Main Tire Alignment Spec

[markyharris]

Hi All,
I measured the Toe-In on the mains on my S7 and was surprised to see almost an inch of Toe-In (7/8" to be exact). I'm currently flying on 8" tires with the stock Grove spring gear suspension.

This would be considered way out of spec on most any automotive application, but I don't know if this is what is needed on a Tailwheel Kitfox. I've seen the axle shims that Kitfox has in their parts catalog, but before I do anything I need to know the specs. I did a search here, but didn't see anything so if I missed it I apologize.

Any info or direction would be appreciated. - Mark

[jrevens]

Mark - is that in the 3-point attitude or level?

[markyharris]

Mark - is that in the 3-point attitude or level?

Great Question I didn't even think of that. I measured in a 3 point attitude. Does the procedure call for checking in level attitude? - Mark

[jiott]

Yes, you check it in level flying attitude. A perfect zero toe-in level will show toe-in when in 3-point. The Grove gear has the axle mount pads machined to a very close tolerance, so it is unusual to find much of any toe-in unless the gear has been bent. The welded cabane type gear is much more likely to have toe-in/out.

[rv9ralph]

Here is a link to Grove Aircraft information on checking landing gear alignment. It also has a table to what shim will be required depending on how far out your alignment is.

Here is the link: https://www.groveaircraft.com/accessories.html

Ralph

[jrevens]

The Grove gear generally has quite a bit of positive camber, and is (as far as I have seen) formed for the axle mount surfaces to be horizontally parallel in the level attitude. That will give you toe-in as the gear is rotated to 3-point. That decreases when the airplane is loaded & heavier, & the gear flexes of course. I decided that since the vast majority of on-the-ground operation is 3 point that I would shim my axles to give me parallel wheels in 3-point, and slight toe-out when level. Slight toe-out is actually stabilizing, vs toe-in which is de-stabilizing. You could also shim for no toe-in or out (neutral) in either position, but that will likely give you more toe-out when the airplane is loaded more heavily and has negative camber the 3-point attitude.

[markyharris]

Here is a link to Grove Aircraft information on checking landing gear alignment. It also has a table to what shim will be required depending on how far out your alignment is.

Here is the link: https://www.groveaircraft.com/accessories.html

Ralph

Ah, perfect. Thank you for pointing this out. It's much appreciated. - Mark