accelerating during a turn for maximum stability - Page 2 - BMW S1000RR Forums: BMW Sportbike Forum
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Old 12-04-2012, 09:41 AM   #11 (permalink)
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Quote:
Originally Posted by noamkrief View Post
makes sense. So a the skinny front tire allows for a quick flick turn in, and then the wider rear tire actually handles the cornering forces.

Thanks for the reply!
Noam
Both tires are handling the cornering force unless you're floating the front on corner exit like Stoner and co.

The rear tire (and front also) will actually have a larger contact patch when leaned over than when upright.
On liter bikes like our s1000rr you get 190/55 rears, but if you look at bikes with a smaller power output, like 600s, they run narrower tires like 180/55 etc.
The reason is because with less power you can get away with a smaller contact patch, and using a smaller crossection gives the benefit of quicker steering.
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Old 12-04-2012, 10:09 AM   #12 (permalink)
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Old 12-04-2012, 02:59 PM   #13 (permalink)
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My two cents,

I am not a pro, i have been to a couple of track days and i have entered a few races with pretty good results. For me i typically get all my heavy breaking done before i get into the corner. Once all my heavy breaking is done depending on the corner i tend to trail break before i hit the apex of the corner. Once the apex is visible and i can see the bend of the corner i start getting back on the throttle and i maintain whatever speed i have going in. But that sometimes changes for me, for sometimes i can get on the throttle a little hard to give me more speed in the actual corner. Sometimes though getting on the throttle to much can sometimes cause the rear to step out. Good balance, little movement and little input into the handle bars helps with going fast.

Everyone has there own method on going fast, A basic understanding of the core principles on turn in and breaking and understanding you bike changes from person to person. Its safe to say that there is no cookie cutter answer for i know i can take a corner differently each time just buy paying attention to what i did in previous and listening to what the bike is doing and understanding what the bike did correctly or incorrectly based off of my inputs.

Again my two cents
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Old 12-04-2012, 03:39 PM   #14 (permalink)
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I've read that the reason for the differing tires sizes on bikes is to make they inherently oversteering for safety reasons - in steady state cornering you want the rear to slip first which is more controllable by the rider; understeering in a single-track vehicle where the front tire starts slipping first is inherently dangerous.

How this objective relates to why the rear is wider is a puzzle to me. I thought the Porsches were designed with wider tires in the rear to make them understeer rather than oversteer.

- Mark
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Old 12-25-2012, 01:21 AM   #15 (permalink)
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Best I can offer you is the following diagram.

Trail braking takes a LOT of practice, patience and skill. You've got to know where to enter the turn and exit the turn. It is not easily mastered so practice, practice, practice.
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Old 12-25-2012, 02:49 AM   #16 (permalink)
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Quote:
Originally Posted by markjenn View Post
I've read that the reason for the differing tires sizes on bikes is to make they inherently oversteering for safety reasons - in steady state cornering you want the rear to slip first which is more controllable by the rider; understeering in a single-track vehicle where the front tire starts slipping first is inherently dangerous.

How this objective relates to why the rear is wider is a puzzle to me. I thought the Porsches were designed with wider tires in the rear to make them understeer rather than oversteer.

- Mark

Porsches have wider rear tyres for 2 reasons:
- to get the power down in a straight line i.e. help with wheelspin
- to help prevent oversteer in the case of throttle lift mid-corner.
This case is not such a problem in the porsche 911 since the 993 variation, but the older cars had a problem with balance being off due to the engine being stuck out the back, and the suspension not being up to the job.
A quick description of the issue is:
imagine driving into a corner on the brakes, and then getting on the throttle just before the apex
( the car will go from loading the front on the brakes, to loading the rear on the throttle), and then imagine you overdid the corner and have to lift off throttle (the car will be turning and the front will load up due to being on a trailing throttle, and the rear light).
In extreme cases the car's engine's moment of inertia will cause the back of the car to come around and it will oversteer violently.
911s were famous for it.

Bikes luckily don't have the engine-out-the-back problem
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Old 12-25-2012, 10:58 AM   #17 (permalink)
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Quote:
My question is this:
Once you get into long turns - 180 degrees or even 270 degree turns, if you enter the turn and flick the bike quickly to an aggressive lean angle and you start accelerating, what would keep you in the turn exactly? The more you accelerate, the faster you go, and the more lean angle required to maintain your radius...
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Cracking the throttle and accelerating can be two different things. Cracking the throttle can mean just achieving maintenance throttle. No longer decelerating but not yet accelerating.
I agree with 1000RR. Donít mistake accelerate with maintenance throttle. In the type of corner you mentioned, if all of your braking is complete before the flick, I would use maintenance throttle until I spotted my exit. Then I'd start accelerating. If you feel you can accelerate sooner, try carrying more entry speed. Remember the same principal holds true on bikes as in cars, your cornering forces will slow you down too.
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Old 12-25-2012, 02:29 PM   #18 (permalink)
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Corner entrance & exit speed is all about where you are then you enter the corner ... how far you can trail brake into the corner before you need that
grip to steer though the turn, there is a fine line there, to much brake you
will loose the front and low side ... Each corner will dictate where you need to be... once off the brakes pick-up the throttle accordingly to what the
corner is doing .... once you have hit the apex , pick-up the throttle...
reduce your lean angle, get on the fat part of the tire..accellerate according
to how the corner finishes ....
Experience, my friend... you & only will know what feels right..............
Track riding , Street riding are too differant worlds ... don't get them confused
Take your time... don't be in a hurry ... be smart, ride with your HEAD.....
not your right hand !!!!!!!!!!!!!! hope that helps
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Old 12-25-2012, 04:14 PM   #19 (permalink)
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Not necessarily accelerating, more maintaining drive throughout that stabilizes the bike.
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Old 12-25-2012, 07:38 PM   #20 (permalink)
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Quote:
Originally Posted by Gamisou View Post
Not necessarily accelerating, more maintaining drive throughout that stabilizes the bike.
Quite right.

A machine (whether it be car or bike) is most stable in a straight line at a constant speed. This allows the front and rear suspension to both not be overloaded and I be balanced so it can do the job its designed for as easy as possible. The three forces that affect a bike are accelerating, braking and cornering forces each of which have to be carefully balanced in order to achieve maximum machine stability.
If you exert more on one of these forces then there is less tyre grip available for the remaining forces.

i e If you accelerate like stink then you're not going to be able to turn a corner very well or if you're really banked over and you open the throttle aggressively then nasty things are likely to happen (I'll let you use your imagination on that one)

As it is in the initial question the safest way to negotiate a corner is at a constant speed. When you do go round a corner one of the reasons why you slow is due to the fact that bike tyres are circular across the width of the tyre. So essentially your tyre circumference lessens as you near the edge which causes your speed to actually reduce. Much like how at a certain rev each gear has a different running speed. So to compensate this deceleration and to maintain a constant speed you need open the throttle enough to achieve that.

Often the term 'driving' through a corner is mistaken for accelerating. It really isn't that clear. What it should say is throttle enough through the corner to maintain that speed (Obviously your speed has to be appropriate to actually negotiate the corner)

Anyway, that's the safest and most stable way to get through a corner. If you want to go as quickly as you can then that's a different matter. I'm sure those that do track days are far more knowledgeable than me in those circumstances.

P. S. Merry Christmas!

Last edited by Porridgewog; 12-26-2012 at 05:48 AM.
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