Handling and Akrapovic

[stratford-steve]

Realy sorry to see some twat has destroyed our site. Lets just get on and rebuild and enjoy!

On to my topic: I have posted about issues fitting an 4-2-1 Akrapovic over the past weeks and thank all for their input. I have a slightly new angle to discuss having now ridden the thing for the first time on a good run.

Firstly i can say it has transformed the whole feel of the bike in a way i thought impossible. You can really feel all that weight gone and the newly acquired power rush over 6,000 is fantastic....however....i didn't expect the following.....

I am used to slamming it down several gears instead of using the brakes when riding fairly quick, it gives a great sense of control and allows great drive out of bends. Doing this as usual i was locking the back wheel. That is without touching the front or rear brake, i was finding the revs suddenly dropping off and the back wheel trying to come round. It might look real cool when Haga is doing it but it scarred the sh1t out of me the first time!

I can only put this down to loosening so much weight, so far back. Anyone else had this happen, will fitting a rear height riser help?

 

[Snowdog]

The weight is the factor here Steve, have noticed it seems to step out quicker when accelerating(Bloody marvelous for leaving darkies everywhere!!!) Changing down is awesome too, although i have had it done on me with other cans on, the Akrapovic system does make it a little more interesting by happening a lot quicker than before and makes for some nice looking rear end slides when banking into a corner...or so i've been told.

All in all you will get used to it, just take it easy for a while and build it up slowly. Then when summer comes....woohooooooo!!!:yo: R#? R#?

 

[Jaws]

Tis like SD says, lack of weight over the back wheel..
But there is also another factor to take in to account here.. The rather saggy front forks.
Ok, when not using the front brake you would think that does not come in to it, but you are still transferring weight to the front.. The forks sag and that adds the weight transfer which in turn makes the arse end lighter still, which in turn helps the wheel to lock..
As a matter of interest, I read a rather interesting article in PB or Bike last month.. They were saying that when you accelerate hard, the rear end does not swuat as we would expect, but it actually rises...
me being the sceptic I am, I arranged to do some tests ( as best I could using simple tools such as a video camera and a couple of willing helpers..
The results were not conclusive.
The R6 did not really move much at all, but I must admit the bird did seem to rise up ! Very VERY odd !!
Does anyone have an explanation for this behaviour.. I find it hard to believe it is just the pull on the chain doing it.

 

[EdCBRCastrol]

If you look at the physics involved:
The pivot of the swingarm is higher than the centre of the rear hub and i think slightly higher than the centre of the chain drive, therefore when 100+ BHP pulls on the chain it will try to shorten the distance between the sprockets thus pulling the swing arm downwards. I reckon the power of the engine raising the bike is a little bit more than the force of 15 stone trying to lower it.
Could be totally wrong but it seems logical to me.

 

[Snowdog]

Jaws I'd say the logical answer to the rear rising when accelerating would be to the effect of downforce on the front end???

Discuss?

 

[Quiney]

It's all in the gospel

according to Keith Code (Twist of the Wrist II)

He comments that most people think that the rear end squats under acceleration, but it actually rises. To prove it he suggests putting the front wheel up against a solid object ie wall, and then begin to engage the clutch with the transmission in gear - the back of the bike will rise.

 

[NoBBy]

Re: It's all in the gospel

Originally posted by Quiney
To prove it he suggests putting the front wheel up against a solid object ie wall, and then begin to engage the clutch with the transmission in gear - the back of the bike will rise.

It may well rise but does it rise more than the front?? Try riding at night and the harder you accelerate the more the light beam rises.

Also it make me laugh how many people claim their bike handles better when they've made a small but expensive weight saving. I can't honestly say I've ever heard anyone ever say how much better their bike handles on an empty tank !!


Paul

 

[Quiney]

Rising headlight beam

is because of weight transfer.

At standstill the bike has approx 50/50 weight distribution front/back.

When you accelerate, the effect is to transfer weight onto the rear and off the front wheel. Less effective weight and the suspension causes the front to rise.

 

[XXscraper]

Jesus...........heavy shit, what have you started steve?

So if the back end is rising under accelleration this means more downward force on the back tyre = better traction when upright....which is good for drag racing :beer:

Does this mean maybe that when accellerating hard whilst banked over there is more of a tendancy for the back to slide out (as happened to me once :h fookin woke me up after stopping the snaking and the tank slapper that followed)



Hang on steve, i have just reread you comments and think maybe the 4 into1 gives you more engine braking and that is all that it is, nothing to do with less weight on the back wheel at all. I have locked up the back before by knocking it down too many gears before a corner with just stock pipes but bet your engine now brakes very well. Lucky you m8, just be ware not to expect it to drive like b4, but think you have already done that :}

 

[stratford-steve]

Won't drive as b4???

Go on give me a clue, what do you mean won't drive as before, it drives fantastic.

I too have had the back end lock up on standard pipes once before, mine was doing it frequently on the maiden voyage with the new pipes but i can't notice any more engine brake, i think it is just down to the weight reduction so far back.

On another topic, i have heard the Akrapovic system produces 149 BHP at the back wheel on a normal injected Bird, but what about when replacing the Cats? We all know Cats reduce power, we were all told that the bird was tweaked to give it more power before the Cats were fitted, so when they were fitted it brought it back to as before, so what has removing them done?

As for the previous thread about reducing weight improving handling, my point is I don't know if it has improved handling, it's just very different and feels sharper.

 

[XXscraper]

No knock

No, i never meant that as a bad thing, think you have misunderstood the context. Does it make it sound more like any other 4 into 1 bike, cos i used to like the way my old Blade sounded - cant beat that sound personally.

Engine braking seemed seemed the most obvious cause after knocking it down a few gears, cant imagine say 15kg less making any difference. You could try reloading the bike with the lost weight and see what happens, but...

Last thought, maybe with the extra rush your consiquently riding it harder and that's all it is :dunno:

 

[morphgarth]

Lumpy, WTF? Why are you re-opening antique posts. It's like time team on a forum. Have you got a dodgy multi-coloured jumper as well??

 

[Duck n Dive]

It's rare that he finds something he can not only sound knowledgeable about provide the bullshit to back it up .......



He's wrong of course ...................























:-0)

 

[Bluey]

A blast from the past,i found it interesting :}

 

[Howard]

shafties rise actually, weight transfer due to the chain pulling on the top of the rear sprocket and the mass acceleration cause the rear to squat.

Mac, Have you really been thinking about this for nearly six years???

 

[morphgarth]

IS this still true for modern shafties? Someone at work was suggesting that modern shafties behave like "proper" bikes now!!!

 

[Barrie]

IS this still true for modern shafties? Someone at work was suggesting that modern shafties behave like "proper" bikes now!!![/QUOTE

Try holding the front brake on while pulling away on a Pan. Back rises. But, under acceleration the back feels like it squats.:dunno:

 

[Para045]

Funny on my Bird the front rises when I accelerate hard - Usually up to about 45 degrees - Then I change up and she comes level again :neenaw: