Different tire sizes affecting ABS???
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On The Tree
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From: Columbia Missouri
Different tire sizes affecting ABS??? I have smoothie II's in 17x10's all the way around. In front I have 275/40ZR-17 Goodyear Eagle F1 GS-D3's and in back 315/35R-17 Nitto NT 555R Drag Radial's. The very first night that i mounted my nittos and went out racing i noticed too late that when i went to brake from racing speeds my brakes simply were not slowing me down nearly quick enough and were going into abs mode when i was not applying full braking force. They simply were pulsing WAY to early as if i were on ice yet i was on concrete. This in turn led to me crashing my car due to not being able to stop in time. Enter the now! My wheels are now on my new 99 Camaro SS and when the mechanic (my good friend) was driving it the other day he went into an s-turn and braked firm and it sent that totally different car into early ABS pulse as well and he almost lost it. His take on things is that even though the tires are very close to the same rollout that by having the 315's on a 10" wide rim as opposed to a 11" wide rim allows the tires to have enough of a rollout difference to upset the ABS system (which i understand is VERY sensitive to exact wheel rotation measurements) and cause it to malfunction. Is this plausable to you deep thinkers in here? He is suggesting that if i stay with my current setup we delete the ABS system and install a proportioning valve. That will work for me if there is no other solution because i love ABS. Any input guys?
I put E/T streets on my car and Randomly while I am driving trac cont light and another (Tired as hell ATM) Will light up.. when this happens I loose Trac controll and abs... Ive noticed that on ocasion that when I brake Hard the brakes will stiffen up a little. I counter this with a harder push and after a few seconds it will loosen up again and I have my normal brakes..
This is very serious, I had no idea this would happen when I purchased my Mt/Et streets..
This is very serious, I had no idea this would happen when I purchased my Mt/Et streets..
The ABS and traction control systems look at wheel speeds sensors at each wheel (4 channel) and compare them to each other with the different tire sizes front to back it might see the difference in speed and think that the wheels are locking up causing the ABS braking event. I know when I run the wheels at the track with the skinnies and the big tires in the back I have to remove the ABS fuse so that it doesn't work so I can brake better at the end of the track cause it doesn't like the different sized tires. I am not sure that there is a way to correct this other than run all the same size tire or disable the ABS system
Thread Starter
On The Tree
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From: Columbia Missouri
Yes its very serious as i braked at the exact spot i always did and would always stop with plenty of room to spare. Brakes themselves were in perfect order post mortem as well as prior as i inspected them when i put the wheels on that very night. I too got that stiff pedal you described and thats when i went into ABS, but when i pushed harder it never recovered and continued to pulse even though it SHOULD NOT have been as my tires WERE NOT SKIDDING WHAT-SO-EVER!!!! It cost me so much stopping room i cant even begin to explain it. And then to have the same wheel/tire combo on a totally different car cause the exact same condition...well that leave no doubt that something is amiss. By the way the wheels check out true and straight and very well balanced so it is not that!
Staging Lane
Joined: Jan 2006
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From: New York
ABS issues a friend asked me to test drive his big BMW sedan with pulsing brakes. Before I got in the car, I noticed one of the front tires was down on pressure a little (as indicated by sidewall bulge). We brought the pressure back up to spec, and the pulsing stopped. Systems are very sensitive.
Staging Lane
Joined: Mar 2006
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OEMs should devise a diameter learning feature (such as learn rotation rates in a straight line with no brake applied). Probably would save a few people that have low tire pressure, or aftermarket wheels'n'tires.
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On The Tree
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From: Columbia Missouri
Originally Posted by RednGold86Z
OEMs should devise a diameter learning feature (such as learn rotation rates in a straight line with no brake applied). Probably would save a few people that have low tire pressure, or aftermarket wheels'n'tires.
This is all starting to make total sense now. Thanks for all the input. Boy the rollout is so slight in difference yet the damn ABS is VERY smart when it comes to this and is sensing it! WOW!!!
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TECH Fanatic
Joined: Jun 2002
Posts: 1,979
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From: Upstate NY
Your tire rolling radii seem to be well within the ABS parameters. I suspect the friction difference (traction) between the fronts and the rears may be causing the ABS to cycle.
Let's assume the rear DRs "bite" better than the F1's, so under hard braking the fronts should start sliding before the rears as if the fronts were on a slippery surface and the rears were not. The ABS releases pressure on the slower turning wheel because it is programmed to think that tire is sliding, so it releases brake pressure on the fronts but not the rears.
Now in a hard stop the fronts are doing 70-80% of the stopping, mainly because we are starting with a front heavy (54-55%) car which transfers weight forward under braking. The worst case is fronts locking (sliding) and the rears gripping. You lose MOST of your braking ability. This sounds like your condition on both cars.
If you were to disable the ABS perhaps by pulling a fuse, and did some controlled braking trials you could determine which end is locking up. If it's the front, you need to get the fronts biting like the rears or vice versa.
Solutions? You could put DRs on the front also. 5-6000 miles is probably about all you'll get on DRs. You could put F1s on the rear and save the DRs for the strip. I strongly suggest you take action on this problem.
My $.02
Let's assume the rear DRs "bite" better than the F1's, so under hard braking the fronts should start sliding before the rears as if the fronts were on a slippery surface and the rears were not. The ABS releases pressure on the slower turning wheel because it is programmed to think that tire is sliding, so it releases brake pressure on the fronts but not the rears.
Now in a hard stop the fronts are doing 70-80% of the stopping, mainly because we are starting with a front heavy (54-55%) car which transfers weight forward under braking. The worst case is fronts locking (sliding) and the rears gripping. You lose MOST of your braking ability. This sounds like your condition on both cars.
If you were to disable the ABS perhaps by pulling a fuse, and did some controlled braking trials you could determine which end is locking up. If it's the front, you need to get the fronts biting like the rears or vice versa.
Solutions? You could put DRs on the front also. 5-6000 miles is probably about all you'll get on DRs. You could put F1s on the rear and save the DRs for the strip. I strongly suggest you take action on this problem.
My $.02
Originally Posted by 98 Z28
So running something like the 17x9.5 and 17x11 Zr1 wheels is going to throw off the brakes on any F-body?
Only if the diameter of the wheels and tires is different not the width.
Launching!
Joined: Jul 2005
Posts: 267
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Originally Posted by dschmittie1
Only if the diameter of the wheels and tires is different not the width.
TECH Fanatic
Joined: Jun 2002
Posts: 1,979
Likes: 3
From: Upstate NY
Originally Posted by CamTom12
I pulled my rear speed sensors (well, not on purpose... They won't fit in my Moser 9" housing) and my buddy did an !ABS mod on his. Both got rid of the ABS issues 
Are you familiar with threshold braking? If not, you should become familiar with it, and soon.
Teching In
Joined: Apr 2005
Posts: 46
Likes: 0
From: MS
Originally Posted by Old SStroker
Your tire rolling radii seem to be well within the ABS parameters. I suspect the friction difference (traction) between the fronts and the rears may be causing the ABS to cycle.
Let's assume the rear DRs "bite" better than the F1's, so under hard braking the fronts should start sliding before the rears as if the fronts were on a slippery surface and the rears were not. The ABS releases pressure on the slower turning wheel because it is programmed to think that tire is sliding, so it releases brake pressure on the fronts but not the rears.
Now in a hard stop the fronts are doing 70-80% of the stopping, mainly because we are starting with a front heavy (54-55%) car which transfers weight forward under braking. The worst case is fronts locking (sliding) and the rears gripping. You lose MOST of your braking ability. This sounds like your condition on both cars.
If you were to disable the ABS perhaps by pulling a fuse, and did some controlled braking trials you could determine which end is locking up. If it's the front, you need to get the fronts biting like the rears or vice versa.
Solutions? You could put DRs on the front also. 5-6000 miles is probably about all you'll get on DRs. You could put F1s on the rear and save the DRs for the strip. I strongly suggest you take action on this problem.
My $.02
Let's assume the rear DRs "bite" better than the F1's, so under hard braking the fronts should start sliding before the rears as if the fronts were on a slippery surface and the rears were not. The ABS releases pressure on the slower turning wheel because it is programmed to think that tire is sliding, so it releases brake pressure on the fronts but not the rears.
Now in a hard stop the fronts are doing 70-80% of the stopping, mainly because we are starting with a front heavy (54-55%) car which transfers weight forward under braking. The worst case is fronts locking (sliding) and the rears gripping. You lose MOST of your braking ability. This sounds like your condition on both cars.
If you were to disable the ABS perhaps by pulling a fuse, and did some controlled braking trials you could determine which end is locking up. If it's the front, you need to get the fronts biting like the rears or vice versa.
Solutions? You could put DRs on the front also. 5-6000 miles is probably about all you'll get on DRs. You could put F1s on the rear and save the DRs for the strip. I strongly suggest you take action on this problem.
My $.02
