Pure bookmark stuff !

Anyweays, from what I have noticed is, from the last couple of years, most of the superbikes(faired litres) have started loosing metal big time !
I know this is meant to in-corporate more aerodynamics and streamlining and other stuff but then IMO they have really lost appeal! EG:- Look at the 'Blade now and look at the one preceeding the 2008 models and the difference is bang on!
Firstly the Blade, then the recent 10R and even the Gixxer! The only model, I presume, that is not doing the same is the ONE !

Agreed, however as I illustrate im my diagram. A steep angled rake will make the front wheel lean more than a perpendicular one. So lets say, bike is leaning at 45 degs this means rear wheel is leaning at 45 degrees, but front wheels will be leaning more for example 35 degs when turning. Where as if the rake is perpendicular, the leaning of front tyres may more or less be close to 45 degs in the same situation. In effect, the steep rake will have a greater chance of sliding its front wheels. Is my reasoning sound so far ?

Agreed , no doubts.
But what I caught in one of the post was "does a few degrees of banking make much difference"
compared to the handling part...there is more than just the banking angle...which is why a few degrees on sports bike is quite alot compared to that on a cruiser.
But are you trying to just say that steeper(larger) rake angle is more prone to sliding than the shorter one..?

R Series - better denotion for that would be Turning Radius.

- Street bikes have smaller turing radius. Which makes them flickable in tight spots. The sitting stance is more upright which gives you the confidence to easily take tight turns at slow speeds.

- Sports bikes & cruisers have large turning radius..

- However in case of sports bikes the handle movement is restricted.. which causes the large turning radius. Another reason for keeping a restricted Handle movement is.. the rear set footpegs.. which causes more sportier stance which restricts the body movement under tight turns on slow speeds.
Ok.. look at Yamaha R1 pic... imagine yourself sitting on yamaha R1.. presuming the handle movement is not restricted (more handle movement).. and you are sitting in a sporty stance. With both legs up on footpegs.. Can you take a tight U turn without you putting your feet on ground? It would be tough doing that. But on street bike its easy..as Riding stance is more upright.

On a sports bike.. you are laying on the bike. On street bike you are sitting on the bike.

- Where as Cruisers despite of having large handle movement.. have large turning radius due to the longer wheelbase.

Nitro correct me.. if i am wrong anywhere.

Not prone as in normal driving condition. But when both examples are pushed to the same amount of high speed and turn. Theoratically, it seems steeper rake will slide sooner than more perpendicular ones. Though don't assume me as any sort of expert. Merely juggling my common sense here.

Me too . See post above

Got it...just missed out on a few points which you mentioned right here

yes it does...but thats secondary..which we would consider in two bikes having same chassis, rake angle, wheelbase etc. after the chassis is confirmed..thats when the weight distribution is worked upon to further decide the handling characteristics.

well if your considering highspeed..then rake angle would not play a role.
consider both bikes going straight..then larger wheelbase will give better stability at the same speed then the one with a shorter one. The sliding will only come into play when turning.

Thanks for the valuable inputs guys! I am not an engineer. But thanks for the technical knowledge.Much appreciated.

My intention was to put forward the general concept in simple english and avoid the boring jargon involved in it!

Btw imagine turning this chopper in a fast tight turn! U would probably skid and fall on one side!




Edit: I will be talking more of styling and less of engineering.

Now we will see how the mass of the streetbike evolved by the passing day. Just by throwing a glance you can see how the area near the steering head became heavy[visually]and tighter. And the open spaces were closed making it appear more fuller and muscular.

The first streetbikes:


The 70-80s bikes


Now,


Notice how the mass moved forward.


Infact the new CB Twister by Honda India is trying to close the gaping hole between tank and engine. Still can't hide other open spaces.

The 70's & for that matter upto 90's the street bikes - I love them. Take our own example of Rx100 & KB100;
We all know that having a straight sitting posture is good for back than leaning forward. What I do not understand is why do the modern street bikes offer a ride position to lean forward & ride to cause more back pain & keep changing the bikes?

The reason is not to give back pain but to give a more aerodynamic posture for riders to go faster.
honestly speaking..i've had the R15 for about 19 months now..but never had issues of back pain. Simple reason is that I keep the spine straight...although its leaned forward.
And more over the leaning position is more of an occurence in sports bikes...not all of them.

Oh!!!, let me explain though...
The idea of my street bike is that you can ride it all through the city, do a little to medium touring & ofcourse not compromising on the speed. Like Bonneville or XJR1300 etc.

With R15 the problem is exactly as what you've specified, lean on the bike for aerodynamics which you can as well do with any street bike. My personal experience with my own Rx100 is, when I sit straight enough, I cannot get past the maximum limit & when I lean, yes I get that extra 5-10 Kmph!!!

So I see a clear advantage of a street bike having a good sitting posture, you lean & get that extra speed; while with the sports bike you saddle sore & a free back pain too. While its possible to sit straight in sports bike (as you sit in R15), I'm sure you'll agree with me that it doesn't offer the same comfort as you get in a real good street bike.

Not trying to defend the street bikes, but still wondering there must be some other reason.

I completely agree, but this choice would change from person to person.
I mean right now if anyone asks me which is the most all round suitable bike..? my answer would be anything apart from the R15.
but again...the category which the R15 belongs to is something specific. I don't think we should go that way.
Are you saying that apart from sports bike....the street bikes also have a leaned down sitting position...?
(Cos for sports bikes I think you should understand that people like it that way)

I guess I am a trifle late with my inputs about motorcycle geometry but then seeing the kind of confusion prevailing on this thread, I believe this post is justified. Lets take a look at these elements in a way that is understandable to anyone keen enough to learn. I'll use technical terms only where there are no substitute words available.

Motorcycle steering geometry has four principle aspects that have maximum influence over the bike's handling.

They are: refer to the figure below..




Rake: The angle that the steering axis or say of the forks makes with the vertical. The 'less' the rake the steeper or more upright are the forks. The 'more' the rake angle the front wheel seems 'kicked' out.

Trail: This is the distance between a line extended downwards from the steering axis (say the bolt on your triple clamp...the one visible near the ignition key slot) and the contact patch of the tyre with the road.

Offset: This is the distance between the fork axis and the steering axis. (i.e. visually it is the distance between a line connecting the two bolts that hold the forks and the steering head bolt.)

The wheel diameter: something that is self-evident.

The best example of 'trail' working in the real world is watching the small wheels of a shopping trolley 'caster' as you roll it. They always seem to get 'in-line' automatically with the direction of travel of the trolley. Notice that their axis (its vertical) lies ahead of the contact patch.

The same 'castering' effect is responsible for the self-straightening of your bike's steering while in motion. An explanation of why this happens would be a trifle involved and so am omitting it for now. To cut a long story short, large trail has a greater self-righting effect, meaning the bike tends to be more stable in the straight line - which also implies its more resistant to turns - i.e. sluggish steering. Short trail has the opposite effect. So its pretty obvious why sportsbikes carry shorter trail than tourers and cruisers. For race-track use, one needs a bike thats more willing towards quick direction changes. Vice-versa with cruisers where straight line stability is in sync with a relaxed riding style that cruisers are all about. And the 'low slung' design of cruisers limits its ground clearence, thus limiting the 'spiritedness' of the bike through turns anyway. So the trade-off of stability vs quick steering doesn't hurt here. The usual trail figures for sportsbikes are anywhere between 3.5 - 4 inches while cruisers can go to 5 inches and even beyond.

Rake and trail move in proportion as long as the steering offset remains the same. So a larger trail requires a large rake - i.e. a more kicked out front wheel. But there are limits to how large the rake can be i.e. how far out the front wheel can be. Too much rake has a strong and strange disadvantage. On turning the handlebars, the steering head tends to drop with the turning of the handle. This can make the front wheel 'flop' over on its side rather suddenly and so the bike falls. This steering head drop is probably what @kyanmantis was asking about in his earlier posts. Large rake makes the front wheel lean further on cornering than a more upright wheel. This adversely affects a bike's cornering ability by robbing the front off its traction quicker than lesser rake. To limit customisers from making outlandish designs that can be dangerous to use on road, some countries have laws restricting rake and trail values within certain limits.

Over the years motorcycle designers and tuners realized that trail could easily be altered simply by 'lowering' the front ride height. This could be done by sliding the fork tubes further into the triple clamps. And if this didn't give them a bike that steered quickly enough, they could further reduce the trail by raising the rear as that steepened the rake which shortened the trail. This 'dropping the front for track bikes' became incorporated into bike design and allied with low C of G, smaller diameter wheels (for lower gyroscopic forces) and ergonomics like rear-set pegs that made it easy for the rider to tuck in to improve aerodynamics, the 'low' look became a standard design element of sports-bike design.

OF

^^ great info there OF!!