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Wheel diameter query

General Tech Talk

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Wheel diameter query

Post by rainsey »

I am due to replace my rubber and want to go up in size. Due to the state of my rims I will probably replace them anyway so forget the current ones.

Ignoring width for the moment my options 32 x 15 or a 265/75R16 which both give roughly the same diameter. Re rims, I will go with either 15 x 8 or 16 x 8 steel.

Being that the diameters are more or less the same, is there any advantage to stick with one particular diameter rim... My thoughts were that 16 265 x 16 is a pretty universal size hence available in an emergency almost anywhere... but I do notice that many modded trucks are running 15's. Why??

Cheers

Rainsey
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Post by mickyd555 »

15's are cheaper.........31x10.5x15 would be the most commen tyre and rim combo i thought
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Post by Beastmavster »

15" is cheaper, but there's probably not a major difference in tyres - maybe $10-20 per tyre.

the rims are about double the price though, so it adds up to about $70 extra a corner.


Are 265 ok on a 16x7" rim though? It's less than 11" so I would think it should be ok.
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Post by mickyd555 »

my 265 75's are on a 16 x 7 rim, they havent come off yet and i run them at 16 psi off road.
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Post by rainsey »

MickyD

I curretly have 31x10.5x15's... Having a Rodeo I am out to get any extra height I can.

Beastmavster... yep you are correct they will go on 7" rims fine. 8" is the max for a 265.

But here is my rational......

I would personnaly like to go 33's but bit concerned over the diff ratio bit. Having never driven on 33's on my truck, do not want to spend over a grand on tyres if it runs like a dog.

What is comming of are very old 15 x 7 with next to no rubber 31 BFG AT's. I want to go muddies (need to get tyres as the current ones could be used at Bathurst as slicks).

The existing wheels go in the garage.. they can go back on when I sell or ditch the ute. I was thinking of going 16's with a Toyota offset (neg 13 I think). I actually have a Trek 2 16 x 8 with a 285 (70% tread) sittting in the garage hence I can use this rim as a spare. When I replace the Rodeo in years to come I will probably going down the Toyota or Nissan option hence the rims can be used for this purpose.

Price wise... 30 buck difference per rim between 15's & 16's... tyres.. yeah.. you are about right.

If it comes down to price I would probably stick with 15's... but I wanted to know if there is any technical reason why one would be better than the other. I would gues that the wall of the 265/75 would be smaller in height than the 32 x 15 being that the diameter is the same .. is a higher profile tyre any better in the dirt or mud than a lower one for example ( my understanding that a 32x15 will be a higher profile that a 265/75 x 16 if the diameters are the same)??

Cheers

Rainsey
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Post by mickyd555 »

if you wana buy a patrol or cruiser later on and want to keep the new tyres and rims to go on that, 16's might be the go. some of the new ptrols and i assume cruisers aswell, will not take a 15" rim over the brakes. depends on what sorta patrol you want........they are 6 stud on patrols too. but i think the new cruisers are 5 stud..
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16 vs 15

Post by sudso »

Being that the diameters are more or less the same, is there any advantage to stick with one particular diameter rim... My thoughts were that 16 265 x 16 is a pretty universal size hence available in an emergency almost anywhere... but I do notice that many modded trucks are running 15's. Why??
One reason I've heard of is that a 35" tyre for example, will bell out better (when deflated for grip) on a 15" rim than a 16" because the side wall height is higher.
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Re: 16 vs 15

Post by Shadow »

sudso wrote:
Being that the diameters are more or less the same, is there any advantage to stick with one particular diameter rim... My thoughts were that 16 265 x 16 is a pretty universal size hence available in an emergency almost anywhere... but I do notice that many modded trucks are running 15's. Why??
One reason I've heard of is that a 35" tyre for example, will bell out better (when deflated for grip) on a 15" rim than a 16" because the side wall height is higher.
and on the other hand the 16" rim will retain a half an inch diff clearance over a 15" rim when tyres are deflated.

There really is no difinitive answer as to which is better.
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Post by rainsey »

To respond to all above,,

Mickyd.. yep In Toyotas infinite wisdom they have decided to move to 5 stud on their 100 series ... their offsets are different as well.

Sudso & Shadow .. I was thinking along the lines of a wider footprint when deflated due to the higher side walls but the extra clerance of the 16's albeit small I had not thought of. It may sound petty but in looking for every millimeter I can get this could answer my question.

Thanks guys

Rainsey ;)
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15 or 16

Post by sudso »

Rainsey, when looking for your new tyres take a tape measure and measure the actual tyre diameter as I have found that most of the claimed diameters are under by up to 1.5".

I have 31/10.50R/15LT Maxxis on my Rodeo and they are definitely not 31" diameter! They are 29" with about 60% tread left.

You should be able to fit an actual 32" tyre on yours but any bigger and I reckon you'll get some rubbing.

You're right about getting every mm of diff clearance on Rodeo's. I've rubbed my rear one a few times in the dirt whereas the front diff on these has excellent clearance and doesn't get touched and the approach angle is about 35 deg. When I wind the t/bars right up, flip the upper ball joints and put 32"s on the angle should be about 45 deg.

If I put actual 32" tyres on mine my rpm will drop 300 at 110kph in top gear. Nothing to worry about.
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Post by Gwagensteve »

Some other things to consider:

it is easier to fit a tall narrow tyre on a car than a tall wide tyre. 16" rims allow you lots more options in relation to height vs width, and on IFS cars where the suspension moves through a more complex (and critical) arc than a live axle car and as such, limiting tyre and rim width will assist in keeping everything behaving properly and limit wear on suspension components.

Personally, I feel that an 8" rim and 11.5" tyre is a bit much for IFS front ends designed for a 16X6.

I would go with a 16x7, if it was up to me. this will allow you to go to a 31, 32 or 33" tyre (245/75, 265/75/, 255/85) and stay under 10.5" of width.

I think that road behaviour will be better than with the 15's, stability will be better becase of the shorter sidewall, and generally p metric tyres have a bit better construction (often seen in a higher speed rating)

Just my $0.02 worth :)
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Post by rainsey »

Gwagensteve,

Good feedback and personally not knowing a lot on the specifics of the IFS setup I will take it all on board.

The big problem is the varying specs of different tyre manufacturers. I have eg, whereas you identify a 265/75 as equivalent to a 33, a BFG Muddy in a 265 is 810mm in diameter that is under a 32. Sudso is correct in his summation that a 31 on most tyres is not a 31.

To get a true 33 on a BFG muddy, you actually need to go a 285/75 which then takes you over to an 8" rim. Go a Simex though, and a 31" Centipede is actually over 32" and a 32 is over the 33'.

Go with a 32 floatation series Muddy tyre in the BFG, you have to go up to an 8" rim as they only seem to come in 11.5".

Ironically, I can go a 33 in the same tyre with my current 15 x 7 rims as the 33 comes in a 10.5.

Thus my confusion as to which way I go.... As I stated earlier, going the 265/75 is pretty universal, and common in the 16 as is the 31 x 10.5 in the 15 (which is what I already have).

Trying to get the best of all worlds in a single set of tyres is certainly a challenge.

Cheers

Rainsey
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tyres

Post by sudso »

check out:

http://www.maxxis.com/products/automoti ... asp?id=190

Shows spec's of actual diameters and widths
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Post by vraamm »

rainsey wrote:Gwagensteve,
whereas you identify a 265/75 as equivalent to a 33, a BFG Muddy in a 265 is 810mm in diameter that is under a 32.

To get a true 33 on a BFG muddy, you actually need to go a 285/75 which then takes you over to an 8" rim. Rainsey
I think he meant the 255/85/16 was a 33" ;)
its goes on a 6.5-8" rim and is a good tyre on bigger 4wd's too.
uncommon but if your stuck one of the wider 33x16s should do.
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Post by Ryano »

One of the main benefits of going with 16" rims and tyres is the added strength that they have. Where the common size 15" are a 6 ply rated tyre, the light truck 16" are 8-10 ply rated with much higher load carrying abilities. This equates to better puncture and impact damage resistance.
(This is generalised)
31x10.50R15 - 109 load rating (1030kg @ max. inflation)
32x11.50R15 - 113 load rating (1150kg @ max. inflation)
255/85R16 - 119 load rating (1360kg @ max inflation)
265/75R16 8ply - 119 load rating (1360kg @ max. inflation)
265/75R16 10ply - 123 load rating (1550kg @ max. inflation)
285/75R16 8ply - 122 load rating (1500kg @ max. inflation)

Another advantage is their handling. With the increase in rim size the sidewall height has been reduced, which in effect reduces the flex through the tyre and provides better handling and more direct steering response.
Hope this helps,
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Post by rainsey »

Ryano,

Thanks for the info... this explains why on the Coopers web page they are bringing out a second 265/75/16 in the STT's, the current is the 123 and the one to come is the 119. I was curious as to why they would hav 2 of the same size tyre.

Cheers

Rainsey
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Post by Utemad »

Have you ever put 33in tyres on your Rodeo? I did once. They were 33x12.5 on 15in rims. They were off a cruiser but had heaps more than the usual offset. To do the nuts you needed a socket and extension bar as the usual tyre brace won't reach in that far. They were my brothers and I just put them on for a laugh but you couldn't turn the steering wheel. This was before I had any suspension or body lift. As soon as you turned the steering wheel the tyres hit the back of the back of the bullbar and the mudflap. I reckon you would have to do a heap of cutting to make them work. The rear looked okay but we didn't flex it.

Image

I had some close up photos of the front but these are from years ago and scanned film photos. I don't know what happened to the rest of them.
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Post by rainsey »

Ahhh... I am getting closer to my quest.... youa re the first that I know that has actually had them on.

12.5 is terribly wide for the poor old Rodeo hence I can imagine that you would have problems. If I went 33's I would probably go the 10.5's if they fitted.

From memory, was it the sheer diameter that fouled them up or the width?

Cheers

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Post by Utemad »

It was the diameter that stuffed it. However in hindsight if the tyre was narrower and less off set it would have probably cleared the wing on the bullbar (ARB winch bar). Then it might have also cleared the guard behind the tyre and only required you to remove/cut the mudflap. Since it is an IFS front I doubt you will have rubbing problems. You have given it a 2in bodylift so in theory the extra 1.5in in tyre height will still have more room above the tyre than 31s without bodylift. It will angle in a little bit more but I don't think that will cause any issues.

Since you have got the 10Rs on already try and do a mental projection of what another 1.5 inches in diameter would do given the same width and offset.

If you have a regular tyre mob you use ask them to fit some 33x10.5s or whatever you end up choosing and say if they fit you will take them.
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Post by Gwagensteve »

I think that the key here is scrub radius. Lets take a 255 85 16 and put it on a 7" rim with 4.5" of backspacing. This will clear in nearly all the placed that it looked like the 33 12.5 on the wrong offset rim was going to hit.

Correct backspacing is absolutely critical to alignment and handling and suspension compenent life with IFS. Many people forget this with If and run rims from wherever. As an example, live axle hiluxes have incorrect backspacing for your car, while 80 series rims are fine for a rodeo.

Once you get the scrub radius right, you will find that the tyres will turn pretty much on the spot so if you have 1" of clearance with the wheels straight ahead, they will pretty much fit at full lock.

this is how I can get a 36 12.5 on my G - I run a beadlocked 7" rim (yes yes I know) - I run 146mm (that's nearly 6") of backspacing. When I steer, the wheels turn absolutely on the spot so I acutally gain clearance at the firewall when the tyres turn.
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Post by rainsey »

Gwagensteve

Oh my god... my brain hurts severly...... I have 2 weeks before my Uni exams and I am trying to comprehend this... AHHHHHHHH...( I have been using this forum as an excuse not to study..hence my frequency of replies)

I am seriously sorry for sounding dumb but what the photon is backspacing. My comprehension (can we get a spell checker on this forum) is from the mount point to the back of the rim.. i.e offset. My 7" rims have zero offset, the 16" I have with a 285 on it has a negative 13 ( I am assuming 13mm) on it so what is 4.5 or 6" of back spacing actually mean. By the way the 16 inch rim I am using as an example is off a Landcruser so I am assuming if I stick with this I will be cool!

You obviously know what you are talking about but I am a mere mortal ( probably less after a few glasses of red and an anatomy text) and I am struggling here.

I have spoken to a few tyre vendors over the past few weeks and if it is not in their book they cannot help me... so .. needless to say, when I mention Rodeo, 15 / 16 diameter with 8" width.. they go ga ga.

Kindest Regards

Rainsey :?
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Post by HotFourOk »

To work out backspacing/offset...

It is the distance between the centre line of the rim and where the mounting point is.
A zero offset rim has the mounting face in line with the centre of the wheel rim.

This is how you get positive and negative offset rims.

Negative offset has the mounting face closer to the outer edge of the rim.

Positive offset has the mounting point closer to the inside of the rim.

Hope it helps
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Post by Utemad »

rainsey wrote:...I have 2 weeks before my Uni exams and I am trying to comprehend this... AHHHHHHHH...( I have been using this forum as an excuse not to study..hence my frequency of replies)...
Ha ha ha I am in the same boat .... there is a direct relationship to the amount of posts and the amount of work I have to do :lol:

Final semester though :armsup:

Good luck with your exams.
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wheel dia

Post by sudso »

For a Rodeo I would go a 265/75/16 10 ply (807mm dia. x 10.6" sectional width)

or,

235/85/16 10 ply (805mm dia x 9.6" sectional width)

Any bigger and you'll need some real decent lifting in a Rodeo.

Both sizes and 10 ply available in Maxxis M/T's

No interest, just got sizes off their website
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