Tyre width on different wheels

Submitted: Thursday, May 10, 2018 at 20:37
ThreadID: 136679 Views:915 Replies:4 FollowUps:18
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Hi all
I've got a tyre question. If I put a tyre e.g. 265/65R17 onto a 17x7.5 and a 17x8 rim, will there be much difference in the width of the tyre at it's widest point.
cheers
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Reply By: Member - shane r1 - Thursday, May 10, 2018 at 21:40

Thursday, May 10, 2018 at 21:40
That’s 1/2” in rim width difference, so they would only be that much wider at the side walls at most. And the tread certainly won’t change.
Are you changing all rims?
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Reply By: RMD - Friday, May 11, 2018 at 07:59

Friday, May 11, 2018 at 07:59
If, and the critical thing is IF, the 8 “ rim has the same offset as does the 7.5” rim ie, the middle of the tread is in exactly the same position in relation to the centre then it won’t are much difference.
In the event the 8” rim has a different offset to the 7.5” then than will change the braking characteristics of the vehicle. If the wider rim does have more offset then the steering and braking, if it is fitted to front, will see the vehicle behave strangely, especially if ABS or ESC has to operate. Make sure you check the wheel offset as it is very important to have them the same at every corner.
AnswerID: 618799

Follow Up By: garrycol - Friday, May 11, 2018 at 17:38

Friday, May 11, 2018 at 17:38
But the OP did not ask that. He basically wanted to know if the tyre is wider with the 1/2" wider wheel - not anything about offsets etc.
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Follow Up By: RMD - Friday, May 11, 2018 at 20:25

Friday, May 11, 2018 at 20:25
Garrycol.
No he didn’t did he, but if asking about the width and effect he may be oblivious to a change in offset which is very common with a wider rim. If it isn’t realised then the fun may begin when the driver is caught unawares.
Maybe a good idea to alert him, if he already knows then no harm has been done.
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Follow Up By: Rob J8 - Friday, May 11, 2018 at 20:48

Friday, May 11, 2018 at 20:48
RMD I am glad you explained fully as I wasn't aware of any change in offset.
A little more information doesn't hurt
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Follow Up By: garrycol - Friday, May 11, 2018 at 21:17

Friday, May 11, 2018 at 21:17
Well if the OP wanted that information he would have asked for it. The first response by Shane r1 - provided the information required.
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Follow Up By: Shaker - Friday, May 11, 2018 at 22:45

Friday, May 11, 2018 at 22:45
Shane r1 also ended his helpful reply with a question to the OP, which up until now has been ignored. I am guessing that the question was to establish if the offsets were going to be different.
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Follow Up By: garrycol - Saturday, May 12, 2018 at 09:51

Saturday, May 12, 2018 at 09:51
An assumption that cannot be drawn from that question. The obvious thought is that he just wanted to know if he was going to mix rim widths - who knows.

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Follow Up By: Member - Suitcase (QLD) - Saturday, May 12, 2018 at 11:36

Saturday, May 12, 2018 at 11:36
See further followups below to answer this guys.
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Reply By: Ron N - Friday, May 11, 2018 at 23:17

Friday, May 11, 2018 at 23:17
Suitcase - The industry rule of thumb is that for every 1/2" change in rim width, a tyre's section width will change correspondingly, by approximately 5mm.

If you fit one rim with a half-inch size difference to the other rims - even though you're fitting the same size tyres - you will notice a small difference in handling response from the side with the smaller rim fitted.

That difference may not show up appreciably, until you do some emergency braking or a swerve at speed.

Cheers, Ron.
AnswerID: 618828

Follow Up By: Shaker - Saturday, May 12, 2018 at 09:19

Saturday, May 12, 2018 at 09:19
It is also unroadworthy to have different size wheels on the same axle.
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Follow Up By: Member - PhilD_NT - Sunday, May 13, 2018 at 23:17

Sunday, May 13, 2018 at 23:17
Shaker, do you have a link to documentation to back up that statement?

By that aren't you claiming that space saver spares that are fitted to many vehicles these days would make them unroadworthy unless with a rear flat tyre you would have to fit a front one to the rear then the space saver to the front. But then what happens where a vehicle has different front to rear tyre/rim combinations or even just directional tyres. Most of these situations are just to get you to somewhere with possible speed and distance limitations and then get the problem fixed.

In the OP's case his tyre and rim sizes are exactly as fitted to my PX Ranger by Ford (and probably the BT50 as well) from new with 4 alloy road rims and a steel spare. No where in the Owners Manual is there any comment as to any requirement as what to do with different scenarios of punctures.

I can't be bothered to go and measure the difference in rolling diameter tomorrow but would think that it would be very little other than the difference caused by the onroad tyres being half worn as against the new spare. If I was concerned with that difference a simple pressure adjustment would take care of it.
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Follow Up By: Shaker - Sunday, May 13, 2018 at 23:48

Sunday, May 13, 2018 at 23:48
A roadworthy certificate won’t be issued to a vehicle with a temporary use spare wheel fitted either. I did say wheels had to be the same on any one axle, they can be different front to rear as long as they are within the parameters set for the vehicle.
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Follow Up By: Member - PhilD_NT - Monday, May 14, 2018 at 00:38

Monday, May 14, 2018 at 00:38
Shaker, you never qualified your claim by mentioning a roadworthy certificate which is quite different to using a manufacturer supplied spare that is different to the main wheels/tyres when experiencing a puncture. Provided you don't exceed any manufacturers limitations in using it how can that make the vehicle unroadworthy. Having them the same on the same axle may be desirable but as I described in various scenarios it isn't a requirement. Your blanket statement that "It is also unroadworthy to have different size wheels on the same axle" is incorrect as that would make so many standard vehicles unroadworthy the moment the spare is used.
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Follow Up By: Shaker - Monday, May 14, 2018 at 17:52

Monday, May 14, 2018 at 17:52
You have to allow for idiots, imagine if there was a 235/70x16 & a 285/75x16 on the same axle that have just on a 100mm difference in diameter, would you issue a RWC?
There are a lot of things that are left to the discretion of the tester.

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Follow Up By: Shaker - Monday, May 14, 2018 at 18:08

Monday, May 14, 2018 at 18:08
This from the South Australian Government requirements as found HERE , I can’t find the Victorian one at the moment.

The overall diameter of a wheel and tyre fitted to a vehicle must not be more than 15 mm greater than the largest tyre size listed on the tyre placard and not more than 15 mm less than the smallest tyre size listed on the placard.

Specifications for overall tyre diameters are listed in the Tyre and Rim Association of Australia - Standards Manual. Note: If tyres are to be fitted with a diameter outside of this requirement then an MR620 Application to Modify a Motor Vehicle (482.3 KB PDF) and a report from a MR426 Chartered Professional Engineer (1.1 MB PDF) is required.

The following requirements must also be met:

The tyres fitted must be suitable for the rim. The tyre retailer should have information about matching tyres and rims. Specifications for overall tyre diameters are listed in the Tyre and Rim Association of Australia - Standards Manual.
The tyres must be free of any apparent defect that could make them unsafe.
The replacement tyres must have a load capacity not less than the lowest load rating specified on the tyre placard.
The speed rating of the tyres fitted to vehicles for off-road must be of at least 140 km/h ('N') when the tyre placard requires a higher speed rating than 'N'.
The speed rating of the tyres fitted to a passenger vehicle must be at least 180 km/h ('S') when the tyre placard requires a higher speed rating than 'S', for all other vehicles a speed rating of at least 120 km/h applies ('L').
Tyres fitted to an axle of a vehicle must be of the same size and carcass construction.
Tyres fitted to vehicles manufactured after 1972 must be made of the same carcass construction - eg radial, crossply.
Tyres fitted to passenger cars may not be treated by recutting or re-grooving of the tread unless the tyre is constructed to do so and marked as such.
Tyres fitted to a vehicle, which do not have tyre wear indicators, must have a tread pattern at least 1.5mm deep on all parts of the tyre that normally come into contact with the road surface. If the tread has worn down to any of the tyre wear indicators, or there is less than 1.5mm of tread depth on the tyre, the tyre is then considered to be unroadworthy.
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Reply By: Member - Suitcase (QLD) - Saturday, May 12, 2018 at 08:50

Saturday, May 12, 2018 at 08:50
Thanks guys
I had this notion of being able to use a 17x8 steel (with appropriate offset) as a spare. I have nearly enough Prado rims for 2 sets of tyres (street and country etc) plus Prado wheel on the van. I am short by 2 rims - the spares on the van and the car. Prado rims are pretty expensive 2nd hand. Might have to keep looking for that bargain that comes along.
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Follow Up By: qldcamper - Saturday, May 12, 2018 at 09:06

Saturday, May 12, 2018 at 09:06
I think your over thinking it.
If it is just spares your concerned about then use the different rims, if your concerned about safety put the spare on the van when needed and use the prado rim off the van on the tow vehicle, or fit the new rims to the van and use the prado rims off the van as spares. Talk to your tyre dealer and they will give you a better run down.
Personally I wouldn't think it would make enough difference when towing as you would be driving more carefully anyway.

I have the same size wheels and tyres on my hilux so I picked up 3 x17 inch steel wheels for the trailer. If I use the original spare and require a second or even a third spare on the hilux id be happy with the different wheel and tyre mismatch as long as the thing is mobile.
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Follow Up By: Ron N - Saturday, May 12, 2018 at 10:31

Saturday, May 12, 2018 at 10:31
Suitcase - Are you saying, your original Prado rims, and the ones you're looking for, are 17 x 7.5" alloys?

I see a very wide range of rims for Prados for sale - it seems there's both 16 and 17 inch and widths from 7" to 8.5" - plus, there appears to be a variety of alloy patterns, to make it even more complex.

Let us know the precise style, type, and size you're looking for - the big auction houses are a good source of cheap rims and tyres, and I spend a lot of time searching out this type of stuff.

Cheers, Ron.
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Follow Up By: Member - Suitcase (QLD) - Saturday, May 12, 2018 at 11:04

Saturday, May 12, 2018 at 11:04
Hi Ron
yes - my Prado is an SX so alloy rims are the same (I believe) as a 150 GXL i.e. 17 x 7.5 with +25 offset.
In an ideal world - like this one - I think later years had a slightly different shape - the size and offset are more important
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Follow Up By: Ron N - Saturday, May 12, 2018 at 14:47

Saturday, May 12, 2018 at 14:47
Wow, you certainly know how to pick the expensive rims! I see what you mean.
Plus, there's a couple of Prado rims with slightly different shape to the spokes, just to make life difficult!

I'll keep my eye open for anything that I see, that might interest you.
The mining companies often send stuff to auctions with no reserve, and often there's a range of unused spares included.

Cheers, Ron.
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Follow Up By: Member - Suitcase (QLD) - Saturday, May 12, 2018 at 15:09

Saturday, May 12, 2018 at 15:09
Front what I can find - all Prado 150 GXLs had the 17x7.5 +25 offset rims - no matter what the shape - that just changed over time.
That would be great - I am in no great rush here - if it happens it happens.

cheers
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