Tire clearance and tire pressure

[wfo9]

Maybe I'm just imagining this.. but it seems like I have seen several people here mention that airing down changes how their tires clear the fenders.

I've never experienced this and can't come of up with the physics on how this is even possible. So if this is real.. please enlighten me and others.

Obviously, you loose ground clearance as you spread out the contact patch on the ground, but this has no impact on the fender clearance from my experience.

This came up because I was helping a friend check tire clearance yesterday and he asked if he should air down...

 

[mikey's2010SR5]

Yeah I don't get it either, so I am in for the physics.

:shrug:

 

[BobsTrail]

I'm running 265/70s and air down to 15 for sand dunes. No clearance problems. I notice the sidewall shows a little bulge, but not enough to matter.

Maybe on larger sizes with less clearance??

 

[wfo9]

I'm running 265/70s and air down to 15 for sand dunes. No clearance problems. I notice the sidewall shows a little bulge, but not enough to matter.

Maybe on larger sizes with less clearance??

The lower part of the tire bulges where it contacts the ground but the areas that need to clear the fenders and body all stay uniform from my experience.

 

[Jeremy556]

My tires only rub only when aired down.

Reason they rub doesn't have anything to do with the fact that they are aired down, it is because the only time I am near full lock steering and highly articulating the front suspension is when off road and aired down. They would rub just as much if they were at full street pressure.

 

[1engineer]

Only reason I can think is side wall roll when cornering. Your tire could move quite a bit depending on pressure and speed.

 

[wfo9]

My tires only rub only when aired down.

Reason they rub doesn't have anything to do with the fact that they are aired down, it is because the only time I am near full lock steering and highly articulating the front suspension is when off road and aired down. They would rub just as much if they were at full street pressure.

Yea, its the only thing I could come up with.. You can actually push the suspension a little harder when aired down because it acts as part of the suspension. So if driving up a RTI ramp... You can go higher aired down before tires come off the ground. So maybe that is what people mean... you can only get into full compression/bushing deflection situations statically when aired all the way down.. but it really has no direct relationship to the shape of the tire under lower pressure.

The tricky part of most IFS clearance scenarios is the deflection factor. Linked suspension are pretty consistent.

 

[wfo9]

Only reason I can think is side wall roll when cornering. Your tire could move quite a bit depending on pressure and speed.

but that would only be down at the contact area. nut up in the fender, frame... clearance area..

 

[1engineer]

but that would only be down at the contact area. nut up in the fender, frame... clearance area..

Depending on Speed, centrifugal force would keep the edge trying to rotate along it's new axis and if we are only talking about a quarter inch clearance normally, I could see someone cornering hard at 15 mph or so and rubbing a bit. Maybe. That's all I got.