Oversize tires = drive ability issues?

CactusJackSlade

Active member
I am running 285 70/17 BFG Ko2's (probably the biggest tires you can possibly run without a lift??!)

The only other mod is the Van Compass stage 4 kit: New shocks all around, rear leaf spring helper kit (levels the rear end back to stock height) and sumo spring helper bumpers up front.

I was just into the dealer and had them check the front collision warning system (not working) and also I've been struggling with the dreaded "turbo lag" or hesitation off the line when rolling to almost a stop and accelerating again - sometimes a HUGE lag, so bad it has been scary at times pulling into traffic. I even tried the Pedal Box with very little improvement.

My speedo is about 9% off at 70 mph (at 70 mph my GPS says 75)

The dealer is blaming both issues on the "inability of the computer to tell the real speed of the vehicle". I mean really? At almost a stop the real vs sensed speed would be off by like maybe 1/4 mph??!

One of my requests was to see if they could correct the speedo for my tire size, they said there is no way to correct for a different tire size?

Is this all correct?... or is my dealer just not knowledgeable enough?
 

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gltrimble

2017 170 4x4
I am running 33” tires on my 170 4x4. I am seeing about 8% difference in the speedometer. From everything posted on this forum it is unlikely the dealer will correct the speedo error. I prefer not to make the correction since it raises my governed top speed another 5 mph.

Regarding the acceleration lag or stumble, this was a problem on my van even with the smaller factory tires. I installed the Pedalbox+ and the van accelerates as one would expect from a dead stop even with larger tires and maximum GVW. Did you purchase the newest version of the Pedalbox+? I am surprised you did not see an improvement. I set my Pedalbox+ to Sport mode (yellow).



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CactusJackSlade

Active member
I am running 33” tires on my 170 4x4. I am seeing about 8% difference in the speedometer. From everything posted on this forum it is unlikely the dealer will correct the speedo error. I prefer not to make the correction since it raises my governed top speed another 5 mph.

Regarding the acceleration lag or stumble, this was a problem on my van even with the smaller factory tires. I installed the Pedalbox+ and the van accelerates as one would expect from a dead stop even with larger tires and maximum GVW. Did you purchase the newest version of the Pedalbox+? I am surprised you did not see an improvement. I set my Pedalbox+ to Sport mode (yellow).



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Thanks for the reply :)

Humm, my tires measure 32.7" Yes, I have the latest version of the PedalBox + from Van Compass.

I am going to install a new fuel filter and do a transmission fluid change and see if that does anything (due to be changed anyway).

My other concern is the forward collision warning system should still work??!.... I think the Dealer just can't figure it out and is blaming the tire size on everything.

...Yes, great to get another few MPH on the speed governor ;-)
 

gltrimble

2017 170 4x4
My Cooper ST Max tires are officially 32.8”. Replacing them this week with 33.1” tires.


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OffroadHamster

Well-known member
Im running true 33's (9% error) and have not had any problems with front collision warning system. Lag is a fact of life and the hesitation when near stop and then hitting it is universal as far as I can tell.
 

err

Member
I bet you have a failed sensor affecting your forward collision system. It’s fairly common.

I’ve been running oversized tires since 1000 miles, now at 54,000, and have had no issues.
 

CactusJackSlade

Active member
I bet you have a failed sensor affecting your forward collision system. It’s fairly common.

I’ve been running oversized tires since 1000 miles, now at 54,000, and have had no issues.
Thank you, yeah i too think a sensor is out
 

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