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Old 12-20-2017, 09:48 PM
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How to fit measurements like these?

Hi All,

So after spending a long time doing the stupid fit merry go round of trying different things and having a couple terrible fits from shops I've finally put my numbers in a calculator to see what I get. I'm at a bit of a loss as to how to find/fit a bike to these sort of measurements given the massive seat tube and top tube disparity. I know that calculators are rough guesses at best but to be totally honest, the stuff it's indicating about short top tube, longer seat tube, more setback all make sense to me.

This fit is actually what I've slowly been gravitating toward in that I've never gotten more comfortable than my current set up that I've pieced together myself based on feel. This csme when I dropped my saddle a good bit, added more setback (and a setback post) and tried to shorten my reach to close to these numbers with shorter stem and handlebars.

Problem is I have a short stem that feels a bit twitchy and overall I'm still more stretched than I want, if I could shave off another ~1-1.5cm of reach I'd feel more comfortable but I'm pretty much out of stem and bar to shorten. Additionally, I'm already riding a 52cm with a stack of spacers and upturned stem so that I don't have a ton of drop.

Anyhow, any suggestions on frames that would work for this kinda body measurements and fit numbers? Can't find a men's bike that has a short enough top tube for what it looks like might fit me....


Specifically the top tube, it seems like every men's frame even in sizes like 50cm or 52cm still have an effective top tine of 53cm or more
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Old 12-20-2017, 11:19 PM
Kontact Kontact is offline
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The fit tool you're using is spitting out somewhat old school data, since it seems to be ignoring the possibility of extended head tubes/sloping top tubes.

Overall, I think this Cervelo in a 51 is the closest to those numbers. Here's why:

https://www.cervelo.com/en/road/r-se...and%20geometry

For smaller frames, the common seat tube angle is 74°, which effectively adds 1cm to the TT length compared to the 73° STA of a medium sized frame. So the horizontal TT length of 531mm on a Cervelo 51 is an honest 53cm due to the 73° STA, which would be 52cm on a steeper STA bike. It is hard to find anything shorter than this. Even Specialized and Trek 49 or 50cm bike have longer effective TTs.

The recommended seat tube length of 56 CT would produce a Stack height on a level TT bike of 53.5cm, and the Cervelo has a stack of 530mm.


In other words, if this bike had a level top tube extending back from the top of the head tube, it would within 1cm of height and length.


I'm not saying buy a Cervelo, just saying this is about as close as you are likely to get in a production bike.


On a custom it would be fairly easy to produce the geometry that suits someone looking for a more upright/short TT bike by relaxing the head tube and extending it up. Short TTs are easier when you have more height to play with. Seven is a good company to work with for such a bike because they can offer so many fork rakes, but their forks are available separately.
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Last edited by Kontact; 12-20-2017 at 11:34 PM.
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  #3  
Old 12-21-2017, 09:14 AM
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finding a frame with a shorter than 52 top tube is going to be a struggle. are you flexible? can you touch your toes? post a photo of your current ride.
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Old 12-21-2017, 09:35 AM
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Wow thanks a bunch for that very in-depth post. I figured the calculation measurements were more of a rough idea where I should be at so not surprised that the info was a bit older, the fit actually is the "Eddy Fit" from the competitive cyclist website, I've used their more modern "Competitive Fit"which indicated a higher saddle, less setback, slightly longer top tube and more reach. That was remarkably close to my old position and what I messed around with for a long time but never truely found comfortable or was able to get feeling right.

Regarding STA, why would a higher STA result in a longer effective top tube, wouldnt it be the other way in that a high angle moves the saddle more forward and thus reduces the reach/top tube?

Also, thanks for the Cervelo Link, might be useful to look into.

Regarding top tube and overall reach, I figured it would be hard to find something with this length, maybe a women's bike in a comparable size may have a shorter top tube/reach? Posing this as a hypothetical since it seems regardless of what size a men's bike might say it is, the top tube and corresponding reach don't seem to go much below 52.5-53cm, 370+mm
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Old 12-21-2017, 09:37 AM
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SolidSnake03 SolidSnake03 is offline
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Quote:
Originally Posted by cmg View Post
finding a frame with a shorter than 52 top tube is going to be a struggle. are you flexible? can you touch your toes? post a photo of your current ride.
Fairly flexible, can touch toes pretty easily but not hands flat on the floor flexible. It more comes down to physical lengths and limits, I can bend and flex but there is only so far t-rex arms will reach regardless of how flexy you are....
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Old 01-01-2018, 01:12 AM
owly owly is offline
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Have a look at a geo chart of the Eddy Merckx Milano 72. Especially the XS size.
(compare the stack and reach to the 51 Cervelo).

It is marketed as a women's bike, but doesn't really look like one to me.
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Old 01-01-2018, 03:33 AM
Kontact Kontact is offline
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Quote:
Originally Posted by SolidSnake03 View Post

Regarding STA, why would a higher STA result in a longer effective top tube, wouldnt it be the other way in that a high angle moves the saddle more forward and thus reduces the reach/top tube?

Also, thanks for the Cervelo Link, might be useful to look into.

Regarding top tube and overall reach, I figured it would be hard to find something with this length, maybe a women's bike in a comparable size may have a shorter top tube/reach? Posing this as a hypothetical since it seems regardless of what size a men's bike might say it is, the top tube and corresponding reach don't seem to go much below 52.5-53cm, 370+mm

The problem is that a 53 TT that starts from a 74° STA is the same as a 54 TT on a 73° STA once you have put your seat to the same set back. With the 74 you compensate for it by sliding your seat back 1cm further in the post than you would with the 73, hence the extra effective TT distance.


Women's bikes don't fix the situation unless they go to smaller wheels. The limiting factor is toe overlap of the front wheel, and how shallow a head tube angle the maker is willing to go. If you can't bring the front wheel too close to the crank and you won't lean the headtube back far enough, you end up with more TT than you want - and changing the STA doesn't change that fact.
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Old 01-01-2018, 06:43 AM
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Quote:
Originally Posted by SolidSnake03 View Post

Regarding STA, why would a higher STA result in a longer effective top tube, wouldnt it be the other way in that a high angle moves the saddle more forward and thus reduces the reach/top tube?
If you think of the effective top tube as the amount of the top tube forward of the BB center line, it's easy to figure this out. Imagine two frames with 55cm horizontal top tubes. The first one has a STA of 60deg and the second a STA of 85deg. Now which frame will have more of that 55cm top tube forward of the BB centerline? The 85deg STA frame will, by a country mile.

The slacker the STA, the more horizontal top tube distance is consumed by the frame setback, behind the BB center line - and vice versa.
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Old 01-07-2018, 07:48 PM
ultraman6970 ultraman6970 is offline
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The steeper the frame the longer will feel.
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  #10  
Old 01-08-2018, 10:18 AM
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what your looking for is a frame with as close to 360cm reach. That is kind of self imposed limit bike manufactures are willing to make before toe overlap becomes really noticeable. do a reach calculation on what you think will fit I bet it's close to 360.
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  #11  
Old 01-08-2018, 10:45 AM
11.4 11.4 is offline
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And it's not just toe overlap. When you get short across the top, you run out of clearances around the front wheel and with smaller frames you run out of head tube. Especially with everybody designing frames to fit at least a 28 mm tire if not more, you're pushing the down tube up and squeezing the whole design. What you might consider is going to a 650C frame. I hate having to use smaller wheels and tires, but more builders are making them for this and related reasons.

However, I'm really questioning your fit, and at two levels. First, it looks, as Kontact pointed out, that you are being fit in an arbitrary way. Those programs can't really fit you properly; it takes someone eyeballing your fit, flexibility, anatomic limitations, riding style, and so on.

But also, a fit program is always driven by your input, and you may want to reconsider how you're fitting yourself. Short reach or compact bars are very common these days to help with this kind of problem; they don't change your effective position but if you're riding big bars you have so much shift fore and aft as you change position that you're never comfortable on them and try to shorten your top tube more. Similarly, excessive crank arm length can cause chest or diaphragm impingement, which causes you to want to pull in your cockpit and shorten the top tube excessively. Having your saddle slightly too low can do the same at times. You've got your saddle back a fair bit, which may be too much; remember that it isn't just frames that have modernized, but saddles also. They are being made with different seating positions in mind and with longer and lower positions planned. You may be able to change a saddle and post and then be happier with a longer effective top tube and stem. As someone suggested, seeing your current ride would help a lot to understand how you like to fit a bike at present. I'd also suggest a photo of you on the bike, preferably a video of you on a trainer or rollers with it. Still, the wisdom you get from any of us is worth about what you're paying. Get a real fitter. I'm usually hesitant to recommend you walk into a store because many fitters are as dated or biased as that program you were filling in. Find riders who consistently recommend a good fitter, and figure he/she will at least get you in the ballpark. It's worth traveling a few hundred miles to find a really good one. And expect to pay a few hundred dollars at least. Best bike expense you can empty your wallet for. On top of that, find a coach who can actually work with your riding. Remember your fit is only as good as your skill on the bike, and it's usually the body that needs more adjustments than the bike -- a coach who will work on your flexibility, address specific limitations, optimize your comfort and stability, and so on.
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  #12  
Old 01-08-2018, 12:00 PM
audiojan audiojan is offline
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I absolutely hate fit calculators... it's using some average fit calculation, basically one size fits all (or should be one size fits no one). With that said, better than just plain guessing.

I'm really sorry to hear that you had some bad fitting experiences... there's a lot of hacks out there and have no idea what they're doing, yet have no problem charging for it. A really good fitter will get you in the best possible position for YOU based on your physiology, prior/current injuries/issues, riding style, distances and terrain you ride, etc. A tell tale sign of a poor fitter is that they more straight ahead to measuring you and the bike, foregoing the most important step, the interview where the fitter gets to know you.
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