Review / Critique my frame design

[NHAero]

If you mean HTA instead of STA, a 71 HTA and a 45mm fork rake yields a trail of 69mm using the linked trail calculator above (25-622 tire.) Preferences vary, for you it handles great - I would not like that handling, especially the wheel flop. This is why it's really a good idea to ride a lot of bikes before having a custom frame made, because different riders prefer different handling bikes.

Originally Posted by Dave

My Cinelli superstar has a 71 degree STA and 45mm fork offset. It handles great. A 71 degree STA with 50mm of offset has less trail, but only if the fork length is correct. A frame could have been made for a shorter fork, otherwise, there should be nothing wrong with the steering.

Colnago and Cinelli use more trail than other brands.

[NHAero]

It's worth saying that the numbers don't always tell the whole story. I had a 54 CAAD10, I think it was a 2011, which according to the numbers I should have liked a lot, but its handling always felt a bit nervous to me and we never bonded.

[Dave]

Originally Posted by NHAero

If you mean HTA instead of STA, a 71 HTA and a 45mm fork rake yields a trail of 69mm using the linked trail calculator above (25-622 tire.) Preferences vary, for you it handles great - I would not like that handling, especially the wheel flop. This is why it's really a good idea to ride a lot of bikes before having a custom frame made, because different riders prefer different handling bikes.

HTA of course. I didn't go far enough to look at the tires. I'm riding 28mm x 700c. Mine figures out to be 71mm. No problem at all. I ride speeds from 5 mph to 56 mph.

One thing I first noticed was how much easier it was to make a slow speed u-turn.

[deluz]

Ok here is version 2 of my frame design.
Due to some quirks in how RattleCAD works I have made some corrections.
The wheel radius was too small, I had to change the tire height from 28 to 34 to get the correct 345mm wheel radius. I don't really understand what they mean by tire height but it does correlate to what I measure on my actual 28C tires.
My saddle height was too high because I usually measure it to where my sit bones contact the saddle, but RattleCAD measures to the center of the saddle.
I changed the fork length from 365mm to 375mm because that seems to be what Mercian uses and what I measure.
I had to increase the top tube slope to 8 degrees to get the seat tube length and stand over I want.
I changed the HTA to 72.5 degrees and fork rake to 50mm.
This reduced the front center and reduced the trail to 56mm.
I am feeling pretty good about this now. Let me know what you think.

[NHAero]

This go-around looks much more "in the ballpark" of what a modern road bike in your size would be. I will of course defer to the pros like Mr. Kirk on this, just my opinion, man. My Firefly (built originally for another PLer) has a 72 HTA and 50mm fork rake and 57mm trail, and it's a wonderful handling and riding bike. It also has 415mm chainstays and maxes out at a 28mm tire. I ride it with GP5000 25mm tires. My custom Strong is designed around 650B tires 38-42mm, so I went with a 73 HTA and 51mm fork rake, yielding 48mm trail, to compensate for the pneumatic trail of the fatter, lower pressure rubber. I'm very happy with its handling too. With 700Cx25 it's also great, trail increases a bit with the larger diameter tire vs 650Bx38.

[Mark McM]

A few comments:

Originally Posted by deluz

The wheel radius was too small, I had to change the tire height from 28 to 34 to get the correct 345mm wheel radius. I don't really understand what they mean by tire height but it does correlate to what I measure on my actual 28C tires.

The most likely source of the error is in the rim diameter used in the calculation. Although a 700c rim is referred to as "622mm" rim, the 622mm dimension actually refers to the diameter of the tire bead, which sits about 5mm below the outer edge of the rim. The actual diameter of a 700c rim is closer to 632mm, which is a radius of about 316mm. When you add the tire height of 28mm, you end up with a wheel radius of 344mm.

Originally Posted by deluz

I changed the fork length from 365mm to 375mm because that seems to be what Mercian uses and what I measure.

Fork length can vary depending on fork construction. 365mm is typical of 700c forks with cast crowns, while 375mm is more common for 700c unicrown forks.

Even for a cast crown fork, 28mm tires is about the limit of what a 365mm fork would be able to fit. If you might ever want to consider using larger tires, you might want to consider spec-ing a taller fork.

Originally Posted by deluz

I had to increase the top tube slope to 8 degrees to get the seat tube length and stand over I want.

I personally would want a longer exposed length of seat post, but what your drawing shows can work.

[yinzerniner]

Originally Posted by Mark McM

A few comments:



The most likely source of the error is in the rim diameter used in the calculation. Although a 700c rim is referred to as "622mm" rim, the 622mm dimension actually refers to the diameter of the tire bead, which sits about 5mm below the outer edge of the rim. The actual diameter of a 700c rim is closer to 632mm, which is a radius of about 316mm. When you add the tire height of 28mm, you end up with a wheel radius of 344mm.




Fork length can vary depending on fork construction. 365mm is typical of 700c forks with cast crowns, while 375mm is more common for 700c unicrown forks.

Even for a cast crown fork, 28mm tires is about the limit of what a 365mm fork would be able to fit. If you might ever want to consider using larger tires, you might want to consider spec-ing a taller fork.



I personally would want a longer exposed length of seat post, but what your drawing shows can work.

I too mentioned in an earlier post the wheel circumference discrepancy, but your figures align similarly. 622 BSD doesn't accurately reflect actual wheel circumference with the tire mounted if it's a clincher/tubeless.

The OP mentioned they're going with a 375mm fork similar to what Mercian uses, not a 365mm as in the previous design, so the OP should be fine for tire size height, if not width depending on fork model.

One thing to note on the OPs drawing is that he's showing only 10mm for the upper and lower headsets. Would definitely need to correct that depending on headset, unless the OP is using an Extralite model.

As for the amount of exposed seatpost and seat tube length, the OP's new design shows a saddle height of 650mm which is very low, thus making it pretty hard to get any real seatpost exposure and increased flex. One method to increase flex would be to go with an integrated seat clamp instead of the 30mm or so shown between seat tube C-C an C-T. The only other design change which could help in that regard are either dropping the seat tube C-C length even further, thus creating an even more sloped top tube, or they can drop the head tube and seat tube lengths -20mm so that the top tube stays at the current angle, and the head tube will have roughly an extra +20mm on top like seen on some Pegorettis. The seat tube C-C would then be 451, head tube 110 with +20 extension on top, and the top tube would remain at the current 8deg angle. And if the OPs feeling really spicy they could use a shim for the 27.2 ID seat tube and use a 25.4 seatpost to get some extra flex. +20mm in length along with a smaller diameter seatpost will probably add a decent amount of comfort.

Pegorettis with extended head tube examples:



And if going with integrated seat binder and slightly extended head tube:

[deluz]

Thanks again for the great feedback.
Regarding the extended head tube, this maybe something Mercian can do I believe I have seen it before on some of their frames.
But what is the advantage over just using more spacers?
Are we just talking aesthetics or is their a functional difference?

[Mark McM]

Originally Posted by yinzerniner

As for the amount of exposed seatpost and seat tube length, the OP's new design shows a saddle height of 650mm which is very low, thus making it pretty hard to get any real seatpost exposure and increased flex. One method to increase flex would be to go with an integrated seat clamp instead of the 30mm or so shown between seat tube C-C an C-T. The only other design change which could help in that regard are either dropping the seat tube C-C length even further, thus creating an even more sloped top tube, or they can drop the head tube and seat tube lengths -20mm so that the top tube stays at the current angle, and the head tube will have roughly an extra +20mm on top like seen on some Pegorettis. The seat tube C-C would then be 451, head tube 110 with +20 extension on top, and the top tube would remain at the current 8deg angle. And if the OPs feeling really spicy they could use a shim for the 27.2 ID seat tube and use a 25.4 seatpost to get some extra flex. +20mm in length along with a smaller diameter seatpost will probably add a decent amount of comfort.

Another design feature which can increase seat post flex is dropped seat stays. This can affect other design/construction details, so it should be run past the builder first.

[NHAero]

Here's an extended head tube on the lugged stainless frame Dave Anderson built for me.

[deluz]

Originally Posted by yinzerniner

One thing to note on the OPs drawing is that he's showing only 10mm for the upper and lower headsets. Would definitely need to correct that depending on headset, unless the OP is using an Extralite model.

As for the amount of exposed seatpost and seat tube length, the OP's new design shows a saddle height of 650mm which is very low, thus making it pretty hard to get any real seatpost exposure and increased flex. [/IMG]

The current headset on my Mercian is a Innicycle which works with a threaded steerer and has a built in threadless adapter. It is really nice and is compact. I measured it to be 10mm on the bottom and 15mm on the top bearings so that is where that came from. The new bike will probably use a threadless headset so I may have to adjust for that.

My inseam is 30.5" (775mm). I normally measure my saddle height as 26.5" (673mm) from the BB to where my sit bones contact the saddle. Since RattleCAD references the center of the saddle I had to adjust it to 650mm.

Also the seat lug protrudes only slight above the top tube so that 20mm shown on the drawing should be reduced to maybe 3mm.

[eddief]

of course I prefer the racer boy look but I am long past that day. I still have this Curtlo after more than 10 years and I still think the proportions are decent.

https://photos.app.goo.gl/xFFQjtBUkQCM4bxd9

[Doug Fattic]

I don't think you have provided enough information to give a complete evaluation. My impression of Paceline posters is that they are a more go-fast (or at least look-fast) crowd than say the people over on the I-BOB list - where you might get slightly different comments. Anyway I'm a long time builder and will only build a frame after I have done a fitting or know who the fitter is. I don't think you have enough information unless you have a fit done.

I'm suspicious that your 74º seat angle might be too steep. It might be the right angle but that depends on the kind of riding you do - which I don't remember you telling us. The reason I think it might be too steep is because your handlebars are level with your saddle and that isn't where fit go-fast guys want their bars. It is where no-longer-skinny older and less flexible recreational riders like their handlebars. Your body shape and age play into your saddle position. For example if your upper body is carrying extra pounds, you should find out where your saddle setback balances your weight over the pedals. That reduces the load on your arms supporting your upper body weight.

I'm 5'8" too but my saddle height along the center of the seat tube line is 73.5. I use 170 cranks and prefer a much lower BB height than your 270. That is production frame height where the designer doesn't know if you are using longer cranks and pedaling through corners. Custom frames (and especially small custom frames) can lower the BB height if they are using shorter cranks (and seems like, with your short legs, 165 cranks are more than long enough) and you are not riding in pace lines pedaling through corners. A lower BB height means a you can straddle a bigger frame which means you can have a longer head tube which reduces the need for more head tube extension above your top tube.

All frame designs involve compromise. If your saddle position after a fitting shows you need a shallower seat angle, then using 700c wheels is a compromise. I'd consider 650B X 28 or 32. Smaller wheels are an advantage for you except for shopping convenience. If you are going with 42s, than they are the same diameter as a 700C by 28. The radius of the tire you chose (345) is the radius of a 700c X 32 tire. Is this the size you chose? A 28 is 340 (this all depends on the brand of tire of course). The radius of a 650b X 28 (they make them) is 320. That 20 mm can help in several ways making a smaller frame.

I think this whole exercise is pointless unless you go get a fitting first. So far you are fitting your body to a design instead of designing a frame to fit your best cycling position. This is especially true as we age. We get fatter, less flexible, want to be more comfortable and are less concerned about shaving a few seconds off of our regular route. I've had hundreds of students take one of my framebuilding classes. It is the rule rather than the exception that they learned their present position was not optimum and required adjusting their new frame design compared to what they expected. The problem was that their current bicycle prevented the from finding they best position. For example their seat angle was too steep. Just to be clear if you are a fit go fast kind of guy, than it is better to fit the body to the frame designed for handling and speed rather than comfort. My guess is that your 1st priority is comfort.

[Marvinlungwitz]

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[weisan]

I know nothing about geometry really, so can't really help, sorry. All I know is whatever Tom Kellogg did with the Spectrum I am riding on, he's spot on.

Here's what the initial owner (Ray) had to say:
Finally time to part with one of my prized Spectrums and since I'm not hardcore enough to take advantage of the travel utility of this bike anymore, it's the logical one to go. It's kind of a brevet light touring type of geometry, with fender bosses and clearance. It takes long reach brakes with plenty of fender clearance (although I take it there are even longer reach brakes now so maybe these are currently what's known as medium reach?) It's unfinished ti (straight gauge - I don't think Tom offer(ed) butted tubing with S&S couplers) with an etched front logo. It's a wonderful bike. It's got longer than standard chain stays and a pretty low BB and the handling is a touch milder and more stable than Tom's signature race bike handling, but it's no dog. It reacts well to jumping out of the saddle and fairly aggressive cornering, with the caveat of having the right fork mounted.

And it comes complete with two forks! Why two forks? Well, I probably mis-communicated to Tom how much I'd be riding this bike with a loaded handlebar bag (and just how loaded such a bag would be). So he originally built it with a higher rake, lower trail fork to handle more predictably with such a setup. Perfect for your brevet rider or light tourer. But I was riding effectively unloaded (or with just a tiny bar bag) almost exclusively and I hated the way the bike handled unloaded. Tom assures me there are people who like that type of handling even unloaded, but it has some odd turn-in behavior that I wan't into at all. I loaded up the front end a couple of times to feel the difference, and it was wonderful with a front load. But that was not how I rode it, so Tom built me a second fork for riding unloaded, which had less rake, more trail, and the bike just felt perfect for my type of riding from that point forward. The first fork has sat unused since, but may be of great use to a buyer of this frame, and god knows I don't have any further use for it, so you get two forks with this baby, one for a loaded front end, one for an unloaded front end. The drawing below shows the original higher rake / lower trail fork spec... Both forks are steel, BTW, and really nicely done, as you'd expect from Tom and Jeff...

I'm not sure how to classify the size - Tom's drawing (see below) shows 64 cm from the bb to the top of the seat tube if the seat tube were extended to where the top tube would be if it were parallel to the ground and as high as it could go on the head tube. But that's more about allowing for a high bar position than the actual seat tube height. I'm about 5' 11" and have generally ridden 58-59 off the rack bikes, so I'd look at this one that way. With a higher bar position than you'd want on a race bike.

Here's the build sheet: