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Open Roads Forum  >  Class A Motorhomes  >  Projects & Upgrades

 > 245’s on a 6 inch wheel?

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Octaneforce

Long island

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Posted: 07/08/22 05:31pm Link  |  Quote  |  Print  |  Notify Moderator

My 1993 p30 currently has the pizza cutter 8r19.5 tires all the way around. Can i put 245/70/19.5 tires on just the front? Will these tires mount onto a 6 inch wide wheel? Ive read alot of instances of dually pickup truck guys doing this swap, but not much info on motorhomes. Really trying to get this **** thing to drive better. Ive been thru the front end multiple times.


1993 fleetwood coronado 30’ class a chuggin along with a tbi 454
An On demand hot water heater was the best thing i ever did

enblethen

Moses Lake, WA

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Posted: 07/08/22 05:55pm Link  |  Quote  |  Print  |  Notify Moderator

I have 245s all around on my 93 P30.
Big thing is to ensure tires have a stiff sidewall. If they have soft sidewalls, it is possible bouncing will allow the rears to hit. I ran Toyos for many years and now run Double Coins.
Biggest change to stop rut tracking was the installation of Henderson Lineup Bell Cranks. Bell cranks


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CapriRacer

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Posted: 07/09/22 06:08am Link  |  Quote  |  Print  |  Notify Moderator

Here's the math:

If you start with 8R19.5's, they are supposed to be 8.0" wide on a 6.00 rim, with an overall diameter of 33.8", a minimum dual spacing of 9.1", and a load carrying capacity of 3525# at 110 psi for a Load Range F.

A 225/70R19.5 is supposed to be 8.9" wide on a 6.75" rim, with an overall diameter of 31.9", a minimum dual spacing of 10.0", and a load carrying capacity of 3640# at 95 psi for a Load Range F.

Assuming for the moment that you have 6.00 wide rims to start with, the 225/70R19.5 will be about 8.5" wide on that 6.00" rim. Since it is common for chassis manufacturers to specify minimum dual spacing rims, the net effect is that there will be a loss of about 1/2" space between the duals. I urge caution in this area.

Also, the diameter change results in 6% change - which means the speedometer will read 60 mph when it is going 57 mph.

And lastly the load. In order to carry the same load the 8R19.5 does at 110 psi, the 225/70R19.5 only needs 92 psi.

So the real danger areas are the rim width (minimum 6.00" for a 225/70R19.5) and the dual spacing (9.6" for the 225/70R19.5 on a 6.00” rim)

So to answer the question asked: Yes, those will likely fit on the front. It is unlikely that a 1/4 inch more width will rub against any bodywork or suspension parts. The real problem is the dual specing.


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Octaneforce

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Posted: 07/10/22 07:13pm Link  |  Quote  |  Print  |  Notify Moderator

CapriRacer wrote:

Here's the math:

If you start with 8R19.5's, they are supposed to be 8.0" wide on a 6.00 rim, with an overall diameter of 33.8", a minimum dual spacing of 9.1", and a load carrying capacity of 3525# at 110 psi for a Load Range F.

A 225/70R19.5 is supposed to be 8.9" wide on a 6.75" rim, with an overall diameter of 31.9", a minimum dual spacing of 10.0", and a load carrying capacity of 3640# at 95 psi for a Load Range F.

Assuming for the moment that you have 6.00 wide rims to start with, the 225/70R19.5 will be about 8.5" wide on that 6.00" rim. Since it is common for chassis manufacturers to specify minimum dual spacing rims, the net effect is that there will be a loss of about 1/2" space between the duals. I urge caution in this area.

Also, the diameter change results in 6% change - which means the speedometer will read 60 mph when it is going 57 mph.

And lastly the load. In order to carry the same load the 8R19.5 does at 110 psi, the 225/70R19.5 only needs 92 psi.

So the real danger areas are the rim width (minimum 6.00" for a 225/70R19.5) and the dual spacing (9.6" for the 225/70R19.5 on a 6.00” rim)

So to answer the question asked: Yes, those will likely fit on the front. It is unlikely that a 1/4 inch more width will rub against any bodywork or suspension parts. The real problem is the dual specing.



Wow that is great info! I guess i could do 225’s on the rear if i ever replace them. I want to do 245’s on the front. I did consider the fact that the 2 rears may rub. Not really concerned about the speedo being off, i barely keep up with traffic as it is.

Octaneforce

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Posted: 07/10/22 07:15pm Link  |  Quote  |  Print  |  Notify Moderator

enblethen wrote:

I have 245s all around on my 93 P30.
Big thing is to ensure tires have a stiff sidewall. If they have soft sidewalls, it is possible bouncing will allow the rears to hit. I ran Toyos for many years and now run Double Coins.
Biggest change to stop rut tracking was the installation of Henderson Lineup Bell Cranks. Bell cranks


Ive had my eye on those bell cranks! Myself and every shop that ive been to says my
Front end is tight. So i havent made that plunge for bell cranks yet.

Im really looking to get big name brand tires because of my terrible experience with the less common names. I may order these;

https://www.ebay.com/itm/2-New-Bfgoodrich-Route-Control-S-245-70r19-5-Tires-24570195-245-70-19-5-/383479866376?mkcid=16&mkevt=1&_trksid=p2349624.m46890.l6249&mkrid=711-127632-2357-0

enblethen

Moses Lake, WA

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Posted: 07/10/22 08:05pm Link  |  Quote  |  Print  |  Notify Moderator

Out here both Toyos and Double Coins are used by delivery trucks and on equipment type trailers.
My dealer installed the 245s, mounted them on rig and verified clearance.
Shops said my front end was tight, but the original bell cranks fell apart when steering linkage was removed.

Octaneforce

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Posted: 07/14/22 08:33am Link  |  Quote  |  Print  |  Notify Moderator

enblethen wrote:

Out here both Toyos and Double Coins are used by delivery trucks and on equipment type trailers.
My dealer installed the 245s, mounted them on rig and verified clearance.
Shops said my front end was tight, but the original bell cranks fell apart when steering linkage was removed.


Did you ever have any vibration/balancing issues with your tires? My cheap 8r19.5’s shake and bounce like crazy

enblethen

Moses Lake, WA

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Posted: 07/14/22 01:45pm Link  |  Quote  |  Print  |  Notify Moderator

Dealer had no problem balancing either brand. I was surprised as to little amount to balance. Have had no vibration, shakes or noises. I have gotten longer services life after using these brands.

Octaneforce

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Posted: 07/22/22 05:36pm Link  |  Quote  |  Print  |  Notify Moderator

I did 245/70/19.5 on the fronts. I got the bf goodriches. The coach drives MUCH better and doesnt shake anymore. I wish i did this sooner. Thank you for the help.

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