I purchased a 1988 Ford Ranger extended cab, the speedometer is off, the tires are 205/75 15's is this the correct size?

These are all the tire size options that your vehicle could be equiped with from the factory
4x2

195/70R14
215/70R14
225/70R14

4x4

215/75R15
235/75R15
265/75R15

usually there is a sticker on the drivers door that will have the original tire size on it. If that sticker is missing you can allways try calling a Ford dealer and see if they can tell by running the VIN number thru there data base.

I’m happy to assist further over the phone at https://www.6ya.com/expert/jeremy_d728a59f986299fa

I believe there were two options 15-22 but i'm sure you can find out by filling it when its almost empty

With enough talent and enough money and enough time, pretty much anything is possible.

I know a fellow that put 5.0 in an older Ranger without any huge problems.

It'll be interesting! Have Fun!

You need to replace the speedo gear on your transmission or differential with the correct gear ratio to compensate for the size of tires your running. Maybe call a 4x4 store or truck accessories store for parts.

Wrecking yard (or as there called up here, automotive recycling) or dealer is the only place. My question, why the entire line?

You would need to have all 4 the same size. Cant mismatch sizes 1 or 2, will through off abs etc. If you change all 4 it will affect your speedometer. If larger tires put on you will actually be going slower than speedometer says. If you can live with being off say 2 to 5 mph, all is well.

What engine size and is it a 4X4 and king cab? Have you checked the driver's door sticker? 225/70/15 is only 1 option.

Should be a diagram on hood, or upper rad support of your vehicle, if not, get back to me with engine size.

most certainly a speed sensor problem!
it may not be pulsing properly or the drive gear is worn etc etc.
Cheers Rob

I have a '88 Ranger XLT extra cab 4X4 w/auto tranny (2.9L V6) that had a 2-piece driveshaft on it. After adding a 4" suspension lift, there was a strong vibration whenever I took off from a dead stop. I replaced the drive shaft with a beefed up 1 piece custom built by a shop specializing in drive shafts. The truck no longer had any vibration, and it hooks up immediately on exceleration. I found the shop on Ebay advertising drive shafts. All I had to do was measure the length from the transfer case/Tranny to the rear differential. The length of the new drive shaft allowed me to adjust almost 3/4" so all I had to do was get it close. I also took close up pictures so the shop could match up the correct flange on both ends of the driveshaft. The last thing I had to do was flip the crossmember brace so it wouldn't interfere with the new drive shaft.