Author Topic: J path blues (Read 8061 times)

shovelon · « **on:** October 29, 2006, 07:54:57 am »

Dang that J-path on the vectors and crosslinks.

Did a nice header last night on a tight singletrack curve. I sometimes correct an overtravel with a sharp fast correction to the inside of the trail. But my new(to me) 956 LE has the conventional carbon Vector with a soft sponge and a helper spring no thanks to Iron Horse. Well nuts, the front end dropped into a rut and launched me right over the bars.

Just any pressure on the brakes at all extends that top link and the wheel moves back about an inch. ME HATES IT!

Anyway, laughed myself silly and finished my ride. One minute descending fast, next minute on my back.

Oh well,
Terry

kiwi · « **Reply #1 on:** October 29, 2006, 07:13:07 pm »

crosslink has much less J path than the vector.I spose you know about adjusting the j path on the vector?

SLIM · « **Reply #2 on:** October 29, 2006, 08:07:57 pm »

tell me more

orange · « **Reply #3 on:** October 29, 2006, 08:31:44 pm »

seconded...

shovelon · « **Reply #4 on:** October 30, 2006, 03:04:39 am »

Whuuuuuaaaaaaaat!!!!!!!

Me too, speak up Mun.

Terry

Colin · « **Reply #5 on:** October 30, 2006, 03:38:15 am »

Correct!
The Vectors have two modes of "J-Path" operation.
I don't think the Crosslinks have this and anyway the "J-Path" is less extreme on them.

Don't blame the "J-Path" or you will be stoned from this forum as a heretic! <grin>

As you quite rightly say, I think the core problem you have is a too soft spring/MCU.

I've tried both modes on my Vectors and there is a slight noticeable difference, however I think the biggest difference and the reason why I've done a few "endo's" is getting the pre-load just right for your weight and unfortunately also the type of ground conditions, which, obviously isn't consistent!
a little pre-load and you get nice sensitive small bump reaction but it can dive under bigger hits, too much and you don't get much reaction until you do hit something big and then it takes you by surprise!
Also, getting the correct spring rate for you is also very important.

Quote from "Girvin Linkage fork - Owners manual"
"Girvin Vector 2 Fork - the most advanced fork on the market"
p.7
A. Axle path adjustment

Sensitive Mode: When combined with minimal preload in the spring, this setting will provide maximum sensitivity to small and large bumps by creating a more vertical wheel motion . In turn, the vertical motion will allow the front wheel closely to follow the contour of the ground. Your fork is factory set in the sensitive mode.

Anti-Pogo Mode: This setting creates an even more "j-shaped" axle path , further reducing the effect of vertical loads created by pedaling motions. The initial movement of the fork leg is backwards - more in line with large bump forces and less in line with vertical rider pedaling motion. When combined with substantial preload in the spring, this mode results in a fork that feels stiff when climbing but accommodates medium and large bumps without limiting wheel travel.

To change the fork setting from one mode to the other:

1. Loosen both upper fork leg pivot bolts two turns

2a. To set the fork to Sensitive mode, insert a small Allen wrench into the chamfered hole in the upper fork leg pivot rod. Using the Allen wrench as a lever, rotate the pivot rod so that the small hole in the middle of the pivot rod runs parallel to the upper link with the chamfered end of the hole pointing back and up.

b. To set the fork to anti-pogo mode, insert a small Allen wrench into the chamfered hole..........blah, blah blah.....rotate until the chamfered end of the hole pointing forward and down.

3. Holding the Allen wrench (still inserted into the hole in the pivot rod) to keep the pivot rod from rotating, retighten the upper fork leg pivot bolts.

Col.

willem · « **Reply #6 on:** October 30, 2006, 01:23:20 pm »

Ah the dreaded J Path...
I love the science. After all, it makes perfect sense to move slightly back and up when impacting a root or small rock.
Not so in love with the ride, though. I've taken a few too many good headers exactly like Terry's.

When ever you change the wheelbase on a bike in a transition (ie, a turn, a G-out, heavy braking, etc) thigns are going to get a little weird.
And when things get weird, riders get boo boos!

Here's an interesting experiment to try... Take the spring out of your XLink and move the upper and lower link farther apart and closer together using headset spacers. Doing this completely changes the travel, the geometry, and the JPath.

Sadly, I can't get the right geometry and spring rate for my oversized bulk. For now, the XLink (with disk brakes!) sits on the workbench. The lightest, stiffest, plushest fork around - and I can't use it without breaking helmets! 'Tis truly a pity.

Carbon_Angus · « **Reply #7 on:** October 31, 2006, 05:57:30 am »

Willem, what is your height/wt and size, do you ride.

for me i have found the way big w/ the longer fork legs just right....

i was very endo prone years back on a large

i am 73 1/2"

shovelon · « **Reply #8 on:** October 31, 2006, 11:42:43 am »

Quote

Correct!
The Vectors have two modes of "J-Path" operation.
I don't think the Crosslinks have this and anyway the "J-Path" is less extreme on them.

Don't blame the "J-Path" or you will be stoned from this forum as a heretic! <grin>

As you quite rightly say, I think the core problem you have is a too soft spring/MCU.

I've tried both modes on my Vectors and there is a slight noticeable difference, however I think the biggest difference and the reason why I've done a few "endo's" is getting the pre-load just right for your weight and unfortunately also the type of ground conditions, which, obviously isn't consistent!
a little pre-load and you get nice sensitive small bump reaction but it can dive under bigger hits, too much and you don't get much reaction until you do hit something big and then it takes you by surprise!
Also, getting the correct spring rate for you is also very important.

Quote from "Girvin Linkage fork - Owners manual"
p.7
A. Axle path adjustment

Sensitive Mode: When combined with minimal preload in the spring, this setting will provide maximum sensitivity to small and large bumps by creating a more vertical wheel motion . In turn, the vertical motion will allow the front wheel closely to follow the contour of the ground. Your fork is factory set in the sensitive mode.

Anti-Pogo Mode: This setting creates an even more "j-shaped" axle path , further reducing the effect of vertical loads created by pedaling motions. The initial movement of the fork leg is backwards - more in line with large bump forces and less in line with vertical rider pedaling motion. When combined with substantial preload in the spring, this mode results in a fork that feels stiff when climbing but accommodates medium and large bumps without limiting wheel travel.

To change the fork setting from one mode to the other:

1. Loosen both upper fork leg pivot bolts two turns

2a. To set the fork to Sensitive mode, insert a small Allen wrench into the chamfered hole in the upper fork leg pivot rod. Using the Allen wrench as a lever, rotate the pivot rod so that the small hole in the middle of the pivot rod runs parallel to the upper link with the chamfered end of the hole pointing back and up.

b. To set the fork to anti-pogo mode, insert a small Allen wrench into the chamfered hole..........blah, blah blah.....rotate until the chamfered end of the hole pointing forward and down.

3. Holding the Allen wrench (still inserted into the hole in the pivot rod) to keep the pivot rod from rotating, retighten the upper fork leg pivot bolts.

Col.

Really now. So the Vector has an eccentric shaft to play with. I am going to mess with it. Basically we will be shortening or lengthening the upper link.

That Bob Girvin, he is such a trickster.

Terry

kiwi · « **Reply #9 on:** October 31, 2006, 04:10:32 pm »

of course there is any amount of adjustment"between the two modes..there is a trick to this...of course you may not know which mode you are actually in,altho i think thats covered somewhere too.Colin?

Colin · « **Reply #10 on:** October 31, 2006, 08:44:23 pm »

Yes, you can tell which mode you are in by looking at the upper fork leg pivot rod and seeing wether the chamfered hole is upright (sensitive) or forward (anti-pogo).

willem · « **Reply #11 on:** November 01, 2006, 03:40:52 am »

Carbon,

I'm 5-9 and 210#. (Ooorah!)
I'm mostly riding a way big 856 with very looooong Xlink "elites"

Just felt cramped on the big 856... that's my guest bike with flat pedals now.

Got the Noleen air forks on the way big now. Very very light and smooth.
Got the whole bike down to 27# with pedals and all!

Carbon_Angus · « **Reply #12 on:** November 01, 2006, 06:09:50 am »

Quote

Carbon,

I'm 5-9 and 210#. (Ooorah!)
I'm mostly riding a way big 856 with very looooong Xlink "elites"

Just felt cramped on the big 856... that's my guest bike with flat pedals now.

Got the Noleen air forks on the way big now. Very very light and smooth.
Got the whole bike down to 27# with pedals and all!

You'll like the Mega~Air Noleen's I have a pair on the Oz. Put'em at 100cm and enjoy!

orange · « **Reply #13 on:** November 01, 2006, 07:34:35 am »

" insert a small Allen wrench into the chamfered hole in the upper fork leg pivot rod"

Always wondered what that little hole was for - thought it might be something to do with greasing it...cool. will give it a go

kiwi · « **Reply #14 on:** November 03, 2006, 02:03:02 pm »

I have rememberd something,I have a manual here somewhere but i cant find it.I think the hole in the upper axle has a chamfer one end but not the other,so the chamfered end of the hole corresponds to one setting or the other....He he eh now youre all as confused as I ussually am.

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Author Topic: J path blues (Read 8061 times)

willem

willem