I have put my full-size spare tire up on top of my jeep by bolting it to the stock roof rack rail things. My dad INSISTS that I should remove it because the wind catching it, the rough kansas roads, and my spirited driving with this extra weight up on top would cause the bolts holding the rack onto my XJ would eventually break. I am just asking if this is an actual possibility or if my dad is just blowing smoke.

 

little bit of truth there. a slim chance though. how about securing it with a "come-along" wracheting strap?

 

Depends on how it's mounted, and what size tire it is.

A 235/75R15 on a stock rim isn't a lot of mass, but a 33" bias ply on a 10" wide steel rim is. When you factor in the inertia forces involved in bouncing down the road, the tire can exert pretty large forces on its mount.

The factory luggage bars are decent, but he's right, if there's some flex and the tire wiggles at all, fatigue failure of the mounting hardware is a real possibility. The bigger the tire, the more force it exerts.

If it's mounted in a good roof roof, preferably a gutter-mounted rack, it'll handle the forces much better.

Worst case, if he's right, and your tire comes off the roof at highway speed, you could have a huge liability problem, property damages, injuries, etc. Always plan for worst case when you can.

Yep, I'm an insurance adjuster.

 

What does your mount look like? How strong? I had mine strapped to the roof rails for a few years and it was fine with regular checks to make sure the straps were tight. Now i have built a mount for it and its been up there for 6 months no problem. My brother has a roof rack with tire mount and it has been fine for 9 years. All those were 31"s btw. Bottom line is if your mount is strong enough it would take quite an impact to come off. Also as previously stated a bigger tire like a 35" isn't a good idea because the more weight up there raises your c-o-g (center of gravity) and will cause bad driving characteristics and could make it dangerous. Also that big of a tire would be near impossible to get up and down alone if needed.

 

Dads don't get old by being stupid. Amazing how the older I got, the smarter my dad got......wished I'd have told him that, and thanked him more often, when I had the chance.

 

Not to hijack the thread, but this reminds me of something I saw in California in the late '90's. I was on a chartered bus returning from a military field exercise in Central California when we came to a near halt on the highway going though Santa Barbra. After about 30-minutes we came upon a mattress in the middle of the highway. You guessed it, there was a roof rack strapped to it. A couple hundred yards up the highway was an SUV (I can't remember what kind) on the side of the road and two people outside it trying to figure out what went wrong (70+ mph with a mattress tied to a rack not designed for such a load is my guess).

In my opinion factory roof racks are good for things like snow skis and bicycles when used with proper aftermarket mounts, but they were not intended for large or heavy items. You may be able to get away with something awkward and heavy for a short time but sooner or later a part will fail.

 

I use ratchet straps to hold mine on.

 

its a 235/75/15 on a stock alloy wheel. Ill try to remember to take and post a picture of my setup tomorrow. I have had it up there for over a year. He is just thinking in the LONG run.

 

I had my 32 up there with a steel wheel, you will likely have no issue
Where in Kansas are you??

 

had my 32" with an alloy wheel up there on the stock cross members. I ratcheted it down to the cross members where they mount to the rack. It survived a week, multiple times on the high way, a trip to rousche creek and back without budging a bit

 

the loss of mpg, and it becoming a projectile that you are 100% liable for in the event of an accident are more likely.

I'd almost bet that if you got hit head on by someone, and that tire went flying and hit someone else, your insurance company would tell you to kick rocks on paying for the damages.

the tire on the roof isn't a great idea, by any means, so I'm gonna side with your dad, not that over time its gonna break, but that its a dumb idea.

 

I've got my 31" with factory steel rim attached to my stock roof rails with 6 solid rubber bungees. Been on the highway, city streets and trails for over a year and it has never moved.