superhondaman Posted June 2, 2007 Report Share Posted June 2, 2007 Ok i have trawled the internet for ideas but in plain english how do you measure the rake. I know its the vertical point down from the head stock then a straight line down the center of the head stock but how do you come to or measure what this angle is? Do you convert your measurements onto graph paper and then use a protractor? or is there some mathematical system (maths & english not my strong points!) and if say you wanted to bring the rake in 1 or 2 degree's then can you convert this to how many mm or cm you would move the forks back or steepen them? Quote Link to comment Share on other sites More sharing options...
feetupfun Posted June 2, 2007 Report Share Posted June 2, 2007 Rake is the angle from vertical of the steering stem. It can be adjusted by changing the relative height of the front and rear of the bike (suspension settings or sliding the fork tubes in the clamps) or by using eccentric bearing seat inserts in the steering head or by cutting and welding the frame. Measuring the rake angle directly can be pretty tricky and is probably unnecessary. If you know how much you want to change the rake angle, the easiest way is to make an exact side view scale drawing of the bike then you can measure off the drawing how much you will need to change things (ie frame tube lengths) to achieve the change in rake angle you want. If you have access to modern drafting software it is possible to create drawings from photographs of structures. Quote Link to comment Share on other sites More sharing options...
jaylael Posted June 3, 2007 Report Share Posted June 3, 2007 Rake is measured with an angle finder which can be placed on the fork tube as per the attached photo. Angle finders are available a most hardware stores for reasonably cheap. A typical measurement on a trials bike is 24 to 26 degrees. Anything steeper than 24 degrees will likely be oversteep which is dangerous to the rider. (ask me how I know) Many old school mx bikes from the '70's run about 28 degrees rake. In the enclosed pic I am adjusting the rake angle to 24 degrees on a project trials bike. Quote Link to comment Share on other sites More sharing options...
copemech Posted June 3, 2007 Report Share Posted June 3, 2007 (edited) That is an interisting way to do it Jay. I guess that is an old Yam? As a side note, I have noticed that, at least on the Sherco, there is a degree or two built into the triple clamps! Which also makes me wonder if the factory riders can change this to suit? Easier than changing frames! Edited June 3, 2007 by copemech Quote Link to comment Share on other sites More sharing options...
feetupfun Posted June 3, 2007 Report Share Posted June 3, 2007 Jays measurement will be correct only if there is no angular offset built into the triple clamps. Many bikes have this angular offset so beware. Quote Link to comment Share on other sites More sharing options...
mad4it Posted June 3, 2007 Report Share Posted June 3, 2007 Yes as said on some models rather than change the frame to alter the offset they simply did this by off setting the bored holes in the yokes. In therory if you got some offset boared yokes & the steerer was of the same length to another bike you could fit them as a way of changing the bike's rake without all the cost involved in modifying the frame. Quote Link to comment Share on other sites More sharing options...
jaylael Posted June 3, 2007 Report Share Posted June 3, 2007 Cost is why I do it this way. I am no machinist, so making special parts is an expensive job. This costs me an afternoon and some serious sweat. For me it is therapy and fun, so it's kind of a win win situation. Copemench, that is a '73 Hodaka Wombat. Quote Link to comment Share on other sites More sharing options...
feetupfun Posted June 5, 2007 Report Share Posted June 5, 2007 Yes as said on some models rather than change the frameto alter the offset they simply did this by off setting the bored holes in the yokes. In therory if you got some offset boared yokes & the steerer was of the same length to another bike you could fit them as a way of changing the bike's rake without all the cost involved in modifying the frame. If you offset the forks or change their offset angle by altering the relationship of the triple clamp holes, you are changing the trail, not the rake. The rake angle is determined by the angle of the steering stem (steering axle), not the angle of the fork tubes. The factory MX teams alter the rake angle to tune the steering for a particular track by using eccentric bearing housings in the steering head. The easiest way to change the rake angle a lot (more than 1-2 degrees) is to do something like what Jay Lael has shown. Small adjustments can often be achieved by shockie length, fork tube height in triple clamps and spring preload front and rear but turning an oldish MX chassis into a Trials chassis normally requires some pretty serious frame work to get the steering nice. Quote Link to comment Share on other sites More sharing options...
superhondaman Posted June 7, 2007 Author Report Share Posted June 7, 2007 Have just recived a 'angle finder' from e bay Will see how i get on with this. It is to alter the rake on a standard cub frame 11/2 degree's. Will post what it is at standard later and a picture. Go to e bay and paste this in Item number: 150128492833 Quote Link to comment Share on other sites More sharing options...
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