Tyre Size - How do they compare

**Baggy** · 2nd October 2013, 10:05 PM

Hi All.

I have an 81 RRC 2 Door.

Currently it has turbine alloy rims with 31 x 10.5 OR15LT tyres

Can any of you Tyre Guru's tell me if there is a formula I can compare circumference of the current tyres (above) compared to the original 16 inch wheels / tyres.

By the way what is the standard size tyre?

Vehicle is stock 3.5v8 carbie with 2inch lift.

Its not my daily driver (company car)

but is the vehicle I drive as much as possible and want to build her up as a general tourer.

Should I be looking at replacing with original 16 inch rims.

Cheers

Baggy

sheerluck · 2nd October 2013, 10:13 PM

I don't know the original size for an 81 Rangie, but when you find out, there's a good tyre size calculator here: Tire size calculator

**loanrangie** · 3rd October 2013, 08:48 AM

Original was 205R16 cheese cutters but no one runs stock size tyres anymore and you might be hard pressed to find them in that size now.

**superquag** · 3rd October 2013, 11:00 AM

Seeing as Spencer-King originally designed/fitted them with bicycle tyres, has anyone actually demonstrated that wider, or much wider/biggger tyres enhance all performance areas ?

- Which ones, and by How Much?

All the busses I drive, from old SA Trus/t/brand new Volvos, decrepit and late Hinos, Mercs and Scanias, all ride (some fantastically) on relatively skinny, high aspect ratio tyres. On some the steering is better than any car I've driven.

Have'nt seen a wide/low profile heavy vehicle tyre for ages... Remember the 'Super-Singles'. ?

**superquag** · 3rd October 2013, 11:03 AM

Originally Posted by loanrangie

Original was 205R16 cheese cutters but no one runs stock size tyres anymore and you might be hard pressed to find them in that size now.

I suspect you're right... From my limited experience, it appears that 235/70 - R16 is a favourite, being the same rolling radius as the original 205 R16
(82% aspect ratio)

**MR LR** · 3rd October 2013, 11:15 AM

Originally Posted by superquag

Seeing as Spencer-King originally designed/fitted them with bicycle tyres, has anyone actually demonstrated that wider, or much wider/biggger tyres enhance all performance areas ?

- Which ones, and by How Much?

All the busses I drive, from old SA Trus/t/brand new Volvos, decrepit and late Hinos, Mercs and Scanias, all ride (some fantastically) on relatively skinny, high aspect ratio tyres. On some the steering is better than any car I've driven.

Have'nt seen a wide/low profile heavy vehicle tyre for ages... Remember the 'Super-Singles'. ?

You might have to look again, I see super singles on the front of most new semis, and on a lot of tanker trailers.

They seem to be making a comeback...?!

My Rangie has 235/85-16's on it, same size as Defender, they give it nice gearing, but I've had to roll the guards in a few places.

Cheers
Will

**GuyG** · 3rd October 2013, 11:38 AM

205R16's were standard on RRC and yes they are still available, equivalent to 29" diameter tyres. We used to run 225/75/16 as we could get them at the right price. Then I think disco's etc came standard with 235/70/16's.

30/9.5/15 is approx 235/75/15
31/10.5/15 is approx 265/70/16

**Baggy** · 3rd October 2013, 07:08 PM

Hi All,

Thanks to everyone for their input especially GuyG as it looks like
the current tyres are very similar to originals in diameter

I do like the turbine mags, however I would like to look at a more
aggressive tyre pattern that will suit the turbine rims when they need to be replaced.

Which begs one final question .... are 15" tyres still popular size price wise or are 16" the way to go.

Cheers

Baggy

**Debacle** · 3rd October 2013, 07:09 PM

Go here Tire Size Calculator - Tire & Wheel Plus Sizing and you can compare the relative widths and diameters of tyres side by side.

**Dougal** · 4th October 2013, 11:25 AM

To summarise all the info that's already been posted here: http://www.aulro.com/afvb/classic-ra...el-arches.html

and here: http://www.aulro.com/afvb/classic-ra...e-options.html

Stock is 205R16 which is essentially 205/80R16. This size is still available, it's standard fitment for many 2wd work utes.
225/75R16 and 235/70R16 are the most common replacements and clear everything even with snow chains fitted.
The 225/75R16 is a LT (light truck) size with tough carcasses and ultimately heavier tyres. The 235/70R26 is a P (passenger) size with a softer and lighter carcass that rides better.
These are all ~29" OD. The 225/75R16 are fractionally bigger.

215/85R16 is the largest size that will clear everything and only requires steering stop adjustments.
It is ~30.4" OD.
Larger sizes and widths are where the butchery starts.

Your 31x10.5R16 are the equivalent width and diameter of 265/70R16. They are not "very similar to originals" in any dimension.

Here is how to convert a random (or inch) tyre size to metric.
1. Start with the width.
10.5" is closest to 265mm.
2. Find the new sidewall height.
31" tyres on 16" rims leave 15" of tyre which is 7.5" for each sidewall. 7.5" is 190mm.
3. Work out the aspect ratio.
This is the ratio of sidewall height to width. In this case 190mm sidewall divided by 265mm width is 0.71.

4. Put it all together.
Width of 265mm, aspect ratio of 71 (round to 70) on a 16" rim becomes 265/70R16.

Compared to stock 205/80R16 you are 50mm tall and 60mm wider. Compared to the biggest tyre that fits (215/85R16) you are still 17mm taller and 50mm wider.

Your choices are basically get some tyres (and rims) that fit or start butchering your vehicle. Reducing suspension compression and steering lock too.

The closest 15" tyres that will fit and work are 30x9.5x15. Tirerack.com list a few, but your local tyre retailer may have nothing.
There is virtually no choice to fit your vehicle properly in 15". Get some 16" rims and your choices are almost endless.

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