CAUTION.... Tire sizes are not what they actually are!

[ISLAND DARK HORSE]

For those of you trying to maximize tire contact patch, or just monkeying around with different tire brands….Be cautious and do your homework.



I’ve been a huge fan of Goodyear Supercar 3R’s and have used them on all my track cars. 305 up front – same as the OE Pirelli Trofeo RS. OE rear is 315 RS. So I took a look under the rear fender and it appeared to have enough room to accommodate a 325 Goodyear (not available in 315/19). It’s only 10mm more right? Well, when the tires arrived I was shocked how the tires differed in size. The tread area of the Goodyear is significantly larger and the side wall and overall tire width is also larger.



I can still make them work. They are going on Apex VS-5RS forged wheels. 19x11 & 19x11.5. Up front I need to run a 5mm spacer to clear the strut. I need at least 2 degrees of negative camber not to hit the fender. For me, this is not an issue as I typically run 4 or 5 degrees at the track and 2.5 on the road. The rear fits without spacers, but I like running negative camber there as well, so I may need a 5mm spacer there as well to clear the damper. For someone like me that was trying to get a big a tire as I could under there, this was actually a bonus for me. I’m just lucky they fit.



Do your research first. I didn’t and it almost bit me. Just because tires have the same advertised sizing doesn’t necessarily mean they will be the same physically.

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[timd38]

Great information! Tire Rack typically provides all the specs, so you can compare them. I did that when I bought winter tires for my wife’s car.

 

[robvas]

Great information! Tire Rack typically provides all the specs, so you can compare them. I did that when I bought winter tires for my wife’s car.

Do they actually measure them or just calculate them from the advertised size?

 

[timd38]

Do they actually measure them or just calculate them from the advertised size?

Two different brand can have two different diameter as an example. You can also find different diameter in different models of the same brand

 

[robvas]

Two different brand can have two different diameter as an example. You can also find different diameter in different models of the same brand

I know that.

but does Tire Rack post the actual measured sizes on their site?

 

[ISLAND DARK HORSE]

I'm assuming, but I doubt it. They more than likely reference the manufacturer's specs.

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