streborx

For everyone thinking about tire and/or wheel upgrades, there's a helpful graphic comparison calculator at https://rimsntires.com/specspro.jsp It's worth checking out even if you've already made the change.

The Butcher

That's pretty cool. I like how it shows you the visual of not only how the tire size changes, but also how the wheel width and offset are different if you go with an aftermarket wheel.

Floobydust

Thank you for posting the link. I couldn't find my bookmark for it, but I have used that site many times in the past for my W124 (with 6 sets of wheels) and it is incredible.

Limey Hooligan

Great site, I had stumbled across it before but forgot to bookmark it.... thanks!

So general question for everyone on their tires... do you rotate all 5, or just the 4 in use?
I had planned to rotate all 5, but my tire guy reminded me that the spare didn't have a TPS installed so I've ended up only rotating the 4.

Which made me think about my next set of tires. I plan on going up to 325/65-18s which will have a diameter of 34.6" and weigh 76lbs (since I plan on the BFG KM3s). My current 305/65-18s have a diameter of 33.6" and weigh 62lbs, a substantial 14lb weight gain.
I'm not so much worried about rotating mass as I am about the spare mount having to support an extra 14lbs. If I continue to only rotate the 4 tires in use, why not go with a lighter tire as a spare, with the same diameter?
For example, if I go with the KM3s, I could feasibly buy a single Atturo Trail Blade X/T spare tire in 18" size, with the exact same diameter of 34.6" and it will only weigh 64lbs, potentially reducing 12lbs of weight on the spare tire holder.

I would assume that as long as the spare is the exact same diameter as the other tires, there will be no transfer case or drivetrain issues if I need to use it. Kind of like having a 'mini-spare'.
Oh, and I save some $$ in the process....

The Butcher

I think you could probably get into the debate about how much more leverage that 12lbs adds, but I'm not sure that in practical terms it will be an issue. If the mount is strong enough, then I think your actual door will be fine. I know guys that have run a 37 on the spare holder and have not had issues (off-roading as well). I'd rather have 5 matching tires, than one oddball. Particularly if you end up shredding a tire, you can just swap on the spare and everything matches. When you go buy your next set of tires, throw the spare into the mix and add a new spare. The only time I've thrown my spares into the mix is on a Raptor that had two spares in the bed, so you could literally go bed to front, front to rear, rear to bed, repeat as needed for each subsequent rotation. Having a 5th tire in the mix gets a little more confusing trying to remember which one it was...and yes, I'm too lazy to write it down...

Also, if the Artturo weighs 12lbs less it has to be sacrificing something, somewhere. I'd guess in sidewall durability, which is not something you want to sacrifice since you actually off road.

streborx

What I find useful about the side-by-side comparison of dimensions is that it can be used to check your clearances before rolling the dice and mounting a new set. Crank your steering wheel all the way to its stop, and use a ruler or piece of wood as a gauge to see how much clearance you have, and use a straight-edge to see how far outside the fender you'll be.
If you don't plan on using a reverse-mount extension bracket as other have done, 14 lbs extra on the OE bracket can't be much worse than hanging the OE spare weight further out 8" or so.
I mounted a matching 275/55R20 spare when I changed out the OE tires. The spare cover wasn't even big enough to cover the OE 275/50R20, so MB slapped on a 265/50R20 so it would fit, and still called it a "full-size spare", but then stuck a "Max 45 mph" sticker on it. So the OE spare couldn't be used in a 5-tire rotation. Glad to be rid of the OE Pirelli's and the OE Continental spare.
I've acquired a new spare tire cover from Boomerang, and will post pics and info when it's installed.
My spare wheel had a TPMS installed on it, although it's not included in the monitoring system -- only when it gets mounted. I'm not sure, but the MB alloy wheels are machined for TPMS sensors and not conventional valve stems. Have your tire guy check your spare again. He might have assumed that since it doesn't show up on the instrument panel, it's not included on the wheel. Even if you have to add one, it's only about $40.