Review / Critique my frame design

[deluz]

I am looking into ordering a custom steel frame.
Being that I am an engineer and DIYer I decided it would be a good idea to learn more about frame design and it turned out that I did.
Since I probably will not be going local I will not have the opportunity for an in person fitting and I did want to just give the builder some vague descriptions like its comfortable or climbs good. I will handing this off to the builder to tweak as they see fit. Here are some of the rational for the dimensions.

Top tube - I am 5'8" and have short legs and arms. I normally ride a 52cm frame which provides low enough stand over. Since I like my bars about level with my saddle I decided a sloping top tube makes sense to get the bars higher using a 135mm head tube and still have a low enough stand over. Also it allows for more seatpost sticking out of the frame. I made the reach the same as my current Cannondale EVO which works for me.

Steering - Had to learn about trail and wheel flop. In the end just decided to go with standard trail of 58mm for a road bike. This resulted in a 71 degree head tube angle and 54mm fork rake.

Chain stays - I have always felt the chain stays and wheelbase on my Cannondale are very short. I went with 415mm on the stays and 1007mm wheelbase. I feel this will give me good stability and balance without overdoing it.

Bottom bracket drop - This is one of those overlooked things. I went with 75mm to get the bottom bracket lower. This helps with stand over and I just like a bike with lower center of gravity.

Some of the ideas came from looking at the geometry of a Cannondale Synapse which seems to have some of the characteristics that I am looking for. If I could find one local in my size that I could test ride I would do it. My wife has one but it is one size too small for me.

Thanks for any feedback

[Mark McM]

That looks like a lot of spacer height under the stem. That might limit the forks that might be used (a lot of forks only allow 30-40mm of spacers). The drawing appears to show a slightly down angle stem, so you might be better off with a 90 degree or slightly upward angled stem. Or if you are sure you'll never be lowering the handlebar, you could increase the stack a bit.

There doesn't appear to be much exposed seat post. The ride might be improved with a longer exposed seat post, so you might want also consider shortening the seat tube a bit. If you increased the stack, shortening the seat tube could retain the same standover as before.

[mhespenheide]

Originally Posted by deluz

Some of the ideas came from looking at the geometry of a Cannondale Synapse which seems to have some of the characteristics that I am looking for. If I could find one local in my size that I could test ride I would do it. My wife has one but it is one size too small for me.

Thanks for any feedback

I'm hardly an expert on geometry, particularly at this size, but considering the time and cost and emotional investment in a custom frame, I think it's a smart move to do an extended test ride (or even buy second hand, try, and re-sell) a similar frame if there's anything production that's close.

(Thumbs-up for the 75mm bottom bracket drop, though!)

[mhespenheide]

Originally Posted by Mark McM

That looks like a lot of spacer height under the stem. That might limit the forks that might be used (a lot of forks only allow 30-40mm of spacers). The drawing appears to show a slightly down angle stem, so you might be better off with a 90 degree or slightly upward angled stem. Or if you are sure you'll never be lowering the handlebar, you could increase the stack a bit.

There doesn't appear to be much exposed seat post. The ride might be improved with a longer exposed seat post, so you might want also consider shortening the seat tube a bit. If you increased the stack, shortening the seat tube could retain the same standover as before.

Good points. I agree on these, too. You could also consider a stem that has some stack built into it, like the one from Velo-Orange.

I think the stack-limited forks are the ones with carbon steerer tubes. If you're using a steel or aluminum steerer tube, I don't think it's an issue.

[charliedid]

I'd go with a shade of blue and disk brakes.

[carpediemracing]

You're very similar in build to me. I imagine your torso is pretty long if your saddle height is virtually identical to mine.

Two thoughts. Length and HTA. And related to length, possible chain stay thing.

Are you sure that frame is long enough? I have a 56.5 effective top tube with a 75.5 deg STA, and with compact bars I'm still using a 14.5 cm stem (originally I spec'ed the length for a regular bar and a 12 cm flat stem).

On prior frames I typically had a 74-74.5 STA and a 53.5 TT.

One consequence of having such a long front end was I found the rear wheel chattered in faster turns (like a crit) even without me pedaling. Going to a shorter 39 cm stay solved the problem - the original 40.5 was too long.

Also, a 73 deg HTA (with 43mm rake) feels so much better in corners and when out of the saddle, compared to a 71. I learned this on a Giant TCR, then confirmed it when I had a SystemSix. I found the bike cornered much, much better, like on rails. The prior shallow angles made the wheel feel like it flopped over and it wasn't as sure in how it carved an arc.

Other miscellaneous thoughts.

I went with a super short seat tube - the one that I really liked was a size S Giant TCR in aluminum. It was 40 cm c-c, just enough to put a large bottle in there. With aero tubing (second frame) the builder had to do a 44 cm c-c to clear a large bottle (barely). I liked the feel of the short seat tube, it gives me a sense of being in control of the bike, like riding "over it" versus riding "in" the bike. This is especially true when out of saddle or if maneuvering when stationary (like you need to turn the bike around on the sidewalk and you just put a foot down).

It also makes clamping the post in a work stand easy, no need to raise the saddle, even with a Blinky light on it.

My wheelbase is I think 102 cm or so, so 2 cm longer than yours; it's just a result of the longer front end. It's a bike of contrasts. Short stays and regular HTA gives it nimbleness, but the long wheelbase gives it stability. I've done long rides on them, 8-10 hours, no issues, but most of my rides nowadays are an hour or so long.

[Dave]

I don't think that the geometry is much different than some of the current endurance model road bikes being sold by the major manufacturers, except for the HTA and fork offset.

[charliedid]

Also, it looks like you built yourself a Gunnar Sport, why not have Wateford build it?

[yinzerniner]

Originally Posted by deluz

I am looking into ordering a custom steel frame.
Being that I am an engineer and DIYer I decided it would be a good idea to learn more about frame design and it turned out that I did.
Since I probably will not be going local I will not have the opportunity for an in person fitting and I did want to just give the builder some vague descriptions like its comfortable or climbs good. I will handing this off to the builder to tweak as they see fit. Here are some of the rational for the dimensions.

Top tube - I am 5'8" and have short legs and arms. I normally ride a 52cm frame which provides low enough stand over. Since I like my bars about level with my saddle I decided a sloping top tube makes sense to get the bars higher using a 135mm head tube and still have a low enough stand over. Also it allows for more seatpost sticking out of the frame. I made the reach the same as my current Cannondale EVO which works for me.

Steering - Had to learn about trail and wheel flop. In the end just decided to go with standard trail of 58mm for a road bike. This resulted in a 71 degree head tube angle and 54mm fork rake.

Chain stays - I have always felt the chain stays and wheelbase on my Cannondale are very short. I went with 415mm on the stays and 1007mm wheelbase. I feel this will give me good stability and balance without overdoing it.

Bottom bracket drop - This is one of those overlooked things. I went with 75mm to get the bottom bracket lower. This helps with stand over and I just like a bike with lower center of gravity.

Some of the ideas came from looking at the geometry of a Cannondale Synapse which seems to have some of the characteristics that I am looking for. If I could find one local in my size that I could test ride I would do it. My wife has one but it is one size too small for me.

Thanks for any feedback

Awesome post and interesting to see you fleshing out the details. If there's anything I can comment on that's hopefully constructive its:

-Will be tough to get a 54mm fork for road, all-road or gravel style riding. The 58mm trail is ideal for all-around riding and handling characteristics, but you should be able to achieve that with a more standard combo of fork offset and headtube angle.
-That being said, it looks like your wheel radius with tire is shown as 336mm, or 672mm diameter. That seems awfully small if you're using clinchers/tubeless, since 700c wheels BSD is 622mm, and generally clincher tires size +4-5mm up from BSD when mounted. So a 25mm tire will generally have a diameter of 622 + 2x(4+25mm) = 680mm. My above math seems to work with the various bike trail calculators:
https://thebicyclewizards.com/index....il-calculator/
http://yojimg.net/bike/web_tools/trailcalc.php
-Given the numbers above the wheelbase shown at 1006 is very long for the given stack/reach figures. It's longer than a 51cm Cervelo Aspero!
-75mm BB drop is great if your tires are 28mm wide/24mm tall and above, and you don't intend on riding much off-camber. Any smaller than 28W/24T and you could get a decent amount of pedal strike unless you use 165mm crankarms
-As Mark McM said, you might be better off with roughly 15-25mm of spacers and a 0deg or +6deg (ie flipped) stem. Won't look quite as nice, but once you get above 30mm+ of spacers underneath you're looking at quite a deep headset compression plug.
-Also as Mark McM said, the seat tube can probably be shortened a bit for more exposed seatpost, although it have the possibly undesired effect of making the top tube slope higher than shown.

Otherwise very cool experiment and thanks for sharing.

[madsciencenow]

It’s cool that you went to all the trouble to put together a CAD drawing for the builder. IME, a good builder will be able to take your body dimensions, description on past bikes, and what you are looking for and come up with a good design. What you have might work well but if your builder is experienced, I’d go with what they cook up. I’m not dissimilar from your proportions and had gravitated to shorter top tube bikes w steeper seat tubes. A couple years ago Dave Kirk presented me with a different design where the seat tube is more slack and the TT is longer and while I would never have guessed it would work, I much prefer it now.


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[deluz]

Thanks for all the great feedback so far.

Charliedid / Dave - I did not intentionally copy an existing geometry but like I said I did look at the Synapse for some ideas.

Carpediem- I do have a longer torso but I find that the 535mm top tube on my Cannondale with a 100 mm stem is right for me. I could go with a shorter seat tube but did not want to go too extreme. This might be a lugged frame which could make that more complicated. Regarding the HTA my Cannondale which has a trail of 58mm feels pretty neutral to me. I have a steel bike that has quicker steering which I do like, so I may rethink this some.

MarkMcM - One of my current bikes has a 110mm headtube and I have 25mm of spacers. So going to 135mm HT should in theory eliminate the spacers. That is with a 6 degree stem flipped up. The Rattlecad drawing is with the stem flipped down. If I did my math right the difference between flipped up / down is 20mm. I have not figured how to measure the stem spacer on Rattlecad. You are right that there is not much seatpost but it is 3cm more than what I currently have. Again trying to not go too extreme on the seat tube but maybe I could cut a few more cm off it. Referencing the Synapse it has a 44.3 ST for size 51 cm frame. I am sure not what effect on ride quality this will have. It seems the frame overall might be stiffer but not sure if it is significant.

I have not figured out how to save my work in Rattlecad so I have re-enter the numbers every time I use it. I wonder if it is because I am using the free version.

[deluz]

Originally Posted by yinzerniner

Awesome post and interesting to see you fleshing out the details. If there's anything I can comment on that's hopefully constructive its:

-Will be tough to get a 54mm fork for road, all-road or gravel style riding. The 58mm trail is ideal for all-around riding and handling characteristics, but you should be able to achieve that with a more standard combo of fork offset and headtube angle.
-That being said, it looks like your wheel radius with tire is shown as 336mm, or 672mm diameter. That seems awfully small if you're using clinchers/tubeless, since 700c wheels BSD is 622mm, and generally clincher tires size +4-5mm up from BSD when mounted. So a 25mm tire will generally have a diameter of 622 + 2x(4+25mm) = 680mm. My above math seems to work with the various bike trail calculators:
https://thebicyclewizards.com/index....il-calculator/
http://yojimg.net/bike/web_tools/trailcalc.php
-Given the numbers above the wheelbase shown at 1006 is very long for the given stack/reach figures. It's longer than a 51cm Cervelo Aspero!
-75mm BB drop is great if your tires are 28mm wide/24mm tall and above, and you don't intend on riding much off-camber. Any smaller than 28W/24T and you could get a decent amount of pedal strike unless you use 165mm crankarms
-As Mark McM said, you might be better off with roughly 15-25mm of spacers and a 0deg or +6deg (ie flipped) stem. Won't look quite as nice, but once you get above 30mm+ of spacers underneath you're looking at quite a deep headset compression plug.
-Also as Mark McM said, the seat tube can probably be shortened a bit for more exposed seatpost, although it have the possibly undesired effect of making the top tube slope higher than shown.

Otherwise very cool experiment and thanks for sharing.

Yes its hard to find a 54mm fork off the shelf especially carbon. But 54mm is no problem for a custom steel fork.

Good catch on the wheel radius! I just measured two of my bike that have 28c tires and radius is about 345mm. That is definitely going to change things like the stand over. I need to fix this and redo everything.

The longer wheelbase is intentional. My Cannondale has a wheelbase 972mm. My steel bike that is touring geometry is 1025mm. I like the feel of the longer wheelbase. I notice that when I am standing it just feels better. So I went with 1007 as a compromise. Did I over do it? On the newest Cannondale EVO they increased the wheelbase to 994mm. If I make the HTA slightly steeper it would reduce the wheelbase and trail both a bit.

My steel bike has 75mm BB drop and 170mm cranks. I have not noticed any problem with pedal clearance. I do not race crits and ride somewhat conservatively.

[madsciencenow]

If you go with a lugged steel bike I don’t believe you can get much in the way of slope for the TT. My limited understanding is a few degrees at most. I’m not the expert on this so maybe others can chime in.


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[deluz]

Originally Posted by madsciencenow

If you go with a lugged steel bike I don’t believe you can get much in the way of slope for the TT. My limited understanding is a few degrees at most. I’m not the expert on this so maybe others can chime in.


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That was also my impression but one builder told me that they can adapt the lugs to make it work. Also why I am trying to not go too extreme on the slope.

[kitsnob]

Originally Posted by madsciencenow

If you go with a lugged steel bike I don’t believe you can get much in the way of slope for the TT. My limited understanding is a few degrees at most. I’m not the expert on this so maybe others can chime in.


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Darrell Llewlyn just built me a lugged steel Manorina frameset with a 6 degree sloping top tube.
If your looking for a lugged steel frame I highly suggest you look at/to Darrell.

http://www.llewellynbikes.com/