Suspension setup

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Suspension setup

Postby MIOB » Sun Mar 25, 2007 2:35 am

I tryed searching the net, but I coudln't find what I was looking for. I once read somewhere something about a relation between suspension set up and the bike wanting to go upright again while braking/decelerating during a turn.

I changed the geometrie quit a lot (raised the rear end) and I'm struggeling a little to get the suspension as I wnat it to be.
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Postby sickle44 » Sun Mar 25, 2007 3:07 am

need more clues to help you dude?
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Postby MIOB » Sun Mar 25, 2007 3:23 am

sickle44 wrote:need more clues to help you dude?


Don't really know what more I can really tell you. I didn't ride the bike all that much in the new set up. The basis seems fine, when static the 'riders sag' is about what it should be, I have no trouble turning in or traction problems. The only problem is that the bike has a large tendency to go upright when I apply less throtle during cornering, making it unstable.
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Postby djalbin » Mon Mar 26, 2007 10:45 pm

MIOB wrote:The only problem is that the bike has a large tendency to go upright when I apply less throtle during cornering, making it unstable.

When you say you set rider sag, I'm assuming you set both front and rear rider sag?
What are your size tires? They can make a difference.
Also, less throttle through a turn is the same as applying brakes; and applying brakes in a turn will cause the bike to go upright.
As you lean over in a turn you are riding on the side of the tire. The side of the tire is a smaller diameter than the middle of the tire. With less RPM, this smaller diameter has the same effect as braking . To offset this effect, maintain or increase the RPMs as you lean.
Another reason to maintain or increase throttle through the turn is to keep the front shocks from bottoming out. Some throttle will take weight off the front and allow it to track through the turn. You lose control if the front forks bottom out in a turn.
The exception to the brakes causing the bike to go upgright is the rear brake. Lightly dragging the rear brake though a turn will tend to pull the bike down into the turn. Since you have your rear raised, I suspect that reducing the throttle is shifting weight forward and acting as if you applied the front brake.
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Postby FZRDude » Mon Mar 26, 2007 10:56 pm

Dang good explaination Don....
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Postby MIOB » Tue Mar 27, 2007 6:32 am

When you say you set rider sag, I'm assuming you set both front and rear rider sag


yes.

What are your size tires


Dunno, the normal sizes for a YZF 750. 180 at the rear wheel.

Also, less throttle through a turn is the same as applying brakes; and applying brakes in a turn will cause the bike to go upright.


I always thought that less throttle would cause the bike to fall to the inside. Thanx for making it clear.

As you lean over in a turn you are riding on the side of the tire. The side of the tire is a smaller diameter than the middle of the tire. With less RPM, this smaller diameter has the same effect as braking . To offset this effect, maintain or increase the RPMs as you lean.
Another reason to maintain or increase throttle through the turn is to keep the front shocks from bottoming out. Some throttle will take weight off the front and allow it to track through the turn


OK, thanx. I have no problems with the front bottoming out.



I finally had some time to futher test the handling of my bike. I noticed that during cornering the fronts seems to feel light and unstabel. I also had some grip issues at the front.

Problem is: mine is a 93 model, so I can opnly ajust spring preload at the front (I do have the 'Öhlins' at the rear). Or I could change the suspension oil and decrease the airchamber or use a thicker/thinner oil, but I have no experience with changing the oil.
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Postby pacer » Tue Mar 27, 2007 2:02 pm

Thicker oil will increase damping, and decrease rebound? Does more oil do the same? Can you play these two against each other to get desired settings? Sorry I always had friends or machanics tweek my suspension. I would say what was wrong they would fix it. I need to learn to fix it myself.
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Postby djalbin » Thu Mar 29, 2007 12:22 am

pacer wrote:Thicker oil will increase damping, and decrease rebound? Does more oil do the same?

Thicker fork oil affects both compression and rebound damping but primarily affects rebound damping. Thicker oil increases the damping and thinner oil decreases damping.
Raising the height of the oil prevents bottoming out. If you're bottoming out under heavy braking then raising the oil height will help.

Preload adjusters on our bikes adjust the preloaded spring tension.
Upgrading the springs is done for different spring rates and upgrading the fork valves is done to affect high-speed and low-speed damping, or to affect compression and rebound damping.

You want to adjust to get the right amount of rider sag (also called static sag) and free sag. Rider sag is the sag with rider and gear aboard. Free sag is the sag with only the weight of the bike (also called spring rate).

The recommended sag for sportbikes is:
Rider sag street = 30 to 35mm
Rider sag track = 25 to 30mm

Rear suspension free sag = 0 to 5mm
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Postby djalbin » Thu Mar 29, 2007 12:49 am

MIOB wrote:What are your size tires?
Dunno, the normal sizes for a YZF 750. 180 at the rear wheel.

I assume the 180 rear is 180/55/17. What is the front tire size? I assume a 120 but what is the aspect ratio? (example: 120/70/17). You get different handling from 120/60/17, 120/65/17, or 120/70/17 size tires.

MIOB wrote:I always thought that less throttle would cause the bike to fall to the inside.

This is true for low speed turns (like when making a sharp angle U-turn at low speed). But the dynamics are different when entering a turn at higher speeds. At higher speeds you want to do most (if not all) your braking prior to entering the turn. Your corner entry speed should be slow enough that you can slightly increase the throttle as you go through the turn. The increase in the throttle is just enough to compensate for riding on the tire sidewall (smaller diameter is like gearing down so you need to increase the throttle to compensate). Once you get past the apex of the turn you can begin to increase the throttle again for acceleration. You can trail brake into a turn but you need to decrease the amount of braking as you lean over and be completely off the brake at the apex of the turn.

MIOB wrote:I noticed that during cornering the fronts seems to feel light and unstabel. I also had some grip issues at the front.

What is the front tire size?
What are the unstable feelings? Bouncing? Tucking in under you? Oversteer/understeer? etc ...
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Postby pacer » Thu Mar 29, 2007 2:48 am

I do understand this stuff a little bit better than my last post suggests, but djalbin I thankyou for setting me straight. I guess my question is what weight oil should I use, and what level. I am 175-180 without gear, and prefer a slightly stiffer fork. I do a fair amount of dirtbikes, and my street style is influenced by that, pretty far forward. I am not saying I want things super stiff, but I had an 04 CBR100RR and that fork was not stiff enough. The spring is the right one for my weight, so what do I do with the oil?
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Postby MIOB » Thu Mar 29, 2007 3:40 am

What is the front tire size?
What are the unstable feelings? Bouncing? Tucking in under you? Oversteer/understeer? etc .


The front tyre is a Michelin Pilot Power 120/70-17.

The unstable feeling is more a total loss of grip. It's understeering and while it's doing that all feel with the front wheel is lost and the steering is extremely light.
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Postby djalbin » Sat Mar 31, 2007 11:47 pm

pacer wrote:so what do I do with the oil?

Fork oil loses viscosity over time. You would be surpised how much of an improvement there is just replacing the old fork oil with new oil; even with the factory specified oil weight and height.
Increasing the oil height helps with forks that are bottoming out; even with proper sag settings and proper spring rate. You want your forks to travel the full range to maximize handling and control. Forks that bottom out, and forks that don't compress, are both bad for handling and control.

If your fork oil has not been replaced in 'who knows when', I would start with new oil with the factory recommended settings for oil weight and oil height. Then set the sag and preload according to your body weight. Then, if you're having a problem with bottoming out - increase the oil height in 5mm increments until you're no longer bottoming out.
The same goes for reducing fork oil height - reduce the fork oil height in 5mm increments until the forks compress properly.

If you're then having a problem with damping (compression and/or rebound) you can change the oil weight.

Some guys go the full route and re-valve their forks and install different springs (Gold Valve Kit, Race Tech, etc ...), but this will cost more money.
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Postby djalbin » Sun Apr 01, 2007 12:38 am

MIOB wrote:The front tyre is a Michelin Pilot Power 120/70-17.
The unstable feeling is more a total loss of grip. It's understeering and while it's doing that all feel with the front wheel is lost and the steering is extremely light.

Your tire sizes are 120/70 front and 180/55 rear, and you have installed the lift kit to raise the rear. Assuming the tire tread is good I don't suspect it's tire size or dynamic ride height (rear too low).

How long has it been since the fork oil was changed? Are the steeering bearings loose or worn? How much tire pressure is in the tires? What's your preload setting on the front forks?

The front will push and understeer if the preload is set too high or there is too much compression damping.
The front will be loose if the tire pressure is too low, the steering bearings are loose/worn, if the fork fluid is too old, or there is not enough rebound damping.
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Postby MIOB » Sun Apr 01, 2007 4:31 am

djalbin wrote:
MIOB wrote:The front tyre is a Michelin Pilot Power 120/70-17.
The unstable feeling is more a total loss of grip. It's understeering and while it's doing that all feel with the front wheel is lost and the steering is extremely light.

Your tire sizes are 120/70 front and 180/55 rear, and you have installed the lift kit to raise the rear. Assuming the tire tread is good I don't suspect it's tire size or dynamic ride height (rear too low).

How long has it been since the fork oil was changed? Are the steeering bearings loose or worn? How much tire pressure is in the tires? What's your preload setting on the front forks?

The front will push and understeer if the preload is set too high or there is too much compression damping.
The front will be loose if the tire pressure is too low, the steering bearings are loose/worn, if the fork fluid is too old, or there is not enough rebound damping.



I don't know how long it's been since the fork oil was changed, at least 3 years. had it planned for next month, but 'm not sure about what viscosity to use and what te leven should be. The Tire pressure is 2.5 bar front and 2.7 rear (Pirelli Supercorsa)

I had the preload at 2.5 rings out, but I increased it to just over 3 if I remember correctly, but haven't really tested the grip since. I installed new steering bearings last october and retightned them 700km's later.


I had no handling problems with just the forks dropped 1cm, the problems started after raising the rear. The front is still dropped, but I manneged to make the jiffy longer last week, so I can set it back to normal without the bike falling over.
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Postby MIOB » Mon Apr 02, 2007 2:50 pm

after reading your post I decreased the front preload and it mad e alot of difference! I have way more grip now. Thanx!
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Postby djalbin » Tue Apr 03, 2007 12:28 am

MIOB wrote:I decreased the front preload and it mad e alot of difference! I have way more grip now.

I'm glad it's working for you.
Now that you have the preload set, you may want to experiment with the tire pressure. I don't have any experience with the Pirelli tires so 2.5/2.7 bar may be the best choice. Experiment with the tire pressure down to 2.2 bar to see what affect it has on handling. Drop the pressure 0.07 or 0.14 bar at a time. Somewhere between 2.2 and your current tire pressure should give you the best handling and feedback from the tires and suspension.
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Postby MIOB » Tue Apr 03, 2007 10:25 am

djalbin wrote:
MIOB wrote:I decreased the front preload and it mad e alot of difference! I have way more grip now.

I'm glad it's working for you.
Now that you have the preload set, you may want to experiment with the tire pressure. I don't have any experience with the Pirelli tires so 2.5/2.7 bar may be the best choice. Experiment with the tire pressure down to 2.2 bar to see what affect it has on handling. Drop the pressure 0.07 or 0.14 bar at a time. Somewhere between 2.2 and your current tire pressure should give you the best handling and feedback from the tires and suspension.


I've done some experimenting with it. 2,5/2.7 works bets for me. Slighly lower rearpressure tire helps it warming up without loosing the feel, 2.5 at the front is nice and hard wich gives it a better feel turning in. (al just how I experience it)
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Postby pacer » Tue Apr 03, 2007 4:04 pm

First off MIOB I hope you don't mind me jumping in on the thread, there is good info here. Second to djalbin. I have Racetech internals, and race tech springs and weigh 175-180 without gear. Would you start the process at stock oil height and weight? I assume the stock height is in order, but what about weight?
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Postby djalbin » Wed Apr 04, 2007 1:05 am

pacer wrote:I have Racetech internals, and race tech springs and weigh 175-180 without gear.

I would look up the Racetech info either in the documentation that came with your Racetech parts, or on the Racetech website if the parts were already installed when you bought the bike. If you can not identify which Racetech parts are installed in your bike, I would assume - as a starting point - that the Racetech is OEM equivalent. I don't which bike we're talking about, your '94 FZR1000 or the '87 FZR 750. I'm more familiar with the '94 FZR1000 because that's what I have.

OEM preload recommendations and fork specs for the '94 FZR1000 are as follows:

Fork spring length
max = 335 mm
standard = 340 mm

Fork oil amount
470 cc

Fork oil level (fully compressed with spring removed)
78 mm

Fork preload
Hard = 1st, 2nd, 3rd groove from top
Standard = 4th groove from top
Soft = 5th groove from top
Solo rider - 3rd to 5th groove (3rd works best for most riders)

Fork oil = 01 Suspension Oil
Yamaha genuine suspension oil 01 - Racing formula
(or equivalent)

What's equivalent ?
According to one Yamaha Tech, Yamaha "01" oil is 2.5W

There are 2.5W, 5W, 7.5W, and 10W fork oils on the market
(you can also get 15W, 20W, and 30W - but these are not for sportbikes)
Yamaha used 10W for the 1987 - 1990 FZR1000, 5W for the 1991 - 1993 FZR1000, and Yamaha "01" oil for 1994-on FZR1000.

The lighter weight fork oil will provide less dampening and quicker rebounds. The heavier weight fork oil will provide more dampening control and slower rebounds.
Don

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Postby pacer » Wed Apr 04, 2007 5:34 am

Good info. Thanks for a good place to start. This is for my 93 1000. I bought the Racetech internals as NOS off of ebay, then before I installed them I sold the bike to my cousin who had them installed. I recently bought the bike back, and am making it my own again. I am still waiting on the engine, so I won't be able to put up results for a while.
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