HELP Please with rear shocks

Gday

I am rebuilding my KZ900 need some advice on rear shocks. am going to buy some new rear shocks this week YSS the standard length is 350mm. The plan is to use something like a JMC swingarm and 150 - 160 tyre on drum rims ( i know i will need new rims ) i see many bikes move the top suspension bracket to create a greater rake and possibly a longer shockie. Should i consider buying a longer like 360 or 380 length? shock and either move the top bracket? or shock mount further back is their any advantage?

this one has been moved don't know what shock length

www.z1ownersclub.co.uk/forum/viewtopic.p...torder=asc&start=105

what you guys think

HHHHHHHEEEEEEEEEELLLLLLLLLPPPPPPPPP :silly:

If you lay down the shocks they will be regressive in their action, as in softer the longer they compress. And wheel travel will be greater, so you must make sure you have enough clearance so the wheel won't hit the fender under full compression.

Personally, unless you are willing to experiment with spring rates and shock lengths, I'd stick with the stock geometry.

you will not know the length imo until you choose the swingarm and tire profile...but in general 13.5 inches is gonna be okay....are you wanting shocks now and more build later...

your asking a question that with pics of what you have and pics of the swingarm ...maybe folks could help with ideas but help id relative and everyone wants different ride settings

front end on that bike is set dif from stock and this is just as important when choosing rear settings

pictures of your bike now would help

the moving of the shocks top mount was to improve rebound and other handling issues with the original superbikes and limited shocks of the era

faffi/triangleladuna

thanks for the replies. i take your point with shock and swing arm set up i am looking at going with www.win-pmc.com/draft/sa/mono-t1.htm i have noticed the bottom mounts are adjustable. so was thinking about a longer shock at a more aggressive angle and keep around the stock height?

i have noticed alo of builds on threads moving top mount and wondering if they are using same size shock longer or shorter and if their was any benefits? Here is one along the same context but im doing with less coin. I need to replace the shocks i have and thought if i buy 13.5inch or 350mm over here i dont want to double back later. This is what led me to look at other projects and notice that they move the mounts around. I will be getting some YSS shockies for rear

www.z1ownersclub.co.uk/forum/viewtopic.p...468a246cdb16c203587e

im thinking PMC swingarm drum hubs wider wheel rims 150 -160 tyres
www.win-pmc.com/draft/sa/mono-t1.htm
so what do you think should i get longer shocks say 360mm and move the rear mounts on the swing arm back for a more aggressive angle what ya think

thanks for the responses

What is important to you, looks or performance? And what type of performance do you want, handling or comfort? Well, you since you're going to use a longer swingarm handling isn't your main concern anyway, but softer shocks will let the bike hunker down more under acceleration, reducing the tendency to wheelie.

Anyway, 10 mm to and fro hardly matter and will make even less of a difference if you lay down the shocks. Just remember that they get softer as you lay them down. Also, the longer swingarm will - if the shocks sit in the stock position, increase leverage, again making the suspension softer. You really should decide the angle you want to use and measure how long the shock must be. Then you must calculate the correct spring for that position and angle, taking into consideration your weight, the bike's weight, the shock angle and the distance from the lower shock mount to the rear axle. Even the weight of the wheel will impact suspenion.

If you're happy just to trundle along, the stock spring rates - regardless of shock length - will offer a compliant ride. The more you angle them down, the more compliant the ride.

moving the bottom of the shocks toward the back of the bike will make them stiffer.

is it easier to cut a wire with the tips of the wire cutters or is it easier to cut the wire when the wire is all the way back in the jaws?

they move the tops forward to creat a more progressive suspension.

if you buy yss shocks you can always have custom ends(the ones on the bottom that screw on)made to increase the length.

my advice would be to ride it with the shocks in the stock locations for awhile and decide if you think you need something changed.

let us know what you decide.

leon

If you say what I think uou say, 531, I think you are incorrect. If you think in extremes, having the shock absolutely vertical will mean that for one inch of wheel travel, the shock will have to compress one inch. Now lay the shock down virtually horizontal and the shock will barely move as the rear wheel moves up and down. Since the wheel can move a lot without having to force the shock much, action will be softer.

The reason they laid down the shocks in the old days was to get more wheel travel in an era when shock travel was limited. Also, having a shock moving less than the wheel helped the limited oil supply stay cooler longer, allowing them to race longer before damper fade made the bikes pogo like crazy. Still, the action is regressive, not progressive with this arrangement. You CAN get progressive action with twin shocks, but it's not used much.

faffi,
when "you" say laydown do you mean move the top or bottom?

leon

The angle is important here since it alters the leverage ratio as the swingarm/rear wheel moves. Once you lay down the shock somewhat from vertical, the more you compress the shock, the softer its action will become since it will actually lay down more and more. And the more it is angled to begin with, the more the leverage will change during the wheel's travel.

Now, if you move the shock back, it will become stiffer since you will get less leverage. As such, the same shock fitted with the same angle will be stiffer the further back it sits. In other words, moving the lower attachment back will give you a stiffer ride than moving the upper attachment forwards.

I haven't thought about this until now, but there may be some angles combined with some rearward shifting of the lower shock mount that can actually give a stiffer ride, at least initially. My math is not good enough to calculate that. But you do have a point. What will not change, though, is that the more laid down position will make the shock act softer and softer as it's compressed.

If the bottom of the shock is closer to the axle you lose mechanical advantage, or leverage. So 1" of travelon the wheel is 1" of shock compression. Move the bottom forward and that same wheel travel might equal 1/2" of shock comp.

If the shocks are serviceable you can always shorten themwith limiters.

here is a good (old)article.

davestestsandarticles.weebly.com/uploads...stoct77susbasics.pdf

hth,

leon