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Switching from max width back to "stickiest" tires for a second:
The Mickey Thompson Street ET are available in 275/40R/18 for $200 each
Their infamous R2 compound ET Street S/S in 285/40R/18, but they'll set you back $353 and will wear out insanely quickly.
The Michelin Pilot Super Sport are available as 285/35ZR/18s (no 285/40s) for only $255.80 from Tire Rack, so they're becoming a legitimate all around perf tire that's not budget destroying anymore, but I really wish they had a 40 sidewall option available (hell, I'd take bigger; I want the increased contact patch and the slightly slower rotation makes for tiny increases in mpg- plus I've got a digital to analog converter box for my speedometer/odometer that can self-calibrate to correctly display the proper speed with larger or smaller wheels than stock).
The Nitto NT555R Drag Radials are comparable to the ET Street S/S and are a more reasonable $286 @ Walmart.com 285/40ZR/18 -UTQG rating of 100, though so again you won't get many miles. -Their tire compound has very real problems with below freezing temperature and hardens and forever loses its stickiness and softness if it gets too cold, though.
The Nitto NT555 G2s can be had for $249 each 285/40ZR/18, but the MT Street ETs seem to be a better value; it shocks me to say that but $200 for the MTs seems way better
Adam
P.S. I'm pretty glad I went with 18s; the selection of legitimate perf tires seems to just be increasing while the costs are coming down.
Last edited by NewbVetteGuy; Aug 2, 2017 at 07:07 PM.
I'll also add that, although there seems to be a lot of agreement that the first thing that becomes a fitment issue is the ebrake cable mount, I noticed last night that my 18" rear wheels' diameter is big enough that it clears the ebrake mount. I don't see where it would be an issue with 18" or larger wheels on my 79. I think I'd hit the trailing arm or the frame up front first. I just don't see how with an 18" rim you'd hit the ebrake cable mount.
Adam
The ebreak mount itself isn't the issue - its the angle of the ebrake cable running to the bracket - it rubs on the inner side of the tyre - I simply slacken the adjustment-off a bit and hook a couple of cable ties around the cable and lower shock mount to pull it away from the tyre!
A few focused questions: We've seen the limit of what can be fit on an unmodified late C3 with Metal Head's 9.5" wide, 285 tread tires; we've got good information on what becomes the "bottlenecks" towards going even wider (e-brake cable bracket & leaf spring); we've heard what's required to go wider (offset trailing arms or fender flares), BUT we haven't yet heard what the max width is and what offset to use if going with offset trailing arms.
1. What is the max width tire supported by a 1" offset trailing arm (if going with 17" or larger rims)? -What is the tax tire width supported by a 2" offset trailing arm (if going with 15" rims)?
I made the trailing offset "pairings" based upon Vansteel's recommendation to go with a 1" offset for 17" or larger wheels and 2" offset for 15" wheels. At first glance it seems like you'd just figure out how many mm are in 1" and add that to a 275mm or 285mm tire, but I THINK the 1" of clearance you gain with the 1" offset trailing arms means you can actually go with a 2" wider (50mm) tires if you get the offset right (if the centerline of the tire stays the same). Does this mean you can fit 325mm wide tires if going with offset trailing arms?!?! Because that would be amazing!
2. If you maximize tire width with offset trailing arms, what wheel offset should you be going with?
3. Same question as #1 & #2 if you go with fender flares; how wide of a tire can you run and what should the offset be?
If we can track these details down, I think we can summarize this thread into a single post and make a sticky for a very commonly asked question.
Adam
Don't think that the offset trailing arm solves anything when using 18" rubber. The limitation on the inner side of the tyre is the chassis, not the trailing arm. As I noted earlier I have a 5" backspace with 285/40/18 on a 9" rim - and yes I'm sure a 9.5" or 10" wide rim with the same 5" backspace would effectively move the centreline of tyre outwards and at the same time move the inner wall of the tyre outwards reducing the risk of rubbing the chassis - but then you run a very real risk of the outside wall of the tyre then hitting the inside of the rear wheel wells. And would you really want even a 285 section tyre 'stretched' over too wide a rim and making what is already a deteriorating ride quality (due to the low profile rubber) even worse?
Awesome! For clarity: Did you have to move the e-brake cable, or bend the rear sway bar(if you have or have had the oem bar on the rear), I can see you've got rear coilovers now but did you try this wheel config with a leaf spring at all?
Also: what year C3?
Final: Do you think another 5 mm of width in both directions would still fit? (if you went up to a 285mm width with the same backspacing?)
Adam
1978 C3. I have the VB&P Rear Sway bar with OEM TA Rear Sway mounting. VB&P Street and slalom rear kit. No mods from factory other wise. The front is a little different. Due to poor pace car spoiler fitment I cannot get full steering lock due to the tire rubbing the spoler after 1 full turn of the wheel.
I looked at 285 and I don't feel they would work. Allowing for tire flex in HARD cornering may rub. The 275 is the widest I trust at this time. My first track day with the 275 is at the end of the month so I will be able to provide a complete assessment of 4.75" bs. But for street use I don't see any problems on my car at this time.
Here is my Rear sway bar connection.
Here is the clearance of the e-brake from the rim. Before I mounted the tire.
Sway Bar Clearance with tire mounted.
Spring Clearance.
E-Brake Clearance.
Last edited by cagotzmann; Aug 2, 2017 at 08:26 PM.
Oh C@#$@#%! I did not know that you did all of that; I thought you had found the perfect backspacing to make it all happen.
Moving the eBrake cable isn't a big issue; I also have a 1" on each side shortened VBP spring, but bending the sway bar is a problem... ;-(
...
No problem, I thought I'd better clarify though! Bending the factory rear sway bar is not too difficult (being so small), I just clamped it in a vice and used a big bar over the ends.
Yea, the lack of a standard between brands for "grip" or even wear, is a very real problem I'm surprised is still a problem.
Adam
The wear (treadwear rating) is at least somewhat standardized, and the AA etc ratings for treadwear give you a ballpark, but ultimately I think they're changing so fast and there's so many variables (car weight, size, alignment, suspension geometry, centre of gravity, roll centre, tyre pressure, driving style, road surface... etc!) that it's near impossible to give accurate standard measurements that will apply to all purchasers. Kinda like an engine build, camshaft/head/compression ratio, or suspension setups. The best setup for one person/car will not be the right setup for another person/car.
Hahaha!; it's great to have such an extreme example here. How many inches shortened on the rear leaf spring? (just 1" on each side or more?)
Are those 2" flares on each side with the wheels then sticking out further still from the 2" flares?
Backspacing?
Adam
Without going home and throwing those tires back on (I need new rubber). I am not sure if those were the 315s or 335 in the pictures. The 335s gave near 13 inches of tread on the ground, and a 13.5 width, and the rims were 12 inches, so essentially 13 inches wide. The flares actually are probably closer to 2.5 to 3 inches, but kind of deceptive as they are blended with quite a bit of glass, maybe an inch think to create the smooth radius into the flat plate, but never really actually have measured them, and can't because the glass is piled up on the original fender, so add the inch or so there. If we could find wider tires, we can still come out farther. The spring holes were trimmed off on both sides and redrilled. The hanger bolt tops arm attachments were changed, so they didn't come in angling in or in contact with the tires. We were about 5-1/4 BS. Our flares honestly could be knocked off, and the original fenders uncut are still underneath the fiberglass. You can see the spring clamps also, which can be repositioned to change spring rates!!!! We were the first to think about that. Kind of turned a leaf spring into a variable rate unit, but it doesn't change it too radically as moving those inboard or outboard is kind of limited.
Last edited by TCracingCA; Aug 2, 2017 at 08:17 PM.
Switching from max width back to "stickiest" tires for a second:
The Mickey Thompson Street ET are available in 275/40R/18 for $200 each
Their infamous R2 compound ET Street S/S in 285/40R/18, but they'll set you back $353 and will wear out insanely quickly.
The Michelin Pilot Super Sport are available as 285/35ZR/18s (no 285/40s) for only $255.80 from Tire Rack, so they're becoming a legitimate all around perf tire that's not budget destroying anymore, but I really wish they had a 40 sidewall option available (hell, I'd take bigger; I want the increased contact patch and the slightly slower rotation makes for tiny increases in mpg- plus I've got a digital to analog converter box for my speedometer/odometer that can self-calibrate to correctly display the proper speed with larger or smaller wheels than stock).
The Nitto NT555R Drag Radials are comparable to the ET Street S/S and are a more reasonable $286 @ Walmart.com 285/40ZR/18 -UTQG rating of 100, though so again you won't get many miles. -Their tire compound has very real problems with below freezing temperature and hardens and forever loses its stickiness and softness if it gets too cold, though.
The Nitto NT555 G2s can be had for $249 each 285/40ZR/18, but the MT Street ETs seem to be a better value; it shocks me to say that but $200 for the MTs seems way better
Adam
P.S. I'm pretty glad I went with 18s; the selection of legitimate perf tires seems to just be increasing while the costs are coming down.
I ran 285/40/18 tires on 9.5" rims with 5" backspace on my 80 Vette with the stock Gymkhana suspension. The only thing I had to do was tie back the parking brake cable.
I had 265/40/18 on the front with 9.5" rims and 4 3/4" backspace. Tires didn't hit anything.
The cheapest 18" tires in a Max Performance is the Goodyear F1 Supercar. It's not the top rated tire, but light years better than most 15's available.
255/45/18 F1 $164.27, 285/40/18 F1 $165.50 at Tire Rack. Can't get a 265/40/18 anymore in the Goodyear.
1978 C3. I have the VB&P Rear Sway bar with OEM TA Rear Sway mounting. VB&P Street and slalom rear kit. No mods from factory other wise. The front is a little different. Due to poor pace car spoiler fitment I cannot get full steering lock due to the tire rubbing the spoler after 1 full turn of the wheel.
I looked at 285 and I don't feel they would work. Allowing for tire flex in HARD cornering may rub. The 275 is the widest I trust at this time. My first track day with the 275 is at the end of the month so I will be able to provide a complete assessment of 4.75" bs. But for street use I don't see any problems on my car at this time.
Here is my Rear sway bar connection.
Here is the clearance of the e-brake from the rim. Before I mounted the tire.
Peruse through the 18" wheel and tire thread over in C3 gen. With 18's a lot of people are running 5.25 to 5.5" backspacing. Look at the original 48 hour Corvette for inspiration.
The 48-Hour has wide 18×10 wheels on all four corners in Forgeline’s GT3C concave style. The jealousy many of you may feel for the ability to fit this wide of a wheel may be building up now, but just wait. Thanks to these wide wheels, they’re fitting 315/30R18 Falken Azenis RT615K tires all around. I know the struggle of being able to fit a wide enough tire in the wheel wells of a classic car, but thankfully the C3 fits plenty wheel and tire with RideTech’s suspension.
Not sure how much is attributable to the suspension but those wheels have 5.25" backspacing.
I've been looking for a cheapish set of 18x10.5s with 5.5" backspace for track rims/tyres. I'm confident I can fit these without issue, and would probably use a 295/35R18, which is short and will look a bit odd - I wouldn't use it daily on the street, but I'm not concerned about it for track use and there's lots of good semis pretty cheap in that size. May end up with an 18x10 instead, as they seem more readily available.
SOOO, I wanted to clarify that when everyone on here is talking about backspacing, they're ACTUALLY talking about backspacing and are not talking about offset and calling it backspacing. -When someone says they're talking about a 4.75" backspacing on a wheel they're saying that there's 4.75" from the inside of the rim to where the rim mounts on the hub, right? -So when people are talking about the same width rim with a 4.75 and a 5" backspacing, the 5" back spacing wheel would be moved further to the outside of the car, buying you more room on the inside and the 5" backspacing wheel would have a slightly "deeper dish" when looking from the outside of the wheel, correct?
(This has been my understanding but I didn't have a very technical term on exactly how back spacing is measured or what the difference between back spacing and offset was exactly until now so I'm questioning whether I've been correctly applying this or not.)
Adam
Last edited by NewbVetteGuy; Aug 3, 2017 at 04:37 PM.
SOOO, I wanted to clarify that when everyone on here is talking about backspacing, they're ACTUALLY talking about backspacing and are not talking about offset and calling it backspacing. -When someone says they're talking about a 4.75" backspacing on a wheel they're saying that there's 4.75" from the inside of the rim to where the rim mounts on the hub, right? -So when people are talking about the same width rim with a 4.75 and a 5" backspacing, the 5" back spacing wheel would be moved further to the outside of the car, buying you more room on the inside and the 5" backspacing wheel would have a slightly "deeper dish" when looking from the outside of the wheel, correct?
(This has been my understanding but I didn't have a very technical term on exactly how back spacing is measured or what the difference between back spacing and offset was exactly until now so I'm questioning whether I've been correctly applying this or not.)
Adam
You can use backspacing to figure out the offset or visa versa if you also know the rim width.
It seems like wheels for newer cars are usually listed with offset. Younger guys with their newer cars usually refer to offset. Us old guys and our old cars use backspacing more.Years ago you never saw offset listed in the wheel description.
SOOO, I wanted to clarify that when everyone on here is talking about backspacing, they're ACTUALLY talking about backspacing and are not talking about offset and calling it backspacing. -When someone says they're talking about a 4.75" backspacing on a wheel they're saying that there's 4.75" from the inside of the rim to where the rim mounts on the hub, right? -So when people are talking about the same width rim with a 4.75 and a 5" backspacing, the 5" back spacing wheel would be moved further to the outside of the car, buying you more room on the inside and the 5" backspacing wheel would have a slightly "deeper dish" when looking from the outside of the wheel, correct?
(This has been my understanding but I didn't have a very technical term on exactly how back spacing is measured or what the difference between back spacing and offset was exactly until now so I'm questioning whether I've been correctly applying this or not.)
Adam
You've stated the definition of backspace correctly, but have the interpretation backwards... Backspace is the distance from the hub mounting point to the rearmost (inner as mounted on the car) point on the rim. An equal width rim with greater backspace sits closer to the middle of the car (less dish on the outside), less backspace pushes the wheel and tire to the outside of the car (more 'dish').
Last edited by Metalhead140; Aug 3, 2017 at 08:22 PM.
Offset is more of a modern focus as that is the leverage location for the tire footprint! I am sure I just lost some here with that one! If the hub mount is more in the center of the rims or pushed toward the outer or a deeper backspace, it also aids with bearing longevity!
The deeper backspace pace gives less clearance toward the inside to the frame, shocks, spring, anti-sway bars etc! Deeper backspace is more rim to the inside of the wheel wells!
Hahaha!; it's great to have such an extreme example here. How many inches shortened on the rear leaf spring? (just 1" on each side or more?)
Are those 2" flares on each side with the wheels then sticking out further still from the 2" flares?
Backspacing?
Adam
Ive got 335x30x18 rear tyres on my 78 vette, with fenders flared out to take the whole tyre, 5 inch backspace, and a vansteel composite spring and 285/35/18 up front
Last edited by corvettedave383; Aug 8, 2017 at 05:58 PM.
Ive got 335x30x18 rear tyres on my 78 vette, with fenders flared out to take the whole tyre, 5 inch backspace, and a vansteel composite spring and 285/35/18 up front
It only took you roughly 25 years to caught up and pass our old car in rear tire size!
That would be fun to drive! Cool car!
Last edited by TCracingCA; Aug 8, 2017 at 08:44 PM.
