Fork Twist


6 replies to this topic
  • BWB63

Posted October 29, 2007 - 10:24 AM

#1

The bike is balanced just the rear ride is not as plush as the front.
My pace has picked up heaps and I now don't know if i'll go to USD's on the front. Would you if you had the option, can USD's work like these do know? # lbs lighter is hard to walk away from for me.
And why does the 650 feel lighter every time it works better.


Conventional forks flex a lot more and this is good for our type of riding over inverted forks. Conventional forks twist a lot more then inverted forks and this is way bad. The front to back flex of the forks works to reduce fatigue, reducing the hit to the rider and inverted (USD) forks translates 90% or more back to the rider but, with almost no twist. Installing a fork brace will reduce fork twist about 70% making the stock forks about 80% as efficient as inverted forks in reducing fork twist but, retaining the front to back flex. This is the reason Scott Summers installed XR650R forks onto his CRF450R to race with. For MX or tight work at a fast pace inverted forks will give much better control. The bike will track true with inverted forks and conventional forks will flex as you dive into and coming out of a turn. Open high speed, whoops and all the other rocks, ruts, stuff that you hit in the desert wear on you faster without the flex of conventional forks. I have had my left wrist worked on five time and it is fused, pinned and the ulna bone is cut in the clear, leaving me with only one working bone in my fore-arm. I broke the fusing in the wrist over clearing a set of doubles on the XR650R and three of the five sets of nerves to the wrist have been removed so I have little feeling in my left wrist. It still hurts if I over use it so, for me I like the flex but, I may invert for the heck of it some day. I will weld the frame where the coil was.

  • martinfan30

Posted October 29, 2007 - 11:35 AM

#2

you're completely accurate.:worthy:

i noticed this after putting a fork brace on my L.

  • weskc35k

Posted October 30, 2007 - 11:58 PM

#3

It's the 3 and a bit LBs lighter that has me wondering Bruce.
But for now my front end is way good.
I'm gunna ring my suspension guy and find out what oil weight he uses in the rear,i think he uses 5wt is in my head somewhere.
If so i'll swap it out for 2.5.
OK i just rang him and he uses an ultra light shock oil so that's off the menu.
Like i said Bruce the bike is balanced and it's handling great but the front is plusher in snot and chop than the rear and i want them the same.Just in the initial, medium to big hits it's great though.
I may take a turn out of the spring i'm at 96mm and really like this setting especially with the way the front is now.Might write down my settings and mess with it ,if it's no better just put it back.
Maybe i'll bite the bullet and revalve it myself.

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  • Billahjack

Posted October 31, 2007 - 09:00 AM

#4

As always, killer info! The latest DR magazine has an article with the KTM 690 designer talking about putting more flex into their front fork for the Baja 1000. He also adds some commentary about competing against the 450X and the differences between the Baja 500 and 1000 race terrain/setup. I really hope they beat the 450X so we can get another big bore Honda.

  • BWB63

Posted October 31, 2007 - 11:18 AM

#5

It's the 3 and a bit LBs lighter that has me wondering Bruce.
But for now my front end is way good.
I'm gunna ring my suspension guy and find out what oil weight he uses in the rear,i think he uses 5wt is in my head somewhere.
If so i'll swap it out for 2.5.
OK i just rang him and he uses an ultra light shock oil so that's off the menu.
Like i said Bruce the bike is balanced and it's handling great but the front is plusher in snot and chop than the rear and i want them the same.Just in the initial, medium to big hits it's great though.
I may take a turn out of the spring i'm at 96mm and really like this setting especially with the way the front is now.Might write down my settings and mess with it ,if it's no better just put it back.
Maybe i'll bite the bullet and revalve it myself.


This is the stuff I like to talk about and it would happen that I am out of town going to Phasor Analysis school. I only get to a computer for a few minutes at break time It's hard to get the whole idea of a thread when I only peak at it and miss most of the points.
2.5wt fluid in the shock is a huge help for the way I setup the shim stack. Lets the compression adjustment be more meaningful to the whole compression movement. Moving the cross over shim up and adding to the slow stack you get much more control over big slow hits but, get a much plusher fast stack movement. You can allow to move more fluid though the compression adjustment (it's a bypass valve) giving a more fluid flow on small quick hits but, at some point you have to push that fluid through the valve and shim stack on the big valume big hits, slowing down how much fluid that will flow in a given time. In the end you have a thinner fluid and you are flowing more fluid through the compression adjustment valve. Not what most would think but, in the end you are compromising less. More bottoming resistance from the extra slow stack shims, plusher mid, and high speed stack because of the cross over shim movement and thinner fluid. To plush the mid stack a little more a 34mm shim is removed and used in the rebound stack with a few more. With the thinner fluid that the shock was designed to use in the first place you can get a plusher ride and then stiffen up the slow stack to the point that it starts effecting that plush ride and have more bottoming resistance then the stock bike had to begin with. This is possible because of the better fluid.

  • weskc35k

Posted November 02, 2007 - 08:41 PM

#6

I got it now Bruce.
I went in 3 clicks of compression on the front,5ml of oil in front,took out half a turn of spring on the rear and added 2 clicks of rebound(stiffer,slower) on the rear and it's magic.I took the speedo cable off the front this is why i needed the 3 clicks i think,as it must hinder the action.
The only thing slowing me down on fire trails is me,the bike does it so well that i poop myself when i realise how fast(for me) i am travelling on these rocky and rutted fire trails.
I get no feedback on some stuff as to if the bike is going to snap or pitch sideways,but i know that even on the CRF450X i had i couldn't have gone near as fast without some swapping and crashing.
Taken a lb off the bike with the loss of the Speedo cable the pipe midmount is gone and ground some stuff from the rear brake hanger,also ground a groove out of the rear pads as they where lockling up too much and it is great now.

  • BWB63

Posted November 03, 2007 - 10:19 AM

#7

It is amazing how much different this bike can be once you make it fit the rider.





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