Question on suspension geometry

[Hak]

So I'm pretty set on changing the front fork assembly on my bike with something modern, which will involve probably getting some CNC triple clamps made. Initially I was thinking about how you could change the rake of the forks by angling the Fork clamps vs. the center tube's angle, but then thinking about it realized this would drastically change turn in angle's and I really just have no idea on how that would affect handling.

Question for you guys, are the forks always 100% parallel to the fork tube on the frame?? Thus making the only way to change the front rake angle by modifying the frame?

Also if anyone has any good info on setting up a good handling bike I'm all for it. I have found a few already and it seems pretty straight forward but like a very long, very calculated process.

I was thinking maybe I could just steal suspension geometry angles off a current known good handling bike and try to transfer all that to mine, if possible.

Last thing I want is a cool looking bike I never want to ride haha

[IanDMacDonald]

With all the money ur spending on buying-up the XS's, you coulda bought a used GSXRbsnd been happy in life . But, some have done R6 fork swaps, other's like Phil and Steve the FJ fork swap.

[Hak]

Haha I know this. The reason I never really got into bikes was because I never really clicked with the modern rocket biker crowd and knew I'd be on my own if I bought a Harley. After owning a twin turbo neon SRT4 I'm no stranger to customization and when I started seeing some of the bikes on bikeexif I knew a totally custom bike would suit me perfectly and be a really fun project to boot. I was thinking I wanna transfer mostly R6 parts over, I like to keep parts in the same family and hate when people put say GSX forks on a Honda café racer even if it looks awesome lol

Seems like I'm finding now that the rake can be changed just switching from special to standard tree's? So the rake can be changed by making custom tree's and leaving the frame's angle stock?

[DGXSER]

Well, rake and trail are not necessarily the same thing. But, yes, you can have custom trees made that would change the angle of the forks to the frame. But it would not change the angle of the steering stem to the frame.

Changing the trail will change the steering response. Fred likes the standard forks in special trees (IIRC the combination) because it makes the steering quicker which works for a side car rig. However, it could make the bike quite squirrelly without the rig.

I do not think the geometry changed that much when BikerPhil did his FJ fork swap. But he can speak to how it effected handling. I know he loves the way the bike handles with them.

Here is a couple articles that discuss the Rake and Trail, the second one gives some good examples of different combinations of rake in the frame and rake in the trees and how that effects trail and handling.

http://auto.howstuffworks.com/choppers2.htm

http://www.seegercycle.com/Rake-and-Trail.aspx

[D0wn5h1ft]

Haha I know this. The reason I never really got into bikes was because I never really clicked with the modern rocket biker crowd and knew I'd be on my own if I bought a Harley. After owning a twin turbo neon SRT4 I'm no stranger to customization and when I started seeing some of the bikes on bikeexif I knew a totally custom bike would suit me perfectly and be a really fun project to boot. I was thinking I wanna transfer mostly R6 parts over, I like to keep parts in the same family and hate when people put say GSX forks on a Honda café racer even if it looks awesome lol

Seems like I'm finding now that the rake can be changed just switching from special to standard tree's? So the rake can be changed by making custom tree's and leaving the frame's angle stock?

Raked trees is a dangerous way of "making the bike look cooler". When you rake your trees it shortens the trail considerably (depending on how much rake). There's thread around but you want 5-6" of trail I believe and our bikes are at 5"-ish from what I remember. Raking the trees will further shorten this making the bike unstable.

Are you trying to achieve something specific or is it more for S&Gs. My personal opinion is that these bikes already have plenty of rake for their stance. Plus when you go touching the front, you have to change up the back to match. If you're looking for a more stretched out look, take a look at my thread where people have posted lots of pictures of achieving a stretched look without raked trees or stretching the neck.

http://www.xs11.com/forum/showthread.php?t=41439

Here's a few:

[Hak]

Awesome! Thanks guys this is exactly the info I was looking for. I'm more concerned with furthering and modernizing the handling of the bike than the looks, but those are of course important too haha

I remember reading about the rake and trail but now it makes a lot more sense. I'll have to do some digging around and see what combinations people seem to like the best

[Schming]

Awesome! Thanks guys this is exactly the info I was looking for. I'm more concerned with furthering and modernizing the handling of the bike than the looks, but those are of course important too haha

I remember reading about the rake and trail but now it makes a lot more sense. I'll have to do some digging around and see what combinations people seem to like the best

On your quest for knowledge, keep in mind the weight and girth of these bikes.

The stock geometry allows pretty nimble slow speed maneuvers for bikes of this size.

For handling, your weight, what you carry and numerous other factors will contribute to the personal adjustment of your bikes suspension that works best for you.

Start off stock, tweak one thing at a time, experience the results, good or bad and adjust from there.

[crazy steve]

A properly done fork swap can be a big improvement on a XS as the stock forks are rather flimsy, although a fork brace can offer significant improvement.

As Downshift said, 'raked trees' are NOT something you want to do. These are semi-popular with some of the Harley crowd, but very few vendors will sell them due to the potential for dangerous handling (and the ones that do sell them usually put a caveat in their ad that these are for 'show use only'). Their only legitimate aftermarket use is on bikes that have been raked at the neck and now have excessive trail; these will reduce the trail back to 'normal' numbers. There are some factory bikes that use raked forks, but they're figured into the OEM geometry and these still have typical trail numbers.

Here's a swap that's been performed successfully several times....
http://www.xs11.com/forum/showthread...ight=Fork+swap
... but is definitely not a bolt-on....

You can also check the XS-UK site, as fork swaps have been popular over there, but be aware that many of the donor bikes they used were never available in the US so would be all but impossible to do here.

A few other things to think about when looking at donors; many of the sport bikes have minimal trail to start with and use steering dampers to make them stable at speed. And many use shorter forks which will lower the front of the XS (and further reduce trail). Can you reuse the XS front wheel, or will you need to accept mis-matched wheels? Almost everything newer you'll look at will need the steering stem shortened as the XS has a rather short neck. Some of these issues can be corrected with custom trees, but the machine work needed on the trees will be more involved compared to what is typically done.

Good luck!

[bikerphil]

With my fork mod, the wheel base is a couple inches shorter, much faster steering, great at all speeds up until 90, after that who knows. I do know that if you hit something in the road unavoidable like a small rock, it gives a very uneasy feeling, kinda like a tank slapper. I have never measured the rake/trail.

[Hak]

Great info, thanks guys. Guess I'm going to be doing some calculating!

[crazy steve]

Stock trail on these bikes is 5.12", which is a rather low number; that's one of the reasons these are prone to tank slappers if pushed too hard. I went a slightly different route from Phil on my FJ conversion by maintaining the stock height, which helps increase trail. Phil's bike is probably real close to 5" due to being lower in the front, mine figures at about 5.3", a slight increase over stock.

Remember, almost any suspension changes you make will effect trail; raising/lowering either end of the bike, tire sizes are 'simple' things that can change geometry, the main item on a fork swap is the offset built into the trees. Less offset = more trail.

[fredintoon]

- - - Changing the trail will change the steering response. Fred likes the standard forks in special trees (IIRC the combination) because it makes the steering quicker which works for a side car rig. However, it could make the bike quite squirrelly without the rig. - - -

Hi Don,
it's t'other way round.
Standards and Specials have the exact same wheelbase, frame rake and steering trail.
It works like this:-
The effin' stylists hung the Special's front axle on the front of the fork slider rather than underneath it like the Standard's.
To keep the front wheel where the designers wanted it to be the engineers had to make shorter 'trees to move the fork tubes
back the same distance that hanging the axle on the front of the slider moved the front wheel forwards.
This allows the sidecarist to mix the longer Standard 'trees and the forward axle Special fork tube assemblies to move the front wheel forward
thus reducing the steering trail and so easing the steering.