KZ400: upgrade front suspension

I haven't been able to find any Progressive springs to put in my KZ400 f orks. Are there any other upgrades available?

What fork performance issues are you trying to correct with Progressive springs, and have you measured the existing springs to see if they are within spec?

Fork performance can be tuned quite a bit through the use of the proper type, weight, and amount of fork oil. When is the last time you changed your fork oil, and what fork oil did you put in? How did you measure the fork oil you put in? Ed

I had my fork seals done at a local reputable shop a few years ago. I think they used 15 wt? Spec amount. I'd like to stiffen them up a bit. 20k+ miles on the original springs.

That's very low mileage on the original springs. I suggest you change the fork oil since it should be done at least every 2 years. Do one fork leg at a time so the forks don't collapse down. Use the instructions in the Kawasaki Service Manual to ensure you measure the correct amount. You can tune the stiffness by adjusting the fork oil weight. Bel Ray sells 7 weights of fork oil ranging from super-light 2.5W all the way up to 30W (see link below). Different weights of their fork oils can be mixed, so you can make any weight in between 2.5-30w. I've been using Bel Ray 15w fork oil since my 1977 KZ650 was new and have never had any fork problems. Ed

www.belray.com/bel-ray-high-performance-fork-oil

I didn't see anything for a KZ400 or CB/CM400, thinking the Honda forks would be similar. Progressive springs are available for the KZ550, but I have no idea if they'd be appropriate for your bike. I would compare the specs on a 550A to your bike. I think Progressive springs are typically shorter than stock & require an extra spacer. or remove the stock spacer & install a longer spacer to make up the difference.

stock springs. you might could install extra spacers or longer spacers to increase the pre-load. or some guys cut the stock springs & install spacers to make up the difference. This may not be the greatest solution, but it is an option, and some say it does work.

There were much discussions about springs in the old KZ400 forums. IIRC after some research Progressive said that Suzuki GS550 springs work for the KZ400/440. Luckily I saved this off. I have not bought either of these myself so I cannot confirm.

Progressive springs for KZ400
Dennis Kirk Part #: 58325
Manufacturer Part #: 11-1115
www.denniskirk.com/progressive-suspensio...p58973.prd/58325.sku

#11-1109 is the part number recommended for KZ440. Same dimensions as other but with a little stiffer spring.

You could go with 11-1115 for a little lighter spring and 11-1109 for a little stiffer.

diggerdanh wrote:

There were much discussions about springs in the old KZ400 forums. IIRC after some research Progressive said that Suzuki GS550 springs work for the KZ400/440. Luckily I saved this off. I have not bought either of these myself so I cannot confirm.

Progressive springs for KZ400
Dennis Kirk Part #: 58325
Manufacturer Part #: 11-1115
www.denniskirk.com/progressive-suspensio...p58973.prd/58325.sku

#11-1109 is the part number recommended for KZ440. Same dimensions as other but with a little stiffer spring.

You could go with 11-1115 for a little lighter spring and 11-1109 for a little stiffer.

Are you sure those springs are suitable for a KZ400? On Kirk's website they don't talk about this bike

Will the 11-1115 model be stiffer than the stock springs? I'm looking for more stiffness but I don't want a strut either.

Feanor_twh wrote:

Are you sure those springs are suitable for a KZ400? On Kirk's website they don't talk about this bike
 

You replied to a message that was posted in August 2016; some things may have changed since then.

Nerdy wrote:

Feanor_twh wrote:

Are you sure those springs are suitable for a KZ400? On Kirk's website they don't talk about this bike

 

You replied to a message that was posted in August 2016; some things may have changed since then.

The web link (DennisKirk) is still working and specifically the item mentioned is still available for sale. What are you talking about?

You replied to a very old post to ask questions to someone (diggerdanh) who hasn't logged in since September 2019.

You are very unlikely to get answers because of that, so you will need to rely on what was posted or figure out another option.

As diggerdanh mentioned, those springs - which are intended for the GS550 - should also work in the KZ400/440. The DennisKirk link mentions the GS550; the DK link will not mention the KZ400/440 because the springs were not intended for those bikes by the manufacturer.

You have to decide if you trust the information from 2016 because - unless someone else can confirm - no new information is likely to appear in the thread. That's what I am talking about.

Ok, thanks for the clarification. I see that you had a KZ400 and still have a 440. What do you think?

Apparently the GS550 weighs 215kg, maybe not a good reference

Useful links (for future reference):

www.dotheton.com/index.php?threads/progr...00.65674/post-752766
www.kzrider.com/forum/5-chassis/599460-k...mods?start=12#688597

You're very welcome. Sorry, I should have been more clear with the initial answer.

In my case, I'm thinking about the stiffer springs. They came from a heavier bike and I am a heavier person these days so it should work out. (I should work out, too... )

If you are a less-heavy person and you do not ride with a passenger, the 11-1115 springs might be better. You can also change the weight of the fork oil that you use and experiment until you get the ride quality that you want. Unfortunately I don't know how the lighter Progressive springs compare to the stock springs.