Help RPO Codes

[Bob Wurtak]

I bought my 95 4 years ago and its been a "Blast", but I'd like to get some info on 3 RPO codes. I don't have the build sheets or the window sticker. There's also some odd ball things with tires and rims which don't match the RPO codes that are on the door and inside the rear storage compartment.

I believe the tires are original to yhe car as the car has 26000 miles on it and the tires are Goodyear Eagle GS-C's and they look like tires with that much wear.

The rear tires are correct size at P285/40 ZR17's and that's what the RPO states. The front tires are P275/40 ZR17's and the RPO code states P255/45 ZR17's causing the car to be hard to steer in rutty roads which is all we got in Canada.

The rims are 95 ZR1 rims or look alikes but are Frt 17 X8.5 and rear 17X 9.5
painted 5 spoke aluminum.

The car has option J55 which is the heavy duty brakes 13" up front and 12'" in the rear and RPO G44 rear axle 3.07 ratio and RPO G92 Rear Axle Performance Ratio and FE1 which the soft ride suspension system.

It almost looks like there were putting together a Z07 package piece meal.

The RPO codes in question are:
R6Z which states control sales item 25
R7K which states special option processing
1SB which states market option package 2

Anyone got any ideas as to what these codes are and whether these ZR1 rims were a factory option?

 

[rrubel]

Huh. My RPO book has none of those three...

It sounds like you've got the wheels off the Pace Car option (Z4Z, 1995 convert. only), which were ZR-1 style but the fronts were 275/40 size (ZR-1 used 315-sized tires).
[RICHR]

 

[FX GS]

R7K: am/fm stereo radio w/single cd

1SB: Pkg Opt 02, Pref Equip Group 1 (coupe)

R6Z: ?

 

[Tuna]

I can help with the RPO codes but I do have a comment or 2 about the wheels.

In 95, only the ZR1 and the Pace Car had the 5-spoke wheels. On the ZR1, they were 9.5 inch wide in the front and 11 inch wide in the rear. On the Pace Car, they were 8.5 and 9.5 f/r. All other 95's can with the 'sawblade' wheels. The Z07 equipped coupes came with 9.5 wheels all around while the base and FX3 cars got 8.5/9.5 combo.

With the 8.5/9.5 combo, the tires should have been 255/45 front and 285/40 rear as you noted. (the Z07 cars got 275/40's all around) You also noted that the 275's provide you with a lot more wander and rut following - one of the reasons GM switched to skinner tires on the front.

I did some checking in the past about recommended wheel width for the 275 tire and I could not find any tire company recommendation less than 9.0 for that size. If you really want to run the 275 or 285 tire, I'd recommend getting the correct 9.5" wheel for them.

I've seem many a Vette that the owner has installed the 275 or 285 tire on the 8.5 front wheels, thinking that was a good idea. (rotate them, or whatever). Sometimes I see one of the skinny wheels on the rear with a wider tire mounted on it and one of the wider wheels moved to the front. This causes more confusion than it helps with better stability. Maybe this is just one of the reasons C5's and C6's have different size wheels front and rear - to keep owners from mixing and matching tires and wheels in all the wrong combinations.

If you really have 2-8.5 wheels and 2-9.5 wheels, I'd recommend going with the original 255/45 tire on the 8.5 wheels on the front and keep the 285/40 on the 9.5 on the rear. This will cut down on the wander and rut following you are experiencing. Another way to minimize this is to increase the toe-in on the front - at the expense of tire wear.

I hope this helps.

 

[Bob Wurtak]

Tuna: Thanks for the reply on the tires and rims. Do you have any info on the RPO codes. I measured the top part of the rims and both are 10 inches which leads me to believe they are 9.5 inches inside. Does this sound correct ? Thanks Bob

 

[Randy Eads]

"I believe the tires are original to yhe car as the car has 26000 miles on it and the tires are Goodyear Eagle GS-C's and they look like tires with that much wear."

Check your tires and look for a D.O.T code date of manufactuer .... the numbers would equate to the week of the year and the year the tires were made ..... i.e 1294 would be the twelvth week (end of april) l994.

... at least I think I got that right ... the mind is the first thing to go!!

 

[Ken]

R6Z - I can't find it either.

 

[Tuna]

Tuna: Thanks for the reply on the tires and rims. Do you have any info on the RPO codes. I measured the top part of the rims and both are 10 inches which leads me to believe they are 9.5 inches inside. Does this sound correct ? Thanks Bob

No, nothing on the RPO codes. I even looked through my service manuals and didn't find anything there for R6Z or R7K.

The wheels should be marked on the back with their size and offset - usually on the inside of one of the spokes for factory GM wheels. Put it up on a lift and get a flash light and see what's there - or pull the wheels one at a time. The factory 9.5" wheel would show 17x9.5x56mm.

Last thoughts on different size tires: If you have 9.5 wheels all around, I would recommend running the same tire all around also. The traction control and anti-lock brakes are calibrated to look for that - same size equates to same RPM at the same speed. If the tires are very different in diameter, the ABS/ASR computer may not know how to handle that. The 285 is slight larger in diameter than the 275 - not much but different and may we well within the computers acceptable range. The 255/45 and the 285/40 are supposed to be the same diameter.

Later,