Progressive Suspension Upgrade for '78 KZ 650

Hey all,

In my slow, student budget fasion, I am trying to upgrade a thing at a time on my KZ, and I thought that this summer I'd go over the suspension, and make it all shiny any new. I figured that since she came with the 4 into 1 and pods, and she got a DYNA last year, the next thing that will really effect rideablity would be suspension. (If this in itself is a false premise, then chime in, but as all else is in generally good running order, I can't think of what else might get more bang for the buck in terms of upgrades...)

In any case, progressive front springs are reasonable, and I can get a new set in easily enough, with new seals, oil and such of course. But, the rear shock/spring combos are costly indeed. Now, I've read a fair deal about people swapping out their stick KZ stuff for older Harley bits. I think this could be a pretty cost effective way of going about, it, but I cringe at the though of having anything harley related getting near my Kawi. Moreover, I found of set of Progressive coil/shocks on ebay not too far from where I am, for a (so far) reasonable price.

Here is the rub: they are exactly the same in dimension as the set which progressive recommends for my bike, so I know they will fit. However, the spring rate is slightly higher than suggested. The rate on the recommended part is 75/120 lbs/in, while the ones available are 105/150 lbs/in. (They are lightly used, off of a newish VMax.)

So... all that being said, I'm really just curious if anyone figures thats gonna be enough of a difference to really ruin my day of riding. I am a pretty slim guy ~150 lbs, but I do sometimes have a passenger, and do some light touring with the bike, ie. strap on a backpack and do some day/overnight trips. So, I will occasionally have a moderate load on. I just don't want to have too stiff of a setup which will shake my old girl to death.

My initial reaction is that this won't be a big enough difference to really mess anything up, and that new suspension all round is going to improve handling and ride quality a little by comparison to the stock stuff that is currently on there. BUT, as always I am hopine there is someone out there with more experience in this that might be able to chime in, and confirm, or deny that and save me spending money on this sorta thing.

As always, thanks in advance.

Jonny

you can adjust the preload on the shocks to soften/stiffen ride ,as far as the frontend goes ive had good luck with running heavier oil versus stiffer springs

Suspension upgrades are a BIG improvement on these older KZ's.As far as the spring rates are concerned , those springs are about 50% stiffer than what is recommended for your bike/weight. A Vmax is over 600 lbs., you may be able to use your 650 springs.

I'm 250 lbs and 105/150 springs on my 750 twin beat me to death, it was like there wasn't any spring at all, like struts.

I now have Progressive fork springs with 15w oil and koni rear shocks, rides like a dream.

Well, thanks all.

So it seems like using that high of a spring rate for my application wouldn't be worth it. Nice to find a bargain on ebay, but not when it ends up being false economy.

Given the price, the progressive springs for the forks are still a good option, but I suppose I will either have to spend the big money, or keep trolling ebay for a set of rears.

Glad to have the warning tho. I'd rather not have bought something that turned my bike into a hartail.

Jonny

There are always shock springs on ebay, sometimes they are quite cheap. If you can get the shocks cheap enough you could probably find a set of springs that are closer to what you need, and sell your heavy ones. I bought a set of stock GS1000 springs for $10, I repainted them and put them on a set of Ohlins.

$10 springs.........

That may be a very good option. Nothing really wrong with the springs on my bike (except they are maybe a little tired) It is really the shocks that I thought might be wanting replacement, and as I mentioned, the ones out of the VMax are identicle shocks, with different springs on them. If the price is right when the auction gets close, it may be worth just blasting and repainting my old springs.

We'll see how it all works out.

btw - that rear looks great. I know a guy with access to an aircraft grade aluminum CNC mill. Did you do the design on that swingarm yourself? Or did someone else have a pattern for you? That would be a great mod for waaay down the road (or really, a second bike). I've always liked the look of KZ's done up as streetfighters.

thats a cal-fab swingarm

wireman wrote: thats a cal-fab swingarm

same one that i have on my bike but mine has the calfab sticker

Thanks to all for the comments, and yes, I know I am bumping and old thread, but as before I am soon returning from extended travels, and of course my thoughts are drifting towards the riding season back at home when I return.

Having taking a quick look at some other option, (Ie, Ohlins, Marzocchi's etc...) I figure they are way out of my price range, and probably a whole lot more performance oriented that I need to a very mildly modded semi-stock KZ. Progressive it is...

I am curious however, if anyone has found that there is a serious performance difference between the gas charged shock and the oil immersion shocks as rears. I have used both in automotive applications, and having worked at a parts counter for some years know the main differences, but am not particularly familiar with how they may effect motorcycle ride performance.

I figure either is going to be a pretty big improvement over the (presumably) stock shocks and springs still on my bike, and again, as a fairly light rider (~155 lbs) who infrequently rides with passengers or panniers, probably the regular duty air shocks should do. I just wanted to ask if anyone has really rave reviews for the 14 series oil shocks, and if its worth the extra cash...

Jon

Get the right springs,your bike and back will thank you.
I run 90/130 springs on some old KYB shocks,I'm 250 and bike is 600ish.

Well, thanks all for the input. At the end of the day, I found a very good price on some NIB progressive 12 series shocks with springs, and a set of progressive front fork springs. I know it nothing terribly fancy, but it should be a big improvement over the somewhat tired stock stuff currently on the bike. I still want to retain the stock look generally, and so the Progressive stuff is great in that regard. I wouldn`t rule out something like an old set of Marzocchi`s or Ohlins to rebuild down the road, but they are very, very spendy everywhere I`ve seen them.

I know this has been a bit of a string for such a small modification/replacement of parts, but as with many others here, but my budget for the bike is sadly much smaller than my imagination and desire. Every purchase has to be a smart one... Also, much of this is preparation for a pretty big road trip at the end of the summer, to go exploring the east coast of Canada. (Another thread on that already....)

Can't wait to get back home and have a pile of new parts in boxes waiting for me.

Cheers all

Jon