[cwebster]

Well, I guess I'll have to answer my own questions. There's not much that's more disappointing than to find a post that exactly matches my problem but leaves the questions unanswered. This is for future drivers looking for answers...

I nixed the Weld Tech wheels because I couldn't get sizes to match my needs (18"x12", 43mm offset w/high pad height). In fact, I could find no US supplier with wheels this size. If I'm going to spend this kind of money I don't want to compromise my standards. I ended up gettIng BC Forged RS40-14 18"x12" monoblock wheels with 43mm offset and high pad clearance and Mickey Thompson ET Street S/S P345/35R18 drag radials. See this post for details: 11's on Street Rubber (post #43)

Answers to Questions:

Originally Posted by cwebster

Question: At first I chose (7.7 / 43) backspace/offset because it matches the stock rims. Now I'm thinking I should go with the (7.6 / 41) option to get the "high" pad height. Reducing the backspace/offset numbers on these 11" rims vs 12" should offer further clearance from the outside edge of the fender well, and inboard components, right?

If I were going with 11" wide rims the 41mm offset option would work best for the reasons noted above.

Originally Posted by cwebster

Question: I'm a little leery of the "medium" pad height option with these big Brembo 4-piston rear calipers. Anyone know how this compares to Chevy's stock, forged aluminum rims? According to my measurements, I'd still have 1/4" clearance with 18" rims of construction similar to stock. Construction of these is unlikely to be similar to stock rims, though. Going from 20" to 18" doesn't give me much calliper room to play with.

They show the following other backspace/offset options.

BS  / Offset
in    mm
7.6 / 41
6.7 / 18
7.7 / 43
8.2 / 56

The "High" pad height option is only available for the 41mm offset with the 18" wheel. This would probably work and only adds 0.1" to backspace of stock wheels.

The "Pad height" option seems to be an undefined relative term, specific to each manufacturer. I could find nothing to specifically define this term as it relates to the inside diameter of the wheels. So, I sought to get the most clearance available, just to be on the safe side.

Regarding the "ET Street R":

Originally Posted by cwebster

Question: Is this a (flexing sidewall) slick or a (stiffer side-wall) DR? I have trouble making the distinction, what with all the tire options available.

No one could seem to answer this question. I've come to believe that sidewall flexibility of radial drag racing tires, whether slicks or not, is a function of the height of the sidewall. The taller the sidewall, the more flexible it will be off the launch. I believe that the so-call wrinkle-wall slicks are only available with the smaller 15" rim / over 30" tall drag tires like MT ET Drag and Pro Drag Radials. I'll never be able to get these for 18" rims with the minimal height clearance of the stock ZL1 wheel wells.

Originally Posted by cwebster

Question:

Tire Pressure Monitoring System (TPMS): Where's the best place to buy TPMS sensors for my new rims that are compatible with the 6th Gen ZL1's system? How often do batteries need replacement?

TireRack.com shows this sensor available for $80 ea. when you plug in the year, make, model info but I could not independently verify whether it is compatible. To be sure, I just ordered from my dealer's parts department and had it shipped to the shop putting my wheels together. The Chevy parts desk was about the same price anyway. I would hate to find out it didn't work after the mount and balance were complete.

433MHz Tire Pressure Sensor

I still don't know how long the batteries last. Hopefully, at least until the tires wear out.

Originally Posted by cwebster

Question: All wheel options and most references for (5th Gen) Camaros cite 5x4.75 lug spacing. I could not find authoritative lug spacing specs for the 6th Gen ZL1. What is the "4.75" measuring and what numbering system is it using? I measured from center of one lug nut to center of the next to come up with 2 13/16".

Turns out this lug spacing measurement is the diameter of the imaginary circle that goes through the center of each mount stud. I measured the radius from the center of the wheel to the center of any stud to get 2 3/8". Multipy that by 2 to get the diameter of 4 3/4" or 4.75". Hence 5x4.75 = 5 lugs evenly spaced and centerd on a 4.75" dia. circle.

I'll be updating the original post with photos from my most recent wheel swap so you can see how much clearance there really is. If not for the proximity of the fabric wheel well liner in the front inboard corner, I could have even gone with 13" wide tires and rims. There is only about 1" clearance on this corner with the stock 12" wide F1 G3 tires. Any tire taller than about 28 1/2" or wider than 12" risks rubbing on that corner.

Let me know if any of this is unclear or there are still unanswered questions.

--Cal