Review / Critique my frame design

[NHAero]

Can you explain why a more upright seating position wants a slacker seat angle?

Originally Posted by Doug Fattic

This extra information about the kind of riding you expect to do and your body type is helpful. Many people base their next bicycle design on what they used in the past with small adjustments. This is a sensible plan but it doesn't mean it is the optimum plan. Production bikes are influenced to put the front wheel where rotating toes won't hit it or the company gets sued for rider injuries. Often this means a steep seat angle - especially on smaller bikes with shorter top tubes. I'm not saying a 74º seat angle is wrong for you but my experience says that for a guy already in his 60's and hoping to ride for many more years, the odds are it probably should be slacker because you will continue to sit more upright. However I wouldn't know until I put you on a fitting bicycle that didn't have any position restrictions to verify. I've learned over the years that many riders thought their position was okay until they had a fitting done. And then its like "oh"! These experiences are why I don't just take the word of a customer/student that they have found by themselves their optimum position based on adjusting their components on a production frame.

I built a go fast frame for myself 30 years ago when I was in my 40's so I could (barely) stay with the big boys on fast training rides. I still ride that bike today but my stem is 2 centimeters shorter and higher than it was when I built it. You should plan for this to happen to you too.

Bottom bracket height is another area where a custom frame design can be superior to the higher heights common in production frames. Those heights were established in the days of quill pedals when that point sticking beyond your foot would scrape the ground when pedaling at speed through corners. Companies took no chances with whatever length of crank or type of pedal or cornering style. They were high enough so a pedal always missed. There are big advantages I've already explained to lowering your BB height if you don't need that clearance any more. That bike I mentioned that I built for myself that used 170 cranks had a BB height of less than 260mm. I'm no longer jumping out of corners trying to stay in the draft. I didn't need a higher bracket height than and even less so now. If you aren't riding crits, you don't need a crit height height.

Just like fitters, there is a huge variety in the knowledge and ability of custom builders. The ideal is Tom Kellogg at Spectrum. He was a knowledgable fitter, and excellent builder and painter. Unfortunately he retired and not everyone has his skills.

[Doug Fattic]

Originally Posted by NHAero

Can you explain why a more upright seating position wants a slacker seat angle?

Sure, think of the extremes. A time trial bike with a low handlebar position rotates the body forward requiring a steep seat angle so the bike's saddle will be under your butt. A dutch type of bicycle (or an English style 3 speed) with upright north road handlebars requires a shallow seat angle around 70º (often less sometimes more) where the resulting hand position rotates the body back. Your butt follows the rotation of your body forward or backward.

This is why it doesn't work well to convert a traditional road frame (particularly a road racing frame) to upright handlebars. In the same way you can't replace north road handlebars with low aero bars either. In either case your seat wouldn't be able to find the bike's saddle.

Popular American production road bicycles are commonly designed like racing bicycles that place an emphasis on speed over comfort. The rider is leaning over to reduce frontal area and supporting to weight of their upper body with with with their arms and core. Furthermore it looks good to have a lot of bar drop. If the emphasis is on comfort then moving the saddle rearward can take their weight off of their their hands. There is a saddle fore/aft position where the body is balanced over the pedals and no longer requires arm and core strength to support their upper body. Finding this balance point is part of the purpose of a fitting bicycle that has lots of adjustment.

Finding a good fit is balancing aerodynamics, biomechanics and comfort. All 3 are in tension with each other. That is why fitting is more like an art form. Furthermore in the past the emphasis on fitting was increasing performance. This is all well and good until the rider realizes he is now too old to win the Tour and wants more riding comfort than speed.

[Mark McM]

Originally Posted by Doug Fattic

Sure, think of the extremes. A time trial bike with a low handlebar position rotates the body forward requiring a steep seat angle so the bike's saddle will be under your butt. A dutch type of bicycle (or an English style 3 speed) with upright north road handlebars requires a shallow seat angle around 70º (often less sometimes more) where the resulting hand position rotates the body back. Your butt follows the rotation of your body forward or backward.

This is why it doesn't work well to convert a traditional road frame (particularly a road racing frame) to upright handlebars. In the same way you can't replace north road handlebars with low aero bars either. In either case your seat wouldn't be able to find the bike's saddle.

Popular American production road bicycles are commonly designed like racing bicycles that place an emphasis on speed over comfort. The rider is leaning over to reduce frontal area and supporting to weight of their upper body with with with their arms and core. Furthermore it looks good to have a lot of bar drop. If the emphasis is on comfort then moving the saddle rearward can take their weight off of their their hands. There is a saddle fore/aft position where the body is balanced over the pedals and no longer requires arm and core strength to support their upper body. Finding this balance point is part of the purpose of a fitting bicycle that has lots of adjustment.

Finding a good fit is balancing aerodynamics, biomechanics and comfort. All 3 are in tension with each other. That is why fitting is more like an art form. Furthermore in the past the emphasis on fitting was increasing performance. This is all well and good until the rider realizes he is now too old to win the Tour and wants more riding comfort than speed.

But the difference between a "performance" oriented position and a "comfort" oriented position can be more than just "rotating the body back. As you say, a very low and forward position can put a lot of weight on the arms/hands. Rotating the body back (by slackening the seat tube angle) can take the weight off the hands. But the "performance" oriented position also frequently has a more acute hip angle than a "comfort" position". If the seat tube is slackened and the hip angle is opened, this can shift the weight back too far, so the weight is no longer balanced over the pedals. To balance the weight over the pedals with an open hip angle, a steep seat angle may be required.

[Marvinlungwitz]

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[NHAero]

My personal experience is opposite to Doug's recommendation. In a position that is “racier”, I want more setback to balance the increased lean forward. Because these days my bars are even with my saddle, I find a 74 STA works best.

[Mark McM]

Originally Posted by Marvinlungwitz

Also, can’t one just use a post with more set back and push the saddle back, along with raising the bars and shortening the stem to achieve the same thing as a slack seat tube bike? That’s what I’m counting on doing as I get even older and less flexible than I already am.

You can do this with an already existing frame to achieve the desired fit of course. but the shorter stem and the rearward shift of the balance point will change the handling a bit. If a frame is designed around the rotated position to start with, then in addition to slackening the seat tube, the Reach and front center can be adjusted to tune the handling.

[Doug Fattic]

Originally Posted by NHAero

My personal experience is opposite to Doug's recommendation. In a position that is “racier”, I want more setback to balance the increased lean forward. Because these days my bars are even with my saddle, I find a 74 STA works best.

And it may work best for the OP too but my recommendation is to find out with a proper fitting. There is a high probability it should be shallower. Particularly in the future as his body ages. He’s going to be spending what to him is a very significant amount of money to get a new frame that hopefully he can still comfortably ride 10 years from now.

Production frame design (particularly small frames) is generally based on front center (so the rider won’t hit the pavement when making a slow turn). One way this is achieved is with a steep seat angle. The result is that cyclists may not be able to try out a position with the seat further back.

A general rule of thumb is that as one ages and gets fatter, less flexible and slower, they need to raise their handlebars to compensate. This results in their saddle needing to have more setback. This is especially true at the age of retirement. The problem with a general statement like mine is that all of our bodies vary resulting in exceptions. That is why I always encourage a fitting before getting a custom bike.

[deluz]

Originally Posted by Marvinlungwitz

Also, can’t one just use a post with more set back and push the saddle back, along with raising the bars and shortening the stem to achieve the same thing as a slack seat tube bike? That’s what I’m counting on doing as I get even older and less flexible than I already am.

I thought the same thing. Currently I could move my saddle back another inch if needed. That is with a zero setback post. If I used a one inch setback post that would give me two inches. Certainly that has to be enough. I don't really think about 10 years ahead, I am thinking what would be optimal for today. If I am even riding 10 years from now it may not even be a road bike.

[NHAero]

I've aged and gotten less flexible and slower (not fatter). Raising the bars hasn't required more setback, it's the opposite because I am not as bent over. I can't find his post, but Dave Kirk explained how a more racing-style position requires the rider to move their butt back to balance their torso and keep weight off their hands.

I agree that if someone isn't sure if they have the best fit, they should pursue getting fit. But there are plenty of us who have worked out their fit on their own too. The proof in my case are long rides without pain.

Originally Posted by Doug Fattic

And it may work best for the OP too but my recommendation is to find out with a proper fitting. There is a high probability it should be shallower. Particularly in the future as his body ages. He’s going to be spending what to him is a very significant amount of money to get a new frame that hopefully he can still comfortably ride 10 years from now.

Production frame design (particularly small frames) is generally based on front center (so the rider won’t hit the pavement when making a slow turn). One way this is achieved is with a steep seat angle. The result is that cyclists may not be able to try out a position with the seat further back.

A general rule of thumb is that as one ages and gets fatter, less flexible and slower, they need to raise their handlebars to compensate. This results in their saddle needing to have more setback. This is especially true at the age of retirement. The problem with a general statement like mine is that all of our bodies vary resulting in exceptions. That is why I always encourage a fitting before getting a custom bike.

[deluz]

Deleted