SwedeSpeed - Volvo Performance Forum banner
1 - 12 of 12 Posts

·
Registered
Joined
·
270 Posts
Discussion Starter · #1 ·
cross drilled and/or slotted brake rotors for the xc90?

Does anyone know if there are slotted and/or cross drilled rotors available for the xc90?

I have noticed significant brake fade due to the recent hot weather. I noticed this getting off the freeway with outside temperatures of around 110 F. The car went a little too unpredictable when gauging stopping distance.

I'm thinking those slots and cross drilling should let some of those gasses caused by braking friction to escape and allow for shorter stopping distance.

The brake fade I saw was significant enough for me to worry, thus the post. I don't think the DSTC would be any good in hot weather either.

...would appreciate any leads.
 

·
Registered
Joined
·
394 Posts
Re: cross drilled and/or slotted brake rotors for the xc90? (crash)

I'm not trying to be a jerk, but your brakes won't notice a 30 degree increase in ambient temps (from 80 F to our sweltering 110 F). Your brakes operate at temps much, much, hotter... in the range of 500 - 1000+ F when really pushed (granted, those are spot readings)! In all honesty, 110 F air will cool your brakes just fine (I was at the track last month in 100+ ambient temps and my brakes never noticed).

I suggest better pads - ceramics specifically (try "PBR Ultimates"). OEM pads are soft, and designed for cool temps. Search for pads that are specifically designed for hard use (aka heat).

Depending on the age of the brake fluid (I'm assuming yours is two-years-old), you may want to flush/replace that too. Try a high-temp fluid like "ATE Blue."
 

·
Registered
Joined
·
23 Posts
Cross drilling and slotting are unnecessary with modern day pads. They actually reduce surface area and introduce stress risers for cracks. Best bet as already mentioned is to get a better pad. EBC sucks, PBRs are decent. Hawk makes an excellent pad such as the HPS.
 

·
Registered
Joined
·
270 Posts
Discussion Starter · #5 ·
Here's the way I like to look at it. cars aren't as heavy as the xc90. For a car to go through the same brake stress that the xc90 does, the car would have to going at over a certain percent faster than the xc90. For example, the braking force required for a car to stop from 105mph would proabably be equivalent to an xc90 stopping from just 75mph. ...make sense?

plus your cars would probably have bigger OEM rotors than the xc90's.
 

·
Registered
Joined
·
592 Posts
Re: (crash)

Brakes are designed to even stop the car with a trailer, they are plenty strong enough to stop the car. Your rims may get dirty, but they work well.

The effect was probably the air thinning by the higher heat, and thus less resistance to the vehicle. You probably also noticed better milage too.
 

·
Banned
Joined
·
3,169 Posts
Re: cross drilled and/or slotted brake rotors for the xc90? (crash)

I wouldn't recommend cross-drilled rotors for large or heavy vehicles. The drilling removes rotor mass, which reduces that amount of heat they can absorb. The rotors can also experience radial cracking, particularly in situations in which the rotor has not been properly prepared.

Keep in mind that cross-drilled rotors came into vogue in the 60s following Porsche's racing successes. Many folks forget, however, that the Porsches used a very strong, light and incredibly heat resistant Beryllium/Aluminum alloy for their rotors. Thus radial cracking was not an issue -- just as it apparently isn't in the newer ceramic matrix rotors on today's very high-end sports cars.

While some rotor mass is removed to create a slotted rotor, the quantity of lost material is very small. The slots are very shallow. This enables the rotor to maintain a higher degree of structural integrity. Nevertheless, a slotted rotor must be carefully designed and machined to prevent cracking, noise and vibration.

ATE markets a variety of slotted rotors under the "Powerdisk" brand name. I've used these rotors for the past ten years. They're easy on pads and quiet except under the heaviest braking, when a slight whirring sound can be heard.

Hope this helps,
 

·
Registered
Joined
·
23 Posts
To add as well, I have cross-drilled rotors on 2 of my track cars - the M3 and a 944 turbo. Both are using the 993tt brake set-up, but the rotors are not really "drilled", rather the holes are cast into the material so as not to weaken them. Even so, under heavy duty microfractures can be seen originating from the holes. The holes were initially meant to help outgassing from older pad materials, which is no longer an issue with modern pads.

Slotting was meant to help prevent glazing of the pad from high heat - the slots would clean off the pad. This is also rarely a problem.

Specifically for brake fade, the issues tend to be cooling/ventilation, with the brake fluid itself, and with pad material. Regarding fluid - need to find a quality fluid with a higher boiling point such as ATE superblue, Motul, GS610, Castrol SRF. Also, the pad material with more heat capabilty will help. Pads with higher heat capability usually will sacrifice some cold performance as the pads perform better when warm.

As Paul noted, the brakes convert kinetic energy into heat to slow a car down. Reduced heat capacity or cooling will exceed the capabilities of the brakes to absorb any more heat. Thus, a rotor with less material of the same dimensions will have worse performance.
 

·
Registered
Joined
·
927 Posts
Re: cross drilled and/or slotted brake rotors for the xc90? (crash)

Try a set of ceramic pads (I have Akebono) and a brake fluid change as mentioned earlier. The pads have the added bonus of low dusting.
 

·
Registered
Joined
·
394 Posts
Re: (eclou)

Quote, originally posted by eclou »
To add as well, I have cross-drilled rotors on 2 of my track cars - the M3 and a 944 turbo. Both are using the 993tt brake set-up, but the rotors are not really "drilled", rather the holes are cast into the material so as not to weaken them. Even so, under heavy duty microfractures can be seen originating from the holes. The holes were initially meant to help outgassing from older pad materials, which is no longer an issue with modern pads.

My 911 Turbo cross-drilled rotors have cracks from my track use too. "Drilled" rotors are excellent for track use, but I'd prefer solid (vented) or slotted for a daily driver - just less of an issue. Brakes on a street car should be an item that rarely needs attention.

Least expensive upgrade is pads. I was quoted about $80 for ceramic PBR Ultimates. You can do them yourself in less than a hour.

Modified by Emission at 9:01 PM 7-26-2006
 

·
Registered
Joined
·
270 Posts
Discussion Starter · #11 ·
thanks for the advice guys. I'll try the pads first.

Hawke and akebono's vs PBR's? which one?

btw, nice toy cars. anyone into 2-wheel racing as well?
 

·
Registered
Joined
·
415 Posts
Re: (crash)

Overall, I suspect the performance of cermic pads from these three will be similar. I bought, but have not yet installed a set of Akebono's, as it seems from comments on this board, that they might be the least dusting. My daily drivers get decent, but clean running brakes. My Triumph sports cars get the shortest stopping, non-rotor eating pads I can find. With them, I don't care about dust, only performance.

Jack
 
1 - 12 of 12 Posts
Top