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i don't understand exactly what you mean

>>> no, of course you don't but i understand exactly what you're about/


i am really not technical ?
>>>is this technical enough for you? Sealioning
lol
 

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There are a number of online articles on this subject and this quote sums up the situation,
"Changing the wheel and tyre size of your car affects more than just the look of the vehicle — fitting huge wheels and tyres à la Pimp My Ride, for example, has significant consequences".
Full article here :-
https://www.driving.co.uk/car-clinic/gadgets/what-you-need-to-know-before-changing-the-size-of-the-wheels-and-tyres-on-your-car/

The underlying problem is summed up by Deebos own words "I am really not technical" so I fear that no matter what we say will go over his head yet he is asking this Forum to operate as his technical advisors beyond the scope of the vehicles original design criteria.
I'm not going to assume that role.


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Discussion Starter #24
I indeed don't exactly understand how a higher tire would destroy the gearbox if i fit the same size allround, if i use a wider tire in the rear with a lower sidewall i sort of understand, but then again, like i said before, suv's by BMW or Mercedes for example that are also 4wd use this all the time, like 275 in the front and 325 in the rear with a lower sidewall so.
And i keep asking this to be sure, because i work at a big BMW dealership (not as a mechanic ofcourse, but as a detailer).
I asked 4 or 5 mechanics with experience from 5-25 years in the business and they all told me they don't see why a higher tire would destroy the gearbox, especially not when i fit the same size allround...
I just keep asking because everyone here says it's a no go...
 

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Tiresize have a good chart: https://tiresize.com/tiresizes/235-50R19.htm

personally I've been thinking of dropping from the 19s to 17s to get cheaper winter tyres and use the 19s for summer only. 20s will look good, but my guess is the ride will be grim.
 

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Nice picture.
The deeper profile sidewall at 65 (on 17s) in my opinion looks more impressive and 'chunky' than all this going down to 40 profile and running on an 'elastic band' :)
 

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Discussion Starter #28
Now i'm really confused :') so 235/65/17 instead of 60 is no problem for the mechanical bits, but 245 45 20 instead of 40 is a problem?
 

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I think Deebo should put the biggest wheels and tyres he can find on his Captiva, as long as he is happy with the "look", If it doesn't work, or something breaks then he can let us know, Since he isn't "technical", I don't think he should worry too much about technical matters, just focus on the look that he is after. I mean nobody wears 5" heels for the comfort, it's about the look.

I thought that BMW/Benz put wider tyres on the back because the bias on those is to sending most of the power to the back wheels, and since the weakest X5 is making at least 110 BHP more than a Captiva, (265 diesel, 300+ petrol) it might, just might be not only about the look, but also about not sliding all over the place.
 

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Now i'm really confused :') so 235/65/17 instead of 60 is no problem for the mechanical bits, but 245 45 20 instead of 40 is a problem?
Deebo, I'm not going to comment on any remarks made by others but I will answer your question above as simply and concisely as I can.

The Captiva has a clearly defined operational range of wheel and tyre sizes set out by GM in the build, test, and operational limitations of its construction. 235/65/17 are within the accepted parameters , 245/45/20 is NOT defined within accepted parameters.

You can look up the operational acceptable tolerances for virtually any vehicle by using the Internet but most owners handbooks also give this information as applicable to the vehicle in question.

Working where you work your colleagues will be fully aware of the defined parameters for a given vehicle build.
Just because some other xyz build vehicle may have some other size doesnt mean that the Captiva is built to use that size.

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Discussion Starter #32
Ok, but still it is strange, no? 235 65 17 is even larger then the 245 45 20? ?
I will fit the recommended tyre ofcourse.
And victor, i am sorry that i am a non-mechanic... No need to give me a hard time... in my mind the few % wouldn't matter that much, especially after reading that 65 is within the tolerance even though it is even larger then the size i wanted ?
Thanks to all for your time
 

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Ok, but still it is strange, no? 235 65 17 is even larger then the 245 45 20? ?
I will fit the recommended tyre ofcourse.
And victor, i am sorry that i am a non-mechanic... No need to give me a hard time... in my mind the few % wouldn't matter that much, especially after reading that 65 is within the tolerance even though it is even larger then the size i wanted ?
Thanks to all for your time

Deebo,

The difference in diameter between the two is just 8.8mm (or only 0.34 of an inch if you prefer that) which is negligible - in fact roughly equivalent of a half worn tyre depth.

How are you defining your BIG? I think you have a fixation on 'Big' being width.

You just dont seem to be understanding that 245/45/20 can have the effect of altering the stress geometries of track, loadings on wheel bearings, road drive/frictional resistances, altered load on suspension etc. Singly these are maybe minor but combined could be serious. That is probably why GM do not Type Approve wheels outside of their design criteria.

I cannot find any GM approval being granted for the Captiva wheels exceeding 235.
You cant say "I will fit the recommended tyre of course" and then inform us you want to fit 245/45/20. The latter is not "Type Approved" and therefore NOT within the recommend sizes.

I have extensively checked technical data listings for both Series 1 Captiva, Series 2 Captiva and the Captiva Sport and there is NO LISTING approval for 245/45/20 wheels/tyres in the entire life production run of this model todate.

Let me spell it out to you. Possibly damaging your vehicle through potential stresses is one thing (your financial loss) but possibly killing someone is a totally different issue. Fitting something that is outside the vehicle 'Type Approval' of its tested safe criteria places you at risk that if you have a smash and injure or kill someone. It could well be claimed that your control of the vehicle was compromised by your modifications. Firstly you will not be insured, and also possibly facing a Manslaughter charge for knowingly altering a vehicle outside and beyond the realms of its approved design criteria.

I see no purpose in debating this further with you other than to say I think you are wearing blinkers in respect of the advice given to you and being unwise in what you are proposing. Think again.

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................ after reading that 65 is within the tolerance even though it is even larger then the size i wanted

Deebo,

Having looked at your comments again I think I can understand your total misunderstanding of tyre data definitions.
You referred to 65 being bigger than 45.
Yes it is simply read as a 'figure' but.... it is not a measurement in millimeters which is what I believe you are thinking it is.

This middle figure of 235/65/17 is a PERCENTAGE RATIO and not a measured size. The actual size that 65 represents (in this example) is the percentage ratio to the tyre width. So the only thing that is 'larger' from this middle figure is the tyre sidewall and not the rolling size of the entire wheel with tyre.

The capability of a tyres sidewall to 'flex' is proportional to its capability for the sidewall to absorb road (or other surface) shock. This absorption capability is carefully designed to work hand in glove with the shock absorbers and the road spring capabilities of the vehicle design.

Your indicated preference at 245/45/20 has considerably less 'absorption / flexing capability' - in fact about 30% less capability than the 235/65/17 which means the shock absorbers and road springs have much more work to do in having to 'take' the additional stresses - which in turn is also transmitted into the body shell of the vehicle.
Accelerated failure of standard shock absorbers and broken springs is therefore much more likely having to deal with stresses they were not designed for (hence GM do not classify your tyre & wheel size as acceptable) combined with an awfully 'hard ride'.

If this has 'gone over your head' then there is nothing more you can learn !
 

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245/45/20 would look cool in certain age. They are still not very good choice as the ride would assumed became terrible. Best choice in my mind would be 235-65-17 if the ride is preferred as first option. But i am an old fart....
 

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Discussion Starter #36
Aussi ed, with the "i will fit the correct size ofcourse" i meant the 245/40/20, that is the size that every aftermarket wheels use for 20's on a captiva ? i thought they had factory 20's as an option too but i am confusing that with the irmscher model i think
 

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Deebo,

The 2008 Series 1 Captiva NEVER repeat NEVER had 245/40/20 wheels/tyres as its design build criteria. (see below build approved data)

Fitting of non specification equipment (of any kind) is at the owners risk. The fact that 20" wheels are available for some vehicles DOESNT MEAN THAT THEY ARE APPROVED OR SUITABLE FOR YOUR VEHICLE.
Wheel manufacturers will supply their products to anyone stupid enough to part with their money on a non approved product.

Wheel & Tyre Design criteria data for GM Chevrolet 2008 variants :-

2.0 D 148hp
215/70R16 6.5Jx16 ET46 5x115 M12 x 1.5 70.2
235/60R17 7Jx17 ET46 5x115 M12 x 1.5 70.2
235/55R18 7Jx18 ET45 5x115 M12 x 1.5 70.2

2.4i 134hp
215/70R16 6.5Jx16 ET46 5x115 M12 x 1.5 70.2
235/60R17 7Jx17 ET46 5x115 M12 x 1.5 70.2
235/55R18 7Jx18 ET45 5x115 M12 x 1.5 70.2

3.2i 227hp
235/55R18 7Jx18 ET45 5x115 M12 x 1.5 70.2
215/70R16 6.5Jx16 ET46 5x115 M12 x 1.5 70.2
235/60R17 7Jx17 ET46 5x115 M12 x 1.5 70.2

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Discussion Starter #38
To kick this up again... I want to buy new tires for my 17 inch original wheels, i want a more rugged tire then normal (pirelli scorpion all terrain plus).
But 235 60 17 is not available, 225 65 17 is available and so is 235 65 17.
The 225 65 is percentage wise almost the same (1,47% bigger).
But somebody in the above reactions fitted 235 65 17 on his captiva, wich was said to be no problem, but they are 3.3% bigger, i also rather want the 235 65, but this is really no problem for my automatic gearbox etc.? I know the speedo is a little different with the bigger tires.
But mechanically there is no problem?
 

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Personally I think the Pirelli tires you want will be heavy and somewhat noisy. On my Captiva i've fitted Vredestein Quatrac 5 all seasons 235/60/17 and i recommend them, last winter i was plowing the streets on a snowy day, and they don't make much noise in the summer on the highway.
 

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Discussion Starter #40
I read many tests and reviews on them and they should be a lot less noisy then they seem :)
 
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