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Stem length math help-completely lost

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Stem length math help-completely lost

Old 07-11-11, 06:47 PM
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Stem length math help-completely lost

After using the search bar to try and figure out a solution on my own I have run into a snag. I am trying to figure out what length stem I need for a good fit as I dont believe my 110mm stem is right for my body. I used the fit calculator at wrenchscience and it said that my perfect reach should be 64.96cm. I measured the top tube on my current frame and it was 20in(if I measured it correctly) or converted to cm is 50.8. and my current stem is 110mm. Then using the search function I found a post where it said that I should use the wrenchscience reach measurement and then subtract the top tube length to get the proper stem length for me.

Using this so far I have not come to any reasonable sane conclusions that even make sense. I converted all numbers to mm since that is what stem length is in and it comes out to 140mm??? What am I missing or doing wrong? So as you can see I am completely lost. Thank you for any help or advice you can give. I am trying to save the 100 bucks for a fitting at my LBS until funds allow.
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Old 07-11-11, 07:18 PM
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Well, the measurements might be a good place to start, but no calculator can tell where you'll be comfortable. Best to take it to a bike shop and see if they'll let you try a few different length stems and buy the one that fits.
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Old 07-11-11, 07:33 PM
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You need the virtual top tube measurement from the manufacturers site....whats the bike maybe I can help. My guess is that you either have a small frame for your size (which is fine as long as you dont mind it being a little aggressive feeling with a shorter wheel base) or you measured the actual top tube of a sloping frame.

If you measured right then you need a 130mm stem.
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Old 07-11-11, 07:34 PM
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FYI that calc got my bike dimensions with .5mm which is crazy!!!
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Old 07-11-11, 07:36 PM
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You know, 3 different fitters may have you on three different stems. Not everyone agrees on fit.

Go buy some cheap aluminum stems of different lengths and fool with it yourself. It's very likely to change if get more fit anyway.......
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Old 07-11-11, 07:36 PM
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Yeah I know that is by far the easiest and best solution but right now I am working part time with school and a proper fit would be an entire weeks check. Not even counting then purchasing a quality stem out of next weeks check. So it could be a month before I save enough so I figured I could atleast do as much research as I could to try and find a stem ballpark range that fits my body measurements. I've had saddle height adjusted and handlebar width checked and they are all right on so I just wanted to get a few opinions on the math about the stem.
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Old 07-11-11, 07:41 PM
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SpaceMunkey-the bike is a 2000 model Trek 1000. Kind of hard to find real specs on the bike, I have looked everywhere and the only thing that I can find is the specs listed on bikepedia which are of no help as always. And the top tube is straight, I just measured it from weld to weld (seat post to where the stem goes in).
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Old 07-11-11, 07:51 PM
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If it helps here are all of my measurments if you can come up with a stem length you think, or if 130 is around what you think it would be for my arms etc...
asurements. Height 68.00 in
Sternum notch 56.00 in
Inseam length 32.00 in
Arm length 24.00 in
Shoulder width 15.00 in
Flexibility 3
Weight 150.00 lbs
Shoe Size 9.50 USMens
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Old 07-11-11, 07:52 PM
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You want to measure centre to centre, ie from the centre of the seat tube to the centre of the head tube, this cancels out any variation in tube diameter. The size of the bike, your height and inseam might help, or at least people with similar dimensions might be abel to offer advice.
Also, what makes you think it isn't right? Sore hands, too upright, etc. Some problems can be solved with a different setback of the saddle for instance.
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Old 07-11-11, 08:04 PM
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The bike is a 56cm frame and I know it is a no no to ever buy a bike not knowing if it fits you but I wanted to get into road biking and a friend of mine had this bike and let me have it for 150 bucks. So I didnt think I would find a better deal than a Trek 1000 for that price so I had to go for it, figured I could ride it and get some base miles under me and the fit felt to close not to grab it. I've done a few 50 mile plus rides on it so far and it feels fine other than anything above 10 miles kills my left elbow when I stop. Its not a constant pain but only when I move my arm a certain way or try to stretch it out completely. Alot like tennis elbow I would imagine. Anyways, the pain is there the rest of the day as I described but once I sleep and wake up and everything is back to normal the next day until I ride. I've checked handlebar width,fore/aft position,saddle height and all of those seem to spot on. So last option is the stem to check out and if that didnt help then I would just bite the cost and save for a pro fit to be done with the matter.
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Old 07-11-11, 08:53 PM
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130mm is about right.
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Old 07-11-11, 09:11 PM
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me I go by feel, and what your body does when your maxed out. If your seat is properly aligned you should be able to lean forward as if your in the drops but not holding onto anything now put your hands where is feels right and estimate from there.
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Old 07-11-11, 09:16 PM
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Some people say that when your in the drops looking down you front hub should be obscured by the handle bars.
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Old 07-11-11, 09:39 PM
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It doesn't sound like this calculator is taking into account saddle setback.
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Old 07-11-11, 09:41 PM
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Originally Posted by Mike F
Some people say that when your in the drops looking down you front hub should be obscured by the handle bars.
that also works for me.
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Old 07-11-11, 09:46 PM
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Try different length stems as each fitter will give you a different position, the correct fit is the comfortable one, not the one that the most experienced fitter gave.

Also you need to understand that "reach" has nothing really to do with top tube length. The reach of a frame is measured from the centre of the bottom bracket to the centre of the TOP of the head tube. Hence reach is unnafected by saddle position but is effected by spacers under the stem.

Also note that stem angle affects reach therefore just buying a 110 stem for example can give a very different reach depending on how it is flipped.

Also note that bar reach is a component of overall reach. common bar reach is between 70 and 95mm so has a huge effect on overall reach.

Never adjust the saddle to try and change reach, all you will do is alter your Gof G and cause other issues. Having said that you may need to adjust your saddle to achieve the correct C of G to allow you to reach out without tipping forward and needing to prop yourself on the bars. If you feel you need to prop yourself on the bars because they are too far away, often the answer is to move your seat BACK, this will re ballance you and result in more comfort.

trial and error is best, bike fitters are only guessing based on how you look on the bike

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Old 07-11-11, 10:05 PM
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Originally Posted by lazerzxr
Also you need to understand that "reach" has nothing really to do with top tube length. The reach of a frame is measured from the centre of the bottom bracket to the centre of the TOP of the head tube. Hence reach is unnafected by saddle position but is effected by spacers under the stem.
This is interesting to me. Why wouldn't you want to consider the saddle's position when determining reach? I would expect the desired reach to be a product of your torso and arm lengths, which would start where the saddle is. Of course, you wouldn't want to move the saddle to change reach, but I don't understand why its position isn't a factor in what stem length you end up choosing.

Also, I've never heard a reference stating how a frame's "reach" is officially measured, and never thought it was ever a real number since reach is a function of the frame plus cockpit parts put together. I've never seen a manufacturer publish "frame reach" in their geometry charts.
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Old 07-12-11, 03:54 AM
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Originally Posted by urbanknight
This is interesting to me. Why wouldn't you want to consider the saddle's position when determining reach? I would expect the desired reach to be a product of your torso and arm lengths, which would start where the saddle is. Of course, you wouldn't want to move the saddle to change reach, but I don't understand why its position isn't a factor in what stem length you end up choosing.

Also, I've never heard a reference stating how a frame's "reach" is officially measured, and never thought it was ever a real number since reach is a function of the frame plus cockpit parts put together. I've never seen a manufacturer publish "frame reach" in their geometry charts.
Check out trek and cervelo, both used to and i think still do quote reach as do many others but not all.

Saddle position (set back ) is determined relative to the bottom bracket to get your knees at a comfortable angle and to get your ballance correct. Stand up and assume a riding position with your arms out forward - you are ballanced and have no weight supported on your arms. You can reach further forward if you want by re ballancing, or sit up more too if you like with no weight supported by your arms. On the bike your seat position determines your ballance point. too far forward and you must support yourself on your arms so saddle position does effect stem length. opposite to what you might expect, moving the seat back often ballences you so a longer stem is more comfortable

However the reach of a frame is independant of setback, you could get the set back such that you are comfortably ballanced but the front triangle of the frame is so long you cant reach the bars at all. Notice that adding spacers under the stam results in the stem getting closer to the BB as does flipping up the stem.

FWIW I can get comfortable with anything between a 90mm and 120mm stem by altering my ballance, seat back = longer stem, it just depends how much you want to be leaning forward when you are ballanced, the more you lean forward the more your back has to do. i ended up settling for a 110 stem as that position suits the riding i do. others may be different
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Old 07-12-11, 04:56 AM
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Originally Posted by urbanknight
Also, I've never heard a reference stating how a frame's "reach" is officially measured, and never thought it was ever a real number since reach is a function of the frame plus cockpit parts put together. I've never seen a manufacturer publish "frame reach" in their geometry charts.
This has been posted before, but a pretty good read nonetheless.

https://velonews.competitor.com/2011/...ndustry_154565
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Old 07-12-11, 05:09 AM
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I don't see how "reach" is important, because your the cockpit length, that is the reach from the saddle tip to the bars, can vary so widely, that this arbitrary number really doesn't do anything except allow you to compare bikes from the same brand.

So, your saddle position will be related to your your STA, crank length, body proportion and fitness. And then your saddle tip to bars will be related to how stretched out or upright you want to be. Now, how can "reach" be important? when there are so many variables affecting your final formula?

1. Adjust saddle position
2. buy a bunch of cheap stems in different lengths and use what feels good
3. sell the stems you didn't like.

that's all there is to it.
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Old 07-12-11, 05:36 AM
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I dont think an analytical approach can tell you how to pick a stem. Once you know your stem length, you can measure up your position an replicate it on other bikes, which may require a different length stem.
I suggest you try an adjustable stem
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Old 07-12-11, 06:02 AM
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Originally Posted by Mike F
Some people say that when your in the drops looking down you front hub should be obscured by the handle bars.
Some people say the world is going to end on 12/12/12 too.
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Old 07-12-11, 06:14 AM
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Originally Posted by Agave
Some people say the world is going to end on 12/12/12 too.
Is that when Jesus is coming back now? Last I heard his arrival was delayed to September, now we're talking over a year late? Sheesh.
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Old 07-12-11, 06:19 AM
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Originally Posted by Agave
Some people say the world is going to end on 12/12/12 too.
12/21/12
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Old 07-12-11, 06:51 AM
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Originally Posted by ARThriller
The bike is a 56cm frame...
This means your horizontal top tube length is definitely more than 50.8 cm and most likely closer to 56 cm. Sounds like your 110 mm stem might be just right for you.
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