Big Bang Bumkum?

From the moment we get on a bike we are told that being smooth is good. Smooth breaking, smooth lines, smooth braking, smooth throttle action, smooth body movement.

Smooth is good.

... Until, that is, it comes to power delivery, it seems.

I keep reading more and more about " ... a tyre having a chance to regain grip between power pulses" with V twin and big bang engines.

So it seems that smooth is not a good thing at all in this case.

Now, if the power keeps coming in pulses this should technically put more stress on the tyre and the smoother the application of power of a straight four *should* be better (becasue it's smoother)?

Surely, for every "pause, allowing the tyre to regain grip" there is a following surge at half the frequency of a straigth four that's trying to break that grip that's just been regained?

Surely the difference is that the twin has (relatively) more torque at the point of peak power than the same size straight four and it is this that allows for more grip.

Torque equals drive and so you get more drive at a lower level of revs with a big bang or V twin and so if things do start to go wrong it's easier to back off to regain grip. This is even more applicable for a single.

Or have I got it all wrong?

Carl

Well PB have done a scientific test:

1. Test a standard GSXR.... in January on a cold track.

2. Do a BB conversion & BORE IT OUT at the same time.

3. Test the bike produced in step 2 in summer, and if it blows up test again in later summer.

4. Surprise surprise the bigger displacement bike in warmer conditions laps quicker, which proves naff all. It might sound good, it may have extra traction but they proved naff all. Where is the control? Bike journalists doing science? No, never, luckily my bag of salt split all over the magazine on the way home from the supermarket (getting extra traction from my 4wd system which being a boxer is semi big bang) before I could shower it with a pinch...

5. I quite like PB normally until they spout sh1te! Just read 80% of the mag.

Hi Tim,

Granted with PB, but this is now starting to spread to other mags such as Fast Bikes and even Bike magazine.

And I endorse your point about a control. If we were to use a control we'd actually need to produce two different engines as well as a different bike.

In producing a big bang/V twin engine that allows for the tyre to regain grip we would also need a second Big Bang/V twin engine tuned to give the same torque and power graph as the original engine (i.e. high power, low torque).

We'd then need to test all three engines in the same frame on the same day. This is the only way we can test one change at a time.

My money would be on the big bang engine that hadn't been remapped to reduce torque and increase power.

My money would be on the increased torque for the corresponding power that was allowing for more traction.

I see this as a new urban Myth taking form. Its a big bang engine/V twin therefore, ergo, QED it must be the pause between power pulses increasing traction. When in fact, there's a far greater probability of it being the higher torque to power ratio.

If we look at the Dyno graphs of a Curvy 650 versus a K1 GSXR 600 K1 (helpfully overlayed on page 148 of May's Bike mag) we see that they have a fairly similar curves until the SV runs out of puff. The Gixer then goes on to rev through to 107 bhp maintaining the same torque as the SV has. The SV runs out at 68 bhp. So the Gixer is producing about 40% more power for the same torque. I belive it is this that is causing the difference and not a relaxation of power between pulses allowing for grip.

If you rode the Gixer round at no more than 8000 RPM (where the power graphs diverge) what do you think would be the chances of spinning out the rear?The SV and Gixer are developing similar torque and power at 8000 rpm (surprisingly)(~70bhp and ~40 lb.ft. torque. Also surprising is that from 5,500 they are producing about the same. It's only below 4000 where there's a significant advantage to the SV.)

So there is the control. Electronically limit a GSXR 600 K1 to 8000 RPM, fit a 160 profile rear tyre and see which is easier to lose the rear end on. My bet would be the gixer would be better than the SV.(as a straight four)

If we increase the torque for the Gixer by making it a big bang engine (so it produces the same power and torque graph as that of a 1000 V twin, We'd have a higher ratio or torque to power and most probably better traction. Or the same traction as a 1000 V twin.

Attributing this to "... allowing the tyre to regain grip in between pulses" seems to me to be smoke and mirrors.

I'd be happy to be proved wrong though.


Cheers,
Carl

Big Bang is a way of extracting more useable power from an IL4 donk. The real alternative to what is sought is the V4.

Rumour has it that the 2008 Fireblade will be the last of the iconic machine, it will be replaced in 2009 by a V4....bring it on!

Hi Carl.
I have thought about this weird problem for ages too. Power pulses causing more grip? Uh? Doesn't make logical human type sense until you think ABS, which I suppose is the exact opposite of not losing friction through forward traction!? It all happens too fast for the human mind to comprehend.
Slipper clutch anyone?
If a slipper clutch can't fully control it then I guess it must be down to power pulses.

[yorkie_chris]

I wouldn't say its got much to do with ABS, all that does is find out how much grip there is by locking the wheel.
Instictively I'd say that the smoother engine would be able to use more traction, as dynamic friction is usually less than static.

I'd say they're talking nonsense and its simply a matter of having more useable low down power.

All IMO and I know nothing about racing...

[northwind]

I can see how it could make sense... If you think about pushing a heavy box, what makes it slide better- not the occasional big push, but getting it going and keeping it going through constant gentler pushing. So I suppose an occasional large pulse could be better than frequent small pulses, since the tyre has more recovery time. But what do I know?

In superbike magazine this month, there's an article about the end of racing twins, about how boring out a 1098 to 1200 for the 1000 series is ridiculously hard. Anyone else read this?

[johnnyrod]

My ass tells me it works...

Do you think the GP teams with pots of money and only one thing on their mind (winning) are going to chase an urban myth?

I wouldn't say its got much to do with ABS

Hmmmmm.... I should have known this would happen!

ABS = lots of little blobs of high friction interspersed with little spaces/rests/cooling periods with less friction! "(to slow you down)"

>It prevents the tyres losing grip and breaking away< (sliding)

V-twin pulses = lots of little blobs of high friction interspersed with little spaces/rets/cooling periods with less friction! "(to speed you up)"

>It prevents the tyres losing grip and breaking away< (sliding)

Geddit??

The rear ends of Ducati's on track certainly seem more planted (in general) than their 4 pot counterparts! I'm not saying it's all down to this single reason but its one of the only "big" differences there are! Weight can't be a factor as less weight means less grip!

Is that why lots of race car drivers say that the V8 cars are easier to drive out of corners than the V10's and V12's??

Is this the reason dirt bikes are invariably single cylinder?? Power pulses?? There's lots of dirt biking where the extra weight and width of a 4 pot engine is of no consequence and more power would be welcomed but.....

.......anyone know if V-twins and singles are better for hill-climbing?? The lighter weight here would be very negative as high grip is paramount but hard acceleration out of greasy, muddy hairpins is a damned good test for power pulse theory!!!!