Reply
 
Thread Tools Search this Thread Display Modes
 
Old 05-04-2008, 05:44 AM   #1
Winnebago Owner
 
Join Date: Dec 2004
Location: wherever we are parked
Posts: 53
We have a Vectra 36 gd. We will be purchasing tires for the rig next year. We are thinking of putting a larger tire on so we can handle more weight. Has anyone increased the tire size? If so, to what size, and what other things needed to be taken care of?
Motorhome05 is offline   Reply With Quote
Old 05-04-2008, 05:44 AM   #2
Winnebago Owner
 
Join Date: Dec 2004
Location: wherever we are parked
Posts: 53
We have a Vectra 36 gd. We will be purchasing tires for the rig next year. We are thinking of putting a larger tire on so we can handle more weight. Has anyone increased the tire size? If so, to what size, and what other things needed to be taken care of?
Motorhome05 is offline   Reply With Quote
Old 05-04-2008, 06:41 AM   #3
Winnebago Owner
 
RVJeeper's Avatar
 
Join Date: Feb 2007
Location: Jacksonville, FL
Posts: 97
From what I've read, going to larger tires won't necessarily increase your weight carrying capacity. It's also the suspension, frame and all the other parts that carry the weight that more limit the capacities. Most folks that do go to larger tires do so because of a bit better ride quality and that's about all they gain. Additionally, larger tires will change the speedometer reading and consequently transmission shift points and a whole bunch of other computer controlled stuff. Bottom line: Generally not worth the expense and trouble.
__________________
Ron, Joan
2005 Itasca Sunova 34A
2004 Jeep Grand Cherokee Overland
RVJeeper is offline   Reply With Quote
Old 05-04-2008, 08:55 AM   #4
Winnebago Master
 
Tom N's Avatar
 
Join Date: Dec 2002
Location: Sarver, PA/Crystal River, FL/Shelocta, PA
Posts: 1,196
Larger tires will decrease your fuel mileage, if that is of any interest to you.

-Tom
__________________
Sarver, PA/Crystal River, FL/Shelocta, PA · FMCA 335149 · W3TLN
2005 Suncruiser 38R · W24, no chassis mods needed · 2013 Honda Accord EX-L · 2008 Honda Odyssey EX-L
[SIGPIC][/SIGPIC]
Tom N is offline   Reply With Quote
Old 05-04-2008, 10:37 AM   #5
Winnebago Camper
 
historyljc's Avatar
 
Join Date: Feb 2008
Location: Pensacola, Florida
Posts: 38
Your present size tires should handle all the weight your axles can carry. If they don't, you might want to go to a higher load range in the same size tire. One of the things you must verify on larger tires is the spacing between the duals. The flexing of the sidewalls on the larger tires may cause them to rub together. You do not want that.
__________________
Travel well, travel safe,
Jim
2006 Tiffin Phaeton - 2011 Cadillac SRX
[SIGPIC][/SIGPIC]
historyljc is offline   Reply With Quote
Old 05-04-2008, 12:33 PM   #6
Winnebago Watcher
 
ricere's Avatar
 
Join Date: Mar 2007
Location: Crewe, Virginia
Posts: 1
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Tom N:
Larger tires will decrease your fuel mileage, if that is of any interest to you.

-Tom </div></BLOCKQUOTE>

Please explain. I would figure in some cases it would increase fuel mileage instead of decreasing, to a point.

Example: 1 have 4.88 gears and 2.75/70 x22.5 tires. I plan on replacing them with 2.75/80 x22.5 tires for a softer ride and better mileage due to larger circumference tires. I know people who have done that and they improved their mileage up to 1/2 mpg.
__________________
2006 KSDP 3909
Cummins ISL 350HP
2012 F150 Crew Cab Towed
ricere is offline   Reply With Quote
Old 05-04-2008, 01:49 PM   #7
Winnebago Master
 
Tom N's Avatar
 
Join Date: Dec 2002
Location: Sarver, PA/Crystal River, FL/Shelocta, PA
Posts: 1,196
If you increase the tire footprint you'll increase rolling resistance.

A large tire size usually results in an increased footprint.

-Tom
__________________
Sarver, PA/Crystal River, FL/Shelocta, PA · FMCA 335149 · W3TLN
2005 Suncruiser 38R · W24, no chassis mods needed · 2013 Honda Accord EX-L · 2008 Honda Odyssey EX-L
[SIGPIC][/SIGPIC]
Tom N is offline   Reply With Quote
Old 05-04-2008, 03:42 PM   #8
Winnebago Camper
 
Brigadoon's Avatar
 
Join Date: Jul 2000
Location: currently in North Georgia
Posts: 5
I did change my tire size from the 275/70's to the 275/80's and had an engine rpm drop of 100 rpms at 62 miles per hour. In my case that was close to a half mile per gallon gain in mileage.
__________________
Terry
'05 Dutch Star 4015, '16 Rubicon OlllllO, & HD Ultra ElectraGlide, NKK14278L
Brigadoon is offline   Reply With Quote
Old 05-04-2008, 10:25 PM   #9
Winnebago Master
 
MrTransistor's Avatar
 
Join Date: Jan 2004
Location: Albuquerque, NM
Posts: 504
I agree with Terry, I changed from 235/80R22.5 XRV Michelins at 556 revolutions per mile to 255/80R22.5 XZE Michelins at 538 revolutions per mile when we were in the 2003 Journey. Much better handling, decreased tread wear, and a slightly increased MPG as a result. (A little stiffer ride)

In theory, the contact patch with the road should be the same if the RVs weight doesn't change and the PSI pressure of the tire is the same. Hence a larger tire will have less sidewall flexing and lower engine RPM, for lower overall drag resulting in increased MPG. Recalibrating the CAT engine computer is a snap.
__________________
Have Fun!! Mark & Donalda 04 Horizon 40WD no TOW 90,900+ miles and counting
Triumph Bonneville & Susuki S40 on the back
MrTransistor is offline   Reply With Quote
Old 05-05-2008, 11:13 AM   #10
Winnebago Camper
 
Join Date: Apr 2008
Posts: 49
before chaning tire size on your coach I would reccomend you look at body cleance with the suspension dumped it is very close on the Vectra,and might require some wheel lip mods.
NO1RAINH20 is offline   Reply With Quote
Old 05-05-2008, 05:35 PM   #11
Winnebago Camper
 
Baby Bear's Avatar
 
Join Date: May 2002
Location: Beaufort SC/ Harmony PA
Posts: 6
I feel the most important item has been overlooked. Check to see if the existing rims will take a larger tire and will there be adaquet clearance between the rear wheels.
I went up one size several years ago and got better handeling,ride and MILEAGE.( you see the diameter is larger, hence fewer revolutions per mile)
__________________
Lee,Marge Living Our Dream-Fulltiming!
Beaufort SC, Winter Harmony PA Summer
Semper Fi In God We Trust
Baby Bear is offline   Reply With Quote
Old 05-06-2008, 04:45 AM   #12
Winnebago Watcher
 
Join Date: Nov 2001
Location: Southern Illinois
Posts: 2
MrTransistor,

Could you explain about recalibrating the CAT engine computer for the larger tires? Is this something an owner can do or must I take it in to a CAT dealer? Thanks.

dreamer.
__________________
'00 Endeavor - 330 Cat
'02 Tracker - Blue Ox
dreamer is offline   Reply With Quote
Old 05-06-2008, 05:43 AM   #13
Winnebago Master
 
MrTransistor's Avatar
 
Join Date: Jan 2004
Location: Albuquerque, NM
Posts: 504
Hi dreamer,

The CAT engine (and I would figure the Cummins as well) runs software that is accessible via a Palm Pilot running a program called PocketTech. It connects to the engine port under the dash or at the engine. I have both cables, one for the older CATs and one for the newer C7s. There is a calibration value that can be set for, basically, revolutions per mile in the engine computer. It's computed a little differently between the two engines and accounts for tires, differential ratio, and transmission output pulses per revolution of the output shaft. Makes it easy to set very accurately.
__________________
Have Fun!! Mark & Donalda 04 Horizon 40WD no TOW 90,900+ miles and counting
Triumph Bonneville & Susuki S40 on the back
MrTransistor is offline   Reply With Quote
Old 05-06-2008, 07:54 AM   #14
Winnebago Watcher
 
Join Date: Nov 2001
Location: Southern Illinois
Posts: 2
MrTransistor,

Thanks for the reply. I have a 2000 Endeavor with a 3126 CAT. I also have a VMSpc which connects to the diagnostic (engine/transmission) port to my laptop computer. I can monitor alot of parameters but can I reset the callibration for the larger tires with this or do I have only a monitor for engines/transmission functions? Thanks.

dreamer.
__________________
'00 Endeavor - 330 Cat
'02 Tracker - Blue Ox
dreamer is offline   Reply With Quote
Old 05-06-2008, 12:50 PM   #15
Winnebago Master
 
Tom N's Avatar
 
Join Date: Dec 2002
Location: Sarver, PA/Crystal River, FL/Shelocta, PA
Posts: 1,196
When I stated you may lose fuel mileage I did not realize you were going to a narrower series tire.

If you went from a 70 series to a large size 70 series you'd have a larger footprint.

-Tom
__________________
Sarver, PA/Crystal River, FL/Shelocta, PA · FMCA 335149 · W3TLN
2005 Suncruiser 38R · W24, no chassis mods needed · 2013 Honda Accord EX-L · 2008 Honda Odyssey EX-L
[SIGPIC][/SIGPIC]
Tom N is offline   Reply With Quote
Old 05-06-2008, 01:26 PM   #16
Winnebago Master
 
MrTransistor's Avatar
 
Join Date: Jan 2004
Location: Albuquerque, NM
Posts: 504
Hi dreamer,

I don't know if VMSpc allows you to change the settings in the engine or not. There are quite a few parameters that can be changed for the better (IMHO).

There are others here that have the VMSpc (John Canfield comes to mind) and may be able to advise you. I have helped others to reset settings on their rigs in the past. If you will be passing through Albuquerque any time soon, I'd be glad to show you these settings and how they change the operation of the engine and transmission.

You can also have an authorized CAT dealer download the latest and greatest software to the computer and make any changes that you want to the functions.

This link explains most if not all the nifty things the engine computer can do and what you may want changed like ˜Latch' mode for the engine brake function. (leave Engine brake switch on and Engine Brake doesn't come on when you let off the gas but when you hit the brake for ½ second or more then stays on till you hit the gas again)

http://ohe.cat.com/cda/files/363929/7/Progrramming%20Pa...05%20LEXT0023-01.pdf

Here are other threads with info on the Pocket Tech (adapter and software for Palm that is no longer available from CAT), tires, and MPG.

http://irv2.infopop.cc/eve/forums/a/tpc/f/2486094452/m/...291090212#7291090212
http://irv2.infopop.cc/eve/forums/a/tpc/f/2486094452/m/...881016831#7881016831
http://irv2.infopop.cc/eve/forums/a/tpc/f/2486094452/m/...291036891#8291036891
__________________
Have Fun!! Mark & Donalda 04 Horizon 40WD no TOW 90,900+ miles and counting
Triumph Bonneville & Susuki S40 on the back
MrTransistor is offline   Reply With Quote
Old 05-06-2008, 02:01 PM   #17
Winnebago Master
 
MrTransistor's Avatar
 
Join Date: Jan 2004
Location: Albuquerque, NM
Posts: 504
Hi Tom,

I agree. If the revolutions per mile remains the same by going to a larger section, lower profile tire at the corrected inflation pressure for the wider footprint then the MPG should be slightly lower. i.e. a 235/80R22.5 to a 255/70R22.5. On the other hand if a larger tire with the same height ratio is substituted, i.e. a 255/80R22.5 for a 235/80R22.5 then the increased diameter at the correct tire pressure should yield a reduced engine RPM and will offset the increased tread contact drag for a net increase in MPG.

The drag caused by sidewall flexing should remain the same if both tires are inflated to the correct pressure for that tire and location.

Another factor is the design of the tire itself. Michelin makes specific tires for specific application. There is the XRV, which has a very soft ride. The XZE, has a very deep tread and harder rubber for long life and better handling. And the XZA3 for reduced tire drag and improved fuel economy.

I choose the XZE 255/80R22.5 for the Journey when we had it and I think they returned the price of the tires when we traded up to the Horizon. The Horizon came with XZE 275/80R22.5 and after installing the ˜Super Steer Motion Control Units' this coach handles like a Jag and rides like a Rolls. And at just over 9 MPG average I figure we may be a little limited in our journey's but we can still afford a few hundred miles a month in our retirement.
__________________
Have Fun!! Mark & Donalda 04 Horizon 40WD no TOW 90,900+ miles and counting
Triumph Bonneville & Susuki S40 on the back
MrTransistor is offline   Reply With Quote
Old 05-06-2008, 03:26 PM   #18
Winnie-Wise
 
Fakrwee's Avatar
 
Join Date: Mar 2007
Location: Carlsbad, Ca.
Posts: 310
I do a lot of 4X4 offroading and we're constantly installing taller tires. Usually if we go to taller tires we install lower gears as to not lose the power band of the motor.

I'm attaching a link to an article that even though it's for 4X4 it applies to all vehicles. Hope it helps.

This is an excerpt in case I can't link it.

Whenever larger-than-stock tires are installed on a truck, it will have a direct effect on the truck's performance. Why? It has to do with the effective gear ratio. Your truck comes from the factory with the optimum axle gear ratio to work with the truck's engine, transmission, and stock tire combination as well as provide a good balance between acceleration and fuel economy. When taller tires are installed on a truck but the axle ratios stay the same; the effective gear ratio is reduced. This means the engine is forced to operate below its power band, and performance and fuel economy suffer as a result. In order to restore the effective gear ratio (and the truck's performance), you'll need to have the axle gears swapped to lower (numerically higher) ratios.

Tires vs gears Calculation
__________________
2007 Itasca Suncruiser 33V
2009 Ford Flex Ltd. AWD Fa. Toad
2010 Jeep Rubicon offroad Toad
Fakrwee is offline   Reply With Quote
Old 05-06-2008, 06:30 PM   #19
Winnebago Camper
 
Brigadoon's Avatar
 
Join Date: Jul 2000
Location: currently in North Georgia
Posts: 5
It is probably that effective gear ratio change, caused by the larger diameter tire, that increased my miles per gallon.

The coach came equipped with 275/70's, and 4.88 gears. This had my Cummins ISL turning 1800 rpms at 62 mph. When I switched to the 275/80's, which are about 2 inches in diameter larger than the 70's, the effective gearing was altered when compaired to the original tires. Therefore, at 62 mph my engine now turns 1700 rpm's.

Cummins has power/fuel economy charts showing the "sweet" spot for fuel economy. The low end of the rpm scale escapes me as I write this, but the upper limit was 1700 rpms. So in my case the larger tires dropped my 62 mph cruising speed rpms to the top of the sweet spot for fuel economy.

Now if I slow down a little more, maybe I can raise my 8.25 mpg average.
__________________
Terry
'05 Dutch Star 4015, '16 Rubicon OlllllO, & HD Ultra ElectraGlide, NKK14278L
Brigadoon 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
Have you heard of upgrading to a larger fridge? kcaravelli Heating, Cooling and Appliances 12 01-08-2012 09:28 AM
Difference between RV Tires and Truck Tires? Dunnpe Running Gear, Axles, Brakes, Wheels and Tires 6 01-15-2008 09:50 AM

» Featured Campgrounds

Reviews provided by

Disclaimer:

This website is not affiliated with or endorsed by Winnebago Industries or any of its affiliates. This is an independent, unofficial site.


Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -6. The time now is 05:33 PM.


Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2019, vBulletin Solutions, Inc.
×