Jump to content
Mopar1973Man.Com LLC

  • Welcome To Mopar1973Man.Com LLC

    We are a privately owned support forum for the Dodge Ram Cummins Diesels. All information is free to read for everyone. To interact or ask questions you must have a subscription plan to enable all other features beyond reading. Please go over to the Subscription Page and pick out a plan that fits you best. At any time you wish to cancel the subscription please go back over to the Subscription Page and hit the Cancel button and your subscription will be stopped. All subscriptions are auto-renewing. 

New Tire Size found 235's to 245's

Mopar1973Man
 Share

Recommended Posts

  • Owner
Mopar1973Man

Mopar1973Man

Posted
  • Author
  • Owner
Posted (edited)

Remember higher the ratio number the higher in the RPM for said speed. This is why I'm running a pair of junk tires on the back of my truck for about a month to find out if I like the ratio or not. So far I love this 245's set up and think the 215's on the 1/2 ton will be awesome too.

Edited by Mopar1973Man
Link to comment
Share on other sites
Marcus2000monster

Marcus2000monster

Posted
Posted
1 minute ago, Mopar1973Man said:

Remember higher the ratio number the higher in the RPM for said speed. This is why I'm running a pair of junk tires on the back of my truck for about a month to find out if I like the ratio or not. So far I love this 245's set up and think the 215's on the 1/2 ton will be awesome too.

The main reason I want bigger tires is lower rpm which means more mpg right? I’m thinking 3:69 is going to be the cats meow. I can obtain that ratio with the 285/75/17. 

Link to comment
Share on other sites
  • Owner
Mopar1973Man

Mopar1973Man

Posted
  • Author
  • Owner
Posted (edited)

Actually, you want to optimize your RPM so your highway travel is around 1,900 to 2,000 RPM.

 

Most of this comes from @cajflynn back in the day his old 2001 Dodge was a 3.73 ratio axle and towed like a dream. Then after see all the 3.55 geared truck and 37" tire troubles. Why I was not really messing with tire sizes. Now after a bit a experience and I'm jumping out to optimize the tires to gears to make the best setup. Remember bigger tires have more rolling resistance especially with 285mm wide face then with all the steel belt you going to have more rotational mass. Just be aware.

 

@Marcus2000monster

I would in your case follow my lead and find a pair of junk tires on the rear axle to play with first before committing on tire purchase. 

 

Like I could do a 215/85 R16 on my truck my problem is I will most likely overwhelm the tires with the amount of torque I produce. So, on the Cummins I'll stick with 245/75 R16 which is a 1 wider than the 215's. I had to change my fuel map for daily driving the fuel comes on too quick and the tires lose the battle pretty fast. 

Edited by Mopar1973Man
Link to comment
Share on other sites
Marcus2000monster

Marcus2000monster

Posted
Posted
6 minutes ago, Mopar1973Man said:

Actually, you want to optimize your RPM so your highway travel is around 1,900 to 2,000 RPM.

 

Most of this comes from @cajflynn back in the day his old 2001 Dodge was a 3.73 ratio axle and towed like a dream. Then after see all the 3.55 geared truck and 37" tire troubles. Why I was not really messing with tire sizes. Now after a bit a experience and I'm jumping out to optimize the tires to gears to make the best setup. Remember bigger tires have more rolling resistance especially with 285mm wide face then with all the steel belt you going to have more rotational mass. Just be aware.

 

@Marcus2000monster

I would in your case follow my lead and find a pair of junk tires on the rear axle to play with first before committing on tire purchase. 

 

Like I could do a 215/85 R16 on my truck my problem is I will most likely overwhelm the tires with the amount of torque I produce. So, on the Cummins I'll stick with 245/75 R16 which is a 1 wider than the 215's. I had to change my fuel map for daily driving the fuel comes on too quick and the tires lose the battle pretty fast. 

According to spicers calculator I would be at 2035 average rpms at 70 mph.

Link to comment
Share on other sites
Marcus2000monster

Marcus2000monster

Posted
Posted
2 minutes ago, Mopar1973Man said:

 

Link please I want to see this calc...

https://spicerparts.com/calculators

I may be wrong but I calculated by entering the new gear ratio hat the tires would make. I entered 3:69 for the R&P ratio and 34 inches for tire height (calculated at tire size website) and 70 mph for speed limit.

Link to comment
Share on other sites
SilverMoose

SilverMoose

Posted
Posted

Not to throw a stick in the spokes but I am very anal when it comes to precision.  I've been in some sort if engineering my entire career and precision is required for that.  I have the hypertech programmer to adjust my tires size.  I think that 33.25" is going to be the correct size for my new tires which are advertised as 33.9".  You will lose some diameter when tires are on a vehicle.  I do this to verify that my odometer matches GPS readings.  My last set if tires, I was right around 2100 rpm's at 71 mph. I'm estimating I will be around 2000 with my new tires.

 

L8tr

D

Link to comment
Share on other sites
Marcus2000monster

Marcus2000monster

Posted
Posted
20 minutes ago, SilverMoose said:

Not to throw a stick in the spokes but I am very anal when it comes to precision.  I've been in some sort if engineering my entire career and precision is required for that.  I have the hypertech programmer to adjust my tires size.  I think that 33.25" is going to be the correct size for my new tires which are advertised as 33.9".  You will lose some diameter when tires are on a vehicle.  I do this to verify that my odometer matches GPS readings.  My last set if tires, I was right around 2100 rpm's at 71 mph. I'm estimating I will be around 2000 with my new tires.

 

L8tr

D

Just what I’m lookin for. 2k @ 70

  • Thanks 1
Link to comment
Share on other sites
  • Staff
AH64ID

AH64ID

Posted
  • Staff
Posted
16 minutes ago, SilverMoose said:

My hypertech use 1/4" diameter increments so I'm stuck with that.

 

Just convert rev/mile to inches. 

 

5280/(rev/mile)/3.14x12= diameter in inches. 

 

The ECM uses rev/mile anyhow, the hyper tech just does the conversion. 

 

Link to comment
Share on other sites
Scottfunk

Scottfunk

Posted
Posted

FYI Grimmjeeper.com has a much more in depth calculator that anything else I've seen. It will give you the actual final drive ratio (trans, r&p, tire size), speed at a given rpm, RPM's at a given speed, plus some other stuff if you want it.

  • Thanks 1
Link to comment
Share on other sites
Russ Roth

Russ Roth

Posted
Posted
On 7/14/2018 at 3:18 PM, SilverMoose said:

@Scottfunk  I just went out and did some highway driving after installing a new VP44.  With my 285/75/17's I was turning 2060 rpm at 71 mph.  I was probably mistaken in my last post about turning 2100 at 71 with my 285/70/17's  It was probably 2150.

 

L8tr

d

 

I made the point of checking mine yesterday on the way to Eugene.  62 on cruise was 1810 rpm and 70 was 2030 so we are close.  That was give or take a few rpm either way since the roads are not 100% totally flat causing rpm to fluctuate a bit as you drive but these are pretty good numbers for my rig.

Link to comment
Share on other sites
 Share
Go to topic listing
×
×
  • Create New...