Losing The Rear On Entry

[Roddy]

I need a little help with this one cause it's really got me stumped. It's happened twice now and I thought I had it figured out after the first time but after the second....It's clear that It wasn't the issue at all.

 

Not quite a 90 degree left hand bend (I'm in Australia so left side of the road), entry speed was about 85-90kph (53-56mph), Closed throttle toes on the pegs, no brakes...front or rear, flicking onto my line which I have taken countless times before. Committed and confident.....and just as I get to my desired lean to get me to my apex, before I've even started to get some throttle back on, the back end steps out.

 

The first time it stepped out only a little bit, but enough to bite back into the tarmac and bounce me slightly up in the seat, standing the bike up and sending me and the bike to the other lane. Thankfully without any oncoming traffic. Stopped to check if there was anything on the road that I may have missed. Nothing there, Nothing on the tyre.

 

I figured that I just entered the turn with some throttle on, or at least constant throttle, cause I wasn't accelerating hard out of the exit of the previous corners so there was no need to slow for the turn. I ride a k6 GSXR 1000.....Usually pretty low revs. 4-6 thousand rpm, especially if I'm cruising and not attacking the exits, so I guess I'd get a 1000 rpm increase as I get on the side of the tyre in the corners. I thought that as I lent over further I was getting more into the meat of the power, therefore getting more power down and increasing lean at the same time.

 

The second time I am absolutely sure that I had a fully closed throttle entering the turn (having the previous moment in the back of my mind). Also, I'm pretty sure there was very little engine braking cause It was fairly low revs. Around 4500. It was also a much bigger moment. The rear stepped out almost at the exact same point. Just as I was finishing my steering input and before the throttle roll on, but it stepped a lot further. I was slightly off the seat so as the rear bit, my but slid over the seat rather than being pushed into the air which probably saved me from a highside. It lost traction, gained it again abruptly and slid again...after which it settled down......I banged my left knee into the top of the left side fairing as well. It was a different corner but similar to the first incident.....Same stretch of road. I ended up on the other side of the road, braking hard and then running off the road onto the verge and up a shallow embankment. Very lucky it was all clear.

 

No throttle this time so I definitely wasn't adding any throttle and lean. I think I was pretty loose on the bars (thankfully or it may not have recovered so quickly) and basically wasn't doing anything but letting the bike get on line. Hadn't even started my roll on. I got off the bike to check the surface again. It was clear apart from a pretty small crack in the pavement. Nothing I would thought could influence anything.

 

Sorry for the long post but I'm really baffled as to what I might have done to cause this. I'd be grateful if anyone could shed some light as to what could have occurred. Heading down for a track day next weekend, so I'd really like to get down there without doubt in my mind.

 

 

[YellowDuck]

That sounds very unnerving. Easy to lose confidence when things like that happen with no clear cause. My first thought was engine braking, but you seem to have ruled that out.

 

Can you be 100% sure you are not grounding any hard parts in these situations?

 

Is there any possibility of accidental rear brake application? (unlikely I know)

 

Is there a painted line on the road? Could your tire have contacted it?

 

Are you running the recommended tire size for the rear rim?

 

Did you examine the tire for contaminants near the edge of the tread on that side?

 

Just exploring ideas.

[csmith12]

The list of possible issues is kinda long. Could you help us narrow it down more please?

 

Sounds as if you could be trail braking very deep into these specific corners and/or charging them somewhat. You mentioned it happens between turn in and getting on the gas. Are you still setting entry speed at that time? Are you waiting until a specific part of the turn to get back to the throttle?

 

Also, please stay safe out there on the streets until you get a handle on what is going on.

[Lnewqban]

It seems to be related to the rear suspension: insufficient compression damping and/or excessive tire pressure.

[Hotfoot]

Lots of good ideas on here already, but I'll add a few other thoughts:

Any tension on the bars? I know you said you are already watching for that, but bracing one or both arms can make the back end wag or come around. Take a good look at your body position on that side and make sure you are solidly anchored for turns and also during braking.

Are you running dual compound tires, and could they be getting worn or greasy at the edges?

Was your rear tire fully warmed up, on both sides? For example, did you do something like a series of right turns, then slide on your first left hand turn? Sometimes one side of a tire can cool off if you have no turns in that direction for a while.

 

As others have said, check to make sure your bike is not spitting any fluids on your tire, that your rear brake is not dragging, and that your tire is in good condition. A really sudden and unexpected rear slide would make me very suspicious of either cold tires, fluid on the tire, or something slick on the road surface.

 

How much are you leaning the bike? When you are in a turn and leaned over, are your head and body aligned with the bike, hung off to the inside, or crossing over the bike to the other side? In a left turn is your face near the middle of the windscreen, near the left mirror or near the right mirror?

[ktk_ace]

85-90KPH in a turn on public roads?

 

1) how legal is it ?

 

2) most public roads are not built to be handled at such speeds posted ... (this is not germany)

 

3) fresh tarmac = slippery

 

4) worn tires ?

 

PS. K6= lightest + shortest wheelbased GSX R1000 atm.

the supershort 1,405 mm + 165KG makes it very easy to get overwhelmed esp with stock parts + heavy rider (anything over 160 pounds on a japanese bike is heavy) imho.

 

ANY slight input will upset it much more easily than other super bikes , this is the price u pay for crazy acceleration + flickability (light bike).

[ScrmnDuc]

Welcome to the forum Roddy.

When was the last time you check the air pressure in the tyres?

 

 

 

@ ktk 85-90 KPH is average speed on dirt roads where I live. If your going that slow on the tarmac your road kill

[Roddy]

Hi all, I appreciate you all trying to help me figure this out.

 

Yellowduck, Nope, there was nothing on the road or the tyre. Pavement was clear of painted lines etc. I checked both times. I stay clear of the rear brake everywhere except commuting through town and ride with my toes on the pegs. Definitely not scraping hard parts. I’m not that talented haha (nor would I want to do that on the street).

 

Csmith, I don’t think I was charging. I was riding with very little acceleration out of the turns (enough to transfer the weight but no hard acceleration) and no brakes at all front or rear most of the time. I was keeping a fairly consistent speed through the turns and the short straight bits in between. Hence thinking that I may not have rolled off the gas enough the first time. I was already at a comfortable corner speed well before I turned into the corner in question. No trail braking.

 

The tyre is a standard size 190/50 Dunlop sportsmart and I run the tyres at the recommended pressures on the street. Actually that's a good point guys, I should check them to make sure I haven’t misread my tyre gauge and put in 10PSI extra in or anything haha.

 

It was happening just as I was finishing my steering input. A little way before the apex. Can’t be sure if I had released the pressure on the bar or just trailing it off. Another half a second and I would have been opening the throttle. I'm not entilely certain that I had finished my steering input but I am cetrain that I wasn't coasting on zero throttle at my desired lean. To be honest I didn't have the opportunity to relax on the bars cause I was still steering or just finishing steering.....I was definitely loose on the bars after it started stepping out though. I guess I could have done something weird on the bars just before. Something to be more aware of in future I guess. As for my body position. I know this still needs lots of work. Trying to get on the inside and not twist around the tank....I am improving slowly, but by no means textbook.

 

Hotfoot, you've got me thinking.....It’s actually a fairly new tyre. It was only my 3^rd ride out on it in the twisty bits. The rubber had already been scrubbed all the way on both sides but maybe not for long enough or hard enough? I was always under the impression that if the sheen has been scrubbed off that means the tyre is at optimum.......is that right?

 

I always thought that if something was to slide entering a corner it would be the front.

 

Haha....85-90 on dirt. Now that's something. The road I was on has an 80kph speed limit so I wasn't much over

[ktk_ace]

Welcome to the forum Roddy.

When was the last time you check the air pressure in the tyres?

 

 

 

@ ktk 85-90 KPH is average speed on dirt roads where I live. If your going that slow on the tarmac your road kill

 

Dang, how do i immigrate?

[ktk_ace]

Hi all, I appreciate you all trying to help me figure this out.

 

Yellowduck, Nope, there was nothing on the road or the tyre. Pavement was clear of painted lines etc. I checked both times. I stay clear of the rear brake everywhere except commuting through town and ride with my toes on the pegs. Definitely not scraping hard parts. I’m not that talented haha (nor would I want to do that on the street).

 

Csmith, I don’t think I was charging. I was riding with very little acceleration out of the turns (enough to transfer the weight but no hard acceleration) and no brakes at all front or rear most of the time. I was keeping a fairly consistent speed through the turns and the short straight bits in between. Hence thinking that I may not have rolled off the gas enough the first time. I was already at a comfortable corner speed well before I turned into the corner in question. No trail braking.

 

The tyre is a standard size 190/50 Dunlop sportsmart and I run the tyres at the recommended pressures on the street. Actually that's a good point guys, I should check them to make sure I haven’t misread my tyre gauge and put in 10PSI extra in or anything haha.

 

It was happening just as I was finishing my steering input. A little way before the apex. Can’t be sure if I had released the pressure on the bar or just trailing it off. Another half a second and I would have been opening the throttle. I'm not entilely certain that I had finished my steering input but I am cetrain that I wasn't coasting on zero throttle at my desired lean. To be honest I didn't have the opportunity to relax on the bars cause I was still steering or just finishing steering.....I was definitely loose on the bars after it started stepping out though. I guess I could have done something weird on the bars just before. Something to be more aware of in future I guess. As for my body position. I know this still needs lots of work. Trying to get on the inside and not twist around the tank....I am improving slowly, but by no means textbook.

 

Hotfoot, you've got me thinking.....It’s actually a fairly new tyre. It was only my 3^rd ride out on it in the twisty bits. The rubber had already been scrubbed all the way on both sides but maybe not for long enough or hard enough? I was always under the impression that if the sheen has been scrubbed off that means the tyre is at optimum.......is that right?

 

I always thought that if something was to slide entering a corner it would be the front.

 

Haha....85-90 on dirt. Now that's something. The road I was on has an 80kph speed limit so I wasn't much over

Whats the ambient temps over there? maybe it hasnt warmed up ?

PS. My shop had a tire gauge that reads 1 psi lower so yeah, good if u get your tire pressure checked at various sources

[csmith12]

When are you getting off the seat? Getting off the seat deep into corner entry can cause instability. Do you know when you should be getting your bum off the seat?

[Roddy]

Ambient temperature was about 25 deg C. The tyres were plenty warm. I had been cornering for the last half hour without any loss of grip. I was off the seat a good while before tipping in. Just checked my pressure again. It's just under 40PSI...2 lower than I would normally run on the street, but still 10PSI higher than track pressure...so if anything I should be getting more grip at the expense of a tiny bit more tyre wear.

 

No leaking fluids that I can spot. Both times happened with this new rear tyre on and since its the same tyre as I had on there previously I can only think that the tyre isn't scrubbed in enough.

[khp]

I've been running the SportSmarts on my R1 road bike, and been doing (unintended) knee-downs on the outlap at CSS in Sweden. So those tires should have plenty of grip available, even when "stone cold".

 

I did have a very surprising low side the first day I used them, where doing very gentle 'snakes' caused the back end to step out to the right and never gripping again. That was less than 50 meters from my home, where I had mounted the tires. Seems that this was caused by oil on the road. Since then, I never ever had any indication of the tires slipping.

 

Honestly, I doubt that this is your issue.

[Roddy]

I don’t think I had changed anything about how I was riding. I guess it’s possible (though unlikely) that I went in a bit quicker than usual and possible (very likely) that my lack of technique is finally rearing up it’s ugly head. Twice in 2 successive rides is a bit worrying. Probably coincidence that it’s a fairly new tyre as it already had been put through at least 30 kms of spirited cornering.

I haven’t done the CSS yet. They don’t run it South Australia so it would entail a family holiday interstate to get access to the school. Definitely something I want to do. Hopefully in the near future.

[csmith12]

This has been a tough one based on your comments, as there is no "smoking gun" thus far. So let's break it down to some bare bone basics.

 

1. Assuming same/similar conditions, bike's don't do something different every few laps or every other time out on the street, only riders do.

2. Trust yourself, not your tires. Purposely bring up the temp of your tires, a cool tire on a cool day can surprise you.

3. Can you flick on tires that are not scrubbed in? No, when in doubt... again, trust yourself. Although, we throw on a new set of tires and take a hot lap, then go hard. Ymmv while on the street though. This is why it's important to asses your own risk and trust yourself.

4. Linked corners can be a challenge to get the setup right "consistently". Perhaps these corners are linked with another befor hand?

 

I rarely blame it on the bike. Even a modern stock bike can enable a rider to drag an elbow with good techniques.

[Roddy]

I think I’ll have to go a step or 2 back on this one and work back up to it. Getting more locked in and keeping a loose grip.

 

My track day this weekend has fallen through so I won’t be able to see what’s going on in a safe(ish) environment. It’ll have to wait for next month. In the meantime I’ll tone it back a notch.

 

The corners were linked with short straight bits. The corner in particular had a very slight right hand arc to the turn point which I basically straight lined (staying in my lane of course).

 

I really do appreciate all the input though.

[StevenAthas]

Just under 40 PSI seems really high. I generally run 33-34 rear, 32 front; even on the street. Sounds like either tire pressure or a tire that isn't fully scrubbed.

 

Just my .02c.

[Jasonzilla]

This is strange happenings. The first thing I thought of while reading this is that you mentioned knowing the throttle is closed. I found on my EX-650, but not on my ZX6, that in some corners I still somehow have the throttle open while cornering. If I know the type of corner coming up, I'll give myself a little extra braking room to ensure I have the throttle closed. The little it's open causes me to go wide, but not cause the rear to step out. Then again, it's a 650, not a 1,000.

 

Your suspension is being mentioned, but unless you've changed your set-up, I don't see how this could be a factor, UNLESS the tires are different. They sound scrubbed in and are new, but I'd question whether they're a DIFFERENT type of tire than you've been using. Could be something about the new tire.

 

Then there is the question of your experience level. I don't know if you're new to steeper lean angles, but while getting used to this degree of lean, there are different sensations the suspension will give you because you're not straight up and down anymore. Things change once you get past the comfort zone/natural block of 20-25 degrees. I always thought my front end was washing going into sharper corners. You get over it. By the way you're describing what you're doing, I'll bet you're more experienced at it.

 

The pressure differences being mentioned (1-2 psi) aren't going to be much of a factor until you become more aggressive. Keeping your RPMs low and not "attacking the exits," I'd say a small difference in tire pressures wouldn't have an effect. My thing, as with Steven Athas, is what you're riding on, 40 psi! I used to ride to the track for trackdays, and even at an early morning moderate pace I knew when I had forgotten to deflate the tires. I pulled straight into the pits because I knew there was NO WAY to work around that problem. 40 psi is recommended for when you're commuting to work. Getting on the track and into trackdays, going through twisties on the back roads is not what 40 psi is for. Even without throttle, it could become a problem, and does increasingly so as you heat the tire up. At the trackday next month, find a a faster rider and ask him what he keeps his pressures at.

 

I'd also think csmith12 was onto something. Changes in your BP, when you're shifting your weight, will do some fascinating and scary things to your motorcycle. If you've progressed your BP, it'd be worth reflecting on whether it was a change for the better. Otherwise, this probably wouldn't be a factor.

 

Unless an external factor, road conditions (which you've said is good), fluids (no leaks found), or one of the changes mentioned (type of tire, pressure, change in suspension, BP, somehow still on the throttle) you've got yourself one of the more rare problems with corner riding. Good luck.

[Roddy]

I don't think tyre pressure has ever been an issue before but, possibly with a slight increase in entry speed and a slightly faster flick, it may have become one. I have always run the recommended 36f 42r on the street. For the track I drop them down to 31f 29r.

 

I'm already getting a bit of triangulation on my front tyre running 36psi.....any lower pressure and the tyre will be destroyed on the sides long before the rear, with still plenty of tread in the middle. I could drop the rear a bit but the cheapskate in me wants to keep the wear down as much as possible. Not keen on having to replace the tyre every 4000-4500km. As it was, I would have been lucky to reach 5000km had I not gotten the puncture. I guess that's pretty standard mileage for sticky tyres though.

 

I went to the track last weekend and I haven't been able to replicate (thank goodness) the stepping out of the rear. Knocked off over 2 seconds and had zero traction problems all day. I was a bit apprehensive before the first session but after half a lap, all doubt was gone and my confidence was back to 100%. Also managed to get rid of some of the triangulation on the front.

 

I do love these tyres (Dunlop Sportsmarts), and the rear is the same (size and compound) as the previous one that got a puncture. The only difference was that the tyre was barely scrubbed in. Each edge of the tyre would have touched pavement only several (??) times.

 

Still working on body position, but I'd like to think that I stay pretty still, if a little bit crossed up, before turning in and through the corner. I did, however, watch some footage of myself from another riders bike and I noticed that I was shifting my weight as I tipped in. That footage was from almost a year ago though.......something I should keep an eye on nonetheless.

 

Yeah that's something I found I was doing, keeping some throttle on going into corners. This only happens when I'm not attacking the exits of previous corners and don't have to slow down for the turn entries. I was very conscious of this the second time the rear stepped out, so I'm pretty sure I can rule that out.

 

Wise words guys. Thanks. Although I may have to leave this issue somewhat unresolved as I'm not too willing to do any experimentation on the street and the track seemed to have yielded no answers. I will however take your advice and drop the rear pressure by 4 or 5 psi.

[johnnyrod]

A lot of tyre manufacturers these days seem to advocate 36/42psi but I think that's more for stability, resistance to potholes, and people who don't check their tyres very often. It always was 33/36 and to be honest I don't think anything's changed, and around 32/30 for the track - all generalisms of course but your bike isn't especially heavy after all. All these figures are for cold tyres, just so we are clear.

 

I would check out your rear suspension settings, it does sound a bit like it's being a bit unforgiving. How were the tyre shoulder wear patterns after a day at the track? Maybe even the front rebound, loading up the rear a bit if it pogoes back up? Though I doubt a GSXR can be set that low on anything, even the rubbish springs in the front of my bike as stock never caused that sort of problem.