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Question
Hello barry
is it possible to use 225 70 19'5 insted of 8-19'5
tvin tires back it,s on a 1979 chevy p 30 stepvan
regards klas lindkvist sweden

Answer
Klas,

An 8-19.5 is 8.0" (203mm) wide on a 6" rim, with an allowable rim width of 5.25" to 6.75", a diameter of 33.8" (859mm), a minimum dual spacing of 9.1" (231mm), and a load carrying capacity of 3195#  at 95 psi  - Load Range E (1449 kg at 6.6 bar)

A 225/70R19.5 is 8.9" (226 mm) wide on a 6.75" rim with an allowable rim width range of 6" to 6.75", a diameter of 33.0" (838 mm), a minimum dual spacing of 10.0" (254 mm) and a load carrying capacity of 3195# at 80 psi - Load Range E (1449 kg at 5.5 bar)

So the answer is maybe.

First, adjusting the width of the 225/70R19.5, it is 8.6" (218 mm) wide on a 6" rim - so it is 0.6" (15 mm) wider.  That might be a problem.

Looking at the other dimensions:  

Diameter:  the 225/70R19.5 is smaller in diameter (2 1/2%).  That means the speedometer will be off (You'll be going slower than indicated by 2 1/2%.)

Allowable rim width - if you have a 5.25" wheel, the 225/70R19.5 will not work.

Minimum dual spacing:  The 225/70R19.5 requires 0.9" (22 mm) more width, BUT the rim widths are difference - and adjusting for that, the 225/70R19.5 requires 0.6" (15 mm) more when mounted on the same wheel.

Load carrying capacity - Use the same Load Range, but the pressure can be 15 psi (1.0 bar)lower.

So here's what you need to know:  

1)  What is the width of the rims?  A 5.25 means no - no interchange.  That dimension should be stamped on the back side of the wheel - and usually it also has a letter following it that indicates the kind of flange the wheel has :  Possibilities are none and W.
 
2) A 6.0" rim width means the minimum dual spacing needs to be 9.7" (246 mm) - AND - there needs to be at least 3/4" (19 mm) clearance around the tire currently being used to be sure the 225/70R19.5 doesn't rub.  Please note:  Measuring clearance on the rear is pretty straight forward, but the fronts require the suspension to be fully collapsed and fully turned (in both directions) - and that is not easy to do.  It might be best to work with someone who is willing to look carefully at this.  

Note:  I'm not going to calculate what is needed for the other possible rim widths as it is likely the wheels are 5.25 or 6.0".  If I'm wrong on this, post a reply and I'll do those calculations as well.

3) And you will need to use the same Load Range.

OK, I am now going to go back and add the metric units where appropriate.  Please note that rim width are always in inches.

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Barry Smith

Expertise

I have over 30 years experience in the design, manufacturing, and testing of tires. I have served as the technical advisor to the "800" number. I have authored or co-authored many publications - usually without credit. I can answer almost any technical question, but please don`t ask me to compare brands. I probably have prejudices because of my work experience.

Experience

Member SAE (Society of Automotive Engineers) Member Tire Society (Tire Technical Organization) SCCA Regional Competiton License holder Authored many training manuals on tires, their care and use.

Organizations
SAE (Society of Automotive Engineers) SCCA (Sports Car Club of America) Tire Society

Publications
You may want to visit my web site: http://www.barrystiretech.com/index.html

Education/Credentials
I am a graduate of the University of Dayton, Dayton, OH - BME, 1971 I attended graduate school at the University of Akron - but did not complete my PhD - something I regret.

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