Any idea why?

**07fatboy** · 31st August 2006, 12:56

This is all too confusing for me...too many big words

**idb** · 31st August 2006, 12:59

Originally Posted by Motu

...with narrow section tyres a lower CG gives less lean.....

I don't follow that statement at all.
I can understand that less lean is needed for narrow section tyres given the same height of CoG but I can't understand why that would reverse the actual effect of the height of CoG on lean.

**MacD** · 31st August 2006, 22:22

The Engineers on the site might be interested in this research group at Imperial College, London.

Somebody has even produced a GSXR1000 simulation.

I'm sure the answer to the original question is in there somewhere! Who wants to find it?

**Back Fire** · 31st August 2006, 22:25

I would pin it down to your insane ability to hang off the bike like a monkey... a monkey that can make a tank move faaarkin fast mind you...

**MacD** · 31st August 2006, 22:36

Originally Posted by Motu

If no one comes up with the diagram to explain,I'll scan my Tony Foales book tonight....after Dr Who.

Motu, did you know Tony Foale has a website (mainly as a promo for his book)?

However you can download some of his older articles, the one on camber thrust is probably the most applicable to the question.

As for Dr Who, I enjoyed the Cybermen last week, definitely the second most scary adversaries after the Daleks!

**Motu** · 31st August 2006, 22:55

Thanks for that,a lot of that stuff is out of his chassis design book,but the illustration I want is not there....and I can't scan it because it has to go through my wife's computer and she's busy working on it.Fig2.31 is the one I want.

''... shows how the contact patch moves away from the centre plane of the wheel or steering axis as the machine is banked,giving rise to the following side effects:

a) A greater angle of lean is necessary to balance centrifugal force;this may involve a higher centre of gravity to restore cornering clearance.''

**Ixion** · 31st August 2006, 23:08

Originally Posted by MacD

Motu, did you know Tony Foale has a website (mainly as a promo for his book)?

However you can download some of his older articles, the one on camber thrust is probably the most applicable to the question.

As for Dr Who, I enjoyed the Cybermen last week, definitely the second most scary adversaries after the Daleks!

Well, I read that and understood it (I think). But I don't see how it answers the original question.

Or the subsequent question. Does a crusier, with a very low CoG and very wide tyres need less lean angle for the same corner speed and radius than a tourer with a high CoG and skinny tyres?

EDIT. this is a very interesting thread

**Motu** · 31st August 2006, 23:25

Originally Posted by Ixion

Or the subsequent question. Does a crusier, with a very low CoG and very wide tyres need less lean angle for the same corner speed and radius than a tourer with a high CoG and skinny tyres?

Jeez,I can't even think that through,it's like tomato sauce on apple crumble.I can't imagine how those chops with the phaaaat back tyres and skinny front tyres go around a corner,the contact patches would be 150mm out of line,and the CG would be inside the contact patch - you'd have to countersteer them to buggery.

After twins and singles all my life,the CB750 came as a hell of a shock when I got it in 1985 - it handled fine,but if I hit a bump mid turn the bike would rip the bars out of my hands and stand up,I was getting scared of it! I couldn't use my usualy ploy of lower wider bars,but finaly figured it out.The higher CoG than I was used to was tossing the bike out of the turn,so I started to toss the bike deeper into the turn,or drop a cheek and get to the inside....destroyed my Ago style.The same style of bike I had been riding,the same tyres - but it definetly needed more angle of lean than the XS1.

**Fishy** · 1st September 2006, 08:15

Originally Posted by Rayza

I would pin it down to your insane ability to hang off the bike like a monkey... a monkey that can make a tank move faaarkin fast mind you...

Neither of us were hanging off.

**McJim** · 1st September 2006, 08:19

Originally Posted by Motu

a) A greater angle of lean is necessary to balance centrifugal force;this may involve a higher centre of gravity to restore cornering clearance.''

Bugger! I got my arse kicked for using that terminology on this thread.

**Lou Girardin** · 1st September 2006, 08:20

Elliot-ness has probably got it. Were you both using identical lines?
A classic racing line requires less lean angle than someone who turns in late and squares off the corner.

**Motu** · 1st September 2006, 08:29

Originally Posted by Big McJim

Bugger! I got my arse kicked for using that terminology on this thread.

Direct quote from Tony Foales,they can't touch me on that one!

**McJim** · 1st September 2006, 08:30

Originally Posted by Motu

Direct quote from Tony Foales,they can't touch me on that one!

Yeah but wait till they have a go at Tony Foale

**Ixion** · 1st September 2006, 08:35

It's not just the height of the CoG, its also the offset sideways. Velos were reckoned good handling because of their very narrow engine design. The early fours were reckoned poor handlers because of the width of the engine putting weight to far outboard. I think this is probably particulaly significant on bump steer, the overhanging weight becomes a pendulum if you hit a bump when leaning.

And what about those slip angles and the SIZE of the contact patch? Since the front and rear weels follow different paths and both are describing a circle (whilst the wheels are rigidly fixed in the frame, ie we are not talking hub centre steering) the tyres MUST have to distort to allow the wheels to "follow" each other. So if the contact patch is very large (and distortion resistant) do you need more lean (a greater alpha angle, steeper sides to the invisible cone) to compensate?