Adjusting the Speedo/Odo after tire size swap

[Iakona]

I apologize in advance if this is on the forum somewhere and I missed it. I am trying to figure out what the maximum tire circumference you can program into the vehicle systems via ForScan without it rejecting it. The original circumference is 2316 mm and the new one is 2434 mm. I am trying to figure out if anyone knows how close I can get to the new circumference without the modules rejecting the new value. I am trying to avoid the insert and see method and doing that multiple times. Thank you for any and all help.

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[bgn]

I believe 235/65R17 is the max it'll do without erroring out. This should be selectable via the "ez mode" instead of providing millimeters in one of the modules.

 

[Iakona]

That is correct. I already have that size selected as I have a Tremor that I upsized the factory tires to the 245/70 so I was trying to figure out what the maximum MM value the computer would accept. At 65, I am actually doing 68-69. I just wanted the speedo and odo to be a little more accurate if possible. Thanks for your help though.

 

[OleKennyRoy]

Hmm, so I had the opposite experience. I had the dealer install the new tires. I expected the speedo to be slow, but it's actually 1 MPH fast at 70. I went from 225/60R18 to 235/65R17. It makes me think they did the adjustment, and it's off.

 

[colinl]

Hmm, so I had the opposite experience. I had the dealer install the new tires. I expected the speedo to be slow, but it's actually 1 MPH fast at 70. I went from 225/60R18 to 235/65R17. It makes me think they did the adjustment, and it's off.

did you see reply #2?

your tires could be set to 235/65-17 and 1 mph at 70 could be explained by many things, not the least of which being gps inaccuracy or variations in actual tire dimensions vs listed/advertised dimensions. (BFG KO2s are notoriously undersized as one example. There probably are some tires slightly larger than spec.)

the OP has a size significantly larger diameter than 235/65-17 and I agree with bgn. the tire diameter cannot be set larger.

 

[Iakona]

did you see reply #2?

your tires could be set to 235/65-17 and 1 mph at 70 could be explained by many things, not the least of which being gps inaccuracy or variations in actual tire dimensions vs listed/advertised dimensions. (BFG KO2s are notoriously undersized as one example. There probably are some tires slightly larger than spec.)

the OP has a size significantly larger diameter than 235/65-17 and I agree with bgn. the tire diameter cannot be set larger.

That's what I am wanting to know from others who have done what I have done. What is the largest value that can be typed into the tire circumference, the value is in mm, that the computer will allow without making all the systems go bonkers. I am not referring the the predetermined selectable tire sizes that are in easy mode. Maybe they can't be different, who knows, but that is what I am trying to find out.

 

[OleKennyRoy]

So, I updated the circumference and now I have an AWD fault... I guess I'll try the Forscan subforum to see what everyone else is doing

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