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help with Race Tire size 39" or 40"?

MTPyle

Well-Known Member
Guys,

We are going with Toyo for 2020 season and having a hard time with which tire to run. The two choices are 40x12.5 or 39x13.5

we can fit either but I am wondering the performance difference? our truck is not as wide as a TT so I would think the wider tire would help with stability? Our truck has a higher CG than most as well. so I worry about making it too tall with the 40"

I see many 40" tires were 13.5 and then they went to 12.5. Whats the advantage of narrow vs wide?

Have anyone ran both of these to know the difference?

the 39" is more like 38.5 and the 40 is true 40" so the height is pretty big difference. I think the 40" is heavier.

Below is a pic of our truck with BFG 40" on it. the 40" look pretty bad a$$


Thanks!!
Mike
 

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MTPyle

Well-Known Member
This got moved to the shop area? I ask a question about racing and it gets moved?

I guess I should have put Robby in the title. Maybe ask what tire should Robby run and then it might be worthy of the desert racing area?

haha so stupid.
Mike
 

MTPyle

Well-Known Member
Haha I wish it was that easy. I can’t afford to buy both and test. Need to make best guess and go with it.

although I just found out the 40” and 39” are both 13.5. We fit BFG 40x12.5. I don’t know if we can fit 40x13.5. The 40x12.5 were pretty tight. So that might force the choice.

bummer as the 40” is a newer design than the 38”
Mike
 

crazyeye

Well-Known Member
Haha I wish it was that easy. I can’t afford to buy both and test. Need to make best guess and go with it.

although I just found out the 40” and 39” are both 13.5. We fit BFG 40x12.5. I don’t know if we can fit 40x13.5. The 40x12.5 were pretty tight. So that might force the choice.

bummer as the 40” is a newer design than the 38”
Mike
Now what about tread design? Are you running the standard mid terrain design or the r/t 's that bj runs?
 

crazyeye

Well-Known Member
Haha I wish it was that easy. I can’t afford to buy both and test. Need to make best guess and go with it.

although I just found out the 40” and 39” are both 13.5. We fit BFG 40x12.5. I don’t know if we can fit 40x13.5. The 40x12.5 were pretty tight. So that might force the choice.

bummer as the 40” is a newer design than the 38”
Mike
Now what about tread design? Are you running the standard mid terrain design or the r/t 's that bj runs?
 

MTPyle

Well-Known Member
the 40" is heavier than the 39" the 40" is a new design, not sure what that means. LOL

We are not sure we can fit 40"x13.5" we test fit the BFG but they are 40"x12.5" not sure the extra 1" will clear. the BFG was tight.

Mike
 

michael.gonzalez

Well-Known Member
39/40 = .98
(39/40)^2 = .95

40/39 = 1.03
(40/39)^2 = 1.05

There is only about a 2-5% difference when you consider diameter only. Not a huge swing but I guess it is still a slight advantage/disadvantage.
 

MTPyle

Well-Known Member
Thanks!

Just found out that all the Toyo guys were running the Toyo 39" at B1K including Ampudia who won. So that answers that question. LOL 39" it is.

Mike
 

MAC56

Well-Known Member
I have more than a dozen BFG 39 KR that are new that will soon be for sale and at least that many good used ones, new motor an changing to 40 KR3 on TT56.
 

MTPyle

Well-Known Member
Thanks Mac, we are for sure going with Toyo. What Motor you going to?

Mike
 
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