Understanding rear spring rates

[BCtiger]

Having read so many posts of rear shocks & springs I am not closer to understanding how the rates are calculated. If a shock rated from 70kg to 95kg what does this mean ? Does mean rider alone or rider, pillion & luggage would not perform well over 95kg ? Or is it calculated with rider in that weight range with some extra weight over the rate spread ? With gear on I am about 85kg or 190 lbs. Traveling with a pillion & luggage puts us at 160kg. Clearly the stock spring is not up to it the task, even with the preload cranked right up.  Does anyone know what the factory spring rate for the rear shock on an 06 is ?
Also, if I went with a non remote adjuster on a new spring/shock would I be able to adjust the preload locking rings with a spanner with the bike on the centre stand ? Looks pretty tight under there, probably skinned knuckles, dirt, grime etc. I understand the preference for a remote, it just all adds up. $'s.
Thanks

[cba191]

Talk to Ted at http://wilbersamerica.com
When I ordered, he asked questions for about 30 minutes about gear, luggage, and things I didn't even think about. All while taking the order to make sure that I got the right shock.  Now, if I could just get the old one off, I'd be golden.

[Chris Canning]

In the 14 years of the net one of the quirks is how North Americans like to understand how things works when a little knowledge is more dangerous than non at all  .

I see you ask about spring rates and yet mention nothing about internal valving and yet the one means nothing without the other!!

If you buy Wilbers their whole marketing strategy is based on the need not to know you give then you honest weight and riding style and they make you a shock,Ohlins is slightly different if you don't ask you'll get a shock with a stock spring and find out the hard way.

All of the above is a minor detail because everyone is different,I have had a shock rebuilt(twice) by the same person who was insistant that's what I needed and it wasn't!!!,in the end I went else where and said this is what I want never mind what you think I want,my problem I run a monster spring the biggest Ohlins do for my shock the internals do not like dealing with it hence why the photo I posted is current and it's being rebuilt(again),I have mine so I use what?? maybe 3" of travel under normal circumstances and the rest in emergencies at either hi speed or major whoops in the road and it's fantastic even now chuckle at the thought of the Multistrada rider trying to hang on to us going to Mugello in 2012 

Re the stock shock it's a compromise it's got to be all things to all people and built as cheaply as possible for the factory,when you go for a custom after market shock it's focused on you,the problem being that the chances are you won't suite the other 95% that the stock one does because it's not particularly good at doing anything apart from being very average to poor.

If you focus just on spring rate and nothing else it's not about just looking at the figures suspension isn't an exact science,so if you go it alone like I have with my Ohlins you pick a starting point( spring wise) and take it from there but in reality as I said earlier the spring is only half the job go out side of that middle of the road spring and you'll need the valving to go with hence why Wilbers have made such inroads into the market because they take the confusion(ish) out of the situation,and why at times I have though of having one made but won't make the mistake I've made before of having someone tell me what I want and then finding out it isn't 

[cba191]

Exactly. He didn't ask me any technical questions. Just a lot of specific questions about how I'm going to use it. How much do I weigh?  How much gear? Passenger?  Will it ever go off road?  What kind of luggage do I have. How tall am I. A million questions that taken as a whole, make all the techie things irrelevant to me... Hopefully.

[akendall1966]

OPs question was about spring rate. Spring rate is the force required to compress the spring a given displacement. So you have to know what that displacement is. Its probably kg/mm.  So for every additional kg of force applied to the spring it compresses a fraction of a mm. So it is not directly related to rider weight. The rear of the bike is a series of levers so without knowing the geometry of these levers you cannot relate loading to the rate of spring required to hold the bike at the correct point in the suspension travel.

When you have 2 numbers like 75/95kg it means its progressive. The spring is made so after a certain amount of compression the rate increases from the lower to higher rate. Shock linkages also create a progressive action I.e. the amount of the leverage changes through its motion effectively changing the ratio between load and spring rate. Giving the same effect as a progressive spring.

As Chris points out changing the spring rate will likely mean the damping is off by more than you can adjust it.  Not a tribal task to address.

[Chris Canning]

The reality!! trying to work out spring rate  it's pointless it's what works for you and you'll never find that in a book,I wish you could I'd be richer but going to the likes of Wilbers and being honest with your info is as short a cut as you'll get.

Doing it my way  I've learned at lot but am I any better off than going to the above  hmmm

[JTT]

akendall pretty much summed it up.  Spring rate is determined by a bunch of factors.  the damping is determined by the valving within the shock.  These are definitely, and closely related.  Make a large chance in spring rate, without corresponding valving, and you'll have an unhappy situation.'

Taken to the extremes, imagine the damping required within a shock for a particular spring rate.  Now, increase that rate, lets say double.  The forces are MUCH more extreme on damping, particularly on rebound (trying to control all that energy).  The inverse is also true, put a very light spring on and you'll have a shock that is equally unpleasant.  It will be squat, and very slow to respond, as the spring will struggle to rebound the damping.

The interesting part is that spring rate is also travel sensitive, meaning the deeper into the travel the greater the force needed to move the suspension.  As a result of this, sometime, putting a stiffer spring on, actually results in a softer, more responsive ride.  Alternatively, valving is speed sensitive.  It doesn't know where it is in the travel (unless your talking KTM PDS crap), all it is concerned with is the speed at which the piston is being moved up and down inside the shock.  It resists this movement with valving, hence the term "damping".  Without this the shock would be like a rubber ball.

[BCtiger]

Thank you all, I appreciate the in depth replies.
Yes, I like to know & understand how things work, especially if I am going to drop a lot of coin for a tailored package. I get that it needs to be both the spring rate & shock valving working together.
I should have asked more directly, this was in large part about controlling the ride height, one of my concerns when I ride with pillion & luggage. The front end gets pretty light unless I keep the tank topped up. I have read numerous posts where heavier duty spring & matching shock combo were used, but then recently stumbled upon this blog. Neil's Bike Page written in 2010, he had purchased a Hyperpro 460-3D emulsion shock w/o the remote preload, but a "height adjust" option instead.  Anyone else done this and can comment on it ?
Thanks again.

[Chris Canning]

You don't really need a ride height adjuster you just drop the forks through the yokes,your needing to keep the tank topped up because you have too much weight on the back be it your weight or the crap shock,but your question about spring rate and valving will be lost on the guy you speak to on the phone,you give your honest details the guys in Germany will crunch the numbers.

Don't get too complicated it'll do you no good,I could put a copy of my Ohlins internals and how the stack system(they don't actually have valves) has been changed to deal with the spring but that brings us back to my first 4 words!!

[JTT]

Chris makes very good points.  No need to over complicate if you don't need to.  That said, if the guy at the supplier doesn't understand the relationship between spring rates and valving, I'd politely pass. 

Height adjustment is used to affect the "attitude" of the bike, not generally to compensate for load.  That is the job of the spring.  If you want to gain ground clearance and load the front end more, raising the shock length can help here.  Far easier and cheaper solution would be to lower the forks as Chris suggested to get a similar effect, only decreasing ground clearance.

I'd suggest your issues are due to a sacked out, or "too light" of a rear spring.  But, as has been mentioned earlier, simply installing a heavier spring can overwhelm the existing damping, particularly as oil and shims stack will no doubt also be tired. 

Valving is the commonly used terminology for the ported piston and stack of flexible shims (washers) on the end of the shock shaft that controls the flow of oil on compression and rebound.  You can see this on the simple diagram posted previously.

[BCtiger]

Took a chance and purchased a used Hyperpro that was offered on ebay. Came off a 06 tiger that suffered front end damage. I made an offer that seller accepted, I really couldn't afford to shell out for a new set up. That all said, it sure is great to feel the bike poised in the corners and to have much better road feel. Still playing around with the settings but so far so good. I did contact Hyperpro before purchasing to ask for the spring rating which was marked on the kit and it fits my weight category. We'll see how it pans out down the road, after all, its a used kit but the price was right.
One item not shipped were the 2 aluminum sleeves Hyperpro provides replacing the steel sleeve, unfortunately the seller had already sold the swing arm. Temporarily I have used a thick plastic bushing that fits, not wanting to cut up my factory sleeve just yet. My question is, does anybody think a nylon or similar type material for sleeve would be a compromise to the set up for the fixing bolt. Worst case scenario is to cut my steel one to size or contact Hyperpro and see if they still carry the sleeves for that swing arm.
As far as the removal & install, it went surprising well as per the manual. I was dreading the sleeve removal, but it just tapped out easily. Pulling the shock out gave me some grief, but what would a DYI project be without some sort of problem. Appreciate any feed back on the sleeve.
Suns shining in Victoria today, the road beckons.

[Mustang]

If you know what you need draw it up and visit your friendly neighborhood machinist and get one made

[BCtiger]

Yes, that is possible, something I considered after posting and may very well be what I do in the end.
Thanks for the reminder.

[Bixxer Bob]

...Pulling the shock out gave me some grief, but what would a DYI project be without some sort of problem.....

You are not alone there my friend ....