Braking power: Rotor size, front vs. back

[ChUkKy]

I also have 203/180 on one of my bikes.... 63kg.....

 

But slowcoaches like you don't need brakes....

 

I weighed 63kg in Standard 6.

 

My balls have grown somewhat since then

[rouxtjie]

Ok now I see , so you use your brakes to slow your down going down into the Hell (example) and then they overheat ? Never had that problem before and believe me when I say , I have done a lot of big downhills in the last 20 years . 

lol....tell us more about these big downhills

[rouxtjie]

I weighed 63kg in Standard 6.

 

My balls have grown somewhat since then

yoh yoh yoh....so...if that is the case come hit haka with us...

 

Next weekend?

[V12man]

 

My balls have grown somewhat since then

Peas do grow as they get older.... till about 7mm...... 

[V12man]

Ok now I see , so you use your brakes to slow your down going down into the Hell (example) and then they overheat ? Never had that problem before and believe me when I say , I have done a lot of big downhills in the last 20 years . 

Where is the hill in De Hell that needs all this braking?

 

Overheating brakes is caused by a combination of several factors - sheer volume of disk/caliper only slows it down somewhat - the trick is to find the minimum brake size that your combination of braking style/terrain/speed/kit etc will not overheat/stress to the point you lose braking capacity/modulation.

 

For me - on my XC bike that's 160/160 - but my enduro bike has more (came that way) and it works for me to have excess capacity on that bike. (both bikes run guides with the same pads)

[V12man]

To add: bigger rotors not only dissipate heat better, they have more leverage because the contact areas are further away from the rotational centre. Meaning you can stop with less force using a 180mm rotor than a 160mm rotor.

The rotor speed at the pad is also slower because of the bigger diameter - this has a beneficial effect on heat production as well, and thus pad life is extended. Modulation is also improved with the bigger diameter.

[Spoke101]

I weigh 61kg and I also have a 203mm front and 180mm back ......more for unduro riding 

 

 

 

 

But i could probably stop faster than my car if I try hard enough

I think you might be needing better brakes . For your weight a 180 is overkill with good set of brakes.

I weigh roughly the same and if I had a 203 on the front the wheel would lock up with me just thinking about braking.

Good brakes and a 160 is enough to put the back wheel in the air even with your weight behind the saddle. Managing the heat then becomes the problem, thus a 180.

[NotSoBigBen]

On my Flash HT I have a 160/140 combination and that works fine for my type of riding, no crazy technical stuff ..... weigh about 75kg's depending when (pre or post pooh). On all my other bikes I have 160/160

[V12man]

I think you might be needing better brakes . For your weight a 180 is overkill with good set of brakes.

I weigh roughly the same and if I had a 203 on the front the wheel would lock up with me just thinking about braking.

Good brakes and a 160 is enough to put the back wheel in the air even with your weight behind the saddle. Managing the heat then becomes the problem, thus a 180.

There is a formula for calculating the benefit of a bigger rotor in additional brake force - but it's not huge - like 5 - 10% from memory - if you keep all the other elements the same (caliper/pad/lever) - so no - you won't have problems controlling your braking if you add rotor size only.

 

I have the formula somewhere if you are interested - usually only racing gearheads are interested...

[NotSoBigBen]

Resin pads right?

 

Mmmmm can't say either way but the 'normal' pads the brakes come with?

[V12man]

One of the things that nobody has mentioned is the fact that no matter how good your brakes are, the brakes only stop the wheel.....

 

TIRES stop the bike (and you - assuming you are still on top of said bike) ..... or more specifically the tire/ground friction....  don't forget that as an important element of improving your braking....

 

and also why Enduro/DH bikes run bigger brake setups than XC bikes - because that big aggressive knobbly tire on the E/D bike can generate more braking before lockup than that lightweight low rolling resistance XC tire....

[ChUkKy]

yoh yoh yoh....so...if that is the case come hit haka with us...

 

Next weekend?

 

I dont have the right type of bike for that place, thats like going to a pub with R10 in your pocket.

[Headshot]

Hi guys

 

So I have notices there seems to be a trend to have a smaller rotor on the back wheel than the front I.e. 160mm back; 180mm front.

 

This seems a bit back to front to me. Larger rotor have better heat dispersion and braking power. So why have them on the front...

 

Having larger rotors on the back wheel makes more sense.

 

I use my back brake far more frequently than the front. So my thinking is that I would better benefit from have a larger rotor on the back.

 

Maybe I ride differently to most?

 

I'd like hear your thoughts on this.

 

Thanks

Oh dear, where do these misconceptions come from? This almost looks like you are trying to take the mickey out of the hub cognoscenti. Bigger back brakes - more braking at the rear? No man.

[Halfdoesyn]

The rotor speed at the pad is also slower because of the bigger diameter - this has a beneficial effect on heat production as well, and thus pad life is extended. Modulation is also improved with the bigger diameter.

I disagree. The bigger the rotor, the faster the tangential speed.

[V12man]

I dont have the right type of bike for that place, thats like going to a pub with R10 in your pocket.

Both of those sound like excuses to me....

[Dexter-morgan]

My new bike has 180 front and back, so far I like it.