Factory speedo adjustment for different size tires?

On older models where you could get either 225x15 or the 31x10.5 tires --- the cars were differently geared. Newer models have computer controlled speedos so suspect it would be a simple reprogramming.

So for vehicles with computer controlled speedos, do Toyota dealers offer this reprogramming for customer's who change tire size, gearing, etc.? I've seen the (fairly expensive) inline devices for adjusting speedometers, but if the main computer is programmable (and assuming the programming is accessible to a technician) it would seem to make these devices obsolete.

Their are different speedo gears for different size tires. Unfortunately they also usually have different driven gears. Not all speedo drive gears and driven gears will mate up, so you will probably have to buy both.

Don't expect your local parts guy to be very enthusiastic about looking this stuff up, Toyota only offers the stock setups, but with all the different rear ratios and tires sizes a little looking will probably get you what you want. For late model trucks, the T100 is a good place to start because they had some really wild rear ratios.

My understanding of what Wolfgang was saying is that the newer speedometers aren't adjusted through physical gears, but instead through programming. Which makes perfect sense - this approach should be both cheaper to produce and more flexible. I was just wondering if that programming is accessible after the truck leaves the factory.

Yes, it is. A speedo shop can calibrate for you, so it would obviously be possible to DIY with the proper equipment.

--- Rich