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**samudranb** · 06-26-2009, 04:10 PM

Originally posted by Old Fox View Post

An incessant curiosity for things not known is anytime welcome at my end.

Thank you OLD_FOX! I have learnt a lot from this thread! And I am really glad I started it!

**dcs** · 06-26-2009, 05:03 PM

Originally posted by pranay View Post

OT:

I totally agree with you on this one. But if you were referring to me and abhijeet's posts as egos clashing, then let me just clarify that it was a mature discussion with good spirit in the interest of biking and nothing else.

It might be OT but I never referred to your and Abhi's discussion, in fact I am glad that we are discussing and sorting out confusions and misconceptions about things that we think we know about. now when I say WE I mean WE which equally includes you and Me.

End of OT

@ Old Fox <<<<< bows down three times and then four times again>>>> Maalik...aap itna Gyan kahaan say laatey ho??

@ All: I would appreciate all of my mates to contribute in this discussion

**abhijeet080808** · 06-27-2009, 12:58 PM

Thanks to OF for such a great reply.

One question - will a bike with softer suspension have more weight transfer on braking or will it be the same as on a bike without suspensions or with stiff suspensions?

I thought a softer suspension leads to more weight transfer (whether it is more than needed is debatable). Please correct me if I am wrong here.

And regarding trail braking what you said is what I had in mind, but you put it much better in words. Trail braking loads up the front and hence aids cornering. A softer suspension will transfer more weight to the front and aid in trail braking (no?).

And no guys, no ego clashes here!

**Old Fox** · 06-27-2009, 03:32 PM

Originally posted by abhijeet080808 View Post

Thanks to OF for such a great reply.

One question - will a bike with softer suspension have more weight transfer on braking or will it be the same as on a bike without suspensions or with stiff suspensions?

I thought a softer suspension leads to more weight transfer (whether it is more than needed is debatable). Please correct me if I am wrong here.

And regarding trail braking what you said is what I had in mind, but you put it much better in words. Trail braking loads up the front and hence aids cornering. A softer suspension will transfer more weight to the front and aid in trail braking (no?).

And no guys, no ego clashes here!

I guess we need to get back to high-school physics to clear this thing up in its entirety.
Weight transfer is a physical reality that has to happen, whether there is a suspension system pre se or not. Refer to the fig in my previous mail that I am reproducing below:

Braking produces a force (because the rider/bike combo is in motion and braking means deceleration) that has eventually to act through the front tyre contact patch where it is countered by the force of friction between the road and the contact patch. Since the connection between the contact patch and the rest of the bike is primarily through the fork, a large component of this force travels down the forks. The exact quantum of this force transfer can be calculated by referring to the fig below:

As the forks are raked at an angle to the vertical, the force transferred through them can be calculated as a product of the total force and the Cosine of the angle of application of the force. Here the angle is the 'rake' angle minus 90deg (since the rake angle is measured against the vertical). Assuming a rake angle of 25deg and a braking force of 1N, the force component acting down the forks would be = 1 (N) x Cos(65) = 0.4226. Meaning that some 42% of the braking force shall act through the forks.

Let us assume a ZMA (about 150kg) with a rider weighing 70kg coming to a panic stop. Stock tyres on clean tarmac can give a decelration equal to about 1G i.e. about 9m/sec2

So the total force generated would be like F= M x A = 220 x 9 = 1980N
1980N x 0.42 = 836N = 85kg (appox)

So the forks get pressed downwards by a force equivalent to 85kgs. No wonder they get compressed.

As you can see, the 'softness' or 'stiffness' of the suspension set-up has no meaning for weight transfer. The 'weight Transfer' is a Force that is generated due to braking. It is just that with a softer suspension, you get a larger deflection of the springs, more dive and so it 'feels' like there has been a LOT of weight transfer occurring.

OF

**Shivanshu** · 06-27-2009, 04:18 PM

Ohhh Myyy GOD

... Old Fox Sir, dont know what to say...... you are like our GURU.. Sir you explain everything beautifully with a complete logic beind it and with examples which can go to a basic physics formulae... Hats off Sir..... really admire your knowledge and patience to explain each and everything in detail.... Thank You Sir thanks a ton for sharing your knowledge with all of us

I really and honestly appreciate it.

This thread is great

**c_sbk** · 06-27-2009, 05:47 PM

what to say. Sir OF is Oxford of biking and any technical knowledge.
bows down three times and then four times again INTO 50 times

.

**abhijeet080808** · 06-28-2009, 12:01 PM

Thanks for the great reply OF. I have some doubts. I will just frankly lay them out here.

Every action has an equal and opposite reaction. When we brake, a opposite torque is generated, which tends to press the front end downward and lift up the rear end. (Opposite to what happens during acceleration.) This force acts down on the front end. This force is related to the mass and moment of inertia of the bike. This causes a bike to dive. So far ok.

But I feel this is not weight transfer. Weight transfer can occur only when there is a shift in center of gravity. A bike with no suspensions can not change its C of G by braking. Weight transfer, if allowed to occur by using a suspension, will allow a shift in C of G and thus contribute to further diving.

And I thought loading up the front delivers more traction to the front wheel during a turn. So it is necessary. If not this, what exactly does trail braking achieve?

Waiting to hear from you. Frankly it is a very interesting discussion.

**Old Fox** · 06-30-2009, 03:07 PM

c_sbk:

A hundred thanks for the appreciation!!

Originally posted by abhijeet080808 View Post

Thanks for the great reply OF. I have some doubts. I will just frankly lay them out here.

Taking your first statement:

Every action has an equal and opposite reaction. When we brake, a opposite torque is generated, which tends to press the front end downward and lift up the rear end. (Opposite to what happens during acceleration.) This force acts down on the front end. This force is related to the mass and moment of inertia of the bike. This causes a bike to dive. So far ok.

Your second statement:

But I feel this is not weight transfer. Weight transfer can occur only when there is a shift in center of gravity. A bike with no suspensions can not change its C of G by braking. Weight transfer, if allowed to occur by using a suspension, will allow a shift in C of G and thus contribute to further diving.

Elaborating on the mechanism of braking further:

Weight transfer = braking force x (C of G height/wheelbase) ratio

Case 1 when C of G is assumed at 20 inches

ZMA wheelbase: 1355mm = 1.355 m

Height of C of G rider/bike combo = 20 inches = 508mm ~ 0.5m

Ratio: 0.5/1.355 = 0.369

ZMA braking force (panic stop 1G deceleration) = 220 x 9.8 = 2156N

Weight transfer = 1470 x 0.369 = 795N = 81kg

thats the load on the rear tyre. No wonder it slides so easily when you try to brake with the rear.

Case 2: assume the CG higher by some 5 inches:

New CG height: 25 inches = 635mm = 0.635m

New ratio = 0.635/1.335 = 0.475

Weight transfer (case 2) = 2156 x 0.475 = 1025N = 104kg

Total weight on front tyre: 104 = 110 = 214kg

And all this by just raising the CG by a mere 5 inches. No wonder the CG location is such a fight for motorcycle designers.

Moral of the story: if you want to make a controlled panic stop without converting it into an inadvertent stoppie, tuck in lower on the bike when you brake hard.

Now keep in mind the change in these numbers if the weight distribution is NOT 50-50 on both wheels but something like 45-55 as is usual in the real world.

Abhijeet: I know this goes a trifle beyond what you asked but then understanding the physics of motorcycling is a lot more interesting when you get practical numbers to relate to.

And I thought loading up the front delivers more traction to the front wheel during a turn. So it is necessary. If not this, what exactly does trail braking achieve?

It is the benefits acquired by loading up the front wheel that makes 'trail braking' useful. Also the rider can carry more speed into the corner by braking later and longer, allowing him a higher overall average speed through the turn, a point that makes a big difference on the track. Trail braking is actually a 'controlled' loading up of the front wheel, a technique using which the rider attains a fine balance of the traction tradeoff between the traction needs for braking and those for turning.

**pranay** · 06-30-2009, 03:55 PM

Originally posted by Old Fox View Post

.....

It is the benefits acquired by loading up the front wheel that makes 'trail braking' useful. Also the rider can carry more speed into the corner by braking later and longer, allowing him a higher overall average speed through the turn, a point that makes a big difference on the track. Trail braking is actually a 'controlled' loading up of the front wheel, a technique using which the rider attains a fine balance of the traction tradeoff between the traction needs for braking and those for turning.

^^ *Bow* Oh my god....physics is such a wonderful thing if clarified/taught like this.

Just wonderful to see you spend so much time with figures, diagrams, formulae and examples, just for the benefit of understanding of another fellow biker.

Coming back to the start of it all, I would like to highlight what OF said in the underlined statement. It is the loading of the front wheel that makes 'trail-braking' useful. IMHO, a softer suspension would
* load the front wheel much lesser.
* load up the front wheel with large amount of force suddenly

I hope I didn't start it all over again. *Peace*

**Old Fox** · 06-30-2009, 04:24 PM

Originally posted by pranay View Post

^^ *Bow* Oh my god....physics is such a wonderful thing if clarified/taught like this.

Just wonderful to see you spend so much time with figures, diagrams, formulae and examples, just for the benefit of understanding of another fellow biker.

Coming back to the start of it all, I would like to highlight what OF said in the underlined statement. It is the loading of the front wheel that makes 'trail-braking' useful. IMHO, a softer suspension would
* load the front wheel much lesser.
* load up the front wheel with large amount of force suddenly

I hope I didn't start it all over again. *Peace*

Pranay: You did. This WILL start it all over again

. And I guess I have written enough on the subject to make for a small book.

Suspension 'softness' or 'hardness' has no great relation to the weight transfer. Weight transfer is force. If the suspension is soft, it will compress it more, if it is hard, then the force can only compress it less. True, the suspension dive does alter the C of G of the bike but this alteration is not so substantial so as to have a huge impact on the force generated. This change in C of G does affect the handling of the bike. We have discussed this at length in my first response.

Trail braking gives 2 major advantages:
1. Allows higher average speeds through the turn
2. Controlled loading of the front wheel to keep it within safe traction limits.

Almost all of the questions that arise in your mind will have their answers in my three posts. I don't feel the need to actually point them out. look for them. they are there. As for anything new...I am game.

**pranay** · 06-30-2009, 04:35 PM

Originally posted by Old Fox View Post

Pranay: You did. This WILL start it all over again

. And I guess I have written enough on the subject to make for a small book. ...

.

LOL!

I have read through the posts two times. I think I am one time short.

But again, there is a lot of automotive physics involved here, which is beautiful, frankly.

**kaynmantis** · 06-30-2009, 06:11 PM

What's "CG"?

Kidding

. Couldn't resist that. Some awesome explanation there 'Old Fox', and 'abhijeet080808' too, for your perspective. It helps make things clearer.

I too have a query. Was wondering how much would the angle of the fork have effects on the handling of the bike. Like some cruisers are angled quiet extremenly while normal street bikes are almost perpendicular. I unserstand, extreme angle would like cruisers would have longer wheelbase hence bigger turning radius, unflickable etc.
But on a normal street bikes we used here, how much would the angle effect the handling characteristics?
I'm also thinking, the contact patch of the tyre on the road will also differ due to angle.

**samudranb** · 06-30-2009, 06:39 PM

Originally posted by Old Fox View Post

Pranay: You did. This WILL start it all over again

. And I guess I have written enough on the subject to make for a small book.

Lol! Please do let us know when it is published! I will be the first to buy it!
You really explain really well!

I have another question: What is the relationship between the weight of the bike with the width of the tyres? I used to think that the wider tyres are for heavier / more powerful bikes, but then what about the Bullets?

**outworldly maniac** · 07-01-2009, 01:04 AM

awesome discussion going on

unbelievable OF sir ......

noob sawal
why do people crave for more cylinder engines ??

like suppose we have two bikes A and B of 250cc
A with a single cylinder with same power and specs like B
B with a twin cylinder n same specs like A

then what does make a difference actually
we are getting the same amount of power... same torque ,,,

@ OF sir
please could you elaborate this
Trail Braking is a technique where the rider progressively reduces his braking force as he gets deeper into the turn and closer to the apex.

i am not understanding this..... we keep the brakes pressed and slowly and steadily keep on releasing it
is it what i am saying ??? then how will we maintain speed or for that matter even ride at a speed with more part of the brakes pressed

or it is that i dont understand what u meant by BRAKING FORCE

please explain sir

**abhijeet080808** · 07-01-2009, 01:01 PM

Thanks for the awesome explanation OF. Cleared a lot of my doubts.

One question -

What are the factors that determines the ignition timings in a 4 stroke engine? How does the following factors affect timings -

1. Compression Ratio
2. Air-Fuel Ratio
3. Altitude
4. Temperature
5. Valve Timing

And any other factors you may think off!!

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