4.8GRX Tyre size

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4.8GRX Tyre size

Post by Getalbo » 12 Mar 2014 21:31

What is everyones experience on this issue. 16" or 17 ". Obviously it effects drive train ratios etc., and to some extent consumption.
Your thoughts and advice please?

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Re: 4.8GRX Tyre size

Post by IanT » 13 Mar 2014 06:06

The 4.8 GRX standard tyre size is 17 inch it is fairly easy to find good AT tyres and even muds in 17 inch these days I was running 265's but a lot of the guys run 285's or even 305's

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Re: 4.8GRX Tyre size

Post by Zantus » 13 Mar 2014 06:45

16"vs 17" doesn't have an effect on ratio's, it's the outside diameter that matters in that regards, i.e. you can have a 15" rim with an outside diameter of 35", which will be way worse than a 17" rim with 31" diameter.

Comparing two tyres with the same outside diameter, but different size rims, the bigger rim gives you more lateral stability, but the smaller rim allows you to deflate more without the chance of de-beading, so that will be better for off-road use. There are more benefits/negatives to both, just giving you a rough idea and I want bring the point across that rim diameter differences should not be confused with tyre outside diameter differences.

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Re: 4.8GRX Tyre size

Post by Peter Connan » 13 Mar 2014 06:59

The 16" or 17" you refer to is the rim size, and assuming you buy a tire that fits on the rim you have, it has no direct bearing on the overall size of the wheel, nor on the gear ratio, fuel consumption nor any other aspect of fuel consumption.

More on this later.

Unfortunately, with metric tire sizes it is quite a calculation to determine the tire's outside diameter (which is the factor that affects the overall gearing). It goes like this (and sorry in advance as I will be working in inches):
The tire size is for example 285/75R16, and this is what it means: The tire width (at the widest point, not the tread) is the first number set (in this example 285mm). The second set of numbers is the aspect ratio. This is the sidewall height, but expressed as a percentage of the tire's width. In this example, the sidewall height is thus 285/75 = 213.75mm Convert this to inches (by dividing by 25.4) and you get 8.4". The third number set is the diameter of rim that the tire fits on. To get the outside diameter of the tire, multiply the sidewall height by 2 and add the rim diameter: 8.4*2+16 = 32.8" Bear in mind that these figures are nominal not exact, they change by at least an inch during the life of a muddy and they change when loaded and depending on tire pressure, and it becomes evident that you needn't worry too much about the commas.

Now, the 4.8's standard wheel size is around 32". I feel a 33" is about ideal, while some are prepared to go all the way to 35". Also bear in mind that width will also play a role, particularly in fuel consumption.

My reasoning for always going up one size is as follows: most times when you get stuck, it's because you have run out of ground clearance. Most times, this is due to a middle-man that has been created by a variety of vehicles. If you have just a little bit more ground clearance than "mr. Average", you avoid most of these issues.

Now rim size: for an off-road vehicle, the higher the sidewall the better. It allows the tire to form a longer footprint when deflated for better flotation, and keeps the rim further away from the edges of the potholes, thus significantly reducing the risk of tire damage.
However, on smooth roads high sidewalls are a disadvantage, as they are not as directionally stiff. Thus high-speed handling suffers a little bit, and may come off the rims more easily during violent high-speed manuevres.

So while I have not given you an answer, I have hopefully given you tools to get your own answer?
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Re: 4.8GRX Tyre size

Post by David » 13 Mar 2014 07:43

On a 4.8 there is apparently a problem going to 16 inch rims as they interfere with your larger brake calipers so I would suggest sticking with your 17 inch rims but go to a 285 (33"). They fill the wheel arch better and give you a little bit more ground clearance.

The down side is it will look like you are heavier on petrol as your speedo will be close to 100% but your trip meter will under-read. In reality there is little difference in consumption.

The up-side will be that your car will look better and perform better off road :thumbup:
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Re: 4.8GRX Tyre size

Post by JohnBoyZA » 13 Mar 2014 12:31

If you struggle to remember the formulas like me ... then you're welcome to use the attached.

My only comment is that sometimes you might need to catch up to mates and you might end up driving these speeds, then don't opt for the higher profiles.

http://www.flickr.com/photos/jhemurray/ ... 4104842583

Not recommended...!
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Re: 4.8GRX Tyre size

Post by Marino4x4 » 13 Mar 2014 15:08

Hi JohnBoy

Dit werk nou sommer lekker. Baie maklik om te gebruik.

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Re: 4.8GRX Tyre size

Post by Getalbo » 13 Mar 2014 18:10

Thanks everyone for your input. I will stick with the 17 " which I have.

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Re: 4.8GRX Tyre size

Post by Peter Connan » 13 Mar 2014 19:24

David wrote:On a 4.8 there is apparently a problem going to 16 inch rims as they interfere with your larger brake calipers so I would suggest sticking with your 17 inch rims
16" rims fit on the 4.8, it's 15's that don't fit.
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Re: 4.8GRX Tyre size

Post by Alex Roux » 13 Mar 2014 22:12

Peter

Does this apply to all the 2005+ facelift models?
Or pre facelift too?
The 2005+ models came out with 17" standard, or only the GRX models, I think?

Christo's Chuck has 15" on (1999 model I think)
Mine is 2004 (pre-facelift) which still had the 16" as factory standard.
But I do not know if I can take 15"?
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