ZO6 Speedo adjustments w/taller tires?

[Redline MS]

I recently installed a set of 345's on my Z06. Every since the install the Engine Drag Control system becomes active on hard decel. I think the taller size tires is putting the rear wheel speed sensors on the edge of telling the PCM that the tires are about to break loose.

I tried making some adjustments in the speedo tab with no luck and think I did something wrong.If I just enter the new tire size height and hit commit.....should that be it? The first time I enter the current rear gear which was wrong as the value needs to be 1. The problem I was getting after playing with it was the speedo was off big time.

Can someone please confirm how to do this?

Thanks

[Russ K]

First, enter the new tire height. Then enter your gear ratio, you still need to enter 3.42 even though your gear ratio is still stock. Now hit the commit button and save the file.

Russ Kemp

[EC_Tune]

The Z06 uses Revolutions per Mile. Just do a roll out of the tire (mark ground & tire, rotate one or two revs: your pick : and measure the distance in inches) take a mile (63360") / roll out (inches for 1 revolution) and you have turns per mile. Drop that into the speedo calculation and you should be good to go.

EC

[Redline MS]

EC,

Can't I just use the information off of Michelins site for tire height and do they math? Regarding the gear ratio; I think I tried entering the 3.42 gear in the gear box and it threw the speedo off big time.

Finally I am assuming my issue with the EDC is from this as I don't really remember this happening until after the 345's where installed. It would be interesting as well to see if my "slight surge" I have been having may be tied into this as well since I don't really remember that either until after the wheels and tires where installed.....

[kabbott]

Tire calc will only get you close,roll and measure much more accurate.
Make sure tire pressure is what you want first as that will affect radius to.

[Redline MS]

Yeah I'll do that I guess. Seems crude but effective!

I am still questioning the gear ratio change. I think it needs to be expressed as a value of 1.

Which parameter I am making the change in?

It asks for REV, MILE, and DIST. Once I figure the rollout distance then what?

[kabbott]

Okay i pulled up a corvette file and it looks like gear ratio is set to 1.00 so if all you have changed is tire size then use 1.00 for gear ratio.
After you measure tire circumference divide by 3.14 to get dia. and type that in tire size.Hit commit.
REV should be same(pulses per revolution)
MILE should change (pulses per mile)
DIST should change(tire revolutions per mile)
Ratio should stay the same(1.00)

[Redline MS]

Thanks for the clarification. Last time I entered the gear again the speedo was reading 20 mph vs the real speed of close to 80!

I'll try this.

Thanks

[Redline MS]

I just checked the roll out of one revolution of the tire. Its 84.375". Now what ?????

Howard

[Russ K]

Divide by 3.1416 = 26.86 dia. Now enter that into the new tire size box. You still have to enter 3.42 into the new gear ratio box. Then hit the commit button. I'm looking at my 2001 ZO6 file and it shows the tire height as 25.21 even though a 295/35/18 tire is listed as 26.1 using the tire size calculator.

Russ Kemp

[Russ K]

Also, compare your latest speedo settings to stock. the only thing you want changed is the tire dia.

Russ Kemp

[Russ K]

Just checked the Tire Rack site, and a 345/30/18 tire is 26.2". So this is how your tables should look.

Russ Kemp

[Redline MS]

Russ,

My screen shot is not the same as yours. I don;t have a rev per mile tab......

Also the stock ZO6 file indicates a gear ratio of 1. When I changed it to 3.42's it really screwed up the speedo. I think the problem here is the available parameters for the LS7 differ from the LS2.

I am still not sure what the other parameters are doing. See the attached screen shot.........if it came out!

[Russ K]

Just found out that you have 2006 ZO6! I've been using my 2001 ZO6 speedo table. Try this one, I set it up for your tires.

Russ Kemp

[Redline MS]

Russ,

Sorry for not being clearer! Yes its an 06 ZO6.

The roll out I measured was as noted above. It equates to a 26.871" diameter. I just checked the Tire Rack site as well as the tire is a 345/35/19 and according to there numbers is 27.4" tall. It also noted that the Revs per mile are 757.

I would be if this gets rid of the EDC on hard decel!

Now its raining so I guess I'll screw with it in the next day. How come the gear is entered as a value of 1 and not by a value as 3.42?

Thanks

Howard

[Russ K]

A 345/35/19 tire is ~.7 taller than stock. With out installing taller front tires, I think you will have problems with the ABS and traction control.
Anyway just input your new tire height and the 1.00 for the gear ratio. On my 2001 ZO6 the gear ratio is 3.42. On the Corvette's, the speed sensor is read from the diff. not the trans output shaft like the F-Body cars. Don't know why GM changed this.

Russ Kemp

[Redline MS]

I have the same size as stock front and I am positive that the rear change, as small as it might be, is effecting the car.

Still wondering why they use a value of 1 as the gear ratio. You would think the 3.42 is the default gear....

[EC_Tune]

Manual transmission... The trans doesn't need to know gear ratio only tire size for speedo calibration.

Corvettes with a *manual* never need gear ratio changes entered in them as they are a transaxle and the speed is picked up from the ring gear area not the output of the driveshaft itself like a standard longitudinal transmission.

With your rollout you take:
Inches per mile / roll out = Tire revs per mile
63360/84.375 = 750.933" Tire revs/mile

[Redline MS]

Manual transmission... The trans doesn't need to know gear ratio only tire size for speedo calibration.

Corvettes with a *manual* never need gear ratio changes entered in them as they are a transaxle and the speed is picked up from the ring gear area not the output of the driveshaft itself like a standard longitudinal transmission.

With your rollout you take:
Inches per mile / roll out = Tire revs per mile
63360/84.375 = 750.933" Tire revs/mile

EC,

I am well aware about the transaxle (which picks the speedo off of axle speed) vs. the F-bodies which pull of driveshaft speed. I was just wondering why the value is 1 but this makes sense.

As far as the 750.993 revs/mile....I don't see which one of the speedo parameters allows that entry.

Howard

[EC_Tune]

Fill in these areas and your good to go.
Or just use 26.85 with Gear ratio of 1
Comes out very close...
EC