How much tire clearance

[fordsbyjay]

How much tire clearance is recommended in the back of my car. I will be running a torque arm with a watts link. I am trying to determine if I am going to just to trim the factory rail some or replace it or just move the whole thing over. The latter seems like the most work so I am not too keen on that idea. LOL.

I trimmed the wheel well back to the frame rail.


As you can see I still have some room if I trim the frame rail lip.


There is about 1/2 on the outside. I will have to remove the outer wheel well as well because it tapers in too soon crowding the tire.

[MrQuick]

At ride height since you are running a Watts, you ca go 3/8 min at the outer edge and 1 1/4" inner minuimum. The more the better. A lower side wall aspect will determine the space. You are going to need more room for a 60 series as you would for a 30 series.

Torque arm link system wil give you an even pivot depending on where your lowers a mounted.

Remember as the diff articulates the tire will go inwards as it goes up. Make sure you are aware of that when you do your inner and outer tubs.


Instead of a full frame move you can take a note from the 4x4 world and put in a 1/8" steel c notch style insert and incorporate a shock/coilover/watts linkage crossmember mount. That is unless your frame rail is rusty or damaged. I don't like the factory 20g stamp steel rear frames but they can be reinforced on a budget.
quick sketch, dark and light grey is old tire local and new. Blue is frame addition top view. Red is coil over. black is link,frame and axle houing.

vince

[JRouche]

Remember as the diff articulates the tire will go inwards as it goes up. Make sure you are aware of that when you do your inner and outer tubs.

Very good advice and it really needs to be looked at.

The lateral (side to side) movement can be controlled with the watts link. But thats only looking at how the rear end moves sideways with a vertical motion of the suspension. Equal vertical travel on both tires. The watts link can hold the rear end within the tubs for equal suspension travel. But when there is body roll it cant.

No more or less than any other suspension. As the body rolls over in a turn the wheels are planted to the road. The horizontal surface. The relationship to that horizontal surface and the vertical tire will meet at some point. Horizontal frame or inner fender to tire edge.

I have 5/8" clearance from the side wall of the tire while resting. I can move the rear end up and down through its entire vertical travel and that clearance doesnt change by a 1/16". BUT.. When I rotate the body in relation to the on the ground rear end it gets close.

At just under 5* of body roll the 5/8" of space is gonzo. Rub time. So I have to keep my body roll at under 5*. Or do a rethink of my entire rear end. But 5* of body roll is alot.

Dont forget, the rotation of the rear end during body roll. The tire will move closer to the hard parts of the car. JR

[MrQuick]

Good points but remember the rims and tires do some funky stuff when going against that lat locations device. Much more so on the inner well than the outer.


vince

[fordsbyjay]

Thank you for the replies.

I think I am going to have to cut out the outer portion of the wheel well which will give me more room. It is tapered in so it is crowding the tire towards the rear of the car too much. I was thinking about just cutting out the one section but by the time I do all that I might as well just replace the whole tub at one time. I am going to shoot for 1" of clearance on the outside. My body line goes down over the wheel so I also need enough room to actually get the tire in there past the hub center and studs. I am going to move the frame rail over so I have 2" of clearance on the inside as well. This will allow enough room that I can run a 325 drag radial if desired.

[The WidowMaker]

i was told 3/8 outside and 3/4 inside by one of the vendors here. im running a watts as well, but body roll is the issue as stated above. and 5* would be both of my shocks almost maxed out in opposite directions. not something i plan on doing.

[JRouche]

Good points but remember the rims and tires do some funky stuff when going against that lat locations device. Much more so on the inner well than the outer.vince

Interesting.. What happens on the inside that needs to be looked at. I was thinking the outside would need more clearance with body roll due to the longer stroke. It being further away from the pivot points. It seems like it would move more. Or angle out more. Curious to learn some info. Some new suspension travel knowledge is always welcome.. So, the inside gets some funky stuff. I wanna know the funkiness My car is kinda funky anyway. Id love to trim some of that down. Oh, and Im not trying to be a smart azz if it comes across like that. Just curious. JR

[MrQuick]

Interesting.. What happens on the inside that needs to be looked at. I was thinking the outside would need more clearance with body roll due to the longer stroke. It being further away from the pivot points. It seems like it would move more. Or angle out more. Curious to learn some info. Some new suspension travel knowledge is always welcome.. So, the inside gets some funky stuff. I wanna know the funkiness My car is kinda funky anyway. Id love to trim some of that down. Oh, and Im not trying to be a smart azz if it comes across like that. Just curious. JR

I know, me too, LOL, but you know me by now.

You figure in a turn the body is leaning that way. The inner wheel/tire is getting unloaded and the body rolls. Basically body is then out of the way so to speak. Bottom of the tire/wheel is being pulled at the lower section slightly increasing clearance at the top.
The most force you can put on a tire is on the outer wheel/tire which in turn gets real close to the inner wheel well. Much more so on a car equip with a 60 series tire over a 30 series. But rims do flex too. Tire/wheel is being pushed and will roll inwards decreasing clearance.


picture:


A well sorted out car can control the roll and minimize tire/body contact. See how a proper rear bar and or lateral locating device can help control the body and suspension.
picture2:



I am not picking on anyones car or passing judgment, those were just the best shots I could find.

vince


vince

[Skip Fix]

My 78 TA with 275/60-15s and a hard body roll(slant driveway) would rub on the inside even with probably over and inch clearance when level due to the solid rear axle.

[MrQuick]

275/60-15, driveway, stock leafs.

that would be a different comparison. 4x4 articulation is extreme, if your suspension articulated that much in a hard race situation turn , tire rub would be the last of your worries. But good point all aspects should be researched for tire clearance.

I bet a 295/35 on an 18" rim with the same space would not rub.


Vince