[moff_quigley]

I've found a steel road frame that I'm interested in, but I have question about what rake the fork should I have. The frame has a 71.5 degree headtube and what little I can glean from a google search a 50mm rake fork might be ideal. Am I off base or would a more standard 43mm rake be better?

Re: fit. Say this frame I found is 1cm too short (I'm going to try to get measured and whatnot this week) can I compensate by getting a 1cm longer stem and/or layback post? I'm assuming I need a 53 or 54mm ETT and this frame has an ETT of 52.5.

 

[Wumpus]

From reading:

Ideal trail is between 50 and 60mm with 57/58mm being the best.

Using this formula: http://www.kreuzotter.de/english/elenk.htm

A head angle of 71.5°, rake of 5 cm(50mm) and tire diameter of 68.5* cm gets you pretty close -- trail = 5.6cm(56mm).

Less rake(43mm) = more trail(63mm)

Can you tell a difference? I don't know.





*I couldn't find much on tire diameter, but they seem to range from 67cm(700cx23) to 70cm.


Here's Grant(Rivendell Bikes) messing around with extremes of trail and the results:

 

[Wumpus]

As far as your extra centimeter, you could probably just slide your seat back a little(5mm) with a regular post. Also, don't forget about the reach of your bars, you can make up a little there.

 

[SuspectDevice]

Never compensate fore reach issues with saddle setback. Setback is one of those things like saddle height that is either right, or wrong.

Sounds like you need a 50mm rake fork to me. Is this a touring frame? If so a higher rake fork would probably be better to compensate for things like the lower bb and longer stays.

Need more info.

 

[moff_quigley]

It's not a touring frame (doesn't have canti bosses anyway) best I can tell. Frame is a NOS RM Solo ST Classic with Columbus Spirit tubes.

Here's the geomoetry:
GEOMETRY
Size 50
Head Angle 71.5°
Seat Angle 74.5°
Horiz. Toptube Length 525
Headtube Length 102
Chainstay Length 400
BB Drop 70
Wheelbase 970
Front-Centre 581
Standover Height 767

 

[SuspectDevice]

The numbers on that bike are really, really odd. Whats your saddle height and saddle tip to bar center reach on your current road bike? Unless you are around 5'2-3" and have a real short torso that bike is going to handle pretty oddly. It's for Birds, methinks

 

[moff_quigley]

The numbers on that bike are really, really odd. Whats your saddle height and saddle tip to bar center reach on your current road bike? Unless you are around 5'2-3" and have a real short torso that bike is going to handle pretty oddly. It's for Birds, methinks

Kinda what I was thinking. Sigh. I'm about 5'8" or 9". I'll measure my seat height as soon as I can, but I don't think the saddle to bar measurement will be reliable as the bike I'm on is way too big for me. It's an old Miyata and it measures almost 23" C to C (TT). My hands are going numb/falling asleep on me when I'm riding my rollers. Don't notice it so much out riding...although it does happen. The place that has the 50cm RM also has a 56. But I still think it will be too long and tall.

56cm GEOMETRY
Size 56
Head Angle 72.5°
Seat Angle 73.5°
Horiz. Toptube Length 560
Headtube Length 155
Chainstay Length 405
BB Drop 70
Wheelbase 994
Front-Centre 599
Standover Height 822

 

[sanjuro]

fyi, the owner of my shop, a master fitter, would not sell you a fork unless he knew exactly the rake and axle-to-crown of the previous fork.

Maybe he was being too much of a worry wart, but I wouldn't play around with rake unless it was less than 3mm.

 

[moff_quigley]

TWhats your saddle height and saddle tip to bar center reach on your current road bike?

Give or take a few mm:

Saddle height = 29"
Saddle tip to bar center = 19.75"