How to select a fork (part I)

[bjf]

So I just bought a custom Legend on eBay, frame only. Now I need to find a fork. I assume the first step is to figure out the head tube angle, right? How do I do that (no spec sheet available)? What else do I need to know to figure out what fork rake I want? And what other considerations go into choosing a fork? Thanks!

[dcama5]

You can go about it that way, but most frames have a corresponding geometry chart that tells fork rake, trail (sometimes), and axle-to-crown dimension of the fork. All you have to do then is find a fork that you like with the same steerer tube diameter and length, and very close rake and axle-to-crown dimensions.

[bjf]

You can go about it that way, but most frames have a corresponding geometry chart that tells fork rake, trail (sometimes), and axle-to-crown dimension of the fork. All you have to do then is find a fork that you like with the same steerer tube diameter and length, and very close rake and axle-to-crown dimensions.

This frame apparently has passed through several hands, and there is no geometry chart available. It's custom, and definitely not square (short and tall).

[Black Dog]

Use the angle Finder on a smart phone to get the head tube angle and then post it. There are a few great builders here who will tell you what amount of rake will work. As for the axle to crown it will likely be the same as the serotta f3 or 02 depending in the age of the frame. You can go to the catalogue section here and find the serial number thread to help you date the frame.

[happycampyer]

Use the angle Finder on a smart phone to get the head tube angle and then post it. There are a few great builders here who will tell you what amount of rake will work. As for the axle to crown it will likely be the same as the serotta f3 or 02 depending in the age of the frame. You can go to the catalogue section here and find the serial number thread to help you date the frame.Not sure how one does that without a fork? Without knowing another dimension (e.g., seat tube angle or bottom bracket drop), it won't be possible to know for sure what the angles are/were supposed to be.

Do you or your LBS have a fork that you can use as a stand-in? The problem is, without a fork, it will be a bit of a guessing game (and it will still be one with one, but less so).

The likely axle-to-crown height that the frame was designed for is 372mm. If you put a fork in the frame and adjust it to 372mm (if necessary), you'll get a good idea what the frame angles are. From there, you can decide what fork would best suit the frame in terms of rake, etc.

[bjf]

Not sure how one does that without a fork? Without knowing another dimension (e.g., seat tube angle or bottom bracket drop), it won't be possible to know for sure what the angles are/were supposed to be.

Do you or your LBS have a fork that you can use as a stand-in? The problem is, without a fork, it will be a bit of a guessing game (and it will still be one with one, but less so).

The likely axle-to-crown height that the frame was designed for is 372mm. If you put a fork in the frame and adjust it to 372mm (if necessary), you'll get a good idea what the frame angles are. From there, you can decide what fork would best suit the frame in terms of rake, etc.

Doesn't the Legend always have a top tube parallel to the ground? If so, then the head angle should be easy to determine (once I figure out how to measure it -- I don't have a smart phone).

[happycampyer]

Doesn't the Legend always have a top tube parallel to the ground? If so, then the head angle should be easy to determine (once I figure out how to measure it -- I don't have a smart phone).Not always—if you look in the catalog section, the 2006 catalog for example shows both the SE and the full ti Legend with a decent amount of top tube slope. Mine has about 4º of slope, which is less noticeable.

You could start out by leveling the top tube, and measuring the seat tube angle and the bottom bracket drop. If the seat tube angle is close to 73º (+/- .5º) and the bottom bracket drop is around 7 - 8cm, then you're probably in the ballpark. Then as Black Dog mentioned, you can measure the head tube angle, and figure out what fork rake you would need to produce the desired amount of trail (taking into account that an Enve fork, for example, will shift the front end ever-so-slightly). You can get an angle finder at a hardware store or online, or your lbs should have one.

If you can find an F3 in the appropriate rake, that would most likely be the fork that the frame was designed for (unless the frame is older). If you track down a Serotta fork, you would also need to decide on stiffness (most likely a 6.5 or 8.5, unless you are really tall/heavy).

[bjf]

Not always—if you look in the catalog section, the 2006 catalog for example shows both the SE and the full ti Legend with a decent amount of top tube slope. Mine has about 4º of slope, which is less noticeable.

You could start out by leveling the top tube, and measuring the seat tube angle and the bottom bracket drop. If the seat tube angle is close to 73º (+/- .5º) and the bottom bracket drop is around 7 - 8cm, then you're probably in the ballpark. Then as Black Dog mentioned, you can measure the head tube angle, and figure out what fork rake you would need to produce the desired amount of trail (taking into account that an Enve fork, for example, will shift the front end ever-so-slightly). You can get an angle finder at a hardware store or online, or your lbs should have one.

If you can find an F3 in the appropriate rake, that would most likely be the fork that the frame was designed for (unless the frame is older). If you track down a Serotta fork, you would also need to decide on stiffness (most likely a 6.5 or 8.5, unless you are really tall/heavy).

This is really helpful, but there's one bit I don't understand. Isn't the ST angle measured relative to the ground? If the TT is sloped, then one wouldn't measure the ST relative to the TT.

Or maybe I don't understand what you're saying. Could you explain again?

[Ken Robb]

Weren't all/most Legends designed to use 43mm fork? Help Dave Kirk!

[Peter B]

So I just bought a custom Legend on eBay, frame only. Now I need to find a fork. I assume the first step is to figure out the head tube angle, right? How do I do that (no spec sheet available)? What else do I need to know to figure out what fork rake I want? And what other considerations go into choosing a fork? Thanks!

I'm with Happycampyer's 372 A-C length. You're probably after a 43-50mm rake, depending on frame size. Likely towards 43 in the larger sizes and pushing 50 in the smaller. What is the frame size (ST/TT)? Is it stock or custom? What year? Got photos?

The other suggestions for mocking up a build and measuring HTA will help too. My inclination is that something in the 56-58mm trail will be good for a typical frame and yield relatively neutral characteristics unless this is an end-of-bell curve one-off design.

[Peter B]

Weren't all/most Legends designed to use 43mm fork? Help Dave Kirk!

I had a stock '03 53cm w/ 72* HTA built around a 50mm rake. So, depends...

[Louis]

Weren't all/most Legends designed to use 43mm fork? Help Dave Kirk!

I thought this was the case also. If not all, nearly all.

It used to be that the answer to the question was "Ouzo Pro" and you're done.

I was amazed how, after being the standard go-to CF fork for so long, the OP disappeared from the scene.

[Peter B]

I thought this was the case also. If not all, nearly all.

It used to be that the answer to the question was "Ouzo Pro" and you're done.

I was amazed how, after being the standard go-to CF fork for so long, the OP disappeared from the scene.

In 2003 stock sizing ranged from 71.5* - 73.5* HTA. Kelly wasn't sending all those out the door with 43mm rakes...:no:

[Louis]

In 2003 stock sizing ranged from 71.5* - 73.5* HTA. Kelly wasn't sending all those out the door with 43mm rakes...:no:

True, but how many 46-50 sized frames were there? Not many.

[Peter B]

True, but how many 46-50 sized frames were there? Not many.

Agreed. But plenty of 53s and as I said, designed around a 50mm F2 (Reynolds) fork.

[bjf]

I'm with Happycampyer's 372 A-C length. You're probably after a 43-50mm rake, depending on frame size. Likely towards 43 in the larger sizes and pushing 50 in the smaller. What is the frame size (ST/TT)? Is it stock or custom? What year? Got photos?

The other suggestions for mocking up a build and measuring HTA will help too. My inclination is that something in the 56-58mm trail will be good for a typical frame and yield relatively neutral characteristics unless this is an end-of-bell curve one-off design.

It's custom, which is why I don't know the angles. The person who listed it says TT is 50 (c-c), ST 48 (c-c), HT 18. Of course if the TT slopes the ETT is longer. If so, it's pretty much like my 54S Fierte with a taller HT, which is exactly why I bought it. I don't know the year -- CLE 54 024.

Keep the ideas coming -- I really appreciate it. Barbara

[Louis]

If it's a custom and you want to know exactly what's going on, measure the head tube angle, decide what trail you want, and calculate what rake will get you that trail.

The equation for trail is:

Trail = wheel&tire radius / tan(HT angle) - rake / sin(HT angle)

For "typical" road bikes the radius is about 340 mm. To be consistent use mm for rake and trail.

Edit: If you're trigonometry-challenged There are plenty of online calculators for this, but you'll have to figure out what numbers to plug in.

http://www.davesbikeblog.com/storage/Trail80rake.jpg?__SQUARESPACE_CACHEVERSION=1381607 601185

[happycampyer]

Iirc, the F2 and the Ouzo Pro had the same dimensions (same mold, different layup). Older versions of the OP had an a-c height of 370mm, but around 2003 or so the fork was redesigned slightly and the a-c height was changed to 372mm. Not sure if the F2 is old enough for it to have gone through the same change or not (perhaps Mike Lopez will notice this thread and chime in). Pretty sure all of the F3/S3's were all 372mm.

The OP and Serotta forks came in different rakes: 40mm, 43mm and 45mm, and I'm pretty sure 50mm. As others have noted, the fork would have been matched with the headtube angle to produce the desired amount of trail.

Without more information about the frame (size, approximate angles, etc.), it's hard to make any recommendations.

[Peter B]

It's custom, which is why I don't know the angles. The person who listed it says TT is 50 (c-c), ST 48 (c-c), HT 18. Of course if the TT slopes the ETT is longer. If so, it's pretty much like my 54S Fierte with a taller HT, which is exactly why I bought it. I don't know the year -- CLE 54 024.

Keep the ideas coming -- I really appreciate it. Barbara

In that size Barbara my money's on a 50mm rake in an Ouzo Pro or an F2 (same shape, slightly stiffer layup).

Longer or shorter A-C fork lengths will slacken or steepen the HTA respectively and so you can adjust rakes accordingly and still hit a target trail number with a variety of fork choices.

I'd fit a headset and (any) Ouzo Pro, put it in a stand and either slap on a wheelset (w/ same size tires) or put it in a stand and carefully adjust till both axle centerlines are equidistant from the (level) floor. Then use an angle finder to measure the STA and HTA. Handling desires and trig will guide you from there. PM if you need to borrow an angle finder.

[happycampyer]

It's custom, which is why I don't know the angles. The person who listed it says TT is 50 (c-c), ST 48 (c-c), HT 18. Of course if the TT slopes the ETT is longer. If so, it's pretty much like my 54S Fierte with a taller HT, which is exactly why I bought it. I don't know the year -- CLE 54 024.

Keep the ideas coming -- I really appreciate it. BarbaraSecure the Fierte (in wheel stands, or have someone hold it), and hold the Legend frame next to it by the chainstay, with the rear dropout and bottom bracket in line with each other. It's not perfect, but you'll be able so see roughly if the seat tube angle is similar, and if the top tube is sloping. Also, see if the bottom of the headtubes are in line. If not, raise or lower the Legend frame until they are. Another thing to try is to put a rear wheel in the Legend frame and, with the Legend and the Fierte next to each other, line up the bottom of the headtube of the Legend with the bottom of the headtube of the Fierte. If you take your angle measurements from there, you should be able to get a ballpark measurement.

My guess is that, with a frame of that size, the headtube angle is probably closer to 72º, and you would probably want a fork with 50mm of rake (assuming a 372mm a-c height). I would add that the 6.5 stiffness would also probably be a good match for that size frame.

Edit: I was typing while Peter B was, and I think we were thinking along the same lines.

P.S. Here's an example of a Legend with a decent amount of toptube slope:

http://forums.thepaceline.net/showthread.php?t=92925&highlight=legend

Of course, if you had the bare frame and leveled the top tube, the seat tube angle would be ridiculously steep.

[Louis]

If it's a small frame I'd put a 45 or a 50 mm rake fork and be done with it. Chances are high that the handling will be fine. Otherwise, you'll have to collect more info by doing some measuring.

[cmg]

try the 50mm rake first. it's probably closer to the correct one. post a picture.

[christian]

Happy is right - this is easy. Get a 372mm ac fork. Or dowel. Set it up and make sure that front drop and rear drop are equal and between 70-80mm.

Then measure the HT angle. Et voila you can figure out what fork rake it's designed for or what fork rake you prefer for your preferred handling.

This'd be a fun Monday-night beer club time-waster.

[happycampyer]

If it's a small frame I'd put a 45 or a 50 mm rake fork and be done with it. Chances are high that the handling will be fine. Otherwise, you'll have to collect more info by doing some measuring.

My thoughts exactly. If an Ouzo Pro or Serotta fork, 50mm would probably be preferable, but given availability, 45mm will probably be easier to find. A 45mm Enve would also probably work well, given its slightly shorter a-c height.

Or, make a drinking game out of it as christian suggests.

[commonguy001]

BlueSea still has a NOS Reynolds Serotta 02 50mm rake fork in the classifieds

http://forums.thepaceline.net/showthread.php?t=161725

If it were my frame I'd buy that one:beer:

[bjf]

BlueSea still has a NOS Reynolds Serotta 02 50mm rake fork in the classifieds

http://forums.thepaceline.net/showthread.php?t=161725

If it were my frame I'd buy that one:beer:

Yeah, last night I asked him to hold it for me, and he is. :banana: