Speedo bad or just the way...

[John M]

My '96 Ranger does have larger tires 225/70 15", OE was 225/70 14". The odometer has stopped and I know what will fix that. Speed has been checked by GPS is OK to 35mph from there it gets worse the faster you go. 55 on speedo = 60, 59 = 65, 63 = 70. Is this 'normal' for oversized tires or is there something else wrong? I am willing to replace the whole cluster or just the worm gear. Whatever will help the most. Looked at alot of posts none seemed to have this issue. Thanks!!

 

[adsm08]

That's the error produced by the bigger tires. Your old tires were about 26.4 inches diameter. The new ones are 27.4. That's a 7% difference, give or take. 63/70=.9, so your speedo is about 10% off, and the allowed error is about 3%, so it was as close as it was going to get before, now it's farther.

There should be a speedo drive gear that can be changed to correct this on that year. The formula is New Teeth = (Current Teeth x Speedo Reading)/Actual Speed.

 

[John M]

So simple when you know the formula. I thought there would be a variance at lower speeds too, but as a % it would be too small under 40 to notice. I bought it this way will probably just get smaller rubber when needed. My odometer will be off by 10% also... Thanks, feel like the previous owner thought 225-14 =225-15 were same.

 

[John M]

Has anyone tried one of these? http://www.ultra-gauge.com/ultragauge/ I tried my Diablo tuner to correct for tires but the tuner was to smart or the Ranger was to dumb. The Ultra gauge says it will work...