Les

I've checked the Tire/Wheels section but it's almost all C5 info, so I thought I'd ask my fellow C3ers-

It's almost time for new tires & I'd really like to stay w/ my current 15X8 wheels. Given that, my tire choices are pretty limited & it looks like it's going to be between BF Goodrich Radial TAs(S rated) or Dunlop GT Qualifiers(T rated). I'm leaning towards the Dunlops w/ the better speed rating but the real question I have is this-

Does anybody know if the 295/50X15 size will fit in the back? It's about 1" smaller in diameter than the 255/60s that I currently have and it's about 2" more tread width. Due to some traction problems ;) I'd really like to put more tire to the ground. I don't want to use 275/60s because they're about 1" taller than the 255s and obviously aren't as wide as the 295s.

I've already ground off some of the E-brake bracket and tied the cable to the frame to gain space for my track tires. So, has anybody tried to fit this size on their C3.... or perhaps know somebody else who has? Or maybe you know somebody at a tire shop that has enough experience with Vettes to answer this. I'll probaly go through the Tire Rack for the purchase, so I'll need to know what will work before buying. Any help would be greatly appreciated.

Dalannex

I don't know about what will fit for sure, but it always seemed to me that my 255/60's were pretty tight.

Your tires are:
10.04 treadwidth/6.02 sidewall height

295/50:
11.61 treadwidth/5.81 sidewall height

275/60:
10.83 treadwidth/6.50 sidewall height


If I'm wrong about my calculations somebody let me know. :cheers:

MikeC

I think Motorheat has 295's on his car... He has at least 275's, the tires are super wide!

GrandSportC3

295/50R15 will fit. However - you should use a larger spacer to clear the emergency brake hardware.
(at least 1/2 inch). I currently use 3/4 inch spacing (my Cragar SS rims require at least 1/2 inch spacing). I went with 3/4 inch spacing.
I am using 255/60R15. There is plenty of space between the tires and the emergency brake hardware to increase the tire size to 295!
I was actually thinking in changing my rear tires to 295/50/R15

Olivier

Les

Mike,
I'd like to get specifics from Motorheat but I tried to find him using the search function & had no luck- any idea how I can reach him????

Les

PRNDL

I was going to suggest the BFG comp T/As which are H rated. I have them in 225/70, but I just checked and the sizes are very limited. MJ

Les

MJ,
Yea, I'd love to step up to a better speed rating....they've phased out so many good tires in the 60 series since rim diameters have gone up that there's not alot to pick from :sad: :sad:

HawkIVette

Sorry to get off topic a bit, but you guy's opened the door.
Tell me more about the rating -i.e T rated,S rated, H rated ,etc. What are the speed ratings and what speeds go with them?

Les

This should give you a basic idea- higher speed ratings are the result of better materials & better construction. You can run at speeds higher than the speed rating for a given tire but not for extended periods of time without running the risk of sidewall fatigue and/or failure. Hopefully that helps. The chart below lists speed ratings in MPH for the various letters.


Speed Rating Characteristics
Tires have always had the ability to change an automobile's driving characteristics. Technology has given the tire an important role as a component of the automobile suspension.

The speed rating of the tire is an indicator of the tire's performance capability. Improving the tire's performance capability will normally benefit an automobile's performance. Conversely, decreasing the tire's speed rating generally lowers the tire's ability to contribute to the automobile's performance.

Changing from the O.E. tire speed rating to another performance level tire will probably change handling in areas such as:


1. Steering Response 4. Cornering
2. Braking 5. Evasion/Recovery
3. Traction

SPEED RATINGS CHART

MPH SPEED

M 81
N 87
P 93
Q 99
R 106
S 112
T 118
U 124
H 130
V*(VR) 149
W**(ZR) 168
Y**(ZR) 186

1Bad69

Les, i think you are looking for Motorhead.....

Les

1bad69,

Bingo!!! Thanks a bunch! MikeC almost had the name right- I was wondering why I couldn't find him...thought I was going :crazy: I'll get ahold of him & post info here for anybody else that was wondering.

HWY 9 - Z06

JUST MY 2 CENTS, BUT I RAN THE DUNLOPS ON MY CAR FOR ABOUT 9 MONTHS. WHAT A CRAPPY TIRE. MEDIOCRE DRY TRACTION AT BEST, AND THESE TIRES ARE FLAT OUT DANGEROUS IN THE RAIN OR WET. AT ANY SPEED ABOVE 25 THE CAR WOULD WANT TO SWITCH ENDS. ENDED UP WITH WHEEL VINTIQUES 16X8'S AND 255/50/ZR16'S WITH FIRESTONE FIREHAWKS. EXCELLENT TIRE AWSOME DRY TRACTION, AND WET TRACTION IS ALMOST THE SAME AS DRIVING IN THE DRY. HUGE DIFFERENCE IN DRIVABILITY. I WOULD SUGGEST STAYING AWAY FROM DUNLOPS THOUGH, I WAS SO DISGUSTED I EVEN SWTICHED TIRE BRANDS ON MY MOTORCYCLE.

VettePower

Correct me if I am wrong, but by changing to a drastically different size tire, won't your speedo be off? And if so by how much? :confused:

Les

HWY 9- '69,
Thanks for the info. I'll definitely take it into account. What tires did you have on the car before the Dunlops? Also, were the Dunlops the same ones I'm looking at? I pretty much need to see how they compare to tires that'll fit my rims...and that means Dunlops, BF Goodrich T/As, or Goodyears- which I also hear bad things about.

VettePower,
Yes, changing tire height affects speedo accuracy but mine's already off since I changed rear gears from 2.73 to 3.55...nobody could figure out which gears to change at the trans to fix that, so I've made do w/o an accurate speedo for awhile now.

jimduchek

w/regard to your traction problems, two points to make... The first is that a smaller diameter tire will effectively raise your rear end gear ratio. The second is that you might consider the Canadian guy's 6-link rear. You always want as little tire as possible (since rolling resistance and reciprocating weight cuts ETs!), so a properly set-up suspension might be better than a couple more inches of rubber. Price, if I recall, is about 3-400 bucks. A bit more than a set of new tires though. You also might do with (if your problem is with drag racing), aligning the car with a bit more positive camber in the back. When your car 'squats' on acceleration the camber tends to go negative...

Jim

Captain Morgan

Les,
A couple comments. First, I think it's a shame that nobody makes a really good tire in the 15 inch size. We are very limited on our choices.

Second, Edit: I was making the same comment about tire height and traction as the above comment.

I know you don't have much choice. It seems that no matter what tire you get, if you want performance tires, you are limited to certain heights. I think stock tire height was 27".


[Modified by sharklover, 2:27 PM 2/27/2002]

Noel Carboni

Generally speaking, here's how:

There's a little nylon gear inside the tranny just under where the speedo cable screws on that determines the speedo calibration. It comes out pretty easily; usually just by removing one small bolt.

Figure out how much, as a percentage, your speedo is off, then pull out the old nylon gear. Multiply the percentage by the number of teeth on the gear and you'll get a number close to the right number of teeth (within 5% or so). Round down, unless the calculation comes close to the next higher whole number. Go down and get a new nylon gear with the right number of teeth. The parts guy should know how to do that.

As an example: Your speedo reads too slow, showing 50 when you're really doing 60. So, your speedo is reading at 50/60 or 83.3%. You pull the little gear out and count the teeth... You find it has 21. Multiply 21 x 0.833 and you get 17.49. Round down to 17. Go down to Auto Parts and get a 17 tooth gear, and your speedo will now read close to the right speed - 61.7 when you're really doing 60.

As a rule of thumb, you'll probably get fewer speeding tickets if your speedo reads a bit high. That's the reason for rounding down. ;)

-Noel


[Modified by Noel Carboni, 8:40 PM 2/27/2002]

Noel Carboni

Yes, that's very close to right.

Some of the manufacturers publish dimensional specs. BF Goodrich (really Michelin) does, in a nice, tabular format. Go the following web page, for example, and click on the "click for PDF" link:

http://www.bfgoodrichtires.com/catalog/radial_ta.html

-Noel


[Modified by Noel Carboni, 8:39 PM 2/27/2002]

MotorHead

Les -> Don't know why I never read this thread until now. You have to be careful if you want to put 295's on the back. I knew they would fit on my car because I saw them on another '80. You should remove the e-brake bracket on the trailing arm and move it to the top or it couldl cut your tire down.

That being said I just ground mine down a lot so they are in the same place. But I check all the time to see if there is any contact. The 295's are great and the BFG 50 series has a stronger sidewall than the 60 series, which helps in the corners, a fact that alot of people aren't aware of.

The 265's on the front fit my car with no problems however yours could be diifferent. The are probalbly about the same diameter as 235 60's, as for the 295's they are only about a half an inch shorter than the 255 60's but way wider :D