Maximum tyre (not rim) size (Updated with Pics)

[Cole]

I have searched… and all the threads I can find here focus on matching the maximum rim size (i.e. 22") with ultra low profile tyres… but I drive on badly pot holed roads, and, for safety reason, I actually want to increase the amount of rubber between my rims and the road.

I know this may look daft to someone with 22” rims and 30 profile tyres but trust me, this setup would not last 10 miles on the roads I sometimes drive down.

Currently I am using 235/65/17 tyres, these give me 6” of rubber between rim and road and a total top to bottom diameter of 29.03".

If I could fit 245/70/17 tyres on my existing rims I would gain 0.74” of extra rubber between my rim and the road, but total diameter would be up to 30.5”. Total circumference, and hence speedo error, would increase 5.1%.

Basically I want to know what is the biggest diameter tyre I can fit on a standard 17x7.5" rim before it rubs on my 2006 X5 3.0D, rear only self levelling air suspension, non flared standard wheel arches?

Whatever I do I will do equally to all four corners so there should be no issues with DSC and ABS etc. I know that my speedo error will increase, and I know my handling will suffer, but it may save me a few bent rims and long walks home so I would like to consider the options.

[sprocket1200]

try searching google for a tire size calculator. that will tell you all you need to know.
obviously the other things you can do are reduce tire pressure and slow down...

[JCL]

You don't need a tire size calculator, you need to know if someone has done it before. I don't know the maximum size, but I know that 265/70 fits. This link is the only example I know of, done for similar reasons by a long-time member.

Xoutpost.com - View Single Post - Wanna fill up your wheel-wells with snow tires?

[Cole]

Originally Posted by JCL

You don't need a tire size calculator, you need to know if someone has done it before. I don't know the maximum size, but I know that 265/70 fits. This link is the only example I know of, done for similar reasons by a long-time member.

Xoutpost.com - View Single Post - Wanna fill up your wheel-wells with snow tires?

Excellent thanks that's exactly what I wanted to know...

265/70/17's will give me 7.3" of rubber between rim and road and a diameter of 31.6". Ground clearance will also increase 1.3" over stock. Speedo will change by 8.9% which is a bit of a bummer but I use an aftermarket satnav that give me accurate speed anyway.

They even look quite good in that link... not too naf!

[Cole]

Originally Posted by sprocket1200

try searching google for a tire size calculator. that will tell you all you need to know.
obviously the other things you can do are reduce tire pressure and slow down...

Reducing tyre pressure is not the answer when confronting a pot hole. If you have soft tyres they compress more easily and the rim impacts the edge of the pot hole all the sooner. If you do this hard enough the rim bends, breaks the tyre's seal, and you have an instant blow-out and a hard time controlling the vehicle whilst it slows down. ABS is notoriously bad at handling blow outs so don't slam on the brakes!

I typically don't drive fast on these road... but when you have 900km (560 miles) to go, crawling at 60Kmh (37mph) is not really an option. The problem with the roads I drive is that they are mostly good tar. It is just that every so often there is a washaway or bad section and if you hit that at 120kmh with 30 profile tyres you are in trouble! Hit it with 70 profile and you have much less of a problem.

[Fraser]

If you are after rim protection and puncture resistance you could also look at a light-truck tyre rather than a passenger car tyre but you'll sacrifice ride quality and most likely speed rating although I'm not sure what's available in your neck of woods. LT tyres can also effect steering quality, but so will a bigger, fatter tyre 'passenger' tyre. I'll be interested in what you settle with. My driving environment is like yours ... low profile rubber is more a liability than an advantage.

[rogerkiu]

Originally Posted by Cole

I have searched… and all the threads I can find here focus on matching the maximum rim size (i.e. 22") with ultra low profile tyres… but I drive on badly pot holed roads, and, for safety reason, I actually want to increase the amount of rubber between my rims and the road.

I know this may look daft to someone with 22” rims and 30 profile tyres but trust me, this setup would not last 10 miles on the roads I sometimes drive down.

Currently I am using 235/65/17 tyres, these give me 6” of rubber between rim and road and a total top to bottom diameter of 29.03".

If I could fit 245/70/17 tyres on my existing rims I would gain 0.74” of extra rubber between my rim and the road, but total diameter would be up to 30.5”. Total circumference, and hence speedo error, would increase 5.1%.

Basically I want to know what is the biggest diameter tyre I can fit on a standard 17x7.5" rim before it rubs on my 2006 X5 3.0D, rear only self levelling air suspension, non flared standard wheel arches?

Whatever I do I will do equally to all four corners so there should be no issues with DSC and ABS etc. I know that my speedo error will increase, and I know my handling will suffer, but it may save me a few bent rims and long walks home so I would like to consider the options.

You may consider 255/60/17 or 275/55/17, these sizes can fit the x5 without confusing the speedometer. Any other size will make the speedometer displaying wrong speed and may affect the range figures and your mileage figures as well.

[Cole]

Originally Posted by rogerkiu

You may consider 255/60/17 or 275/55/17, these sizes can fit the x5 without confusing the speedometer. Any other size will make the speedometer displaying wrong speed and may affect the range figures and your mileage figures as well.

Thanks, but this rather defeats the object though as I am trying to get more rubber between the rim and the road... not in terms of width, but in terms of distance from the tar. These options are just wider, but because of the lower profile the net result is that the rim is still going to be 6" from the tar. In fact the 275/55 profile tyre would put the rim slightly closer to the tar at 5.95". In terms of grip they would be better than my standard 235/65/17 tyres due to the bigger footprint, but they would not really offer better pot hole protection, which is what I need.

There is no option to achieve what I want without disturbing the speed calibration... but the average speedo in most X5's over reads by a few % anyway, and a slightly bigger diameter tyre will then actually improve the speedo's accuracy, providing you don't go too big, and then it will under read... (sorry officer but my speedo only said 120kmh... I am sure I wasn't doing 200!)

[Cole]

Originally Posted by Fraser

If you are after rim protection and puncture resistance you could also look at a light-truck tyre rather than a passenger car tyre but you'll sacrifice ride quality and most likely speed rating although I'm not sure what's available in your neck of woods. LT tyres can also effect steering quality, but so will a bigger, fatter tyre 'passenger' tyre. I'll be interested in what you settle with. My driving environment is like yours ... low profile rubber is more a liability than an advantage.

Yes I agree... I am kind of favoring the Bridgstone Deulers, not the full off road A/T versions, but perhaps the highway version. Don't know if they are popular in Aus but out here they use them a lot on light trucks and real 4x4's...

[sfcl]

I'm using 275/55/17 on original rims, no problem.