Any thoughts on the best size to replace the 7.50/R16's on a 1988 Chevy P-3 chassis with 158.5" wheel base? Apparently the 7.50's are not being made anymore. My tire shop is recommending the 235/85/16 as having the same diameter.

Bill B

How much weight is on each corner?

How wide are your rims? They are stamped, but hard to see unless you clean them up. I use Scotchbrite and Castrol Super Clean. resist the temptation to use steel wool. It will take off paint and start a rust farm.

Your rims should also be stamped for max pressure.

Thanks for the prompt response. Unfortunately, I got distracted ("Honey, have you taken care of ...... yet?"). I will have to dig up the weight data and have never checked the numbers on the rim, but the VIN label for the chassis shows the rims as 16X6K, front and rear. Mfr date for the chassis was 06/88. The label shows 65 psi for the front and 55 psi for the rear, GVWR 12,300 lbs, GAWR (FRT) 4880 lbs, and GAWR (RR) 7500 lbs. The same data is on the Barth Data Tag. The coach weight loaded is close to or at the weight limits, with more on the left side than the right. I will pass on the weight data as soon as I find it.

Thanks,

Bill B

It would be a good idea to get a current weighing when loaded for a trip. That way you can buy the right tires and inflate them properly.

www.Bridgestonetrucktires.com and www.Michelinrvtires.com have some pretty good info on their sites.

quote:

recommending the 235/85/16 as having the same diameter.

Well, almost

I went w/ Mich. 750's on rear and 235/85's on the steer when I last bought...My thinking was that the 235's, being LR-E as opposed to the 750's LR-D, gave an added peace of mind. Now that 750's are a tough find, I'll probably go w/ 235's on duals next time - just gotta make sure there won't be any sidewall clearance issues with the Alcoa wheels. So far, 30+k miles totally trouble-free.....

Tirerack.com is a good place to check out sizes and prices.

Lee --

Thanks for the input. Looks like the 235/85/16 is a good replacement. As you say, the dual wheel spacing will be critical; it's warmed up today so I can go out and check the spacing.

Enjoyed the photos of your 24' Barth. Our first one was a '78 24' with a custom layout that we liked so well we cloned it in our '89 25'. Very fond memories.

bill h; Marvin and Doris --

Tirerack has so much info now it can be hard to find what you need. I'll be checking again and will also try Bridgestone and Michelin.

Bill B

Do yourself a favor, go weigh the coach first, then determine what load range you will require. Download the load - Inflation tables for the tire you desire and go from there. You do not want to put an E if a D is called for. Ride quality will deteriorate if you do that. We weighed our Sovereign on the way to the FL GTG to find that we were over a thousand pounds overweight on the front and at rated load on the rear, using the tires listed on the Barth Data Tag. I changed them last week to 11x22.5's and now we are "legal" again.

Merry Christmas

quote:

Originally posted by Bill B:
will also try www.Bridgestonetrucktires.com and www.Michelinrvtires.com

Sites made clickable. Spend a little time on the Michelin site. My preference for the P30 is Bridgestone, but there is a lot of good information on the Michelin site.

quote:

You do not want to put an E if a D is called for. Ride quality will deteriorate if you do that.

Billy,

I'm not very savy about this issue, so I find your comment interesting......

When I went from 7:50R16 LR-D to 235's LR-E on the steers, I asked a couple local tire reps, who concluded: You can use Load range E's in all situations where a Load Range D is specified. (The reverse is not true.) Obviously, they had to confirm that the Alcoas would accept the higher PSI, and unsprung tire weight difference was neglible......('Course, selling tires does not make anyone a tire expert either

The 7:50's were not overloaded, meaning the 235's are even less so. Seems that a tire being loaded to a lower percentage of its design limits would be a good thing, resulting in extra safety margins.....

Sometimes, handling characteristics can be largely subjective. In my case, I actually considered it an improvement, perhaps less sidewall squirm. If ride is supposed to be more harsh, I haven't noticed.

7.50R16's seem to be going the way of the dino, so lot's of folks are gonna have this quandry down the road.......So far, going to LR-E rubber has been a no harm/no foul situation for me.....

Thanks to everyone for the input. I haven't had a chance to pursue it today, but have found that the dual wheel spacing is 250 mm, so if 235's were installed, there would be only 15 mm space between the tires -- not enough to suit me. Will need to go with 215's there, but might use 235's on the front. Unfortunately, I haven't been able to find the pressure stamp on the wheels; the outsides of the rims are covered by the wheel covers. If worse comes to worse, I'll find out when the wheels are pulled to replace the tires -- may be some last minute decisions made. dexstarwheel.com shows a 16X6K rim with a capacity of 3000@110 psi, so running them at 80 psi will probably be okay. I still need to do some checking on the different diameters with different brands and widths. At 65 psi, the load ratings for the 215's are pretty much the same as the 7.50's.

Bill B

Lee,
I did not look up the particulars on either tire so my comments are very general. What I have found is that if your weight is well within the capabilities of a D tire then go with that. The Pressure @ rated load for a D is 65 PSI, and the E is 80 PSI. If the D is capable at say 55 PSI and you went with an E instead, you would have to run the E tire at a lower pressure to obtain the same ride/load capacity of the D. With the stiffer sidewall of the E, the center of the tread would wear as an underinflated tire, that is IMHO. In reality, most gasoline motohomes would require the greater capacity E's.

Bill, I would not use different sized tires front to back. If spacing is an issue, get some wheel spacers for the rear and keep the tires all the same size. Besides, the 215's will effectively lower your rear axle ratio, speeding up the engine, burning more fuel. Try to keep the tire diameter as close to stock as possible. These things are geared low enough without speeding things up with smaller tires.

Merry Christmas!

Now that Christmas is over, it's time to get back to the tire size issue. After digesting a lot of good input, it looks like the best bet is to go with 235/85's all around. It looks like they'll be Load Range E's; I didn't see any D's in the 235's and very few in the 215's. I would not expect the ride to be seriously affected; Lee's experience seems to confirm that. And as he noted, the extra load capacity in the front is a definite advantage. If the spacing between sidewalls on the duals is not adequate and wheel spacers are not practical, then the 215's would have to be used. We'll see, but I think the spacing will be okay. Right now, I'm looking for the air temperature to rise a bit before doing anything. Will keep you posted.

Bill B

I have been studying your recent posts about tire size as my 1976 Barth needs at least 2 tires replaced. What I have found that seems to present something of a problem in my case is my wheels are set up for use with tubes. My two front wheels were replaced with later units, and those two are tubeless wheels. Does anyone have any input? Should I just continue to run tubes? Is there a cost effective way to modify my current wheels to accept tubeless valve stems? Should I just find the right tire shop to help me? Any help would be greatly appreciated.