what difference does the rear hoop make to the chassis/suspension? if i order a new one from motowheels or S&P or someplace, is it going to add adjustability? i am really looking for a way to add a few inches to the rear, but i am worried just unscrewing the heim joints on my oem hoop will reduce the strength of the connection (that's not a technical term, obviously). [laugh]
The one from MotoWheels add 10-20 mm, which is quite a lot if you don't also want to raise the front.
the oem hoop actually has a LOT of adjustability. as long as the length of heim joint that is still in the hoop is the same or greater than the width of the threads, you will not be sacrificing any strength. and when you adjust, remember that the amount you adjust it at the heim will result in roughly 4 times the amount at the wheel. so if you adjust it 1/4inch at the heim it will raise the wheel 1 full inch. or more.
I just want to mention that there's only so much adjusting that you can do before you really screw up the suspension geometry. When I got my monster, the PO had a Showa rear shock with a remote reservoir (I think from an 888 or something), and had also installed a 1" spacer to hoop mounts (just a M/F standoff spacer that threaded into the hoop, and the ball joint end link screwed into the spacer).
The shock was ruined from this modification. It started leaking oil all over the place from the bottom, and the problem became evident after I removed and disassembled the shock. The rod on the shock had been bent from the misalignment caused by the modified suspension geometry. It would not have been possible to install the shock with the adjustment spacer installed, but it was possible to force the spacers in with the shock installed by pulling down on the swingarm because you had so much leverage.
There is room for adjustment without damaging the shock, but there is a limit. I would suggest that if you want to make a dramatic change in the length of the hoop, the safest way to go would be to disconnect the bottom of the shock, change the length, and then reconnect the bottom of the shock. If you've changed it too much, then I don't think that you'll be able to reconnect the bottom of the shock.
thanks very much for the info! [thumbsup] i may look into the motowheels hoop. i will discuss all of this with the guys at ECS as well, as they just installed a new penske shock for me. i am also still planning a gsxr fork swap, and that will add a bit of height to the front, so i think a raised rear should be done anyway...
anyone think of any other benefits to the aftermarket hoop?
Quote from: bond0087 on August 18, 2012, 11:28:05 AM
I just want to mention that there's only so much adjusting that you can do before you really screw up the suspension geometry. When I got my monster, the PO had a Showa rear shock with a remote reservoir (I think from an 888 or something), and had also installed a 1" spacer to hoop mounts (just a M/F standoff spacer that threaded into the hoop, and the ball joint end link screwed into the spacer).
The shock was ruined from this modification. It started leaking oil all over the place from the bottom, and the problem became evident after I removed and disassembled the shock. The rod on the shock had been bent from the misalignment caused by the modified suspension geometry. It would not have been possible to install the shock with the adjustment spacer installed, but it was possible to force the spacers in with the shock installed by pulling down on the swingarm because you had so much leverage.
There is room for adjustment without damaging the shock, but there is a limit. I would suggest that if you want to make a dramatic change in the length of the hoop, the safest way to go would be to disconnect the bottom of the shock, change the length, and then reconnect the bottom of the shock. If you've changed it too much, then I don't think that you'll be able to reconnect the bottom of the shock.
how could it damage the shock? the shock just floats between the rocker and the swingarm. lots of 851/888 owners fit the extensions. if you can't get the shock in then something must be physically hitting on something else. is the swingarm sitting on the cases underneath the swingarm?
the amount winding out the adjusters lifts the rear is reduced by the fact the shock is mounted to the swingarm, so dropping the swingarm moves the bottom of the shock down too, probably at a 50% ratio (distance of shock lower mount and pushrod mount from swingarm pivot). so winding the adjusters out 10mm might give you effective 5mm at the hoop distance from the swingarm pivot. which gives you more at the axle obviously, due to the length ratio. but i don't think it'd be 4:1. i think from my playing with my 851 it's much closer to 1:1. i forget now.
i measured a m900 here. shock lower mount is 90mm from swingarm pivot, hoop rose joints 240mm from swingarm pivot and axle 500mm from swingarm pivot.
rocker is 110mm on hoop side and 65mm on shock side, giving 0.6:1 ratio there.
if you add 10mm to the hoop side, the shock lower mount drops 3.75mm. the shock top mount on the rocker will drop by the same amount, which means the hoop side of the rocker goes up 6.25mm, giving you 3.75mm effective extension of the hoop.
which is 7.8mm at the axle. an effective ratio of 0.78:1
although the geometry is making my head hurt, i'm sure it's not that simple.
i realised i was thinking about it wrong, i should have been starting at the axle.
so, if you want to raise the back 25mm (1" nearabouts) at the axle, you effectively lower the axle 25mm. which lowers the hoop rose joints 12mm. it also lowers the shock lower mount 4.5mm. lowering the lower shock mount lowers the front of the rocker 4.5mm, raising the rear of the rocker 7.6mm.
meaning the hoop needs to be 12 + 7.6mm longer, 19.6mm. so the ratio at the rear axle for a given hoop change is 25/19.6 = 1.28.
i'm happy with that. anyone see any errors?
Quote from: brad black on August 18, 2012, 11:58:58 PM
how could it damage the shock? the shock just floats between the rocker and the swingarm. lots of 851/888 owners fit the extensions. if you can't get the shock in then something must be physically hitting on something else. is the swingarm sitting on the cases underneath the swingarm?
the amount winding out the adjusters lifts the rear is reduced by the fact the shock is mounted to the swingarm, so dropping the swingarm moves the bottom of the shock down too, probably at a 50% ratio (distance of shock lower mount and pushrod mount from swingarm pivot). so winding the adjusters out 10mm might give you effective 5mm at the hoop distance from the swingarm pivot. which gives you more at the axle obviously, due to the length ratio. but i don't think it'd be 4:1. i think from my playing with my 851 it's much closer to 1:1. i forget now.
I may be totally wrong here, but I'm going to look more closely at it and post what I find either way, along with a picture of the bent shock rod (it was bent right where it threads into the bottom rod end).
Here's all that I know for sure:
It had an aftermarket Showa shock on it that should have been compatible
It had extensions on the rear hoop
It leaked from the bottom of the shock shortly after I bought it
When I tried to reconnect the damaged shock (long story on why), no matter what angle that I moved the swingarm to, there was never a point where the shock lined up properly, but when I disconnected the hoop it was easy to align it.
The rod in the shock was significantly bent
The rest was just an educated guess. It could be the alignment issues when I tried to reassemble were solely due to the bent shock, and the shock got bent some other way (although I can't think of many ways how). My guess was that the shock could only pivot so many degrees relative to the frame or swingarm without contact with something, and the modified geometry pushed it out of that bound when the suspension was fully compressed. That's just a guess, though, so like I said, I'll look into it more.
Quote from: brad black on August 19, 2012, 07:05:41 PM
~~~SNIP~~~
lowering the lower shock mount lowers the front of the rocker 4.5mm, raising the rear of
the rocker 7.6mm
~~~SNIP~~~
Due to the angular geometry of the rocker, I guesstimated and calculated that the 7.6 should be more like 11.
That'd give you 23 at the hoop for 25 at the axle... more like the 1:1 you recalled from your 851.
I've got to grease the joints on M750 hoop, perfect timing to check.
Quote from: Speeddog on August 20, 2012, 08:55:56 AM
Due to the angular geometry of the rocker, I guesstimated and calculated that the 7.6 should be more like 11.
How so?
Just measured, 25mm at the wheel is 21mm at the hoop attachment to the swingarm.
That's with the heim joints screwed nearly all the way in (bike low).
Cool.
25mm at the axle is about 1 degree steering head angle change.