Steering woes: Skinny tires vs. Fat tires?

[Gweiner]

I have been struggling to get my 74 to drive and track well on the street for months. The truck is "nervous" and darts around under acceleration, bumps, etc. at speeds over 35mph (I won't drive over 50). After tinkering for a while, I finally broke down and brought it to a local shop which has experience working on EB's and other 4WD vehicles. They spent the last few days looking at it and made some minor adjustments including putting my steering stabilizer back on, centering the ps box, adjusting the ps box (it's a new Delphi unit, they loosened slightly to find the center), centering the axle, adjusting toe-in.

They did what they could but said it is marginally better and not perfect. Suggest that I should consider changing my tires? My set up is as follows:

WH 3.5" suspension lift with 11 pack leafs and bilsteins
Drop pitman arm
Track bar riser and 3-way adj track bar and track bar drop bracket (welded)
New 7 degree c-bushings
New body mounts all around
New collapsible lower shaft and flaming river u joint
Just added 6 degree shims in rear

Tires are new 33x10.5 BFG KM2's on stock 15x5.5 wheels. My mechanic is suggesting tires are too skinny/tall and recommends a wider tire but I am looking to go back to uncut and want to keep the tires under the wheel well and avoid flares (going back to LUBR).

Appreciate any thoughts or ideas on how to make this thing drivable on the road.

 

[fordfan]

I think that a wider wheel, like a 8", would help. The 10.50 width tire on a 5.5" rim has the sidewalls of the tire arched inward and that lets the sidewall flex and creates 'roadwalking' ..The tire tread is also not flat on the road, and even with low pressure the center of the tread is contacting the pavement first.

I would try a different set of tires and wheels so you could isolate the problem, but I think it's going to be the 10.50 on a 5.5" rim.

 

[65 mustang]

that 5 1/2 wide wheel may be the issue. 10.5 wheel should be on a 7" or 8" I'm no expert. I' m not sure which offset wheel u would need for a lubr and a 10.5 wheel. Scott

 

[Gweiner]

Thanks guys. Trying to find a stock steel wheel that will work. Did they make 15x8 steelies?

 

[JWMcCrary]

Not sure why you would need a trac bar riser and a drop bracket and a drop pitman arm, that makes me question the steering geometry, but I would think the shop verified that.

 

[904Bronco]

Thanks guys. Trying to find a stock steel wheel that will work. Did they make 15x8 steelies?

http://www.summitracing.com/parts/WVI-62-575504

Try these... They are what I am using. Doug

 

[Gweiner]

Thanks Doug. What size tire are you running on those wheels?

 

[Joe473]

Lower the tire pressure or see if you can borrow a set of skinny tires for a test ride.

I have 30 x 9.5 and after new track bar and radius arm bushings its pretty good

Not to highjack this but has anyone tried the wheels posted above on an uncut with hubcabs?

 

[904Bronco]

Thanks Doug. What size tire are you running on those wheels?

31 x 10.5 x 15 getting them back from the painters tomorrow and tires mounted this week. I bought one rim to do test fitting before buying the other 4.

 

[904Bronco]

Not to highjack this but has anyone tried the wheels posted above on an uncut with hubcabs?

The rim clears 77 big drum brakes in the rear and GM disc brake conversion on a 74 D44. It is a close fit in the rear, I may have to roll the inner portion of the fender, the ultimate test will be with the tire on.
I could not find a rim with more back spacing, 4.5" would have been my choice.

(I have a 2.5" suspension with a 1" body lift)

 

[broncnaz]

I agree it could be due to the wheels to a point. But there are others running that combo of wheel /tire with no issue. but as was said you may want to play with the tire pressures. I had a set of 10.50's installed and left the tireshop and the bronco was all over the road found they had 50 psi in the tires lowered it down close to 30 and it was driving great again. Also you may need more toe in than the shop set it at. a lot of times bigger tires need more toe in.
While your shop may know some stuff did they give you any of your alginment specs? a 3.5in lift is about the point where some broncos are not even close to being within stock specs even with 7 degree C bushings. You may need more caster to get it to track straight.
Of course its not uncommon for lifted vehicles to dart when accelerating. soft suspensions can be part of the cause.

 

[DuctTape]

I second checking caster first. I've been chasing the same issue with my 3.5. If your caster is low that could be the problem. I hand measured mine at 1.5 degrees (with 7 deg c bushings) and I think spec is between 3-6.

There are two other options I didn't see mentioned by your shop. One is changing the radius arm geometry (via either pricey angled arms or arm drop brackets). Two is cutting and rotating the knuckles. I'm assuming they checked everything else simple like bushings and ball joints.

Check out duffs and bcbroncos for angled radius arms, toms or wildhorses for drop brackets. Both of these solutions may result in a bad driveline angle in front.

From my research the best solution is cutting and rotating knuckles. You can set whatever caster you want while maintaining good driveline angle.

It seems that factory caster varied wildly. Some 3.5" people seem to do fine with just c bushings, other people (like you and me) have issues. Good luck.

 

[snipes243]

What shop did you take it to. Also what does your track bar angle look like compared to your drag link.

 

[surfer-b]

The tire/wheel combo may be some of the prob but I doubt that is the whole prob. I have a set of 10.50's on stock steels and 2.5" lift on my 74, it drives as good as any 4x4. I would do as others stated and chk the caster. I don't know why but some require more than others. My 74 has 3.5* pos on driver, 3* pos on the pass side, and it will track as straight as any car on the road and return all the way to center very quick. Now on my 76 I set it up the same way, got the caster 4*pos on driver and 3.5* pos on pass side, it would track straight with no prob however when turning and releasing the wheel for it to return to center it would go all the way back to about 11 or 1 depending the direction you turn, and this would cause the driver to have to pay attention all the time, you just couldn't relax. I finally pulled the axle and rotated the yokes to where I had 8* pos caster in both sides and this fixed the problem, now it can be driven and relax like a modern 4x4. The only thing I can figure is its in the machining of the yokes, which determines how fast it ramps up when turning or how fast it tries to roll the tires up on ball center, whichever way you want to describe it. If its a gradual ramp it will almost return all the way. If its a direct ramp, it tries to roll the tires up on ball center soon as the slightest movement of the steering wheel, it will return all the way and want to stay there.

 

[Justafordguy]

X3, check the caster, sounds like you need more. Mine darted bad even with 7 degree bushings and only 2.5" lift. I added radius drop brackets and it tracks very straight now even at 75mph. The difference was night and day.

 

[Gweiner]

UPDATE: I went down to the shop and drove the truck. It's still really nervous on the road (if not worse) after theor adjustments. We discusses rotating the knuckles and they suggested that they might be able to do that with different angled ball joints. Has anyone heard of this? They were not fans of cutting the knuckles as they are worried they may not hold up on the road. We also discussed getting radiius arm srop brackets. Can i use the stock radious arms or do i also need to get extended ones? One other possible issue with all this is messing up the front drive shaft pinion angle. What a pain in the ass! All i have is a 3.5" lift. I did not think it would be this complicated to get it to drive right.

Thanks for everyone's help here. Will keep you guys posted.

 

[surfer-b]

We discusses rotating the knuckles and they suggested that they might be able to do that with different angled ball joints. Has anyone heard of this?

They were prob referring to these, you will only be able to achieve 1.5* which may help some but not enough. https://www.rockauto.com/catalog/moreinfo.php?pk=274804&cc=1101902

I would try the drop brackets first, if its still not right you can add the cast/camber bushings to help out.

They were not fans of cutting the knuckles as they are worried they may not hold up on the road.

I would say if they are not a true 4x4 shop no one is gonna touch this, its a lot of work and they are prob concerned about liability issues, also I wouldn't want some shop doing this for me unless I really knew and trusted them. However, if done right its the best way to correct the prob, you can get the pinion angle where it should be and get the caster/camber where it should be.

 

[Justafordguy]

X2, Try the drop brackets first. It made a huge difference on mine. My pinion angle isn't bad with the stock arms and drop brackets. My truck is only used for mild off roading but I've never had an issue with the front drive shaft/pinion.

 

[DirtDonk]

...All i have is a 3.5" lift. I did not think it would be this complicated to get it to drive right...

It usually isn't. But it is for some, so I guess you're one of the "lucky" ones now.%)

What are the chances we can get some good pics of your setup G? Like some side angle shots of the tires, and some good front end shots showing the steering linkage layout between the wheels?

Even though it's not as good as hands-on like you and the shop have the ability to do, it might help. Maybe one of us can see something amiss from here.

Paul

 

[Ohio Bronco 21]

I don't believe its your tire rim combo.