Deceleration Rate Measurements: OEM vs. 40mm Rear Brake Calipers (Negative "G's")

[GTS Dean]

They'd fall somewhere - OFF the chart! Gen 3 brakes are staggeringly good.

[Tom, F&L GoR]

Catwood, might be near Torrance, but not until later this summer.

PLEASE NOTE TIRE SIZE - if you are using larger fronts, you are getting more "stick" than 275 size tires and therefore the rear end of the car will be "lighter." You indeed might get better braking with an adjustable prop valve because the 40mm with that combination a wee bit too much.

Thanks for the update, Mike.

KepRight, a Gen 3 with a four-piston rear caliper would be way far off the right side. No, it is not "bad" since there is a proportioning valve and ABS to reduce the brake line pressure so the amount of braking out of the rears is balanced with that of the front brakes. It puts you back somewhere in the middle "flat" area. Same thing with the Gen 2 ABS car - it has a 43mm rear piston, which is slightly too much (I believe.) If you re-enable the ABS, the electronics will modulate the caliper so it doesn't lock up.

Any four-piston caliper in the rear added on should also add an adjustable proportioning valve. If you use the stock prop valve (or none) the rear brakes will be working at 100% and lock up very easily.

Good question, because it points out the many choices - but in the end, it is the balance that feels good. You can make the "large" OEM front brakes smaller (using Stoptech calipers), you can make the "smallish" rear brakes bigger (OEM to 40mm piston size), or you can add-on a "really large" rear caliper and dial it down.

They'll all work and decisions are made on secondary factors (cost, appearance, brake pad size for racing).

[Catwood]

Hi Dean.

Yes...305 front "used up" VRL slicks.

I have used the Hawk HT14 (fronts) and Blues (rear) and they felt like they stopped harder. I'll probably go back once I test an old set that still has a little life in them. The hawks put alot of wear on the rotor but I pull them after every event. I left the brakeman in since they don't feel as bad when they are cold. hawks needed heat or both feet to stop

Carl

Originally Posted by GTS Dean

Carl,

What are your tire sizes - 305/335-18? I'm also assuming Hoosiers?

BM #3 are OK for rears, but lack the bite and release characteristics of PFC. BM also wear LOTS faster.

Dean

[ViperRay]

Great evaluation Tom! and good discussion.

I have had Tom's 40 mm rears now for 2 seasons on the track car and they are great indeed. I removed the prop valve to get as much to the rear as possible and then figured out what I needed to make sure the fronts locked first.

I started with BM3's all around but that was a close call on lockup for front and rear with 315 up front and 345 out back. I went to PFC 01 up front for more bite and I'm back to occasionally flatspotting the fronts again so I'm happy (I guess?).

[TexasPettey]

I've got Tom's 40mm upgrade as well. I just got back from my first DE event on the track with Kumho 315-F/335-R & BM-3's. It did seem to me like the rears were at the edge a bit before the fronts. How are you guys adjusting the proportion?

I am looking for a bit more brake bite all around. Coming down from 165 to 90, I felt that the BM3's didn't have enough. I was braking a lot earlier than I would have liked, as the tires weren't close to lockup at the higher speeds. I've got a line on inexpensive rotors, so I'd rather have rotor eaters with better grip and longer wear. Any suggestions?

[Catwood]

Originally Posted by TexasPettey

How are you guys adjusting the proportion?

Contact Dave Cawthorne aka Racecars. He sells a preformed kit. Lookk for him over in the new product/supplier special section.

Originally Posted by TexasPettey

I've got a line on inexpensive rotors, so I'd rather have rotor eaters with better grip and longer wear. Any suggestions?

Like I said earlier the Hawk HT10s on the front seemed to have more grip. The down side is they needed heat. They felt wet to me when they were cold.

What's inexpensive on the rotors? Please share.

Carl

[TexasPettey]

Originally Posted by Catwood

What's inexpensive on the rotors? Please share.

Carl

For some reason, Autozone has rotors for $29 each with a 2 year replacement warranty. They can't be the best quality rotor. I change from street to track pads/rotors for each event, so if the rotor looks close to bad after an event, I can just take it back to get a new one. A friend of mine does the same thing with NAPA rotors on his Z06. For some reason on his car, the NAPA rotors are 1/2 the price of the Autozone.

Thanks for the tip on the Hawks. I'll check them out.

[ruckdr]

TexasPettey,
At that price for rotors, absolutely give them a try. Like you said:

For some reason, Autozone has rotors for $29 each with a 2 year replacement warranty. They can't be the best quality rotor. I change from street to track pads/rotors for each event, so if the rotor looks close to bad after an event, I can just take it back to get a new one.

You can approach them carefully: 100MPH, 120MPH, 140MPH, etc. to make sure they stay together............

Then let us all know how they work out.

Later,

[TexasPettey]

I used them this weekend without issue, plenty of 150 to 90 braking. They certainly got plenty hot. I have front brake ducting and was very careful to not touch my brakes on the cool down lap to make sure that they didn't crack waiting for the next session. I'll probably finish out these BM3's and then look for a more agressive pad. We'll see how they stand up to the rotor eaters.

[Purdue_Boiler_Viper]

Tom, very interesting data. I'm trying to sort out what improvements can be made to a Gen II car with ABS. Is it correct to interpret that you can add braking power on either axel and achieve improved braking with ABS, without compromising balance and control?

[ViperJames]

You can actually feel the car "squat" down and stop on all fours in stead of just the front droping down doing all the work.....Best Performance mod for the $$$$. I love mine, thanks Tom.

[Tom, F&L GoR]

Originally Posted by Purdue_Boiler_Viper

Tom, very interesting data. I'm trying to sort out what improvements can be made to a Gen II car with ABS. Is it correct to interpret that you can add braking power on either axel and achieve improved braking with ABS, without compromising balance and control?

Purdue BV, the answer is no.

You technically have enough clamping force at both ends to find a good balance. The ABS is doing that for you. Your only choices now are better ABS electronics (4-wheel version instead of 3 channel) or if you do a lot of track time, a set of calipers that allow larger brake pads. Larger pads will dissipate heat better, be more consistent, and last longer under more extreme conditions.

I can't vouch for this, but if you wanted to experiment, you could disable the ABS and add an adjustable proportioning valve. Then you could tune it to your car's specific threshold braking level, which the "experts" say should be better than ABS performance under some/many conditions.

If you have ABS, then you already have a larger master cylinder - the same as the Gen 3 cars. (The reservoir is different to clear the hood.) You could go to larger calipers to be able to use larger pads.

Stoptech has a good article that seems a little negative towards changing calipers on ABS cars. I suspect they just want to ensure someone doesn't go too far away from OEM.

http://www.stoptech.com/tech_info/wp...rakekits.shtml

[AviP]

Originally Posted by Tom, F&L GoR

example for 0.8, 1.0 and 1.2 G
distance from 60 MPH = (1.4666*60)^2/(2*32.2*.8) = 150ft
distance from 60 MPH = (1.4666*60)^2/(2*32.2*1) = 120ft

Those 30' make all the difference between a fender bender and a close call. Good job as always Tom.

[Catwood]

sorry to bring up the old thread again but if anyone is taking note.

I have Hawk HT10 not 14s on the front. I changed them yesterday for the track and noticed I'd mis-spoken.

I'll post my deceleration rates with this set up later this week once I download.

Carl

Originally Posted by Catwood

Hi Dean.

Yes...305 front "used up" VRL slicks.

I have used the Hawk HT14 (fronts) and Blues (rear) and they felt like they stopped harder. I'll probably go back once I test an old set that still has a little life in them. The hawks put alot of wear on the rotor but I pull them after every event. I left the brakeman in since they don't feel as bad when they are cold. hawks needed heat or both feet to stop

Carl