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-   -   custom geometry -- any problems? (http://www.bikeforums.net/framebuilders/939686-custom-geometry-any-problems.html)

liannsun98 03-23-14 04:45 PM

custom geometry -- any problems?
 
1 Attachment(s)
Hi,

Long time stalker here. Can't decide if I'm going to try and build the below design myself (steel) or find someone to build it (ti), but I was wondering if you all could take a look at it and see if there are any problems wrt the geometry that I should be worried about. I think that stack and reach are tentatively OK, since it's on par with bikes that fit me well, but i'm worried about handling. FYI -- I'm a 5'4 female with a longer inseam and shorter torso.

ps- the seat tube is 50.3 c-c, i think rattlecad is doing c-t. thanks!

http://bikeforums.net/attachment.php...hmentid=370590

unterhausen 03-23-14 05:38 PM

what tires are those, 700C by 23?

If they are, I think you should go with longer chainstays

JohnDThompson 03-23-14 06:21 PM

Quote:

Originally Posted by unterhausen (Post 16604440)
what tires are those, 700C by 23?

If they are, I think you should go with longer chainstays

Agreed. You'll have awfully tight clearance at the seat tube otherwise.

Andrew R Stewart 03-23-14 07:34 PM

The other aspect that i picked up on is the possibility of toe overlap. The front center being only 578mm with 172.5 cranks. If you go to larger tires and/or have large feet and/or use a rearward set cleat that possibility is a real one. Whether toe/tire strike is a concern of yours is your to decide on.

I also agree with the CS length being fairly short.

If you go to a TI builder i suggest a full fit up by him/her and listen to the results. Andy.

duanedr 03-24-14 01:13 AM

Would a fork with more offset help the toe overlap thing? 62mm of trail seems like plenty and adding some offset might be enough to get to 50mm trail and add 10-12mm to the toe overlap buffer. I'm not sure how that will play with 70.5* HT angle though.

fietsbob 03-24-14 09:34 AM

maybe a curved seat tube to make more rear tire clearance?

Jack Taylor did that decades ago ..


there is the Ms.Terry solution , use a 600 wheel rather than a 700 up front.

or 2_600 wheels , and a bit less BB drop ..

JohnDThompson 03-24-14 10:22 AM

Quote:

Originally Posted by fietsbob (Post 16606127)
maybe a curved seat tube to make more rear tire clearance? there is the Ms.Terry solution , use a 600 wheel rather than a 700 up front. or 2_600 wheels , and a bit less BB drop ..

Or rear-loading track dropouts. And shorter crank arms for the pedal overlap.

fietsbob 03-24-14 10:29 AM

short chainstays required? seen dents pressed in the back of straight seat tubes ,
and then there was the RiGi solution, split the seat tube in to 2 tubes so the wheel passed between them ..

reddog3 03-24-14 10:50 AM

Other than the drawing having too many dimensions... enough to confuse me and make my old eyes tired. LOL

One dimension I have concern about is BB to saddle height. At that length it would be appropriate for someone with an inseam of 32.5-33" I know you're a long legged short lady but... Ladies tend to run that way and sometimes making a frame fit is just little more work.

I also question the HTA. It's slack to make for a shorter TT to fit your short torso? Of course, any steeper would also reduce FC.

172.5 cranks? Depending on what characteristic makes your legs "long," this crank length may not be appropriate.


I like the others think the CS is a bit short. You didn't mention the purpose of this bike (geared or not) but if the axle slot isn't totally vertical, or the wheel loads from the rear (as is SS or track drops) you may have trouble loading an inflated tire/wheel.


Don't know where you got your fit dimensions but I'd suggest you try elsewhere, and get at least another opinion. I've had good luck using the "fitting" calculator over at Strawberry's site. Strawberry Cyclesport Handcrafted Bicycle Frames

And, like others have said- if you're having the frame built by someone else, let them do the math and be receptive to their input. Ain't nothing worse than spending big bucks on a custom frame and it don't fit!

MassiveD 03-24-14 02:48 PM

Is this another one of those I am having my frame built in china threads? I get suspicious when I hear someone say they don't know how to design a frame they are planing on either building themselves, or "having built in Ti".

ftwelder 03-24-14 04:37 PM

It's like an idea bomb just exploded in my face. What size tires are you planning to use? Is this for dirt or pave?


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