Modified my geometry

Jan 8, 24 16:26

Post #1 of 24 (1729 views)

One of the things I've noticed on all my bikes, both conventional road and my tri bikes, is I always feel like I can't adjust the seat far enough forward. This has always bothered me because I feel like I'm pushing the pedals forward at the top of the stroke rather than pushing down. This, in turn, pushes me back on the seat. So I always feel like I'm pushing back, scooching forward, push back, scooch forward, back, forward, back forward. It has gotten very aggravating.

Now, I'm a nurse by profession but I have some engineering background thanks to my military service, and I have always just kind of had a solution oriented thought process.

So if I can't find what I want to fix my issue, I'll make it. Without going into all the details (which I can do if anybody is curious), I bought a cheap straight seat post and made a bracket that allows me to locate the seat as much as 2 inches farther forward than the forward most position I could get with even a "zero offset" seat post.

Here's the original configuration with an off-the-shelf zero offset seat post. I have a red line drawn through so you can see the most forward position I am able to adjust with this geometry.

This is the bracket I made in an attempt to test my theory.

And finally, the bracket as mounted with the seat. As you can tell, the seat is now around 2 inches (5cm) farther forward than the previous forward-most adjustment, and I still have another inch or more I could go if I really want.

When I first put it together, I had it moved all the way forward but that really wasn't comfortable. I moved it back to the position it's in now and that feels pretty good, although I've only ridden once with the new bracket. But that only attempt was a 30 mile route where my previous best was just under 1 hour, 48 minutes. Even on tired legs (5 mile run the day prior) I crushed that previous best by almost three minutes.

I still have some fine tuning to make. And I need to figure out how to secure my bottle cage holder better, but as of right now, I'm very happy with the way this has turned out.

Last edited by: VegasJen: Jan 8, 24 16:35

Re: Modified my geometry [VegasJen] [ In reply to ]

Jan 8, 24 16:30

Post #2 of 24 (1724 views)

Hmmm. Don't know why by my pictures aren't showing up. I'm going to give something else a try. BRB.

OK, so not sure why I can't upload and attach here, but I got them posted anyway.

The whole point of this is that I don't feel like I'm moving around nearly as much now as I was before. And I believe that's largely because when I'm putting power into the pedals, that power is pushing down more than pushing forward.

One ride is not enough for a definitive conclusion, but I like where I am a lot more now. I will be taking it out on longer rides here in a couple weeks.

Last edited by: VegasJen: Jan 8, 24 16:38

Re: Modified my geometry [VegasJen] [ In reply to ]

Jan 8, 24 18:11

Post #3 of 24 (1670 views)

Cool project. Profile design made something similar; a forward offset seat post called the 'Fast Forward'.

Re: Modified my geometry [mhepp] [ In reply to ]

Jan 8, 24 18:19

Post #4 of 24 (1662 views)

I have seen that but it wouldn't work for me. The bend is simply too far down on the post. You can see from my photo, I pretty much have the post bottomed out as it is. This is a small frame tri bike and I'm almost out of adjustment already. If the seat was any higher, I would run out of leg by the bottom of the pedal stroke.

Re: Modified my geometry [VegasJen] [ In reply to ]

Jan 9, 24 5:48

Post #5 of 24 (1566 views)

VegasJen wrote:

I have seen that but it wouldn't work for me. The bend is simply too far down on the post. You can see from my photo, I pretty much have the post bottomed out as it is. This is a small frame tri bike and I'm almost out of adjustment already. If the seat was any higher, I would run out of leg by the bottom of the pedal stroke.

Were you a serious runner before you got into cycling?

Re: Modified my geometry [VegasJen] [ In reply to ]

Jan 9, 24 6:27

Post #6 of 24 (1550 views)

Here's my take on what you've done... it may be working for you, but it's ill-advised for most people. You haven't really changed your geometry, you've changed your position. The geometry of the bike, particularly the front end, isn't designed for someone to have their weight that far forward and for most people it could possibly be quite dangerous to have their center of gravity that far forward. There's a reason that the front-center is quite a bit longer on bikes with steep seattube angles, to get the front wheel out there where it belongs. As a general rule, whenever you need to take extreme measures to get your position fixed, you don't need to fix the position, you need a frame that will work in the first place. IMO

Re: Modified my geometry [VegasJen] [ In reply to ]

Jan 9, 24 6:46

Post #7 of 24 (1532 views)

Cool project and fabrication.

But riffing on mudge, maybe the pictures of the saddle are just with it loosely installed, but it looks tilted up slightly in both pictures, which could make the position feel odd. Generally saddle manufacturers design the saddle so the neutral position is with the rails parallel to the ground. Assuming your top tube is a parallel-to-ground type, your rails appear tilted. I could be wrong.

Also saddle configuration is personal, so if that's just the way you like it, I get that. But if you tilted it back to try to stop the "typewriter return scooch," might try to tilt it to neutral?

The "pushing the pedals forward at the top of the stroke" sounds odd to me. That part of the stroke is before you should ever be applying any more force to the pedal than just enough to continue the motion over the top, which takes a tiny fraction of the force it would take to move your whole body backward. It's just not where power application should happen. Just bringing it up because maybe the more extreme saddle position (assuming the bike frame is appropriate size) is fixing a symptom rather than a root cause of something.

But if it works, and you're happy, why not!

Last edited by: trail: Jan 9, 24 6:48

Re: Modified my geometry [Hanginon] [ In reply to ]

Jan 9, 24 22:02

Post #8 of 24 (1413 views)

Hanginon wrote:

VegasJen wrote:

I have seen that but it wouldn't work for me. The bend is simply too far down on the post. You can see from my photo, I pretty much have the post bottomed out as it is. This is a small frame tri bike and I'm almost out of adjustment already. If the seat was any higher, I would run out of leg by the bottom of the pedal stroke.

Were you a serious runner before you got into cycling?

When I was much younger. But not in the last 20 years or so. Why do you ask?

Re: Modified my geometry [Mudge] [ In reply to ]

Jan 9, 24 22:10

Post #9 of 24 (1409 views)

Mudge wrote:

Here's my take on what you've done... it may be working for you, but it's ill-advised for most people. You haven't really changed your geometry, you've changed your position. The geometry of the bike, particularly the front end, isn't designed for someone to have their weight that far forward and for most people it could possibly be quite dangerous to have their center of gravity that far forward. There's a reason that the front-center is quite a bit longer on bikes with steep seattube angles, to get the front wheel out there where it belongs. As a general rule, whenever you need to take extreme measures to get your position fixed, you don't need to fix the position, you need a frame that will work in the first place. IMO

I would not disagree with that assessment at all. The problem seems to be finding triathlon frames that fit me (and still run 700c wheels). My road bikes are all 49-50cm frames. It seems to be very difficult to find anything smaller than 51cm in a TT bike. Again, running a 700c wheel. I don't want to hassle with different size wheels between my various bikes.

I have found a used Kestrel Talon X road bike that seems to have a very similar geometry as to what I created. It's a smaller frame and I'm hoping to talk the seller down in price. If I can, I will just set it up as a TT bike.

I think this Ridley is a bit more of a "relaxed" geometry so far as TT bikes are concerned. Overall, I like the bike, but I have never felt comfortable down on the aero bars for the reason stated.

Re: Modified my geometry [trail] [ In reply to ]

Jan 9, 24 22:15

Post #10 of 24 (1406 views)

trail wrote:

Cool project and fabrication.

But riffing on mudge, maybe the pictures of the saddle are just with it loosely installed, but it looks tilted up slightly in both pictures, which could make the position feel odd. Generally saddle manufacturers design the saddle so the neutral position is with the rails parallel to the ground. Assuming your top tube is a parallel-to-ground type, your rails appear tilted. I could be wrong.

Also saddle configuration is personal, so if that's just the way you like it, I get that. But if you tilted it back to try to stop the "typewriter return scooch," might try to tilt it to neutral?

The "pushing the pedals forward at the top of the stroke" sounds odd to me. That part of the stroke is before you should ever be applying any more force to the pedal than just enough to continue the motion over the top, which takes a tiny fraction of the force it would take to move your whole body backward. It's just not where power application should happen. Just bringing it up because maybe the more extreme saddle position (assuming the bike frame is appropriate size) is fixing a symptom rather than a root cause of something.

But if it works, and you're happy, why not!

As I mentioned in that other thread about getting comfortable in the aero position, I do have the nose up a bit. I rest my pubic bone on the nose and it relieves pressure on the "soft tissue".

As for the pedal stroke, maybe I'm not explaining it well. Or maybe I'm just an odd duck. OK, I already know I'm an odd duck, but that's beside the point. I also think part of my discomfort is that I have shorter legs, even by my height standard. And honestly, I should probably be on 165mm cranks, but it's really hard to find anything with 165mm cranks.

Re: Modified my geometry [VegasJen] [ In reply to ]

Jan 10, 24 1:44

Post #11 of 24 (1365 views)

VegasJen wrote:

trail wrote:

Cool project and fabrication.

But riffing on mudge, maybe the pictures of the saddle are just with it loosely installed, but it looks tilted up slightly in both pictures, which could make the position feel odd. Generally saddle manufacturers design the saddle so the neutral position is with the rails parallel to the ground. Assuming your top tube is a parallel-to-ground type, your rails appear tilted. I could be wrong.

Also saddle configuration is personal, so if that's just the way you like it, I get that. But if you tilted it back to try to stop the "typewriter return scooch," might try to tilt it to neutral?

The "pushing the pedals forward at the top of the stroke" sounds odd to me. That part of the stroke is before you should ever be applying any more force to the pedal than just enough to continue the motion over the top, which takes a tiny fraction of the force it would take to move your whole body backward. It's just not where power application should happen. Just bringing it up because maybe the more extreme saddle position (assuming the bike frame is appropriate size) is fixing a symptom rather than a root cause of something.

But if it works, and you're happy, why not!

As I mentioned in that other thread about getting comfortable in the aero position, I do have the nose up a bit. I rest my pubic bone on the nose and it relieves pressure on the "soft tissue".

As for the pedal stroke, maybe I'm not explaining it well. Or maybe I'm just an odd duck. OK, I already know I'm an odd duck, but that's beside the point. I also think part of my discomfort is that I have shorter legs, even by my height standard. And honestly, I should probably be on 165mm cranks, but it's really hard to find anything with 165mm cranks.

Yes shorter cranks would mean there is a better chance that when your pedal is at 3 o'clock position, you'll have more knee over pedal and will be pushing directly down rather than mainly down but slightly in horizontal plane also. It would also help with toe overlap on small frames (which can be an issue if doing slow turnarounds in triathlons). I think you should be considering shorter than 165s also.

Re: Modified my geometry [VegasJen] [ In reply to ]

Jan 10, 24 5:18

Post #12 of 24 (1333 views)

Agreed on the shorter cranks

I’m 6’1” and am on 165s.

I would think at your size 155 would be a good one to try. Many fitters have adjustable cranks to try

Re: Modified my geometry [MrTri123] [ In reply to ]

Jan 10, 24 6:00

Post #13 of 24 (1322 views)

As per the suggestion about fitters another useful approach could be to hire these:
https://www.applemanbicycles.com/shop/2xr-fit-crankset-rental/

Re: Modified my geometry [VegasJen] [ In reply to ]

Jan 10, 24 8:12

Post #14 of 24 (1302 views)

You should probably be using 150mm cranks.

Re: Modified my geometry [VegasJen] [ In reply to ]

Jan 10, 24 8:45

Post #15 of 24 (1289 views)

At your height you should be running less than 165mm cranks. I'm 6' and I run 155mm, I could see you going shorter than that. Rotor is a great option for short cranks.

Re: Modified my geometry [imswimmer328] [ In reply to ]

Jan 10, 24 9:49

Post #16 of 24 (1267 views)

Thanks guys. I have long suspected I needed shorter crank arms. I would happily try 160 or even 155. The biggest problem is simply availability. That and the idea of spending the money to try something that may or may not prove to be a correct fit. All the more reason to invest in a professional fit that considers crank arm length. Of course, that then means converting all my existing bikes. For the life of me, I can't figure out why these smaller frame bikes come with 170 or 175mm crank arms to start. I'm sure it all comes down to expense. It can make sorting out a bike (or several bikes) on a budget very frustrating.

Re: Modified my geometry [VegasJen] [ In reply to ]

Jan 10, 24 11:08

Post #17 of 24 (1247 views)

Bikes come stock with 170mm cranks because that is typically the shortest that is normally available from the big manufacturers. 165mm and 160mm are becoming more common from Shimano.

A fitter will likely end your fitting with the conclusion that 150mm or shorter will be best for you on a triathlon bike.

You do not need to change all your bikes.

Re: Modified my geometry [VegasJen] [ In reply to ]

Jan 10, 24 18:19

Post #18 of 24 (1161 views)

VegasJen wrote:

Hanginon wrote:

Were you a serious runner before you got into cycling?

When I was much younger. But not in the last 20 years or so. Why do you ask?

As a rider changes to a position that is more forward with less bend at the waist, and with less intrusion from their thighs (due to shorter cranks), they are essentially assuming a position I call "running on a bike". This is opposed to the classical riding position of being further back with more waist bend and thigh intrusion, which I call "sitting on a bike". Look at any of the old Eddie Merckx or Sean Kelly pictures to see this. This is a gross generalization, because there is that big grey area between these extremes - but this should give you an idea what I'm referring too.

IMHO, people who were serious runners before getting into Triathlon easily, and naturally, adapt to the former.

Re: Modified my geometry [Hanginon] [ In reply to ]

Jan 10, 24 18:28

Post #19 of 24 (1154 views)

Gotcha. I spent 5 years in the USMC and we did a lot of running. Besides that, I used to go on runs on my own just for giggles. At my peak, I was probably over 75 miles a week. After I got out, that largely died off for many years, so I don't know if maybe it's just muscle memory or something else. But I do get what you mean. In fact, part of my objective is to give me more of a running stance, at least from the hips down. Maybe not so much running, but certainly more like a jogging cadence.

I think another thing, which has been mentioned, is that I have rather short legs and with 170mm crank arms being pretty standard, it creates a bit more of a forward "reach" than I like. I have no idea if that's a thing. Just a theory I'm considering.

Re: Modified my geometry [VegasJen] [ In reply to ]

Jan 12, 24 5:45

Post #20 of 24 (993 views)

VegasJen wrote:

Gotcha. I spent 5 years in the USMC and we did a lot of running. Besides that, I used to go on runs on my own just for giggles. At my peak, I was probably over 75 miles a week. After I got out, that largely died off for many years, so I don't know if maybe it's just muscle memory or something else. But I do get what you mean. In fact, part of my objective is to give me more of a running stance, at least from the hips down. Maybe not so much running, but certainly more like a jogging cadence.

I think another thing, which has been mentioned, is that I have rather short legs and with 170mm crank arms being pretty standard, it creates a bit more of a forward "reach" than I like. I have no idea if that's a thing. Just a theory I'm considering.

Certainly, at your height, you should be on shorter cranks - but you already figured out a really important piece by yourself, the (relative) seat tube angle. I'm going to ask you watch the following YouTube video. It is extremely complicated, he's a real engineer - watch it at least twice, then we'll talk more.
https://www.youtube.com/watch?v=S0SpYdxg1UY

Last edited by: Hanginon: Jan 12, 24 5:47

Re: Modified my geometry [Hanginon] [ In reply to ]

Jan 12, 24 6:11

Post #21 of 24 (983 views)

Interesting video, but the analysis seems fairly obvious. What was your takeaway from the video? Why did you suggest it?

Advanced Aero TopTube Storage for Road, Gravel, & Tri...ZeroSlip & Direct-mount, made in the USA.
DarkSpeedWorks.com.....Reviews.....Insta.....Facebook
--

Re: Modified my geometry [DarkSpeedWorks] [ In reply to ]

Jan 12, 24 8:38

Post #22 of 24 (957 views)

DarkSpeedWorks wrote:

Interesting video, but the analysis seems fairly obvious. What was your takeaway from the video? Why did you suggest it?

While the velocity and acceleration/deceleration of your legs might be obvious to you, IMHO, it is certainly not obvious to those who only think in terms of angles and impingement.

Re: Modified my geometry [Hanginon] [ In reply to ]

Jan 12, 24 10:29

Post #23 of 24 (918 views)

Hanginon wrote:

While the velocity and acceleration/deceleration of your legs might be obvious to you, IMHO, it is certainly not obvious to those who only think in terms of angles and impingement.

I didn't quite get it either. The title is "Bicycle Crank Length Debunked," but I didn't catch anything debunked.

And he openly admits that you can't really conclude anything from the velocity/acceleration graphs because he didn't model either force or physiological fatigue, so it's just sort of speculating at maybe heavier limbs being less efficient when undergoing higher acceleration, but who really knows.

The overriding conclusion seemed to be that shorter crank lengths do indeed affect hip angle, which is exactly the conventional wisdom about why shorter cranks may be beneficial for some.

Edit: Interesting analytical tool, though. If you came in with some specific goal, like "I want to minimize femoral angular acceleration" with constraints X, Y, Z, that'd be a good way to do it. But I think the speaker well knows that it's a ton more research required to determine that things cyclists might want to optimize around. Which is unclear. All the studies that did empirical, real world expermentation of crank length mostly concluded "length doesn't matter much for performance, just go with what's comfortable."

Last edited by: trail: Jan 12, 24 10:39

Re: Modified my geometry [trail] [ In reply to ]

Jan 12, 24 12:12

Post #24 of 24 (903 views)

trail wrote:

Hanginon wrote:

And he openly admits that you can't really conclude anything from the velocity/acceleration graphs because he didn't model either force or physiological fatigue, so it's just sort of speculating at maybe heavier limbs being less efficient when undergoing higher acceleration, but who really knows.

The overriding conclusion seemed to be that shorter crank lengths do indeed affect hip angle, which is exactly the conventional wisdom about why shorter cranks may be beneficial for some.

Edit: Interesting analytical tool, though. If you came in with some specific goal, like "I want to minimize femoral angular acceleration" with constraints X, Y, Z, that'd be a good way to do it. But I think the speaker well knows that it's a ton more research required to determine that things cyclists might want to optimize around. Which is unclear. All the studies that did empirical, real world expermentation of crank length mostly concluded "length doesn't matter much for performance, just go with what's comfortable."

Yes, you are correct.
Follow this up with (starting at 23 min in) https://www.youtube.com/watch?v=tqXh3nbj3-0
AND https://www.youtube.com/watch?v=XlRfw15EhRc

We are now off into the realm of anesthetic gases, which I did not want to confuse the OP with.

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