cormacf

I've been told by multiple bike fitters that I'm one of the n% of clients who could actually benefit from a custom frame.

I have short legs (jeans inseam of 30", height just a bt more than 5'9"), but a lot of that comes from very short femurs, apparently. Short cranks (I run 165s on all my bikes except an old Super Le Tour that has the original 170, I think) and steep seat angles are my friend. Unfortunately, that comes at a cost of throwing a lot of weight forward, which probably contributes to the feeling that (even after a professional fit) I'm going to endo in the drops when descending. I've never ACTUALLY endoed, mind you, but no matter how I set up the bike, the forward weight makes the drops feel "wrong" unless the front wheel is flat or on an incline.

The longer the front-center, the less I feel this. Slack headtube angles are my friend. My rigid hardtail feels great in descents (comparison of the roadie and the MTB here), and a gravel geo would probably work pretty well, too.

So, to my question (thanks for putting up with that), what exactly would a custom frame do? Would it basically be just slacking out the headtube angle (in which case it's basically an off the rack gravel bike), or is there a more nuanced set of options in which (and I'm just making this up) some combination of maybe a longer top tube with more traditional road headtube angles or a gravel geo with shorter chainstays or some other wizardry would give me the normal roadbike experience all the non-wonky-shaped folks get?

Thanks!

Andrew R Stewart 

I suspect some of the "endo feeling" comes from what is likely a long stem too, not just a small seat set back amount. Relaxing the head angle (and rake to end up with some trail you like...) is not the first way I would address this. A longer top tube will both get that longer front center as well as open up steering geometry options (angle, rake/trail). Running short crank arms means that a lower BB height (or greater BB drop) could be considered, this would lower the CG a bit.

Since I make my own frames I have far less cost in ending up with a custom geometry/fit than most do. I generally don't suggest a custom frame for most riders but as you have been told and seem to be finding out there are some riders whose body dimensions don't work well with the middle of the bell curve of fit that pretty much all "bike brands" are economically driven to offer. I think you are one of these too.

As example my BB to seat top is 67ish cm (170 cranks) with a 45ish mm seat set back. But my top tubes are 55/55.5 cm long and the stems are 90/100mm long. What is called an over square design. The 52/53.5 long top tubes often found on 48/52 cm sized bikes are just too short for my tastes, I like a bike that isn't truck like in the steering so I avoid sub 72* head angles for all but my touring bike. The long top tube helps reduce the toe clip overlap but maintain nice steering. Andy

Polaris OBark

I have very similar dimensions. I had a custom frame built, and it was worth every penny. However, the frame geometry is extremely similar to a 54 Trek Domane. I also have a 110mm stem.

cormacf

Thanks! Clearly, there are too many variables for me to sort out without an in-person visit. Because if I just went by what's felt right in the past, I'd be trying to fuse the back half of my old Omnium track bike (felt PERFECT in terms of my hips and legs, but I literally never turned the thing and only every rode in one direction) to the front of an old 80s beater Peugeot hybrid (I think it was an '83 Saint somethingorother from Canada) that had a top tube so long you could take your hands off the bars and eat a sandwich.

unterhausen

I also have an inseam of about 30" and I'm maybe a little taller than OP. Maybe my femurs are a bit longer than OP's. I don't use steep seat angles, but I have been experimenting with long top tubes and shorter stems. It makes sense to have less setback, but is it really impossible to get it with a zero setback seatpost? I fit fine on stock bikes, although I like something else usually.

cormacf

Good question. The first roadbike I had as an adult was a Rivendell with a 72 degree seat tube angle, a standard setback seatpost of some sort, and 172.5mm cranks. I was having knee pain and just generally not feeling right (but I hadn't ridden in 25 years, so I didn't know how much was normal). I went to a fantastic fitter who was also a physical therapist (three cheers for bike fits you can put on insurance!), and he did a fantastic job of adapting that bike as well as it could be adapted. All three of those measurements probably combined to give me some level of discomfort, probably made worse by my terrible conditioning (which led to poor form). The fitter did most of the adjusting with seat height and placement (slammed forward), but that may have been because he couldn't change the length of the cranks or the seat tube angle. He also prescribed some stretching and strengthening exercises, some of which were just general good practice, and some of which were related to previous injuries.

Some years later, as I had him going through a commuter bike, he made reference to a possible custom frame, mentioning a slightly sloping top tube (more for convenience than anything else, I believe), a 73.5ish seat tube, a zero setback post, short cranks, and, I believe, a fairly long top tube, but that was just an off-the-cuff remark, and he suggested I go in to a frame builder (Rodriguez and Davidson were the big local ones up there) to have them work with me on specifics. I will say that my Lynskey Sportive has a 73-degree seat tube and a zero setback, and it feels much better than the Riv, for whatever reason. But I feel MORE like I'm overly forward.

dsaul

I'm a fan of the long top tube and short stem to get the front wheel further ahead of the hand position and eliminate that "over the bars" feeling on descents. My personal frames get a 74 degree seat tube angle and a 50-70mm stem depending on their intended use(off road or road) You have to get away from worrying about the aesthetic of a bike with a short stem not looking traditional and worry more about how that bike performs for you.

Seat tube angle should not just be a number picked out of the air, though. It should be the result of the angle necessary to the place the center of the saddle rails at the proper distance back from the center of the bottom bracket at the correct saddle height for the rider.

sdodd

As a short rider with a really short inseam (5'7", 28.5" inseam) I struggled for many years on 'standard' square road frames. My old 56cm trek 560 was ok for toptube length (56.5, 120mm stem) but i couldn't stand over it without 'interference'. The replacement cannondale 3.0 52cm frame had minimal 'interference' during standing but my 150mm stem put me way over the front wheel and still left me hunched up. But, as a junior racer I just lived with it and put in my miles.
When I was 30 I purchased my first custom road frame from Bernie Mikkelsen in the bay area. While I was a plane ride from him, he had a customizable fit-bike that you could ride. It allowed me to get all sorts of adjustments and see how they felt. In a classic frame design with a flat top tube I ended up with a 47cm seat tube and a 57cm top tube with a 110mm stem (we moved to a sloping top tube with equivalent dimensions). For various reasons we chose 650c wheels, making a fairly funny looking bike that was really enjoyable to ride on.
Recently I've built a couple of my own frames - the black / orange cyclocross frame and the Ti/blue hardtail. all have really short seat tubes and long top tubes and I love them! My angles are fairly standard - seat tube is determined by BB height, seatpost design, and where I want my body on the bike. The headtubes I keep pretty tame - 73.5 on road/cx and 69 or 70 on my hardtail.
My opinion is that if you like riding, find a fitting and frame builder and see what your options are. Spend some money figuring out sizing. Then you can decide if a certain brand might fit you better or if you really need something custom. At one point in time I found an old Tom Kellog/Spectrum custom Ti frame that was 52/56 on ebay and used that for a while. While not perfect, it was a better fit for less than a custom frame.

simon

Doug Fattic 

There are advantages of a custom frame even for riders with normal proportions. Production frame design is about reducing company liability so they have to assume longer cranks might be used and the rider will be pedaling fast through corners. Therefore the bottom bracket height will be higher than my ideal. A lower BB height not only improves the way I like a bike to feel and handle, it reduces the top tube height for the same size frame making swinging your leg over easier. And a bigger frame for the same straddle height can be a benefit if one's handlebars are close to seat height. That way a bicycle doesn't look goofy with too many stackers or quill stem extension.

In addition production companies don't want their frame to break if it is ridden by an extremely fat person so the tubing will be thicker/heavier than what's best for anyone near the 50th percentile. In a steel frame anyway lighter tubing has a more lively feel. It isn't about the actual weight of the frame but rather how it feels when ridden.

My design philosophy on seat angle is based on the relationship of the height of the rider's handlebars compared to their saddle. The higher a rider likes their handlebars for comfort, the shallower their seat angle needs to be. This is why tri bikes have very steep seat angles, racing bikes steep angles, touring bikes more shallow angles and bikes with upright handlebars have very shallow seat angles. I like to do the fitting myself because fitting philosophies vary and it is common that the principles used might be based on efficiency rather than comfort. The desire/need to go faster is the driving force with many fit studies to improve a racer's efficiency. For a recreational cyclist not concerned that they can gain a few seconds time over their normal route, a more upright relaxed position might be more preferable. This is particularly true as we age. The goal of saddle setback in this case is to find the balance point of the rider's weight over the BB. This unloads their upper body weight that needs to be held up by their arms and body core. In other words comfort rules over aerodynamics and perhaps biomechanics. Just to be clear a different saddle setback (requiring a different seat angle) is needed if one is looking at the back wheel just mms in front of them or preferring to be able to look around while riding.

Once I have established the purpose and position of the rider on a stationary fitting bicycle, I recreate their saddle/handlebar/BB relationship on my Ukrainian made fixture and slide the pieces that represent each tube to match that position. This will also involve toe clearance and wheel size and handling characteristics. This not-so-brief explanation hopefully illustrates why you don't have to be at the extremes of the bell curve to benefit from getting a custom frame.

edit: I'll add that production companies base seat angle on getting toe clearance with 700C or similar size wheels. This is fine when speed is the goal but might not be the best as handlebars get up closer to saddle height for rider comfort.

cormacf

Those bikes look awesome and comfortable. They kind of remind me of 80s first-gen mountain bikes (in terms of proportion, not angles), and I mean that in the best possible way. I've always thought Specialized should reissue a 1984 Stumpjumper with hydraulic discs. I would ride that thing everywhere.

niknak

You say that steep seat tube angles are your friend, but you also say you feel like you're sliding forward. It sounds like your saddle may be too far forward right now. Try sliding it back on the rails 1cm if possible and see how it feels. You might have to use a slightly shorter stem to compensate for the reach and maybe lower the saddle a hair.

When designing frames, I like to use the horizontal measurement from the center of the BB to the center of the seat post clamp. For me I like around 210mm for drop bar bikes with the bars slightly below the saddle and about 180mm for my hardtails. This is with the saddle rails more or less centered in the clamp. The seatpost I plan to use will dictate the seat tube angle.

You should measure your saddle clamp setback on your current bike and on your Riv if you still have it. You can measure it easily with a laser lever with the vertical line going through the BB. Or if you don't have a laser level, park your bike's rear wheel against a vertical wall perpendicular to the wall. Measure the horizontal distance from the wall to the BB. Measure the horizontal distance from the wall to the saddle clamp. Subtract the two and you have your number.

Once you get your saddle position dialed, then you can worry about your reach to the bars.