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Framebuilders Thinking about a custom frame? Lugged vs Fillet Brazed. Different Frame materials? Newvex or Pacenti Lugs? why get a custom Road, Mountain, or Track Frame? Got a question about framebuilding? Lets discuss framebuilding at it's finest.

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Old 03-09-13, 10:42 AM   #1
corwin1968
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Geometry question in relation to fork rake

After a lot of researching and deliberation, I'm about ready to pull the trigger on a custom fork. There is a local frame builder who will do it for $200.

The bike I currently have has the following geometry:

Headtube Angle: 71.5
Fork Rake: 40mm
Chainstays: 43cm
Top tube: 57cm
Trail: 74mm

The fork I want to have made will have 55mm of rake. This will drop the trail down to 59 and since the builder is local I can take the stock fork to him so he can make the new one the exact same length, taking out that variable in regards to the angles.

I'm currently running a cheap aftermarket fork with 50mm of rake and I like the ride of the bike. However, the fork is hideously ugly (thin unicrown). I thought about buying a Cross Check fork (44mm of rake) but decided that if it's worth $100 to get less than half-way to where I want to be, then it's worth an extra $100 to get what I really want.

Is moving to a fork with 15mm more rake than the original bike had likely to throw anything out of balance in regards to handling? Adding 10mm didn't so I'm assuming 5mm more would be fine but you never know.

I would actually prefer to just buy a new frame in the Surly/Soma price range but what I can't find what I want, which is basically a fairly stout cro-moly frame with road bike type angles that is spaced for 135mm hubs.
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Old 03-09-13, 11:09 AM   #2
unterhausen
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you shouldn't notice anything bad, although the light feeling of low trail steering takes a bit to get used to.
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Old 03-09-13, 12:33 PM   #3
corwin1968
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I'm going to add some questions and maybe you guys can help.

Is there likely to be any significant difference in tube quality between mid-90's True Temper OX and the current 4130 that companies like Surly and Handsome are using? I ask this because the Handsome Devil is close to what I'm looking for (73/73 angles with 45mm rake fork yielding trail of about 60) and it's made of "4130 cro moly". However, a guy on the commuter section said he had a Handsome Devil and got rid of it because it was too heavy in weight and handling. I thought the Devil was the frame for me but his comments give me pause. I don't mind weight because I'm a super clydesdale but I want more nimble handling. Now, he might be comparing that bike to a carbon road bike or maybe the 4130 they are using actually is heavier. I can get to the same place by having the custom fork made for my True Temper OX bike and the fork plus new paint would be maybe $100 less than the new frame, but it would still be a 17 year old frame.

Is a mid-90's True Temper OX frame in any way "better" than a new "4130 cro moly" frame?

Basically my decision has come down to this. Aside from head angle and fork rake, the two bikes are very similar in geometry.

I assume that mid-90's True Temper OX is NOT the same as the highly regarded OX platinum that is available now.
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Old 03-09-13, 06:33 PM   #4
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4130 is a material specification for a tough steel alloy. It doesn't have anything to do with the quality or engineering skill of a manufacturer. 'same with the OX tube. It's basically heat treated/hardened 4130. If you don't use the right amount it don't matter anyway and it's up to the brand manager to figure that out and there are a lot of choices.

When it comes to frame materials it's a matter of you trusting what the mfgr tells you and that they selected the right profile/thickness for the job. If you are a clyde, they aren't thinking about you so try the bike yourself and draw your opinion from that. What may be heavy and dead to someone else may come alive in your hands.

I have an awesome custom bike but spend plenty of time on an old peugeot that just makes me feel fast.
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Old 03-29-13, 08:56 PM   #5
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If you have Android phone or tablet this app might help with trail calculation. https://play.google.com/store/apps/d...c015VHJhaWwiXQ
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Old 03-30-13, 08:12 AM   #6
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The real problem is that you can know the frame tubing material and still not know anything about the tubing "design", i.e. wall thicknesses and butting and the resultant weights. Higher strength steels like the TT OX you mention ALLOW the use of lighter gauge tubes, but don't necessarily mean that is what is going on. Having said that, it is USUALLY true that premium materials are used for a purpose, e.g. when the object is weight reduction and more compliant ride. You just can't be sure what the actual final product is like by knowing the steel used to build the frame. What can be said is that 4130 is basic chrome-moly steel, stronger than so-called high tension steel and tolerant of a lighter build. If, as mentioned by another poster, the OX is heat treated chrome-moly (maybe heat treated 4130), that means it is stronger yet, and therefore, tolerant of an even lighter design and build. To answer your direct question, the TT OX SHOULD be lighter than the basic 4130 frame, because it can be and why use if for any other reason. You just never know, however.
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