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Discussion Starter · #1 ·
When I ordered my D300 HSE, I specified 20 inch wheels. I noted that summer tyres would be fitted. I informed the sales rep that I would be replacing the summer with all seasons tyres. The rep said he would arrange to have the new tyres fitted for the hand over.

When I was notified my new car was on it's way, I asked the dealer to confirm the tyre size. He told me 255/55R20. So I purchased a set of tyres and they were fitted by the dealer on the day I collected the new car.

My question is this. I got a message from the TPMS the other day that one of the tyres was a little soft. So I stopped at a local garage to use the air pump. When I checked the required pressure on the info plate, the 20 inch wheels were listed as 255/50R20.

So is there any potential risk from having 255/55R20 tyres fitted instead of 255/50R20 tyres?

I've not noticed any instability or problems with braking or cornering. The fuel consumption calculated by the trip meter is almost the same as a brim to brim calculation after filling with diesel.

I'd appreciate any insight on my situation.

Thanks.

George D.
 

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When I ordered my D300 HSE, I specified 20 inch wheels. I noted that summer tyres would be fitted. I informed the sales rep that I would be replacing the summer with all seasons tyres. The rep said he would arrange to have the new tyres fitted for the hand over.

When I was notified my new car was on it's way, I asked the dealer to confirm the tyre size. He told me 255/55R20. So I purchased a set of tyres and they were fitted by the dealer on the day I collected the new car.

My question is this. I got a message from the TPMS the other day that one of the tyres was a little soft. So I stopped at a local garage to use the air pump. When I checked the required pressure on the info plate, the 20 inch wheels were listed as 255/50R20.

So is there any potential risk from having 255/55R20 tyres fitted instead of 255/50R20 tyres?

I've not noticed any instability or problems with braking or cornering. The fuel consumption calculated by the trip meter is almost the same as a brim to brim calculation after filling with diesel.

I'd appreciate any insight on my situation.

Thanks.

George D.
I was actually looking into something similar for getting winter or all-season tyres for new car (still waiting for delivery), especially with temperatures now freezing.

The official supported tyres are listed in the User Guide here




It includes several 255/50R20 and 255/55R19 options, but does not include any 255/55R20 options.

So according to that document, your tyres would not be supported, because the aspect ratio is not correct for 20-inch rims (55% instead of 50%), so the sidewall would be slightly too large (140mm vs 127mm).

Other forum members may know what the practical impact might be, but I would assume some degradation of stability or handling, as well as speed and distance instruments reading artificially low (due to circumference being slightly too large).

Interesting you haven’t noticed any issues, but maybe only apparent in really controlled environment or in more extreme/emergency situations?

Or maybe 55R20 tyres would be perfectly safe and acceptable, but it is simply not a tested / approved combination by JLR.

Also, perhaps insurance cover might be invalid or disputed by the insurer in the event an accident?


Definitely interested in more knowledgable replies from others…
 
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The rolling radius is just over 1% greater so your speedo would under read by 1%, at 80mph it would read 79mph that’s well within the tolerance allowed. As for different handling there will be far more variation between different brands and tread pattern.
 
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By my calculations the rolling diameter of the 255/50R20 and 255/55R19 tyres is 30 inches, and the 255/55R20 is 31 inches, which is a 3.3% increase. When the speedo thinks you are going 70 mph you will now be going 72.3 mph i.e. the speedo will under read by 3.2%. I have 30 inch vs original 29 inch tyres on my Discovery 2 and the maths are pretty much the same. Most speedos over-read (none should under-read) so I suggest that you hit the cruise control at 70 mph and then use a separate sat nav or mobile with a speedo app to measure your actual speed so at least you know for the future.

You must tell your insurers of the change in tyre size.
 
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More of a concern to me would be the fact that the dealership have supplied and fitted tyres not approved by JLR.
 

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More of a concern to me would be the fact that the dealership have supplied and fitted tyres not approved by JLR.
I agree. The tyres should be a 255 50 20. I would go back to whoever stated the incorrect size and get that dealer to swap them for the correct size. As previously stated, this “wrong size” is classed as modifying and your insurer needs to know, plus, again, as stated, it puts your speedo out because of the rolling circumference.
 
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Discussion Starter · #7 ·
Well I have some good news.

I visited my dealer yesterday and explained the situation. After a quick consultation with the sales manager, they have agreed to replace the tyres with the correct sized tyres at no cost to me. The new tyres are on order and they will let me know when to come in to have them fitted.

I was a bit surprised they did not put up an objection, as I had bought the tyres myself and the dealer only fitted them for me. It seems the fact that the sales rep had advised me of the wrong tyre size and that they did not notice the tyres I gave them were wrong, meant they had to accept responsibility.

So I'm pretty pleased all things considered.

George D.
 

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Well I have some good news.

I visited my dealer yesterday and explained the situation. After a quick consultation with the sales manager, they have agreed to replace the tyres with the correct sized tyres at no cost to me. The new tyres are on order and they will let me know when to come in to have them fitted.

I was a bit surprised they did not put up an objection, as I had bought the tyres myself and the dealer only fitted them for me. It seems the fact that the sales rep had advised me of the wrong tyre size and that they did not notice the tyres I gave them were wrong, meant they had to accept responsibility.

So I'm pretty pleased all things considered.

George D.
Brilliant news. Not all dealers are bad
 
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Good result for you, and well done to the dealer for stepping up, worth a mention?
 
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Discussion Starter · #11 ·
I got my new tyres fitted yesterday. It may be my imagination, but the ride seems quieter and smoother.

Kudos to Park's Jaguar Land Rover in Inverness for being so helpful in sorting this problem out.
 

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I got my new tyres fitted yesterday. It may be my imagination, but the ride seems quieter and smoother.

Kudos to Park's Jaguar Land Rover in Inverness for being so helpful in sorting this problem out.
The quieter aspect could be a change in brand, but there are only 4db difference really between best and worst on the market
 
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Discussion Starter · #13 ·
The quieter aspect could be a change in brand, but there are only 4db difference really between best and worst on the market
The new tyres are the same brand and type as the old ones. Pirelli Scorpion Zero All Seasons.

The only difference is the side wall size. The old ones we're 255/55R20. The new ones are 255/50R20.
 

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The new tyres are the same brand and type as the old ones. Pirelli Scorpion Zero All Seasons.

The only difference is the side wall size. The old ones we're 255/55R20. The new ones are 255/50R20.
The main thing is you are now on the right size and it was done by the dealer. So it’s a win win all round.
 
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And this is the crazy worl we live in. Cars with GPS & electronic speedos, but they under read the speed ALWAYS, they could just use GPS as a reference to adjust digital which would take into account tyre wear. Most speedos over read by 3-5mph above true speed. Changing tyre aspect ratio has basically ZERO influence to a cars handling or safety, except at the limits of adhesion. A car (especially SUV) that would just pass the elk test on std tyre sizes, may fail or flip on high profile ones. Your life your choice.

There are some advantages though, the higher profile, will ride softer than a lower profile, so the car will possibly feel more comportable when cruising over poor road surfaces. The tyres may run a little warmer due to increaxed flex of the carcass, this will help with cold temperature grip, but lead to increased wear in the warmer temps. As noted above the speedo will read closer to true speed which is a bonus on open roads, but a bind when your are doing a true 30mph in a 30 zone & the car in front appears to be doing 25, because their speedo says 30 :(

I have always GPS tested my speedo's so I know there inherent error & then set cruise control to the true speed limit, for my F-pace its 4mph low at all speeds, so set to +4mph above indicated speed limit on cruise everywhere. I've done this for 20years on various cars, never had a ticket from a spped camera. Remember to only use GPS speedo checking on straight level road. Many will not compensate for altitude or corners, as they use a distance/time calculation between two points, some cheap units only update every 5 seconds, which is far too long if the road curves &/or decends at anything other than a constant angle.
 
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