jonnya123

Hello,

I have a 53cm Diamant frame. The forks broke and I disposed of the fork before I noted the rake of the fork. I have now services and reassembled the bike but want to know the correct rake of fork I need to have befroe I buy a new fork. How do I find this out?

I have contacted Diamant directly but have had no response.

Cheers, Jon.

Cyclist0094

IIRC, Diamant is owned by Trek, try contacting them.

fietsbob

Generic to type of bike , look at similar bikes of that type ... Same sort of wheel size and head tube angle ,
and measure those bike's forks

unterhausen

axle to crown (a-c) is the most important measurement. But isn't saying you have a Diamont sort of like saying you have a Ford and asking what tires you need?

Andrew R Stewart 

An informed person might view this moment to have that chance to dial in the steering feel that they wish for. To do this well it will take some efforts. A fork of around the correct axle to crown (axle to brake hole plus brake hole to crown seat) length to nearly attain the top tube's slant, or horizontalness. Then minor corrections for final A-C dimension and trail (or rake).

I suspect that the top tube was designed to be fairly level. This then establishes the head tube angle, not that knowing it really is important for this. Dropping a plumb line from the axle to the ground and measuring forward to the front tire contact point gets you the trail. By measuring the mule fork, rake and a-c, one can then figure out what trail changes one gets with rake changes. Additionally the a-c dimension can be played with if needed. But this dimension's changes result in fairly minor steering angle changes. As long as the wheels intended are what the rear triangle ad brake reach likes and one matches these in the front handling geo can be played with to some degree.

But if this is all jibberish or "greek" to you then just get a fork that fits the head tube and ride the darn bike. Andy (who writes from 3000 miles from his desk).

Ryder1

I just measured all 37 bikes in my shop. Each time the measurement came out to 0.

Dancingbear

See the drawing here for how trail is measured. A picture is worth......https://en.wikipedia.org/wiki/Bicycl...cycle_geometry

CliffordK

You're supposed to measure it on a hill

Yeah,

Quite a few different fork rakes, I'm not sure if there really is a single magic number.

Find a fork you like, and try it out. Give it a few miles to get used to it.

unterhausen

rake generally doesn't matter if you get the a/c right. That's pretty tricky unless you are making a fork

Road Fan

The correct measurement will be small - 35 mm for low trail to 60 mm to emulate the vast majority of erstwhile racing bikes. It's easy to get it wrong.

I assume the OP bike is vintage? East German? If so i would not imagine Trek have any real data. Id assume the geo is 1960s, so id guess that 50 mm rake (not trail!) is a reasonable build target.

CliffordK

On a flat, level floor, with round wheels, the contact point has to be directly below the hub/axle. Think about it. No need to even have the bike attached.

Dancingbear linked to the Wikipedia article about Bicycle Geometry



Trail and Rake are measured with respect to an imaginary line drawn down from the center of head tube.

Ryder1

Wait, you mean I didn't have to measure all 37 bikes in my shop???

unterhausen

I'm sure Andy just posted in a hurry and didn't say what he meant. He's riding across the U.S.

CliffordK

Did you have one of these in your shop?

Or one of these?
Reel EFX, Inc - ReelEFX.com

Ryder1

Yep, got one of each. We like to close early on Fridays, huff some paint, and race 'em down the boardwalk in our birthday suits. It freaks the tourists out.

Road Fan

Um, Clifford, are you saying my suggestion was off-base? Please explain. I have measured trail directly in the past, and i find it challenging. I find it much easier to measure the key parameters (offset, angle, diameter) and then calculate the trail. But for the Diamante, the OP cannot take either approach. But if he can give a frame builder an axle to head tube required length and a reasonable target value for trail, he can get a fork built. Or he can dump the frame on the builder and say "please make me a fork that would steer like ... (insert description), he can get a fork built.

unterhausen

for just a frame, you're pretty much left with calculations anyway. Although I'm guessing that it had 45mm rake and any road fork off a racing frame will work in an acceptable manner. An experienced bike mechanic could probably find a fork that would work.

Andrew R Stewart 

I'm back home and catching up here.


Ryder- Do you now understand?


Jonnya123- Did you end up with a fork yet? If so how goes it? Andy