You sparked my curiosity Tripod and got me to do some digging, and what I found out was rather interesting (to me).
We have a set of the Peerless "Auto-Trac" (automatic tensioning) listed in our wedding registry right now, something we want to acquire for future trips to visit family in Snoqualmie pass (WA) but probably won't have much use for in Minnesota. When I added them, I simply went and looked up what model # would fit our tires and gave it no more thought. I'm glad you got me to look a little closer.
I looked up that the smallest/tightest rating for tire chains is "S" class, for which a "minimum tread-face clearance" is required to be at least 1.46 inches (37 mm) and a minimum "side-wall clearance" of 0.59 inches (15 mm). That is to say, basically there needs to be about an inch and a half of open space between the tread of the tire and any part of the inside of the fender, and a little more than a half an inch between the sidewalls and any strut or hose or whatever on the inside of the tire.
OK so... do we have that? I promptly got out the scissors and cut myself a little piece of cardboard about 37mm long and 15mm wide, and out to the Jeep I went to do some exploring.
Most people are probably thinking the same first-thought as me, "that darn rear-tire and how its not positioned to be centered in the rear wheel well!
" Let me point out first, the owners manual states in the Tire Chains section "Install on front tires only
" in addition to the information Tripod quoted above. So technically speaking, Jeep throws the idea of putting tire chains on the back right out the window. I understand that in most cases chains would usually only be necessitated on the primary drive wheels but I also thought "if two chains are good, four must be better!" and had planned to have two sets to be able to do all four tires (I have two sets listed on our registry).
So already I am learning that I did not know enough about usage of tire chains to be buying (or asking other people to buy) a couple of sets for us. I looked and at least the sets I had picked out are "S class" so I didn't start out wildly off-base or anything, but now I must get to the bottom of it all...
Right, so, back to rear tires. Lets just say we choose to say "thanks but no thanks" to the manual's instruction of only installing chains on the front tires. How did my cardboard test pan out? Have a look for yourself:
Driver's Side rear tire:
As you can see, we don't quite make the clearance thanks to that stupid pinch point created by the tire not being centered in the wheel well. This is the only problem point I see for the rear tires.
I have the stock 225/55R18 continental tires. Generally speaking, a 225/55R18 is going to be approximately
27.7 inches tall and 8.9 inches wide. There is some variance from one manufacturer to another (just like with clothes/shoes), so actual measurements listed on tirerack for this specific tire are listed as 27.8 inches tall and 9.6 inches at the widest point (on a 7.5 inch wide rim).
The owner's manual says S class chains are ok if you are running a 215/65R16 tire, which generally speaking would be about 27.0 inches tall and 8.5 inches wide, give or take the slight variance from brand to brand.
This makes sense, just a little bit smaller tire and my cardboard test would pass, but who the heck wants to run SMALLER than stock tires on a Jeep? Pretty much nobody right? ..Other than a physics major who may pop in and point out that smaller diameter, lighter tires would technically slightly increase acceleration and handling performance, possibly MPGs too... but still, the principle of the matter, most of us just aren't going to do that. Its some kind of mental issue we have with size, eh?
Back to topic, everyone wants to know about the front now too right?
The front tire has plenty of room to clear the plastic fender liner all around, but, one place there might be an issue you might not immediately think of is clearance of the bottom of the strut spring:
I think in reality things would probably
slide by here, but only if you have excellent-fitting chains or cables that do better than the minimum requirements for S-class chains. Just because the specification says 1.46 inches or whatever doesn't mean your particular set will actually be lifting that high off the face of the tread (hopefully). But when a tire is spinning the chain or cable would certainly be able to lift some amount and if its too much, or your chains become loose or break, they could really beat up the bottom of that spring perch....
Similarly in the back, good fitting chains or cables might not reach out and clobber that liner but ill-fitting ones sure could. As far as the insurance company is concerned, you have no leg to stand on
if something goes awry and you get the snot beat out of your liners or spring perch, official instructions said you were supposed to be running a significantly smaller tire than stock AND not to put them on the back at all, so clean coverage for accidental damage here is probably non-existent, just some food for thought.
With all that in mind, those zip-tie based el-cheapo / one-time use / throw-away traction devices that Tripod linked to are starting to look really good
. The zip-tie mechanism means they will fit as tightly as possible, no clearance issues, and they can't loosen. They can only break off, in which case being strips of plastic they don't weight enough to do any damage, they would probably just sling to the side of the road more or less harmlessly. What I don't know is whether something like that meets the requirements of local law enforcement for those regions in the mountains where tire chains can be legally required...
If anyone has some experience or knowledge in that area, I would like to know what would happen if we drove all the way from Minnesota to the mountains of WA, and suddenly say bad weather crops up and local highway patrol has elected to use their option of stopping and requiring all vehicles going through certain passes to have at least one set of tire chains... and all we have is a fistful of plastic zip-tie thingers to show them... are they going to let us through on that?
I think might need to pull one or both of those tire chain sets from our wedding registry...
I have seen first-hand some of the kind of damage that occurs when tire chains loosen and come flying off. Between that and the clearance issues I feel personally inclined to avoid using tire chains ever as much as possible, but I do want to be able to meet requirements to be allowed through a mountain pass in WA. If we drive all the frick way across Dakota and Montana just to get stopped because of bad weather cropping up and inability to safely fit and use chains when required, then our mighty Jeep has let us down in a big way.
This is a whole new level of deterrent for me on getting larger tires. Many of you know about my other thread
where I agonized over whether I could or should get a little bit bigger tire when I replace these crappy stock tires. Right now clearance for chains in the front looks marginal, add even a half and inch to the sidewall height and the problem gets much worse
I do not want to have two sets of rims and tires just for mountain vacationing and daily driving at home. I don't want to run significantly smaller tires than what I have currently all the time just for one or two trips a year. Blarg!
Digging into this has really helped me a lot though so thanks again for sparking that, Tripod. I haven't posted on that other thread in a while but I have been looking some more at the two relevant sizes of Geolandar G015's and the Michelin Defender LTX's. Sh*t guys, I even have a spreadsheet:
A little embarrassed how much I over-analyze *everything* but hey, if it helps someone else at some point, then great. I realize its going to be a small set of 2nd gen Compass owners because I'm only ever looking at options for the 18 inch rims but whatever, I'll still throw it all out there, quite a few limited's floating around too.
Anyways those are the three tires I've been looking at and I want so badly to justify a "bigger" tire but I don't think its gonna happen. The stock size Geolandars in 225/55R18 are hands-down the best option for my needs. As you can see, actual measured height of the 225/55R18 Geolandars is actually a tenth of an inch SMALLER than my stock contis. It will about kill me to purposefully have something fitted that is even microscopically smaller than stock, from a mental standpoint, but every little bit will help when it comes to possibly having to make the decision to either put tire chains on my front wheels or turn around and drive 1000+ miles back home and cut our vacation short...
As long as I'm yacking about my spreadsheet lets note that the next size up Geolandars move from an SL to an XL rated tire and they become massively heavier
. That was the main reason I was shying away from the 235/60/R18s, the weight/performance loss but now knowing that it would also destroy my clearance for possibly legally required snow chains... forget about it.
Another interesting thing I found regarding the Michelin Defender LTX; Although the smallest size they make for an 18 inch rim is 235
/55R18, which would typically be about 28.2 inches tall, they actually run small and only measure at about 28.1 inches tall, ie only about 3 tenths of an inch taller than my contis (and a tenth wider) which means it turns out they would not really be a huge jump up. It would still hurt chain clearance, but not nearly like the 235/60 tire would. I'd have a much better chance of "getting away" with the Defenders if I was bound and determined to put something slightly bigger on.
Do you guys mind if I ramble just a little bit more? It really helps me, I come back and read what I wrote like some kind of weird public diary... Its at least partially relevant though I promise!
While I was out doing the cardboard test I had a thought about improving the clearance for chains. Much like with people who want to fit larger tires, there is some potential for wheel spacers
to be of use in this area. Yes, I know, I've opened a whole new can of worms here and wheel spacers come with some major concerns but its all just hypothetical anyways. If a person had significant wheel spacers installed, say around an inch or 25ish mm, you would gain some distance from the bottom of the spring perch in the front, and you would also gain a little bit of distance from the plastic fender liner in the back. The rear fender "opens up" as you move towards the outside edge, its only on the inner-most part of the tread that the cardboard test fails...
You know where I am going with this... simply flop some 1 inch spacers on and the 1.5 or 2 inch lift kit and badda-bing-badda-boom, rear tire probably moved far enough away from the liner to meet S-class chain clearance requirements! Maybe even with one-size larger tire on!!!
I know what you are thinking, and, yes, I will
do just about any
mental gymnastic you can think of to try to justify to the future wife why we "need" to get a small lift kit and wheel spacers
But I feel like I have a solid argument here. A lift and spacers would indeed help with the clearance for tire chains.
I'm straight outta luck on going to a 29 inch tire, though, until some aftermarket manufacture mercifully produces us some replacement struts that give us the same lift as the 1.5/2 inch spacers and move the springs up
that distance. Man, that would help a lot
, if such struts existed.
Ok, I'm finally done here. On behalf of everyone else, thanks a lot @Tripod
for putting the quarter in me, but I'm happy with what I've figured out here today, helps me a lot for future planning. I guess I'll leave those chains on the registry for now, maybe we'll get them and then we'll have
to get the spacers and lift so we can use