First Track Day

[GAS]

Hey guys!

I've recently done my first Track Day (beginners group, haven't taken classes yet) and below is a short clip of one lap. The track is Interlagos, the Brazilian F1 track.

At the end of the video you can see the tires still have chicken stripes, and you can see a (for me) huge slip at slow speed. Could you gys help in finding what went wrong?

Consider it like a '89 US GS500E (is the same model we had here in '97)
That was in the 4th lap, so I believe the tires were hot.
My bike is totally stock (even the exhaust)
I was using stock size tires (Michelin Pilot Activ). But they were underpressured (30/30)
The bike is a '97 GS500 with stock springs and shocks, harder dial ond front and rear

http://www.youtube.com/watch?v=1G-QBjLo2gA
tks guys!

[utgunslinger13]

No clue, sorry I can't help but that looks like a killer time!

[burning1]

Where in the video was the slip (minute/second?)

[burning1]

I see it - right near the end of the video. When the tire started to slip, did you first feel it in your arms, or in your ass?

[GAS]

Where in the video was the slip (minute/second?)

at the end, after the lap. I've made a cut to show only the slip.

[GAS]

I see it - right near the end of the video. When the tire started to slip, did you first feel it in your arms, or in your ass?

I first felt it in my ass. I felt the bike going away from me, and the front of the bike started to aim to the inner part of the curve.
I minimally reduced the throttle and it went back quickly to its trajectory. I believe that if I was quicker it could have resulted in a high side...

[burning1]

To me, it looks like the rear end stepped out slightly on the gas. I noticed that the camera started to point into the corner, and the RPMs went up slightly. You panicked and chopped the throttle which is what caused the bike to shake. Watch that reaction - if your rear end had stepped out far enough, you could have been thrown off the bike.

The cause could be a lot of things. You seemed to be relatively smooth and you weren't riding super aggressively... So, I don't think you overwhelmed the suspension. Were you moving around on the bike at all when it slipped?

Another possibility is that your tire pressures are all wrong. I don't know the recommended track pressures for the Michelin Pilot Active, but I can tell you that I run 23PSI in the rear on my GS500 with Bridgestone BT003RS. I *highly* recommend that tire for track use.

4 laps is more than enough to warm up the tires. If your pressures are correct, 1 lap should be enough.

[burning1]

I first felt it in my ass. I felt the bike going away from me, and the front of the bike started to aim to the inner part of the curve.
I minimally reduced the throttle and it went back quickly to its trajectory. I believe that if I was quicker it could have resulted in a high side...

Yep... You probably wouldn't have high-sided, because the rear end wasn't that far out. But you could have created a fishtail or a tank-slapper.

[burning1]

I'd see if you can find a Michelin track-side vendor. Ask what pressures they recommend for that tire, on that bike. Ideally, they should tell you how much the pressure should rise between hot and cold.

Again, although some race tires require it, 30psi sounds like an awful lot for a GS500. I used to run 27-29 on a GSX-R 600. My GS is 26 front, and 23 rear cold, and 29/26 hot.

[GAS]

To me, it looks like the rear end stepped out slightly on the gas. I noticed that the camera started to point into the corner, and the RPMs went up slightly. You panicked and chopped the throttle which is what caused the bike to shake. Watch that reaction - if your rear end had stepped out far enough, you could have been thrown off the bike.

The cause could be a lot of things. You seemed to be relatively smooth and you weren't riding super aggressively... So, I don't think you overwhelmed the suspension. Were you moving around on the bike at all when it slipped?

Another possibility is that your tire pressures are all wrong. I don't know the recommended track pressures for the Michelin Pilot Active, but I can tell you that I run 23PSI in the rear on my GS500 with Bridgestone BT003RS. I *highly* recommend that tire for track use.

4 laps is more than enough to warm up the tires. If your pressures are correct, 1 lap should be enough.

As I remember, the slip occurred before I give throttle to exit the curve. I remember only closing it a little bit as I felt the rear of the bike running under me.

In a case like that, you told me to watch my reaction.... What does it should be if I feel a back end slip?


I wasn't moving over the bike as I remember, I was exactly as my picture here on the left side... And I'm only putting some guilt in the rear shocks since they're probably the original ones, (13 years old) and they're in position 7 and the static SAG is still almost 30mm.

These BT should be sweet! But unfortunately we don't have them in small sizes (like GS one) down here...


Anyway, 23 PSI scared me, nobody here told me anything about a so low pressure. I put 30 and some people thought it should be even more! lol!!! I'll try it next time!

[Deros514]

The speedo is hanging on for the ride lol. Can't offer any valuable input but free bump!

[burning1]

The standard BT003 isn't available in sizes for the GS. The BT003RS is. Look into it; you may have some luck.

Listening to the bike and watching your tach, I'm pretty sure you were at least giving it maintenance throttle. As the tire slides, the RPM increase by 500 or so. But... You aren't giving it nearly enough gas to actually spin the tire up. Even with your knee on the ground, the GS really shouldn't spin.

Question... You said you were in the beginners group. That group usually goes out first in the morning. I also notice that the sun was very low in the sky. Was this the first session of the day? If so, the track is probably cold, which would mean that there's very little grip available.

My recommendation would be to shoe-horn in a Katana 750 shock, and upgrade the front end. Find out what tire pressures you should be running, and consider fitting up some high performance rubber. If you sort the bike out properly and take it easy on the first session, I doubt that you'll have a problem like this again.

[GAS]

The standard BT003 isn't available in sizes for the GS. The BT003RS is. Look into it; you may have some luck.

Listening to the bike and watching your tach, I'm pretty sure you were at least giving it maintenance throttle. As the tire slides, the RPM increase by 500 or so. But... You aren't giving it nearly enough gas to actually spin the tire up. Even with your knee on the ground, the GS really shouldn't spin.

Question... You said you were in the beginners group. That group usually goes out first in the morning. I also notice that the sun was very low in the sky. Was this the first session of the day? If so, the track is probably cold, which would mean that there's very little grip available.

My recommendation would be to shoe-horn in a Katana 750 shock, and upgrade the front end. Find out what tire pressures you should be running, and consider fitting up some high performance rubber. If you sort the bike out properly and take it easy on the first session, I doubt that you'll have a problem like this again.

Tks for the reply, burning!

Actually, the season it ocurred was at 3pm, it's winter here. Night is falling at 6pm... the temperature at that moment should be something like 50-60F.

Altough the track was probably cold, my tires went very hot. Is this any signal of grip, or not necessarily?

Unfortunatelly these bike upgrades are very expensive here, since we've never had a katana in Brazil. I'm thinking in have a GSXR1100 soon, if I can get the money!

[burning1]

The track it's self is heated up by a combination of the sun, outside temperature, and by the bikes riding over it. I've had some very bad slides during the first session of the day on a cold morning, but never at 3:00 in the afternoon. So, it's probably not a cold track.

Is there any chance you could order parts internationally? I found my Katana Shock on Ebay for about $30 (US), and you may be able to find a GSTwins forum member who has one handy. For the front, springs, fluid, and one of Buddha's braces would be the big upgrade. That could be done for $130 or so (US).

I'll ask around and see if I can find the recommended pressure for your tires. I strongly suspect that 30PSI is too much.

BTW: You can easily tell if your tires are warm enough. After you get in from your ride, put your hand on the tire. It should feel hot enough that you want to move your hand away after a second or two... But not so hot that it burns.

As a wild guess, I'd say you want to see the pressure increase 3-4 PSI when hot. E.g. If you have 30PSI in the tire when cold, it should read 33PSI hot. If you read 31PSI hot, you should let some air out... Say, 2 or 3 PSI, and try again... E.g. Start at 27PSI cold, and see if it goes up to 30PSI hot.

You can play around with tire pressures during your street rides. Try feeling the tire. Check to see if your pressure increases when hot.

Also keep in mind, that your tire pressure gauge may have an error. Some of the most accurate gauges are the inexpensive digital gauges you can buy at auto-parts stores. The one I have reads .5 psi off. My dial gauge is sensitive to barometric pressure, so it's error varies. I've seen it anywhere between 1 PSI and 3 PSI off.

[GAS]

Cool, Burning!

For the front forks, do you think it should be a good upgrade to swap the springs? I'm using 15W fluid and my bike has the pre load adjustment that I use at the harder setting. I actually feel the front quite stable, but it maybe can get better, obviously! About the braces, they're a good ideia but I've never felt any steering force when braking.... Probably I'm not pushing it too hard to feel anything!

For the rear shock, I found this at Ebay: which one would do a better job?

http://cgi.ebay.com/ebaymotors/2001-Suzuki-750-Katana-Rear-SHOCK-_W0QQcmdZViewItemQQhashZitem4cf00758a9QQitemZ330444527785QQptZMotorcyclesQ5fPartsQ5fAccessories#ht_500wt_749

http://cgi.ebay.com/ebaymotors/rear-shock-assembly-Suzuki-GSX750F-Katana-750-89-97-_W0QQcmdZViewItemQQhashZitem3f003c02deQQitemZ270586872542QQptZMotorcyclesQ5fPartsQ5fAccessories#ht_1730wt_732

Are they direct swaps or I'll need any heavy grinding?

Now about the pressure! Unfortunatelly we don't have any support from michelin here in teeling us how much to inflate our tires at tracks. I was only wondering that a few pounds less than stock would be fair. Stock pressure is 33f/36r as it says for solo ride and stree ride. And it is what I'm using on the streets, am I doing bad?

I'll try o use your rule of 3PSI hot/cold and check what I find! I'm also purchasing a new digital gauge!

tks man!

[burning1]

The shock with the remote reservoir is the better of the two. I ground a little bit of the spring down to install it on my GS, but you could achieve the same result by grinding a little material off the swing-arm. You shouldn't need to remove very much material - I installed mine using a dremmel.

33/36 seems high, but it's confirmed by the GS Wiki... I'll talk to my rep the next time I go racing. Any chance you could email bridgestone's customer service, to ask what they recommend?

[spaceboy]

Why is the speedo going so crazy?

[GAS]

I really don't know, the cable is brand new, but probably is not properly lubed. I threw some oil inside it but it's still oscilating. I'll try grease next week and see what happen. Maybe it's a problem with the speedometer itself (I hope not)

[burning1]

Be careful about greasing cables. In some cases, lube or grease will ruin the cable.

It should be relatively easy to test the speedometer housing using a power drill. Just don't test it *too* much if you have plans to eventually sell the bike.

[redhenracing2]

I really like two things about this video:

1. The speedometer gives you a vague idea of how fast you're going, more like a friendly estimate 

2. Them supersports fly past you on the straightaway, but then you pass them in the next few turns. GS>SS