Campag must have a real tough time trying to fit himself onto one of those newfangled TT bikes with the 90deg seat tube that does not intersect the bottom bracket. I mean, OMG, the "effective seat tube angle" changes depending on saddle height!

The thread has been cleaned up. Please stop the bickering. Campag4life, please leave this thread.

CbadRider
Forum Moderator

Really? I was hoping to get a picture of myself on my bike to "prove" to him that my bike fits me properly.

Obviously you can see how much of a priority it is, as I have not gotten around to it yet....

One thing I'd like a few people to come away with here is that the same Reach on two frames with different Stack measurements, does *not* give the same fit. I explained it above. That's my main beef with Reach... it is nearly as silly as using ETT. For your statement to be correct, Reach would have to be calculated at a fixed height above the bottom bracket, and not the top of the headtube.

Stack and Reach relate to bar position only. If Reach was calculated at a fixed height above the bottom bracket, then they'd both be fine ways characterize a frame for bar position.

Frame dimensions relating to saddle position are totally separate... they should not be blended in any way.

It's pretty similar to the forward frame dimensions telling you what stem to buy and how to orient it. You are much less likely to have issues with the seatpost... especially if you are ok with buying any post that is necessary to make it work. But if you have a particular post you'd like to use, and your personal fit dimensions are not so average, it can easily be an issue. For instance, I couldn't use my Thompson post with a new frame, because I couldn't get the saddle far enough back.

So... I think it would be a good idea to have a frame dimension term that relates to the saddle fore-aft. Don't know what the best way to do that would be...

2 inches on a 73deg headtube changes the reach (shortens it) by a little over half an inch. 20mm change in height changes the reach by 6mm. Yes, it changes. No, it doesn't change by much. 6mm is less than the width of my pinky nail.

You have to start somewhere, and getting to within +-10mm on stack and reach will put you in the range of stem and saddle adjustments. That's all you need to do for choosing a frame size. It does remain that if the stack and reach of two frames are identical, then you can get identical fits regardless of any other frame measurements.

Brian described it a few posts above. It's setback measured from the BB center to the nose of the saddle. It's useless if you switch saddles, which happens often when you're a newbie or uncomfortable, but rarely once you find a saddle you love.

FWIW I ride a thomson zero setback setpost.

All the bike companies I've seen include seat tube angle, which is as good a measure as any. That and your personal saddle height will tell you what seatpost will be acceptable. The reason why manufacturers harp on reach and stack is because handlebar height is far harder and more expensive to modify than saddle position, especially if you choose the wrong size frame. A good stem is over $50, and most are towards $100. Most seatposts are more or less identical in terms of dimensions. It is not a stretch to say you should size your frame solely by stack and reach and figure the saddle position later, during the fit.

A good example is when I was given a warranty replacement frame to replace a 2007 58cm 5.2 Madone. The replacement frame was the new "H2" fit, whereas the old frame was what is now known as an "H1" fit. Had I replaced the old frame with a 58cm new frame, I would have had to resort to a track stem or even some sort of crazy adjustable stem to get my bars right. So I replaced it with a 56cm frame so the bars fell into the right range. Saddle position never came into the calculations at all, but I agonized for days about the stem.

In all honesty datlas, I want to see you on bike just to further my understanding of bike fit. When I looked at your bike I assumed you are pretty much all legs... Wondering if my assumption is right

I dunno what the deal is in this thread, but...

This saddle stuff is what I'm struggling with right now. I've found my previous favourite-ever saddle, the Arione, has limited comfort in events over 300kms. So, I went with a Gilles Berthoud Aspin - very comfy, but the comfy bit I like to actually sit on is far forward from the rear of the saddle and the rails have limited length. So I've ended up with a odd-looking amount of setback and am struggling to get the setup exactly right.

So for me, STA is critical. I need to be able to put the saddle where I need it, after all. I would suggest that the only reason people here are saying it doesn't matter, is because they either:
a) haven't put in the time to really nail their fore-aft position
or
b) are fortunate in that their body proportions and their favourite saddle allows them correct setback with standard components on most frames

Earlier, Mr. Ratliff here mentioned 2cm as the difference between two frames, suggesting that this is immaterial. In my opinion, 20mm is rather a lot! Easily enough for me to buy one frame over another.

It is also not a stretch to say that a very large majority of riders on the right size frame will be able to get the saddle setback properly set using a combination of the saddle rails and 0-35mm setback seatposts. The setback can be a problem on bikes with an integrated seatmast, though, depending on your femur length in proportion to the rest of your body. (You could get hosed if you're too far on the long or short side.)

I can ride a 57-58cm frame in most road bikes with a very long stem, 120-140mm. I can ride 60-61cm frames with a 100-110mm stem. Many frames, but not all, have the same STA (and chainstay length) between these two sizes. If you are on small frames below 54cm then there is no doubt that geometry varies a lot more, especially as small as 48cm (assuming 700c wheels).

I think you were also spot-on with A). Some people don't have their fit dialed at all, including their saddle setback.

35mm? I'm only aware of a very few seat posts with that much setback, and only one that wouldn't look out of place on a modern bike - and it's quite expensive.

Fine, and you're right. Reduce this number to 30mm and you have a wealth of options. Even more at 25mm or less.

The 2cm difference in frame size is all front end. Chainstay length is mostly identical, which means seat tube angle is pretty close, within half a degree. All the difference is at the front end.

I would suggest that your saddle is not for you. If you are struggling to use a saddle that requires you sit forward of where you are supposed to traditionally sit on the saddle, then perhaps it's the saddle itself, not the setback, that is the issue.

Obviously, if you are right at the edge of adjustment, then some of these variables are going to matter more to you than to most people. Keep in mind when given generalized advice that you are giving generalized advice. Most people are not all that worried about getting their saddle in the proper place; otherwise there would be many more options of saddle setback seatposts on the market. The amount of adjustment built into the saddle rails is sufficient for most people. Most people are very much worried about getting their bars correct, because that's where the expensive bits live and large adjustments cannot be made with just an allen key and even then only in discrete increments.

Yes. I think many people are aware of this and more will learn it. It's only a matter of time before a good calculator is available to play with and visualize the differences. With a calculator you can get those differences by adjusting the stack height.

I don't think there is one that is better than STA. But only to have an idea of where the seatpost clamp will end up, not to adjust for rider reach or other fit dimension (as opposed to frame dimension).

If you're comparing sporty racing bikes, maybe you are right, I don't know. But I have bikes with STAs ranging from 74.5 to 71.5, and the effect is quite dramatic. At 704mm seat height, the amount of setback variance (47mm) is well out of range of most seatposts. It's certainly enough for me to sell the 74.5 frame, given my preferences.

Regarding the saddle, you may well be right. I hope not, because the 'comfy spot' really is very very comfy.

That isn't a frame dimension, though. We need a number that characterizes "setback" that doesn't change depending on any of the other dimensions... which means the height cannot be a variable either.

STA is usually ok, except for frames that have a ST origin that doesn't intersect the BB. I can't think of a good way to accommodate that... so I nominate STA. Frames that are unconventional can compute effective STA for the typical range of saddle heights for each size.

Yes, if you try to fit a road race position to a touring bike (or vice verse), you might have problems. I would suggest moving the bars up and back on the touring bike to accommodate the slacker seat tube and get yourself into a more upright position so you are using the bike as intended. If you are going the other way and trying to apply a touring fit to a race bike, I'd suggest rotating your position forward, by moving your bars down and away, to get yourself into a more aerodynamic position, again, to use the bike as intended.

People lionize "bike fit". It's funny. The only part of bike fit that is important for physiological reasons is saddle height. Saddle setback, handlebar height, reach; all these things are more or less to the rider's preference. Some riders even change these according to mood. Many racers change these according to the event.

My point is that this error would be easily avoided if they'd just define Reach at a fixed height above the bottom bracket.

why? stack is the height. each person's required stack height is different.

use them together and you have your handlebar position. very simple X-Y coordinates.

No, I don't agree at all. I don't think any rider changes their setback according to their mood. Riders certainly change height and reach, of course.

Setback is set in stone, or it should be. No matter what purpose you are putting the bike to. Finding this position on my racing bike, after much trial and error and finally getting a pro fit was a complete revelation in both power output and comfort.

Yea, this is not useful. The point of reach and stack is to fix the top of the headtube (where the stem typically sits) in space relative to the bottom bracket. The whole point of offering several sizes of bike is to eliminate the requirement for lots of spacers under the stem. The typical rider has a stem and handlebar in mind; the frame is sized to minimize the need for spacers and stem length changes.

Incidentally, this is why you don't see what whole "compact" frame sizing thing much anymore, even though most bikes have a sloped top tube. There was a fad in the late 90s where frames were basically S, M, and L, and you chose stems and seatposts to fit.

Think about it. Yes, you probably want the three contact points to be fixed relative to each other; however, there is no reason why you can't rotate the whole constellation around the bottom bracket to get a different position. There are plenty of riders who fit their saddles further back and their bars slightly higher and closer to create more power for climbing. Plenty of riders who have a bike with a longer, lower, more saddle forward position for flat races and sprints. Most time trialists and triathletes move their bars down and away to accommodate the much steeper seat tubes of modern time trial bikes.

Fit is all about getting the constellation of contact points right; position relative to the ground is a different story all together.