Last post on Oct 20, 2013 at 11:13 AM
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#1984 of 2028 Re: Why is is...? [Mr_Shiftright]
Dec 03, 2010 (10:50 am)
I understand and I agree but if the old rotors were well within spec I don't see how a replacement rotor could stop you any faster.
#1985 of 2028 Re: Why is is...? [isellhondas]
Dec 03, 2010 (8:49 pm)
Simple physics; the thicker the rotor the greater the thermal mass, the greater the thermal mass the better the stopping power. Why? Because the rotor stays cooler during a high energy stop. While a worn rotor may still be "in spec", that in no way means that it's able to sustain stopping power as great as it could when it was thicker.
#1986 of 2028 Re: Why is is...? [shipo]
Dec 04, 2010 (5:55 am)
the thicker the rotor the greater the thermal mass, the greater the thermal mass the better the stopping power. Why? Because the rotor stays cooler during a high energy stop
We're talking very little thermal mass here from a machined rotor to a non-machined. Hot rodders spin their rubber tires to generate heat for better road contact, so I don't see how a slightly cooler /slightly heavier rotor will stop a car quicker. It would be like spitting in the ocean and trying to measure the rise in sea level.
#1987 of 2028 Re: Why is is...? [jipster]
Dec 04, 2010 (6:28 am)
>so I don't see how a slightly cooler /slightly heavier rotor will stop a car quicker.
I do not know that the tenet is that a thicker rotor will stop the car quicker. What it will do is stay slightly cooler as the predetermined quantity of heat is transferred into it. Staying slightly cooler may mean better braking, but in my thinking it means the rotor is slightly less likely to suffer distortion at the end of the stop due to the extreme heating during a hard stop or a long braking period such as a long downhill run.
But I have another observation. That is that the inside fins of most rotors are covered with a rust material. That has to insulate an old rotor from the air going through the fins and somewhat lower the transfer of heat to the air through those openings. That's why if I drive a car hard or I have had brakes that warped slighty I feel it's time for a quality new rotor that has a cleaner surface on the fins with which to transfer heat to the air that's interior to the rotor as well as the external surface air. If it's my 180,000 mile Buick that's driven mostly gently around the suburban and rural region, I think less about new rotors.
#1988 of 2028 Re: Why is is...? [shipo]
Dec 04, 2010 (8:39 am)
So, if I machine the rotors on one of our CRV's leaving it well within specs and someone with an identical CRV REPLACES his rotors and we both make a panic stop from 60 MPH, are you telling me that there would be a measurable distance in stopping?
Of course, this assumes identical tires, same road conditions etc?
I'm not buying that. Sorry.
#1989 of 2028 Re: Why is is...? [isellhondas]
by MrShift@Edmunds HOST
Dec 04, 2010 (8:44 am)
I was thinking that there's a certain amount of glazing on pads and burning on old rotors, and some roughness, so all together yeah, you might get a few extra feet out of brand new rotors and pads vs. a set that's been working hard for 25,000 miles. Perhaps it's the overall combination of all the things about a "new brake job" that gives me that confidence.
#1990 of 2028 Re: Why is is...? [Mr_Shiftright]
Dec 04, 2010 (9:13 am)
Well, I was assuming both cars had new pads. One had NEW rotors and the other had freshly resurfaced in tolerance rotors.
Speaking of which, our 2003 CRV has 53,000 miles on the original brakes. 10,000 miles ago, they still had lots of pad left.
Time to take another look!
#1991 of 2028 Re: Why is is...? [isellhondas]
by MrShift@Edmunds HOST
Dec 04, 2010 (9:38 am)
I drive pretty darn hard, so I'm not comfortable with shaving any appreciable metal off a rotor. I'm okay with cleaning them up but I wouldn't run mine if they are close to minimum tolerance. I'm just too hard on brakes to take a chance.
#1992 of 2028 Re: Why is is...? [isellhondas]
Dec 05, 2010 (12:24 pm)
Lets say the stop is from 70 to zero; yes, there will be a measurable difference if said stop is at impending lock-up. Now lets say the rotors are already hot from heat yet to be dissipated from previous stops, then the difference stopping distance will be even more pronounced.
#1993 of 2028 Re: Why is is...? [shipo]
Dec 06, 2010 (7:22 am)
Is this fact or theory? Measurable difference? How much is total weight of an average rotor face? How much is machined off? How much heat would need to be dissipated before it would affect performance?
Sounds like something the auto parts industry would fund if putting on new rotors were noticeably more beneficial than machining. I mean why not put on a new set of tires after every 10,000 miles... same thing.