Coefficient of friction at brake drum and on road 2

[quark]

Excuse me if this question is silly. I just want to know if there is any relation between the coefficients of friction of break shoe to break drum and tyre to road. What should be the maximum difference allowed or is it really critical anyway?

Thanks in advance.

 

[GregLocock]

No, there is no correlation in particular. Typical brake linings are around 0.35, while the tyre road interface might be as high as 0.95 in the dry, or even 1.4 or higher for some tyres.

The allowed values for each depends on the entire system performance, and the trade off with other aspects of the brake pad's performance.



Cheers

Greg Locock

 

[quark]

Thank you very much Greg. Somehow, I thought you would answer me. I am a silent viewer in some of the forums you participate and I always wonder how you can keep track of even the smallest details.

The reason for asking this question relates to violent skidding of bikes when we apply brakes on oil spillages(even if they are small).

Is it that we can balance the bike as long as the coefficient of friction between tyre and road is equal to or higher than that of brake pad and brake drum?

PS: Just ignore if my question is not relevant.

Thanks again

 

[GregLocock]

No, sadly not. Otherwise it would be relatively easy to design an ABS system for bikes.

Very roughly, when you lock a wheel it loses a large proportion of its capacity to develop lateral grip. Say 50%. As if that was not bad enough the potential grip has already dropped tot he coefficient of friction of rubber on the oily surface, say 0.1-0.3. So, overall you are only developing 5-15% of the grip you were expecting.

As a rider you are expecting a certain amount of grip, and usually move around on the bike in anticiaption of that. In its absence you can maintain balance by pulling the bike underneath you, but that is not instinctive.

One other aspect worth investigating is how the wheel locks up in the first case - in particular how the brake force varies at the pad as the speed drops. You may be able to get some value for 'grabbiness' for this, and the same for the tyre/road interface.




Cheers

Greg Locock

 

[MintJulep]

Quark,

Its related to the instantanious adhesion demand. Given the contact patch, friction between tire and road and other related factors, there is only so much force that can be transmitted from the tire to the road.

If you ask too much of the available adhesion, you skid (if braking), slide (if cornering) or spin (if accelerating).

On a bike, when you hit a slippery spot things happen faster than mere mortals can deal with.

 

[quark]

Thanks to both of you. It's clear to me. Now I agree with the adage, that says "Stupid questions are those which are not asked".

Greg!

Congratulations on being Tip Master of the Week.

Best Regards,