Spare wheel dilemma?

[Surfer]

We have the 2018 Grand Cherokee which has 20" wheels and an 18" spare wheel.  If you are travelling with loads of luggage i.e.e suitcases and other camping equipment in the boot area, have a puncture and need to change the wheel what do you do with the 20" which will not fit into the space occupied by the 18" wheel as the lid will not close and you need to reload your luggage?

[digger]

At least two   options  ,

1. cut out and weld in a bigger wheel carrier space . I think someone on here did this a while back if you can find the post.

2. I had an  XJ Cherokee a few years ago. I built a roof rack for it with the spare wheel mounted flat ,on top at the back, with which I had no problems.

 

 

[V]

EU whole vehicle type approval on 20" rims/tyres yet the car was not originally designed to take them in the spare wheel well. I think somebody may have got carried away in the styling department. The problem of what to do about the full size wheel has plagued everyone that has ever had a tyre problem with a car equipped with a skinny spare. Keeping a tyre bag on board and a sheet of clean polythene as a work mat will make it easier to cover the full size wheel to keep your clothes and the car interior clean when man handling it into the Jeep.

 

Do the tyres on the 18" and 20" rims have different outside diameters? If so, using the 18" spare may not be a good idea on a long journey or for a prolonged amount of time. Check what your user manual says about tyre tread variation for tyres of the same size. If the tyre on the 18" wheel is 14mm smaller on outside diameter, that's 7mm variation on rolling radius. The tread depth comparison between 18" and 20" becomes irrelevant. For dissimilar tyre sizes the rolling radius should be the same to avoid transmission problems.

[Surfer]

59 minutes ago, V said:

EU whole vehicle type approval on 20" rims/tyres yet the car was not originally designed to take them in the spare wheel well. I think somebody may have got carried away in the styling department. The problem of what to do about the full size wheel has plagued everyone that has ever had a tyre problem with a car equipped with a skinny spare. Keeping a tyre bag on board and a sheet of clean polythene as a work mat will make it easier to cover the full size wheel to keep your clothes and the car interior clean when man handling it into the Jeep.

 

Do the tyres on the 18" and 20" rims have different outside diameters? If so, using the 18" spare may not be a good idea on a long journey or for a prolonged amount of time. Check what your user manual says about tyre tread variation for tyres of the same size. If the tyre on the 18" wheel is 14mm smaller on outside diameter, that's 7mm variation on rolling radius. The tread depth comparison between 18" and 20" becomes irrelevant. For dissimilar tyre sizes the rolling radius should be the same to avoid transmission problems.

Tread is the same pattern.  Normally we would be towing a caravan, but as caravan is already loaded cannot add anything more into it. I was thinking that as spare wheel well is empty perhaps moving some stuff in the rear into that are and then carry the punctured wheel upright in the rear?

[Wildjeeper62]

Have you tried to remove one of your 20" wheel and put it in spare wheel compartment to see if it fits?

I have a 2016 Grand Cherokee WK2 and my spare wheel is a 20" full size wheel so I would be surprised that they reduced the size of the spare wheel compartment from 2016 to 2018. 

[Surfer]

1 hour ago, Wildjeeper62 said:

Have you tried to remove one of your 20" wheel and put it in spare wheel compartment to see if it fits?

I have a 2016 Grand Cherokee WK2 and my spare wheel is a 20" full size wheel so I would be surprised that they reduced the size of the spare wheel compartment from 2016 to 2018. 

 

Thanks for the heads up. At the moment that would be too much of a faff to test the theory as would need to remove wheel, test  and then put it back on the vehicle if I could manage.  I must admit that as we tow a caravan quite often a 20" spare would be preferable to the 18"

[Ludders]

If you use a tyre size calculator, and compare the 20" tyre versus the 18" tyre, you'll more than likely find the overall size of tyre to be near identical. 

The 20" wheel should fit within the wheel well.

 

The only reason you get a smaller wheel, is the savings made at manufacture to supply an 18" wheel & tyre over a 20". Sell 100,000 cars, saves £1 per wheel = £100k saved... Save £1 per tyre too, and now you've saved £200k. 

[V]

26 minutes ago, Ludders said:

The only reason you get a smaller wheel, is the savings made at manufacture to supply an 18" wheel & tyre over a 20". Sell 100,000 cars, saves £1 per wheel = £100k saved... Save £1 per tyre too, and now you've saved £200k.

I reckon the savings will be a lot more than a £1 per wheel, but I agree it's a cost saving that would appeal to any manufacturer even if it upset a lot of customers when they discover an odd wheel and tyre in their set.

[UKTJ]

6 hours ago, Surfer said:

Tread is the same pattern.  Normally we would be towing a caravan, but as caravan is already loaded cannot add anything more into it. I was thinking that as spare wheel well is empty perhaps moving some stuff in the rear into that are and then carry the punctured wheel upright in the rear?

Wow, there is really nowhere you can put the spare in an entire caravan in an emergency?  If the caravan is that crammed full how do you get into it when you stop?

 

That said if I had a vehicle so stuffed full that there was no room for the changed wheel, towing a caravan so stuffed full there is nowhere for the changed wheel I really would not want to be driving with that much weight relying on a space saver spare.  Space savers typically have a max speed of 50mph, do they not also have a max load below that of the fuul size tyre?

[UKTJ]

Just checked the AA website.  Apparently a space saver only has a tread depth of 3mm typically.  They also advise if towing a caravan that a space saver should not be used to continue a journey, but only to allow you to get to the very nearest tyre specialist to get the original tyre repaired or replaced.  So you would not need to have the wheel with the puncture in it stored other than on a very temporary basis.

 

Other advice online also suggests that you should not use a space saver spare on the rear when towing.  If it was a rear puncture you would need to switch a front wheel to the back.

 

It really does not sound like using a car with a space saver spare as a regular towing vehicle is ideal from a safety perspective.

Edited March 28, 2023 by UKTJ

[V]

40 minutes ago, UKTJ said:

It really does not sound like using a car with a space saver spare as a regular towing vehicle is ideal from a safety perspective.

I think in this case the 18" wheel is a base model road wheel.

[UKTJ]

4 minutes ago, V said:

I think in this case the 18" wheel is a base model road wheel.

Ah OK, that sounds a bit less scary then!

[Mike WK2]

My WK2 was the same, came with 20” wheels and tyres and an 18” spare. It’s just the tyre size that is varied on the 18” spare to give you same diameter as the 20’s, still a full size wheel and tyre. It’s not a spacer saver, it’s a £‘a saver as V was saying. 
 

My 20” fitted in the spare carrier under the boot board when it needed to changed. 
 

That was before I went to 18’s all round and removed the spare wheel from under the floor so I could house the aux battery though

[Surfer]

11 hours ago, UKTJ said:

Wow, there is really nowhere you can put the spare in an entire caravan in an emergency?  If the caravan is that crammed full how do you get into it when you stop?

 

That said if I had a vehicle so stuffed full that there was no room for the changed wheel, towing a caravan so stuffed full there is nowhere for the changed wheel I really would not want to be driving with that much weight relying on a space saver spare.  Space savers typically have a max speed of 50mph, do they not also have a max load below that of the fuul size tyre?

 

No insult to you, but it seems fairly obvious that you have very little knowledge of caravans.  Trailers like cars, caravans etc have a maximum gross weight that you cannot exceed.  In the case of caravans ours comes from the factory at minimum weight of 1800kg and has a maximum weight of 2000kg so we only have a user payload of 200kg.  Fitting an AWD motor mover takes up 60kg, the air con another 30kg, the satellite dish another 20kg.  Then you add in bedding, crockery, cutlery, pots and pans and you have soon used up the available payload, but the caravan still looks empty on the inside. 

[UKTJ]

8 hours ago, Surfer said:

 

No insult to you, but it seems fairly obvious that you have very little knowledge of caravans.  Trailers like cars, caravans etc have a maximum gross weight that you cannot exceed.  In the case of caravans ours comes from the factory at minimum weight of 1800kg and has a maximum weight of 2000kg so we only have a user payload of 200kg.  Fitting an AWD motor mover takes up 60kg, the air con another 30kg, the satellite dish another 20kg.  Then you add in bedding, crockery, cutlery, pots and pans and you have soon used up the available payload, but the caravan still looks empty on the inside. 

No insult, and you are 100% right I have no experience of caravans.  I simply took the point about the caravan being fully loaded to be referring to space not weight, my mistake.

[Fireman Iain]

On my 2017 WK2 a 20" wheel fits in the spare wheel well. I run slightly wider and taller tyres than standard so I had to lose the storage bins around the spare and make up a new boot floor that's spaced up from original. But the OE 20 wheel and tyre fitted in there before i changed things.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

[Surfer]

13 hours ago, Fireman Iain said:

On my 2017 WK2 a 20" wheel fits in the spare wheel well. I run slightly wider and taller tyres than standard so I had to lose the storage bins around the spare and make up a new boot floor that's spaced up from original. But the OE 20 wheel and tyre fitted in there before i changed things.

 

 

That is good news and as mine is the 2018 I doubt very much if there will be any difference.  Maybe time to shop around for a second hand alloy wheel?  If I recall correctly I think you used too also tow a caravan at times?

[Gerald F]

I have been thinking of replacing the 20" wheels with 18"; last time I looked the price of 4 18" wheels with tyres was less than 4 new 20" tyres! 

I haven't tried fitting the 20" wheels into the spare well, but some Australian WK2 owners complain it is a little too wide – though the diameter is the same. I would just prop the cover on top of the punctured wheel, which will probably be deflated. You could just pile the luggage on top of that for the completion of the journey, only adding another half hour onto the replacement!

The WK1 had a winch to lower the wheel from under the rear floor; you could change the wheel without emptying the boot, but the spare would already be rusty and dirty since it had no cover. Hobson's choice!