Tire upgrade

[Damon2014]

I currently have a 2006 Coachmen Sportscoach Elite 402TS Diesel Pusher with 275/70 R22.5 and would like to upgrade to 275/80 R22.5. There is more than enough clearance but I just wanted to know if anyone else has done this.

[wildebill308]

Welcome to the forum. That is not that radical of an upgrade. It will give you a little overdrive of 5.6%. You can compare different size tires with a tool like this. https://tiresize.com/comparison/

Bill

[richard5933]

If you're planning to do this on the duals in the rear, be sure to check the space between the tires. There will be a difference in clearance from the new tires, and the tire manufacturer will have a minimum for this.

[manholt]

Damond2014.  Welcome to the Forum!

Why?

[tireman9]

Dual Spacing is a function of wheel offset and tire width.

You might read THIS post on the topic on my blog.

[Damon2014]

14 hours ago, manholt said:

Damond2014.  Welcome to the Forum!

Why?

Because I hear it is a much better ride and the newer Sportscoach has this size

[Damon2014]

22 hours ago, richard5933 said:

If you're planning to do this on the duals in the rear, be sure to check the space between the tires. There will be a difference in clearance from the new tires, and the tire manufacturer will have a minimum for this.

I spoke with the tire manifacture and the only difference is the height of the tire, the width is exactly the same. Great point though, I didn’t think of that.

22 hours ago, WILDEBILL308 said:

Welcome to the forum. That is not that radical of an upgrade. It will give you a little overdrive of 5.6%. You can compare different size tires with a tool like this. https://tiresize.com/comparison/

Bill

Awesome, thank you

[hermanmullins]

Damon, That is good news about the width. However if you have a Tag then you have two tire where the treads will be closer together and there may be an issue.

Tag = Possible Problem                                  No Tag = No Problem.

Good luck,

Herman

[Damon2014]

18 minutes ago, hermanmullins said:

Damon, That is good news about the width. However if you have a Tag then you have two tire where the treads will be closer together and there may be an issue.

Tag = Possible Problem                                  No Tag = No Problem.

Good luck,

Herman

It is not a tag so I should be good

[tireman9]

On 10/9/2018 at 8:16 PM, WILDEBILL308 said:

Welcome to the forum. That is not that radical of an upgrade. It will give you a little overdrive of 5.6%. You can compare different size tires with a tool like this. https://tiresize.com/comparison/

Bill

Bill, That site is reasonable but it does not have any info on Dual Spacing.  IMO its always better to get & confirm tire dimensions from the manufacturer as almost all are slightly different dimensions.

[rayin]

For those of us that get out-of-touch with stuff we used to know.

This website explains dual-tire spacing and its importance; along with other good-to-know tire information that has been around since the development of radial tires.

[wildebill308]

On 10/13/2018 at 1:20 PM, tireman9 said:

Bill, That site is reasonable but it does not have any info on Dual Spacing.  IMO its always better to get & confirm tire dimensions from the manufacturer as almost all are slightly different dimensions.

Where do you think they get the dimensions to do the comparison? I will bet the difference is no more than the manufactuers dimensional tolerances. If you are going to make big statements like that you need to show me that the differences are, well enough to make a difference. 

Bill

[manholt]

OK, children, play nice and re-read the OP!  Damond had no intention of changing the size of Drive axle tires!  Just the steer axle.   I expect he has done so, by this time! 

[kaypsmith]

1 hour ago, manholt said:

Damond had no intention of changing the size of Drive axle tires!  Just the steer axle.

 

1 hour ago, manholt said:

OK, children, play nice and re-read the OP! 

Reread the OP Carl.

When reading the tire size, 275/70 22.5, the second # 70 indicates that the sidewall height is 70% of the tire width, likewise if it were 80, that means that it is 80% of the tire width. Bill is correct in indicating that the circumference will be 5.6% greater.

[alflorida]

On 10/10/2018 at 1:40 PM, tireman9 said:

Dual Spacing is a function of wheel offset and tire width.

You might read THIS post on the topic on my blog.

Tireman9,

You write in your blog post that " there is also a CRITICAL dimension that you can't measure with a tape measure and that is called "Minimum Dual Spacing". "

I don't understand why I can't take a tape measure and measure the distance between the center tread groves on both installed tires on my dual tires and come up the the the "Dual Spacing" on my tires and wheels.   I believe this distance is determined by the wheels installed and does not change when different tires are installed.  I do understand that wider tires require larger Dual Spacing.  However if the distance I measure is greater than the Minimum Dual Spacing required for the new tires, then I should be good to go with new tires.

Would you explain why my thoughts are incorrect?

[wildebill308]

Al, I think you are correct. Look at page 45 for information on measuring Dual Spacing. 

https://www.michelinb2b.com/wps/b2bcontent/ZIP/PLNA/Michelin_Truck_Tire_Service_Manual.pdf

Bill

[richard5933]

Regardless of how one can measure the dual tire spacing, I hope we all can agree that the important thing here is to remember to consider that measurement when deciding whether or not to change tire size. Most people consider spacing in the wheel wells, problems with steering clearance, etc, but not everyone is even aware of this measurement.

[manholt]

That's true!

Herman, brought up the other thing.  A 2006 coach & chassis, may not be engineered to handle the new size wheels of a 2018 same coach!  Technology, has really changed a lot, in the past 12 years! 

 

[rayin]

18 hours ago, alflorida said:

Tireman9,

You write in your blog post that " there is also a CRITICAL dimension that you can't measure with a tape measure and that is called "Minimum Dual Spacing". "

I don't understand why I can't take a tape measure and measure the distance between the center tread groves on both installed tires on my dual tires and come up the the the "Dual Spacing" on my tires and wheels.   I believe this distance is determined by the wheels installed and does not change when different tires are installed.  I do understand that wider tires require larger Dual Spacing.  However if the distance I measure is greater than the Minimum Dual Spacing required for the new tires, then I should be good to go with new tires.

Would you explain why my thoughts are incorrect?

If I may, I'll chime in; look at the chart here, it requires section width of the tire for the calculation, now assume your exact tire size is not listed, a simple measurement is not adequate. In addition to preventing dual tires from rubbing  together and eventually failing, there should be enough clearance to prevent stones from lodging between the tires and busting your windshield if you are unlucky enough to be following that truck/MH. Ever get behind a dump truck with a sign on the tail-gate saying ""stay back 300 feet, not responsible for damage"?

[alflorida]

5 hours ago, RAYIN said:

If I may, I'll chime in; look at the chart here, it requires section width of the tire for the calculation, now assume your exact tire size is not listed, a simple measurement is not adequate. In addition to preventing dual tires from rubbing  together and eventually failing, there should be enough clearance to prevent stones from lodging between the tires and busting your windshield if you are unlucky enough to be following that truck/MH. Ever get behind a dump truck with a sign on the tail-gate saying ""stay back 300 feet, not responsible for damage"?

Please read my reply again.

Quote

I don't understand why I can't take a tape measure and measure the distance between the center tread groves on both installed tires on my dual tires and come up the the the "Dual Spacing" on my tires and wheels.   I believe this distance is determined by the wheels installed and does not change when different tires are installed.  I do understand that wider tires require larger Dual Spacing.  However if the distance I measure is greater than the Minimum Dual Spacing required for the new tires, then I should be good to go with new tires.

Would you explain why my thoughts are incorrect?

I am referring to dually spacing on my installed wheels to verify that the spacing is far enough apart to install different tires that the mfg specs on the tire are less than the spacing I have on my wheels.

For example the dually tire spacing on my diesel pusher measures 13 3/8" between the inner tire center tread and the outer tire center tread.  So it looks to me that if the mfg of a tire states the minimum spacing is 12 1/2" then there should not be a problem installing them on my wheels. 

That is why I am wondering why I can't just measure the distance between the tread groves to find the existing dually tire spacing on a RV to see if there is enough spacing for different tires.

[manholt]

Al.

After reading the blog again, I came to the conclusion (I hope it's correct) that it depends on the wheels, not tires.  If the inner steel wheel takes a smaller tire size, than the Alcoa, then you need to go with the steel.  When you measure center to center, it's static, so you need to take into consideration, expansion. How the coach is loaded, PSI cold/hot, ambient temp. etc, that will all change the measurement between the side walls! 

[rayin]

Rogers blog is correct, as is the link I provided.

It does change when different tires are  installed, review "section width". Different tires have different section widths, which also depends upon inflation and sidewall deflection/section width.

Lets look at the information for 275/70R22.5 Bridgestone R250ED truck tires. Section width is listed as 10.7", loaded section width is 11.8". This means the distance between these specific tires in a dual configuration must be a minimum of 2.3" to prevent rubbing when fully-loaded, then one should account for hitting potholes/bumps that can cause further sidewall deflection; thus the better 2 1/2" space between duals. Change tire size and a total recalculation is required, as sidewall deflection/section width has also changed.

What is NOT mentioned in the charts is the distance between sidewalls, as the charts assume you're only using the vehicle mfgrs recommended size. I remember back when I was in high school and my part time job was changing truck tires (remember split-rims?) It was drilled into me to never have less than 1 1/2" inches between sidewalls for duals,2 1/2" was better. Less than 1 1/2" when the truck was empty meant when fully-loaded(or more) the sidewalls could rub together. I never knew there was such a chart for distance between duals back then.

 

Carl, the rims must be the same size, although the offset may be different for inner and outer, which is why most are normally made so they cannot be reversed. The rest of your conclusion is correct.

If I am off on any of what I wrote, please forgive my memories from 58 years ago mixing with today's dual spacing and charts.

All that being said, there are manufacturers of spacers for up to 10 lugs to fit between the rear rims to increase dual tire spacing.

[kaypsmith]

There is only one thing that I would like to point out. The reason given for changing tire size from 275/70/22.5 to 275/80/22.5 is to improve ride, if only on the steer tires, then dual spacing is not an issue, but if for drive axel, then there is an issue. The reason that the ride is more comfortable is that there is more height of the sidewall, which allows for more flex in the sidewall, this in turn means that the dual spacing can not be the same because of the fact there is more flex. One could just measure the difference between treads because that is not the correct place to measure spacing. One should only use the manufacturers spacing because you can not measure that spacing unless you are willing to change weight and tire pressure for all possible occasions, this will change as those factors change. The manufacturer has already taken this into their specifications for you. If one is going to a taller size, then to keep that spacing the same, you will also need to increase the sidewall plies, which in turn lessens the flexibility and goes right back to the stiffer ride. Just some reasoning on the subject.