Go Back   iRV2 Forums > TRAVEL TRAILER, 5th WHEEL & TRUCK CAMPER FORUMS > Trailer Towing and Tow Vehicles Discussion
Click Here to Login
Join iRV2 Today

Mission Statement: Supporting thoughtful exchange of knowledge, values and experience among RV enthusiasts.
Reply
  This discussion is proudly sponsored by:
Please support our sponsors and let them know you heard about their products on iRV2
 
Thread Tools Search this Thread Display Modes
 
Old 01-30-2014, 08:57 PM   #1
Junior Member
 
Join Date: Feb 2012
Posts: 11
Upping wheel and tire size

I have a Ram Cummins with 17in wheels and 31.7in dia tires. I want to go to 18 in wheels. The tires go from 70 to 65 but are still 1 in larger in dia.
My question is what will this affect?
__________________

__________________
kohana is offline   Reply With Quote
Join the #1 RV Forum Today - It's Totally Free!

iRV2.com RV Community - Are you about to start a new improvement on your RV or need some help with some maintenance? Do you need advice on what products to buy? Or maybe you can give others some advice? No matter where you fit in you'll find that iRV2 is a great community to join. Best of all it's totally FREE!

You are currently viewing our boards as a guest so you have limited access to our community. Please take the time to register and you will gain a lot of great new features including; the ability to participate in discussions, network with other RV owners, see fewer ads, upload photographs, create an RV blog, send private messages and so much, much more!

Old 01-30-2014, 09:13 PM   #2
KIX
Senior Member
 
KIX's Avatar


 
Join Date: Dec 2006
Location: St. Augustine, FL
Posts: 3,579
Quote:
Originally Posted by kohana View Post
I have a Ram Cummins with 17in wheels and 31.7in dia tires. I want to go to 18 in wheels. The tires go from 70 to 65 but are still 1 in larger in dia.
My question is what will this affect?
1. Speedometer and odometer
2. Warranty if that's still an issue
3. Engine RPMs will be lower for a given speed
4. Potentially tire scrubbing
5. The higher the lift (more air space under truck) the lower the MPG

I know that's only 5 but that would be enough to dissuade me from only a 1" diameter increase. Good luck
__________________

__________________
KIX
'02 Ultimate Advantage 40J Spartan MM - Cummins ISC
2013 Jeep Rubicon JK Unlimited
KIX is offline   Reply With Quote
Old 01-31-2014, 05:58 AM   #3
Senior Member
 
wandering1's Avatar
 
Join Date: Nov 2007
Location: NC
Posts: 450
Send a message via ICQ to wandering1
Run the tires identified on the plate inside the door jamb.
__________________
Wandering1
wandering1 is online now   Reply With Quote
Old 01-31-2014, 07:00 AM   #4
Senior Member
 
Join Date: Apr 2004
Posts: 1,078
Hmmm not much tech info for a good answer other than a generally speaking.

I see BFG All Terrains in a LT265/65-18 E at 31.7" diameter.

The 70 psi to a 65 psi is confusing but IMO your talking derating your OEM E tires to a D load range on a 2500/3500 Dodge/Cummins which IMO isn't a wise idea for tires carrying heavy loads. Your Dodge/Cummins came with a 10 ply rated (load range E) at 80 psi for good reasons.
The D tire at only 65 psi is a softer sidewall tire and can lead to carcass roll when carrying heavy loads.

Nothing wrong with 18" tires and wheels in the proper load range. They are OEM on the newer SRW Rams and a option on the 2500 trucks.
__________________
'03 Dodge 2500 Cummins HO 3.73 NV5600 Jacobs
'98 3500 DRW 454 4x4 4.10 crew cab
'97 Park Avanue RK 28' 2 slides
JIMNLIN is offline   Reply With Quote
Old 01-31-2014, 07:55 AM   #5
Senior Member
 
Franka548's Avatar
 
Freightliner Owners Club
Retired Fire Service RVer's
Join Date: Apr 2011
Location: N E Ohio
Posts: 3,451
JimnLin,
I think the OP was talking about the series of the tires, not the psi, going from a 70 series to a 65 series

Kohana,
I agree with JimnLin that you should be able to find a tire that has the same OD or at least very close. Just make sure that the new rims are the correct width for the tires that you choose, and that the load rating on the new tires and wheels is at least the same or greater than the ones that you take off.
Frank
__________________
05 Alfa Gold 40' Motor Home "Goldie" 03 Malibu Toad towing 4 down
03 Silverado cclb 3500 drw, D/A, Reese 22k hitch
07 Alfa SeeYa Gold 30RL,2 slides,power everything Above for sale PM me for details
Franka548 is offline   Reply With Quote
Old 01-31-2014, 09:03 AM   #6
Senior Member
 
caissiel's Avatar
 
Join Date: Oct 2011
Posts: 1,312
I went from 265/70/17 tires on the F250 for load and wear reasons. I could not find load index higher then 121 compared to my previous truck with 16 in tires.
18 in tires are optional on my truck so I changed to 275/70/18.
At first I inflated to 75 psi with load on and they were very comfortable compared to the 17s. As I always aired my tires to 80 psi with load on.
But now I do air them to 80 psi and the ride seam to be similar loaded to the 17s.
I did find that my truck feels much better at 65 mph compared to 62 before the change.
I never had a speed calibration problem as I just programmed in the OD tire size in my Hypertech Max Energy programer.
The truck looks much better as these tires fills the fenders much better and the trailer rides as well as ever.
I do have to be careful not to drive harder to keep the fuel consumption down.

275/70/18 will give a load index of 126 or 3750 lbs and 275/65/18 only give an index of 123 or around 3300 lbs.
__________________
Barbara and Laurent, Hartland Big Country 3500RL. 39 ft long and 15500 GVW.
2005 Ford F250 SD, XL F250 4x4, Long Box, 6.0L Diesel, 6 Speed Stick, Hypertech Max Energy for Fuel mileage of 21 MPusG empty, 12.6 MPusG pulling the BC. ScangaugeII for display..
caissiel is offline   Reply With Quote
Old 01-31-2014, 09:40 AM   #7
Senior Member
 
jimcumminsw's Avatar
 
Join Date: Dec 2010
Location: Oswego IL
Posts: 1,257
Quote:
Originally Posted by kohana View Post
I have a Ram Cummins with 17in wheels and 31.7in dia tires. I want to go to 18 in wheels. The tires go from 70 to 65 but are still 1 in larger in dia.
My question is what will this affect?
You may want to look at 19.5 tire and rim package for your truck instead of the 18" size. Several members of Turbo Diesel Register. Com use this size of tire to tow with on their trucks; here is a link to a thread on that site.
http://www.turbodieselregister.com/forums/showthread.php?245711-19-5-quot-Tire-Selection
These seem to provide the necessary loading requirements when towing a 5er that is heavy. The one who is posting is using a 3500 SRW 05 Ram truck.
Jim W.
__________________
Jim & Jill
Sold: 2010 318SAB Cougar:New: 2016 Cedar Creek 34RL. 2008 Dodge 6.7LCummins the original 6.7L engine, w/68RFE Auto
jimcumminsw is offline   Reply With Quote
Old 01-31-2014, 11:00 AM   #8
Moderator Emeritus
 
SmokeyWren's Avatar


 
Join Date: Jun 2011
Location: Midland County, Texas
Posts: 3,328
Quote:
Originally Posted by kohana View Post
I have a Ram Cummins with 17in wheels and 31.7in dia tires. I want to go to 18 in wheels. The tires go from 70 to 65 but are still 1 in larger in dia.
My question is what will this affect?
You don't say why you want to go from 17" to 18" tires. Assuming it just the image (looks) of the tires/wheels, then here's the scoop.

Wheel diameter does not make a difference. Tire diameter does - or more specifically the tire revolutions per mile (revs/mile), which is calculated from the rolling radius of the tire. The taller the tire, the fewer revs/mile.

Calculate the percentage difference in revs/mile. That same percentage difference will apply to your speedometer, odometer, and trip meter. And it will also apply to the effective rear axle ratio.

Example:

Your tires have revs/mile of 656. So if you can find an 18" tire with revs/mile of 656, then there will be no change in your speedo/odo/tripmeter or axle ratio.

Aha! Here's one: BFGoodrich All Terrain T/A KO LT265/65R18E.

Or if for example, you want a Michelin LTX AT/2 tire, then the closest they have is LT265/70R18E with 637 revs/mile.

656 minis 637 = 19
19 divided by 637 = rounded 0.03 = 3%

So a 3.83 axle ratio would "feel like" 3.83 minus 3% = rounded 3.72. Not a huge difference but definitely a small reduction to your towing power.

And assuming your speedo/odo/tripmeter are accurate now:

70 MPH indicated would be 70 + 3% = 72 actual speed on Officer Bob's radar.

400 miles on a tankful of fuel per the tripmeter would be 400 + 3% = 412 miles

40,000 miles on the odo would be an actual 41,200 miles.

With the right tool, you can calibrate your speedo/odo/tripmeter to be accurate again. But the loss of towing power will stay with you unless you change the ring gear and pinion in the differential(s).
__________________
Grumpy ole man with over 50 years towing experience. Now my heaviest trailer is a 7,000-pound enclosed cargo trailer, RV is a 5,600 pound Skyline Nomad Joey 196S, and my tow vehicle is a 2012 F-150 3.5L EcoBoost SuperCrew.
SmokeyWren is offline   Reply With Quote
Old 01-31-2014, 05:49 PM   #9
Junior Member
 
Join Date: Feb 2012
Posts: 11
Thanks for all the input. I was referring to the series of tire. My reason for going to 18 in tires is for the load increase. A visit to Discount Tires confirmed that 285/65 18 tires will fit on my truck with no interference issues. These tires are rated at 3640 lb giving me almost another 900lb of cushion over my 265/70 17s, but they are 1" bigger in outside dia.They will make my feel better when I'm working my through the Rockys for the summer.
However, another issue has occurred to me. Can I use my 17 " spare being 1" smaller in OD for a short run to tire shop no 4 wheel drive?
__________________
kohana is offline   Reply With Quote
Old 01-31-2014, 06:57 PM   #10
Senior Member
 
caissiel's Avatar
 
Join Date: Oct 2011
Posts: 1,312
I plan to find a proper sized spare but for now I am not to concerned as in 20 years of towing I have only had one flat. I will install it up front for a short emergency run.
My 18 in tires are about $18 difference in price from 17 in. Not sure if series 65 will be as well priced.
The 275 series work well on my F250 and not sure of the 285 series clearance.
__________________
Barbara and Laurent, Hartland Big Country 3500RL. 39 ft long and 15500 GVW.
2005 Ford F250 SD, XL F250 4x4, Long Box, 6.0L Diesel, 6 Speed Stick, Hypertech Max Energy for Fuel mileage of 21 MPusG empty, 12.6 MPusG pulling the BC. ScangaugeII for display..
caissiel is offline   Reply With Quote
Old 01-31-2014, 09:50 PM   #11
Moderator Emeritus
 
SmokeyWren's Avatar


 
Join Date: Jun 2011
Location: Midland County, Texas
Posts: 3,328
Quote:
Originally Posted by kohana View Post
However, another issue has occurred to me. Can I use my 17 " spare being 1" smaller in OD for a short run to tire shop no 4 wheel drive?
Sure, but two rules:

1] Mount the spare on the front axle only. If your tire problem is on the rear axle, then move a tire from the front axle to the rear, then mount the spare on the front axle.

2] NEVER put the truck in 4-wheel-drive while you have that mismatched tire size on the front axle.
__________________
SmokeyWren is offline   Reply With Quote
Old 01-31-2014, 10:17 PM   #12
Senior Member
 
caissiel's Avatar
 
Join Date: Oct 2011
Posts: 1,312
Not everyone can do that as some have no free wheeling hubs or axles.

Sorry Ram is one that has problem with the free drive shaft if 4x4 application.
__________________
Barbara and Laurent, Hartland Big Country 3500RL. 39 ft long and 15500 GVW.
2005 Ford F250 SD, XL F250 4x4, Long Box, 6.0L Diesel, 6 Speed Stick, Hypertech Max Energy for Fuel mileage of 21 MPusG empty, 12.6 MPusG pulling the BC. ScangaugeII for display..
caissiel is offline   Reply With Quote
Old 02-01-2014, 05:49 AM   #13
Senior Member
 
onechaddude's Avatar
 
Join Date: Jul 2011
Posts: 1,540
Quote:
Originally Posted by caissiel View Post
Not everyone can do that as some have no free wheeling hubs or axles.

Sorry Ram is one that has problem with the free drive shaft if 4x4 application.
It is still not turning in the transfer case unless you put it in four wheel drive. That's where it would bind up with different size tires. And even then, if surface was slick, (ie, snow ice) it would just slip a little and you would never know it as close as size is.
Chad
__________________
onechaddude is offline   Reply With Quote
Old 02-01-2014, 09:22 AM   #14
Senior Member
 
caissiel's Avatar
 
Join Date: Oct 2011
Posts: 1,312
Quote:
Originally Posted by onechaddude View Post

It is still not turning in the transfer case unless you put it in four wheel drive. That's where it would bind up with different size tires. And even then, if surface was slick, (ie, snow ice) it would just slip a little and you would never know it as close as size is.
Chad
My remarks were aim at the wear inside the differential with axles turning at different rpm. The balancing gears would turn.
__________________

__________________
Barbara and Laurent, Hartland Big Country 3500RL. 39 ft long and 15500 GVW.
2005 Ford F250 SD, XL F250 4x4, Long Box, 6.0L Diesel, 6 Speed Stick, Hypertech Max Energy for Fuel mileage of 21 MPusG empty, 12.6 MPusG pulling the BC. ScangaugeII for display..
caissiel is offline   Reply With Quote
Reply



Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Winterized Class C Has a Flat Tire bhounds Class C Motorhome Discussions 3 01-31-2014 05:12 PM
Checking MH tire pressures with/without removing wheel covers? mikecosgrove Forest River Owners Forum 3 01-22-2014 01:01 PM
06 Knight upgrading to larger steer tires? Rob-K Monaco Owner's Forum 11 11-28-2013 04:57 AM
The LAST goodyear tire I will ever own Ramblin Just Conversation 37 09-09-2013 08:01 PM

» Virginia Campgrounds

Reviews provided by


Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -6. The time now is 01:25 PM.


Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.