31 replies to this topic

[Crash106]

I was checking out the video in Eirik's thread about early superbike racing when I noticed one of the guys over brake at the entrance of a curve, slide the rear tire and low side. I've also seen more than one current superbike rider over brake the front tire and low side. BUT ... in all the racing videos, crash videos, mountain rides and twisty road videos, I don't think I have EVER seen someone slide a tire and low side JUST from turning. No, wait, I did see one guy crash a brand new Kawasaki Ninja by turning and adding a lot of throttle at the same time. And I have seen people fall over midway through a turn by adding TOO MUCH throttle.

Am I imagining things, or is turning the bike--without adding brakes or gas--pretty darned safe?

[Eirik]

If the road is dry and clean, you cannot turn hard/rapidly enough to slide the front. On black ice, OTOH, all bets are off

[ktk_ace]

Crash106, on 31 March 2012 - 05:59 AM, said:

I was checking out the video in Eirik's thread about early superbike racing when I noticed one of the guys over brake at the entrance of a curve, slide the rear tire and low side. I've also seen more than one current superbike rider over brake the front tire and low side. BUT ... in all the racing videos, crash videos, mountain rides and twisty road videos, I don't think I have EVER seen someone slide a tire and low side JUST from turning. No, wait, I did see one guy crash a brand new Kawasaki Ninja by turning and adding a lot of throttle at the same time. And I have seen people fall over midway through a turn by adding TOO MUCH throttle.

Am I imagining things, or is it turning the bike--without adding brakes or gas--pretty darned safe?

If its not in a state of de/acceleration, yes, from my experience...(because it doesnt upset/change too much the front back tire loading ratio)

But without gas or brakes, some bikes can still brake / accelerate (i've ridden a few ...not my cupa tea)

[fritzdacat]

Crash106, on 31 March 2012 - 05:59 AM, said:

I was checking out the video in Eirik's thread about early superbike racing when I noticed one of the guys over brake at the entrance of a curve, slide the rear tire and low side. I've also seen more than one current superbike rider over brake the front tire and low side. BUT ... in all the racing videos, crash videos, mountain rides and twisty road videos, I don't think I have EVER seen someone slide a tire and low side JUST from turning. No, wait, I did see one guy crash a brand new Kawasaki Ninja by turning and adding a lot of throttle at the same time. And I have seen people fall over midway through a turn by adding TOO MUCH throttle.

Am I imagining things, or is it turning the bike--without adding brakes or gas--pretty darned safe?

pretty darned safe but not totally safe. Make sure your tires are warmed up, it is possible to lose the front if you don't roll on the gas fast enough after having reached your lean lean angle. Correct me if I'm wrong, the quickflip goes hand in hand with an as early as possible smooth rollon IMHO.

[Eirik]

We are talking pretty deep lean before that comes into play, fritzdacat. At about 35 degrees of lean you still have around 85% of your grip available to brake/accelerate/change direction. I think what Crash is asking is whether he risks crashing from intiating the change of direction, something he will not do under normal conditions, even on a wet road. You need sand, standing water, oil spill, huge bumps or ice - ie noticeably reduced grip - before the turn-in can overpower available grip, at least when it comes to road riding.

[Crash106]

Eirik, on 31 March 2012 - 12:15 PM, said:

I think what Crash is asking is whether he risks crashing from intiating the change of direction, something he will not do under normal conditions ...

Your right, Eirik. I am afraid to change directions under ANY conditions. Pesky darned corners!

[fritzdacat]

Crash106, on 31 March 2012 - 03:10 PM, said:

Eirik, on 31 March 2012 - 12:15 PM, said:

I think what Crash is asking is whether he risks crashing from intiating the change of direction, something he will not do under normal conditions ...

Your right, Eirik. I am afraid to change directions under ANY conditions. Pesky darned corners!

Sorry, hadn't meant to make you more insecure...

Just be aware that with a smooth rollon the bike is in it's most stable condition (after having reached the intended leanangle) , it's sort of like the "zone diet" for motorcycles. The safest way to add (or change) lean angle is without throttle or brakes, you're right about that, it's "pretty darn safe"  

[chipset]

I've never slid the front tire unless it was on a less than decent surface.  And yes, I saved it.  But it was an FJR with ABS on a gravel/dirt road.  

That being said, the front is not going to break loose unless you are:
On a bad surface
Overload the front (which rarely happens unless you give too much brake)
Have cold tires.

The concept is simple.  The front may slide a little bit?  And how do you correct it?   Add more throttle, as it will remove the load on the the front tire.

[Eirik]

Crash, have you ever had to sverve violently to avoid an unexpected obstacle of any sort? Most riders have been in such situations, and when it happens you just yank on the handlebars to get out of danger. There is no time to think about grip, and even if there were, people would still rely on grip to save their arses instead of opting for a certain crash. And even so, I don't think any rider ever lost grip under normal road conditions to such violent inputs.

In other words, the best thing you can do, Crash, is to relax and just accept that the front will stick no matter what - at least until you are beginning to lean far enough to start throwing sparks. Once you accept this, which is basically a faith thing, you can let down your shoulders, loosen your grip and move your focus to stuff that matter. And with focus redirected, you will soon lear to trust the front and simply forget about it.

[Matt]

Crash106, on 31 March 2012 - 03:10 PM, said:

Eirik, on 31 March 2012 - 12:15 PM, said:

I think what Crash is asking is whether he risks crashing from intiating the change of direction, something he will not do under normal conditions ...

Your right, Eirik. I am afraid to change directions under ANY conditions. Pesky darned corners!

There are few things in this world that are 100%. There is always some risk of crashing.

Fear, uncertainty and doubt are often more harmful that the original concern though. These contribute to SRs. When riding, confidence is essential. The only way I've found to develop this confidence is by previous experience. Most riders, after a few track days or a school, experience the limits are much greater than they previously thought and become confident routinely turning (and braking and leaning, but not all at once!) at much higher levels. Then when encountering the need to turn suddenly to avoid a car e.g. it is a practiced skill - reaction - and doesn't trigger SRs as much, leaving attention for other things.

[Crash106]

Eirik, on 31 March 2012 - 06:54 PM, said:

Crash, have you ever had to swerve violently to avoid an unexpected obstacle of any sort?

I haven't had to swerve for real, but I do practice swerving and that is one of the few times I get some feedback or a feeling my tires are gripping. I have often wondered if I could just keep that level of swerve going and use that much speed at the entrance of a curve. I haven't fallen over yet! That supports my theory that it is pretty hard to slide the front tire just by turning.

Now here is something that might explain the seamingly contradictory feedback I get from my tires.

I saw this new product called a Leanometer. It measures lean angle and acceleration forces. For exampe, in the video below, at 1:46, you can see the bike has just rounded a corner with 34 degrees of lean, a pretty good lean angle for the street, and those bars over at 2-o'clock indicate only .5 Gs of lateral accelleration. I have heard street tires are good for 1.2Gs and race tires might go 1.4. So, the rider in the video is leaning over pretty far, but using less than half the tire's available grip. Even on that supermoto, he might not have a good sense that the tires were gripping.

[Lnewqban]

Crash106, on 04 April 2012 - 01:43 AM, said:

Now here is something that might explain the seamingly contradictory feedback I get from my tires.
........... Even on that supermoto, he might not have a good sense that the tires were gripping.

Could you explain this a little further?

[Crash106]

Sure. If I read the Leanometer correctly, in the street bike segment, the rider is leaning over a fair bit, but according to the meter, he is not putting much stress on the tires. I see five hatch mark segments lit up across the top of the display. The literature at the website seems to indicate that five hatch marks means the rider is only generating .5 Gs of side force.

If I were driving a Mazda Miata at 35 mph, around a corner that the tires and vehicle could take at 70 mph without sliding, well, I would probably get very little feedback from the tires. They would not be sliding, squeeling, screaming, wiggling or doing much of anything really. At that speed, the tires might not even be properly warmed up yet.

So, if I'm just riding around one up, at the speed limit, on my motorcycle, I might be getting very little feedback from the tires because they just don't have much to say. They aren't howling because I'm not breaking very hard. I don't get a sense of GRIP because I'm just not asking them to grip very hard. I feel uncomfortable turning in because I'm getting so little feedback, when that's exactly what I SHOULD be getting when I'm riding well within the bike's and the tire's traction limits.

In other words, I'm just over thinking the whole turn in "problem."

-----

However, what confuses me in the video is, if you keep watching, you'll see the Leanometer in race mode. On some corners, I see numbers like 48-degrees maximum lean. Okay. Race bike. On the track. Completely believable. But it LOOKS like those hatch marks around the top are indicating 2 Gs of side force (20 hatch marks). Please correct me if I'm wrong, but I don't think ANY motorcycle race tire will give you two gravities of grip. So, I may be full of beans.  

I'll contact the sellers and report back with their answers.

[Crash106]

I wrote to the folks at Leanometer and detailed the issues from the above post. Here is what Steve had to say:

Thanks for the email.

Firstly, congratulations - you're very observant! Secondly, you're absolutely right - motorcycle tyres could not achieve 2g of lateral force.

The footage taken at Qatar was with development software, which scaled the lateral force by a factor of 2, so each hatch mark is in this case 0.05g, giving a total range of 1g. The reason for doing this was for road riders: most road cornering is taken at a more sedate pace, and we thought it would be a good idea to increase the resolution of the scale. For the road this works well, as you can see more clearly your level of cornering force. However, for a well-ridden race bike on slicks, the scale maxes out too easily, and you can see this in the video. The accompanying data from the ride shows about 1.25-1.3g maximum lateral force, which is what you would expect. Since then, we have changed the scale to make it more suitable for the track. In future, we'd ideally make the scale adjustable by the user.

Please feel free to share this response - in fact we're always happy to talk about this and other aspects of cornering.

Best regards
Steve

Makes sense to me. Also, very interesting how much MORE force is being applied to the race bike tires than the street bike tires.

[Lnewqban]

You really look carefully, Crash106.

Consider that the instrument measures the inclination of the frame respect to a vertical plumb (internal gyroscope).

However, the actual angle that corresponds to the acceleration and force vectors is always smaller than the inclination of the frame, unless the rider hangs off enough to compensate that difference.

This discrepancy of the angles comes from the off centering of the contact patches respect to the center line of the frame.

In the video example,  the bike has just rounded a corner with 34 degrees of lean; however, the 0.5 Gs of lateral force corresponds to 26.6 degrees.

The instrument also contains an accelerometer, which is able to measure the total acceleration that acts on the horizontal plane.

The total acceleration can be  split in longitudinal and centripetal acceleration values.

The centripetal acceleration is what the lean of the bike compensates.

However, the angle of lean is not directly proportional to that acceleration and its reaction: the friction force or grip of the tires.

The proportion goes like this:

10 degrees: 0.18 g
20 degrees: 0.36 g
30 degrees: 0.58 g
40 degrees: 0.84 g
50 degrees: 1.19 g

[Eirik]

60 degrees equal 2G, I'm led to believe.

[ktk_ace]

Eirik, on 31 March 2012 - 12:15 PM, said:

We are talking pretty deep lean before that comes into play, fritzdacat. At about 35 degrees of lean you still have around 85% of your grip available to brake/accelerate/change direction. I think what Crash is asking is whether he risks crashing from intiating the change of direction, something he will not do under normal conditions, even on a wet road. You need sand, standing water, oil spill, huge bumps or ice - ie noticeably reduced grip - before the turn-in can overpower available grip, at least when it comes to road riding.

only on modern 17"  bikes with fat tires i believe...

Ride a 10" scooter and you'll be surprised how much degres of lean  it can take before turning nasty...  

[Lnewqban]

Eirik, on 08 April 2012 - 09:25 PM, said:

60 degrees equal 2G, I'm led to believe.

Close; at 60 degrees the centrifugal force and tires' lateral grip are 1.73 times the static weight.

2G would be reached not far from 60: at 63.4 degrees.

At those extreme angles, forces escalate quickly and things may go out of control soon; hence, proper throttle control there becomes more critical.

"A motorcycle becomes potentially less stable as lean-angle increases......as we have seen, throttle-control plays a huge part in stability; the steeper you go, the better throttle control must be." - K. Code in TOTT2

Attached Files

•  G force vs Lean Angle.JPG   22.63K   17 downloads

[Eirik]

Thanks, mate, for clearing it up further

[mugget]

Hey Crash, it sounds like you were spot on with your observation about the turn in speed. You've practiced swerving - you bet you can turn at the same speed into a corner! I think it was Keith Code himself who has been cited as trying to quick steer so fast that the front lost grip, and he didn't manage to do it. Adding throttle, brakes, or making additional steering inputs are what will bring you undone. This is true for every single example I've seen. The MotoGP/WSBK etc. replays are great to see this - take a close look next time and you'll be guaranteed the rider makes a change to throttle/brakes/steering to cause the crash. It is never just because of turning in.

You should be confident that you can turn quick and you don't need to pick up the throttle straight away either. That is just about another topic in itself, but for the sake of road riding consider an example where you are approaching a turn faster than you planned - in this instance the best course is to leave the throttle and brakes alone, just concentrate on turning. You can use high lean, right to the apex or past it, without throttle. And I mean literally closed, zero throttle. Once you 'accept' this and have confidence in it, it leaves so much free concentration to focus on turning.

(As always, all the points I mention are assuming good tyres at operating temperature, good road surface etc.)