dcs

wosh.........and I thought I knew every aspect of braking, biking, wheelbase , electricals etc. But my mates have made me think otherwise.

My humble request to all who are reading this and who all are/will be posting in the thread.... lets not let our egos clash, lets make this a platform to discuss and learn. ( am trying to potray myself as Future Mod of xBhp, right now am happy being a Mood (Iri) tator.)

as for the braking wrt to suspension...my point of view is a lot of things work for a common goal. why would a particular bike do a stoppie and why some other wont(easily) we can not just talk about the Brake Dia and the suspension only. it has a lot to do with the rake, with the travel, definitely the tyres, the weight/ CG of the vehicle too.

samudranb

Old fox... It seems we are waiting for you to say the last word

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pranay

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.

And with all due respect to OF and other highly knowledgeable people in xBhp, I think discussions from less knowledgeable members with differing point of views should be encouraged because if you can substantiate your views like both of us did, it relates to more thought process required while doing your research about bikes.

I am sure most of us will agree on this fact which applies to all: 'Learning never stops'.

Sorry for the long OT, let's back to the discussion.!

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Old Fox

So far so good Abhijeet with just a couple of exceptions. It is true that we need 'some' dive to allow for 'cushioned' or 'graded' weight transfer onto the front contact patch. And that too stiff a front would be almost akin to a bottomed spring. This was actually the reason for the decline of the once favored 'anti-dive' systems (the Honda TRAC and the Kawasaki AVDS). Too stiff a springing would make the wheel chatter and skitter over small bumps.

It is also true that there is a certain reduction in the wheelbase which increases instability which in turn contributes to some extent in making the bike easier to turn in (more 'flickable). But the major contributor here is the reduction in the bike's 'trail'. See fig below:



The front suspension compression under braking reduces trail (the steering head drops lower and the contact patch spreads rearwards) and this reduction in trail leads to quicker direction changes.

So in conclusion, we tread the middle path by 'tailoring' some amount of dive into the front suspension to get the best of braking without compromising on comfort and inducing too much instability.



Pranay: I'd thought you were asking about the 'pre-load' thing.

As for what you've stated above, the 'link and lever' suspension has links and levers just to multiply the available suspension travel. A shocker/damper compresses just about a couple of inches before bottoming out. To get 4 inches of wheel travel with the same shocker unit requires the use of some sort of linkages and levers. The 'progressiveness' of the suspension comes from what are called 'variable rate' springs. The spring coils, visually speaking, are far apart towards the top of the spring and get closer together towards the bottom of the unit. The top coils get compressed easily under light loads while the bottom coils deflect less and need higher loads to compress. So, on the whole, the coil spring acts like a 'soft' spring under light loads and as a 'stiff' spring under heavy load. More expensive units also provide variable damping but then that would be another story.

There seems to be some mis-conception about 'trail braking' here. I'll start with a diagram that I've taken from a book 'Sport Riding Techniques' by Nick Ienatsch.



The orthodox riding technique staees that we finish all our braking and gear shifting while the bike is upright, enter the turn on constant throttle and just past the apex, feed in the throttle progressively. But the preferred method now is using 'trail braking'. 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. This progressive and smooth reduction in braking is to use a progressively larger share of traction for turning, a need that hits its maximum at the apex, where the braking input is reduced to zero. Trail braking has two major benefits: 1. It allows for braking while turning, allowing the rider more control over his situation. and 2. The rider can carry speed deeper into the turn and by slowing progressively towards the apex, has more reserve traction to trade for the same needed for turning.

Post-apex, progressively openng the throttle makes for gradual rearward weight transfer allowing the rear tyre time to gain traction and transfer power for acceleration.

In practice, the overlap between trail braking and powering out is a smooth blend, always balancing the available traction to the traction needs.




Ref to the bold part: weight transfer 'causes' front end dive. Weight transfer is NOT the result of front end dive. Again a fig below:



Weight transfer WILL occur even with no suspension springing at all, ex. the bicycle. The bicycle skids (on loose surface) or does a stoppie(on tarmac) because with no suspension to 'gradually' load up the front tyre, a sudden load forces it to stop. If the tyre grips, the whole bicycle rotates around the front contact patch that acts as a pivot. If the tyre does not grip (i.e. the coeficient of friction between the tyre and road is small), the it locks up and skids.

And abhijeet, hope I've managed to clear the air about the 'trail braking' part. And yes, trails braking is a useful skill, whatever the turn is like.

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

Ride long and safe...

OF

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samschenker

This thread is getting better & better.....its clearing lots of doubts for people like me....

OF, your explanation to things.....i'm awestruck....thanks a lot for the Gyan!!

Thanks a lot to all contributing here, I am sure it will help lot of us in xbhp...

samudranb

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

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dcs

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

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!

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Old Fox

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.

And about Trail Braking: Loading up the front during a turn is not a ‘needed’ thing. It just happens because of braking and also because of the centrifugal force generated during a turn that compresses the suspension. Ideally, a completely unloaded front is the best as all the available traction is there for resisting the slide (the tangential force that wants to slide the bike ‘out’ of the turn). But in the real world, we can only strike a workable balance between the various forces to our benefit.

And suspension dive is what the rider needs the ‘least’ during a turn. The ‘quick steering’ benefit is way offset by the detrimental effects of a bottomed out suspension and an excess demand on the traction reserves.

OF

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Shivanshu

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

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