Suspension Question (rear spring rate)

[Shaun Chandler]

Hi all

I had a question that I hoped somebody would have a good answer for. Suspension can be a abit complicated I know. I picked up a new set of progressive shocks for my xs400 off a guy for 50 bucks in the box still. Mine were shot (no dampening left).

Now they came off a larger bike but the eye to eye was correct so I thought what the hell worst comes to worst I can sell them later. I did a mock up of my bike a couple weeks ago and they are way to stiff I can't even really compress them. I'm not a big guy (160 on a good day).

The manual for my 78 shows a spring rate(actually two)

1.7 kg/mm
and
2.1 kg/mm

I've been trying to get my head around spring rate but I'm having trouble figuring out why there are two spring rates. My thought is that it has to do with 1 spring by itself then adding another spring in on the opposite side changes the spring rate. But I'm not clear.

If someone could give me a springs for dummies explanation I would appreciate it. I want to find a new set of lighter ones but don't want to just trial and error it (that gets expensive)

Shaun

 

[drewpy]

Hi Shaun,

If you check the figures the first 0 -55mm of travel is 1.7kg. then from 55 -80 its 2.17.

this know as progressive spring rate.

basically the springs are manufactuered with a section of tighter curled springs in there (25mm long at a guess) these are your 2.10 kg springs, then the coils open out with more gaps which are your lighter rated spring. these soak up the little bumps so when they coil bind, the stronger rated springs take over.

hope that explains it!

 

[bcware]

Do the shocks have an adjustable base? Often people leave it on the setting they come on, which is usually as loose as they go. Perhaps they were tightened though. Depending on your riding style it might not affect you too much.

If you ride very fast on real-world roads an overly stiff shock won't respond well to many surface imperfections. Realistically, however, only the comfort is going to be an issue. At least you know you won't be over-loading the rear for touring or bottoming out on bumps any time soon

 

[Shaun Chandler]

Hey Guys

Yes that does help to explain Drewpy. My problem is when buying progressive springs they only seem to quote one value such as 1.7kg / mm. So any idea what weight spring I should pickup that would closely match what the stock ones were. I didn't know the stocks were a progressive spring. It's to bad cause my new springs are powder coated black which I like. Thanks for the info I was looking at those figures wondering what they were saying.

Bc- Ya they are adjustable. Like I said I got them new in the box so they came with the wrench. I adjusted them to as loose as they would go but they were made for a Harley. This ain't no Harley. Your right though it sure won't bottom out. I did hard labour for about 15 years before getting into teaching though so my back won't do well with these heavy springs.

Shaun

 

[XSLeo]

Call Michael Morse at 650central. He has raced vintage bikes, mostly the XS650 but he sell progressive shocks and builds them to suit your bike and weight. He can hook you up with the springs you need.
Need to call him, 209-533-4346
Leo