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Understanding That I Have Never Cornered A Motorcycle


faffi
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Just read an old test of the 1986 Ninja 250. Among the scenarios it was put through, was a day at Willows. Reaching an indicated 100 mph over the straight, it headed into turn one with the throttle wide open, yet lost 25 mph through the corner! In fact, cornering zapped so much power that they had to shift down at the exit of most corners to get enough power to continue, despite having the throttle pinned virtually the whole lap.

 

I cannot recall ever having cornered hard enough to lose 25 mph from friction losses. Not even close. Hence the conclusion that I really haven't cornered.

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We had 2 of those bikes for a while at the school, some of the coaches rode the snot out of 'em. That was a couple of the years I wasn't there, so didn't really have a go personally.

 

They also had a class there and raced them, good fun from what I hear.

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They are sick fun on a tight track and all around good fun. I still toss mine around quite often and have a full race season planned this year in the 250 class. Can't say I have ever lost 25mph cornering though. Although it would be easy to loose that much speed with a heavy rider, long uphill sweeper with the wrong gearing. 27-30hp don't go very far. lol

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Just read an old test of the 1986 Ninja 250. Among the scenarios it was put through, was a day at Willows. Reaching an indicated 100 mph over the straight, it headed into turn one with the throttle wide open, yet lost 25 mph through the corner! In fact, cornering zapped so much power that they had to shift down at the exit of most corners to get enough power to continue, despite having the throttle pinned virtually the whole lap.

 

I cannot recall ever having cornered hard enough to lose 25 mph from friction losses. Not even close. Hence the conclusion that I really haven't cornered.

 

So... just out of curiosity, how much speed DO you think you lose (or have lost) in a given corner? I'm not sure that is the easiest thing to figure out or observe, unless you have telemetry to tell you. My racebikes don't have speedos but even if they did I'd be unwilling to look at the speedometer at wide-open throttle at 100 mph at turn in and again immediately after!

 

(I do have a GPS timer that could probably tell me.... if I could get around to setting up the software and comm link to a laptop.)

 

BTW, Turn 1 at Willow IS uphill, and banked (and a comonly used line DOES partially climb the bank), and I think the last bit of straight before it is uphill also. The poor Ninjas are doing everything they can just to overcome the wind drag at 100mph, let alone go up a hill... :)

 

I wonder if a sharp lane change on the freeway (without changing throttle position) would generate enough friction loss to see a noticeable change on a digital speedo?

 

And I do so agree that Ninja 250 racing is a blast, easy to get into and relatively cheap and really competitive. The grids are pretty big right now, although the advent of the Ninja 300 may cause trouble by splitting up the grid into two separate classes.

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When I raced a 250 ninja I could "only" reach about 110 on the front straight (long uphill) of Road America but could reach 128 coming down the hill into turn 5. I didn't have that problem on 600cc bikes though, both directions the speeds were the same. Perhaps I shouldn't have paid attention, but sometimes I felt I was simply camping on the straights and had time for a glance. To some extent I used that speed as some indication of how well I was getting off the last turn.

At BIR, I would also be 128 coming into turn 1 and keep it pinned all the way through and slowly lose speed the entire time. I don't remember the number but I seem to think I exited about 10 mph slower. Again, I didn't have that issue with the 600's.

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I think 100 mph is the top speed of the Ninja 250.You will loose speed quickly at the top end because it is going all out, and getting off the throttle or leaning hard will slow you down pretty quick from the top speed to maybe 85-90 mph.Besides it takes a bit of road to hit 100 mph, compared to say a 600.

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Not to split hairs or anything;

 

2007 and earlier 250 Ninjas had a production top speed of 108

 

2008 and later it is 98

 

Now when you set up for racing either can surpass 110

 

My 250 was actually a 285, web cams, bigger valves, along with a few other goodies. I didn't race a production class with it, or what is now thought of as the 250 "spec" class which locally is only for 2008 and newer models.

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Assuming that the engine is working at the rpm's that produce maximum HP (since the bike is moving at its fastest reachable speed), when leaning the bike, those rpm's increase due to the reduction of the diameter of the contact strip of the tire.

 

That increment of rpm's move the engine over the performance curve to a point of lower HP (toward the right of the peak of the HP's curve).

 

Since HP = rpm x torque and rpm's did increase, then the torque on the rear wheel got reduced much more than the increment of the rpm's.

 

As the rear wheel is weaker and pushing with reduced thrust, the bike encounters more resistance due to:

 

-The deformation of the rubber of the front tire to keep a circular trajectory.

 

-More weight due to the G induced by the centripetal acceleration (which translates in bigger contact patches).

 

-More aerodynamic resistance due the rider's hand up position during the turn.

 

-Uphill of that turn (as described by Hotfoot above).

 

Those extra resistances consume energy and naturally slow the bike down.

 

Rpm's return back to the point of max HP (peak of the HP's curve), but because the torque available there is still not sufficient to compensate for the increased resistance, the engine regime continues moving back over the performance curve, loosing more rpm's but approaching and eventually reaching the point of maximum torque (peak of the torque's curve, which is around 11,000 rpm for that bike).

 

An opportune downshift from that point, will move rpm's closer to the point of max HP again.

 

Engines of higher cc's and torque have more tolerance to changes in rpm, so the reduction in torque in similar conditions is not so pronounced as for a 250.

 

You may have cornered hard enough, Eirik, its only that you have not done it on a 250. :)

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  • 2 weeks later...

(I do have a GPS timer that could probably tell me.... if I could get around to setting up the software and comm link to a laptop.)

Hottie, just saw your post. I believe you have the same brand GPS timer as me - Starlane. Installing the software is fairly easy, but if you have one of those with bluetooth download it can be a bit of a hassle to get to work. If you had stopped by the schools at Willows (big/street) in beginning of October I could have helped you get it rolling.

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