Wider wheels/track width and turning radius

[Darwin]

I have been racking my brain about the physics of changing to a new wheels that stick out farther than my current wheels, basically going from +18mm of offset to 0mm of offset and how that might affect my turning radius. My gut tells me that a wider track width would equal reduced reduced turning diameter....True??

 

[DaveInDenver]

Rim offset definitely has an affect on geometry, specifically the scrub radius and inclination angle.

Adding offset (e.g moving the tire out) will change the center of the tire contact patch out relative to the pivot point. Going out makes scrub less negative and potentially go positive, which generally means the steering becomes less stable. But it's not a simple thing to work out or predict after the fact unless you tear in to measure and sketch your front end.

I dunno if the actual turning radius is going to be changed much but the truck will certainly feel like it wants to under steer and become more reactive, e.g. you'll feel bump steer more, it'll wander more, etc.

Scrub radius - Wikipedia

en.wikipedia.org

 

[tacollie]

It definitely affects the turning radius. The amount you're talking about probably won't be a big deal. On short wheelbase it may drive better. The best mod I ever did to my 4Runner was 1.25" wheel spacers. It was more stable and tracked better.

 

[DaveInDenver]

It definitely affects the turning radius. The amount you're talking about probably won't be a big deal. On short wheelbase it may drive better. The best mod I ever did to my 4Runner was 1.25" wheel spacers. It was more stable and tracked better.

I went to 3rd gen 4Runner wheels on my Tacoma, which have about 0.75" less backspacing and found the opposite. Even a year on I still think about going back but have grown to like the look now. With the super skinny tires the stock rims look like one of those railroad trucks tucked under so much but even with the wider 265/75R16 the 5 spokes are kind of unique looking on a 2nd gen.

 

[billiebob]

turning radius is not the big deal. the negative of wider track is the change in the stress on all the steering components. you are altering what was developed thru a lot of engineering and design by the factory. you are also changing the effect of hitting slush or standing water or just a soft spot in the road. the wider the track, wider the tire the more sudden the pull on the wheel. I have been working the opposite for the past 5 years and love the handling and ride improvement of skinny tires and a narrow track.

7.50R16 vs stock 245/75R16 a wee bit taller, a lot skinnier, smoother ride, better gas mileage, longer range between gas stops.
going the other way, same backspace, 6.5" rim vs 8" rim, narrower vehicle, I never felt any difference in turning radius.
my TJR is fully 2" skinnier than it was with factory rubber and rims.

 

[DaveInDenver]

turning radius is not the big deal. the negative of wider track is the change in the stress on all the steering components. you are altering what was developed thru a lot of engineering and design by the factory. you are also changing the effect of hitting slush or standing water or just a soft spot in the road. the wider the track, wider the tire the more sudden the pull on the wheel. I have been working the opposite for the past 5 years and love the handling and ride improvement of skinny tires and a narrow track.

7.50R16 vs stock 245/75R16 a wee bit taller, a lot skinnier, smoother ride, better gas mileage, longer range between gas stops.
going the other way, same backspace, 6.5" rim vs 8" rim, narrower vehicle, I never felt any difference in turning radius.
my TJR is fully 2" skinnier than it was with factory rubber and rims.

I now run 265/75R16, same width but taller than the original 265/70R16 it came with but 235/85R16 (31.8 x 9.25) is what I ran the last time. These are close to 7.50R16 (31.8" x 8.75"). I assume you compensated for the rim width change? For example my stock rims are 16x7 +32mm offset, which would be right at the upper limit to mount a 7.50R16 (BFG recommends 5.5" to 7" for the KM3 in 7.50R16).

My experience with 235/85 on 7" was lots of lip damage (one of the reasons I had to replace the rims). So say I went to a 6" wide rim I'd need to use a +45mm offset to retain the same backspacing and thus not change the front end geometry (e.g. centerline of the contact patch relative to the king pin). Since you narrowed your track you may've kept the same offset, thus made the scrub radius more negative?

 

[Deleted member 9101]

I put 1.25" wheel spacers on my F150 and couldn't tell a difference other than how it looked.

 

[Regcabguy]

I wonder how the truck's with firepit negative offset rims handle?

 

[tacollie]

I went to 3rd gen 4Runner wheels on my Tacoma, which have about 0.75" less backspacing and found the opposite. Even a year on I still think about going back but have grown to like the look now. With the super skinny tires the stock rims look like one of those railroad trucks tucked under so much but even with the wider 265/75R16 the 5 spokes are kind of unique looking on a 2nd gen.

It was a 3rd gen 4Runner. It felt twitchy coming from a 2nd gen Tacoma. The wheel spacers definitely made it feel more stable.

I ran first gen Tacoma wheels on my first second gen Tacoma. I went back to the stock wheels but I can't remember why?

 

[Darwin]

So many more options for the lighter weight vehicles, unfortunately there are not as many options when it comes to trucks weighing in the 12,000 to 14,000 lbs range.

 

[Mighty Dodge Ram]

Running wider tires on wheels with less backspacing was the first misstep I made on a long, dark journey into suspension/steering hell. It definitely changed the turning radius on the truck. I’m now a fan of taller but narrow tires on stock rims. Unfortunately, most tire mfgrs are now wedded to the wide tread low profile trend.

 

[Darwin]

Running wider tires on wheels with less backspacing was the first misstep I made on a long, dark journey into suspension/steering hell. It definitely changed the turning radius on the truck. I’m now a fan of taller but narrow tires on stock rims. Unfortunately, most tire mfgrs are now wedded to the wide tread low profile trend.

Right now I am at +18 mm offset not a bad compromise, I rub on the stock sway bar though just barely, no where else. If my final weight puts me at 8000 lbs on the rear, I will be right at my tire capacity, which I do not like. My only other option would be to go with 13.5 wide Toyo MT's for a safety margin of 600 lbs. It's too bad you can't find many tires with that 131 load index.

 

[b dkw1]

If you are going to taller tires you can go with a little more offset and still have a decent scrub radius.

Offset really doesn't effect turning radius unless your tire is now rubbing on something. Running more offset will make the tires swing more and potentially hit the firewall or bumper.

On my 2000 Stupid duty it rubbed pretty bad with 35" tires at full lock. I just redid the suspension and mover the beam pivots out an inch to help get the tires away from the frame. I can now turn full lock on the steering box without it rubbing the frame or radius arms. It does now slightly hit the plastic lower part of the bumper which is pretty easy to trim.

 

[hoser]

If you want to retain the factory scrub radius and you've changed to larger diameter tires, you would have to change the offset (more negative)/ increase track width. It won't be a lot though.