Rear suspension upgrade!!!

Started by treedragon, October 02, 2012, 05:50:33 AM

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treedragon

Well I figured it about time I posted a little more detail around the current goings on only this time it is suspension orientated.........

As some will remember I experimented with dropping the bike down the forks a little, around 35-36mm as a final choice, until I found the sweet spot that gave superb straight line stability and withstood any abuse in the corners while remaining featherlight to steer, (and this in relation to the standard setup).

So my attention of late has been to the rear suspension and the new YSS rear shock I put in some 56000k ago, (my my do the k's/miles pass quickly :-) very nice but the spring choice was a bit on the hard side particularly as I have evolved somewhat slimmer and lighter of late. As it happens a Marzocchi out of a Paso became available and was duly reconditioned, fully adjustable with a big "BUT" - it is around 35mm longer. This hoists the rear in the air somewhat when fitted.

Initial feel was that of - "not as nice as the other" but I did rather like the effortless bump handling, smoooooth.
Rake is somewhere in the vicinity of 23-24 degrees which is supposedly around the ideal on modern bikes, and trail ------ well it measured just a tad on the short side but.......... well I did rather like the smoooooth suspension.  So as it happened it was a ride coming up with the Ducati boys, ie: plenty of backup if it turned to all 9 shades of mouldy custard........ I did it.

I discovered the bike went around corners rather nicely when pushed with no propensity towards tossing me into the weeds, a bonus one might say, and I LOVED the extra clearance as for once I didn't try to take the ends out of my boots. About 150k into the trip there were these long straights, relatively un-policed that begged to be tested particularly in light of the new exhaust and it was there I might have found a weak point in the current high-assed arrangement (although the very mean rear quarter winds might have played a part).

Coming up 170kph there was this interesting flag waving effect, fishtailing with a vengence if speed be allowed to increase, controllable, just, (if the throttle wasn't opened any more), and that brought to mind the debateable lack of aforementioned trail...............

Usually one expects that a steeper steering angle equates to quicker steering but not so in this case, a bit more effort was required and hoovering into corners decidedly preferred more power to the ground. Funnily enough downhill was particularly nice and that was a touch unexpected. An interesting point was one particular bump/pothole I performed through with a Ducati 1198 Corse up my rear and the XZ just blinked a bit while the 1198 had to bitch about it according to it's owner......

Currently my thoughts are to move the front mount point for the shock forward as I have the shock without spending any more folding green, (an important aspect as an Ohlin's unit is not quite on the radar at the moment), I can just about make up the 35mm difference and still retain a degree of extra height over my current setup thus helping keep the integrity of my boots.



PS: got all the bits sorted to start on the Weber carb conversion, it's off a Paso as it happens :-) :-)
There is always a way

Rikugun

Is the shock's stroke greater or is it just physically longer? I'm wondering if re-establishing the original ride height by moving the top mount will have negative ramifications if/when the suspension bottoms out? Will anything rub that's not supposed to?

It is far better to grasp the universe as it really is then to persist in delusion, however satisfying or reassuring.  Carl Sagan

treedragon

Just physically longer, and can be moved forward without hassle, many will have done similar before I am sure.

I find it interesting how the bike seems happy within a wide range of rake and trail. I was expecting quicker steering rather than what I got which was a bit heavier and a tendency to go a little wide unless the power was on.

While sitting pondering, coffee in hand, I could see that with the rear end up so high it is a viable thing to tuck the radiator under the rear........... now there is a thought  ;D
There is always a way

Rikugun

QuoteI find it interesting how the bike seems happy within a wide range of rake and trail. I was expecting quicker steering rather than what I got which was a bit heavier and a tendency to go a little wide unless the power was on.

That is an interesting and a bit unexpected observation. Did you try taking your hands off the bars and see what happens? For that matter, have you done this with your prior setup and if so what was the outcome? Does the dreaded handlebar oscillation set in?
It is far better to grasp the universe as it really is then to persist in delusion, however satisfying or reassuring.  Carl Sagan

treedragon

No oscillation. Making sure the wheels are properly balanced is the trick with that.

Previous setup, hands off no worries and eventually I tried and found I could ride even tight corners with just one hand lightly on the bars. I haven't been game to try that with this set up  :o ;D  ;D  ;D

The interesting thing about the fishtail effect at speed is how steady the bars and front wheel is, just the rest of the bike doing it's bum waggle. I do have suspicions about the rear aerodynamics of the tail at speed with rear quarter winds.
There is always a way

Rick G

Some time in 2005 , I had occasion to ride back  from my work , at that time, and needed to get my son back with me . We were on the XZ and went up I-40(speed limit 75 mph), two up, from Beale st. to  Stockton hill road, a  distance of 2 miles up hill . I was 268 lbs  at that time and Bill was about 280 lbs. I proceeded up the hill, WFO  and topped off at an indicated 93 at the top of the hill. Due to the over load condition  she wagged her tail all the way up the hill. My son was alarmed , but since the Bum waggle was not severe , I was not concerned. Its the only time  I have ever had a XZ do this.
Rick G
Go soothingly on the grease mud, as there in lurks the skid demon
'82.5 Yamaha XZ550 RJ  Vision,
'90 Suzuki VX800, 1990 Suzuki DR350.
'74  XL350   Honda , 77 XL350 Honda, 78 XL350 Honda, '82 XT 200 Yamaha, '67 Yamaha YG1TK, 80cc trail bike

fret not

Aerodynamics could certainly be a cause of instability at speed, especially with your tail higher in the air.  I wonder how you will get along in better weather (no cross wind).  You have probably taken care of any looseness in the swing arm, but it wouldn't hurt to check again if the wheel can be pushed side to side at all.
Retired, on the downhill slide. . . . . . . . still feels like going uphill!

treedragon

I happened to have the seat off the bike while I had a partoff saw nearby........... dangerous  :o  ::)

Decided to cut off the whole upper rear shock mount / cross piece, carefully of course, moved it forward a bit and re-glued with a dose of the good old lightening in a cable.

I now have just a little more ride height than my preferred setup and pretty much the same magic geometry I had arrived at previously......... that is if my hooning around the roundabouts etc is anything to go by  ;D  ;D  ;D  ;D

........... not to mention the very nice suspension of the Marzocchi. Today was a good day.

 
There is always a way

Rikugun

You have a way with words my friend  :D  "re-glued with a dose of the good old lightening in a cable"!? electric welder I'm a guessin'?  Glad it's working out as you hoped.  :D
It is far better to grasp the universe as it really is then to persist in delusion, however satisfying or reassuring.  Carl Sagan