Question for c4c5specialist regarding tires

[cavettefan]

How sensitive is the Active Handling on the C5 regarding different tires? For example, the Goodyear Eagle F1 tires on the Z06 have a specification of 824 revolutions per mile for the front (265/40-17) and 801 revolutions per mile for rear (295/35-18). Another tire brand that I am considering has a specification of 819 revolutions per mile (same 265/40-17 tire size rating) for the front and 793 revolutions per mile (also, same 295/35-18 tire size rating) for the rear. I was considering the Goodyears; however, when I saw the specification regarding performance in the wet, I was underwhelmed. If the Active Handling is too sensitive to the lower revolutions per mile of the alternative that I am considering, I may have to re-think switching from the Goodyears. Lastly, to add further complexity, what impact will the tires have on speedometer and odometer accuracy? Can the odometer and speedometer be adjusted to account for the different revolutions per mile?

 

[c4c5specialist]

HI there,
While there has been numerous debates on this particular issue on c5, the following is fact.
First, you can mount the upsized tires on your car. Second, they will work. Third, the speedometer will not be overly affected by this change.
HOWEVER, Active handling is the concern because this system relys on rolling frequency of the tires, just as you have noted in your post. You can use these tires, and they will work without causing any adverse effects to the traction control.
The system will simply not be optimized for an active handling system event, as if the stock tire size were used.
Rolling frequency is critical as to how and why the active handling works. Your sizes are basically ZO6 that you would be using.
Usually, if a customer wants to do this, and they really use the A/H feature alot, I simply explain to them that the EBTCM computer which controls all ABS and Active handling functions,will have to be replaced. Then programmed with the ZO6 tire sizing.
If you are just cruising, the chances of your changing tire sizing creating a problem are very slim.
Safety is not something that should be chanced, and this is why optimizing the high quality system such as Active Handling, should always be considered.
Allthebest, c4c5

 

[cavettefan]

c4c5specialist, thank you for your post. Some follow-up questions: You refer to replacement of the EBTCM computer followed by re-programming. Is the original EBTCM computer that is installed at the factory not capable of being re-programmed? Second, if replacement and re-programming is required, can the exact tire specification be programmed in? Or, is programming limited to selection of pre-defined defaults such as the original Z06 tires? Third, if replacement of the EBTCM computer is required, can the programming be revised later? (I am considering using the original wheels for rain tires so that I can drive the car in the winter as well - it only gets rainy in the part of northern California where I live.) Last, is a special tool required for the re-programming and is the tool available through the dealers parts department?

As you note in your post, safety is not something to be trifled with. I am very much a believer in not screwing up the safety systems. If it is not possible to "dial-in" the EBTCM computer for the alternative tire that I am considering, then in all likelyhood, I will be passing on the alternative tire.

 

[bluecoupe]

Good question! I rely on A/H to help keep me out of the trees.
I am also very interested in this post.

Here is some light reading while you are waiting for C4C5's reply.

http://service.gm.com/gmtechlink/arcv_pdf/2_00_e.pdf


http://www.babcox.com/editorial/bf/bf20136.htm

 

[c4c5specialist]

Hi there,
The calibrations for the EBTCM are VIN specific, so while updating calibrations is common, you cannot change the VIN that is within the module.
This is where the replacement comes in.
As for the programming, there is only one, TECH2 that can do this.
In my dealership, there is only 2 tire sizes that I mount, standard coupe and convertible, and ZO6.
Because I cannot optimize the AH for any other size, I do NOT mount them in my dealership, on c5.
Allthebest, c4c5

 

[bluecoupe]

I'm guessing that means as long as the outer diameter of the tires is the same as a stock tires it should work fine. Do you know the outer diameter messurment of the C5 and Z06 tires? Does lowering the car affect the A/H too?

 

[cavettefan]

c4c5specialist and bluecoupe, thank you for your respective posts. The posts were very informative. However, some additional questions occur:

1. Based on the GM Techlink post by bluecoupe, it would appear that a tire chart is maintained in the PCM which contain both standard and factory optional tire data. Is this the circumstance for the C5? Also, it would appear that the data contained in the PCM would control the powertrain interaction with the tires, so there would seem to be a requirement to match the PCM to the tire size as well. Is this in fact the circumstance (e.g. a need to re-program the PCM in addition to the EBTCM)?

2. It sounds as if there are likewise a selection of data points in the EBTCM for different tires (e.g. factory standard and optional tires). Is this the circumstance?

3. What is the range of optional tire settings? Are the optional tire settings expressed in revolutions per mile? Or, in tire size format (e.g. 265/40-17)? Or, some other format? (For both PCM and EBTCM.)

4. In my instance, I have been looking for a tire that could provide the performance increase in dry driving conditions of the Goodyear Eagle F1, while having better performance in the wet than the Goodyear tires. I have found such a tire; however, as I mentioned in my original post, the specifications of the alternative tire were not the same as the Goodyear tire. Is it possible to re-program the PCM and EBTCM to match the alternative tire that I have found by entering/selecting revolutions per mile (which would provide an exact match to the alternative tire) that correspond to the alternative tire?

5. It sounds like two special tools will be required for this exercise in re-programming: a.) TIS2000 PC, and b.) TECH2. Is this in fact the circumstance?

6. Since I would not be changing VINs, is there still a need to replace the EBTCM? (The EBTCM that was originally delivered with the car is the one that would be re-programmed to reflect the new tire size; the VIN before re-programming is the same as the VIN after re-programming.)

I am new to working with the PCM and EBTCM; please pardon my detailed questions. I am only attempting to get as precise as possible an understanding of what is involved so that I get everything "first-time-right". I really appreciate all of the information that has been posted.

Lastly, bluecoupe, regarding lowering affecting PCM or EBTCM, I would tend to doubt it, as lowering does not affect tire revolutions per mile. The real issue that affects Active Handling is the tire revolutions per mile. If it is possible to match the tire revolutions per mile to a tire that is programmed into the PCM and EBTCM, you will not have any degraded Active Handling performance. Which is why c4c5specialist only mounts factory original or Z06 tires, if I am correct in my understanding of everything.

 

[c4c5specialist]

Hi there,
The service technicians document that was taken from the GM service website is a generic document, and does not take into account c5 technology as far as active handling is concerned. This is for all GM vehicles, and is meant to be a refresher for GM service technicians.
The 'optional' data that is referenced here is only for trucks in the GM line, and the EBTCM is different. There is no tire sizing option in Corvette as of this writing.
The are only the 2 setting given in the programming of the Corvette, ZO6, and coupe/vert.
If you are using the same size, there will be a small difference in rolling circumference when new tires are mounted, and this is learned by the EBTCM.
No, lowered will have no affect on the active handling, we are only looking at tire rolling frequency.
Allthebest, c4c5

 

[bluecoupe]

Thanks for all the good information. Also I was able to find the outer "overall" diameter of the tires on www.tirerack.com