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How hard is it and what tools are needed (e.g. computer programmer) to downgrade/upgrade the computer to know the size of the wheels put onto a 370z?
For instance, if I buy a package with the 19" wheels and want to put 18" wheels on it, the speedometer, odometer, tripometer, oil estimates, etc. would all be off due to the difference in 1" of diameter. So, what can I do to reprogram the computer to know that it has 18" instead of the 19"... or visa verse.
How hard is it and what tools are needed (e.g. computer programmer) to downgrade/upgrade the computer to know the size of the wheels put onto a 370z?
For instance, if I buy a package with the 19" wheels and want to put 18" wheels on it, the speedometer, odometer, tripometer, oil estimates, etc. would all be off due to the difference in 1" of diameter. So, what can I do to reprogram the computer to know that it has 18" instead of the 19"... or visa verse.
Thanks!
Hang on, I'm about to blow your mind. How about using a tire with a taller sidewall so that the 18" wheel/tire combination is the same height as the 19" wheel/tire?
Using fancy maths, you can take the stock 19" wheel/tire heights, which are 245/40WR19 (front) and 275/35WR19 (rear) and calculate the total height, OR you can just use the same tire size that Nissan does with their 18" wheels, which are 225/50WR18 (front) and 245/45WR18 (rear). Notice that the second number on the 18's is bigger? That's the tire's aspect ratio.
O.K., here's the deal - the total circumference of the wheel and tire will stay the same. If the wheels are an inch smaller in diameter, a tire size will be spec'd that has taller sidewalls. No adjustments are necessary.
How hard is it and what tools are needed (e.g. computer programmer) to downgrade/upgrade the computer to know the size of the wheels put onto a 370z?
For instance, if I buy a package with the 19" wheels and want to put 18" wheels on it, the speedometer, odometer, tripometer, oil estimates, etc. would all be off due to the difference in 1" of diameter. So, what can I do to reprogram the computer to know that it has 18" instead of the 19"... or visa verse.
Thanks!
you sure are living up to your user name.
considering it would be nothing you would be able to buy online, i would say it would be impossible for you to do this by yourself. plus if you do the wheels/tires correctly (using th eonline tire size calculators) you woud not need to "reprogram" anything.
__________________ "There's a sucker born every minute" P. T. Barnum
ok, thanks for all the assistance. to tell you the truth, i was un-aware of the height-aspect ratios when it came to tires. I know of the different numbers on the tires and speed ratings, but never really knew how they all fit together.
i apologize if this seemed like a stupid question, but thanks for the lesson in math.
Maybe just go up on the side wall size from 35's to 40's.
Actually,I think it depends. The benefits I see in using larger wheels is being able to fit big brakes in there, more compliant ride. If you down size slightly is like changing gear ratios in the drive train, and there is less inertia and it is lighter. So you may gain some acceleration. But the overall contact patch is changed too.
So actually, I would be curious how you would change the speedo, etc. to compensate for a smaller overall diameter?
If you want to keep the same overall diameter I found this for you....
" Virtually every vehicle manufactured since 1992 is equipped with an electronic speedometer that uses a sensor to read vehicle speed rather than a mechanical cable. The speed signal is also a big factor in the overall performance equation. When tire height and / or axle gearing is altered, the vehicle's Engine and Powertrain Control Modules receive an erroneous speed signal. This translates into subtle, yet real reductions in performance and fuel economy.
Our TruSpeed calibrator addresses all speed signal-related problems; it doesn't just correct the speedometer. How? The TruSpeed module installs in-line with the factory electronic speed sensor and converts the wrong speed signal into the correct one for your vehicle's new tire and / or axle gear ratio combination. Because the signal is altered at its source, all speed-sensitive vehicle systems will receive the correct speed data, which restores all proper functions. The TruSpeed is available for most domestic and import vehicles equipped with an electronic speedometer"
ok, thanks for all the assistance. to tell you the truth, i was un-aware of the height-aspect ratios when it came to tires. I know of the different numbers on the tires and speed ratings, but never really knew how they all fit together.
i apologize if this seemed like a stupid question, but thanks for the lesson in math.
I personally would NEVER go larger but might go smaller diameter. You may even be left with a situation where you want to keep your stock wheels and go with a lower aspect ratio tire, thus changing the overall diameter as well.
You might want to go 40 series sidewall (40% of 245mm). So, 245mm * .40 = height of sidewall. Take that number times 2 then add the 18" for the wheel and you should get the overall diameter.
Last edited by newtkindred; 02-03-2009 at 07:39 AM.
Downgrading 19" to 18" wheels?
you sure are living up to your user name.
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