Incorrect speedo with oversize tires...

1BADAWD · 10-02-09, 09:11 PM

Okay i have an 86 toyota pickup, it has 32's and of course the speedo does not read the right speed because of the wheels. What can i do to correct the speedo being off?

2ndGenToyotaFan · 10-02-09, 09:42 PM

I don't know if there's some little gear box that you can buy to install between the speedo cable and transmission.... but regearing your differentials to compensate for the tires would do it... Or you could just remember that you're going 14% faster than shown on the dash... (assuming you have 4.10 diffs and it came with 28 inch tires...) That's what most people do...

NorCalBorn · 10-02-09, 10:20 PM

Even better, auto or manual transmission? (No I'm not stupid, I realize you most likely have the 4 or 5 speed, but this'll help for searches later.)
*From what I have seen..things are always a little different sometimes, but this should all be correct for up to 1995 vehicles.

There's different gear outputs for the manual that you can swap in and avoid the whole speedo correction gearbox nonsense.

IIRC you probably have a 17-18 tooth and want a 19.

The bolt that holds the speedo output is on top of a small plate and is a 10mm. Unbolt it, look at the plastic gear to get your count, then step it up however many teeth to correct things.

IE: My R150 came with the newer output and 31 teeth for 28" tires. I wanted to run 31's.

31"/28"=1.1071429

1.1071429x31t=34.32143..33t being the closest I had available.

So, let's say you have gone similarly, from 28's to 31's and have a 18t output..

31"/28"=1.1071429

1.1071429x17t=18.821429.. go with the 19t since it'll put you closer than a 18t would.

Make sense?

If it's an auto, you can do similar, but only if it's a 4wd version, as the 2wd's tailshaft assembly uses a different style output that is not interchangeable.
(4wd=Transfer case, all the transfer cases use the same output as the manuals do.)

alteredraptor · 10-02-09, 11:46 PM

im his buddy, we both went out today and got it... it is a 5sp manual... while on the highway the truck said i was doin 65 but in actuallity i was really doin like 75... im just confused on why someone would put 32s on it... and hopefully tomorrow well find out the gearing, and we will also check the teeth and that little gear

1BADAWD · 10-02-09, 11:54 PM

Quote:

Originally Posted by NorCalBorn

Even better, auto or manual transmission? (No I'm not stupid, I realize you most likely have the 4 or 5 speed, but this'll help for searches later.)
*From what I have seen..things are always a little different sometimes, but this should all be correct for up to 1995 vehicles.

There's different gear outputs for the manual that you can swap in and avoid the whole speedo correction gearbox nonsense.

IIRC you probably have a 17-18 tooth and want a 19.

The bolt that holds the speedo output is on top of a small plate and is a 10mm. Unbolt it, look at the plastic gear to get your count, then step it up however many teeth to correct things.

IE: My R150 came with the newer output and 31 teeth for 28" tires. I wanted to run 31's.

31"/28"=1.1071429

1.1071429x31t=34.32143..33t being the closest I had available.

So, let's say you have gone similarly, from 28's to 31's and have a 18t output..

31"/28"=1.1071429

1.1071429x17t=18.821429.. go with the 19t since it'll put you closer than a 18t would.

Make sense?

If it's an auto, you can do similar, but only if it's a 4wd version, as the 2wd's tailshaft assembly uses a different style output that is not interchangeable.
(4wd=Transfer case, all the transfer cases use the same output as the manuals do.)

Yeah that makes sense man. We'll check a few things out tomorrow or sunday. Overall im pretty happy with the truck. Im used to having the speedo off cuz a previous car of mine was 10mph off, but its just bothersome. Thanks for the responses. If you have anymore ideas, please post up.

2ndGenToyotaFan · 10-03-09, 10:06 AM

Not 10 mph off, it's a ratio. 32" tires are 14% larger than the stock tires. 0 mph on the speedo is still 0 mph in the truck. 14% of 65 mph is 9.1........ 9.1 + 65 = 74.1

Make sense?

1BADAWD · 10-03-09, 12:00 PM

Yes that makes complete sense. Thank you. Thats what i meant i was just using basic terms, lol.

NorCalBorn · 10-03-09, 03:38 PM

As to the reason you pose about why would someone use 32's on a truck/4Runner..

Well, the ratio 4.56 is for 31's and 4.88 is for 33's. Toyota did not make 4.73's so if you wanted a little more clearance like you would get with 33's, but did not want to fork out for a 4.88 swap, you ran 32's back in the day. In fact, you'd be surprised how many of us can and do still run the (now harder to get a hold of) BFG TA-KO 32's. I almost ran them, but like the usable power band instead. A lot of expedition folks are pretty much using 32's just usually in metric form rather than inch. Basically, I still might eventually end up on 32's for just this reason. Yeah, only a half-inch ground clearance change, but they do air down to a little better pattern. Besides, my odo would only be slightly under, 63mph vs. 65mph.

If you like the power band, the tire size, etc, stick with it.

alteredraptor · 10-03-09, 11:14 PM

i know i like it... i checked the gearing for him and the plate under the hood says it has 4.10... my 87 runner has the same gearing, with 31's but it sux on the highway

1BADAWD · 10-03-09, 11:40 PM

Yeah the truck def. drives good. I was just looking for future ideas for the speedo being off. Thanks guys.