Different size tires on pickup

Lamont in NC · Oct 26, 2015

I've been running for a few years now with P245/70R16 tires on the front and P235/75R16 tires on the back of my 2001 GMC Sierra. They're pretty close on diameter when I've used Tirerack's comparison tool. No ill effects noticed.

I assume the speedometer is based on driveshaft speed--correct?

I've also wondered how this affects the ABS system. I'm fairly certain it's 3 channel on this truck meaning the rear is again based only on driveshaft rotation vs individual rear wheels. I'm in need of 2 new front ones and again found a great deal on P245/70R16 tires. Comments?

stevob671 · Oct 26, 2015

Speedometer Won't matter too much if close to original size or not 4WD. If 4wd, you want same size front and rear or there is strain on driveline and shifting in/out of 4wd can be difficult. Keep the same size on same axle though. I'm not sure about the abs functionality...

MSM · Oct 26, 2015

Your speedometer is controlled by a tone ring with a sensor on the ring gear.(on most vehicles)Your ABS is controlled by sensors on each wheel. If the front to rear tire diameter is dead on or no more than 5% or so off the ABS will do what it is supposed to do. It basically monitors the rpm of each wheel. If you hit the brakes and one wheel or one axle slides,the rpm drops,the ABS computer will modify the braking force to that wheel/axle. This is the pulsing you feel when you hit the brakes hard.

Mark - IN. · Oct 26, 2015

As I recall, tire tire size is in pretty good shape up or down a size. It seems to me that if you go to a tire dealer, their info suggests as much.

I remember reading an article in a 4x4 magazine back in the '90's about fellas getting their lift kits so that they could put huge monster mudders and the like on, you know the 44 inchers and the sort without having their truck's computers downloaded for the new much larger diameter and then having the ABS since 1988 be thrown way off, and then trying to come to a stop and driving up the back of someone's car because of computer miscalculation.

Mark

Lamont in NC · Oct 26, 2015

Mine's 2wd. But your right, doing this on a 4x4 wouldn't work well.

Sprint 6 · Oct 26, 2015

Your truck is three channel, with the rear being figured off the sensor and tone ring on the trans output shaft. There is no sensor in the axle, Ford and Dodge use sensors on the rear ring gear. Your truck's ABS is pretty sensitive on the front channels by design. If you have not noticed any false ABS activations, you must be close on loaded diameter. Personally, I like all tires the same so they can be rotated.

mj · Oct 26, 2015

(quoted from post at 16:21:23 10/26/15) ...........If 4wd, you want same size front and rear or there is strain on driveline and shifting in/out of 4wd can be difficult...........

Reverse direction for 10 or so feet to relieve 'torque bind'. 8)

Different size tires on pickup

Lamont in NC

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stevob671

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MSM

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Mark - IN.

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Lamont in NC

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Sprint 6

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mj

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