[DogOnBoard]

This subject has come up in other threads. Running a smaller spare may causes undue stress and wear on AWD systems because the system perceives it as constant wheel slippage and attempts to compensate. In the past, Subaru has said that replacement tires must match within 2/32" tread depth, which would be 1/8" in diameter, but I don't think they specify the maximum distance you should run on a temporary spare that is smaller than that allowable difference. Most owners manuals recommend limiting your speed on a donut tire and replacing it with a properly-sized full service tire ASAP. That advice is likely based on safety concerns (handling and braking), but could also have relevance to AWD system stress.

I drive in rural areas far away from tire shops, so I always have a spare tire because the green slime doesn't work on every flat. IMO, if you upsize the tires on your RL, you should be cautious about using the stock donut spare. If I buy an RL, I will be mounting a full service tire in the bed (won't fit in trunk) for any road trips that involve significant off-pavement travel. That tire will be matched in size to whatever tires I'm running on the truck.

 

[DogOnBoard]

...Chit because **** gets marked out by the forum software.

I just hate $hitty software like that! >

 

[DogOnBoard]

So I dug a little deeper into the Honda Press Kit to find out that the RL temporary spare tire is 165/90R17 size, which is 28.7" diameter. That's nearly an inch smaller than the 245/60R18 stock RL tires that measure 29.6" diameter. Apparently, Honda feels that's OK for emergency/temporary use and won't damage the iVTM-4 AWD system. IIRC, the G2's Large Project Leader (Kerry McGuire, I think) commented at Camp Ridgeline that the donut spare was load-rated for the RL so that it could be used if necessary even when towing. Someone can look in the RL's owners manual to see what it actually says about the limitations of the temporary-service spare.

We've been told that Jsport's Ridgeline Chase leveling kit includes AT tires that add about 0.5 inches of ground clearance, plus spacers that add 1.5" to the front suspension. My guess is those tires are 265/60R18 Nitto Terra Grappler G2 tires with a diameter of 30.5". AFAIK, the Chase kit does not include a taller spare tire to replace the OEM donut. OK, now you're looking at 1.8" diameter difference between the temporary spare and those Chase tires. Is that something to be concerned about, especially with regard to the RL's AWD system? IMO, only Honda can answer that.

 

[DogOnBoard]

...It would be interesting to hear from Jsport or a dealer that installs lifts with larger tires to see how they would handle a flat...

Yes it would, but could you really trust their answer unless they were able to verify it with Honda R&D engineers? I might give some credibility to the Jsport guys on this question because of their association with Honda Racing Development. Regardless, I would probably choose to carry a full-service spare that matches the tires on the truck, even though I'd have to give up bed space to do so.

 

[DogOnBoard]

^^^That makes a lot of sense and it's something I've been meaning to add to my own toolbox. Last flat tire I got was on a rough backroad when a rock punctured the sidewall. A plug probably wouldn't have worked for that one, so I was really glad to have a full-service spare on the truck.