Tyre size??

[ashy22]

I own a 1971 454 LS5 coupe on standard rallye wheels.
Can I fit a 255/70 R15 Cooper cobra GT tyre to this rim to give it more ground clearance as the hooker header collector flange catches the floor at the slightest pothole.
I have 255/60 R15 Eagle GT fitted at present.

Cheers
Paul

 

[sac001]

Paul,

Perhaps I misunderstand, but I don't think you will gain any ground clearance by changing from 60 series to 70 series tires (tyres).

As far as I know, the 255 stands for the distance from the rim, to the tread. The 60 or 70 represents the width of the tread, and the 15 is the rim diameter.

Steve

 

[ashy22]

Tyre size

Steve

They mix the metric and imperial system to make it confusing on tyre sizes. Excuse my UK english spelling of tire. LOL

The 255 stands for 255mm width.
The 60 or 70 stands for the aspect ratio between width and thickness (profile).
The R15 is a 15" diameter steel wheel rim.

A 255/70 R15 Cooper cobra has a overall tyre diameter of 28.95 inches whereas a 255/60 R15 is 26.11 inches.

Therefore the 255/70 has a larger diameter.
The problem is - can I fit this larger diameter tyre without fouling the wheel arch?

Do you see what I mean?

Cheers
Paul

 

[sac001]

Paul,

Well you've obviously learned more about tyres than me, so now I have to go with your spelling. LOL

It seems to me that you only have to worry about another 1.5 inches of clearance for the Cooper tyres (half of the overall almost 3 inches of diameter).

Unfortunately I just don't know if they'll fit. I would think the rear would be fine, but the front may have some clearance problems.

Good luck,
Steve

 

[wolf_walker]

If your into handeling at all, you may not like the 70 series tire. The sidewals flex a bit more than the 60's. Not a huge deal, but I wish I had gone 60 instead of 70 on the 74...

Dunno if they will fit though, sorry...

 

[Big Fish]

I've been doing a little research on the best tires for my 75. I see a lot of people running the 255/60R15's, but a 245/60R15 will clear the front fenders better, particularly around turns with some bouncing affect. The best tire I have found for performance however is the 225/70R15 (stock size) in a police interceptor tire. They are V rated and will stick to the road better than any of the 60 series, tires which are mainly marketed as a low performance but cool looking tire. The performance tires in the 15" size are few and far between. Seems like the manufacturer's have been putting more attention into the bigger wheel sizes used on the later model cars. I guess it just depends on what your goals are? I have been told there will be a article on this in the Corvette Restorer magazine later this year, I'm looking forward to reading it.

 

[page62]

New springs will give you more lift than new tyres.

 

[ashy22]

Thanx for all the advice guys.

One last question.

Can you have a pair of 255/70's on the rear and a pair of 255/60's on the front.

Cheers
Paul

 

[69MyWay]

Thanx for all the advice guys.

One last question.

Can you have a pair of 255/70's on the rear and a pair of 255/60's on the front.

Cheers
Paul

I don't see why not. The staggered tire profile is a common thing to do. It gives the car a more aggressive look.

Michelin has a great website with a PDF section that gives exact tire size based on the numbers. You might want to check that out, then take a tape measure to the car.

I think any tire over 26" tall looks bad on the Shark Body, but it is all in what you like as you are the owner of the car. I see you are trying to get the car higher off the ground, so in that effort you may give up some of the "low" profile ground hugging looks of the car.

I had a 1985 coupe that I did some significant mods on and had headers. I also lowered the car and had the 1988-1991 tire profile.\ 275-40-17. It would scrape/snag the header collector on speed bumps, I just eventually got a feel for what it could and could not clear. This car was so low to the ground under the exhaust that if I picked up a soda can on the freeway, it would stay lodged between the ground and the rear Y split exhaust pipe until it would grind it down and spit it out.

With all that said, it sure looked good.

 

[69MyWay]

I have been digging for an old photo and have not found it yet. I had a 74 vette with 255 60 15 on the front and 275 60 15 on the rear with stock ralley wheels.

It is no longer my taste in wheel and tire combo, but it did look good and ride decent. I had to shim up the rear spring to make sure the tires did not get into the fenders (spring was worn out), but it otherwise looked good.

However, I don't think this will solve your problem, as a 276 60 on the front would make it look like a truck.

 

[vmrod]

Check out www.coopertire.com If you go to the tire section, you can see the dimensions of all their makes of tires. (diameter, width, tread width...etc.) It is very helpful.

 

[Zektor]

Tyre problem...

Hi Ashy,
I'm based in the UK as well and have an '82 Corvette. Not sure why your car fouls the headers... but my car also has Hooker Headers installed. For wheels, I'm running American Racing Torq Thrust 2's which have the same offset/dimensions etc of the standard '82 alloy (15x8). Originally, when I bought the car it was running 225/70-15 tyres (Goodyear GA). These were crap tyres!!! The handling was rubbish etc.

When I got the new alloys I looked into getting a decent tyre for the car... and I considered Cooper Cobra's for my car. I actually made a trip to Sinton Tyres in Milton Keynes to check out the tyres they had. In the end I went with General XP2002 2's in a 255/60-15 size, they had a more modern tread pattern and a 380 wear rating. In the wet they are ok but not fabulous... but in the dry, absolutely brilliant. When warmed up, they stick like glue!!! When cold, they're is lots of cops & robbers style screeching from the rear... Ace! The handling changed immensley. Before, it was scary to take corners at speed. Now I can throw my '82 round almost as hard as my Probe 24v. I reckon it will handle as hard as the Probe if I pushed it... but it's my baby and I don't want to prang it!!!!

If you've got problems with the exhaust... take it down to Pipecraft in NE London and get them to cut the headers and angle them so they don't foul anything. I had my true duals done at Pipecraft and the guy there did a cut and weld on the main pipe as it leaves the header to give a better angle against grounding out.

Also, my car sits quite low at the front (check out my profile for a pic) and never seems to hit any potholes!

What size are the wheels on yours... 15x7?

Cheers
Dazza

 

[ashy22]

Hi Dazza
I've got 15 X 8 wheels on the vette and just bought 2 tyres for the back - 255/70-15's Cooper Cobra's 75 quid each fitted.
I thought it was a good deal - not the best tyres I know.

Next thing I need is a complete exhaust kit from the headers back. I am really interested in putting on a chambered setup without the back boxes (mufflers). I see what you say about Pipecraft - only one problem - I am in Manchester.
What system have you got on yours?
Speak to you again I'm sure
cheers
Paul

 

[Zektor]

Ashy,
I'm don't think there is much difference between the General's and the Cooper's really. It was only the tread pattern that was the deciding factor for me. The other thing I liked was the solid white letters (which the Cooper's had as well). My old Goodyear GA's had outlined white letters which dont show up half as much... it's all about image! eh? Ha! Ha!
As for exhaust. I wanted to replace the 2 into 1 to CAT to 1 to 2 again, if you catch my drift!!! The CAT had to go! I took a visit to Pipecraft who are exhaust fabricators. They can make an exhaust for any car in mild or stainless steel. I went down there and said, I want a true dual system, I want it loud and the CAT has got to go... oh and provision has to made for the O2 sensor. I left the car and came back 2 hours later. He did a great job, I had it done in mild steel on this occasion. The car just had two "Cherry Bombs" either side for silencing. And believe me they do not "silence" much. It's like a 10-gun salute out the back when revved up!!! Fantastic! Really throbs!!!
Next time I'm going for a stainless system, by them of course with the loudest stainless mufflers they can get!

But, currently, I've just ordered a brand new interior kit for Corvette Kingdom. Just waiting for it to arrive!

Cheers
Dazza

 

[ashy22]

Exhaust system sounds great. If you don't mind me asking - how much did it cost.
I am looking at 350+ quid for a bolt together chambered system from Corvette Kingdom.
Cheers
Paul

 

[Zektor]

Ashy,
My exhaust cost me £240. Obviously, it was more expensive to have it done in stainless steel. I'm going to consider an SS exhaust next year. At the moment I am concentrating on restoring the interior. The car has had various mods up till now... Those being...

Unrestricted Air Filters
True Dual Exhaust System
No CAT
No EGR
No Smog Pump
700R4 Lock-up Bypass
Davis Unified Ignition, 50K Coil, Bronze points etc.
DynaMod Ignition Module.
Magnecor HT wires.

Also, the car has had a full engine out rebuild.

The car has been tested, before the new ignition system went in...

0-60mph was 7.61 seconds
Estimated Crank Horsepower was 226Bhp.

The standard car was supposed to be 8.1 seconds to sixty and 200Bhp at the crank.

With the current setup I reckon with a good launch I can get it down to about 7.2 seconds. With about 230Bhp at the crank.

Next on the performance front is a set of 1:6 ratio roller rockers. Hopefully, this will take power up to about 245-250Bhp.

If I am really lucky, I might just hit 6.9 seconds to sixty!!!

Not bad for an emissions restricted '82... but nothing on your 454!!!!

What have you done to yours?

Cheers
Dazza
ps. Did you go to Knebworth this year?

 

[JHL]

Hi ashy,

I had the same dilema as you and Dazza when it came to exhausts and after looking around I couldn`t find the proper silencers at a reasonable price. I eventually bought a couple of straight thru motorbike alloy race cans. They were 2-1/2" slip fit and with a couple of clamps and brackets I had them on in a morning. It just took the edge of the noise as I had been pushing my luck for some time with none at all.

Micron Silencers

If you can`t find anything else it might be worth a visit to the local motorbike shop.

J.