I’m having a mental block. I think I know the answer, but I would like some fresh opinions on my over thought conundrum. Thank you.
Can anyone describe to me what you think is happening here? I will state in very simplistic terms what I have done and I would like you to tell me what the result might be.
Basic background: Audax bike, relaxed geometry, 50cm bike, short stocky rider, strong core and upper body, long distances. I have put in the work here on TR and out on the road in terms of mileage. My body has adapted well and I have slowly been stretching myself out over a period of two years. But until yesterday I have been achieving this by slowly moving the saddle back and the seat post is now near the front of the saddle rails. I am in a comfortable position.
Apart from the saddle position looking odd, I was concerned my power was suffering. With a mission to bring my power back over the BB I have fitted a new stem which is 20mm longer. In return I have moved the saddle 20mm forward. After an hour an a half on the turbo, I feel good. Obviously I will know for sure on 12 hour+ rides. I haven’t touched the height of the saddle, handle bar/rotation etc. Nothing. JUST the stem and saddle, as a pair, they have moved 20mm further forward. Not even the height of the saddle has changed.
Can you tell me in terms of power and anatomy, 1/ what changes will have taken place with my feet, knees and hips? And 2/ whether any tweaks should have been made to the bike or cleats? Or 3/ will the changes be so small I just need to adapt physically? (I am assuming nothing has happened to my neck, back, arms and hands.
You’ve moved your entire position forward on the bike and obviously the bottom bracket didn’t move, so I would be concerned with where your pedal circle falls relative to your hips and knees. Are your knees moving forward of your toes now? Could lead to knee issues over the long haul, and reduce your power output. A cleat move might help, but would kind of be a band aid. Crank length is another thing you could look at, but I like to pick a crank length and stay with it, adjusting around that of the length is appropriate for that rider (usually me). Ultimately, 20mm isn’t a ton, so if it’s comfortable with zero pain and no power reduction, no biggie.
Note: not a fitter, but I play one. Chad will be along shortly with better info.
Note that by putting a longer stem on, your weight over the front wheel has changed, and the bike will corner differently. Not something you’d notice on the trainer.
I’ve measured from the front of the hoods and my contact patch is almost directly below that point. I haven’t been out yet to feel how it handles. With the previous stem I never felt twitchy.
Also when I am in a natural riding position on the turbo, the hub of the front wheel is obscured by the handlebars when sighting it. I’ve heard this is a good thing. (Too short a stem it is sighted in front. Too long and it’s behind)
You moved the saddle forward 20mm. This is generally a ‘flat’ move that does not change the saddle height.
You swapped to a stem that is 20mm longer. This may seem to be the same, but it depends on the stem angle installed on the steer tube and the head tube angle of the bike.
What stem angle did you have before and what did you replace it with?
The overall impact in most cases, assuming a -6* angle on stem on a 71* head tube means a 20mm length change will move the stem forward about 18mm and up about 3mm.
Note, I’m not at my CAD PC to actually model this and I’m too lazy to do the trig, so the above is a rough guess.
Overall point is that a seemingly similar length change on the stem will be slightly different than the flat seat adjustment.
Ignoring if you had a good or bad fit, the pure action of sliding the saddle purely forward will lead to:
More closed leg extension angle at the bottom of the stroke.
More forward position of the knee at the 3 o’clock position.
Higher knee and thigh at the top of the pedal stroke.
The variable of the front end change that might have happened may alter the thigh to lower back angle with the leg at the top of the stroke.
That’s all pure geometry impact with no consideration to good/bad fit. That’s tough to discuss without more of a picture we could develop.
While moving the saddle horizontally does not change the height, it changes the distance between the BB and the saddle top (assuming you sit in the same place on the saddle).
What was the purpose of stretching yourself out by moving the saddle backwards over time? And did you lower it slightly to take into account the extra stretch, or did you leave the height alone?
Moving the saddle forwards and extending the stem will result in more weight being on your hands. It might not make much difference, but over a long ride you may notice it - worth testing before a specific event.
Great reply. Over time I feel as if I have become more supple and my butt was directing me to move the saddle back. Complacency and budget dictated a delay in changing the stem. Without dropping the stem any further for comfort reasons I was keen to reduce my aero profile. Coincidentally I dropped the saddle very slightly due to slight knee pain. That has stopped.
On the turbo my hands still feel light although like you say, it’s going to take a 200km+ ride to know for sure.
Since Mr. Chad is apparently a bike fit guru, do you mind if I half-hijack this topic with my own bike fit question? I’d be happy to post my own topic, but I didn’t know that there was an actual bike fitter here!
I just want to put in that the saddle to bb distance and angle should be adjusted completely separate to choosing stem length. First make sure saddle height, angle and fore/aft(?) position is correct and then choose stem length and angle according to preferences/flexibility.
I’m beginning to feel like a professional bike fit is necessary for most people to avoid injury and achieve power. That said, you can do a little self assessment and I find the articles on this site very useful and informative.
I thought it fair I let you know how I have got on. I lengthened my stem by 20mm with a 6 degree rise and moved the saddle 20mm forward. After 117km I was experiencing some frontal knee pain so I raised the seat post by a smidge. Having an amateurish rinse of my setup on Bike Fast Fit, all my angles and dangles are nicely within the recommended criteria. The main thing is I am very comfortable, my pedal stroke feels fluid without dead spots and powerful. (For me)
