revs/mi.

[SCooper]

I am needing the revs/mi. for BFG 315's the book says it is 601 which is way off ! Any help would be appreciated. TIA

 

[XJSuperman]

601 is NOT way off. I had 315's on my '04 4x4 and it was exactly right ... varified with GPS AND 2 other vehicles traveling with me.

 

[Gunnernmybike]

You know, I've seen several different answers to this question. I just had my speedo recalibrated the other day and the tech set it at 610 rev/mile. I think he just punched in the tire size and thats what the computer spit out.

 

[SCooper]

well at an actual speed of 65 mph my speedo said I was doing around 75 mph. I guess if it is going to be off it is better to be to fast than to slow!

 

[grfraz]

With my BFG 315's I had the tech enter 604 rev's pm based on info found here and other sites. Mine is dead on.

 

[XJSuperman]

SCooper... I honestly don't see how your speedo is 10 MPH off IF the delaer did indeed set it for 601 revs. Maybe by 1-2 MPH at most... but not 10.

My money is on they messed it up as that's WAY off.

 

[SCooper]

If 601 is indeed correct than it could be the fact that it was done by a service writer but a tech came over and checked it after he was done. The tech , I think , changed something. But Monday I am going back to have my usual tech look at it. so I will let you know what I find out then.

 

[JVolpe]

Well 601 is the BFG Specification for rpm for 315/70R/17 All-Terrain T/A tires. I think this is based on optimum rim width (8. 5-10), 50psi inflation, 45mph and a overall diameter of 34. 5". All of these specs can be somewhat different, my rim 8", tire inflation 45psi, etc. The overall diameter as best as I can come up with on mine is not quite 34. 4".



I spoke with equivalent Ram owner with same setup as mine. He used 605 and said checked it multiple times with GPS and was as close to exact as he could get.



I have mine at 605 and checked OD many times on straight Interstate against mile markers for 10 and 20 mile stretches. I have never been more than 1/10 of mile off. This is close enough for me.

 

[XJSuperman]

Well 601 is the BFG Specification for rpm for 315/70R/17 All-Terrain T/A tires. I think this is based on optimum rim width (8. 5-10), 50psi inflation, 45mph and a overall diameter of 34. 5". All of these specs can be somewhat different, my rim 8", tire inflation 45psi, etc. The overall diameter as best as I can come up with on mine is not quite 34. 4".



I spoke with equivalent Ram owner with same setup as mine. He used 605 and said checked it multiple times with GPS and was as close to exact as he could get.



I have mine at 605 and checked OD many times on straight Interstate against mile markers for 10 and 20 mile stretches. I have never been more than 1/10 of mile off. This is close enough for me.

It'd be close enough for me too... but I really think someone messed up when they did SCooper's truck. The difference between 601 and 605 revs is not 10 MPH. That's the only explanation I can think of.

 

[JVolpe]

XJSuperman I agree completely. 601 or 605 should be very close. The dealer must have made a mistake on the reprogramming. Unfortunately need the Dodge DRBIII tools to do this.

 

[sag2]

If you want exact REV/Mile use the following. It gives you exact rev's and takes into account tire pressure and rim width etc.

Put a dab of grease on the tread, roll truck so the grease spot hits the ground twice. Measure distance between center of the spots (lets assume 104 inches).

The number of inches in a mile is 63,360 (12 inches times 5,280). Divide 63,360" by distance between spots, 104", and you get rev's per mile. 63,360/104=609 revs/mile.

 

[grfraz]

I would be willing to bet you that the tech did save changes before backing out and unpluging the DRB.