Serious question

[Finn]

We all know that cars can out corner bikes mainly because of the amount of rubber on the ground. Taking this into consideration, why doesn't my bike have a 190 size tire on the back AND front? While I realise the turn in would require a bit more energy, the grip would be most excellent... surely.

Go on, rip apart my hypothesis.

[dnos]

Why don't ya try it and see?
A bit of an experiment.

Oh and can ya video it too please so we can have a laugh.

[Finn]

While I also appreciate that most of the grip when accelerating and cornering comes from the back because of weight distribution, surely it would help for everyday riding??? Some scooters use the same size.

[onearmedbandit]

Look at 125GP bikes for your answer Finn. Tiny as tyres (width) yet out corner the MotoGP bikes (I realise there are other reasons they out corner the larger bikes, just giving an example of a bikle with excellent grip yet a narrow tyre). It's more to do with putting the power down on the road then actual cornering grip. From where I see it anyway.

[The Stranger]

We all know that cars can out corner bikes mainly because of the amount of rubber on the ground. Taking this into consideration, why doesn't my bike have a 190 size tire on the back AND front? While I realise the turn in would require a bit more energy, the grip would be most excellent... surely.

Go on, rip apart my hypothesis.

Is the amount of rubber the biggest issue?
You see many people on real skinny tyres doing some real bloody fast laps.

I would have thought the biggest issue is countering the centrifugal force. A car has a large mass already inside the corner. The weight is transferred to the outside wheels on the car on a corner, thus virtually the entire weight is inside.

A lighter bike (or car) has less force acting on it in the corner, hence less to counter, thus better cornering.

Just a guess.

[White trash]

Too heavy to steer mate. You may think it's a little difference, but feel the difference between say a Widglide with a skinny front tyre and a Fatboy with a 130 section front tyre and you'll be amazed.

The effort required to turn the wheel in the "wrong" direction for counter steering is the issue.

[The Stranger]

Odd that you feel the need to head it up as a serious question.

I think we have reached a milestone on KB. Finn's first serious post.

[Pumba]

After having a Holden SS with the widest rear tyres I have seen on a modern car (he was in frount till I passed him) folow me through the paraparas on the way to wanganui over easter I see the logic in your statement.....

However

Take the average tyre size of a run of the mill 250cc bike and the average tyre size of Chopper, I know what I would rather go into a corner with.

Just my two cents.:done:

[Finn]

And why doesn't counter steering work on a car?

This one is for The Stranger...

[Crasherfromwayback]

Too big on the front also 'bump steers' badly

[The Stranger]

And why doesn't counter steering work on a car?

This one is for The Stranger...

The same forces act on any wheel.
Problem with a car is it isn't going to lean because of the second track.

[ManDownUnder]

The smaller/tigher radius on the tyre gives a wheel an increased tendency to roll over (i.e. turn more easily). Makes sense to have that on the front as it's the most dynamic, influences steerage in addition to the up and down motion of the rear.

Once it starts to lean, the rear has no option but to follow...

[Ixion]

We all know that cars can out corner bikes mainly because of the amount of rubber on the ground. Taking this into consideration, why doesn't my bike have a 190 size tire on the back AND front? While I realise the turn in would require a bit more energy, the grip would be most excellent... surely.

Go on, rip apart my hypothesis.

Consider a car tyre. The tread area is flat across the tyre. The manufacturers try very hard to make it that way. Flatter it is , the more rubber on the road.

Now consider almost any bike tyre. Hm, the tread section isn't flat. It's curved.

Like a section of a circle.

Now, imagine a little circle. A narrow bike tyre. And draw a straight line tangentially to it. The road. Now imagine a big circle. A big bike tyre. Draw a tangential line. Notice something about the contact areas of the circle and the line? They're the same. Real world, not quite because the tyre deflects a bit and squashes flat. A fat tyre will squash a bit more than a little tyre . But not much.

And that squashing actually makes handling worse. because it makes the tyre into a flattish section tyre. Like a car tyre.

Imagine having a flat section tyre on your bike . (Sidecar tyres are like that). Now lean the bike over. Hm. What happens to that tyre. Oh, its either resisting leaning over and bulging a bit (you ain't gonna go round NO corners like that !). or it's tipped over onto the sidewall. Oh. big expensive painful bang.

Cars and bikes corner by TOTALLY different mechansims. Except for sidecars. And trials bikes. EDIT: In deference to Mr Motu : And flattrackers. And a few other odd ball types. And bikes going very very slow.

This has got to be THE most misunderstood issue in the whole of biking. The number of times I've answered it here. And every newbie that jumps out of a cage and onto a bike always asks it again. Gee. I want fatter tyres. No you don't .

On a bike - skinnier the tyre, faster you corner. Only reason to make rear tyres fat is because of the weight and power of big bikes. Little tyres would get ripped up. No reason at all to make front tyres fat.Except maybe comfort, big soft squishy tyres soak up bumps better.

But still we have things like the Honda Hornet, with a rear tyre wider than a Manx Norton. Cos Honda know that if they don't put a big fat tyre on it, ignorant newbies will go "Oh no, look at the skinny little tyres".

[doc]

Consider a car tyre. The tread area is flat across the tyre. The manufacturers try very hard to make it that way. Flatter it is , the more rubber on the road.

Now consider almost any bike tyre. Hm, the tread section isn't flat. It's curved.

Like a section of a circle.

Now, imagine a little circle. A narrow bike tyre. And draw a straight line tangentially to it. The road. Now imagine a big circle. A big bike tyre. Draw a tangential line. Notice something about the contact areas of the circle and the line? They're the same. Real world, not quite because the tyre deflects a bit and squashes flat. A fat tyre will squash a bit more than a little tyre . But not much.

And that squashing actually makes handling worse. because it makes the tyre into a flattish section tyre. Like a car tyre.

Imagine having a flat section tyre on your bike . (Sidecar tyres are like that). Now lean the bike over. Hm. What happens to that tyre. Oh, its either resisting leaning over and bulging a bit (you ain't gonna go round NO corners like that !). or it's tipped over onto the sidewall. Oh. big expensive painful bang.

Cars and bikes corner by TOTALLY different mechansims. Except for sidecars. And trials bikes.

This has got to be THE most misunderstood issue in the whole of biking. The number of times I've answered it here. And every newbie that jumps out of a cage and onto a bike always asks it again. Gee. I want fatter tyres. No you don't .

On a bike - skinnier the tyre, faster you corner. Only reason to make rear tyres fat is because of the weight and power of big bikes. Little tyres would get ripped up. No reason at all to make front tyres fat.Except maybe comfort, big soft squishy tyres soak up bumps better.

But still we have things like the Honda Hornet, with a rear tyre wider than a Manx Norton. Cos Honda know that if they don't put a big fat tyre on it, ignorant newbies will go "Oh no, look at the skinny little tyres".
Can you repeat the question

[BarBender]

Taking this into consideration, why doesn't my bike have a 190 size tire on the back AND front? While I realise the turn in would require a bit more energy, the grip would be most excellent... surely.
.

Was thinking the same thing as I slid home from work today...

[BarBender]

Now, imagine a little circle. A narrow bike tyre. And draw a straight line tangentially to it. The road. Now imagine a big circle. A big bike tyre. Draw a tangential line. Notice something about the contact areas of the circle and the line? They're the same. Real world, not quite because the tyre deflects a bit and squashes flat. A fat tyre will squash a bit more than a little tyre . But not much.

And that squashing actually makes handling worse. because it makes the tyre into a flattish section tyre. Like a car tyre.

Imagine having a flat section tyre on your bike . (Sidecar tyres are like that). Now lean the bike over. Hm. What happens to that tyre. Oh, its either resisting leaning over and bulging a bit (you ain't gonna go round NO corners like that !). or it's tipped over onto the sidewall. Oh. big expensive painful bang.
.

Ixion - I agree in part...but what if we started from scratch, turned it on its head and based the design of a motorcycle around a 190 on the front and on the rear? What would be the finished product and what would that look like?

[terbang]

In 'a twist of the wrist' there is reference to ideal weight distribution during a corner, can't remember the actual figures, but its something like 60/40 to the rear wheel that therefore needs a larger tyre contact. Thats why we turn better with the gas on. Interesting enough, if you increase the diameter of the wheel, while keeping the same width tyre, you will increase your tyre contact as well. However you will add a whole host of other issues with a larger wheel.
Cars and motorcycles turn the same way when the bike's speed is below around 15 kays. Turn wheels left, vehicle turns left and vice versa, but when the bike gathers speed there you turn bars left and the bike leans right (countersteer) and the lean angle presents the tyre to the road as a segment of a cone thus providing a turning force. Greater lean, greater turning force. I often wonder if a lot of our modern wide tyres have some sort of aesthetic value thrown in there as well. They look so cool.

[Ixion]

No reason you couldn't do it. But it wouldn't handle as well as it would with narrower tyres. .Some scooters have had fat tyres front and rear. So did the old Sunbeam S8s. Reason was for comfort in the days of crude suspensions. Big fat soft squishy tyres as shock absorbers.

The main point, in response to the oruiginal question, is that on a car, a wider tyre means more rubber contacting the road. The tyre is flat on the road, double the width and you double the contact area (more or less) .

On a bike , a wider tyre doesn't mean much more if any more rubber contacting the road (the actual amount will depend on the amount of "squish" in the tyre's shape, and thus on the weight of the bike etc). All the extra width is just out there touching nothing but air (think of those circles again)

EDIT: a larger DIAMETER wheel is another matter.

[Motu]

Big fat front tyres work well.....in the right conditions.Flattrackers run the same size tyres front and rear - when you first ride one you can feel this huge heavy front tyre,it's like there is a tractor tyre on the front.But when you get to use that tyre it's just so fantastic,you feel like a unicycle and feel you don't need a rear wheel.Sideways and nearly falling off the seat with the lean angle....and flapping this monster front tyre around,good stuff.I've run 4.00x18 and 3.75x19 front tyres on the dirt track.

[BarBender]

The main point, in response to the oruiginal question, is that on a car, a wider tyre means more rubber contacting the road. The tyre is flat on the road, double the width and you double the contact area (more or less) .
out there touching nothing but air (think of those circles again)
.

Just being hypothetical here - Would a fat front and rear combo be as agile if the the motorcycle were two wheel drive?
Sure it wouldnt have as much contact on the road as say a car....but could possibly guarantee both contact and - as Terbang mentioned - the constant 60/40 rear to front weight ratio?

[The_Dover]

who the fuck cares?

knob.

[Ixion]

Just being hypothetical here - Would a fat front and rear combo be as agile if the the motorcycle were two wheel drive?
Sure it wouldnt have as much contact on the road as say a car....but could possibly guarantee both contact and - as Terbang mentioned - the constant 60/40 rear to front weight ratio?

Well two wheel drive is going to allow greater cornering force. Because the rear tyre would only be passing half the amount of torque (assuming a 50.50 split). And a tyre can pass a certain set limited amount of torque, either sideway (for cornering) or forwards for traction. Less needed for traction = more for cornering.

But the fat front would make for fairly dodgy steering (outside special cases such as Mr Motu's flattrackers).

Which may be why the only 2WD bikes I've heard of are off roaders.

[Finn]

The same forces act on any wheel.
Problem with a car is it isn't going to lean because of the second track.

Thanks but that was me not being serious.

[James Deuce]

Car suspension is also much better at separating and isolating steering, braking , and acceleration forces than a bike. Except front wheel drive cars. That's a silly idea designed to make cars small and cheap to mass manufacture. Except Honda front wheel drive cars. The clever buggers do some interesting things with front wheel/hub offsets to all but eliminate torque steer.

Interestingly, thanks to about geological epoch of development on telescopic forks, they still work better than for instance, BMW's duo-lever front end. Separating braking forces from the steering on a bike has the effect of not providing much braking feel when you really need to know what's going on.

[Big Dave]

Because it would look like a Van-Van

[James Deuce]

Van-Van's are cool! Put big panniers on them and you can go on adventure rides AND go white water rafting.

[motoGP]

Actually got a very good article in one of the latest BIKE magazines. R6 vs. a Lotus (?) both with very similar horsepower output. The bike accelerated much faster, and thus had to brake earlier at corners because of its higher speed. Ultimately the R6 won by a few seconds, both machines use their power in very different ways, but a very interesting article. Compare prices, well that’s a whole other ball game…

[Mr. Peanut]

Would be hard to counter-steer a large front wheel at speed. Also increases unsprung weight.

[The Stranger]

Thanks but that was me not being serious.

I suspected you weren't, that's why I kept it short.

[86GSXR]

Great thread guys. I see mention of "a twist of the wrist". I assume this is a book, would someone be kind enough to post the author's name and where I could get a copy? Cheers.

[dnos]

Keith Code

read this:
http://www.kiwibiker.co.nz/forums/showthread.php?t=39313&highlight=twist+wrist+pdf

[WRT]

One other thing - as you lean over the contact point between bike and tarmac moves, into the corner. You lean right, the bike rolls onto the right side of the tyre. Hanging off the bike allows your body weight to keep the COG in line with that contact patch. The wider the tyres, the more the contact patch moves, and the more you would have to either lean over or hang off in order to keep the combined COG in line with it (bearing in mind that the COG is combined for both you and the bike, and is affected by gravity itself and the g-forces pushing you outwards on the corner).

Hence, the skinnier the tyre, the less weight you have to shift inwards to compensate for this shift (or, conversely, the faster you can go round a corner for a given lean angle).

Naturally, we are only talking a few mm that the contact point is shifting, but due to "leverage" it can make a big difference up where the rider is sitting, and can add a few KPH onto how quickly you can go around the corner at max lean angle.

[SwanTiger]

Didn't John Britton (or whatever his name is) develop a way to harness and manage the benefits and side effects of having a front and rear of equal size?

[Crasherfromwayback]

Because it would look like a Van-Van

Except the 125 which was my first ever bike! Smaller front than rear....

[86GSXR]

Keith Code

read this:
http://www.kiwibiker.co.nz/forums/showthread.php?t=39313&highlight=twist+wrist+pdf

Brilliant! Thanks! I'll definitely get myself a copy.

[MisterD]

You're a man with some disposable Finn, buy one of these and try it out...

[Indiana_Jones]

A serious question on KB?

send it to PD!!!!

-Indy

[CB ARGH]

My diagnosis is that there is a smaller tyre on the front to improve the aerodynamics of the motorcycle. I would much rather the wind hit the radiator rather than the front wheel. :Oops:

EDIT: Holy shit that is a bump.