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Old September 16th, 2019, 11:06 PM   #1
AbleOpus
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Emergency Braking at higher speeds

So I decided to try some emergency braking going around 70-80kmph. Unlike at lower speeds, my bike destabilizes and wobbles a bit even if I am going straight. Is this suppose to happen? How can I avoid it if possible?
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Old September 17th, 2019, 01:45 AM   #2
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Make sure you release throttle completely when you brake. A lot of riders inadvertently don’t close throttle, or actually increase throttle under hard braking.

Are you using rear brake? You want to initially grab both. Then gradually let off rear as it gets light while you increase front brake. It could be rear tyre locking up and sliding around that you’re feeling.

Try using only front brake only, is bike more stable? Under maximum deceleration, very little braking force comes from rear tyre due to minimal weight on it. So most braking force comes from front.



One thing to check is rear & front wheel alignment using string test.
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Old September 17th, 2019, 05:59 AM   #3
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Originally Posted by DannoXYZ View Post
Under maximum deceleration, very little braking force comes from rear tyre due to minimal weight on it. So most braking force comes from front.
With my 250, and confirmed by the photo above, "very little braking force" is an understatement. Using any rear brake during max braking will do nothing but lock the wheel, reducing steering stability.
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Old September 17th, 2019, 08:14 AM   #4
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Originally Posted by Triple Jim View Post
With my 250, and confirmed by the photo above, "very little braking force" is an understatement. Using any rear brake during max braking will do nothing but lock the wheel, reducing steering stability.
That's always been my theory as well.

In normal conditions with a good front tire, adequate brakes, and practice, there shouldn't be much contact from the rear wheel to get any amount of braking from it. If you are getting any significant braking from the rear during a hard stop you need to be utilizing the front more.

The other factor is mental. Too complicated of a braking procedure will over-tax you in a stressful situation. Sure you can add and subtract rear brake in a parking lot when you are relaxed and practicing, but surprised and under stress it's too much workload IMO.

Keep it simple. Concentrate on modulating the front. That gives the largest benefit.

Others will disagree.

Best thing is to anticipate a potentially dangerous situation and react or remove yourself before emergency action is required.
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Old September 17th, 2019, 08:54 AM   #5
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Best thing is to anticipate a potentially dangerous situation and react or remove yourself before emergency action is required.
Right, and as @AbleOpus is doing, practicing emergency stopping is invaluable.
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Old September 17th, 2019, 10:17 AM   #6
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at speed and threshhold braking, the rear getting loose is more than likely your bottoming the front out, maybe a little more preload/ compression, the bike will cope better and you will brake even harder and the process will repeat ,
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Old September 17th, 2019, 10:22 AM   #7
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Yep, anticipating and avoiding problems will be the best thing. Practicing quick-stops will be the next best thing.

I've locked up the rear a couple of times, just a little. Feels weird but can be somewhat controllable if you know what it's going to do.
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Old September 17th, 2019, 12:56 PM   #8
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at speed and threshhold braking, the rear getting loose is more than likely your bottoming the front out, maybe a little more preload/ compression, the bike will cope better and you will brake even harder and the process will repeat ,
I hadn't thought of that, but with stock front suspension it was very easy to bottom it. For me a pair of Sonic springs cured that.
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Old September 17th, 2019, 01:06 PM   #9
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Quote:
Originally Posted by AbleOpus View Post
So I decided to try some emergency braking going around 70-80kmph. Unlike at lower speeds, my bike destabilizes and wobbles a bit even if I am going straight. Is this suppose to happen? How can I avoid it if possible?
My bike doesn't have an emergency brake.
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Old September 17th, 2019, 05:53 PM   #10
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The wobble happens whether or not I use the back brake. I will probably figure it out with some more practices. I am trying to program in my mind emergency braking at higher speeds so I can do it well when it is needed.

So far, from what I can tell, pressing the rear brake while emergency braking does not provide much stability or braking power at all. It just introduces the possibility of the rear brake locking up. Just touching it while emergency braking can cause it to lock up on my bike. I feel it is not worth using for emergency braking since it could cause problems when emergency braking is applied in a real-world situation.
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Old September 18th, 2019, 02:57 AM   #11
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Yup, testing shows really no benefit from rear brake in maximum-deceleration efforts.

Put zip-tie around fork-blade to record maximum travel usage.

When was last time forks were serviced? Oil may have thinned out and needs replacememt.
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Old September 18th, 2019, 05:57 AM   #12
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A few things that may be causing the instability during hard braking are loose steering head bearings and a worn/scalloped front tire.

Also check the fork travel with a zip tie and service the forks like Danno suggested. If it's totally bottomed I would expect that to have an adverse effect on stability as well.
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Old September 18th, 2019, 07:56 AM   #13
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Remember to 'hug' the tank hard with your thighs when you brake so you take pressure out of your hands thus having morre control on the braking lever and the handlebar.
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Old September 18th, 2019, 08:10 AM   #14
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There's often a rush to blame something mechanical for any issue, because *of course* the rider can't be doing anything wrong, yeah?

IMHO the most likely cause of wobble is you. Chances are you're pushing back against the deceleration and putting unnecessary input into the bars. The bike is fighting you.

As well it should, because as we all know bikes are smarter than we are. It's our job to get out of the #@$#()@ way and let them do their thing. This is a really common cause of tank slappers. The bike hits a bump that causes a steering deflection and the instinctive response is to put a death grip on the bars. That only makes things worse. Chillax and the bike will sort itself out.

In this case, the deflection is likely caused by you inadvertently steering the bike because you're gripping harder to counteract deceleration forces.

So to avoid this in the first place, use your legs and core (i.e. belly), lock into the tank and don't put all your weight on your hands.



On a separate note about hard braking:

Something really important to understand about threshold braking... first LOAD the tire, then WORK the tire.

Never ever grab a fistful of brake all at once. That can instantly exceed your traction budget. If you brake progressively -- first squeezing moderately then squeezing HARD -- then the tire squishes into the pavement, the contact patch gets larger, and the available traction goes up.

It can all happen very quickly, but the key is to be progressive, not abrupt.

Relevant footage about this starts at about 4:20

Link to original page on YouTube.

Another advantage of load-then-work is that when you load the tire, the chassis settles down and gets stable before you ask a lot of it.

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Old September 18th, 2019, 09:59 AM   #15
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Bike status

I recently got the front tire replaced and the bearings were checked during that. They said it was all okay. The bike was not taken care of by the previous owner so the forks might not have been serviced for 19,000km or 9 years. I did the zip tie test. It appears that the forks are bottoming out, but only when I emergency brake. This is normal right? I haven't ridden other motorcycles but the forks do seem a little soft for someone 195lbs. Perhaps I can just swap out the oil to something heavier/thicker.

I managed to mostly eliminate the wobble just with straddling harder and not touching the rear brake. Thew wobble still occurs when I get down to 30 km/h on a slight decline but this may be unavoidable.
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Old September 18th, 2019, 12:15 PM   #16
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Quote:
Originally Posted by AbleOpus View Post
It appears that the forks are bottoming out, but only when I emergency brake. This is normal right?.
It's not unusual for stock suspension, but it's not good. See my post about replacing my front springs above. If it's not severe, you might try a higher fork oil level to increase air pressure in the fork when compressed, but research recommended levels a bit first. There's some information here:

https://faq.ninja250.org/wiki/How_do...he_fork_oil%3F
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Old September 18th, 2019, 04:29 PM   #17
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, i service fork oil once a season, i bet your way under sprung for your weight, when you bottom out the forks the suspension cant compress anymore and the bike will rotate around the front wheel. but your just chasing fairies untill you get the suspension sorted to your weight and skill. my track bike is down right miserable to ride on the street. its skittish and harsh, you got to strike a balance between the 2.
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Old September 18th, 2019, 04:34 PM   #18
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Re

Ok I will look into that thanks.
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Old September 18th, 2019, 07:08 PM   #19
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As noted - your fork spring rates are most likely way too light for your weight.

Oil isn't going to change that. You need the correct springs with the correct oil at the correct level.
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Old September 18th, 2019, 07:14 PM   #20
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As noted - your fork spring rates are most likely way too light for your weight.

Oil isn't going to change that. You need the correct springs with the correct oil at the correct level.
Well, I don't think @AbleOpus told us his weight. Adjusting oil level per the information in the how-to link I posted certainly can make the front less easy to bottom, and if he's a light person it could be enough to fix the problem.
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Old September 19th, 2019, 05:47 AM   #21
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Well, I don't think @AbleOpus told us his weight. Adjusting oil level per the information in the how-to link I posted certainly can make the front less easy to bottom, and if he's a light person it could be enough to fix the problem.
I was going by Post #15 where he said -

"... the forks do seem a little soft for someone 195lbs."

The stock springs are going to be way too soft for a 195# rider I'm pretty sure, especially if he does any amount of "sporty" riding. Getting the correct rate for his weight and riding style will make the front much more predictable and confidence-inspiring.

Then there's the rear...
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Old September 19th, 2019, 07:06 AM   #22
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I was going by Post #15 where he said -

"... the forks do seem a little soft for someone 195lbs."
Right, there it is. Instead of speed reading the thread I should have searched for "lbs".

If I'm correct, he has a 2010 250 though, and I understand that they are spring better than the pregens were. I don't know specifics though.
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Old September 19th, 2019, 03:25 PM   #23
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Factory new-gen spring-rate is 0.65 kg/mm.

For his weight and current bottoming symptoms, he should use something around 0.80-0.90 kg/mm springs for road-use.
For track, we're looking at 1.00-1.10 kg/mm with slightly lowered front-end.
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Old September 24th, 2019, 10:30 AM   #24
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Now that I've read a bit more into it, it does seem like the right approach to replace the springs if I plan on keeping the bike for a long time. Trying to compensate the spring rate with heavy oil, in my case, will slow down the rebound and cause the forks to feel a bit sluggish.
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Old September 24th, 2019, 04:55 PM   #25
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Now that I've read a bit more into it, it does seem like the right approach to replace the springs if I plan on keeping the bike for a long time. Trying to compensate the spring rate with heavy oil, in my case, will slow down the rebound and cause the forks to feel a bit sluggish.
Yes, heavy oil just increases damping. Adding oil reduces air space and effectively increases spring rate with an air-shock sort of result. You really can fine tune the front suspension by tweaking oil level.

But since you're not a light person, starting with stiffer springs would be the right thing to do. My 0.70kg/mm Sonic Springs (10S-070) were a bit under $100 for the pair, including shipping, a couple years ago.
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Old September 24th, 2019, 07:15 PM   #26
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My 0.70kg/mm Sonic Springs (10S-070) were a bit under $100 for the pair, including shipping, a couple years ago.
Unfortunately for me, the base price is $105 for the 10S-080, and I am in Canada. So I'm looking at $160 for a pair of springs. Shoot my face. I cannot find cheaper options.
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