K2 / Proflex Riders Group
General => Tech Forum => Topic started by: 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
-
crosslink has much less J path than the vector.I spose you know about adjusting the j path on the vector?
-
tell me more
-
seconded...
-
Whuuuuuaaaaaaaat!!!!!!!
Me too, speak up Mun.
Terry
-
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.
-
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.
-
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"
-
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
-
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?
-
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).
-
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,
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!
-
" 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
-
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.
-
Sensitive mode is the chamfered end of the hole
pointing back and up (running parallel to the upper
link),
Anti pogo mode is chamfered edge pointing down and forward,
Guess who's got an origional Vector 1 and 2 manual.
Simon.
-
I thought I'd said in my previous posting that the instructions were direct from the Vector 2 owners manual? This included how to tell which mode you were in...............sigh...........
........I wear my fingers down to bloody nubs typing this stuff in and am I appreciated? Am I?................<grin>
Col.
-
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.
Col.
sheesh he is riight...anyone going to the stoning.?....
-
I thought I'd said in my previous posting that the instructions were direct from the Vector 2 owners manual? This included how to tell which mode you were in...............sigh...........
........I wear my fingers down to bloody nubs typing this stuff in and am I appreciated? Am I?................<grin>
Col.
Blimey I'd of thought you would of realised by now
everything has to be repeated at least 3 times,
well in my experiance this has always been the case,
posts just get a cursory glance (lol) its the law didn't you know,
Simon.
-
........And a message came down from the Almighty Girvin......
......"trust in the J-Path my son and all will be well with your travels on the singletrack".
Anyone caught "dissing" the almighty wisdom of the "Girvin" will be stoned as a Heretic!
p.s. I though it was just my wife who had to tell me things 3 times...............?
"chamfered" isn't a real word according to my spellchecker anyway........ha, ha , ha
Col.
-
I know I'm relitively new here but here are some observations about the J-path blues.
I am 6'2" and 220 lbs on a Large 5500 with a carbon Crosslink. I have a set of Fox Float RL AVA's 7 7/8" long (it'd take a whole 'nother thread to explain what all that means) on the bike. I designed and had adapters made to fit the Fox's onto my bike. As heavy as I am I am running 45-50psi in the front shock but after so much time off the bike the technical trails and the cursed J-path (which I have never heard anyone get blasted for talking about) kept sending me over the handle bar. Now part of it was rusty techique. The other was that I had the same rebound setting for the front shock as I did the rear which was at 200psi (10 clicks from full hard). I backed the rebound completely off and set the AVA to 2 and now I have no issues. So after you set the preload make sure to run as little rebound as possible if you have that option.
I may play with the AVA some more to see if I need it with the current dampening settings. I really want to send it to Push and have them set it up, almost just for the "HUH?" factor. :D When I have the money. [sigh]
-
I designed and had adapters made to fit the Fox's onto my bike. As heavy as I am I am running 45-50psi in the front shock but after so much time off the bike the technical trails and the cursed J-path (which I have never heard anyone get blasted for talking about) kept sending me over the handle bar. Now part of it was rusty techique. The other was that I had the same rebound setting for the front shock as I did the rear which was at 200psi (10 clicks from full hard). I backed the rebound completely off and set the AVA to 2 and now I have no issues. So after you set the preload make sure to run as little rebound as possible if you have that option.
I may play with the AVA some more to see if I need it with the current dampening settings. I really want to send it to Push and have them set it up, almost just for the "HUH?" factor. :D When I have the money. [sigh]
I know what you mean when running a slow shock. The carbon vector I have with the soft sponges is wicked fast in compression and rebound. It is almost a luxury, if not for the over softness.
Let us know how the PUSH works.
Terry
-
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).
OK, so I tried it both ways, and like the sensitive mode with more preload in the spring. By shortening the upper link by rotating the shaft inward, I am increasing the rake, and shortening the "J" path.
-
I know what you mean when running a slow shock. The carbon vector I have with the soft sponges is wicked fast in compression and rebound. It is almost a luxury, if not for the over softness.
Let us know how the PUSH works.
Terry
I would say if you want to firm up the ride you want to increase the compression and leave the rebound alone. But you would have to have a suspension expert rip you shocks apart and play with the bits inside. Good luck finding someone, muchless affording it. And it looks like it will be a long time before I will be able to afford the PUsh services. But I'd love to be the fly on the wall when I tell them that the one shock goes in a Noleen fork. :D
Oh, and I have completely rebuilt my sportbike forks at one time (and changed the dampening inside them) so I have an understanding of how suspension works, but I was under guidance, so I do not consider myself any kind of expert.
Later,
Rich
-
But I'd love to be the fly on the wall when I tell them that the one shock goes in a Noleen fork. :D
Oh, and I have completely rebuilt my sportbike forks at one time (and changed the dampening inside them) so I have an understanding of how suspension works, but I was under guidance, so I do not consider myself any kind of expert.
Later,
Rich
tell me more
1) sport bike?
2)How would the set up of the shock be different for the crosslink.It would be similar to a linkage rear wouldnt it except the ratio would be quite low...yes?
No dissing the J path,although i had a massive unexpected OTB once,off balance leaning too far forward,big bump....
-
tell me more
1) sport bike?
2)How would the set up of the shock be different for the crosslink.It would be similar to a linkage rear wouldnt it except the ratio would be quite low...yes?
No dissing the J path,although i had a massive unexpected OTB once,off balance leaning too far forward,big bump....
Ah haha. you've asked for it now. :D
1. Yes an 1991 Honda VFR750F. I have a lot of little mods but by far the most effort is into the suspension, because that is where the real speed comes from. I do have a Pipe/Jet Kit/High flow air filter on as well. With over 30k miles on it I got peaks of 95.4 hp and 50.5 ft-lb of torque on the Dyno. Any way, the forks needed to be redone. I had a moron for a mechanic that put progreesive springs in sport bike forks. So I needed new springs, and some internal bits that had worn out. I also new that I wanted some adjustablitity so I got CBR600F3 fork internals that bolt right in and provide preload and rebound adjustability. I also knew the real trick was to redo the dampening rates, and that would make the biggest difference, although with my wieght the right springs would be quite noticable. I called Traxxion Dynamics (a very reputable motorcycle sus company here in the states) and ordered springs, their recommended fork oil weight, and a Penske 4 way adjustable rear shock (of course with spring rates and dampenning set to my and the bikes weight and rding style, mmmm). So, I had a comtact who used to work for this company and he told me what shims to buy and how many of each to put for the compression and rebound sides of the piston in the cartridge forks I have. So I took aout the stock internals out of my VFR's fork legs and then reshimmed the CBR's fork internals. Now I should have gotten the Traxxion Axxion valves but they won't sell them to anyone, because to many people installed them wrong, so my contact sent me some shims that basically acted like a shim preload and gives the forks that same feel with the stock valves as the Axxion valves upto and just over the 90% pushed range as per an AMA pro rider. I figured his 90% was probablly my 115% (atleast) and more than fine for a street rider like me. So th rebuilt and dialed in forks pronptly saved my behind when at a VFR ralley a few days later when I was in a group going at a clip not reccomended by the local fuzz [cough] and the nice smooth raod ended and a rough one stated without warning. The front wheel just stuck to the road and saved me from saying hi to the trees. And with the Penske in the back, not only do I have a lot of buttons to play with but I gained about 10-20% in cornering speed.
Its funny because I got into suspension when I got my '98 2000, and then carried my knowledge to motorcycles, and learned more, and am now appling that back to my 5500. Funny how things come full circle.
2. The rear swingarm is linear, and I don't know enough to figure out the linkage thing but I don't think it is completely linear. But, your right other than lighter forces it shouldn't really be that different than anything else they that is out there. But really, I bet they have never gotten a shock going in a Noleen or Girvin fork before. It's just so odd ball that it's bound to make them scratch their head for a minute. But to figure out how to properly set the dampening they do need to know how it the linkgae affectes the shock. They'll need to back way off on the rebound, and some on the compression.
I was going over the bars it seemed like every other mile until I sat and thought about my settings. I hope this was interesting. ;)
Rich
-
very interestin to me!.I used to ride motorbikes(I think there is a lot of crossover actually,i bet a higher proportion of mountain bikers(not sure about roadies) are motorcyclists.My last few bikes were completely different,A Ductai 900(suspension didnt move until 140 km hr was reached),BMW K100RS,(the opposite),but the suspension and shaft drive gave incredible traction ,if not the best control,and last bike was a Yamaha FZ 750,had very well sorted suspension when i bought it,it had been a production race bike in an earlier life.I rode a VFR 750 a few times after that,very capable feeling bike.I am actually considering another motorbike,cos my commute to work is a bit expensive in my other"project/hobby" a bmw 535.Is your VF a carb or FI model?.I tend to be a "momentum type rider,dont use the brakes or throttle very hard ,seem to carry more corner speed than most ,A Vf is a model I am considering,also a BMW twin.I dont think a GS but maybe an S or ST
Paul
(maybe we should start another thread!)
-
My VFR is carbed. You don't get FI until the '98 Honda VFR and Suzuki GSX-R750 (well the RC45 as well, but those were $25k limited production bikes). The torque, wieght, and setup of the VFR work better with momentum riders than the point and shoot types. But, when you can get the rear end to slide around it is lots of fun. The VFRs have a big rep for being a do everything well bike. I have always used mine as my main vehicle until I got home to the winters of Maine. But in the summer my Jeep gets little use. I have used for everything but a track day. 2up touring, 2up hauling ass, commuting, riding across the country, ect. But there are guys who use them on the track and surprise the crap out of everyone. I love my VFR, can you tell. ;) I have a VF500F Interceptor that I am turning into a track bike to.
Later.