Embarassed to ask: Check my autoCAD design to make sure i dont kill myself-1st frame

[mmoore]

Hi guys....

I do a lot of welding of automotive engine parts (photos in flickr) but I have decided to do some frame building for myself and my wife... But i have little experience in frame design and drew something up based on my existing bikes with some changes for my first frame.

It would be reassuring if someone could comment on the design to tell me if its going to be a dangerous ride in terms of geometry or not.

Woops, seat height is all jacked in theis picture.

Screenshots of CAD design.

First frame design by HellaFab, on Flickr

I've been holding off building the frame for the last several months to do a lot of reading and i think this is going to be the best iteration yet.

I have the tube set and all of the apurtances to build the frame now and put all of the dimensions in to make sure the joints are outside of the butted area... I have the fork and incorporated it into the design and I have the Sram group/bb7road discs to use...

Any thoughts would be appreciated. Its a basic road disc bike that I plan to use as an all around bike... so i hope to build it to handle 35c tires to do a little bit of dirt when im up at the cottage.

Cheers,
Matt Moore

[NBC]

matt,

without other measurements, the figures you currently have are somewhat meaningless ! try include things like fork rake, bottom bracket drop, ST and TT length c-c, and saddle nose to handlebar centre, and handlebar drop, fork length and wheel/tyre size would be pretty useful too !

best of luck

NBC

[Stijl Cycles]

Dangerous might be too strong a word to apply to this question.
I think that if there was danger it would apply to the bike failing from poor process rather than poor design.
If executed well, I'm sure it would ride fine.
I can say that the amount of stack you have under that stem makes me a little uneasy.
The head angle is too tight for my likes.
I would suggest decreasing the offset between the top of the head tube and top of the top tube, as much for structural reasons as aesthetic ones.
The seat tube insert weld joint would be better served more central to the mid point of the top tube.
As the bike is for you, do as you want.
If it fails, build another and another until you have it right.

[mmoore]

matt,

without other measurements, the figures you currently have are somewhat meaningless ! try include things like fork rake45mm, bottom bracket drop75mm, ST 497mmand TT548mm length c-c, and saddle nose to handlebar centre550mm, and handlebar droproughly 120mm, fork length370mm and wheel/tyre size 700x35 max would be pretty useful too !

Dangerous might be too strong a word to apply to this question.
I think that if there was danger it would apply to the bike failing from poor process rather than poor design.
If executed well, I'm sure it would ride fine.
I can say that the amount of stack you have under that stem makes me a little uneasy.
The head angle is too tight for my likes.
I would suggest decreasing the offset between the top of the head tube and top of the top tube, as much for structural reasons as aesthetic ones.
The seat tube insert weld joint would be better served more central to the mid point of the top tube.
As the bike is for you, do as you want.
If it fails, build another and another until you have it right.

My appologies in the way it looks in the "picture" I had the stem and seat too high from playing around over the last few months. Seat and post came down to where the stem would have a 20mm stack over the HT. This will work well with the 15mm stack of the Cane creek ZS40/28.6 with tall cover.

Can you confirm this statement? my dementiais kicking in on this friday afternoon.
The seat tube insert weld joint would be better served more central to the mid point of the top tube.

[NBC]

370mm fork definitely isn't long enough for 700x35C tyres !!

try something like 72.5deg HTA, same fork rake, but try going 10mm longer on the stem, keeping the bar in the same location, to help keep the front center measurement sensible !

75mm bb drop is rather alot tbh ! 70mm is more usual, again that's dependent on crank length and wheel diameter, just a consideration !

NBC

[mmoore]

370mm fork definitely isn't long enough for 700x35C tyres !!

try something like 72.5deg HTA, same fork rake, but try going 10mm longer on the stem, keeping the bar in the same location, to help keep the front center measurement sensible !

75mm bb drop is rather alot tbh ! 70mm is more usual, again that's dependent on crank length and wheel diameter, just a consideration !

NBC

Thanks for the ideas. I will model it and see how it works out.


The fork is tight with the 35s I have on my mock up wheels in that fork. It has more clearance than my carbon bike has from the seat post near the bb though,so I'm not stressed of that. Just if a stone were pulled through between the tire and the fork I suppose.

[steve garro]

Try shit out.

I had a 26" MTB that I made with 15.75" eff chainstays, around zero BB drop, a 72* ST angle, and a short front center.

It RIPPED and you could ride it onto a picnic table in a snap……and pull 180* switchbacks….but it would put you on your ass SO fast.

I see what you have there as this.

You have many of the #'s pushed far from center, and you will notice this.

Good or bad?

You'll find out.

- Garro.

[Crowemagnon]

here's my 2 cents,

build that and ride it.
if after a number of iterations and several months of thinking that is where you are, then completing the circle by building it and riding it will be mega-valuable because it will help you to develop your process, rather than continue modifying the same design, (which will only develop your product).

if i WAS going to comment on the geometry, i would only say whats already been said, provided you are sure on that seat position, keep the same handle-bar position, longer stem/bar slacker HTA. though in contrast to whats been said, 75mm bb drop is right up my alley and i think wil be rad, though i've only been around the block a handfull of times.

[mmoore]

I wish i were able to get one of the angleset headsets for 44mm head tube and a tapered steerer I would love that. Being able to adjust the angle to see how it affects the ride is interesting to me since so many people have different thoughts on it and its use...Unless I find or make a 7005AL tapered head tube some how for a 44/49 headset.


I will stick with the 75mm bb drop.



As i said in the OP (edited because i noticed as soon as i posted) the seat height must have been jacked in one of my interations over the month. Here is a more accurate render of the setup with proper handlebar reach and drop (same as before) but the saddle in the correct location. I havent tried moving things around yet based on others oppinions, but i think like some of you have said, just try it.
frame2.jpg

[mmoore]

370mm fork definitely isn't long enough for 700x35C tyres !!

You were right, I looked again at what I had. they are only 32C tires with an urban style tread. Do more off-road specific treads run larger?

That sizing is fine for this though.

[mmoore]

You have many of the #'s pushed far from center, and you will notice this.

Thanks for the reassurance. I will build it and ride it and see how it fares.

Im wondering what exactly your referencing here; the center of what and from what imaginable centerline? I know this is more of an advanced topic, as i have read some things referencing center of mass or similar but I havent gotten that far into it yet.


I want to guess though, just to see if i can get it right and so i can understand how to modify a design if this build doesnt feel right when riding.
------>Your referencing center in regards to keeping the weight of the rider centered over the bike for balance in the riding position for best handling? i.e. weighted front wheel to keep from skidding out in a bend when riding the hoods.


Cheers,
M

[steve garro]

Thanks for the reassurance. I will build it and ride it and see how it fares.

Im wondering what exactly your referencing here?
Cheers,
M

74* HT is on the steep side
75mm BB drop is kind of on the low side
418 CS is kind of on the short side
38mm rake is kind of shallow
You fork is too short for tires that big, and make sure you don't rub the back of the ST as well.

Definitely not in the play it safe arena, so like I said, You'll See.

Not a bad thing, that's why they call it learning.

- Garro.

[duanedr]

74* HT is on the steep side
75mm BB drop is kind of on the low side
418 CS is kind of on the short side
38mm rake is kind of shallow
You fork is too short for tires that big, and make sure you don't rub the back of the ST as well.

Definitely not in the play it safe arena, so like I said, You'll See.

Not a bad thing, that's why they call it learning.

- Garro.

You don't say what the typical riding scenario will be - gravel grinding, centuries, touring, CX racing or road racing??

I would worry that 370mm is too short OR you're measuring it weird. My cross bikes have 32's, I measure 395 ATC (and that's by 2 different experienced builders) and I have a touring bike that I built for 32s and the fork is 385 with what I would consider the minimum for clearance - I live in Seattle and usually add fenders. Even Trek extends their forks for pro road races when they use 27s. I guess, I'm just saying I'd go longer there.

Taking what Garro is saying a step further, you seem to be pushing boundaries in all directions. Perhaps, use standard geometry and change one variable and determine if you like the results. with so many dimensions at the edge of what's typical, it will be hard to determine WHY you do or don't like what you ended up with.

Short chainstays with a lot of BB drop cuts into seattube clearance so...careful there. Also, if you ever want to use 23's, your BB may be quite low so, no crit racing on this thing!!

Good luck and keep us posted!

[mmoore]

You don't say what the typical riding scenario will be - gravel grinding, centuries, touring, CX racing or road racing??

I would worry that 370mm is too short OR you're measuring it weird. My cross bikes have 32's, I measure 395 ATC (and that's by 2 different experienced builders) and I have a touring bike that I built for 32s and the fork is 385 with what I would consider the minimum for clearance - I live in Seattle and usually add fenders. Even Trek extends their forks for pro road races when they use 27s. I guess, I'm just saying I'd go longer there.

Taking what Garro is saying a step further, you seem to be pushing boundaries in all directions. Perhaps, use standard geometry and change one variable and determine if you like the results. with so many dimensions at the edge of what's typical, it will be hard to determine WHY you do or don't like what you ended up with.

Short chainstays with a lot of BB drop cuts into seattube clearance so...careful there. Also, if you ever want to use 23's, your BB may be quite low so, no crit racing on this thing!!

Good luck and keep us posted!

Not sure what the rad way is to say it... somewhat of a commuter, casual riding bike that if the short cut is through a hiking park with some "rough" terrain i can rip through it... I guess its like a CX bike, but I dont plan on racing-if i do, i would build a bike for it as to keep this one straight and as a "primary" bike.

Would I be out of line if i were to make a "build thread" so to speak with developments and questions? (or turn this thread into one?) I feel like I will have more comments and questions as I go.

M

[duanedr]

Given that use I am more convinced that a bit less 'extreme' dimensions would be good.

I am also a big fan of 'just build it and see' as a good way to learn!

A build thread is now a requirement! Include pictures of successes and mistakes - us new builders can learn from both.

Good Luck!

[Crowemagnon]

I will stick with the 75mm bb drop.

Join my gang?

-looking foreward to build thread.

[mmoore]

Thanks all for the suggestions. I will use this as a build thread, or should I start a clean thread for this?

Still playing in CAD while I wait for time to get out there and start making my frame jig to build this thing up.

Update to the rendering with some details added on how im going to add some personality to the bike.

frame3.jpg

Notable changes:
1. changed head tube angle a bit, down to 72.5 from 74.
2. Changed seat tube to a hybrid solution. 35mm sleeved at the bottom that will go just above the front derailleur clamp with a 31.8 seat tube from there on up. it will be welded together, and sanded smooth. Its mostly an aesthetics thing, but will allow me to keep all of my bikes using 27,2 seatposts... not a big deal but interchangeability (new word?) between what i have would be nice.
3. Ordered different seat stays when I ordered the tubes for the tandem bike im building after this. the stays for this bike will be smaller since the rest of the bike is pretty overbuilt.
4. Aesthetic detail in the seat tube top.
5.Through drilled chainstay brace. The tube will be welded on both sides, but filed on the outside. aesthetics here, and a touch I like to see. the through tube is relatively small too so its not going to look THAT much like the old drilled frames.


Thats about it for the changes. Im done changing my plans now... I just want to get my hands dirty-I have some customer work to finish first which is dragging me down being that its slowly getting nicer out.


Ive started collecting the component part for the rest of the bike as well... I assume that it will go together quite quick once I get a little time.

M

[progetto]

KISS, learn how to build a solid ,straight frame before you worry about the other details.....or not

[e-RICHIE]

5.Through drilled chainstay brace. The tube will be welded on both sides, but filed on the outside. aesthetics here, and a touch I like to see. the through tube is relatively small too so its not going to look THAT much like the old drilled frames.

Thats about it for the changes. Im done changing my plans now...

Make one change atmo. Scrap Line Item number 5.

[mmoore]

KISS, learn how to build a solid ,straight frame before you worry about the other details.....or not

While on that topic, what is the industry standard on tolerance to be considered acceptable for a client/sale. I realize a bike for yourself might have a higher allowance for something being bodged. (open statement, not directed specifically to you.)