Wheels! What size tyres?

4256stephen · 2025-09-04T13:20:29+0100

Hi, I'm new to the range rover sport scene, I have purchased a 2010 RRS, Last night in the rain the car felt awful, sliding on roundabouts etc, checked the tyre pressures they were 34 front 37 rear, upon checking on google by numberplate it says my tyres should be 275-40 r20 I have 255-55 r20 are these the wrong size? I have attached a couple of pictures? Any info would be much appreciated.

300bhp/ton · 2025-09-04T13:30:31+0100

What brand/tread are they?

It really shouldn't slide very easily, unless you were really hooning it. Although they are big heavy cars, so can push to understeer fairly easily.

I doubt a 255 would really cause a sliding issue over a 275, although they are smaller, but you'd be talking about on the limit grip differences, so again driving very aggressively.

I would think either the roads where slippery if it was very heavy rain and maybe hadn't been rained on for a while. Could have been spilt diesel on the road, that is very slick.....

Else it is probably the age/tread/brand of tyres maybe.

Does the vehicle drive ok otherwise? No clonks of odd handling in the dry? If there are other issues, then suspension could be causing some odd handling, as good a poor suspension geometry. Might be worth spending out on a new set of tyres and a tracking/geo check & adjust.

4256stephen · 2025-09-04T13:38:55+0100

300bhp/ton said:
What brand/tread are they?

It really shouldn't slide very easily, unless you were really hooning it. Although they are big heavy cars, so can push to understeer fairly easily.

I doubt a 255 would really cause a sliding issue over a 275, although they are smaller, but you'd be talking about on the limit grip differences, so again driving very aggressively.

I would think either the roads where slippery if it was very heavy rain and maybe hadn't been rained on for a while. Could have been spilt diesel on the road, that is very slick.....

Else it is probably the age/tread/brand of tyres maybe.

Does the vehicle drive ok otherwise? No clonks of odd handling in the dry? If there are other issues, then suspension could be causing some odd handling, as good a poor suspension geometry. Might be worth spending out on a new set of tyres and a tracking/geo check & adjust.

Car drives and feels great in the dry, what I was wondering was are these wheels 275 wide? and would a 255 tyre fit on it?

4256stephen · 2025-09-04T13:41:52+0100

300bhp/ton said:
What brand/tread are they?

It really shouldn't slide very easily, unless you were really hooning it. Although they are big heavy cars, so can push to understeer fairly easily.

I doubt a 255 would really cause a sliding issue over a 275, although they are smaller, but you'd be talking about on the limit grip differences, so again driving very aggressively.

I would think either the roads where slippery if it was very heavy rain and maybe hadn't been rained on for a while. Could have been spilt diesel on the road, that is very slick.....

Else it is probably the age/tread/brand of tyres maybe.

Does the vehicle drive ok otherwise? No clonks of odd handling in the dry? If there are other issues, then suspension could be causing some odd handling, as good a poor suspension geometry. Might be worth spending out on a new set of tyres and a tracking/geo check & adjust.

Car drives and feels great in the dry, what I was wondering was are these wheels 275 wide? and would a 255 tyre fit on

Grrrrrr · 2025-09-04T13:45:09+0100

4256stephen said:
Hi, I'm new to the range rover sport scene, I have purchased a 2010 RRS, Last night in the rain the car felt awful, sliding on roundabouts etc, checked the tyre pressures they were 34 front 37 rear, upon checking on google by numberplate it says my tyres should be 275-40 r20 I have 255-55 r20 are these the wrong size? I have attached a couple of pictures? Any info would be much appreciated.

Possibly more to do with the tyre than its size. 255 is a decent footprint.

I tried some Kumho H-something on my Omega once. The U ones were OK but the H (for hard wearing, apparently) were horrible. Any damp on the road and the back end stepped out like it was on ice. Chinese Ditch Finders of the highest order.

Grrrrrr · 2025-09-04T13:47:52+0100

4256stephen said:
Car drives and feels great in the dry, what I was wondering was are these wheels 275 wide? and would a 255 tyre fit on it?

Depends on the bead and some cars come with different options. Thinner tyre has less grip but also less thirsty and less road noise. Most cars are over the top these days.

Softer tyres tend to grip more, especially in winter, but wear faster. I find the General Grabber AT range works well on my P38A.

marjon · 2025-09-04T13:55:51+0100

Tyre Size Calculator

A better easy to use tyre size calculator. Use our tyre size calculator to find tyre diameter, width, sidewall, circumference, and revolutions per mile.

tiresize.com

You can see by the comparison of sizes.
The car sits higher.
The tread width (contact patch with tarmac) is smaller than your recommended size.

But I am not saying they are wrong.

The are many factors for tyre choice and some cheap brands dont perform aswell in certain situations. but of course situations can vary so much too.

Is there a sticker on the door pillar which may give a couple of tyre sizes and recommended pressures.

Are they a cheap brand? Maybe thats all the PO could afford.

J

4256stephen · 2025-09-04T14:06:40+0100

Grrrrrr said:
Possibly more to do with the tyre than its size. 255 is a decent footprint.

I tried some Kumho H-something on my Omega once. The U ones were OK but the H (for hard wearing, apparently) were horrible. Any damp on the road and the back end stepped out like it was on ice. Chinese Ditch Finders of the highest order.

What pressure would you advise for the 255 55 20?

4256stephen · 2025-09-04T14:08:59+0100

Grrrrrr said:
Possibly more to do with the tyre than its size. 255 is a decent footprint.

I tried some Kumho H-something on my Omega once. The U ones were OK but the H (for hard wearing, apparently) were horrible. Any damp on the road and the back end stepped out like it was on ice. Chinese Ditch Finders of the highest order.

What pressure would you advise for the 255 55 20

4256stephen · 2025-09-04T14:18:10+0100

Grrrrrr said:
Possibly more to do with the tyre than its size. 255 is a decent footprint.

I tried some Kumho H-something on my Omega once. The U ones were OK but the H (for hard wearing, apparently) were horrible. Any damp on the road and the back end stepped out like it was on ice. Chinese Ditch Finders of the highest order.

pirelli scorpion all weather

4256stephen · 2025-09-04T14:19:30+0100

300bhp/ton said:
What brand/tread are they?

It really shouldn't slide very easily, unless you were really hooning it. Although they are big heavy cars, so can push to understeer fairly easily.

I doubt a 255 would really cause a sliding issue over a 275, although they are smaller, but you'd be talking about on the limit grip differences, so again driving very aggressively.

I would think either the roads where slippery if it was very heavy rain and maybe hadn't been rained on for a while. Could have been spilt diesel on the road, that is very slick.....

Else it is probably the age/tread/brand of tyres maybe.

Does the vehicle drive ok otherwise? No clonks of odd handling in the dry? If there are other issues, then suspension could be causing some odd handling, as good a poor suspension geometry. Might be worth spending out on a new set of tyres and a tracking/geo check & adjust.

pirelli scorpion all season

norseman · 2025-09-04T15:16:13+0100

Another question is .. how old are the tyres?

I'm a RRC man myself but I have found that older rubber, even with good tread depth, will cause reduced levels of grip in the wet.

4256stephen · 2025-09-04T16:06:13+0100

Front tyres 2 years old, rear tyres 1 year old

pwood999 · 2025-09-04T19:33:31+0100

You current tyres will be just over an inch taller, and 0.8" narrower. Also assuming speedo uses ABS sensors, that will be slightly out as well. The taller sidewall will flex more on corners, but should absorb bumps better.

IMHO the tread & rubber type will affect grip more than the 0.8" difference in tyre width, but I could be wrong on that.

As said above, chances are wet & greasy roads are what you are encountering, rather than tyre issue, especially as they are only 1-2 years old. What's the tread depth ?

Also for pressures & size what does the owners handbook say ?

275/40-20	255/55-20

kermit_rr · 2025-09-04T19:35:46+0100

If the suspension bushes are in a worse state of repair then that will impact how the car behaves in the wet

gold rover · 2025-09-04T20:25:01+0100

4256stephen said:
Hi, I'm new to the range rover sport scene, I have purchased a 2010 RRS, Last night in the rain the car felt awful, sliding on roundabouts etc, checked the tyre pressures they were 34 front 37 rear, upon checking on google by numberplate it says my tyres should be 275-40 r20 I have 255-55 r20 are these the wrong size? I have attached a couple of pictures? Any info would be much appreciated.

Is it some sort of optical illusion due to angle of photo? Or is that tyre very worn down?

4256stephen · 2025-09-04T20:43:28+0100

pwood999 said:
You current tyres will be just over an inch taller, and 0.8" narrower. Also assuming speedo uses ABS sensors, that will be slightly out as well. The taller sidewall will flex more on corners, but should absorb bumps better.

IMHO the tread & rubber type will affect grip more than the 0.8" difference in tyre width, but I could be wrong on that.

As said above, chances are wet & greasy roads are what you are encountering, rather than tyre issue, especially as they are only 1-2 years old. What's the tread depth ?

Also for pressures & size what does the owners handbook say ?

275/40-20 255/55-20
View attachment 349179 View attachment 349180

Thanks, this is part of the problem, the handbook doesn't state a pressure for the 255/55 r20 as it's not a recognised size for the car.

4256stephen · 2025-09-04T20:45:38+0100

gold rover said:
Is it some sort of optical illusion due to angle of photo? Or is that tyre very worn down?
View attachment 349182

I'm not sure what you are seeing, the tyres are literally in brand new condition, only done just shy of 2000 miles

4256stephen · 2025-09-04T20:47:43+0100

4256stephen said:
Thanks, this is part of the problem, the handbook doesn't state a pressure for the 255/55 r20 as it's not a recognised size for the car.

I think the problem arised after I put the pressure front 34psi rear 37psi! But I'm not sure what the pressures should be, as the tyres area recognised size for the car

gold rover · 2025-09-04T21:09:33+0100

4256stephen said:
I'm not sure what you are seeing, the tyres are literally in brand new condition, only done just shy of 2000 miles

Then as per previous post, it must be a trick of the light.

275/40-20	255/55-20
View attachment 349179	View attachment 349180

Wheels! What size tyres?

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