285's and speedo

[silveradoreb]

Is there any way other than buying a hypertech to re calibrate for 285's? Thanks

[Tungsten]

Yeah you can either buy the Diablo which is $419.00 Or buy the Jet thingy thats like $159.00 The part # for summitracing is...... Jet-50108

[canadianchevy33]

I think your dealer should be able to recalibrate your speedo for you. I don't no up to what size of tire they can recalbitrate up to but im sure they could for a 285.

[MountaineerTom]

Unless they have changed recently, the dealers can't recalibrate for 285's. I can't remember exactly, but they can either only go as high as 265's or can only reprogram for tires sizes that are avaialable on the truck. Either way, 265's are the biggest offered from the factory.

[Wingnut]

Unless they have changed recently, the dealers can't recalibrate for 285's. I can't remember exactly, but they can either only go as high as 265's or can only reprogram for tires sizes that are avaialable on the truck. Either way, 265's are the biggest offered from the factory.

They have not changed...I was in to get new fogs, and take care of the "steering clunk" on Friday. I asked if they would re-calibrate for my 285s. They said that they wished they could. But nope.

 

Good thing I went in Friday too...My odometer rolled past 36k on Sunday.

[chvythndr]

Is there any way other than buying a hypertech to re calibrate for 285's? Thanks

Superchip! But I wouldn't recommend any programmers unless you're using them for much larger tires. Your spedo can't be off that much w/ 285s. I got the SC b/c I put 36s on my truck, am going to regear to 4.56s soon, and wanted the upgrades performace. These 3 things made the $300 worth while.

[rtbrick]

I have recently put 285s on my stock rims and also wondered how much the speedo might be off. Some have mentioned that it is off by as much as 5-7 miles an hour. Well, I am in the Army and live on a military installation. One speeding deterent that the Provost Marshall uses are those side-of-the-road radar trailers. You know, the ones that display your speed as you approach. The trailer that has sat just down the street from me has shown that my speedo is only off by 1 mph at around 25 mph. Does the difference between speedo reading and actual speed increase as speed increases?

[speedshifter]

I've got 265/70-17s on some stock escalade rims for my '97 Yuke and was able to re-calibrate it with a Tech 2. If I can do it, you dealer can too.

 

I'm not sure if the choices went as high as 285s, but there were a ton of sizes to choose from. I'll have my dad bring home the Tech 2 tonight from work and ill look it up on my truck.

 

rtbrick, if you put taller tires on your truck, the speedo will read slower than you are actually going. For instance, your speedo might say 30mph, but you might actually be doing 35mph.

[Redapple]

If you change from 265's to 285's your error would be 3.7% on the slow side.

 

Example:

 

@ 60 MPH indicated you will actually be traveling at 62.2 MPH

 

IMHO not enough error to worry about. But if you want to recalibrate, any of the programmers will do it. Superchips, Hypertech, etc.

 

 

Bill

[Firetiger(MN)]

Does the difference between speedo reading and actual speed increase as speed increases?

Yes, it does. The speed difference is not linear so the faster you are going, the more you'll be off. I had 285's on my '02 HD which came with 245's. It was off about 5 mph at 70.

[speedshifter]

see, thats important for me. I do a lot of highway driving. In Michigan, for instance, speed limits are 70mph and most people do 85~90mph. If doing 85~90 according to the speedo, but actually doing 95ish, thats a big deal and could be the difference between the cop not thinking twice and a hefty ticket.

 

i haven't had time to look at the tech 2 yet. ill let you know what I find out.

[Redapple]

To calculate the error, all you have to do is multiply the indicated speed by the total error.

 

Example:

 

Error @ 60MPH indicated

60 * 1.037 (amount of error) = 62.22 MPH Actual Speed

65 * 1.037 = 67.405 MPH Actual Speed

70 * 1.037 = 72.59 MPH Actual Speed

75 * 1.037 = 77.775 MPH Actual Speed

80 * 1.037 = 82.96 MPH Actual Speed

85 * 1.037 = 88.145 MPH Actual Speed

 

The total error over 10,000 miles would be 370 miles

The total error over 100,000 miles would of course be 3700 miles

 

These examples are based on changing from 265's to 285's

 

Hope this helps

Bill