Hey forumies, Just pulled off the centrifical supercharger install and the Nitto 555 275-40-R18's are useless. I like to take the car to the track a couple times a year, no point unless I get grip. I know I can get 285's on the back by moving the e-brake bracket to the top of frame, any1 else been able to get bigger combo's without hacking the bodey or flares? Also any idea's for radial slicks? Tough to find sizes Im after. Nitto NT 05's are interesting but worried they wont grip enough, Hankook ventus z214's are looking interesting and come in 275-35-R18 but I want wider.

 

Traction with decent power and an 18" tire is a tall order......you want traction then you need a 15" with a 275 Drag radial! An 18" tire just does not have the sidewall and is why you see C5's,6's and 7's running a 15" wheel when at the track. As far as the street you have to control it with your right foot.

 

We used to run 335-17s for Autocross with our straight wheel well flare! That was the biggest available at the time, but we could have went outward another inch based on spring rates and shocks! Anything more in width, the flare/wheel probably would have hit!

 

Plenty of cars over in C7Z running sub 1.6's and sub 1.5's on 18"+ ....

https://www.corvetteforum.com/forums...fast-list.html

IIRC with proper offset you can 3XX rear tires on a C3

 

I am thinking about 295/45/18 on the back. They are 28.46" tall so would help a lot with traction. It would also fill the rear fenders out nicely.

Mickey Thompson and Nitto both have tires in this size. MT has a drag radial and Nitto has the NT05 and NT555 tires.

Mike

 

I currently have 285s on 17"x9.5" wheels front and rear. I've been thinking of buying some 18"x10" or 10.5" wide wheels and 295 or 305 tyres on mine for trackday use. I could fit these under my car without flares (relocated handbrake cable, modified sway bar, shortened leaf spring). The Ridetech 48 hour Vette had 315s under stock fenders (now has flares).

FWIW, a change in tyre compound will yield far greater grip increases than width. If yours are standard 555s and not 555Rs then you'll get a huge increase in grip from a stickier tyre.

 

285's are less than half an inch wider than 275's - I would have thought it was hardly worth bothering to make the change. Can you source Toyo 888 275/40/19 trackday tyres?
I have 285/40/18's Toyo Proxes on the rear fitted to 9" rims with 5" backspace. Fits within the fender openings and clears the trailing arm. The tyre just 'touches' and 'polishes' the chassis during 'energetic' turns. Should change the trailing arm bushes to poly I guess. I did remove the rear sway bar (which rubbed on the tyre)
Am I happy with the set-up? in terms of handling, most definitely. Don't do track days so can't comment but with 600+ ft/lbs torque would any tyre handle things? - when this rubber need replacing I may go with the Toyo 275mm 888's and chance the differential and U/J's in the search for more 'grip'

 

These are MT 295 55 15's, and for what it's worth I used to run 295 50 15 street tires, so the size difference did not change much.

The real change was the tire compound. MT's grip like glue, the street tires I could blow at a 55 mph roll.

 

Surly those tires must rub the fender off the line, mines auto and when I load it, it "squats" a lot.

 

You guys see any professional drag racers running 18" rims? While you can run them, the car will be faster with the proper 15" tire. Problem is fitting those tires on a new car with huge rotors. They have to settle for the minimum rim size that fits.

You don't.

 

No rubbing of any kind. Been on for about seven years now. I do run VB 360 lb rear spring and QA1 shocks,...so not a lot of squat.

 

Thats awsome! Similar to what im planning, im just going stiffer rear spring, as far as the above comment by maj75,very true... But when we see professional..... The laughing starts... Come on man!!!

 

Problem with 15" tires is, unless you are just looking for straight line performance only, as in drag radials, there is not a single modern performance tire available. Decades old all season radial designs is all there is.

18" wheels give you a large selection of modern performance tires, and they grip way beyond anything in 15" except drag tires. Handling, stopping, acceleration all are much improved.

How many supercars capable of sub 4 second or even sub 3 second 0 to 60 mph times do you see running 15" wheels and tires?

Mike

 

Bingo! Correct!

15 inch street tires for C3's are frankly complete crap. BFG's, Firestones, etc are at best barely mass market economy tires with fancy raised white letter, in some cases. Most modern eco cars with some performance package have infinitely superior tires than the 15 inch C3 tires.

Any 17/18 inch ZR (W/Y rated) ultra high performance tire will completely embarrass just about any 15 inch tire from rubber compound (much softer) and tire carcass strength construction which will offer much superior dry traction, wet traction, braking, handling and steering response...THERE IS NO COMPARISON...NONE!

A 15 inch drag radial is NOT a street tire.

I chuckle when I see big wide S rated tires on C3's offering supposedly big traction/handling benefits....These tires have very hard rubber, big sidewalls that flex immensely, and weak tire construction all combining to adversely effect the handling/traction/ride/braking of a C3. When folks say that they can spin the tires in any gear especially with sub 500 Gross HP engines, especially when already rolling, the tires have much to be desired. You need better tires like ultra high performance summer only 17/18 inch ZR rated tires....no spinning in any gear unless the engine has enormous HP/Torque.

 

This is turning into a great thread so far.

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

 

A different follow-on question:

Many people are making the point in this thread that the fastest way to improve traction is to go with a stickier tire compound; which tires are the current leaders on "stickiness"?
How do you find the stickiest tire? Is tire wear rating alone good enough or are there other factors that aren't factored into the wear rating?


Example: Last year Nitto released a new version of the NT555; the NT555 "G2"- supposedly it uses a newer, even stickier tire compound- how do we validate that in the detailed tire specs to know how much stickier it is than the G2. People say that the Mickey Thompson are famously sticky tires- what spec can we pull from the detailed tire data to tell whether the Mickey Thompson or something like the NT555 G2 are stickier, or how much stickier to do a value determination?



Adam

 

before you spend any money on trailing arms remove your rear tire and measure from the top of the wheels well to the frame and body, that will tell you how wide you can get under the car without some type of body mods. If you measure bottom of TA to ground you can use that to reproduce ride height, this will allow you to measure your your height and see where your new bigger tire will rub.

 

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

 

Yea, it seems like the 15" drag radial is too big of a compromise in a street/strip application. Going with a wider 17" or 18" wheel gets you increased traction AND handling.


Adam

 

Not true. Avon CR6ZZ's have a great reputation as a track worthy, D.O.T legal speed rated tire with sizes applicable to our cars. I am going to run them. Haven't heard any complaints on them other than cost. Guys are even getting decent street miles out of them.

Totally agree with above that the S and T rated tires in 15 inch are complete crap. They all are single cap ply tires which leave much on the table construction wise to the speed rated tires. Fine for the way most drive their cars. In my case, I am upgrading suspension so it would be a waste to put bad tires on. Nice to have an option in 15's although they are quite spendy. I am going for the road race look and in my opinion, 15's look just right.

In regards to the width question, my 69's rear wheel wells are just over 11 inches from lip to frame. A 275 is 11 inches wide and a 295 is 12 inches wide, depending on the wheel width. A 295 may fit with the right backspace and wheel width, but don't see how anything bigger will fit no matter what the diameter. I am going to run the Ridetech rear including their trailing arm and they said a 295 may fit.