[heatstroke]

I am thinking about picking up an older ti frame ( airborne lancaster) This is designed for a 443mm a-c. What will happen to the HT angle if I stick a 470 mm fork on it ? It will get slacker - but by how much?
What is the impact on eff TT length ?
This is the 18", with the 23,8" eff tt and a 71 HT angle.
Does anyone know the exact numbers ?

Thanks in advance

 

[Corvette]

20 mm equals 1° slacker HT angle...

 

[shiggy]

20 mm equals 1° slacker HT angle...

Closer to a 17mm change in A-C = 1 degree angle change.

Longer decreases the angle, shorter increases.

 

[Wish I Were Riding]

Closer to a 17mm change in A-C = 1 degree angle change.

Longer decreases the angle, shorter increases.

Does the same change occure at the seat tube?

 

[DeeEight]

And the change also depends on the wheelbase of the bike... shorter wheelbases (meaning smaller size frames usually) will have more of a geometry change than longer wheelbases, not to mention longer forks because they're at an angle to the ground, will also change the wheelbase of the bike. As to the seat tube, yes, the seat angles do slacken/steepen also, the whole frame is tilting relative to the ground afterall, and the saddle height position will need to be adjusted as well as its nose angle, and your effective TT length can change too. I also find a 443mm A-C design measurement as comical, as that's 17.44" and that's just TOOO precise a figure to mean anything other than the frame is designed for a specific brand and model fork.

 

[Wish I Were Riding]

Is 38mm of rake the same on a short fork and a long fork? What I mean is would the shorter fork have more of an angle on the legs to acheive 38mm, whereas the longer fork would have less leg angle?

I don't know why any of that would matter, but I had to ask...

 

[Ricisan]

Similar Situation

I had a POS Indy C fork w/65mm travel. It was about 440mm A to C. The bike was a little more twitchy than I liked and I wanted more travel for smooth ride. I like to ride w/o hands to stretch my back.
I got a 07 Manitou R7 470mm. The sag took 1/2 the extra length which left about 15mm longer fork. This did slow things just a bit and I have enough travel for big curbs and bumps. Don't forget the bars will rise the same ammount 15mm. Hope this helps.

Ricisan