345/30/19 effect on 3.07 ratio??

[Tommy K]

Anyone know the effect of the taller wheel/tire on the final ratio? Or know of threads for reference? TIA

Tom

 

[ViperJoe]

Taller tires equal a higher (numerically) ratio.
In essence more of a top end or highway gear.

Although I really don't think it has that much of an efect going from 18-19 ecept on your spedometer.

 

[Tom F&L GoR]

Get your calculator.

345 is the sidewall width in millimeters. Divide it by 25.4 to get it to inches.

30 is the aspect ratio; one sidewall height is 30% of the number your calculated in step 1.

There are two sidewalls from top to bottom, so multiply by two.

Add the 19 inch for the rim diameter. You now have the diameter. Should be 27.15 inches.

Your speedo will be off by the amount that 27.15 divided by the tire diameter of what you were using.

If you were using a 335/35/17, which would be 26.23 inches, your gear would be like 26.23/27.15*3.07, or like a 2.97.

 

[Tommy K]

So, if that's true, a 3.31 rear would be like 3.2, and a 3.45 would be like a 3.33. I really liked my 3.31's in my last car. Now, what does the s/c car want? Thanks Tom

 

[PhoenixGTS]

Using this gear calculator as a guide:

gear ratio calculator

For the stock 335-30-18 which is 26.1" tall, you get the following top speeds in gears 1-4:
57, 85, 117, 152

For the 345-30-19 which is 27.4" tall, you get the following top speed in gears 1-4:
60, 90, 123, 159

You can see that the 345s result in ridiculously tall gearing. You would have to run a 9 second quarter mile to max out 4th gear.

If you run 3:54 gears with the stock tires you get these mphs:
49, 74, 101, 132

If you run 3:73 gears with the 345s you get these mphs:
49, 74, 101, 131

So having 3:73 gears with the tall tires is exactly the same as having 3:54 gear with the stock tires.

 

[Go Fast For Life]

I have the same 345/30/19 on my car and a stock 3.07 rear gear. I also have a speedo recalibrator which is set at 1.05:1 (5%) over stock 3.07 (effective rear end of 2.92). This corrects any speed problems the speedo might have.

 

[venomblue550]

so let's say going from 335/35/17 to 345/30/19, will i have speed problem if i don't do anything else?? big difference? and how can i fix the speed problem?