safety considerations

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19th March 2010, 07:51 AM
Tombie

Quote:

Originally Posted by beanie_205

18's are just not that suitable for off road work anyway- they will ride rougher, be more fragile (tyres & rims) and if you ever venture anywhere remote and need new tyres you'll be waiting for a while.

What :eek:

The rims and tyres are no less capable, and are easily as strong.
18" tyres are common in a lot of out the way places now.

Only reason to change is $$$ value or tyre selection.
19th March 2010, 11:08 PM
wanglemoose

18 inch tyres dont hang onto the top of ruts like 16s (only because there isn't enough sidewall to let them down) damn thing cost me a carton, it was sitting on the diffs with the wheels off the ground. luckily no damage from being skull dragged out.
20th March 2010, 11:12 AM
ozscott

Yep...its not that hard...the smaller the rim and the higher the sidewall the better off road...so yes 16's are more off road capable than 18's whether holes or sand - its just not seriously debatable.

Cheers
21st March 2010, 10:33 AM
CJT

Check your tyre placard instead of your manual. The trye placard on my D2 V8 has four different tyre sizes compared to the three listed in the manual.

I have;

215/75/R16 on 16x7J = 728.9mm
235/70/R16 on 16x7J = 735.4mm
255/65/R16 on 16x8J = 737.9mm
255/55/R18 on 18x8J = 737.7mm

As stated previously in QLD you can only legally go +15mm over the largest standard tyres size, so largest diameter is 752.9mm.

You can also go up to 1.5 times wider than the standard widest option but not narrower than the lowest option (215 in my case).

So I am going for a 225/75/R16 in either the BF Goodrich MT (744mm) or Cooper STT (750mm) overall size according to supplier websites.
21st March 2010, 02:44 PM
StephenF10

Quote:

Originally Posted by harlie

...
The last time I used (one of the many) a tyre calculator the largest 16’’ tyre that is legal on a D2 is a 245/70. I also know the insurance companies are now checking these in the event of a good accident.

There is also legislation around speedo accuracy. Basically the speedo must be within 10% but CANNOT read slower than the actual vehicle speed

That seems to rule out the 245/70's. With the 235/70 XPCs my speedo was spot on (as compared to two GPS units), but with 245/70 Goodyear Silent Armors the speedo now reads 2% slow.

Stephen.
'01 D2 TD5 Auto
21st March 2010, 09:51 PM
beanie_205

Quote:

Originally Posted by Tombie2

What :eek:

The rims and tyres are no less capable, and are easily as strong.
18" tyres are common in a lot of out the way places now.

Only reason to change is $$$ value or tyre selection.

Fair enough Tombie they are probably as strong- and I've never heard of anyone breaking a 18 alloy rim so i stand corrected there:angel: and as for remote spots you may well be right there too it's a small world these days :angel:- but a 16 rim gives you two more inches of air and rubber between your rim and the corrugated/rocky etc surface you're driving on, so they would cushion impacts better and allow more flexibility with tyre pressures
22nd March 2010, 07:48 AM
harlie

Quote:

Originally Posted by StephenF10

That seems to rule out the 245/70's. With the 235/70 XPCs my speedo was spot on (as compared to two GPS units), but with 245/70 Goodyear Silent Armors the speedo now reads 2% slow.

Stephen.
'01 D2 TD5 Auto

That’s right, a point always overlooked. If your speedo is correct to start with (most read slightly over because this ADR has been law in the EU for a while) then you also need a speedo mod… My D2 speedo was always 2-3% over when compared to GPS...

However if you're in a big bingle the insurance co won't be looking at how accurate your instrumentation is - they will check the tyres (larger tyres affect braking - thats why the law is there)... Speedo accuracy is only going to be questioned when you say to the officer "I was only going 60 sir, my speedo says so"
22nd March 2010, 01:36 PM
Tombie

Quote:

Originally Posted by beanie_205

Fair enough Tombie they are probably as strong- and I've never heard of anyone breaking a 18 alloy rim so i stand corrected there:angel: and as for remote spots you may well be right there too it's a small world these days :angel:- but a 16 rim gives you two more inches of air and rubber between your rim and the corrugated/rocky etc surface you're driving on, so they would cushion impacts better and allow more flexibility with tyre pressures

Actually the difference is only 1 inch :)

Also, rim design is very different internally, meaning an 18" rim can have the same air volume as a 16" rim running the same O.D tyre.

Only difference is 1" less sidewall. And often the flex in a tyre is dictated by its construction, not its profile.

I've seen multitudes of tyres offroad and some wont bag out even at 10 psi where others at 18 psi are bulging like crazy.

Elongated tread length is far more capable than a bulging sidewall offroad as it provides area without the width causing drag.

Tread pattern, tyre construction and pressure all have much more effect offroad than profile.

Whilst a higher profile rim *may* provide a marginal amount of extra rubber in event of driving over a gibber and clipping the rim, the actual real world implications are rare and unlikely.

I've driven thousands of km's on 16's, 17's and 18's and noticed no performance degradation in any of them. Its all down to driving style, speed and as mentioned earlier pressure and construction.
22nd March 2010, 03:37 PM
stevo68

Quote:

Originally Posted by Tombie2

Actually the difference is only 1 inch :)

Also, rim design is very different internally, meaning an 18" rim can have the same air volume as a 16" rim running the same O.D tyre.

Only difference is 1" less sidewall. And often the flex in a tyre is dictated by its construction, not its profile.

I've seen multitudes of tyres offroad and some wont bag out even at 10 psi where others at 18 psi are bulging like crazy.

Elongated tread length is far more capable than a bulging sidewall offroad as it provides area without the width causing drag.

Tread pattern, tyre construction and pressure all have much more effect offroad than profile.

Whilst a higher profile rim *may* provide a marginal amount of extra rubber in event of driving over a gibber and clipping the rim, the actual real world implications are rare and unlikely.

I've driven thousands of km's on 16's, 17's and 18's and noticed no performance degradation in any of them. Its all down to driving style, speed and as mentioned earlier pressure and construction.

All I know is that I went from 19's to 18's on my D3....and now 16's on my D2...give me the 16's over the 18's every day of the week. The options for 18's are still limited......though did see a nice pair of Bighorns in 265/70/17's on a D3...but 18's with allowable tyres.....my rims got hammered over rocky terrain due to bugger all side wall.

When I get another D3......I would only look at the diesel 2.7...for the 17inch rims. Even the KM2's in 18's whilst a much better option...I have seen then come off the rim where Smokey and the 16's sailed up. More rubber..more clearance...more options......with 16's....

Regards

Stevo
22nd March 2010, 04:00 PM
optimax90

Quote:

Originally Posted by StephenF10

That seems to rule out the 245/70's. With the 235/70 XPCs my speedo was spot on (as compared to two GPS units), but with 245/70 Goodyear Silent Armors the speedo now reads 2% slow.

Stephen.
'01 D2 TD5 Auto

after changing from 235,s to 245,s have you noticed a change in the gearing of the auto?

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