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Hi all,

I live in Dubai and want to do more sand dune off roading. I am wondering whether I can change from 40's to 45's on my Touareg V8 without any repercussions such as tyre rubbing or hitting shock housing under braking? That would give me more tyre when deflating for the deep sand conditions.

I currently have PZeros 275/40/20 106 Y's which are in need of changing. Unfortunately the second hand market is crap here so I can't cost effectively buy new rims. Does anyone have any other solution? Either changing manufactuer, tread design or ideally switching from 40's to 45's?

Thanks for your help,

Dougie Bogged down in the Sand
 

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Chairman
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The largest diameter tyre/wheel combination that fits inside a Treg wheelarch is 31.6 inches

Here's a thread showing a Treg on 17 inch wheels with 265/70/17 fitted:

http://forums.vwvortex.com/zerothread?id=2427967

Your current tyre/wheel combo of 275/40/20 gives an overall diameter of 28.7 inches so you've got some room to increase the depth of the sidewall, but NOTE - this will be at the expense of high speed handling and cornering.

Your proposed 275/45/20 will give an overall diameter of 29.7 inches so these should fit ok, but I wouldn't have thought an extra half inch in the depth of the sidewall would make that much difference when in deep sand even a low pressures.

You might be able to go to 275/50/20 - diameter 30.8 inches, sidewall depth 5.4 inches versus your current 4.3 inches.

But I think 275/55/20 would be too large at 31.9 inches.

Here is the tyre size calculator to help you:

http://www.miata.net/garage/tirecalc.html

Note again, fitting different spec tyres may affect the handling of your camel, sorry, vehicle.
 

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Hi All
I could also do with a little bit of advice similar issue but the reverse. I dont off road (sorry guys) I currently have 275/45 R19 108Y - I have been offered some Pirelli's at a very good price but they are 275/40 R19 105Y - I have been given conflicting advice - some say it will effect the diff and could burn it out (a little extreme I think as difference is only 5m) and other says it will effect my insurance as the weight is not the same. Does anyone have a clue whether I can put these on without causing any damage for the future.

Any advice would be grately appreciated

thanks in advance
 

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Superman
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2,258 Posts
Hi All
I could also do with a little bit of advice similar issue but the reverse. I dont off road (sorry guys) I currently have 275/45 R19 108Y - I have been offered some Pirelli's at a very good price but they are 275/40 R19 105Y - I have been given conflicting advice - some say it will effect the diff and could burn it out (a little extreme I think as difference is only 5m) and other says it will effect my insurance as the weight is not the same. Does anyone have a clue whether I can put these on without causing any damage for the future.

Any advice would be grately appreciated

thanks in advance
One big word of advice, don't touch the Pirellis Unless you're willing to change your boots in another 4-6k miles (unless you're talking scorpions, of which I don't recall anyone using them on here in 4 years) I've personally run pzeros which lasted 5k miles.

Do a search on tyre depth differences affecting the diff/transfer box, it's been discussed to death. Think it's 2mm difference/tolerance between tyres, so always advised to change all where poss.

Hankook Ventus RH06's or General Grabbers are by far the tyre of choice here, even convinced a friend to put them on his Cayenne, and he hasn't looked back.
 

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Chairman
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I think we established it's 2mm difference side to side on the same axle and 3mm difference front axle to back axle to avoid damaging the transmission.

Hankooks or Grabbers get a lot of support on here.

Try www.event-tyres.co.uk [they come to you but don't cover all of the UK yet] or Camskill.

Here's the tyre size calculator:

http://www.miata.net/garage/tirecalc.html

The overall difference in diameter between the two tyres sizes you stated is 27.5mm [that's over an inch less for the new tyres you mentioned!] and NOT the 5mm you think it is.

I'll explain why.

The 275 is indeed the width of the tyre in millimetres, BUT the 45 and the 40 [the profile or depth of the tyre wall] are each a PERCENTAGE of the width and therefore these are not specific measurements in millimetres.

The 19 is the wheel diameter in inches. {No, I don't know who decided to mix metric and imperial measurements!]

Using the calculator above, you will see that the 40% profile tyres do 453 revolutions per mile whilst the 45% profiles you've got do fewer revolutions at 436 per mile so already you can see your smaller diameter tyre will wear out 4% faster.

With such a big difference in the overall diameter should you to fit just a pair of the smaller tyres to one of the axles you'd wind up and seriously damage the transmission very, very quickly indeed.

If you fit a complete set of 4 new tyres of the smaller profile, your speedo will over-read your speed by about 3% so, given that it already over-reads by a few percent anyway, you shouldn't get any speeding tickets!

However, the 105 load rating in not adequate for the car and could invalidate your insurance in the event of a serious accident.

Overall then,the cheap tyres are not a good idea IMHO.
 

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Just to add some info re changing load rating etc.
When I replaced the run flat tyres on my 5 series BMW with normal tyres I checked with my insurance company first. They said as long as the tyres were the same size and at least the same speed and load rating then they didn't have a problem. Which leads me to think that even changing just the tyre size may be an issue. You should certainly at least check with them first.
 

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Elite Member
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Kumho do some decently priced tyres - I have 2 x KL16 on my 2.5 TDi and th ewear is very low and the tread is certainly good enough for off roading.
 

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Telemetrically Superb
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I can certainly recommend Event Tyres - quick, cheap and friendly

With some trepidation, I just had my Goodyear Wrangler SRA's replaced with Grabber UHP's after 30k miles of faithful service - and that was only because there was uneven tyre wear on the rear passenger side tyre which was down to 2mm - rest of em still had 6mm left so I could have probably had another 10k miles out of 'em!


Immediate thoughts are that the Grabbers are excellent on the road with decent grip and a comfy ride. As for offroad, they are very good and if you want a recommendation, look no further than the Touareg Unlimited Team who use them on their cars
 
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