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Brake bias question

Old 01-30-08, 09:34 AM
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Brake bias question

After running my FC IT-S at a number of events I feel that I'm overcoming the brakes quite a bit. Coming into every corner I have to really tiptoe my way around break lockup way more than I think I should. I'm currently running Ra-1s with a 6/32nd shave ( a little less then full shave). My friends using the same tires with a nearly identical car says that his braking is confident, and the only difference I can see is that his car has a bias valve installed. Wouldn't the bias valve only proportion less or more braking to the rears? If I'm overcoming the fronts this wont do anything to help.

What are your suggestions?
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Old 01-30-08, 02:56 PM
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There are a bunch of things that can cause this. First would be driving style, are you trying to go as deep as you can every corner? Try braking earlier, more controlled, smoother and work on your exit speed, not entrance. Slow in, fast out doesn't seem as fast but usually is faster.

Poor shocks, corner weights and alignment make the list after driving style. Is it always the same side, or either side. If your locking the fronts a bias adjuster on the rear won't help.
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Old 01-30-08, 03:16 PM
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I honestlly won't rule the driving style issue out at all. My past experience running smaller lighter cars deffinately feels like it messes with me a bit under braking. I just bought a G2X datalogger so I will be comparing my braking points with some friends, as well as my dad who shares driving duties in the car with me. Obviously Im not locking up on every corner like a maniac, but I just feel that the overall braking is less confident than the sum of the parts would seem to indicate.

After getting a ride in my buddies s2000 powered race miata it seemed like he was braking with much more force than I was, later, from a higher speed, and still keeping everything more under control, so I started thinking that it was all a tire issue as he was running much stickier compound. He also has a bias valve, so...

I doubt that it is an alignment problem as I do my own alignments, and I recheck everytime after an event. I am running a minute dose of toe out in the front, and an equally small amount of toe in in the rear. Camber is set to 3 in the front and about 1.8 deg in the rear.

I should have gone with the full shave on the Ra-1s, but I was talked into it considering I was getting the car sorted, and would have more meat.

What do you guys think, am I just hotrodding into the corner, or is there any other factor at play.
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Old 01-30-08, 03:17 PM
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What kind of pads?

I run Hawk Blues and RA1 or Hoosier w/ no bias adjuster. I brake late, very late and people comment on it, but I also trail brake. Thought about adding a bias adjuster but have not as the rears rarely lock, it's more in the pace lap when I accelerate/brake to warm the tires and brakes.

If you haven't spent the money to have the car setup and corner weighted, it'll be a great investment. It needs to be done as often as you can afford. Bias adjuster doesn't sound like the answer.

Edit: I see you do your own alignments, BUT is the car corner weighted? You didn't mention that very important part of a setup. Corner weighting tells you if the car is balanced. An unbalanced car isn't going to stop like a balanced one.
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Old 01-30-08, 03:46 PM
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Yup..I'm running the hawk blues as well, and the car was just corner weighed at a shop about a month ago. I ran a few events before corner weighing, and I was thinking that that would be the culprit as well. Turns out that the car was only about 15lbs off on diagonal, and it felt identical after the corner weighting.

Ive been using a lazer alignment tool and a camber guage to align, and the shop verified that everything was working properlly and that the alignment was dead on.

Everyone that runs Ra1s tells me about how great they are, and considering this is the first set ive used, Im starting to wonder if its all due to the added tread depth. Could 2/32nds really have that much of an impact?

SCCAITS..seems like we have virtually the same setup, but with opposite results!
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Old 01-30-08, 04:18 PM
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Originally Posted by designfreak View Post
Yup..I'm running the hawk blues as well, and the car was just corner weighed at a shop about a month ago. I ran a few events before corner weighing, and I was thinking that that would be the culprit as well. Turns out that the car was only about 15lbs off on diagonal, and it felt identical after the corner weighting.

Ive been using a lazer alignment tool and a camber guage to align, and the shop verified that everything was working properlly and that the alignment was dead on.

Everyone that runs Ra1s tells me about how great they are, and considering this is the first set ive used, Im starting to wonder if its all due to the added tread depth. Could 2/32nds really have that much of an impact?

SCCAITS..seems like we have virtually the same setup, but with opposite results!
People say fully shaved RA1 is 2 secs faster than full tread Laguna Seca. I never driven on full tread RA1.
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Old 01-30-08, 04:19 PM
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Originally Posted by designfreak View Post
Im starting to wonder if its all due to the added tread depth. Could 2/32nds really have that much of an impact?

I've never ran 6/32, only 4/32 and below. Are the tires getting too hot? You check pressures at the end and are they under 40 PSI?

Not sure if you built or bought the car, I assume you've checked and there is not a brake bias control hidden somewhere other than the obvious within drivers reach. How is pad wear?

I don't recall ever being able to lock the fronts, only the rears.

Edit: I have ran 8/32 but that's only in the rain, doesn't count.
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Old 01-30-08, 04:49 PM
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I built the car, so it wouldn't be hidden anywhere. I'll have to look at my logs to get the exact tire temps and PSI, but I've taken measurements off of them, and I don't recall anything out of the ordinary, or too hot. Do you guys know what the reccommended temps for RA-1s are?
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Old 01-30-08, 06:40 PM
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***Wouldn't the bias valve only proportion less or more braking to the rears? If I'm overcoming the fronts this wont do anything to help.***

Oh yes the proportioning valve will help in your case because more stoping from rear brakes will mean less work for the front brakes to do therefore less brake lock up. If the rear brakes do more of the stoping of the car the front brakes do less stoping of the car. If you have the OEM porportioning valve the rear brake line pressure is something like 40 to 60 % of the front brake line pressure. More likely than not your rear piston diameter is smaller than the front piston diameter therefore the force to the brake material is less yet than the front. Add the proportioning valve (maybe 50 to $80.00) & adjust at the track (each different track each day for the different track conditions) for each event untill your rears lock up first, then back off the rear adjustment a bit untill the rears don't lock up.

Have Fun
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Old 01-31-08, 08:00 AM
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Originally Posted by designfreak View Post
Do you guys know what the reccommended temps for RA-1s are?
According to Toyo, 140-220 with optimum around 200. Get them to about 38 PSI hot and you are in the ballpark.

You got Hawk Blues around, the setup is correct, no hidden brake bias controller, maybe it is driver but I don't think I could lock up my fronts if I tried. I'm assuming you are getting relatively even pad wear and you've looked the calipers over.
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Old 01-31-08, 09:27 AM
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A bias adjuster in the rear lines would only be able to lessen the rear line pressure, not increase it, so it can only reduce rear braking effectiveness. If you bypassed the stock bias valve then you could have more rear pressure though.
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Old 01-31-08, 12:13 PM
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***If you bypassed the stock bias valve then you could have more rear pressure though.***

Sorry, presumed the driver knew that the OEM prorortioning valve came off.
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Old 02-01-08, 08:01 AM
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Ok guys, I think this makes sense, especially considering the cost in light of the added adjustability. Im gonna try it out, and Ill keep everyone informed on the results. Thanks for the help!
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Old 02-01-08, 09:20 AM
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I'm guessing that if your rears aren't locking up then it's technique. You have to get the weight transferred to the front to get the car to plant the front tires then you can really turn these cars inside out under breaking. To do this you first apply the breaks kinda light and then "gradually" increase the pedal pressure so you transfer more weight, then add more brake pressure which transfers more weight... etc. Of course you will be doing this much faster than you can even read these words, but I think the idea is pretty basic. If you just nail the brakes there's no weight transfered to the front and the front's will lock up immediately... especially with grippy pads like the hawk blues. When you're getting the most out of your front breaking I think you'll find it's the rears that like to lock up. Then you'll want that proportioning valve.
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