PromptCritical 

TiCycles in Portland teaches a frame building class every year, where they teach how to build a frame in steel or titanium and each attendee leaves with their own new frame.

I'm planning on attending the next one and I'm trying to find a resource to learn about frame geometry. I could copy one of my current bikes, but none of them are a perfect for me (long legs and short torso makes a bike fit challenging for me), so I'd like to learn how to make changes and ensure the geometry and ride are still good.

Anyone know of any resources?

TIA

GrayJay

Play around with rattlecad

PromptCritical 

This is an AWESOME app and it even has a MacOS version - many thanks!

Do you know of a source that can help with what the design should be? Sort of a theory of framebuilding so I can learn what would work well?

Andrew R Stewart 

I would reach out to the instructor and ask if they offer fitting or design help too. If they use a specific design program (and if so perhaps see if you can play with that prior to attending the class).

There are a number of books (some available on line) that sort of cover the writers' views of fit, geometry and materials but we don't even know which kind of bike you seek, most books seem to focus on road/tour riding.

Many do as you suggest and copy a known bike and just alter the fit numbers to suit, the steering geometry remaining basically the same. Others are OK with experimenting more than some and will try out geometry they have wondered about.

Whatever the design I would not place too much importance on this potential frame being "perfect". Between the mistakes you'll make on your first, construction and design wise, and that you will also change over your years I suspect there will be more bikes in your future. Andy

PromptCritical 

Thanks Andy. Do you have any favorite books you'd recommend?

unterhausen

The top ten list of books on framebuilding is blank. Or maybe it includes the C.O.N.I. book. Periodically someone the industry convinces everyone they need a different geometry, and the other companies just follow them. Although right now, there are some competing ideas about geometry.

What do you think is wrong with your bikes right now? Start with fixing that

PromptCritical 

Nothing is wrong, per se, as I've been able to adjust the fit with stem risers, etc., which I'd like to avoid with a new build. I want to make sure I don't make a change that causes a problem. Also, there are always myriads of details that aren't evident to a newbie which I'd like to learn about before the class.

unterhausen

Part of the advantage of a custom bike is that you don't have to have outlandishly sized stems or a lot of spacers and things like that. Some designers are moving to longer top tubes for various reasons, as an example. The difficult part of frame design for me is getting the clearances right for the wheels and crank.

PromptCritical 

I just started play with RattleCAD that GrayJay recommended, and it looks awesome. That might help you.

unterhausen

I use bikecad. The issue is you have to enter in the dimensions of your parts. That's enough work that I haven't done it. I'm sure rattlecad has the same issue.

Andrew R Stewart 

I also use BikeCad. I will again suggest that the design method the OP starts playing with might be best if it is the same as what the class/instructor will use. less translation or getting up to speed when taking the class.

As to books- I can't say there's even one or two that offer a thorough and overall view of geometry for a wide range of bike types and intended use, or at least among those I've looked at. Here's a few that I have used in the past: The Paterek Manual, Touring Bikes (Tony Oliver), Bicycle Design (Hadland and Lessing), Bicycle Science (Wilson) and the CONI manual. There are others but these are what I have on my shelf. Most don't go into much depth about steering geometry however Bicycling Science is, perhaps, the most in depth here and has Jim Papadopoulos contributing (for those who don't know of Jim P he's, perhaps, the most knowledgeable person about the relationships between angles, diameters, and rakes/trail alive today. Do know that predicting the actual handling manor of a bike is hard to do for at least one reason, the rider's body and brain vary from rider to rider and even day to day. Andy

An interesting read but of little real world value is the Scientific American article on the unrideable bike. Andy

unterhausen

It might be worthwhile to look at Paterek, Talbot and the Proteus manual. Just treat them all with skepticism. I'm sure Dave Levy has more experience and knowledge than all those authors combined.
I wouldn't buy Talbot, hopefully OP can get it at a library. Some versions of Paterek are available online. So is the Proteus manual. I don't know if you can find the CONI manual online, it's pretty expensive to buy nowadays.

Delving* deeper into bike steering geometry is an interesting idea, but in the end there's a reason why upright bikes are designed with a relatively limited range of steering geometry. Probably best to try to understand what that range is and how you want to the bike to handle. I always recommend sticking with something that's well-tested for an initial few frames.

*apparently, recruiters think that if you use "delve" in your resume, you used AI to generate it. I swear no intelligence was used in crafting this post.

PromptCritical 

Thanks Andy - that's very helpful!

Doug Fattic 

I'm a builder that has been teaching framebuilding classes since the middle 70's. There are 2 common approaches to designing a frame. The 1st most commonly used is to design a frame for maximum speed with good handling. If you are young and fit and fast, this is a good approach. However there are many cyclists that have issues (extra weight, loss of flexibility) that prevent them from contorting themselves into a go fast position. For this group, I start the design process by 1st establishing their seat/handlebar/pedal relationship on a stationary adjustable fitting bicycle. For some being comfortable is their primary concern. I have even designed my fixture (laser cut and etched out of stainless steel in Ukraine) to convert a person's position into a frame design. Of course this method probably involves some compromises. To sit a bit more upright might affect handling for example. No matter it becomes the design that works best for that particular individual. The chapters in my framebuilding class manual on proper fit and frame design variable are pages long so I can't very well abbreviate them here. Your teacher Dave should be able to provide insight during your class.

PromptCritical 

Thanks Doug! That's my situation. My flexibility has decreased over the years (although I was never Gumby) and I have arthritis in my shoulders. I'm interested in building a frame to get away from the "work-arounds" and I also think it would fun.

My specific concern is how to shorten and raise the top tube a bit (2" or so) without causing geometry problems or ending up with something looking like a "Franken-bike". How have you addressed this in the past?

unterhausen

Raising the top tube is somewhat problematic, I think. Do you really want less standover height? I don't think it's super important, but I'm sure there's a limit I could tolerate. Shortening the top tube is something you can explore using rattlecad. I would look at toe overlap. A lot of bikes for people with these concerns have tall head tubes. Yes, certain online communities will make fun of it. That's their problem.

Andrew R Stewart 

When riding with a more upright body the seat tube angle often is slacked back a bit. Which worsens top tube length and/or toe overlap. I suspect that the slack head tubes used back in the day, on balloon tired bikes and classic English 3 speeds as examples, helped stretch the front center back out and retain toe clearance.

With first time builders I usually suggest taking a known bike that fits well as the model if at all possible. But here I think Mike (the OP) might be looking for more than what a shorter stem with a riser/tall stem might result in on his current bike. "Shorten and raise the top tube a bit (2" or so)" is with what bike and bars/stem combo? Presumably your current bike, and the 2" is from your current bars location. Is there any way to test this out with your current bike, even if the handling is compromised? I have real questions about wanting to build a bike with a fit that is not either already confirmed (as from some previous bike) or designed with fairly minor differences that are well understood.

A year+ is a lot of time to explore the fit and perhaps learn what you don't want the class frame to be. Andy

base2 

Plus one on RattleCAD. It is a really comprehensive program with a steep learning curve.

Don't be afraid to have or experiment with longer chain stays than is commonly available on commercial bikes. Moving the axle back has the effect of moving the center of gravity more central between the wheels. If you intend to sit more upright than not or you have longer legs than an average person, keeping the cg more central (is more towards a 50/50 split in distribution) will counter any front end lightness that can occured when you are basically sitting over the rear wheel where a longer legged person would be at (hypothetically) 90/10 or 80/20 or 70/30 or whatever. The net effect is a more balanced/proportional bike for the intended rider.

The cool thing about designing your own is making a bike for you and you alone that is proportional for your personal dimensions so you own a bike that rides like it should. I can't stand it when someone gets a size 61 or 63 or 65cm bike and all the builder did was make the head tube & seat tube longer, keeping the wheel base the same. Cheap & looks like a circus bear on a childs bike. Silly. You have the opportunity to scale a bike to your proportions...Why not use it?

I'm the opposite of you. 31 inch inseam but 72 inches tall. All torso & arms. Long wheel base mixtes with 58-60mm of trail is what I've found ride best for my tastes. I'll never buy an off-the-shelf bike again.

Doug Fattic 

Once a person's fit position is known, then I use my fixture to create the frame design. I place the chosen seat/seatpost and stem, in the same position as was discovered on the fitting bike. Like Andrew mentioned, a more upright position combined with the body balanced over the pedals (so you don't have to use effort to hold up your upper body) typically results in a shallower seat angle (in other words less than 73º).

A big advantage for me using actual components and designing a frame life size around those components, is that it is easy to see if eventhying looks proportionally correct. Markings on the fixture make it easy to set dimensions. For example if you are wanting to raise your handlebars and not have them look stupid, you can adjust several variables. 1st lower the bottom bracket height so you can have a larger frame with a longer head tube. Production companies have to assume you are going to pedal through corners and as a result need a higher bottom bracket height. Next you slope the top tube a couple of degrees and as a result that raises the top of the head tube a bit (or slope it a lot if tigging or fillet brazing), And 3rd you can add a bit of height to the top of the head tube. Because I'm using my actual stem, I can adjust this height precisely so the amount still looks proportional.

My fixture also has markings to show the height of the top of the top tube off the ground so the seat tube length can be adjusted to the mm to a person's straddle height. Of course the frame design can be played with once it is created and adjustments can be made. For example it might be necessary to shorten the stem so better toe clearance can be achieved. Or maybe the reach can be extended from perfect to acceptable to do the same thing.

using actual components to create a frame design

PromptCritical 

This is super helpful! Thank you.

How does changing the seat angle and so forth change the handling and ride?

Doug Fattic 

When designing a frame, it is necessary to prioritize what is important and compromise on what less so. For example some cyclists that are older, fatter and less flexible can no longer ride in the position that makes them most efficient. They are leaning over too far and putting too much weight on the hands, arms while trying to support their upper body. The solution is not difficult design frame wise. And that is to slide your butt back until your weight is balanced over the pedals and - like magic - you no longer strain to hold up your upper body. Of course this more upright position makes you less aerodynamic. US bicycles with drop handlebars are not designed for this situation. There is a zillion go fast bicycles in all materials that are designed with speed as a priority. They are not designed with a shallower seat angle (maybe 71º) to sit more comfortably upright. Because then you will run into toe clearance issues. And so the compromises to best handling begins. That might include smaller wheels or being more conscience of keeping your foot out of the front wheel when turning. For many people as they age, they will find that if they are not comfortable riding, they just won't ride so "how does the bike handle" becomes a non-issue. It is possible to design a frame with a shallower seat and - as a consequence - swallow head angle that rides okay. The alternative is to lose 50 or more pounds or become younger so you can go back to riding the bikes of your youth.

Lots of my framebuilding class students have retired and designed their frames for a more upright position and as a result continue to enjoy cycling (maybe at a slower pace). And by the way, it is not hard to figure out a comfy bike position. I have several fitting bikes (I've provided a schematic to a DIY one on this forum) and they don't need bells and whistles to provide trustworthy results. It is the guys/gals trying to shave a few seconds off of their results that are the bigger challenge. They will go to a store with one of the latest fitting bikes that are computer controlled with video feedback to make sure they are buying the right carbon bike.

guy153

I made my first frame (which was for me obviously) according to the traditional Italian principle of make the ST the same length as the TT. It seemed to fit perfectly so I stick roughly to that. Most commercial bieks are longer than this-- either so you have more seatpost sticking out (which might give you some suspension I suppose but I think it looks goofy if it's too much) or you get more reach. Perhaps I also have long legs and shorter torso, or I like a more upright position. Not sure. In my experience you tend to get used to riding any frame within reason and then it feels fine, so I think it's very hard to be objective about the different handling qualities etc. you get from different geometries. So I would prioritize fit first and then aesthetics.

schnee

Personally, I'd find a professional bike fitter, and get yourself fit to the kind of bike you want to ride, and bring those measurements in to the course.

. I did one and it was revolutionary. I met the fitter through a road riding club, he was a coach for a local racing team and he was really good - he had lasers and a fully-configurable stationary bike. I used his recommendations on my then road bike (a Giant OCR) and a lot of post-ride tension in my shoulders and neck went away. He even identified the fact that my hips were so wide that I should put pedal spacers on my road bike - the Q-factor was too narrow. A lot of knee pain went away permanently after that.

I brought those numbers with me to Yamaguchi's framebuilding course, and Koichi used my fit as the basis for the handling I wanted, and we tweaked the frame design from there. Example: I wanted stability and comfort, so he lengthened the chainstays and head tube.

It's the single most comfortable bike I've ever ridden.

PromptCritical 

I've had my road bike fitted, which was a huge help. However, I had to use a long stem extender, so it is a bit of a frankenbike. Making a frame that will fit me will involve some geometry changes, and I want to make sure I know what they will be before I build the frame. Besides, I'm a recovering engineer, so I need to know everything!

Doug Fattic 

The problem with your request is that if your primary concern and controlling factor in frame design will be based on a comfortable fit and that will involve some compromises to a frame design. Those compromises will result in using variables that have to be adjusted from perfect. In fact unlike a production frame, you can't test ride a custom design until it is actually finished. For example you might ask what is the best head angle/fork rake combination to use on a bike I'm riding on average at 15mph for maybe 25 miles at a time that is using 700 X 32 tires. The answer you get from what might be the best combination for that situation is not what will fit best into a frame that matches your more upright riding position. All their variables interrelate with each other. They are not stand alone dimensions. But the adjustments from what is best if you were 25 again will probably be still okay just not optimal. The solution of course is to find someone with experience making the kind of frame you are wanting to build and trust their opinions on frame design choices.

I'll repeat what I've suggested before. Use a lower BB based on your actual crank length and pedaling through corners style. Production frames will be higher to avoid hitting a pedal when going through a corner. Make the frame size be as large as you can comfortably straddle to the millimeter. Production frames have 2 cm steps between sizes. Slope the top tube either a bit if using lugs or a lot if fillet brazing or tig welding. Both of these factors raises the top of the head tube so there isn't an ugly amount of spacers or quail extension above the head tube. Additionally add mms to the head tube length to reduce spacers or quill extension. Use a lighter weight tubing based on your actual weight and pedaling strength. Production frames have to assume you are super fat and powerful and have to use thicker/heavier/bigger ø steel to prevent breakage. It isn't the weight that is a problem but rather the ride quality of too much steel. I vastly prefer the ride quality of lighter/thinner steel tubes. Again it is not about extra weight.