Sorting out forks

[Slaninar]

Been to a track day yesterday. Forks are too soft, dive too quick.

I'm 78 kg heavy. Are original springs OK? I was thinking of adding a 2 to 5 cm pieces of plastic tube, to preload springs to a bit better. Will that be smart? I'm not on a budget to pay for new springs, but want to make forks a bit stiffer. Not too much.

Also, should I then go for 15 w oil?  A mate who races said he would recommend 90w gear oil, or 15w50 engine oil - says 15 w will be too thin if I ad 4 cm more of preload.

Any thoughts, suggestions, ideas?

[anzacinexile]

Increasing pre load does not increase spring rate with linear springs 

[kebab19]

The OEM springs are the problem - dual rate, but the combo is poor, with the 'softer' part of the spring too soft & the harder rate too stiff.
You'd really need alternative springs to sort it out to an acceptable level but that of course means money

Adding oil & raising it's level within the forks changes the final third of travel, you could get some benefits there but it's masking the problem and you start increasing the chances of blowing fork seals

[Slaninar]

The OEM springs are the problem - dual rate, but the combo is poor, with the 'softer' part of the spring too soft & the harder rate too stiff.
You'd really need alternative springs to sort it out to an acceptable level but that of course means money

Adding oil & raising it's level within the forks changes the final third of travel, you could get some benefits there but it's masking the problem and you start increasing the chances of blowing fork seals

What about adding spring preload, with the correct volume of thicker oil? Will that make it a bit better, like half way there, or just make it lousy in a different way - like you said - masking the problem?         

[Motorbreath]

Use SAE20 fork oil and add a bit of preload, 1cm or so. Do not use gear oil, I have ridden a bike with that and it sucks. Fazers have almost no low speed compression damping. I have for sale a couple of very stiff springs but they will be too hard for your weight on the road, and 2002 preload adjusters and spacers for '98 bikes.

[Slaninar]

Use SAE20 fork oil and add a bit of preload, 1cm or so. Do not use gear oil, I have ridden a bike with that and it sucks. Fazers have almost no low speed compression damping. I have for sale a couple of very stiff springs but they will be too hard for your weight on the road, and 2002 preload adjusters and spacers for '98 bikes.

Thanks Doctor Motorbreath - I know you've tested most of it.   

So 1 to 1.5 cm of preload and 20 fork oil?

My bike has preload adjusters, it is 2001, but they are maxed and it still is too soft.

[Motorbreath]

Yes try that first. On winter you will notice how dampened the fork will become, not good for big bumps though. On summer it will thin a lot: the higher the grade the more temperature sensitive it becomes. Having preload adjusters at max I'd go for stiffer springs but it will a pain as you said Serbian roads are bumpy? The solution would be mate kebab's emulators.

[Slaninar]

Yes try that first. On winter you will notice how dampened the fork will become, not good for big bumps though. On summer it will thin a lot: the higher the grade the more temperature sensitive it becomes. Having preload adjusters at max I'd go for stiffer springs but it will a pain as you said Serbian roads are bumpy? The solution would be mate kebab's emulators.

Yes, I'd rather not risk putting too much oil. If 1 cm of preload added would make it effectively harder, I'd try it. Also, if 15, or 20 w oil will make forks not bounce back too quick (and compress even harder), I'd give it a go.

I thought OEM springs were at least decent, but at the end of the track day, a 60 kg mate took it for a ride and it was too soft for him.

[Motorbreath]

The problem is that more preload will not make it exactly stiffer: the forks will have more travel when breaking and hitting bumps, but at the expense of having less travel when extending (when the wheel goes over a hole for example). As Anzacinexile said if springs were linear more preload would just change ride height. But as the springs are dual rate you will have less soft travel rate and more stiff travel the more you add preload. I do not know if I am explaining it well sorry.

Use 20 oil. There is little difference between 10 and 15, specially if they are from different brand they could be almost the same real viscosity.

I still think oem springs are decent, the problem is the lack of damping makes them seem too soft, and the dual rate is too soft and later too hard trying to mask that. My ace's springs are soft and the bike is 229kg and 86 myself, and they work perfectly. Maybe somebody changed them? I have to investigate it.

[Slaninar]

Yesterday I changed oil for 20w, as well as seals. Also added 1 cm "washers" to put a bit more preload on the springs. Haven't been able to test thoroughly, but first impression is that forks dive normally when braking, and the bike wobbles less when braking hard, then turning it. Also, front brakes seem to be workig better now - old oil was probably too thin (10w, but over 2 years old) - so no diving, bottoming out, guess it puts less weight on the front wheel.

On bumpy roads I don't feel things have gotten (much) worse - to my amazement.


Will test it more in the spring, see how it feels. So far, since I have adjustable preload forks (2001 model), the washers I put in can be neutralized by turning preload adjusters all the way out, while still leaving heavier oil in the forks for better damping. So far very pleased, will see how it goes.

[darrsi]

I found 15w to be a big difference on the road compared to the 10w, maybe it is a brand thing? Although i'm not using it on the track at all.
There's no way i'd want heavier than what i've got now, and i'm not exactly a lightweight!

[richfzs]

There is a huge difference between some brands take on a  15w oil, and another brands. There's a great post on the tiger800 forum that discusses this, I'll try and find it...

[richfzs]

Found it.... Some of it discusses tiger800 specific info, but generally it's a good description of oil weights / brands etc...


That's correct -- as far as it goes...
Trouble is: If you may be expecting to change the damping by changing fork oil, you may need to know more..?
The fork oil used in the T800 is Showa SS 8 -- which falls into the range of SAE-10 oils. If you use Showa SS 8 fork oil, you'll get OEM damping. If you use some other SAE-10 fork oil you may get different damping -- more or less.
The SAE viscosity scale is somewhat coarse and groups a wide range of viscosities into limited measurements like: SAE-5, SAE-10, SAE-20, etc. In some cases, a "10" can have a viscosity similar / close-to another brand's "5" or some other brand's "20".
What's needed is to compare Showa SS 8 fork oil viscosity measured in centistokes (cSt) with what ever fork oil you plan to use as a replacement -- it's viscosity also measured in centistokes.
Centistokes (cSt) is a much more accurate, laboratory, method of measuring viscosity and will serve the suspension tuner better than relying on the broader SAE measurements.

[richfzs]

Original post is here..

http://www.tiger800.co.uk/index.php?topic=8423.msg111989.msg#111989

[Slaninar]

I used this one:

http://www.motul.com/rs/en/products/89

I ride in 25+ degrees celsious, mostly.

[darrsi]

I used this one:

http://www.motul.com/rs/en/products/89

I ride in 25+ degrees celsious, mostly.

 
Are you trying to cheer us up? 

[Slaninar]

Weekend was nice.

Now it's rain and under 20 C.   Got soaked this morning, if it makes it easier on you.     

[darrsi]

Weekend was nice.

Now it's rain and under 20 C.   Got soaked this morning, if it makes it easier on you.     

Oh okay, i feel better now.