Triumphrat

jaak

I haven't heard of a Tiger owner who's completely happy with their front suspension yet. (OK, there are guys with straight rate springs and RaceTech emulators who seem to be content after $300).
I have an 06 with stock springs and 15w fork oil. It still dives a bit too much (I am realistic in my expectations, a bike with 170mm travel will always dive more than a race-replica). It is harsh over bumps. I started reading about suspension setup and have arrived to the conclusion that the stock springs are too soft (duh!) yet they have too much preload. How I came to the latter conclusion - a bike should have a static sag about 25-33% of it's travel. Source: http://www.triumphnet.com/st/acc/racetech/setup.htm
Stock 06 fork travel is 170 mm. I should have roughly 50mm static sag. I need to get two buddies into my garage to help me measure it, but by eyeballing I don't think it's there. It's probably around 30-40 mm. Thus the conclusion - the soft springs are compressed with spacers to give them preload. Due to the excessive preload small bumps won't move the forks enough and the roughness gets into bars. Due to soft spring rate (and lack of modern valved damping) the fork still dives too deep under heavy braking.

After this long theory, here's my question;
has anyone accurately measured their static sag? Would you mind posting your bodyweight, model year of bike and sag in mm?

I know the cure - thrash the triple rate springs, buy straight rate springs + RaceTech emulators, tune and live happily ever after. I am cheap and like to tinker. I am considering
the cheapest mod - increasing spring rate buy cutting them shorter and adding spacer lenght accordingly, all discussed in the link below, I won't go into it:
http://www.calsci.com/motorcycleinfo...aseForkSprings
I want to end up with stiffer springs, yet reduced preload.
Then I should be able to go to thinner fork oil to reduce damping and have a more precise predictable fork action. It's not like the $300 solution, but it should be an improvement.

blacktiger

That would be the opposite of what you're asking for. A soft spring rate but pre-loaded will still absorb bumps easier than a stiffer rate spring without pre-load. The spring rate is the key thing. I don't know what exactly Triumph did to the '05 on forks but a mate of mine had an '01 955i and then changed to an '05 and he reckons that the forks are less comfortable on the '05 but don't dive so much.
My suggestion is to take some pre-load off the spring AND reduce the air gap on top of the oil (i.e. increase the oil level). Air is a natural rising rate spring so the further the forks move the stiffer they get. Also try a slightly thicker oil to reduce the speed of dive. It's a fine balancing act and will probably always be a compromise.
Of course, the real answer is to buy some really expensive Ohlins forks.

__________________
H
'02 Tiger955i in black.

jaak

[quote=blacktiger;834123]That would be the opposite of what you're asking for. A soft spring rate but pre-loaded will still absorb bumps easier than a stiffer rate spring without pre-load. [quote]

I Disagree. I'm too lazy right now to go dig up all the articles I've read, but stiffer spring with proper preload that gives you the right amount of static sag is the best suspension setup. A Quote (presented as I remember it) from Pridemore's book "Racers tend to use stiffer springs with less preload and less damping than street riders". And racers care about the same things -precise handling, absorption of bumps (keeping that wheel on the ground for traction) and less dive. Yes, they do race on much smoother surfases than we ride. Once again, I'm not trying to replicate a gixxer fork action on a Tiger. Our forks are longer, softer, and will travel/dive more. It's just the matter of finding a good balance for your riding style.
Key here is to have a proper rate for your bike/weight- if the spring rate is too stiff for your bike/weight then even little or no preload gives you enough sag. The stock springs are usually calculated by the manufacturers for a 150 lbs rider and still tend to err to the soft. I'm 210.

In our case probably the main culprits are the triple-rate springs, in essence progressive springs, that sound good at first but don't live up to it in real life. The straight rate spring acts in a progressive manner, if properly damped and adjusted with fork oil height/air gap.
I might skip the cutting business and get a set of stiffer straight-rates, should be under $100.

jaak

blacktiger

[quote=jaak;834144][quote=blacktiger;834123]That would be the opposite of what you're asking for. A soft spring rate but pre-loaded will still absorb bumps easier than a stiffer rate spring without pre-load. You said it yourself. They race on smoother surfaces.

I'll stick by what I wrote. It's the spring rate that matters. A single rate spring will always be the same rate throughout its movement, regardless of the amount of pre-load. Pre-load adjusts when the spring comes off the stops and starts to act as a spring. So a 20lb/inch spring will deflect 1" for every 20lbs put on it. If you pre-load it by 40lbs and then add 20lbs on that it'll still move 1". A stiffer spring rate will always be stiffer and will be harsher on bumps. Which is why I suggested you decrease the air gap to get a rising rate spring assistance. Your forks will still have an initial reaction to the bumps at the soft rate of the original spring but as the forks dive the rate will increase as the air gets compressed.

The problem with multi rate springs AND pre-loading them is that the pre-load just uses up the softer part of the multi rate. I think with your weight you probably do need a stiffer spring overall. Hagon or Wirth do some. Afterall, one reason why a Rolls Royce is so comfortable is that it weighs several tons and the springs are soft and absorb the bumps BUT that's also why it will never handle like a Lotus. You need to accept that the Tiger is like a Jeep in that it has long travel suspension and a high centre of gravity. It'll never handle like GSX-R.

Keep experimenting and post your results on here for everyone to gain from your efforts.

__________________
H
'02 Tiger955i in black.

jaak

you say:
Pre-load adjusts when the spring comes off the stops and starts to act as a spring.
I say: Bingo!

That's why excessive preload feels harsher on bumps, even if the spring rate is lower.
And this is why a stiffer spring with less preload "acts as a spring" sooner, hence - better absorption of bumps.
The key being the right spring rate and the right preload (latter showed by correct static sag).

Agreed in all other points

robbie

I'm trying to follow this but getting

Equilibrium
Issac Newton had a few ideas about apples and forces and until E=mc2 came along was thought to be the bees knees.

let's do Math

so:

preload= the spring rate* (free length-installed length)
installed length-compressed length= static sag
me + bike weight acting down = spring rate * compressed length acting up.

so:

you can have the same sag with a stiff spring that is compressed less or a soft spring compressed more. but at the critical sag position both springs are exerting the same force.



am I right so far?

__________________
Robbie and 'Mohan' the original Silver Tiger
TIGER 955i 2003
My Photos

jaak

Robbie, your conclusion is correct - yes, you can have the same sag with different springs, you just need to adjust the preload. (Of course the extremes; too weak of a spring will collapse to an unacceptable level regardless the preload and too stiff will not give you sufficient sag even without preload).
However, static sag is the travel of suspension caused by the weight of the bike+rider, not the difference between free and installed lenght of the spring .
To measure static sag; very brief summary: extend the forks fully, measure from a fixed point on the fork to a the triple clamp. Then sit on the bike and have your buddy measure distance between the same points. The difference is exactly how much the suspension is compressed. At lenght, please read here:
http://www.triumphnet.com/st/acc/racetech/setup.htm
I also googled "static sag" and got some other good links

EDIT: Robbie, I thought about it this morning and realized I might have misuderstood your term use. If by
installed length you meant the length of the the springs indside fully extended forks, and by
compressed length you meant the length of the springs in the fork with the bike's and your weight sitting on top of it,
we are on the same page. I just hadn't seen these terms being used before this way and it confused me, but in the essence,
if your definitions match with what I described here, you are spot on!

cheers!

welcome to the dark arts of suspension setup!

blacktiger

No,no,no.
Lets consider a hypothetical, very simple, bike.
You have a 100lb weight (the bike) and a choice of two springs. A 20lbs/inch and a 33.3333lbs/inch spring.(to make the maths easy)
You want a static sag of 3".
The 20lbs/inch spring will move 5" when the 100lbs is sat on it. So, to get a sag of 3", you need to jack it up (pre-load) by 2".
The 33.333lbs/inch spring will just move 3" without any pre-load.
So, you see you have 3" static sag with both springs. The 20lbs spring has moved 5" but the bike has been jacked up back to 3" sag with pre-load. The 33.333lbs spring has moved 3". Both springs are mid length. i.e. part way through their length and can bounce up and down.
Now, lets consider the next inch of movement.
The 20lbs/inch spring will only need 20lbs to move the forks 1". The 33.333lbs/inch spring will need 33.333lbs to move the forks 1".
Do you still think the stiffer spring is less harsh?

__________________
H
'02 Tiger955i in black.

itchyfeet

I have to say, speaking from an uneducated lay-mans point of view that I totally agree with Blacktiger on this.
I've tried thinking about it from Jaak's view but just can't get my head around how a stiffer rate spring irrispective of preload could absorb road imperfections better than a softer rate one.
Its the introduction of oils and air gaps that change the effectiveness of both springs. Would a stiff spring in a light oil not compress at the same rate as a soft spring with heavy oil? The compression rate can't be the only consideration here as surely a softer rate spring simply needs less force to create a reaction, meaning higher absorbtion of bumps?

if not i'll get my coat.....!

jamie_fixit

OK I'm new here and my front end is a bit sloppy so I've partially been this route already. But... Variable rate springs such as Wirth's available on eBay for about £62 a set, might seem to answer both problems? Or is this new boy foolishness?

Look here for the ones I was looking at:

http://cgi.ebay.co.uk/ws/eBayISAPI.d...MEWA:IT&ih=001

Jamie.