Tires: chevy step van

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.