[LiLBull]

hey JD on your bike and I have seen it on a few other kick ass bikes.
Your forks are above the tree.Did you fit a brand that has more travel or is it the stock forks and you lowered the front end .Im not up to speed with this activity of forking around.So please enlighten this fork-hopper.
And stop forking around all of you!
George

 

[jbranson]

I'm not JD, but both my race bikes have forks that extend above the tree. On a race bike it's desirable to be able to drop the front end, which effectively decreases the rake angle and speeds up steering response. Also nice for making adjustments to the front/back weight bias. Typically on a smaller race bike you add larger forks...they are usually longer too...this allows you to raise the front to correct geometry changed when you do things like change the rear swingarm angle. I like a good bit of down angle on the swingarm, this raises the rear end a bit...depending on how the front feels I might want to raise the front to level things back out...or leave the front down to put more weight up there and speed up steering. Just a nice option to have if you need it.
JohnnyB

 

[Geeto67]

can't speak to JD's bike but it is a common practice to lower the bike by sliding the forks up further in the tree. Personally I do this too when I am mounting clipons and I want to keep the stock headlight fork ears. most modern sprot bikes do this now a days to mount their clipons so I imagine is it pretty safe, well as safe as loweing the bike and changing the geometry on your bike can be.

Edit: there goes branson, getting the holeshot again...

Edited by - Geeto67 on Dec 07 2005 09:25:06 AM

 

[LiLBull]

thats good to know just looking at the cb 450 the angle looks like a longer reach to me.Just eyeballing it the angle looks more like a touring bike and I was thinking about that and how to change it .I even thought of cutting the frame to change angle(in my mind )but then I noticed my other bikes have different fork widths and tree configurations and decided it wasnt as simple as just changing the angle.And decided Id have to buy some bike chassis/frame books to investigate deeper into it. But on my building theory "if it looks wrong" "It probably is" the angle of the cb 450 looks alittle bit off from a quick steering bike.

 

[jbranson]

Most of the vintage bikes have a pretty large rake...30+ degrees in most cases...while most modern sport bikes are down around 25 degrees. Rake works with trail though...you can get away with less rake if you have more trail, etc.
In most cases it's not going to make a difference on a street vintage bike...other aspects of the design will probably have a more detrimental effect on handling than the steering angle. Inferior suspension/frame, heavy wheels/brakes, high center of gravity, vintage profile tires etc.
I'd say certainly not worth altering the rake on a street bike...much better ways to spend the time and money, light weight bits, reworked forks, alloy wheels etc.
JohnnyB

 

[LiLBull]

I hear you JohnnyB any books you found good on this subject.Id like to be more informed ...Id hate to start another library thru trial and error....i mean some books are usful some are all fluff and pictures, anyone have good bike technical books they keep on top of their other books let me know.
besides reading puts me to sleep so I wont be up all night like Johnnyb.
Thanks again George

 

[Geeto67]

I have some articles on rake and trail from the chopper world, and there is a book on motorcycle perfromance sispensions and frame design out there.

IMHO, don't fuck with jap bike neck angles unless you are willing to redesign the entire frame. From my expirence with honda choppers, bad things happen when you second guess the little japanese engineers that designed these frames. Jap bikes of the 1970s are for the most part the best handleing street bikes of the 70's. you want to get them to handle better, make them lighter and move the rider down in the frame a little, but adjusting the rake and trail will cause the frames to flex in ways they weren't intended - these frames were designed at a time when the general concensus in motorcycling is that a bike frame needed a little flex to be truely good handeling and so all the bikes have a natural flex, distrubing that can cause cracks, breakages, and overtime frame failure.

ever see a hacked stock honda frame from the 70's chopper craze? you could spend all day counting the frame cracks and those bikes are not ridden as hard as a cafe racer.



edit: realized I contradicted myself through unclear wording: sliding the forks up through the trees is ok because even though it changes rake the changes are not radical and the trail changes appropriatley to compensate. When you start to think about cuttin the neck off and rewelding on to the frame at a completely different angle (like say from 30 degrees to 25 degrees) that is where you run into trouble.

Edited by - Geeto67 on Dec 07 2005 5:28:45 PM

 

[Geeto67]

TOny Foale, that is who wrote the book I couldn't remember:

http://www.amazon.com/gp/product/08...103-1059390-2822256?n=507846&s=books&v=glance

he designed some really cool racing frames in the 1970s. Huge spine tubes that doubled as oil tanks to save weight...great stuff:

http://www.satanicmechanic.de/foale.shtml

 

[JD]

sorry bull, didn't see this topic. johnnyb is on the money as usual with the tech bit. my racebikes too have longer forks. unfortunately in my case the 550 originally was a semi-chopped baby blue caferacer in disguise with hard bags, sissy bar, engine guards and giant windshield. after the first conversion to mostly stock we never noticed that it sat different than other 550's until sitting them side by side. I've never measured them but I'm pretty sure the forks are longer than stock. So now the bike is just below stock ride height and I have all that fork above the tree. I have picked up stock forks before but they always end up on somebody's racebike before they get on the 550.

JD