Fork flip/swap?

[nicescooter]

I am currently in Afghanistan and have a lot of time to think about what I want to do to my bike (Catherine-85' 250R) next. I was looking up tips on rebuilding the front forks and came across someone talking about Honda using 350x fork bottoms to change the placement of the axle (under vs over). Supposedly this increases stability at high speeds. It seems legit being as the front tire would be pushed out a little more and lower the front end a little. Has anyone done this or have feedback from someone that has? On top of that why cant you just flip the 250R forks over and gain the same results? Seems like you could just reroute the brake lines and what not and it all should work out. Again, I cant just hop out to the garage and check on all this so I am hoping that the years of experience (good and bad) will shine through here. Thanks guys!


-nicescooter

[wonderboy]

The fork tube diameter on the 3rd gen R's (85,86) is larger than the 350x, so you won't be able to swap the fork lowers. The 350x and the 2nd gen R's (83, 84) is the same though (35 mm).

By the way, thank you for your service! Stay safe.

[nicescooter]

Thanks frank, what do you think about just switching the forks (left/right)? It would put the axel over instead of under and it doesn't seem like it would cause any mechanical issues and should have the desired effect. I cant help thinking there is something I am forgetting about though.

Ill keep my head down but I cant promise safe. Safe just isn't nearly as much fun.

-nicescooter

[Red Rider]

First off, thank you very much for your service!

I wouldn't reccomend changing your front suspension from trailing axle to leading axle without changing the rake/trail that is built into your triple clamps. While the leading axle setup will give you a longer wheelbase, the change to your steering's trail will have undesired effects on your steering. I experienced this firsthand when I first put inverted front forks on my '86 250R. I modified the stock triple clamps to accept the larger diameter forks, but kept the rake that was built into the triple clamps. The forks were mounted in the leading axle configuration, and I absolutely hated the handling qualities. I should have done my homework on the subject before I rushed headlong into the project, but I thought, "Nah, it can't make that big of a difference." I spent a lot of time & money modifying my triple clamps, which ended up being a waste. Before going that route, I should have at least swapped my stock fork legs around to the leading axle position, and taken it for a ride, to see the effects. If I didn't like the way it handled, I would have changed my game plan and not modified the stock triple clamps. Then, all that would have been wasted was a little time in the garage wrenching on the bike.

Since all you are talking about is gaining some stability by flipping them around, why not try it? I don't think you'll like the way it handles afterward, but there's no money wasted to try it, other than a little time in the garage, but you know the old saying, "Time is money." The only expense would be, if you decided to keep it leading axle, you'd probably want to get a shorter front brake line, since it's now going a shorter distance from the brake lever down the right forkleg.

[nicescooter]

Red Rider,

That is exactly what I am going to do. Going to be a little bit before I will be back state side that's why I was asking around. If it doesn't drive right after the flip then I will just swap it back to stock. I have no problems now but the whole idea intrigued me. I am just gathering ideas/thoughts for when I get home. Plenty of time to think, and there is always room for improvements. lol


-nicescooter

[wonderboy]

So I have zero experience messing around with front end geometry such as this, but since you'll have some time on your hands for a while, here is some bathroom reading material to consider:

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

Pay attention to the section on "trail". As the information states, trail will have a big influence on handling. By doing nothing else other than moving the axle to the front of the axle, you'll be reducing the trail, which I think has a destabilizing effect on the front end (it will not want to track straight ahead if you let go of the bars) but this is a tradeoff. More stable means it is also takes a little more effort to throw it into turns. On the opposite side of things, if you have minimum or negative trail, then the front end will turn with almost no effort and throw the machine into a turn (or at the extreme, you'll have to constantly hold the bars straight to avoid it turning on it's own). Somewhere in the middle is the happy balance between a nice stable tracking while driving straight ahead, but also the ability to easily enter and negotiate turns.

[DohcBikes]

I did exactly what you are describing on my 200x. It sucked. Bike steers wayyyyyyy too quick and wanders like hell. I even tried changing the rake to compensate. Theres just too much trail to overcome.