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.

[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.