The Bike Fitting Mega-Thread


I watched the video you posted. There is a part at 6:40 or so where he’s saying “If I go lower at the front then I’m more aerodynamic, but I’m closing my hip angle too much and can’t generate power”. This is why people move their saddle forwards - it opens up the hip angle again. Looking at his bike, you can see that he has the seatpost with as much setback as it can give him, and he’s running the saddle mid-way back on the rails. It’s a position that mimics a normal road-bike setup, but it’s not the norm for a TT setup.
If you look at the top TT guys, then you will see that they are a lot further forwards (and they are restricted by UCI rules in how far forwards they can go). Eg:
You can see a similar position (usually further forwards because the UCI rules aren’t relevant) if you google for most triathlon fits.
If you want your TT fit to mimic your road fit, then his method is probably really good. If you want to be aero, then I think you have to accept that your TT fit and your road fit are going to be significantly different.


I have nothing to contribute with but I do have a couple of questions!

About 15 months ago I got fitted using the Retül system. At the time, my weight was about 6kg (13lbs) higher than nowadays.

I’ve been really happy with the fit, but lately I’m starting to feel like I’m sitting a bit low, with increased loads on my knees.

Maybe I’m a bit paranoid, but could the weight loss (e.g: thinner tights, thinner glutes) vary my position that much?

Apart from this, what would be the best way to swap a saddle replicating the original position as much as possible?



If you are happy and comfortable on your current bike, you may not need a fit. I still like doing them sometimes to ensure that you are properly set.

But let’s assume that you are on a properly sized bike and close to your ideal fit. First item of to find the geometry of your current bike. Get the chart and identify your size. Get the Reach and Stack values for sure, but I gather all the other info too.

Using the Reach and Stack, you can evaluate bikes from any brand and size, and estimate how close the fit is to your current bike.

Additionally, I recommend using a quality bike shop and having the “size” you to the bikes you are considering. Hopefully they have someone who can help you beyond the old “straddle test” for sizing.

But that’s why it’s nice to go in with some info ahead of the visit. You can estimate the sizes you think are right and see what they say in comparison.

We can consider more specific recommendations with a pic or two of you on the bike, and the current bike info.


Hard to say for sure. I know that losing a but of belly fat can impact the back angle and even curve shape (because the belly isnt as much of an interference to bending). It can also impact lateral pedaling motion of legs. The gut can touch the upper thigh, and lead to later knee and leg movement.

It’s possible to loose that interference and maybe your leg is traveling straighter, with an effectively shorter distance now.

Fitting is part science and part black art. I always tell my clients they can experiment within about 5mm up-down and such from the fit in the session. I didn’t do your fit, but I think you can consider trying a 3-5mm saddle height increase as a test.

I would record the saddle position (if they didn’t already give you the info from the fit) before making any change. It allows you to get back to “home” if your test us unsuccessful.

As to measurement, I will try to find a good reference.

You generally want to have saddle height from the center of the BB up to the top of the saddle (viewed from the side) in the middle of the saddle.

Then get saddle setback by measuring from the BB again, horizontally back to the nose of the saddle. There is a nice truck I use to make this easy, and I will add it soon.


Do you change the point on the saddle you measure to if you have different shaped saddles? Switching to an ISM split nose from a regular shape for example?
For height, I just measure from a specific point at the top of the seat tube to the top of the saddle (along the angle of the seat tube). It’s not super precise, but it’s repeatable enough…


Short answer: yes

Depending on shape, you may need to determine a level position that you can take an accurate measurement from. ISM actually provides a good rule of thumb on their website about how to position in relation to a standard saddle. Typically most measurements are X/Y axis, with the X anchoring from a plane level with the bottom bracket.


Good question. The answer is that it seems this varies from person to person.

  1. Nose of Saddle: This is convenient and consistent to access, but with the new short nose saddles, it makes comparison between regular-length and stub-nose models complex.
  2. Middle of Saddle: This is a somewhat better than the nose, but is still influenced by the length of the saddle in relation to the actual seating area.
  3. Wings of Saddle: This is a bit more new and nuanced, but it more related to our actual position on the bike. Some people estimate the middle of the “wings” (widest part of the saddle) and use this position. I find this makes the most sense, but it is a bit tougher to find.
  • Unfortunately, there is no “perfect” solution. The key is to pick one method, use it consistently, and understand the impact of that choice.

For saddle height, I’d suggest using the center of the BB at least, so you have a number that is a decent start for other bike setup. Measuring from the Top Tube is super bike specific and worthless unless you are refitting to an identical bike.


Here is a decent guide on capturing fit data:


Measuring from the Top Tube is super bike specific and worthless unless you are refitting to an identical bike.

Agreed - this is when working on just one bike.


I’ve had my Canyon Aeroad for a couple of years now and i’ve tweaked the fit a few times since getting it and thought and felt pretty good.

I was getting a Bike fit done on my TT bike at the weekend and thought i might as well get the Aeroad done as well (there was a discount for 2 bikes). It was a Retul system fit. Amongst other things. They ended up moving my saddle forward 4cm. I repeat 4 cm! just shows what i know about bike fitting. I haven’t been out on the road yet, but the new position felt much better. Shows how much i know. The fitter said it was set up more like a recumbent bike. ha ha !


Wow, that is a big change. I am guessing you had the saddle about maxed out to there rear position in the rail clamps?

What did you like better about the new position overall?


It might be a can of worms you do not want to open (so, no offense taken if you say “no”); but if I uploaded a pic or two would you mind giving some pointers? I feel like my saddle is too low/my saddle angle is off because after 2-3 hours I have some serious leg pain. I’d like to get it sorted before my first “race” March 2. Which, is why I have taken a keen interest in this thread, lots of helpful information for sure.


I am happy to take a look. As expected, any remote interaction is a bit more complicated, but I will do what I can :smiley:

What type of pain and where is it located?

For saddle height evaluation, it is best to use a video (60 fps if possible), located from a pure side angle,.
Then capture a single frame from the video, with the typical leg extension when the crank is roughly inline with the seat tube angle. This is intended to catch the max extension point.

It can also be helpful to see a rear angle to make sure the hips are stable and not rocking. This can be a dead rear angle or 3/4 rear/side angle. In a fit, I walk around the rider during active pedaling.


Thank you very much @mcneese.chad I will start compiling the videos, measurements, and post here in the next day or two. The pain is mostly outside of the knees and hips…


I have just booked myself for a bike fit with a fitter that uses the STT 3DMA system. Does anybody have any experience with it?


I haven’t seen or heard of it.
Looks like an interesting data capture method.


I’m due in next Wednesday so I’ll report back once done if you’re interested.


Sure! I love hearing about fitting experiences (good and bad) so I can try to improve on my process anytime I learn something. And getting a customer perspective from another fitter is golden for me, as it is a more open comment system in general. Much appreciated :smiley:


I understand your reasoning. But you are setting yourself up for failure at your new endeavor. What you are doing now is trying to enjoy swimming up stream, when you could enjoy moving with the current in its most fluid state.

The fact that you are seeking advice is a great thing. You have already taken the time to make a better, fitter version of yourself; something that instills confidence in your athleticism in the sport. But I recommend cutting out the guess work and give yourself a prime opportunity to hone your craft with the fit. It will take out any guesswork as to getting you more “aero” and it would help get you on a bike that makes you the most comfortable, though having the “tri” posture isn’t often the most comfortable.

Getting your fit dialed-in is much like dialing in your nutrition. I’m sure you can tell the days when you did not fuel your body for the demands you placed on it compared to those when you did fuel well. If you want to optimize both your experience and performance in triathlon, I suggest you consider a professional fit. It will only boost your confidence in the sport and promote longevity as you will stay healthier longer and more than likely ride more often.

I can recommend a great fitter in the Dallas/Fort Worth, Texas area if you are close, or can get here. In the meantime, good luck with your training.


It feels like a much more balanced position. Before I think I was reaching too much and would sometimes ride with my hands just in front of the hoods. Feels like I can generate more force on the peddles now as I’m sitting more above them rather than behind them. The fitter did say I could probably do with a longer stem now. But as I’ve got the aero integrated stem and bars. A replacement from the canyon website is £360. So it’s not really worth it.