85 Wheel/Tire Question

[robdunn1]

Hi All,

I have to go order tires today and really need some advice from experienced 85-87 Owners before spending $1300-1400 on tires.

I just bought a 1985 C4 from a friend of mine (same car I posted questions about a month ago but now it's mine!). I am picking it up next weekend and driving it 1400 mi crosscounty back to my house. Car has been well maintained and was a daily driver before being garage stored for the past 9 years but had all fluids replaced about 4 years ago and was started and run through the gears periodically. Problem is it has a set of Gatorbacks that need to be replaced (very good tread but has sat in on position for a very long time plus the asymetric wear pattern has set in and they are very rough/noisy). I would like to put Michelin Pilot Sport A/S tires on it. To do that I need to move to 17" wheels (no 255/50ZR16 available in this tire). I am buying a set of 91 C4 Wheels (silver painted sawblades) and need advice.

1. Will the 50mm offset 91 sawblades work without spacers on the 85 Corvette (38mm offset)?.

2. In case, I bought 8mm and 12mm spacers. Do I need longer studs for these thickness spacers?

3. I want to preserve the speedometer calibration and suspension design. Means I need a 26" diameter tire, right? Should I use 245/45ZR17, 255/45ZR17, 275/40ZR17, or 28540ZR17 size tires? Seems like the wider I go the greater the fit problem will be but I have no experience in this area.

4. The 91 Wheels don't have center caps. Any idea what centercaps will fit? Are these interchangable with ZR-1 or Z06 wheel caps or orther generic caps. For now I am not picky, just want caps so I can drive cross country without holes.

5. What preventative maintenance would you recommend besides the tire swap? (Asked this question before but am always interested in other's insight and opinions. Was told I should through an alternator in the back)

Need to order the tires today to have them in place next weekend when I to pick up the car and get it ready to hit the road. Thanks for the help!

Rob

 

[ErnieN85]

Spacers? well it's best to get the right ofset. but you can use them for a while longer studs would be the way to go as you need alteast the threads going through the full depth of the nut when seated.

as to size 275 40 17 matched almoost perfect so no spedo errors!
Seriously I'd look into a set of wheels with the correct offset
they are available
Tire rack has BBS in 18" and a matching size of tire also
285 35 18 i believe

 

[ErnieN85]

checks before a road trip. radiator for debris, belts for bad cracks, coolant hoses stiff or split,
battery connections, (clean them and put back on) all fluid levels and a couple of times on the way as a seal can go bad after sitting!
Good luck

 

[robdunn1]

Thans for the information about wheels. I plan to buy better wheels in the near future but since I need to buy tires now and get the car back to California this was the solution to getting the car back where I can work on it. I was hoping to use the 275/40ZR17's so thanks for confirming that that is a good match.

The car had a AC/Delco water pump put in shortly before it was stored by my friend and at that time he pulled the radiator and had it cleaned so debris have been cleared (he said that there wasn't anything there but it had been cleaned). Coolant is crystal clear and conventional green 50/50. He has maintained battery charge on a commercial grade trickle charger and posts are clean. Fluids are good but I plan to swap for new redline oil/tranmission fluild/differential lube. He previously used redline but last changeout of all fluids about 3.5 yrs ago was by the Chevy Dealer and he doesn't remember whether he specified synthetics. Car hasn't been driven any distance at all since the fluids where swapped. Also plan to do spark plug/wire changeout since he hadn't done that recently and car is at 110k miles. Understand that pulling plugs can be a real challenge on this car.

Thanks again for the advice.

 

[rrubel]

Mad Mic has a similar set of wheels on his 87 without spacers; they rub occasionally during aggressive driving (but he also has wider rear tires than you'd need). If you want to do it right, though, buy the spacers made for this conversion. Corvette Central sells some for about $200/set. They have new studs already mounted, and come with an extra set of nuts so all you do is bolt them on, then bolt the wheels atop them. I've got a set and love them.

As for tire size, are they all four 9.5" wide, or are two 8.5" wide? For the 9.5's, use 275/40 and for 8.5's use 255/45 tires. That's what I was told to use, and that works best. After upgrading from 16's on my 86 to 17's with this size, I took my GPS and checked the speedometer. Dead on. 60 on the GPS was 60 indicated.

I've forgotten - do the 91 wheels have small or large center caps (do the caps hide the lugnuts?). If they have the small caps, you can use any from 86-96 except for 88-90 with the large ones...

As for other maintenance, make sure the distributor cap and rotor are clean inside (no rust/oxidation on the contacts). Keep an extra couple quarts of oil in the car because you'll probably be leaking some through seals that dried out somewhat from disuse.

Pulling plugs isn't that bad; #8 is tough (passenger rear) but the rest aren't a huge problem with a universal joint in your toolbox...

Good luck, and drive safely... if the car has sat as long as you say it has, I would avoid high speed or hard acceleration until a really good mechanic has checked it over...
[RICHR]

 

[robdunn1]

Rich,

Thanks for the all the information. With regard to wheels and tire fit, the wheels I bought are all 9.5" (wanted to stay consistent the 9.5" all around width that came with my Z51 package) so will go ahead with ordering the 275/40ZR17's Michelin Pilot Sport A/S from Costco. I really like Costco's tire shop. I have always had first rate service; no quibbling, beyond my expectation service on replacements for road hazard/tread wear; and finally the one price includes all (installation, lifetime balance/rotation,road hazard, etc) really appeals to me.

I will probably just replace cap/rotor and go over hoses real well. Plan to carry hoses, belts, lubricants and coolant (driving from Fort Worth, TX to Southern California so will be hot). Also will load steel wire, epoxy, duct tape, and inner tube since my college years in the grain elevators taught me that you could improvise a lot with these few items. Already have the Helm's Shop manual that came with it in read and stored in the back along with reasonable toolset for the road and a good meter.

Thanks again,

Rob

 

[c4cruiser]

If the wheels you are buying are OEM Corvette wheels, you should get a set of adapters not spacers. Adapters have their own studs and come with a set of lugnuts that are used to bolt the adapters to the spindle. You bolt the wheel to the adapter studs using the OEM lugnuts (or aftermarket ones. OEM wheels have a recess on the mounting face that allows the lugnuts for the adapters to clear the flange. Adapters are expensive (close to $250 or so) but they will mount the wheel properly and provide a strong mounting surface.

Spacers move the wheel outboard on the original studs so there is effectively more stress on the stud at its end. Not a good thing in a hairpin turn at speed....

Just out of curiosity, are you going to have Costco do the mounting and putting the wheels on the car? The last time I was in the local Costco tire shop, I was looking at a larger tire for my 99 Silverado and the manager refused to mount the bigger tire on my truck. I could buy them outright and take them elsewhere for mounting, but they refused to mount any tire/wheel that was different from the OEM standard or optional wheel and/or tire size. You may want to ask them first before buying the tires if you are getting them mounted on the car in the shop.

 

[robdunn1]

Thanks for the information about the adapters and the Costco caution. I will call the Costco I was going to use in Ft Worth and ask them. That would be a real bummer if they won't mount them. If they won't does anyone know a good tire shop in Fort Worth? A major reason for using Costco is that they are in Ft Worth to get the tires put on and they are here in my local area to service them when I get back. BTW the wheels are stock 91 GM sawblades .

Rob

 

[rrubel]

Just as clarification, what I called spacers from Corvette Central actually are the adapters that c4cruiser talks about...

Their current catalog shows them for $229 a set.

Regarding the Costco issue, I wouldn't think they'd have a problem since he's getting the proper size tire for that wheel and that is a standard wheel - just from a different year. He's doing what's called a plus-1, and all our local tire shops even advertise plus-0, plus-1, and plus-2 packages for various cars.
[RICHR]

 

[robdunn1]

Thanks Rich,

I did call the Costco tire shop in Fort Worth, TX where I will be picking up the tires and the manager I had talked to before was out until Monday but the gentleman that helped me said basically the same thing but I should confirm it with the manager on Monday. Looks like the wheels can be shipped there and the tires mounted then I drive over and get them put on. Should work out well.

Thanks for the advice,

Rob