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TOPIC: Front Suspension

Front Suspension 02 Oct 2019 22:25 #811667

  • gordone
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Hi,
When I rebuilded my bike I replaced some parts in the fork suspension to get it good as new, so my current setup is from the top, below.
My question is pre compression of the spring, right now I have nothing installed, its only the cap fork top who is pushing the spring down...
I`m a heavy person around 140 pounds, so I was thinking maybe the driving handling is not optimal? and can be better?

Cap Fork Top
440291005

Fork Spring Kit
www.z1enterprises.com/fork-spring-kit-11-1106.html

Pipe Fork Inner
39093-1067

Cylinder Fork Gearhead
44022-1071

Oil
248 cc
1981 KZ650-D4, with 1981 z750L engine (Wiensco 810 big bore).

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www.kzrider.com/forum/11-projects/607213...sr-1981-z750l-engine

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Last edit: by gordone.

Front Suspension 03 Oct 2019 03:37 #811673

  • Warren3200gt
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what fork oil are you using Gordone? Changing the fork up to a thicker one makes a big difference and is easier and cheaper than messing with springs or spacers. Thicker oil gives slower compression, ie stiffer and slower rebound.
75 z1b, 77 z650 b1, 77 z650 b1 period custom, 77 z1000 a1, 82 z1100 elr, 89 zxr750h1, 01 zrx1100r

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Front Suspension 03 Oct 2019 04:10 #811674

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I don't know what the fill level is on that bike...but, what you can do is cheat it some with putting maybe about and inch/25mm more of oil. That will increase the air pressure inside the forks when it comes to compression. My ST1300 is a little weak on the fork springs, but the oil level is only about 65mm. Many bikes are maybe around 100-155mm. Anybody correct me if I'm wrong.

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Front Suspension 03 Oct 2019 05:11 #811675

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While sitting on the bike and not moving the ideal situation is for 25% of the fork (& shock) travel to be compressed. That leaves the other 75% of movement to absorb bumps on the road. If you have more than 25% add a spacer into the fork to lift the front end. If you have less, then your fork springs are too stiff.
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Front Suspension 03 Oct 2019 05:27 #811676

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Nessism wrote: While sitting on the bike and not moving the ideal situation is for 25% of the fork (& shock) travel to be compressed. That leaves the other 75% of movement to absorb bumps on the road. If you have more than 25% add a spacer into the fork to lift the front end. If you have less, then your fork springs are too stiff.


Thank you !
Will test these!
When it comes to the filling level shall I just follow recommend filling level from the service manual?
1981 KZ650-D4, with 1981 z750L engine (Wiensco 810 big bore).

Project:
www.kzrider.com/forum/11-projects/607213...sr-1981-z750l-engine

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Front Suspension 03 Oct 2019 06:31 #811680

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As I recall, the factory suspension was designed for a 150 pound rider, which in the U.S. is very light for male riders. Nessism is correct about setting sag befor changing anything else. Ohlins used to have a really good article on the subject on their website. I know there are others on the web.
1982 KZ1000 LTD parts donor
1981 KZ1000 LTD awaiting resurrection
2000 ZRX1100 not ridden enough
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Front Suspension 03 Oct 2019 06:40 #811681

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1982 KZ1000 LTD parts donor
1981 KZ1000 LTD awaiting resurrection
2000 ZRX1100 not ridden enough
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Front Suspension 03 Oct 2019 14:29 #811710

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140 lbs is a very light rider. Did you mean 140 kg?
I have a couple of Z1B's restored, an '80 KZ1000LTD restored, a 1981 KZ550 restored and a 2008 KLR 650 for off road fun. My wife has a 2019 Suzuki DR 650 for on and off road.

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Front Suspension 03 Oct 2019 14:45 #811714

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gordone wrote:
I`m a heavy person around 140 pounds, so I was thinking maybe the driving handling is not optimal?


A "heavy" 140 Pounds of an rider is a light weight 70 kg Person. gordone , what´s your real weight???

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Last edit: by Scirocco.

Front Suspension 03 Oct 2019 23:06 #811751

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Scirocco wrote:

gordone wrote:
I`m a heavy person around 140 pounds, so I was thinking maybe the driving handling is not optimal?


A "heavy" 140 Pounds of an rider is a light weight 70 kg Person. gordone , what´s your real weight???


My real weight is 110-115kg
1981 KZ650-D4, with 1981 z750L engine (Wiensco 810 big bore).

Project:
www.kzrider.com/forum/11-projects/607213...sr-1981-z750l-engine

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Front Suspension 04 Oct 2019 04:54 #811756

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By gordone: My real weight is 110-115kg

So you're about 240 pounds. not 140. probably had a typo in the topic post.
I think the fork spring kits typically require a spacer. some guys make a spacer from pvc pipe.

....

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Last edit: by martin_csr.

Front Suspension 04 Oct 2019 06:06 #811762

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martin_csr wrote: By gordone: My real weight is 110-115kg

So you're about 240 pounds. not 140. probably had a typo in the topic post.
I think the fork spring kits typically require a spacer. some guys make a spacer from pvc pipe.

....


While sitting on the bike and not moving the ideal situation is for 25% of the fork (& shock) travel to be compressed. That leaves the other 75% of movement to absorb bumps on the road. If you have more than 25% add a spacer into the fork to lift the front end. If you have less, then your fork springs are too stiff.

Guess I shall make a spacer based on these test fail and trie serval times ?
1981 KZ650-D4, with 1981 z750L engine (Wiensco 810 big bore).

Project:
www.kzrider.com/forum/11-projects/607213...sr-1981-z750l-engine

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Front Suspension 04 Oct 2019 07:06 #811766

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Guess I shall make a spacer based on these test fail and trie serval times ?

That's what I'd do. The fork springs are probably 25mm O.D. In the USA 3/4" pvc pipe has an O.D. of about 1" >> 1 inch = 25mm
Others have reported using pvc. but if you don't like the idea of pvc in there, you could then make a spacer from steel or aluminum after determining the correct length.


....

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Last edit: by martin_csr.

Front Suspension 04 Oct 2019 08:24 #811778

  • TexasKZ
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The spacer is explained in the link to the springs at Z1E in the original post. However, since Gordone is heavier than the mythical average Japanese rider, he may need to use slightly longer spacers, or even stronger springs.
1982 KZ1000 LTD parts donor
1981 KZ1000 LTD awaiting resurrection
2000 ZRX1100 not ridden enough

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Last edit: by TexasKZ.

Front Suspension 04 Oct 2019 08:32 #811781

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Racetech has a calculator. I plugged in 1980 KZ650, commuting, and rider weight of 240lb. As you can see, they recommend a much stronger than stock spring.

racetech.com/ProductSearch/12/Kawasaki/KZ650/1977-80
1982 KZ1000 LTD parts donor
1981 KZ1000 LTD awaiting resurrection
2000 ZRX1100 not ridden enough
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Last edit: by TexasKZ.

Front Suspension 04 Oct 2019 09:06 #811785

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Before you insert the spacer you need to measure the "Sag" of the forks. then adjust preload from there.

www.motorcyclenews.com/advice/maintenanc...rebound-compression/
-Vic
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'78 kz1000 LTD long term project

'80 kz750G project

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Front Suspension 07 Oct 2019 03:15 #811958

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Thank you all...

Since it looks like I should have a stronger spring I have started to think about…. install emulator valve + new spring...

If I install a new spring now and then install emulator later I need to by another new spring... ???
1981 KZ650-D4, with 1981 z750L engine (Wiensco 810 big bore).

Project:
www.kzrider.com/forum/11-projects/607213...sr-1981-z750l-engine

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Front Suspension 07 Oct 2019 05:21 #811971

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No. The emulator only adjusts fluid movement.

As far as springs go, when you preload a spring by adjustment or adding "spacers" you are only changing the ride height /preload of the spring. The spring rate is still the same. You can calculate and shorten the spring, then add spacers to what you removed. To calculate you can put a broomstick in a vice, place the spring over it, add weight and calculate the amount it compresses.
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Front Suspension 08 Oct 2019 01:56 #812050

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Kidkawie wrote: No. The emulator only adjusts fluid movement.

As far as springs go, when you preload a spring by adjustment or adding "spacers" you are only changing the ride height /preload of the spring. The spring rate is still the same. You can calculate and shorten the spring, then add spacers to what you removed. To calculate you can put a broomstick in a vice, place the spring over it, add weight and calculate the amount it compresses.


ahh okey, but the emulator will also make a preload since it "building", so I need to go down in spacer when I install the emulator, but hopefully the emulator is not "building" more than the spacer?
1981 KZ650-D4, with 1981 z750L engine (Wiensco 810 big bore).

Project:
www.kzrider.com/forum/11-projects/607213...sr-1981-z750l-engine

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Front Suspension 08 Oct 2019 12:57 #812068

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Shortening forks is a fairly common modification in vintage flattrack racing.

Removing coils from the upper & adding a spacer of similar length to the lower (topping) spring pulls the ride height down.

Ride safe.
Don't be ridiculous! It's only a flesh wound!

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