[Nibile]

I need some help from the "UKB hell for leather posse".
The current setup of my bike features a low seat, mainly because it's stripped to the bone, and because there is almost no cushioning, just 2 cm of foam. So, when at a stop, in can comfortably keep my feet on the groud. When riding, the low position gives me a nice feel in the bends: I am extremely prudent, but I still like to lean, and I'm working my way to the more pronounced leaning angles with more confidence.
Now then: I'd like to change the seat position a little, for two reasons: one is purely aesthetic, the second for comfort. I'd like to make the seat more horizontal (now the front part is quite lower than the back), by adding a 2,5 cm plastic thickness under the front bolts of the tail section, leaving the back bolts at same height.
The question is: will this alter much the driving, especially in the bends? I don't care about the possible discomfort on the wrists due to the low clip ons, I'm only interested in how much - if at all - the driving will change.
I think that even this small change will alter the center of gravity a little, and I also think that the lower the bike, the higher the leaning angles that it can sustain. Am i right?
Or, will this change be so minimal that the bike and the tires will still be well below theri limit? And well above my driving abilities?
So, has anyone had some experience in this case?
And yes, I will try and see how it goes anyway...

[DAVETHOMAS90]

This is interesting Lore.

I saw a CBR the other day, and my first reaction was "that's starting to look like a Harley". The seat looked really low.

It's worth remembering that at higher lean angles, mass that's higher up when the bike is vertical, moves closer to the apex when leant over - especially when scraping your elbow Lore 

[Nibile]

 
Now you've got me lost Dave, I'm afraid...
Could you clarify for me? Sorry...

What I think, is this: at the same lean angle, a higher bike will have its centre of gravity further out, and will need more speed to stay put, is this right?
Also, a higher bike will lean more quickly and will go back straight more slowly?

[DAVETHOMAS90]

Hi Lore.

The closer you can get the mass to the centre of the turn, the lower the forces will be. That's one of the most important benefits of hanging off. It's not really about "getting lower".

Some interesting discussion - and confusion! - here:

http://forums.superbikeschool.com/topic/500-center-of-gravity-high-or-low/

Quoting from the forum:


"Yeah, I was a little off base with my comment above, I was half right. I did a little research last night and found something pretty interesting.

 

1)   High CofG will help a bike turn quicker as explained in the quote above. A good example of this is the changes made to the '06 ZX10R. Kawasaki wanted to make the bike turn in faster, so the raised up the engine in the frame to raise the CofG. When you turn a bike you basically steer the wheels out from under it and it falls over, the higher the CofG, the longer the lever gravity has, the quicker the bike falls. So I think I had this part right before.


2)   The interesting thing I found last night reading through Tony Foale?s book is that a lower CofG requires more lean angle then a higher CofG. My misunderstanding was that I thought when you hang off a bike you were trying to lower the CofG so that the bike could remain more upright. But that is not how it works, when you hang off you move the CofG to the inside of the corner and that is why you don?t have to lean the bike so much, not because the CofG is lower but because it was moved left or right."



https://books.google.co.uk/books?id=84hF-qoR5I8C&pg=SA3-PA20&lpg=SA3-PA20&dq=center+of+gravity+motorcycle+foale&source=bl&ots=FZA7yJJeLi&sig=b744JtvQoIL7fG75fIXjVFxB7Vo&hl=en&sa=X&ei=3DMPUcCVIerr0QH-mICwAQ&redir_esc=y#v=onepage&q=center%20of%20gravity%20motorcycle%20foale&f=false



I think it's interesting what the Tony Foale book says about things like sub-frame construction. I thought that might be particularly interesting for you too!

Videos of you experimenting please!!

[Nibile]

Tony Foale book. Want.

[Nibile]

Thank you so much Dave, so interesting!!!

[DAVETHOMAS90]

Glad you found it useful!

It's the sort of thing where the internet is full of all sorts of discussion and speculation, but in depth analysis in book form still wins.  

Found the stuff about size of tyre really interesting too.

[Nibile]

Tony Foale book. Want.

For sale on Mazon at 1.416 Euros...
 

[DAVETHOMAS90]

Tony Foale book. Want.

For sale on Mazon at 1.416 Euros...
 

  indeed!  YYFY !

[Nibile]

This free .pdf is much better. Mega YYFY.
https://www.dropbox.com/s/obazkrio1trciw9/Motorcycle%20Handling%20and%20Chassis%20Design.pdf
Already saved on my pc...
 

[DAVETHOMAS90]

Brilliant.

Unfortunately my phone doesn't recognise the format. I'll check out Amazon though.   

I downloaded some of the bike pics. Hope that's ok. The yellow Harris Yamaha is very self-explicit. No argument there.

[Nibile]

In any case, still on the matter of experimenting, after my trip to the Dolomites I tried to change the setup a little bit.
I lowered the front by 3 mm more. I think that it had raised a lot due to the new front forks kit that is stiffer and more resistent to the bike and to the driver's weight. Now they dive less even when the bike is at still, and the handlebars felt too high, and the front wheel a little "light".
With the front lower, I got a nice feeling back.
But, the magic was done by opening the clip ons by a good 15°. Wow what a difference it made. On the very first trip in the hills around Siena, I managed new lean angles and the bike felt a lot more precise and reactive (even too much in S turns...).
I got home with a huge grin and a lot less rubber on the sides of my tyres...