Newbie Build Carbomania

[Russ]

Howdy Folks,

I've been lurking in this forum for a while now.  It's been awsome to see some actual success stories people have had with Chinese carbon frames, after reading the terrifying and misleading articles put out by some of the overpriced mainstream distributors.  I decided to pull the trigger on a new build.  Here is a link to my spreadsheet:

https://docs.google.com/spreadsheets/d/1SFEGAjU5dLwT4NkwGubcJb-hSKwenQd_uUx86Qq0bfM/edit?usp=sharing

Parts were ordered a couple weeks ago, I'll update actual weights as they come in.  Haven't heard much about Carbomania on this forum yet, so I'm a bit nervous about the frame.  I'll update here if I have any issues with it.  I like the boost spacing, and price, but not too happy with the 27.2mm seatstay and 2.3mm tire width.  Gotta compromise somewhere to build a ~22lb bike for #1,300.  We'll see how it comes together. 

[carbonazza]

I look forward to your updates.
Never heard about Carbomania, it is always good to read about new providers. Thanks.

[ChinaCruz]

Geo chart says 506mm atc fork. You bought a 140mm fork, that's like 545mm atc.

[Russ]

Yerp, I wanted a bit more cush up front then you can get out of a 100mm.  You are correct, the axle-to-crown is 545mm.  I figure after 20% sag that gets you down to 517mm, close enuff to 507mm.  I guess I should have done the math to see how exactly that affects HTA, stack, and reach, but I was trigger happy. 

By way of update, the shipper returned the frame to seller because it was overweight... They shipped a new one with upgraded shipping, so hopefully it gets here before I go crazy.  Starting to get other parts in; fork, wheels, brakes, rotors. 

[sclyde2]

Yerp, I wanted a bit more cush up front then you can get out of a 100mm.  You are correct, the axle-to-crown is 545mm.  I figure after 20% sag that gets you down to 517mm, close enuff to 507mm.  I guess I should have done the math to see how exactly that affects HTA, stack, and reach, but I was trigger happy. 

You do realise that the geometry charts are almost always specified for an unsagged bike?  A ~505 a-c spec equates to a 100mm fork, which would be at least 30-40mm shorter than your fork, whether you view it as sagged or unsagged (like for like).  That is a LOT. You are kidding yourself if you think that 140mm fork is anywhere near appropriate for that ~1100g frame.   Not only will the geometry be all crazy (slack seat angle, raised BB), if you intend to ride that fork on the kind of terrain it is designed for, that frame will not last.

Please don't become another one of those "victims of Chinese carbon", and blame the frame when it fails.  If not the headtube, my money is on the stays.

[Russ]

Okay, so I did the math.  Table/screenshot below is from a parameterized sketch I made. I As the title implies, I am no expert on bike geometry.  Help me understand in practical terms what this means.  I am seeing a slackening of the HTA of about 1.8 degrees, but still in the lower range for an XC bike.  The shorter reach and taller stack I can deal with.  The higher BB is kinda scary, especially with the narrower seat stay.  Considering what I paid for the frame, I am trying to decide if I want to take the risk and deal with it if/when the frame fails or sell it off new and get more of a "trail" frame that I can put this fork on (and some meatier tires).  Any suggestions for good frame I can mount a 140mm fork on?  I seems like most all the Chinese offerings spec a 506mm atc. 




Also added a tab to the table in Docs. Same link as above. 

[carbonazza]

If I understood well sclyde2, it says the geometry will just end odd, but that is for handling/stability issues.
But the main point is a 140mm fork will call you to go much harder on some descents, and the frame may not resist.