of 90 degrees.

The rationale for our method:

1) Maximum extension is a relative measure to effective seat tube angle. It is a slightly different crank angle for road bikes vs. tri bikes but it is always maximum leg extension.

2) The issue is maintaining an "open angle" at the hip in order to prevent the expected loss of power if the hip angle gets too low. We measure the actual angle. The Slowtwitch method measures a closely related angle but not the actual angle.

I would expect that the difference in the Slowtwitch hip angle the Enduro Sport hip angle to be 10-15 degrees. We do set people up in a slightly higher, more conservative position than Dan.

The future of hip angle:

1) We are going to change the way we measure hip angle based on some of the discussions we had at the FIST camp. We are now going to measure *minumum* hip angle by measuring at 180 degrees from when we used to. If we are concerned about how *closed* the hip angle gets then we should measure how closed it gets. This will also take into account femur:tib-fib ratio, foot length, crank length and foot angle into better account.

2) Before we worry about all this precision we (or somebody) needs to do a really good study of hip angle and its effect on power output. We have our theory on this but *no one* has ever tested it (if any one has please email me!). Until we know how small this angle can get before power output is affected precision is not all that important.

So that's my two cents on hip angle... I'll try and contribute to the forum more regularly on fit issues. I think we are just starting to scratch the surface on many of these issues and the FIST camp was and (hopefully) will be the sort of place to really advance our understanding of tri bike fit.

Dan Rishworth
dan@endurosport.com
Quote Reply
Re: 90 degree hip angle fit question [goathead] [ In reply to ]
Quote | Reply
Again on the subtle differences between the Slowtwitch method and Enduro Sport method of tri bike fit, we like the perpendicular upper arm angle, however, as Dan points out, you may run into knee/elbow interference issues depending on your particular dimensions. We therefore look for an torso-upper arm angle of no more than 90 degrees and no less than perpendicular to the ground.

On the subject of arm rest drop, we are going to look at Dan's new (old) formula for drop with our past fits based on discussions at the FIST camp. Dan does prefer lower positions than we do so I'm sure it won't match what we do, but the really issue is how consistent is his formula with what we do?

When we measure some one before a fit, we take is upper and lower arm measurements separately. We use the upper arm number to estimate how much drop is necessary. As you point out two riders with identical dimensions but different upper arm lengths will need different arm rest drops to achieve the "same" position.

We are looking at a formula to define this drop but it is complicated by back shape and flexibility which are hard to quantify. Of course there will always be a range based on the inescapable "rider preference."

Dan Rishworth
dan@endurosport.com
Quote Reply
Where else but Slowtwitch... [ In reply to ]
Quote | Reply
Another example of how the information available on Slowtwitch is without equal. Thanks for the willingness to share your expertise!



Quid quid latine dictum sit altum videtur
(That which is said in Latin sounds profound)
Quote Reply
Post deleted by The Committee [ In reply to ]
Re: 90 degree hip angle fit question [not a PCer] [ In reply to ]
Quote | Reply
I've looked and I haven't found. If you could point me in the right direction, I'd appreciate it.
Last edited by: Dan Rishworth: Mar 19, 03 7:15
Quote Reply