Fellows, if I go to ttIIs 16x8, what tire size should I order to keep the speedo accurate? 72 convertible currently with stock ralleyes.

 

Same "height" as you have now if you feel speedo is correct.

 

255/60r15 on rally wheels is pretty close to the original gr70 tires.

 

I am confused. And I wasn't clear. I currently have 15 inch ralleyes and I am buying 16 inch TT2s. Therefore, doesn't the height of the tire need to be less in order to keep the same overall diameter of the wheel/ tire? I'm still not sure about the correct tire to get.

Be gentle.....I've been out in the garage too long.......

 

Take the car to the tire store and roll the new tires out beside your existing tires-if they are the same height the speedo will read the same.The wheel size is not important it is like you said the overall diameter of the tire.

 

What year car, and what 15" tire size are you running now?

Is your Speedo accurate with these tires now?

Typically, you're likely to be running one of these:

a) 255/60/15 = 27"
b) 245/60/15 = 26.5"
c) 235/60/15 = 26"
d) 225/70/15 = 27.4"

...and most C3's with 16's run:

255/50/16 = 26"

What sizes are available will depend on what tire you want (ultimate dry perf, all seaon high perf etc)?

Doug

 

http://www.tyretraders.com/index2.html?lmd=38890.586586

try these guys it worked for me click on tire comparison calculator

 

I am running 225/70/15s on my 72 convertible....speedo is accurate.

So with a 16 inch wheel what do I buy to run the same diameter?

 

I believe your current tires have a diameter of 27.5". So simply find a 16" tire that's the same diameter, in a width that agrees with you.

You might call your local Discount Tire,..they'll give you your options.

 

The problem is width vs height, vs supension stiffness and ride height, vs Wheel Offset/Back Spacing. The taller the tire the more likely the clearance problem etc. All wide tires will likely harmlessly rub the frame up front at full lock, but if too tall and wide then you'll possibly break fiberglass at the wheel well. Also, if you go to 17's you can probably tuck the wheel in more via a slightly larger Back Spacing which can help too.

The the 235/60/16 would be around 27" in diameter (if anyone even makes one in a perf tire?), though you'll need to test fit it carefully etc as you don't want broken fiberglass. This would likely work?

A 265/50/16 will be about 26.5", though it will probably rub depending on ride height, and you'll need to wire tie the Handbrake Cables to the Trailing Arms for clearance too. This would likely rub.

A 275/50/16 would be at 27" and would most surely rub.

If you go shorter you can go wider, such as the 255/50/16 at 26", though your Speedo would be off a little. There are many good tires made in this size as it was a C4 Corvette size, and many people run it on C3's. This is your best choice in a 16" IMO.

You could also change your Tran's Speedo Drive gearing as well.

I'd advise you to choose a tire type first, and see what's available size wise etc (ultimate dry perf, all season perf, race etc?). The whole purpose of going to a larger rim is to be able to run modern tires etc, so start there...

Doug

 

Thanks to all for their input. You've given me lots to think about.

I need to get this baby ready for my daughter's wedding in three weeks. It won't be perfect but it will be roadworthy.

 

Closest match is 235/60/16 = 27.1" height.

That is what I am running on my car. Here's a picture and a link to pictures with stock and TTII's:
http://forums.corvetteforum.com/show...60832#poststop

 

Here is a really nifty tire size calculator that will let you choose and compare different tire sizes.

http://www.miata.net/garage/tirecalc.html


Not only does it give you all the measurements, ie diameter, circumference and revs per mile, but it even tells you the speedometer difference between the 2 tires. For example, if you plug in 225/70 15 for your stock tire and 235/60/16 as your new tire, it tells you: "Speedometer reading with nonstock tire is 1.1% too fast. When your speedo reads 60 mph you are actually traveling 59.3 mph"

 

Does anyone know the overall diameter of original F70/15 Firestones.

 

Size: F70-15

The stuff below is from the Coker website on the F70-15 tire

Construction: Polyester/Fiberglass
Overall Diameter: 26.90
Cross Section: 8.30
Tread Width: 6.50
Load Capacity: 1500 @ 32 psi
Tubeless
For Your Corvette: See Wheel Package
Details
SKU 62450
Weight 31.00 lbs
Size Full F70-15
Price: $ 154.00

 

This forum has been so helpful for the short time that I have been here. More information than I thought I would receive. Thanks.