High speed stability probs after switching to Dunlop D209's

Mmelmann · 06-18-2007, 02:21 PM

Man, this is frustrating. I recently decided to run a set of the D209's. I am used to running Pirelli Dragon Supercorsa Pro's in a SC1 front and SC2 rear compound. The SCP rear was a 190/55/17. These D209's are a taller 190/60/17 profile and it changed my geometry a little bit.

So anyways, last weekend I was experiencing high speed stability problems like never before. Every time I came out of a high speed corner into a back straight, my bike would show signs of an impending tank slapper... the oscillations would begin as I pass through 110mph or so... so I'd back off the throttle and they would go away.

Well, I was getting fed up with it lap after lap so I decided to come out of a fast corner and let my 1000 go wide open. I lit up the rear tire at about 110 mph (according to a guy behind me) and went into a full on tank slapper at 120mph. It almost cost me my life (the straight turned into a slight righthander and off to the left was a guardrail that I was headed straight at). It freaked the two guys behind me out so bad that they had to take it straight to the pit lane and call it a day... it really wigged them out.

So, I'm running a stock suspension with settings as per sportrider.com. I ran them before with the Pirelli's and I didn't have any issues at high speeds. Is the D209 an unstable tire? Is my suspension to stiff, soft, or what? Who's ever experienced this before and found a solution?

tilejerky · 06-18-2007, 02:50 PM

Have the balance on the front tire checked.

I had similar front end stability problems on my first track day with Pirelli Corsa III's, and was miserable. After checking out everything from the suspension settings to the head bearings, I figured that the tire balance might be off. I took it back to the guy that mounted it, and sure enough, it was WAY off. It was so far off, in fact, that it would have been closer to balanced if he had added NO weight at all! I'm not sure how he got it so far off in the first place, but after he rebalanced the tire I did two more track days and had no problems whatsoever.

If it's not the balance of the tire, then the only other thing I can think of is that the profile is a different height compared to the supercorsa's, and you may have to slide the forks in the triple clamps to compensate.

Mmelmann · 06-18-2007, 03:30 PM

We mounted the tires the budget racetrack way... i.e my buddy mounted and balanced the tires in his front yard using his equip and a static balancing device (whatever it's called). This could possibly be my problem for sure and I suspected it last weekend. Friggin every time I encountered a small set of bumps on the track while I was at a 3/4 to full throttle setting... I would get a head shake that wouldn't go away till I closed the throttle a bit to get the front end planted. It was so frustrating and it probably cost me a 3-4 sec a lap. I had to ride the bike as if it had only a 600's power. I had no confidence in the bike.

Problem I have now is that I the tire's are totally buggered up (CMP is an aggressive track). I'm worried that all those buggers and bits will throw off the balance of the tire. I guess I just need to make it street legal again and wear those things off before I take the wheels in for another balance.

I'm glad you gave me some good input to back up my suspicions. Thanks.

Mmelmann · 06-18-2007, 03:40 PM

Additionally, I changed the fork height 3 times during the day. I went through three different ranges from flush to 8 mm of fork tube showing... trying to find a sweet spot to make up for the increased rear ride height that came with the 60 series rear tire. All three settings gave the same result at high speeds.

That 120 mph full tank slapper made my butt pucker... and the other guys feel sick to their stomachs. I remembered to pump my front brake since that tank slapper caused the calipers to spread apart from the rotor a little. That was miserable, but I kept on going a few more laps. As if that wasn't enough... on the immidiate corner following the straignt that I got the tank slapper... I came out of the turn and almost high sided at 120! I smoked up the rear again while leaning and that was my sign that yeah... that tank slapper shook me up pretty good.

tilejerky · 06-18-2007, 04:50 PM

Damn, that sounds scary as hell. Makes me glad I've only got a 600.

Based on what you've said, I'm even more suspicious of the front tire balance. Especially since none of your set-up changes seemed to have any effect.

When I rode on the unbalanced front it felt like I was riding a jackhammer down the front straight at Grattan. Then it got worse when I rolled off the throttle and started braking. Definitely not a nice feeling at 130mph.

I'd take it off the bike and take it to a shop before you start to street ride on it. Any street miles that you put on it will wear the tire and maybe mask or distort what the problem was by the time you take it in. I really don't think that the little rubber boogers will throw it off that much, and if it worries you, you should be able to just rub most of them off with your hand.

Mmelmann · 06-18-2007, 05:04 PM

Well actually the bike was stable and smooth under hard braking where the rear is wiggling around a bit. It was just the range between 110-145 mph down the straights where it would start to oscillate. When I was running the Pirrelli's, I could be going down straights at wot and hit small bumps that would cause small wheelies to happen even while passing 140 or so mph and the bike was stable and true. The GSXR-1000 has pretty wicked power and I used to have all sorts of confidence going straight. The only obvious problems that I had to concentrate on were coming out of corners and worrying about the rear tire's traction. I would have never thought that I had to worry about going straight.

BTW, if you've ever seen the Isle Of Mann footage where a guy had a tank slapper and hit the wall on a right hand corner... well that's what I went through. I think that he was riding a black Fireblade. Have you seen that footage before?

tilejerky · 06-18-2007, 05:08 PM

No, I've never seen the footage, but I can imagine.

I just thought of another possiblity. Is it possible that your rear tire was misaligned when it was installed? I could see that causing some high-speed problems, especially on bumps.

Mmelmann · 06-18-2007, 05:32 PM

Some of the guys out at the track said that too about my alignment. I checked the lines on the rear axle... they seem right on but maybe I could still be wrong. That is probably the culprit. I'm taking the bike to a suspension guru as soon as I can.

OreoGaborio · 06-19-2007, 06:09 PM

friggin a... i wrote a big long reply & hit submit just as the forum crashed yesterday & it didn't get posted.

Anyway, here's a recap:

1 - Obsiously, as you know, the rear tire is now larger in diameter... that raises the rear suspension reducing rake and trail, making the bike more prone to exactly what you described. High speed instability, oscilations, tank slappers etc.... First thing I'd do is either raise the front or drop the rear to even it back out & see if that fixes it. I see you already adjusted the front, so try loweing the rear.

2 - don't EVER trust someone else's suspension settings, even if it's from an online motorcycle mag or whatever... First of all, there's no way a writer can give you proper settings based on YOUR rider weight, YOUR track, YOUR riding style, YOUR current suspension condition (oil breaks down and loses its viscocity over time which means damping effectivness is reduced as time goes on) etc etc etc... Those suspension settings you got are intended for dummies that don't know any better, need to be given a starting point on a silver platter & aren't gonna be pushing all that hard.

3 - I doubt it's a tire balance issue. Tires are pretty uniform now so any balance issues are more likely to be in the rim, not the tire. But it's possible, so re-balance things & make sure the rims are mounted on the bike & aligned properly. Tires getting boogered up won't throw off the balance.

4 - Do the "String Thing"... check the rear tire alignment by using a piece of wire or something that won't stretch & check the distance from the center of the axel to the center of the swingarm pivot on each side of the bike.

I think the part that confuses me most about your situation is this.... If you're having trouble or experiencing some symptoms that your suspension isn't set right, the last thing you wanna do is push HARDER to "test it out". That doesn't make ANY sense to me whatsoever... If something feels wrong, WHY push harder?!?! Slow down, come in, troubleshoot, make a change, go back out & see if it solves the problem. Yer damn lucky you didn't learn that the hard way, that bike coulda EASILY put you on your head to teach you a lesson.

Mmelmann · 06-19-2007, 08:23 PM

I didn't mean to convey that I was going out there and pushing harder... I just wanted to pull away from the pack after I passed them up. Then blamo, tankslapper 101 begins... and I was the only one that mistakenly enrolled. I took myself to school and it almost kicked my ass.

So anyway, I call some suspension guru's up today. I go to visit one guy that is a total anti-dunlop disciple. I didn't get much input from him other than he telling me that I need to get back on the Pirrelli's, never use Dunlop again, get some better suspension soon, and that my '06 GSXR-1000 forks suck ass. Alrighty then.

I call up another guy and he tells me that running D209's on my bike is just not recommended with stock suspension components... he tells me to get some Ohlins or Penske shocks or run a tire with less grip. He said that the grip of the D209's coupled with the power of the thou just isn't a good comination... and the stock suspension just can't keep up.

So damn, I got nowhere today and I want to sell my bike for a proper race bike. An R6 may be in the works. Who knows. I just know I hate selling my baby. ( I just sold my 406 bhp Evo IX and I'm regretting that one... before the Evo, I drove a BMW M Coupe and I really regretted selling that one). I don't want to add the gixxer thou to the list.

Mmelmann · 06-19-2007, 08:34 PM

Here's the video of the tankslapper that I was talking about. http://www.youtube.com/watch?v=ymvVv_zbOjk

OreoGaborio · 06-19-2007, 08:38 PM

Oh man... I can't believe you sold the M Coupe

I say make the 1k a street bike & pick up a used SV650 that's already been race prepped for 2-3g's. That's my plan for next year.
It may be slow, but it's cheaper to run, cheaper to fix & it'll bring you back to the roots of racing & give you an opportunity to work on the fundamentals.

Mmelmann · 06-19-2007, 08:44 PM

I used to race YSR's... I got to appreciate the fundamentals more than I wanted to. (my team mate was all about it... me, not so much) Me likes raw power too much. I also like twins a lot as well. I would love to rock an old Mille or something like that. A SV with the 740 bore kit would be fun too. I wish I could find a good one.

And yeah, I can't belive I sold the hooligan mobile. I found out that my M Coupe's subframe was separating and in bad shape, so I sold it. My wife actually cried pretty hard when we left it at the dealership (I shed a couple too). Man what an icon of a car. The new one's just don't do it for me.