Daveboy120

I have a basically stock 2005 corvette. When I exceed speeds of 60 mph my car says "traction control active" on the DIC. It doesn't allow more throttle input. It acts as if I'm loosing traction. I've been just putting the car into competitive mode every time I get in the car to avoid this. But I wonder why this is happening? I know I'm running a different rear tire than stock. 295/30/r19.
But is that enough of a difference to cause this?

sevinn

Some cars seem to have less tolerance for front to rear tire size than others. My bet is that the short rear tire is doing it.

What's on the front?

el es tu

Yes its very likely the tires are the cause.

IIRC There is supposed to be a 3% window for differences in front to rear ratio. Your shorter tires are spinning faster than the originals (in comparison to the fronts).

btw if you hold the button for tc/ah down a bit longer you can just run the car with everything off instead of comp mode which still allows some active handling

madmatt9471

Just have your tuner set the new tire height in the PCM and you'll be fine - it will correct the perimeters and everything will be set.

Thanks,Matt

sevinn

Sorry but the tune won't actually affect the ah/tc stuff since that's in the BCM. All the tune adjusts are the speedo and shift points on an auto.

madmatt9471

Sevinn,
Did you actually follow the post or are you just responding to what I wrote?

If indeed the tire size is different, smaller or larger in diameter and is activating the A/H Traction control system and the stock tire size diameter was not - and throwing the other perimeters off (speedometer etc.)

Then a Tuner or if the OP has HP Tuners he can go in the PCM and set the "NEW" tire size and all the perimeters will he back to as if it were the stock tire size/height again and this stop setting off the TCS.

If I had my HPTUNERS with me here I could open it and take a picture of the tables for you.Not tuning the BCM, you can also change gear ratios as an example which would cause the same problem if it was not changed in the tables when gears were changed.

I hope this helps clarify any confusion you might of had to my answer.

OP you can take your Vette and have a tuner adjust the tire height in the tunable table to the new height.

Thanks,Matt

sevinn

Yes, I was responding to you and following the post.

I'm well aware that you can change the tire size in hptuners. All you are changing is speedo calc and transmission parameters:


What I was trying to say, and hopefully this clears up YOUR confusion, is that the active handling and traction control systems cannot be touched by tuning software. You can change the tire size all you want in HP Tuners or EFI Live and all it will do is affect the speedometer and the transmission shift points. The bcm keeps track of the individual wheel speed sensor inputs and determines if the tires are spinning or not, not the PCM which is all that HPT can touch.

The speedometer can be wildly off all you want and the traction control and active handling systems wouldn't have any clue.

The tune will not fix this issue.

madmatt9471

Try it and see what happens. You'll understand then.

Thanks, Matt

sevinn

I'm not sure I follow, this is something that has been well known on these boards for years, just do a search.

For the record, even after properly scaling my car with hpt for my 26" drag radials I have this issue on the highway with my street tires on the front...

Unreal

Sevinn is correct. Change the tire size in HP tuners does not fix this, as it is a BCM function.

Gearhead Jim

So is there any way to program TC/AH for non-stock front/rear wheel relationships?
I seem to recall some people being pretty far out but still able to make it work.

Unreal

Nope. You can remove the BCM/ecu/etc if you want to go all out race car.

Dano523

Yep, its a problem in the scaling of the front tire to rear tire size, so the BCM is reading all the tires covering the same amount of ground at the same time as the car is moving.

So given rule of thumb is that the rear tires need to be 1.04" larger in OD, than the front tires. Break this run, and the BCM sees either the front tires cover more or less ground that they should for the back tires isntead.

Even if you use HP tuner to re-scale the rear tires to get the MPH correct, your still have a problem with breaking the 1.04" difference in OD sizes front to back that the wheel speed sensor for all 4 tires is sending back, and this is what is causing your problems in the first place.

As for a program that can re-scale for tires way off the 1.04" rule front to back OD sizes, not sure anyone has come out with such yet.

madmatt9471

I do apologize - I did not realize that his tire size was that far out of sequence in size - the over 1" programmed rule -

Question then:

Could the OP get smaller front tires to compensate, in order to put in back within the perimeters?

Thanks,Matt

sevinn

Yeah

If OP gets something close to 25" it will probably be fine. Something like 255/35/18 and it would be perfect

irok

are you using TPMS's on the rear?I run 295x45x17 MT with sensors and never an issue with AH/TC as long as air pressure not below 25 lbs.I set my sensors in the pvc tube at 30 lbs but actual 15 lbs in tire

sevinn

I'm not running TPMS in my rear drag setup, but this happens as soon as I leave my driveway (I live on a 55mph road), and the tpms usually don't complain for 10-15 mins.

Your tires are also closer to spec than mine, and its weird that some people have this issue when others don't with the size I'm using.

I appreciate the advice though, I've been meaning to build a tpms tube so I can drive farther without a Christmas tree on the dash.

irok

I would bet money your problem will go away as soon as you install TPMS's and pressure reading 25+lbs.cheap fix $25.

sevinn

It takes the car a long time before it even notices the tpms are missing. Maybe one day I'll find out, but there are so many folks with this issue that I doubt it. Doesn't bother me anyway since I don't drive on the street with my DRs anymore anyway since I moved farther away from the track unless I'm making a test hit somewhere.

I just bought some front runners too so I gotta figure out how to fit them in there too




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Dano523

Lack of TPMS, and wheel sensors not reading correct so the car sees all 4 tires covering the same amount of ground is two different problems.

When the car reads a TPMS problem, most of the time it will not allow you kick the nannies out via holding the TC button for 5 seconds.

In the wheel sensor problem with the front to back tire OD sized too far off, you can turn the nannies off to semi solve the problem instead. I stated semi, since with the nannies off, your all on your own, and if the car gets sideways, there is nothing the car is going to do to save you isntead.

Note, with Tc and Ah off turned off, ABS is still active at all times!!!!!