Spedo is correct....

[misfitt006]

Well I got my new 285's put on last night!!! WOOHOO!!!! I LOVE them! The give the truck such a different look and I'm already riding higher even without putting on my Ford keys yet. Now here is my question. My town is VERY strict on speed limits and have the roadside radar trailers all over that tell you the speed limit and how fast you are going. This one in particular has been parked in the same spot for about 4 days and every time I drive past it, it is dead on with my speedometer. I put the bigger tired on it and then went to drive past with to self calibrate my speedometer and it was still dead on accurate with the radar. Is this normal? I was expecting between 3-5 mph difference gong from 265's to 285's. Anyone else have this experiance? Should I also assume that my odometer is still correct??

[BlenderWizard]

I went from 260/70's to 265/70's and my speedo was off a good bit

[Rollingbones]

If you're worried, take it to the dealership and ask them to adjust the speedometer and make sure you get a receipt and keep it in the truck in case you get pulled over. (I beat a ticket once a long time ago on a simular issue.) If the cop tells you you were doing one thing and you felt you weren't, the receipt will help tyou fight it, but just the same the dealership will be able to figure it out. BTW, I went from 255.75.R16 to 285.60R18 and the height of my tire went up by over an inch. Fortunatly I have a Hypertech and was able to correct it immediately.

[misfitt006]

Originally Posted by Rollingbones

If you're worried, take it to the dealership and ask them to adjust the speedometer and make sure you get a receipt and keep it in the truck in case you get pulled over. (I beat a ticket once a long time ago on a simular issue.) If the cop tells you you were doing one thing and you felt you weren't, the receipt will help tyou fight it, but just the same the dealership will be able to figure it out. BTW, I went from 255.75.R16 to 285.60R18 and the height of my tire went up by over an inch. Fortunatly I have a Hypertech and was able to correct it immediately.

Yeah I called the local dealer and they said they can adjust it for $45 but as much as I trust dealers they'll look at it, find that it's right and still charge me $45 or try to tell me that they found problems they can fix for $800 like Alan Jackson says....lol I'm getting my Nelson in February so I might just wait until then.....

[Rollingbones]

Yeah, that's a bust..45 bones for a three minute job!!! So much for Mister Goodwrench. Just hold the speed back by 2-3 mph in town and about 3-5 on the fwy. Do expect you miledge to appear to drop though if it's off as you'll be travelling a bit further than you vehicle thinks it is, but on the brighter side you'll log a few less miles on your odometer. But anyway, congrats on the tires. When I put my 285's on it was a world of differance in the feel how it rides on the road and cornering improved tremendously. I'm really happy with them. They're also rated for the speed of "H", which is 130 mph!!!

[misfitt006]

Originally Posted by Rollingbones

But anyway, congrats on the tires. When I put my 285's on it was a world of differance in the feel how it rides on the road and cornering improved tremendously. I'm really happy with them. They're also rated for the speed of "H", which is 130 mph!!!

Yeah it's like night and day!! I love how much higher I'm sitting, I haven't noticed any cornering difference but I haven't had to chance to drive them much yet. I was impressed with the fact that they are so quiet as well. I hear almost no difference at all between the new ones and the old ones. Can't wait for my Ford keys so I can get the alignment done so it'll stop drifting to the left....

[jethro_3]

Go to some of the tire websites, (Discount Tire) and do the tire size calculator. It can tell you how far off the speedometer will be...