Is there a way to adjust the computer (mileage, odometer, speedometer, etc.) to accomodate larger tires in the calculations?

 

How big are you thinking?

 

Here's a very slick little calculator for tire size results when changing from stock. This is from a Mazda Miatta message board - but the calcs will work for virtually all automobile tires.

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

It's really very clever!

Hope this helps!!

 

When you say larger tires, what do you mean? Larger as in physically larger in diameter than what's stock, or wider but keeping the diameter the same? I went to wider 235x70-16 (from the 225x70-16) on my 99 RX and this only adds fractions of an inch to the overall diameter and clears the wheel well and suspensions.

Main concern here shouldn't be what to do with the computer, but whether getting a much larger tire is going to clear your steering/suspension components. Typically you would increase to a larger size wheel (say 17" or 18") but keep the same width and decrease the aspect ratio to have the "same" size overall wheel.

Anyway, there's plenty of information on plus sizing and you can go onto tirerack.com and read up on it.

Good luck.

 

I think your train of thought is wrong.

You can't alter the size of the wheel and tire (see explanation) and then try to accomodate the altered size with the computer adjustment, which co-oncidentally can't be adjusted for such a process.

Explanation- altering the factory size wheels and tires CAN be done with success, provided you maintain the same overall diameter of wheel and the suspension/ fenders can be cleared, while keeping in mind offset... Out2L8 provides a handy chart for calculating such alternate tire/wheel sizes.

The car is engineered to a certain spec for a specific tire diameter and width, when you alter the tire size you change many more things, than just the odomoter, speedomoter and general handling caracteristics.

The ability to save a few bucks with an anternate (read more readily available) tire size may be more costly down the road...

All the above said, I understand that 235/70-16 has been used by other Club Lexus members with success.

Cheers,
Fern

 

I have put P235/70R16 instead of the P225/70R16's. A buddy of mine has a Jeep Grand Cherokee and he replaced a chip to accomodate the larger tires so the readings on fuel ecoinomy, etc. are correct. According to the calculator that OUT2L8 put the link to (THANK YOU!!!), I will be going 65.2 MPH when the Speedo reads 60. That's a bigger difference than I thought it would be.

Thanks everyone for your posts,
Pete

 

Actually, you will only be going 61.2mph with your new tires when your old tires would have indicated 60. Taking into account that most speedometers read 3%-5% fast, you should still be going slower than your indicated speed.

 

The RX300 speedometer shows 1 mph higher than the actual speed. I've checked mine against many road side speed radars. So when the speedometer shows 75 mph, I am actually going 74 mph.