New Tires, Should I Get Computer Re-flashed?

Paul58 · July 5, 2007

I just replaced the stock 245/70-17 General Tires with 255/75-17 Bridgestone H/L Alanza Tires. The new tires are about 31.5" tall (about 2" taller than the originals). I checked the speedometer against my GPS and when the speedo reads 70 mph, the GPS is registering 71 mph. I'm guessing it was probably averaging about 67-68 mph when the speedo was reading 70 mph before the tire swap. Will this have any effect on the transmission shift points? Just curious if it's worth a trip to the dealer or should I just leave as is? Thanks for the help.

Nice rig · July 5, 2007

You have to think that it will make your odometer be off as well. Your tranny shift points will be alright, just get the speedo calibrated. On a side note, what size travel trailer is that in your pic...nice.

Paul58 · July 5, 2007

You have to think that it will make your odometer be off as well. Your tranny shift points will be alright, just get the speedo calibrated. On a side note, what size travel trailer is that in your pic...nice.

Thanks! It's just a tad under 24' and only weights 4900 lbs fully loaded. It pulls nice behind the truck.

Now, another question that I hadn't thought of till you brought it up... If the speedo was reading 2-3 mph less than actual with the original tires, was the odometer actually accurate? I would think it the speedo is only off by 1 mph now that the odo would be closer to accurate. I guess I'll check on my ride home and see if the odo turns over with the mile marker or before. I certainly don't want to be racking up more miles than I've actually traveled, less wouldn't be a bad thing...

zozmanGMC · July 5, 2007

Your old tires were 245/70/17. You replaced them with 255/75/17. Your speedometer is 5.1% too slow. When your speedometer reads 60 mph, you're actually going 63.1 mph. Your best option was to replace the original tires with 255/70/17 which would have been only 1.8% too slow, at 60 mph you would be going 61.1 mph.

You should have replaced your stock tires and wheels with 245/55/20 which would have been 60.2 mph at 60 mph.

By the way, my stock 2007 GMC came with 265/70/17 which I replaced with the Alenzas at 275/55/20 for a speedometer error of less than 1%.

zoz

Paul58 · July 5, 2007

Your old tires were 245/70/17. You replaced them with 255/75/17. Your speedometer is 5.1% too slow. When your speedometer reads 60 mph, you're actually going 63.1 mph. Your best option was to replace the original tires with 255/70/17 which would have been only 1.8% too slow, at 60 mph you would be going 61.1 mph.

You should have replaced your stock tires and wheels with 245/55/20 which would have been 60.2 mph at 60 mph.

By the way, my stock 2007 GMC came with 265/70/17 which I replaced with the Alenzas at 275/55/20 for a speedometer error of less than 1%.

zoz

When I set my cruise control to 70 mph, my GPS shows I'm actually going 71 mph. I have to assume that with the stock tires the GPS would have shown I was going less than 70 mph when the speedo showed 70. I wanted a taller tire, and when I compared sizes on Tire Rack's website, the 255/75-17's were a tad bit taller than the 265/70-17's I was looking at and had the same tread width. I went taller mainly for looks, and 5 tires were way cheaper than tires and wheels! In fact, Indy tire gave me such a great deal, I got 5 255/75-17 Alanza's, mounted and balanced with road hazard for $425.00! They had $125 in rebates and gave me a $65.00 credit per tire for the OEM Generals. I really couldn't pass on the deal. The ride is awesome, I'm just wondering if it's worth my time and expense to have the dealer service department make an adjustment to the ECM if my speedometer is only 1 mph slow, according to my GPS? The ride on these tires is awesome as well, way smoother and quieter than the stock tires.

zozmanGMC · July 6, 2007

No, getting your computer re-flashed for 1 mph difference is a waste. If you had stabiltrack in a car with wider than stock tires, yes. Your truck and you won't notice the difference as your equipment indicates.

zoz

wdidn · July 8, 2007

No, getting your computer re-flashed for 1 mph difference is a waste. If you had stabiltrack in a car with wider than stock tires, yes. Your truck and you won't notice the difference as your equipment indicates.

zoz

With your new tires being about two inches taller than your old ones it seems your speedometer show you going faster than you really are by maybe 4mph. I had 265/70/17 and went to 285/50/20 and the height difference is about 3/8 of an inch taller on my new set, which puts me at about 1 mph difference. The taller the tire from the originals means less actual miles on your odometer.

Paul58 · July 9, 2007

No, getting your computer re-flashed for 1 mph difference is a waste. If you had stabiltrack in a car with wider than stock tires, yes. Your truck and you won't notice the difference as your equipment indicates.

zoz

With your new tires being about two inches taller than your old ones it seems your speedometer show you going faster than you really are by maybe 4mph. I had 265/70/17 and went to 285/50/20 and the height difference is about 3/8 of an inch taller on my new set, which puts me at about 1 mph difference. The taller the tire from the originals means less actual miles on your odometer.

Actually, it's the other way around. When my speedometer is reading 70 mph, my GPS shows my actual speed is 71 mph. When I clock the odometer to the highway mile markers, my odometer is only hitting .9 of a mile when I pass the next mile marker. So, I am traveling farther than what the odometer is registering by .1 mile, but I'm traveling faster than the speedometer reads by 1 mph. I'm hoping this can be corrected when I get my custome tune doneby Wait4Me Tuning. But if not, it's not off enough to cause me much concern. I know the tire calculater showed a significant difference between the OEM 245/70-17's and the 255/75-17's I replaced them with, but when I measure the actualy height of the new tires they are only 31.25" tall, not 32.?? the tire calculator showed.

If you look at the specs on Tire Rack, you'll see the same size tires from different manufactuaers actually vary in size by as much as an inch! The new tires are 2+" taller than the original ones on the truck, so I have to question how far off the speedometer and odometer was to begin with!

There have been a few law suits lately against Toyota and Honda because the odometers were off and it was costing customers who leased vehicles money due to excessive miles because of the discrepancy in the odometer. I suspect all cars and truck are the same. I know my Nissan Frontier regitered 68 mph on the GPS when the speedometer was dead on 70 mph! This was with the OEM 265/75-16 tires.

rswithds · July 9, 2007

No, getting your computer re-flashed for 1 mph difference is a waste. If you had stabiltrack in a car with wider than stock tires, yes. Your truck and you won't notice the difference as your equipment indicates.

zoz

With your new tires being about two inches taller than your old ones it seems your speedometer show you going faster than you really are by maybe 4mph. I had 265/70/17 and went to 285/50/20 and the height difference is about 3/8 of an inch taller on my new set, which puts me at about 1 mph difference. The taller the tire from the originals means less actual miles on your odometer.

Actually, it's the other way around. When my speedometer is reading 70 mph, my GPS shows my actual speed is 71 mph. When I clock the odometer to the highway mile markers, my odometer is only hitting .9 of a mile when I pass the next mile marker. So, I am traveling farther than what the odometer is registering by .1 mile, but I'm traveling faster than the speedometer reads by 1 mph. I'm hoping this can be corrected when I get my custome tune doneby Wait4Me Tuning. But if not, it's not off enough to cause me much concern. I know the tire calculater showed a significant difference between the OEM 245/70-17's and the 255/75-17's I replaced them with, but when I measure the actualy height of the new tires they are only 31.25" tall, not 32.?? the tire calculator showed.

If you look at the specs on Tire Rack, you'll see the same size tires from different manufactuaers actually vary in size by as much as an inch! The new tires are 2+" taller than the original ones on the truck, so I have to question how far off the speedometer and odometer was to begin with!

There have been a few law suits lately against Toyota and Honda because the odometers were off and it was costing customers who leased vehicles money due to excessive miles because of the discrepancy in the odometer. I suspect all cars and truck are the same. I know my Nissan Frontier regitered 68 mph on the GPS when the speedometer was dead on 70 mph! This was with the OEM 265/75-16 tires.

Is their a chart somewhere for this?

jrtrip · July 11, 2007

I personally would just get a power programmer and change your wheel height which will fix the speedometer issue. Hypertech makes a fairly reasonably priced one.

Capt.Slim-Jim · July 27, 2007

Changed tires from stock to 35" after a lift kit.

Installed Hypertech chip and programmed it with the actual height of the tire afte installed on the truck and loaded as I would normally drive it.

It is dead on when I pass the Police speed trailers that they set up in "problem" speed areas

DannyS · September 19, 2007

Changed tires from stock to 35" after a lift kit.
Installed Hypertech chip and programmed it with the actual height of the tire afte installed on the truck and loaded as I would normally drive it.

It is dead on when I pass the Police speed trailers that they set up in "problem" speed areas

If you are getting a tune from Wait4me, Jesse will be able to correct that. Just let him know what stock tire size was and what you have now.

DannyS · September 19, 2007

Changed tires from stock to 35" after a lift kit.
Installed Hypertech chip and programmed it with the actual height of the tire afte installed on the truck and loaded as I would normally drive it.

It is dead on when I pass the Police speed trailers that they set up in "problem" speed areas

If you are getting a tune from Wait4me, Jesse will be able to correct that. Just let him know what stock tire size was and what you have now.

Paul58 · September 19, 2007

Changed tires from stock to 35" after a lift kit.
Installed Hypertech chip and programmed it with the actual height of the tire afte installed on the truck and loaded as I would normally drive it.

It is dead on when I pass the Police speed trailers that they set up in "problem" speed areas

If you are getting a tune from Wait4me, Jesse will be able to correct that. Just let him know what stock tire size was and what you have now.

I ended up getting the Edge Evolution and that took care of the problem! All is good now!