[cwebster]

After exhaustive research and meticulous measurements, I've narrowed the field to the following rims and tires for use at the drag strip with my 2017 ZL1. I need more rim options, though. See measurements and clearances near bottom.

There are several questions I have, related to the information I've collected. These are highlighted below with bold, red underlined heading "Question:". I'd be grateful if someone would kindly answer these.

Thank you in advance for suggestions, references, or comments.

--Cal Webster

[UPDATES 20170405]

1. A new photo illustrations have been added in "Clearances" section below.
2. The "Fitment Calculator" link and results have been updated to reflect the wheels/tires I purchased.
3. Additional cautionary notes were added after the Fitment Calculator regarding clearance for wider tread width.
4. See post #2 below for answers to questions.
5. See "11's on Street Rubber Post #43" for details on what I ended up buying.

[/UPDATES 20170405]


[Wheels]

According to my measurements and research, I'd like to get 18x12" rims to maximize tread width and sidewall height. I'd prefer to get some that look similar to the stock 20x12 rims but these are difficult to find. The rims below are from Weld Tech, a highly recommended brand by others in the Camaro6 forums. However, the widest 18's I can find are only 11". Mickey Thompson says you can use tires that are +- 1-inch difference in width but I'd prefer to get the same width and offset/backspace as the stock rims to ensure proper clearance and maximize tire options. These look nothing like the stock rims either. They cost more than I really wanted to pay too. Neither do I like having to wait a month to get them. Wheel model name below links to the Weld Tech web page. Suggestions and recommendations here would be most welcome.

Weld Tech S76B Wheels

Price:            $705.20
Make:             Weld Tech
Model:            S76B
Size:             18x11
Color:            Chrome with black painted spokes
Backspace/offset: 7.6"/41mm
Bolt pattern:     5x4.75
Pad Height:       high

Availability: 3-4 Week Lead Time

Details

WELD Racing brings its application flexible racing technology to the street
with a budget friendly 3-pc modular wheel using a unique welded assembly
process. This wheel has the classic WELD Racing look and continues the WELD
Racing tradition utilizing a forged billet center and cold forged rims. This
unique wheel offers 3 mounting pad heights to clear specific drum and multi-
piston opposed calipers.

– Center is available in black anodized
– Wheel widths from 4.5" to 18" with a wide variety of back spacings
– 15" Require shank lug nuts
– 17", 18", and 20" require conical lug nuts
– Center cap and valve stem included
– Beadlock availble on 15" and 17" RT-S Wheels. Call a WELD Dealer more info
– Made in Kansas City, USA

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?

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.


[Tires]

Mickey Thompson has a good reputation and many have recommended their tires so I've listed the tires from their web site that would fit 11" or 12" rims. Based on my clearance measurements (see "Decision Summary" and measurements below) it seems I'm limited to a max of about 28" wheel height. I'm assuming these numbers (i.e. 27X13.50R18) are for unloaded tire. Tire model names are linked to their page on the MT site.

ET STREET R - STREET LEGAL DRAG TIRE

A drag tire that can be driven on the street. ET Street R from Mickey Thompson is a D.O.T
street legal drag tire with proven race compounds and incredible traction.

    D.O.T. approved for street use
    Minimal Tread Void provides excellent tread-contact
    Available in most popular sizes
    Tubeless construction provides lead-free seal without the expense and hassle of tubes
-----------

Size            Wt     cmpnd  rim    sec    tread    O.D.     circ.   Matl #          Part #
                                     width  width    
P325/35R18
27X13.50R18     TBD    R2     11.0    0.0    0.0     TBD      TBD     90000028455     3581
P305/45R18
29X12.50R18     32     R2     10     11.8   10.7     29.0     91      90000024661     3580

I'd prefer to go with these "ET Street R" slicks because they should flex and maintain grip better. However:

The 27" high P325/35R18 tire shows 27X13.50R18 size. If I go with the Weld Tech wheel above that would seem to risk rubbing the fabric liner in the forward, inboard corner of the wheel well. There's only about 1" clearance with stock 12" tires.

The 29" high P305/45R18 tire shows 29X12.50R18 size. While the 12.50" width would very likely clear the liner in the front inboard corner, the additional 2" height would likely rub the liner's front wall. There's plenty of room (3-5") along the top and rear of the liner.

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.

ET STREET S/S - STREET TIRE FOR THE DRAG STRIP

A street tire that can be driven on the track, the ET Street S/S from Mickey Thompson is a
high performance street to strip tire with radial construction, R2 compound and more;
15- to 20-inch fitments.

    D.O.T. approved for street use
    Equivalent Tread Void as the ET Street Radial II, redistributed for improved hydroplane
resistance while providing plenty of tread contact for excellent dry traction
    Proven R2 compound, the same proven compound used on the quickest “drag radials” on the
planet provides superior traction at the strip with little or no burnout required
    Tubeless construction provides leak-free seal without the expense and hassle of tubes
-------------

Size            Wt     cmpnd  rim    sec      tread    O.D.    circ.     Matl #          Part #


P275/45R18
28X11.50R18     32     R2     9      11.3     10.0     27.8     87.3     90000028443     3484     
P305/35R18
26X12.50R18     33     R2     11     12.2     11.2     26.6     83.6     90000024570     3480     
P285/40R18
27X11.50R18     29     R2     10     11.3     10.5     26.9     84.5     90000024571     3481     
P305/40R18
28X12.50R18     33     R2     11     12.2     11.1     28.0     87.9     90000024572     3482     
P345/35R18
28X13.50R18     38     R2     12     13.5     12.4     27.8     87.3     90000024573     3483

Looks like the 28" P305/40R18 tire is my best bet for fitment within the wheel wells, given rim constraints and measurements. Its size of 28X12.50R18 seems like it would leave 1/2" clearance in the front inboard corner and front wall of the liner while offering another 1" height to allow for more sidewall flexing.


[Decision Summary]

Minimum Rim Diameter: 18 inches

A 2-inch reduction in rim diameter would bring the inside circumference 1" closer to the caliper, leaving 1/4" clearance - assuming similar construction to stock rims.

Maximum Rim Backspace: 8 inches

Backspace of 7 5/8 inches for the stock rims leaves at least 2-inches of clearance from all brake and suspension components. However, with stock rim/tire combo there is only about 1 inch of clearance at the fabric lining inside the fender well on the forward, inboard corner. This corner is shaped at a radius similar to that of the tire, so a 1/2 inch increase to backspace and/or tire height is as close as I'd dare to push it. The new 2018 ZL1 1LE boasts 13-inch wide tires so I have to assume they've modified the lining or sheet metal in the fender wells, rims, or suspension to accomodate them.

Maximum Tire Height (loaded): 27.5 inches (or about 28 inches unloaded)

Based on the below measurements, there's at least 2" of room from the rim to any obstruction inboard of the wheel. However, the limiting factor is going to be the 1" of clearance at the inboard front corner of the wheel well. However, that corner is curved like the tire so adding 1" of backspace or height would probably only consume about half that clearance.

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?


[Rear Wheel Clearances/Measurements]
(with stock rims/tires)

Specs/Measurements:

Rims:

Description: (Stock) 5-spoke, split-spoke, black, forged alluminum
Size:                      20" Dia. x 12" Width
Offset:    1.69291" (43mm) (All the Facts: 2017 Camaro ZL1)
Backspace (calculated):    7.69291" (195.399914 mm)
(based on 43mm offset)
Backspace (measured):      7 5/8 (7.625" or 193.675 mm)
Lug spacing (measured):    5 x 2 13/16 (2.8125" or 71.4375 mm)
Lug spacing (stock spec):  ???

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".


Wheels:

Make:         Goodyear
Model:        Supercar F1 G3
Spec:         305/30ZR20 SL
Load rating:  99 1,709 lbs (775 kg) per tire
Speed rading: Y (over 186 MPH or 300 KPM)
Max pres:     51 PSI

 Uniform Tire Quality Grade (UTQG) Standards

Tread wear:         220 (moderate)
Traction:           AA (Above 0.54 G's)
Temp (dissipation): A (highest - over 115 MPH)

Clearances:
(measured from original equipment wheels/tires)

Brembo caliper -> inside rim: 1 1/4"

Wheel (rim) width: 12" (305 mm)
Mount flange -> outboard edge: 4 3/8" (4.375" or 111.125 mm)
Mount flange -> inboard edge: 7 5/8" (7.625" or 193.675 mm)
(backspace)

Tire outboard edge (prot. lip) -> fender top inside surface: 1/8"
Wheel outboard edge -> fender top inside surface: 3/8"

Tire height loaded: 26 1/2" (unloaded about 27")

Tire Clearance inside fender well (tightest fit):
Top: 5"
Inboard: 3-4"
Rear: 2"
Front: 1" (inboard corner)

Rear stabilizer bar (behind wheel): 2"
Brake fluid line (behind wheel): 2 1/2"

Fitment Calculator: Updated 20170405

Existing:

Tire:    Width    Profile    Diameter
         305      30      20
Rim:     Width    Offset
         12       43

New:

Tire:    Width    Profile    Diameter
         345      35      18
Rim:     Width    Offset
         12       43

Results:

                    Existing    New
Diameter            691mm       698.7mm
Circumference       2170.8mm    2195mm
Poke                109.4mm     109.4mm
Inset               195.4mm     195.4mm
Speedo error        0%         -1.1%
Reading at 30mph    30mph       29.67mph
Reading at 60mph    60mph       59.34mph
Ride height gain    0mm         3.85mm
Arch gap loss       0mm         3.85mm

Compared to your existing wheel, this new wheel will have an inner rim which
is the same distance from the suspension strut as your current wheel. The
outer rim will poke out the same as before.

[Updated 20170405]

!!! New Tires could be a tight fit at the inboard, front corner of the wheel well.

If MT specs are correct, new DR tread will be only 0.2" closer to the inboard, front corner of the wheel well; based on the stated tread width. This should be no problem, leaving over 3/4" clearance. If we go by the tire size numbers (305 vs 345) it will be 3/4" closer at that point, leaving barely 1/4" clearance. MT specs show a 13.5" section width (sec. width) for this tire, which corresponds to 343mm but this is measured at the center of the bluge on the sidewall (See TireRack.com illustration).

Original tread width: 12.00 in. (305mm)
New tread width: 12.4 in. (315 mm)
Difference of 0.4" / 2 for one side: 0.2"

I'll Update this thread when I put them on and measure clearances again.

--Cal

[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

[Harry76]

I came across this post while doing a search for backspacing, according to my research we can fit 17 inch wheels on the ZL1s with 40 - 43 mm offset or 7.7 inch backspacing.

[mlee]

Originally Posted by Harry76

I came across this post while doing a search for backspacing, according to my research we can fit 17 inch wheels on the ZL1s with 40 - 43 mm offset or 7.7 inch backspacing.

Pretty sure you can and I believe some are running them.

I really wish this thread would have taken off and now that more have had time to actually get wheels maybe it will.

[ReevZL1]

For the 2017-2018 ZL1 Camaro you can run 17x10" with 44mm offset and 7.2" back spacing on the Weld Racing Wheels. I'm Running those and 20x7.5" wheels up front. I purchased the welds from Carlyle Racing. For those of you that want to buy Billet Lug nuts they are 14mm connical which were also purchased from CarlyleRacing.

[ReevZL1]

The wheel on the Scale is a 20x7.5" weighs in at 22.2lbs
The 17x10" wheel weighed in at 24.2lbs with the Bead lock ring on.

[ReevZL1]

Ok I just test fitted the welds 20x7.5" and 17x10" and they fit. However the 255/35R20" Mickey Thompson Tire that Andy@CarlyleRacing told me to get does not fit the 20x7.5" wheel. The only other option from Mickey Thompson is the 245/45R20 tire. I ordered those last night and they should fit this time. I'll post an update if they do not fit. The tire size recommendation says it will.

[trm0002]

2017 1LT OEM tires blow in the snow. So... completely off the wall... I have a set of Blizzaks almost brand new from a Charger my old man totaled. 235/55/19 That puts the tire height at 29.2 vs OEM 27.7 if I bought a set of aftermarket 19" rims. +1.5" is a hell of a lot (don't care about the speedo). Would they fit or not? .75 bigger radially Hey, $700 in tires is $700

[VcrusaderV]

Originally Posted by cwebster

After exhaustive research and meticulous measurements, I've narrowed the field to the following rims and tires for use at the drag strip with my 2017 ZL1. I need more rim options, though. See measurements and clearances near bottom.

There are several questions I have, related to the information I've collected. These are highlighted below with bold, red underlined heading "Question:". I'd be grateful if someone would kindly answer these.

Thank you in advance for suggestions, references, or comments.

--Cal Webster

I know this post is dated but I’ve been researching this topic and stumbled across this write up. Just wanted to say thanks for putting in the work and then documenting it like you did. It makes things much easier and I just wanted to say thanks. Very thorough and very well written. Thanks

[Goohead]

Carlyle racing 15” kit


Fitting 325/50/15 Nitto on forgestars

[extermemator]

I have a 675 horse ZL1. I wanted to get more tire on the road. I heard weld makes a good wheel lokking for a 16 or 17 inch rears. Just wondering if anyone has used a weld 17x10 rim? what other options for wheels are out there. I have factory brakes currently. also if any one has suggestons on a good tire and wheel size combo. I really like how the car rides now but I I just want it plant them tires better. Any good feedback would be appreciated. This is for a 2017 ZL1

[mlee]

Originally Posted by extermemator

I have a 675 horse ZL1. I wanted to get more tire on the road. I heard weld makes a good wheel lokking for a 16 or 17 inch rears. Just wondering if anyone has used a weld 17x10 rim? what other options for wheels are out there. I have factory brakes currently. also if any one has suggestons on a good tire and wheel size combo. I really like how the car rides now but I I just want it plant them tires better. Any good feedback would be appreciated. This is for a 2017 ZL1

I'm not sure you're going to get 17's over the front Brembos.

[SienarSystems]

https://4aah2h38qz0d1pp9jb46vzfw-wpe...Guide-2018.pdf

17x9.5 will fit on the rears with no modifications (see link). My question is whether the MT 315/50/17 (30”) tire would fit. 305/45/17 MTs were on a member’s car and look to be the max size that will fit without mods. Pic is @xCROOKS______x‘s car

[Goohead]

There is quite a gap on the SS on stock suspension even with 325/50/15