Always Accelerate During A Corner - For Real?

[noamkrief]

So every source I've read or heard says to accelerate through the corner.

The reason is simple - the rear tire is wider and can handle more load. Therefore - you must accelerate to transfer some weight to the rear to give the rear tire it's fair share of load.

 

Even in the riding school to get my motorcycle license they say to brake, and once leaned, crack the throttle open and accelerate.

 

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... So if I start with a maximum lean angle initial turn in, and I accelerate - won't I have to increase lean angle to maintain the same radius turn? If it's a constant radius turn - that could pose a problem.

 

If we take this one step further - a 360 degree turn non stop round and round - how can we possibly accelerate at the recommended .1-.2 G's? Eventually, we will go too fast to stay in the turn...

 

Maybe this is one of those beginner B.S. techniques?

When I first started tracking cars - it was the same thing. Accelerate through the corner. When I started getting faster and faster and got into actual racing, it was obvious that technique would never work because on long turns you can't accelerate forever - you'll either start pushing the front or oversteering - simply put, you end up going too fast during the turn.

With cars, when you start really going fast, you trail brake carrying loads of speed all the way right before the apex. That point is your slowest point. By no means - SLOW. Because you are going in so hot into the corner under light braking that the back end is always just about to give up... Once at the apex (a bit before depending on the corner) you get on the throttle and accelerate. The acceleration plants the rear end, but also rotates the car since the rear tires are on the verge of being overloaded and slip a little bit. That slip (slight oversteer) points the front towards the inside of the turn. (THIS is not a drift, it's very subtle and probably only the driver is aware of it through steering wheel feel).

 

Anyway, if I would drive a car and get on the throttle right as I turn, and I can accelerate through-out the long 180 degree corner and stay on the road it only means one thing - I'm loosing time because my entry speed was too slow. Most common driving error in comparison to really going fast? Overslowing for a corner. I could have carried more speed into the corner.

 

I remember when I first started tracking cars, the advanced group seemed impossible to achieve. They were so fast.

Now after having to run with the front runners in actual racing, when I go to a track day in the advanced group - even with a 20 year old BMW, it's like a parking lot - they are SLOW! And it's obvious why. The advanced group drivers have good car control. They can drive at the limit from the apex to corner exit. That gives them good speed down the straights. But they are still using the old methods that you learn in car control clinics - slow in, turn, and power through the corner... They are all overslowing for each turn.

Without getting too technical, to truly go fast in a car, and maybe in a bike, there should NEVER be a point in which you have a constant radius turn. In a 90 degree turn that is constant radius, you should choose a line that is as follows:

1)You start your turn in at high speed

2) As you trail brake into the corner your speed decreases and your radius increases.

3) once at the apex - that's your slowest point, and tightest radius

4) at the apex you start accelerating and naturally unwinding the steering wheel - which increases the radius

 

So at no point you maintain a constant speed and radius. It's constantly changing.

 

I'm inclined to think the same applies for bikes, but I'm new to all this so I thought I would ask.

 

 

PS - On the other hand - there is a thing called "momentum cars" and "high powered cars".

In high powered cars - it's like point a shoot! You slow way down, get the car rotated to the exit - and get on the gas - hard!

 

What are bikes like? Point and shoot? Or momentum?

 

PPS - I've been reading that flicking the bike quickly on turn in in is KEY! In cars, we "build up" traction. Meaning that i can't just turn a car from a straight and do 1.5G's. You kind of have to ease into it to let the tires build up lateral traction. So when we flick the bike too quickly, are we not letting the tires build up lateral traction properly? Just thinking...

[faffi]

You want primarily to accelerate to put the suspension in its best range - meaning roughly 40% weight on the front and 60 on the rear. This also balance the grip available on most modern bikes, as you noted about width. However, you can at least partly achieve this without gaining speed since it takes a lot of power simply to maintain a constant speed. It's called maintenance throttle, and that's what you use until you can see your exit and know you can increase speed without running out of road.'

 

At least that's how I understand it.

[noamkrief]

I think I understand. Even though your speed stays the same, you are still accelerating hense achieving the 0.1 G's in acceleration Code speaks of to transfer 60% of the weight to the rear. I can live with that!!!

 

Funny how motorcycles have thin tire in the front and wider in the rear. For cars - that's a formula that would guarantee an understeering car = slow!

 

But i'm sure the engineers have already got this figured out - staggered setup is best on motorcycle. Just don't really understand why.

 

If I had to guess, a motorcycle doesn't actually need the front tire during mid corner and especially corner exit phase. I can imagine a motorcycle exiting a turn with an aggressive lean angle with the front wheel hovering about an inch over the pavement. The front wheel doesn't actually do the turning - as in a car. The LEAN does the turning! I think I got it no???

 

The front wheel is primarily in charge of initiating the lean - just like in a car, you steer left, the bike turns left (for a split second) as the weight transfers to the right, and the bikes pretty much falls over to its right side - and there you have a rightside lean - and a right hand turn.

 

I've read alot online about why the rear tire is wider. Most common answer - because it needs to accelerate the bike.

That doesn't make much sense to me - because braking force on a motorcycle or car is much greater than acceleration force, so with that reasoning, the front tire should be wider....

[eugenef15]

If the front tire was wider it would be heavier and take more effort to get the bike leaned over as well as not being able to do it as quick decreasing the amount of speed you can carry into a corner. This would also make the rider use a lot of energy.

[Lnewqban]

... So if I start with a maximum lean angle initial turn in, and I accelerate - won't I have to increase lean angle to maintain the same radius turn? If it's a constant radius turn - that could pose a problem.

 

If we take this one step further - a 360 degree turn non stop round and round - how can we possibly accelerate at the recommended .1-.2 G's? Eventually, we will go too fast to stay in the turn...

 

Your logic is correct.

 

However, the recommended 0.1 ~ 0.2 g acceleration to balance the load on the contact patches only adds 3.22 ~ 6.44 ft/s (2.2 ~ 4.4 mph) of speed for each second spent on the turn.

 

Hence, the entry-out speed difference will be smaller for high speeds, precisely the conditions that generate higher skidding forces (lateral g's) and therefore, require better balance of tire's loads and better suspension's ranges.

 

For slower or higher radius turns, lean angles (skidding forces) will be less dramatic; hence, the acceleration may well be less than recommended in order to make the entry-out speed difference less dramatic (due to the increased time that the turn will take).

 

Example: In MotoGymkhana practices, going around cones a couple of turns (~700 degrees rotation / ~5 seconds) with the steering bar against its lock, we don't accelerate at all.

 

..........I've read alot online about why the rear tire is wider. Most common answer - because it needs to accelerate the bike.

That doesn't make much sense to me - because braking force on a motorcycle or car is much greater than acceleration force, so with that reasoning, the front tire should be wider....

 

You are correct, acceleration is not the reason.

 

A stoppie proves that the front tire can handle deceleration (more than 1 g) and full weight of bike+rider.

 

I believe that the reason is gyroscopic effect (or angular momentum), which helps in the rear for the reasons that you explained above.

 

For quick turns at high speeds, minimum gyroscopic effect on the front is desirable.

 

Even during a wheelie, inadvertently steering a strong gyroscope in the air would upset the balance of the bike.

 

Consider that gyroscopic effect decreases/increases directly with the mass of the tire, and is proportional to the square of the angular velocity (or speed of the bike).

 

http://en.wikipedia.org/wiki/Gyroscope

 

[faffi]

Also, a wider tyre is far more affected by bumps, causing steering torque. Holding a precise tracjectory will be very difficult with a 200 mm front tyre. Plus the already mentioned heavy steering.

[ktk_ace]

IMHO

 

bikes dont have the luxury of 4 wheels to load and spread the weight in a corner.

 

Just forget about everything that you have been taught and start on a clean slate on the book and DVD. I did and it helps tremendously,

 

ANything pior to that is just excess luggage and WILL get in the way (at least it for me, having to unlearn is not optimal)