Question about braking

It all depends... The Brembo kit will lower your corner weight and rotational mass, so you could go slightly larger rims BUT beware some cheapie rims weight considerably more and THAT weight is further away from from the hub so you take a BIG hit at lower performance.

My descision for the 308GTS QV here was to go with Kinesis Motorsport K27 that are 17 inch rims (versus metric 15.5 or 16) and 8 front and 9 rear (versus 7 front and 8 rear). The weight between the stock and Kinesis was negligable, BUT i could not fully analyze WHERE the weight was as you'd want to keep as little weight of the outside of the rim (the point furthest away from the hub). With Mich Pilot Sport PS2 rubber i have more grip than engine pertaining to accelleration. Naturally better tires that are also wider provide more grip and more stopping/turning capability.

There is a limit to going wider, too, besides weight. There are handling issues... Speaking of which, if you go the Brembo front, i highly recommend SLOTTED and not drilled IF you are not going with a straight disc. Also, there is a matching alu center and floating outer for the rear made by Girodisc i can highly recommend. At the same time i suggest eighter lowering the grip of the stock Brembo DS1100 pads and keeping your rears OR keeping the Brembo stock DS1100 and using Fredo 3000 rear pads to keep the brake bias (balance) near stock. Hope this helps.

 

New Ferrari cars also come with drilled, not slotted. Makes no sense to me, but hey, since when does having a Ferrari 'make sense' ;-)

 

Absolutely, better gripping tires will yield better braking.
Do this first, along with whatever rim is appropriate But keep in mind that most big brake kits will require a larger rim, (16 inch for the Brembo). So if you think you might want to go to bigger brakes, go for a bigger rim

I would refer you to the many high performance tire threads for tire advice.

Lighter rims offer better handling, cost is inversely preoportional to the weight.

As has been recommended many times before, if you want better brakes, first make sure everything is in good condition and properly adjusted. You might be surprised what higher coefficient pads, bleeding and stainless lines will do, particularly if you have performance oriented, fresh tires. I don't mean you have to go the "street legal" race tires, but some top of the line bridgestones or michelins will amaze you.

Given a "modest" budget, I would go with the 7.5 and 10.5 by 18 inch 360 rims with Michelins, QV Londons 355 front kit, a good proportioning valve and the Girodsc rear floating discs. I would like to use the same pads front and rear for predictability, but i am probably getting way ahead of myself here as i still have stock wheels and tires and the car hasn't run for 6 months.

Maybe i should quit jabbering and go out and get it running.

hth,

chris

 

FWIW, the holed rotor so commonly seen on Porsche's does NOT really have drilled drilled holes. It is a CAST hole. Porsche did this to help minimize the effects a hole has in creating a stress riser in the surface of the brake rotor. A drilled hole goes directly through and interrupts the grain structure of the metal. Where as a cast hole has the grain structure formed around it in an uninterrupted flow. All holes in a brake rotor will eventually show signs of stress cracking. A drilled hole will crack much sooner than a cast one.

Agree with Gabe: A "slotted" or gas vent rotor is even better. These vents can be machined in various configurations. A ball shaped cutter is used to prevent any stress risers. The purpose of these vents is the same as the cast holes: to give gases, water, and other dirt a place to go under hard braking. This is the most durable track or race rotor.

 

100% agree.

Agree... but there is a sweet spot and larger for larger sake needs to be defined. Also depends on what suspension setup as 18 inch rims may be too harsh for a stock setup. Of course the "Law of Diminishing Returns" applies to very low weight rims and also they may have a limited 'durability' so consider the roads you drive (potholes, etc.).

100% agree. Both the Brembo and Girodisc package include Goodridge steel braided lines as i recall. Modern rubber (Mich Pilot PS2 here) are LEAGUES better than what i felt driving a stock metric shod 308. i still can't believe the people who pay HUNDREDS OF DOLLAR for each metric tire and put up with the crappy metric tire's (cough) performance.

Have you driven with the 10.5 inch rears yet? The 9 inchers seem VERY wide on the 308GTS QV here and i can't imagine HOW you'd fit 10.5 inch without using spacers (bad news IMHO) and have to be VERY careful about rear tire well clearance. The rear clearance is more than just rolling the fender, i mean as in rubbing issues as the tire (i think) would hang out about half an inch outsoide the tire well itself. Naturally i could be wrong. Also, am curous about handling issues with such a large rear tire. Color me inqusitive/curious...

As for brake pads and bias, there are various ways to "skin the cat"... FYI: i am still considering using a brake bias setup and will decide better after a few days of track time here at Lime Rock.

 

Cast rotor holes, chupa cabra, loch ness monster...

 

Your point aside from trying up your post count?

 

Hmm... no need to be MENSA here... Lemme take a crack at it. My guess...

Things that are not real, but are perceived as such because others have repeatedly said it (so that makes it a "fact").

BTW: Was at Lime Rock Park for the FCA event last weekend and took a careful look at MANY drilled rotors. About 80% of the rotors that had usage were showing sighs of playing 'connect the dots' or at least starting to crack at the holes.

Just say no to drilled. Please, pretty please with sugar on top and a cherry get slotted or solid.

Of course if you drive like Grandma i guess it makes no difference. If you drive like me (see www.ispexperts.com/limerockbigbend.wmv ) then drilled do not stand a chance.

 

Cool video Steve! I probably would have gone spinning through the grass in that first corner of the S-turn so for me it wouldn't matter whether I had slotted or drilled.

 

Pete, am sure you'd be fine. Just begin braking at the 5 board and trail brake as you enter the turn. i chickened out and started hard braking at the 4 to 3 board, yet my instructor said i could have began at the 2 board(!) because i had so much stopping power with the Brembo/Girodisc package and the Nick Forza (Fchat sponsor) suspension was doing great. Keep in mind you are doing this www.ispexperts.com/limerockstraight.wmv when you get to the numbered boards and then make the turn onto Big Bend.

As for speeds, i guess you go from about 135mph (fifth gear at 4,500 rpm) to 60 or so (third gear at about 5,000 rpm). Was too busy braking, steering, and changing gears to look at the speedometer. i DO remember the rpm only because i KNOW the SOUND of the car.

Color me a amateur

Next time it WILL be the braking hard at the 2 board and perhaps more speed on the downhill leading to the straight. This was the car's first real track test after various mods and felt that some caution was best. Am busy doing a thorough testing of components and bolt tightness on the suspension/brakes/etc to see what type of wear/tear she incurred. So far all looks very good other than tire wear DAMN those Mich Pilot Sport PS2 tires grab like a.... for a 'normal' street tire.

And for the record, i did have a spin out entering the first turn when she would not go into third (shifter was not engaging into the tranny's third gear inset) and in frustration i guess my hand moved a touch upward and she engaged into second gear (!) and stupid me let off the clutch! Needless to say engine braking occurred BIG TIME and the rear naturally lost grip and the back end rotated causing a 180 spin into the grass. Reflexes kicked in so i depressed clutch and full brakes. Went back on track, did a feel/shake and all seemed fine. Went into pits, all looked fine. After that session i checked the rear end/etc and all seemed fine. Drove her the remainder of Friday track sessions (two twenty minute) and all Saturday sessions (six 20 minute). Seems nothing was damaged other than a lesson learned. Life moves on.

As i always say...

 

Steve,

It was good to meet you at LRP this past weekend. I think your estimate of speed on the main straight may be a little high. Unless my speedo is way off (and I've observed this driving several different cars), you were not up around 135 mph on the straight. Probably more like 115 to 120. I was turning some pretty good times, considering I was in the old Mondie, and when I glanced down on the main straight, I was topping out around 120 to 125 before braking hard at the 3 mark. I'm sure some of the higher horsepower cars that can really accelerate down the straight get up to 135 or higher, but not my Mondie or your 308, IMHO.

Tires do make a big difference in brake performance. I'm running the stock brake set-up on my car (rotors and calipers), with Porterfield R4-S pads front and rear. When I drove at LRP in June on street tires (Yokohama AVS) and stock brake pads, I had to brake at the 6 mark to avoid locking up to get the car settled down to turn into Big Bend. Since then, I got a set of Kumho Victoracer V700's on 16" rims, and my brake point went down to 3 (sometimes 2), and was still able to pull the car down and dive into Big Bend well under control. Between the new brake pads and the Kumhos, I knocked 6 seconds off the times I was running in June.

Are you going up to Watkins Glen the end of the month? Hope to see you there. LRP is fun. The Glen is a blast!

Regards,
Steve

 

Well, I've read in automotive mags that the rotors were forged cross-drilled so I'm guilty of believing them.

I agree, cross-drilled probably shouldn't be used on TRACK cars but I see no harm for STREET cars. I've yet to see a street setup crack.

 

I like to do one upgrade at a time, so that I can learn all about how it affects the car before I try another upgrade. I put Brembos on the front of my 308 over a year ago, but I havn't upgraded the wheels yet because I still have a lot to learn about useing the brakes to maximum effectiveness. The car did allready have 16" wheels. If yours are smaller, you will have to change them. Just my preference.

Ben

 

Having been an engineer for Porsche for five years, and then leaving to start a brake company, I have a small amount of knowledge about these infamous cast holes. The holes in Porsche rotors are machined in and radiused on the face of the rotor. The inside of the vane is "as cast" and has burrs and jagged edges where the hole is drilled through creating stress risers just like all other holes do. Porsche GT3 cup guys throw rotors away because they crack, not because they go past the wear limits.

I have a set of Porsche GT1 rotor rings and hats in our shop, drilled holes... you can see the swirls inside from the drill bit.

I'd also like to see the forging dies that create vented rotors...

Steve, you explained my first post perfectly!

Looks like my post count went up one more. ;-)

Hope to see alot of you at Concorso, we'll have some cool stuff for you to look at.

Martin

 

Okay, this is a much better post that actually EXPLAINS and GIVES DETAIL to your statement. This is the route you want to take.

Now your post count is up by one legitimately