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Discussion Starter #1
Hello, i have a 2008 2.0 diesel 4wd automatic gearbox captiva, but i was wondering how 4wd it is, is it constant, or it only kicks in when needed? And how is it controlled when the rear wheels kick in?

And the tire question, because it is 4wd,i have to put the same size on the rears?
I am going to fit 20 inch, but fronts are 245 40 20, and rears 275 35 20, about the same diameter, but do or don't? ?
 

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As far as I can see the system runs in front wheel drive until it detects any slippage then the rear wheels are brought it to use and it goes into 4wd.
Cannot advise on tyres as don't know the full spec on the awd system. But would guess you would need both front and rear tyres to have the same rolling circumference.

There has been a few comments on this forum about wheel sizes affecting the comfort of the ride.
 

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Deebo, My first reaction is that as you joined the forum three years ago I am assuming you've owned your Captiva for that time.
How can you own a vehicle for three years and not know what kind of 4 wheel drive you have ? Your handbook should explain this.
For clarity the Captiva is an 'on demand' four wheel function.
It is wise for stability to maintain equal tyre sizing on all wheels. Make sure any change of wheel size provides suitable projection clearance for suspension and brake components.

I'm not sure what vehicle regulations you have in Belgium but make sure that it will comply with your vehicle road regulations (unless you are modifying it for private track use) and probably you will need to notify your insurance company of the change from the OEM 'build' with evidence of road compliance.

My next question is why are you embarking on this wheel change?
Are you aware that 35 & 40 profile are virtually like riding on 'bricks' and will have little or no sidewall flexing and is virtually the equivalent of solid rubber tyres of the 1880's . We have had pneumatic tyres for over 100 years!

Make sure you give this full thought before embarking upon it.

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Aussie, I joined the forum 3 years ago for a question my mother had about her Orlando. I own my Captiva (and first Chevrolet) since 3 months, I read the manual almost instantly about these questions, but can not find clear information about the 4wd, only about what you said, that it is not constant, and can not be turned on or off manually, but I wanted to know more ?
I am used to driving low profile tires, my last car was a lowered Alfa Romeo 156 with 225 40 18, I am pretty sure that was harder then this will be ? i was thinking of mounting 245 45 20 instead of 40.
I know this will make the speedo a little different but i will get used to that, and m.o.t.-wise it is not allowed but i need to go in wintertime so then the 17 inch original wheels will be on anyway.
The question for the rear tires being wider was just that it would look better from the rear ?
I thought, if the overall diameter of the tire would be the same it wouldn't matter, since all those BMW's and Mercedes 4wd suv's with 20 inch+ allways have tireslike 275 in the front and 315 or 325 in the rear with a little lower profile
 

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Discussion Starter #5
245 45 20 alround wouldn't be a problem for the gearbox or anything? Normally 245 40 20 would be fittet but i like the 45 more ?
 

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Aussie, I joined the forum 3 years ago for a question my mother had about her Orlando. I own my Captiva (and first Chevrolet) since 3 months, I read the manual almost instantly about these questions, but can not find clear information about the 4wd, only about what you said, that it is not constant, and can not be turned on or off manually, but I wanted to know more ?
I believe it's been covered on here before but, briefly, the drive on the rear axle is brought in by an electronic clutch mounted on the rear diff unit. It’s a good system for icy roads or wet grass but not a true 4x4 system.

Your gearbox output is primarily through a differential to the front wheels but there is also a transfer box permanently engaged with your gearbox. It’s a single speed mechanical box and it turns the propshaft which is connected to the rear diff pinion flange. Simply turning the rear diff pinion flange, however, does not result in rear wheel drive. The rear diff has an electronic clutch which is OFF by default but it gets activated when the cars’ electronic systems determines it is necessary.

The original design was by Toyota and manufactured by Aisin. It’s a system that’s used by a number of different vehicle manufacturers and generally works well, any problems are usually related to wheel speed sensors or active yaw control systems.
 

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The question for the rear tires being wider was just that it would look better from the rear ?
I thought, if the overall diameter of the tire would be the same it wouldn't matter, since all those BMW's and Mercedes 4wd suv's with 20 inch+ allways have tireslike 275 in the front and 315 or 325 in the rear with a little lower profile
I don’t think there’s going to be any problems with the tyre sizes you quote since the difference in rolling circumference is negligible. However, before you fit expensive wider rear tyres you need to be aware of a problem the Captiva has with worn wishbone bushes affecting the camber angle. Several owners have reported uneven tyre wear even with the standard wheel / tyre set up and it would pay you to check your existing tyres and probably even get a full wheel alignment check done before you change anything. See this thread for further info; https://www.chevroletownersclub.co.uk/forum/17-captiva/5515-rear-tyre-wear-help.html
 

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Discussion Starter #8
Thanks victor!
And what about allround the same size, but 5 higher? Instead of 245 40 20, 245 45 20 (just for comfort and better wheel arch filling)
 

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Can't give you a definitive answer on that Deebo, haven't heard of anyone who's done it so I don't know whether there's any problems eg clearance from wheel arch panels.

I looked up one of the tyre comparison sites about upsizing from a base tyre size of 245 x 40 x 20” to a 245 x 45 x 20” and noted the following:

The proposed upsize has a circumference of 78mm which is 3.5% greater than the base tyre.

This exceeds the recommended upper limit of 1.5% for upsizing.

The vehicles’ actual speed would be 3.5% greater than the indicated speed.

IF the speedometer reading was 100% true that would be illegal but most vehicle speedometers err on the optimistic side by around 10% so in practice I don't think it would lead to any problems however it's your decision.
 

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Discussion Starter #10
Victor, thanks again, clearance and such i am not concerned about, but i mean for the gearbox and such it should be no problem? (about the mechanical stuff i know very little so i rather be sure :))
 

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im no expert on the captiva by any means, but from experience with other vehicles/manufacturers is'nt it more important to keep the speedo programmed in with the exact tyre size on an automatic gearbox, due to sensors in the box ? not as important on a manual...
 

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Calam1ty, Indeed you are correct this may have an adverse effect. It is very probable the huge difference in what Deebo wants to fit may well destroy the wheel bearings and other drive components as well. There are reasons that Chevrolet (indeed any motor vehicle manufacturer) define the scope of wheel and tyre sizes all part and parcel of the product design from an engineering, safety, ride comfort and compliance point of view.

Purely as a personal opinion I think that Deebo is pushing the boundaries too far but if he has the money to spend 'playing' with his vehicle then so be it. It doesn't sound as if this needs doing because of functional terrain necessity ; in fact all he seems to have stated is he thinks 'it looks good' ! Handling, safety, ride comfort and engineering tolerances dont seem to be within his remit. So long as he has money to replace the gearbox, differential and other components then who are we to stop him. All of us probably do something that later on we question why did I do that or spend all that money on xyz. This might prove to be his. I think this has got future trouble written all over it.
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Discussion Starter #13
Ok, then i wont do it, the 275 in the rear would be for looks, but i wasn't going to do that either if it's bad for the gearbox. the 5 higher was for a little more comfort, and... because, 245 40 20 is what they recommend, but that is also almost -2% of the overall size i have now, 245 45 20 is +3% or something, so only 1% more diffrence then the 40 high, so why wouldn't i ask...?
 

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Discussion Starter #14
Checked again, 245 40 20 is -1.37% and 245 45 20 is +2.04% difference of what i have original (235 60 17). So not even 1% bigger difference then the recommended size. Officially because of the speedo you can not go above +1,5% but would this 2% in the circumference destroy the gearbox?
 

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Can't give you a definitive answer on whether it will affect your gearbox, it's a question of final drive gear ratio. I have the 6 speed manual gearbox and 6th gear is a very high overdrive ratio. I wouldn't fit tyres with a higher aspect ratio to mines because it would lead to situations eg in climbing long hills fully loaded it would struggle so I would be changing down to 5th more often and I could see it being a pain in normal driving. With yours it will change down automatically. You're the one who is best placed to assess whether your transmission would be placed under excessive strain ie how high is your gearing and how torquey is your engine?
 

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Discussion Starter #16
Mine is a first gen, only 5 speed gearbox, and always normal flat roads (belgium/holland)
 

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Mine is a first gen, only 5 speed gearbox, and always normal flat roads (belgium/holland)
Yes, I know, probably the Aisin Warner which AFAIK is a good transmission. What you have to decide is how high geared it feels when you're driving and whether you'd like to have it even higher geared.
 

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Discussion Starter #18
I don't understand exactly what you mean, that means that it would shift later? Or sooner? I am really not technical ?
 

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I would go for 235 or 255-50-19 instead of 20" rims. My opinion is that all 4 wheels should be of same size. Car is still front wheel drive in normal conditions and i think all 4 wheels should have exactly the same diameter to avoid possible problems with the power train....
 

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Have just been reading on the Kia Sorento forum that a difference of 3-4 mm on tread depth on the standard wheels is enough to warrant replacing all tyres due to the 4 wheel AWD system. So, if you play about with different wheel sizes front to back you may need to replace the tyres at a much lower mileage. The reason for the wear/diameter limit is that, if the fromt wheels have a smaller diameter they will turn faster than the rears and the AWD system will "think" that the fronts are slipping and bring in the rear wheel drive, thus leading to additionsl transmission wear. I would guess that the above also applies to the Captiva
 
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