| Author | Message | ||
     Zac |
We took Elaine's (my wife) "new" 03 XB9R out to Arroyo Seco Raceway (near Demming, NM) this past weekend for a shakedown. The plan was to use the Saturday track day to get a feel for the bike and start working setup. In the end she only got two sessions on Saturday. We threw on some new tires, Michelin PR-5 rear and soft slick front. They looked to be almost identical in radius to the 208s that were on the bike, so we left the ride height as is. It took me a while to change the rear, having delt with the belt for the first time. I set the suspension to the "owner's manual" settings, knowing that it would be too soft but would at least be a starting point, and sent Elaine out. The best comment I could have heard when she came back in was "It handles just like the MZ". She was very happy with the chassis geometry, but both ends needed compression and a lot of rebound. We checked sag, and added a little preload to the front to get 30mm on both ends, then tweeked some clickers. Her second session I followed her around a few laps, and could tell she was still lacking rebound, which she confirmed, but otherwise she was diggin' the bike. Wind and sporatic rain came in, and we never got another dry session the rest of the day. No use working setup on a semi-wet track with a slick. We decided we would run the Buell in the Team Sprint race on Sunday for fun, mainly because I hadn't had a chance to ride the Buell yet, and I was obviously going to be working with my own bike for raceday practice Sunday morning. After our first couple races Sunday, Elaine wasn't feeling it on the MZ, so she decided to run the Buell in LWGP just to get more time on it. We dialed in a little more rebound front and rear to account for some of the wallow from Saturday. About halfway through LWGP I got a waving yellow on the front straight, and saw the Buell off the track in turn one and Elaine walking out of the impact area. Crap. I finished the race, then took the pit bike over to the ambulance. She faired pretty well, with just a deep cut on one elbow and some deep brusing. She said she had spent the race moving up her brake markers, and that lap as she was braking into turn one it just started to tankslap and tucked the front under, tossing the rear up and around. She was only making one downshift into that corner, and she was done with that before the headshake started. It was just before she would have started to trail the brakes off into her turn in. The bike faired OK, those frame pucks really work. The shifter pivot got torn out of the primary cover, leaving a hole in the cover. I'm trying to think of a way to protect that area. Other damage included the shifter and linkage, clip-on tube and some scrathes on the bodywork (it was the stock stuff). Now the question is why did it tankslap? All I can figure is that because we were probably undersprung on the front and oversprung in the rear, as she was braking the chassis just got too steep until it was unstable. A damper might have helped, but is not the solution. I don't really want to slow down the chassis (lower the rear, raise the front), because she was loving the handling at neutral throttle/brake. So were to go? We'll but in proper springs, but I can't imagine that to be enough to make the bike that unstable. We'll also add a damper, but that is just a bandaid. Any ideas? Thanks, -z. | ||
| Rocketman |
Now the question is why did it tankslap? I can't account for the specifics of your scenario but a very steep rake will accentuate tank slap when it can. An often contributory and somewhat overlooked factor I find is rider weight. If the rider is lightweight, for arguments sake around 140lbs give or take, then tank slap is something one should take preventative measures for, like a steering damper. Rocket | ||
| Sloppy |
I've had tank slap a few times but never during hard braking -- once on my S3 and another on my XR500R. I've typically heard of tank slap when the front end is lightly loaded, not heavily loaded under hard breaking. Are you sure it wasn't a front tire lock up that initiated the slap? A front tire lock up would unload the front as it starts to tuck and thus could cause the slap. Of course it's hard to form a valid opinion when you're getting it third hand  | ||
| Diablobrian |
I'd agree that tank slappers usually happen with a lightly loaded front. In the cold/wet a front end locking and slipping could feel similar. I'm glad your Wife and the bike came out of it pretty well. I'd definitely say get it sprung for her weight and get the damping upgraded. The race internals for a GSXR showa fork should do the trick. Max at Traxxion Dynamics is very good with the Showa suspension. A penske rear is a worthwile upgrade too. Suspension upgrades should come before motor upgrades if you have to choose one over the other. Software comes even before that (education and practice on the track) but you already knew that! | ||
| M1combat |
Maybe she lifted the rear just a tad (or maybe just a decent amount of slip angle because the rear was really light) and it just set wrong and started the tank slapper? Maybe it was little out of line and she caught a section of tarmac that had more/less traction or a bit of a bump? Can she remember if the rear was swaying back and forth just before the slapper started? I'm sure I weigh a good deal more than she does but it seems with the short wheelbase and steep rake that my bike likes to sway itself into turns if I'm hard on the brakes. It's probably something I'm doing wrong though. | ||
| Blake |
Sounds like the front lost grip and then regained it again in violent fashion. I agree strongly with your comment about a steering damper being a good idea. There isn't a motorcycle on the track that won't find itself in a tank slapper under just the right conditions. |
