Destroying Tires 2: Mid-Ohio Mystery

I couldn't agree more. And to be honest, that basically was keeping me from posting this. However I did want to get some added feedback and at least be able to filter through it as best as possible.

 

Lap times last year were the fastest we had gone to date at Mid-Ohio. About two seconds off winning pace. The green rears were doing it with less than 10 laps on them. For the AMA 600 Shootout during the AMA Pro weekend, we went on a limb and tried a DOT white (super super soft) which lasted about 6 laps (at race pace) and then went off. Earlier this season, it was just a trackday and the same problems were already happening. Now granted, the suspension isn't identical to last year, but that's reason enough I feel to see there's an overall problem.

Handling complaints before the tire shredded? Nothing noticeable. Although this being my 2nd year on a 600 now, I'm pretty sure I'll have better feedback regarding the changes being made (whether or not improving the tire life is hurting handling for example).

 

Bike has been turning great. Better this year than it ever did last year.

I've heard both opinions on rebound - both adding it and removing it. Granted, nothing is apples to apples here, but I think we might have to try a few clicks each way on the rebound knob and see what happens.

One issue we're concerned with is being able to tell if it's better or worse. Is going out and doing say, 2 laps enough? Is 4 enough? Too many? If the tire is shredding and we make a change that improves it, is it going to clear up the tire and show it? Or will the tire be too far gone?

These are the questions keeping me up at night.

 

I'm no suspension expert, but I did sleep at a Holiday Inn Express one night...

From the position of the tearing, a couple of things are clear:

1. The tear is happening when you got on the throttle
2. The lack of debris in front and behind the tread pattern, points to the tire skipping...i.e. spring rate / preload and/or rebound

Hope that is helpful and not just "stating the obvious".

Oh, and +1 on increasing the tire pressure.

 

1. Yes. And it's not happening at full lean; it's when I'm hard on the throttle, picking the bike up.

2. That doesn't really narrow it down.

 

Yeah, I know. I should run for political office with answers like that, eh?

But seriously, I would think you could eliminate the Spring rate / Preload by making sure you sag is in the 1 1/4" range or so.

Then, pushing on the bike should reveal which way to go with rebound.

Right?

 

Check the rear spring, you said it was the correct spring weight wise but is it truly the correct rate? For example; Ohlins tends to undervalue their weights, I use a 542 lb or .95kg on the rear shock. For me with gear and weight of the bike this on the light side. By the numbers I should be running a 100kg or 571 at least. I did have the same issue at Mid-O with the 100kg. The bike on the gas is too stiff exiting corners. Be careful it doesn't highside you to the moon! I replaced the spring and it went away.

The rear spring operating range or the amount you should pre-load the spring is about 10mm. More than that the spring is too light 0~3mm the spring is to heavy. Check this first make sure you are in the correct range and see if that works. If everything checks out then reduce rear ride height to where you get a good compromise of turn in and rear grip.

I was running D-lops however, just a few thoughts.

 

Again, apples to oranges, but we're only a few turns "in" on preload with the shock. To the opposite with the front, we're only a couple turns "out" from being fully maxed on preload.

One thought we had was that if we were to try weight bias/preload and see if that had any effect on the tire, we would add the remaining preload in the forks, and take out couple turns of preload dialed into the shock. Since there isn't much at either end, doing both would essentially be going together in the same direction, and we could see if that made the tire any better or worse.

 

Maybe. I don't know if pushing on the bike would necessarily give an answer that "lights the way", sorta speak.

 

Not really apples to oranges; yes we (and I no longer compete at any level) are running two different setups and tire combinations but the geometry physics are similar.

I would re-measure front and rear sag with rebound and compression settings in the middle of their range and go from there with minor rebound or compression tweaks.

To me from what you describe the front sounds a bit too soft spring wise or the air gap (oil level) is too low. The last 1/4 inch of fork travel is controlled by spring and oil height and if is wrong it will effect the whole stroke. If the spring is too soft up front cranking down the preload adjuster to max effectively takes you out of the sweet spot of the spring. Make sense?

The tire is wearing like that because the bike is not transferring weight properly from front to rear leaned over on partial throttle. I'm just trying to help; does it do this at other tracks with the same tire compounds?

Eddie, I might have raced in what you think was the Stone Age but I spent 10 years working with some pretty knowledgeable people in the race community.

 

I just meant apples to oranges in that there were some different variables present, not that what you're saying wouldn't be applicable in some way. Sorry if it came off that way.

Interesting point on the front spring though. That brings me to this question that I've been sitting on for a couple days:

Does a set of .95 springs (as an example) with 3/4 of the preload dialed into them, behave the same way as a set of 1.0 springs with 1/4 preload dialed into them (assuming sag is the same)?

When you set your front sag, you're going for springs that will basically give you the right sag numbers, correct? Because if you're almost maxed on your preload with the .95 springs (with corrrect sag numbers), but can get more range of adjustment with 1.0 springs (also dialed into the correct sag numbers), how do you choose what springs you should have? The two quantities (spring rates) shouldn't be identical, even though your sag numbers can be. Spring rates are more or less used to get each rider in the right range for their bike (from what I know). So if that's the case and you can get that "range" with two different rates of springs, how do you choose what springs you want then? What other variables are at play?

In my opinion, preload amounts and sag numbers are a baseline setting that may not be the same for each rider. We've added or removed preload based on what I've felt on the track, as a means to make the bike handle better. Maybe that's taken us out of our "baseline sag numbers", but it's added adjustability - a potential benefit. However, I'm apprehensive about just swapping springs, based on other variables/side effects that we might not be aware of from a mere spring swap.

 

I suggest the heavier spring a less preoad. Cranking all that preload in to the lighter spring changes how the spring will react, what part of the stroke you are using, etc.. Think how much stored energy you are adding to the spring by adding a lot of preload to it.

 

The forks have been working absolutely great so far this year though, that's the thing. So do you start swapping out rates in the front to potentially try and cure an issue in the rear?

 

Sure why not?

 

Well .. so far we have these things to try:

- Tire pressures
- Shock rebound
- Shock preload
- Shock compression
- Shock ride height
- Tire compound
- Fork preload

.. and now fork springs. Do you want to supply tires and track time for this?

 

Well you could just leave it the way it is.

 

That definitely won't work. Going slower on the track and going faster through tires seems to be the opposite of what I should be doing.

 

I would think there is a lot of info on 05 R6 set-up out there. You're using good components that have been serviced recently right? I'd think a 600 lb. spring in the rear and somewhere around .95 KG springs up front (maybe a little lighter) would work for you. Is that close to what you're running? If so, I'd start to question the rear ride height and make sure after all your playing you've not got the pre-load way out of whack.

What is the official word about pressures with the new Pirelli's?

 

.

Yes they definitely will behave differently as Strick mentioned. 1.0 Springs will require less preload to get you in the desired range as apposed to the lighter .95kg. One thing we noticed is that some springs depending on the spring manufacturer was that even though they were marked as .95kg when we dynoed them they were actually .92 or .93kg.

That's correct; the springs support the bike and rider. With 1.0 springs if in fact your fronts are truly .95kg then a 1.0kg will give you more range with less preload needed to get to a certain sag number.

There's a ton of variables that affect handling and the only real way is to change one thing at time. I would start with just a spring swap and then move onto oil height, adding 5mm at a time if the springs didn't work totally. Don't change oil weight unless your forks were revalved and recommended by the tuner who did the revalve.

Other than this the clickers such as rebound and compression should only need tweaks from track to track.

Don't worry your not alone I'm chasing a few gremlins on my 1000 that had me scratching my head for the better part of almost 2 riding seasons. I think I got mine under control finally. I'll find out tomorrow at G-man.

Good Luck and don't be affraid to make spring changes, I used to carry at least 3 sets of fronts and 3 rears at all times. :up:

 

That's pretty close. We have a couple good sources for info, but no one seems to know an all out solution to this problem.

New pressures on the Pirelli's are around 32/28 hot; at least that's what we use.