Cornering and Braking g comparison q's ??

This past weekend I used Hoosiers for the first time, previous tires where always Kumho Victoracers.

I was comparing g load data from the two different tires:
Kumhos:
cornering ~ 0.95
braking ~ 0.8

Hoosiers:
cornering ~ 1.15
braking ~ 0.8

Am I right in saying that the limiting factor for the braking loads must be the brake pads? Meaning I should try a pad with more bite? I am currently using Hawk Blues.

For an IT car are you guys seeing similar data or are your braking g's closer to your cornering g's?

Dave,

There's several factors that could be affecting your ultimate braking gee forces. Some of these would probably be, front weight bias, brake rotor diameter, brake pad swept area, and also your pad compound. Only the pad compound is under your control, and maybe to a lesser extent the weight ballance. Hawk blue pads can definetly be upgraded, I'm running the HT-10 pad, but DTC-70's are a higher torque pad. As for non Hawk pads, I've heard good things about Performance Friction pads PFC-03.

Assuming that you are actually threshold braking - that if you stood on the pedal even the tiniest bit harder, the tires would lock - AND that you CAN lock the tires with your current brakes, then pad compound has zero to do with the equation. It's all tires.

K

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Originally Posted by Knestis

It's all tires.

K

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And camber.

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Originally Posted by Eagle7

And camber.

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Would I be correct in assuming this is because with more camber you have a smaller contact patch with your tires when rolling in a straight line?

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Originally Posted by spawpoet

Would I be correct in assuming this is because with more camber you have a smaller contact patch with your tires when rolling in a straight line?

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You got it.

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Originally Posted by spawpoet

Would I be correct in assuming this is because with more camber you have a smaller contact patch with your tires when rolling in a straight line?

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Yep... often if you max out the camber setting for ultimate cornering grip, you'll not have much in contact in a straight-steering condition. Tradeoffs.

Other things coming to play... weight distribution, brake force distribution (adjustable prop valve? Could you put more braking to the rear and still be stable?)...

Sometimes you can go for a softer pad in the rear, to use it a bit more - particularly if you have no adjustable valve (I don't) - but only if the chassis will tolerate it.

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Originally Posted by Eagle7

And camber.

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An excellent point!

K

As you increase static camber you can trail brake more as you will have more contact patch in the corner vs. approaching it. Bill Auberlen brakes in this manner, or at least his car setups lead to this conclusion. Also, as the weight transfers to the front the camber gain will decrease the contact patch. How much the contact patch decreases depends on your cars specific camber gain curves.

How long are your braking zones compared to other cars? Depending on your brake temps you could be braking later and harder.

I'd have to look at my data, but I seem to recall seeing higher peak numbers. There's quite a bit of skill to braking.

Adjustable prop valves make it possible to get the fronts really working at their max if you are locking your rears. I actually adjust my prop valve a couple times a lap at certain tracks due to braking areas that are hilly. Some guys run TWO adjustable prop valves, one for each rear wheel.

David,

I would say I brake later than others.


I agree 100% with what you guys are saying in relation to the reduced contact patch due to the camber, which results in less grip under braking than cornering.

What caught my attention was that the braking load did not increase with the new tires. Its obvious it increased in the corners meaning the Hoosiers are doing what they are supposed to be. Shouldn't it also have increased under braking, because the stickier tires will provide more grip under braking too? Maybe not by the same amount but at least a bit. Thats what made me think the limiting factor must be the braking system, and since the only legal thing to change is the pads, I should try something with a higher CF than Hawk Blues.


Those with data loggers: how do your braking g's compare to your cornering g's ?

I'd consider getting away from the blues for a number of reassns, even if one isn't peak torque.

1 - wear. blues eat rotors.
2- feel. blues are pretty binary when up to temp. newer pads like the DTC line have a more progressive feel - they come on a bit slower but theres a lot more brake there if you keep pushing. you might have to play with a prop valve to get teh balance right but these are great. carbo XP line are also good.
3 - variety. both of the above compound families have multiple compounds in them. this means you can tune the torque requirements to the axle with the pads, but still have simillar behavior on both axles.

blues are kinda the defacto IT pad - but theres a lot of offerings that are far superior today. like kirk said - if you are locking them up, tires are the controlling issue - but you might still getter better braking results (not just peak g's) from a pad that lets you modulate the force better. if you aren't locking - find a way to up the torque until you are able to.

Regarding data - I can clear 1.0g in decel on my ITB car, but don't - great way to fail and end up in the kitty litter. I usually only work at 0.8g, and that's sufficient to out-brake most. Car will manage 1.2g in the corners (peak).

Regarding pads - Chip has some great points. Depends a bit on the offerings for your car, but I've loved the KFPs since day 1, and would never consider switching away. Well, actually, the DSR has Hawk Blues, but it came that way, and once they're done, I'll be reverting to KFPs. :D

What he ^ said. SOMEtimes I hit 1.0G or so but that's only at certain tracks, like Road Atlanta at the end of the long straight. Other tracks I'll flirt with that, but end up trail braking (Lime Rock is a classic example).

Cornering peaks bounce around 1.2. And I stopped using Hawk blues long ago. My rotor wear is different now, but I still replace them often. Now it's because I'm braking harder and deeper (and going faster) and they are cracking. With the Hawks, I could only really brake well 1 out of 3 laps. I wore the rotors out, but didn't really cook them.

It all adds up.

Vaughan and Jake,

Thanks thats the kind of data I was looking for.

Dave,

You should be consistantly getting the highest braking gee's on Phil Hill. It is an uphill brake zone after all and after a long stretch of easy corners from the 25A CW configuration, from the bus-stop to PH is all go with no brakes or lift.

James,

Im assuming you were referring to me.

I don't really fully brake going up to phil hill. After putting an airdam and splitter I can take it alot faster than before. Thats probably the turn where they have paid of the most out of any turn/track. After this past weekend I realized I think I can do a little less braking too.

Plus my ITB car gains alot less speed after the bus stop than yours probably does. :eclipsee_steering:

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Originally Posted by Sandro

James,

Im assuming you were referring to me.

I don't really fully brake going up to phil hill. After putting an airdam and splitter I can take it alot faster than before. Thats probably the turn where they have paid of the most out of any turn/track. After this past weekend I realized I think I can do a little less braking too.

Plus my ITB car gains alot less speed after the bus stop than yours probably does. :eclipsee_steering:

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Since I don't have a speedometer, I have to guess that the last kink in the bust stop is probably 50-60mph, then accelerate on around, my race car's probably ~110 or so there. So you aren't braking untill Star-Mazda, and that's a bumpy brake zone too, you should see how hard the FA's brake for Star-Mazda.

Vaughan and Jake,

The F1 guys are hitting 4.1 G's what's wrong with you guys! :) jk but watching F1 today I thought of this thread... and wow they really are pushing over 4gs!

Stephen

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Originally Posted by StephenB

Vaughan and Jake,

The F1 guys are hitting 4.1 G's what's wrong with you guys! :) jk but watching F1 today I thought of this thread... and wow they really are pushing over 4gs!

Stephen

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...and they make something like 2g (negative) due JUST to aero drag, simply by getting off the throttle at top speed.

K