ABS going of due to mismatch tire size

[PSUCOBRA96]

So my ABS is going off above 45 miles an hour. I have old MT 305/35-18 drag on the rear and a nitto 265/35-18 93 W on the front. I measured them and about 25 inches on the front and 26 and a quarter on the rear. Websites say that the MT is a 27 inch and the nittos are 25.28 diameter tire.

I am surprised it is setting the ABS off since by the measurements they are only about 1.25 inches off. I like the look and want a wide meaty tire but I need my ABS to work at all speeds so I want to know what everyone else is running.

I looked at some NT05 for the rear and wondered if the 295/35 18's. Nitto says the diameter is 26.18 which brings me to less than an inch. I am gonna need some good wide sticky tires for the rear as I will be seriously upgrading power level sin the next year or two.

so what combos do you run?

 

[mwolson]

If you are willing to use two Dallas Mustang Speedcals to adjust the ABS signal frequencies for two of your wheels, I can figure out the Speedcal settings you will need to set to make it work.

No one has done this yet, so you could provide some very helpful research for the Mustang community. But I am highly confident this will work since the ABS sensors and the VSS/OSS sensors all work the same way.

What do you think? Want to try it?

 

[PSUCOBRA96]

If you are willing to use two Dallas Mustang Speedcals to adjust the ABS signal frequencies for two of your wheels, I can figure out the Speedcal settings you will need to set to make it work.

No one has done this yet, so you could provide some very helpful research for the Mustang community. But I am highly confident this will work since the ABS sensors and the VSS/OSS sensors all work the same way.

What do you think? Want to try it?

lol that would give me a total of three speedcals in the car, maybe if they were not so expensive I would give it a try. I still have to buy 500-600 in rear tires so I think I need to just find the right size lol. thanks for the offer to help Mark:rockon: In fact I still haven't even installed the first speed cal since my new rear hasn't been put it.

 

[DVJ38]

1.25 inches is a lot to be off, I'm not surprised you're getting a light.

 

[PSUCOBRA96]

1.25 inches is a lot to be off, I'm not surprised you're getting a light.

so whats an acceptable difference, i know people are running larger diameter tires in the rear, just what is the max

 

[mwolson]

Per 1010tires.com, your 305s have a tire revs per mile of 787.8. Your 265s have 822.1 tire revs per mile. The 265s are 4.4% bigger than the 305s. 1010tires.com recommends you stay within 3% or you are risking brake failure (I assume they mean ABS.)

 

[Shifty Powers]

Ive had larger tires on my car and just recently the ABS light has come on as well.. But all the time. Not sure if this is the reason. But something ill have to look into

 

[PSUCOBRA96]

Per 1010tires.com, your 305s have a tire revs per mile of 787.8. Your 265s have 822.1 tire revs per mile. The 265s are 4.4% bigger than the 305s. 1010tires.com recommends you stay within 3% or you are risking brake failure (I assume they mean ABS.)

thanks Mark, I will go on that website and play around with tire combos to get into the 3% mark

 

[PSUCOBRA96]

oh yeah anyone got any tire size combos they can share with me that is not setting off your ABS?

 

[98$vt]

I have 275/40zr17s up front with 315/35r17 in back and I get no light

 

[98$vt]

BFg g force in front and nitto 555r in back

 

[PSUCOBRA96]

BFg g force in front and nitto 555r in back

what are the sizes?


In all honesty I should have purchased a 40 tire instead of the 35 and I likely would not have had the issue.

 

[98$vt]

I have 275/40zr17s up front with 315/35r17 in back and I get no light

One up

 

[Blown_By_You]

pull the fuse

 

[Ryan2KRedL]

I just had this exact problem on my 95GT.

I had swapped on a set of saleen wheels (18-9" front and rear) and the rears had M/T 305-35-18 drag radials.
My ABS light came on just like yours.
I put a set of Nitto 285-35-18 tires on it (555 ZR type) and no more issues.

Good luck!
Ryan

Pic of car with M/T (first pic) and Nittos (2nd pic).

 

[Blown_By_You]

This thread just made me realize that I deleted my Abs years ago lol

Sent from my ADR6400L using Tapatalk 2

 

[P49Y-CY]

pull the fuse

This thread just made me realize that I deleted my Abs years ago lol

lol i was going to tell him that too, but his first post says that he wants to make sure it works. i have one of those beuatiful prb-machining manifolds ready to go on mine.

thanks for that tire site mwolson!

 

[mwolson]

thanks for that tire site mwolson!

I really like that tire site because their tire revs per mile calculator compensates for the tire deformation that comes from the weight of the car. Most other sites just use the unloaded tire radius, so the tire revs per mile come out too low and don't match the real world. Not that it's a huge deal, but I am a perfectionist.

Because of this thread, I learned that our ABS rings have 50 teeth.

With your 305 tires (787.8 revs per mile), at 60MPH, you get 787.8 revs per minute. Multiply that by 50 and you get 39390 ABS pulses per minute. Divide that by 60, you get and ABS tone of 656.5Hz.

Comparing that with your 265 tires (822.1 revs per mile), at 60MPH, you get 822.1 revs per minute. Multiply that by 50 and you get 41105 ABS pulses per minute. Divide that by 60 and you get an ABS tone of 685Hz.

Since the ABS compares the ABS tone from each of the wheels to look for a difference in tone with one or more wheels, it assumes your 305s are skidding a bit and will modulate those calipers a bit. But since the ABS tones are always different, the ABS system is smart enough to know that there is something wrong, so it throws a code and probably disables ABS.

Since a Speedcal does frequency shifting for VSS/OSS sensors and those sensors are the same as ABS sensors, I can't see why two speedcals couldn't be set up to compensate for the differences in ABS tones.

I have been trying to get someone with bigs & littles to try the Speedcal fix to re-enable ABS for them, but so far no takers.

Interesting topic...

 

[PSUCOBRA96]

Ford must have a percentage they are allowed to be off, since not all tires are perfect and sometimes people mismatch old and new.

 

[alexandros]

Anyone know the maximum percentages of tire sizing?