I just purchased a Cobb seat due to the fact that I felt like my junk was going to fall off with the stock vision seat on my SC. The Cobb instructions have you measure inseam from the floor next to your foot tight up into your crotch. You then take this measurement x .889 to find seat height (measure from center of crank arms to center of seat at the top of seat).
I took this measurement yesterday and found my seat to be OVER AN INCH too low! Not a centimeter…an INCH. I bought my bike from a LBS that definitely does NOT specialize in Tri bikes, but they surely should be able to set seat height (they measured my knee angle). I always kind of felt my seat may be too low.
For reference my wife took her measurement and I checked her seat height using the same formula (Madone road bike bought at same shop) and her seat was dead on to the 1/8" of the Cobb formula! She did have a different fitter.
So my question is this. For those of you using the Cobb formula is it dead on in your experience and secondly how tight to my crotch am I holding the tape? Am I jamming it up there until I hit bone / hard tissue or simply holding it to the soft tissue areas (it makes quite a difference). I’m looking for personal experience from others and will also call Cobb today.
Pedaling last night with my seat an inch higher I didn’t notice any hip wobble so I think I am at least fairly well off with my seat that full inch higher. Unreal. That sure was an easy way to get low in the front!
Mine on the tri bike was dead on, but that doesn’t count as John did my fit. But it was bang on on the road bike which a friend fit me on ages ago that I am very comfortable on.
cobb’s forumla does not take into account crank length. so it can’t really make total sense.
I thought that as well. Wouldn’t it make more sense for someone to come up with a formula to measure from the top of the pedal while the crank is in it’s lowest position to the seat? But I suppose even that would be out since it doesn’t take into account the higher profiles of certain pedals/cleats.
It’s “probably” just a ballpark estimate to get you pretty close. Having been fit by John, he generally puts a set a tad bit lower than some other fitters might. But, it’s individual. He’s working on some videos to try to explain things further.
cobb’s forumla does not take into account crank length. so it can’t really make total sense.
You measure to the middle of the crank arm. So yes, it takes crank length into account.
That doesnt mean it takes it into account. Imagine someone using 200mm cranks as an extreme example, the seat would be way too high they probably would have their heal straight up.
cobb’s forumla does not take into account crank length. so it can’t really make total sense.
You measure to the middle of the crank arm. So yes, it takes crank length into account.
That doesnt mean it takes it into account. Imagine someone using 200mm cranks as an extreme example, the seat would be way too high they probably would have their heal straight up.
How can using crank length as part of the measurement not take crank into account?
I never said anything about the usability of the Cobb method. This thread is the first I’ve heard of it. Jackmott said crank length wasn’t considered. According to op you measure from mid crank arm. That means crank length is part of the formula. You say it doesn’t. But it does. Whether or not it produces the correct seat height is another issue.
I may be slightly green in the terminology department. Center of crank not crank arms. So if removing the crank arms completely it would be a measurement from the center of bottom bracket (hope that’s correct terminology)??? or center of bearing…I hope that’s more clear.
So I’d agree with Jackmott…if this formula is accurate for 165mm cranks and I adjust seat height accordingly no way would I be able to reach a 200mm crank.
I may be slightly green in the terminology department. Center of crank not crank arms. So if removing the crank arms completely it would be a measurement from the center of bottom bracket (hope that’s correct terminology)??? or center of bearing…I hope that’s more clear.
So I’d agree with Jackmott…if this formula is accurate for 165mm cranks and I adjust seat height accordingly no way would I be able to reach a 200mm crank.
cobb’s forumla does not take into account crank length. so it can’t really make total sense.
You measure to the middle of the crank arm. So yes, it takes crank length into account.
That doesnt mean it takes it into account. Imagine someone using 200mm cranks as an extreme example, the seat would be way too high they probably would have their heal straight up.
How can using crank length as part of the measurement not take crank into account?
I never said anything about the usability of the Cobb method. This thread is the first I’ve heard of it. Jackmott said crank length wasn’t considered. According to op you measure from mid crank arm. That means crank length is part of the formula. You say it doesn’t. But it does. Whether or not it produces the correct seat height is another issue.
It is not the center of the crank arm. It is the center of the bottom bracket or crank bolt or “center of the crank”. Crank arm length is not part of the Cobb equation (at least in my understanding or use).
I believe this formula is the same as what Greg Lemond published in his book what … about two decades ago now? If I recall correctly (and I might not), it results in a saddle height that’s slightly lower than some other fitting formulas I’ve seen. If it resulted in you raising your saddle by an inch, I’d say something went wrong in your original fitting.
As for how tightly into your crotch to measure, the best approach I’ve heard for taking this measurement is to stand facing a door frame or a wall where you don’t mind making a pencil mark. Take a book with about a 1 inch binding and shove it (binding edge up) into your crotch until the pressure on your crotch approximates pressure you might feel on a saddle. Make sure you’re close enough to the wall and make a mark where the book binding is … making sure to keep it level so the mark you make is the same height from the floor as where the binding is stuffed into your crotch. Repeat it several times and use the average.
only difference is lemond = .883 while his is .889, tried both and went with the .883. Only thing i did differently was i measured from the nose of my saddle instead of the middle part of the saddle, currently on an adamo - the tech from adam suggested this i do, so far so good.
Yeah, it’s just a variation of the “LeMond” formula that Guimard used with his Renault tram back in the 80’s. Back then 170mm was the pretty much universal crank length for roadies. Greg’s book notes some adjustments for sole thickness of the shoe (in the pre-clipless era the distance from the sole to the pedal axle was fairly constant).
A formula like Cobb’s should get you close, but won’t be as dialed as a reputable fit.
The Renault/Gitane team did physiological testing I believe under Guimard and used that 0.883 to centre BB, but Hinault used 172.5 and Lemond 175mm cranks, so that would skew results. I think I remember talk by Lemond that he brought the saddle up a good way (20mm?) after the tests, to his new height.
If you do want to include crank length, multiply leg length, from Greater Trochanter to floor, by 1.09.
