How do you measure rake

[brent j]

After reading some comments in the HL500 thread about shock length and rake angle I'd like some ideas of how people measure the rake.

How do you measure it?

How do the manufacturers measure it? They seem to list it in the specs but what do they mean?

To start off. Up until now, I sit the bike on a stand under the balance point so both wheels are just touching the ground. I measure the angle of the fork leg (all my triple clamps are parallel) with an adjustable bubble level.
I'm not saying this is right but it is consistant and repeatable.

I've always aimed for certain rake angles but my way of thinking is changing. Im not after any particular angle but concentrating on what works, and that's by trial and error. With the emphasis on error!

It seems to me there are so many other variables that rake angle is not that important, it is just one of many things in the mix.
The main thing I've learned about how motorcycles handle is that the more I learn the more I realise how little I know

[oldfart]

expalined here .
http://en.wikipedia.org/wiki/Bicycle_and_motorcycle_geometry

[brent j]

Good link Stew,

What I'm asking is how people are measuring it themselves. I often read references on here of a rake angle of such and such but what is the state of the bike when they measure it themselves?

[Oppet]

For the steering angle, put bike on straight floor and in straight line.
Take string of line with bobby weight, keep it next to front suspension tube and use mmm angle finder, or what is the correct tool in english.
ive seen some angle measuring devices that you can put straight on tube and read, but that would be too easy 

[RMJJ]

Rake doesn't change regardless of supension compression. Only the castor changes.

[mick25]

The way i work the rake out is close to you brent ;with the bike on a stand and on a level postion i use a builders bevel and sprit level.
To work out rake deg but wouldnt say its %100 1 deg eva way

but i have the same throughts where is the frame postion right ?to work out the angle with out knowing the specs

If you know the frame spec rake angle then it makes life easy to find the frame postion.

The way I worked out changeing a frame was to rock the frame or bike back and forth untill the frame rake is at its specs say 30 deg .Then once the angle is to specs fix bike or frame to that spot

Useing a sprit level find a spot on the frame (swing arm pivot hole) example,
Now use the sprit level to find a level spot from swing arm pivot hole to front of frame and make a level mark.
So if you remove the steering head to change the rake,and need to put the frame in the same org spot as first done then use the level spots as above
So you can change the frame to suit your new angle wanted 27 deg (example) or wheel base measurements
 
I have been working on modern bike specs wheel base lengths ,seat heights swing arm lengths foot peg postions etc

may sound confusing to some but its my own throughts

[cheapracer]

How do the manufacturers measure it?


It seems to me there are so many other variables that rake angle is not that important,

Spring adjustments central, 70kg rider in seated position.

Trail is more important, rake or caster adjustments change the trail and that what you feel most.

[chrisdespo]

Its a hard thing to describe, you must remember that fork length ( slideing the fork tube up or down thru 3 trees) will have an effect on trail.when tubes hang out of clamps at top trail reduced droped into clamps by a few mm will add trail. forks with axle mounted in center  of fork tube say like on a tm will have less what on a bicycle fork you call rake as fork and axle center is the same. on later bike like rm it all changes with the axle off set to the center line of the tube more like a bicycle. depending on the track we used to move the fork tubes to change the handeling of the bike much more noticable on flat track speedway and road raceing but still has a noticable effect on mx bikes in my experience.on my old it465 once the suspension was set for the rider weight you could really feel the effect of small changes in caster you could add or remove head shake depending on the surface you were on like fraser island beaches but there you had very high speeds. after reading this again the differance between steerer tube center and fork tube center is the same as the rake on bicycle forks ie the bend in fork blades.

[brent j]

Mick, I like the idea of checking the original angle to provide a starting point, it’s something I hadn’t thought of.

RMJJ, you're right about castor not changing with suspension movement but only if the bike remains level.
Castor, rake and steering head angle are all different names for the same thing.

Reading the latest issue of MXA they give figures for most of the modern bikes on the market.
Most are 25.5-28.2 degrees rake with 114-122mm trail. Then there’s the RMZ Suzukis. Two bikes reputed to be the best turning bikes around and they are 30.2 degrees with 140mm trail for the 250 and 29.4 with 130mm of trail for the 450.
Are the Suzukis that much different or do they measure things differently?
From numbers I’ve seen for older bikes the RMZ450 is just about the same as an RH250 or a TM125.

I’ve tried to copy angles and measurements from other bikes but have now gone completely away from that idea, now I’m trying as many different setups as possible and I’ll use the one that gives the best results. The last lot of changes I made went against everything I’ve thought about motorcycle handling but produced the best result to date. Incidentally the bike is now very similar to an Eric Cheney Yamaha 500 working from scaled photos.

Motorcycle handling is a balance of so many things and rake and trail are just a part of the mix.