Can I replace 255/70/17 tires with 235/56_17 and be alright?
I think you mean 235/65/17. Thats getting too narrow and a lower profile, I wouldn't do it. It will change the handling, ride comfort, fuel consumption, and load carrying capabilities. It you must do something don't go less than a 245/70/17, you need to maintain the tire profile. If it were mine I would put 265/70/17 on it.
235 is shorter than 255. The 235/ in a 65 series tire is even shorter than the difference between 235 & 255. In lue of 255/70 the 2nd number to make tire wider needs to drop and to be same height the first number needs to rise. Example: 265/65 or 275/65.
Don't do it.
Yes you can. the first number 255 or 235 is the width, and has nothing to do with the height of the tire. You will lose 20mm of width -or- 3/4". Not a big deal. The secoind number is the aspect of the sidewall height in relation to that width. To remain close to the same height, you would want to go with a, perhaps, 235/75-17. This get's you to a height that is about 1/2-5/8" of the original size . The reason yo udon't want to go overboard on tire height difference is because, this of course affects how many times you tires turns, for the same distance traveled. This affects your service reminders, speedometer and anthing else that is distance-based on a car. the difference in size here though is only reflected in you reading 1/4mph difference overall so,.. not a big deal. Narrower tires on an SUV/Truck give you better performance in snow, where you do not want flotation, -vs- say, mud, wher you want a wider tire FOR flotation. You will usually see better gas mileage with a narrower tire but in this case, the size is so close as to not matter either way. No idea why you would want to do this but,.. that's not what you asked. You asked if you could and the answer is that it would be no change in safety etc.
In reference to the above,.. plug in your current and future numbers here: https://www.tacomaworld.com/tirecalc?tires=255-70r17-235-55r17
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