Tire Size Question

[Skywagon]

I like the look of narrow tires also, and used them for years on various Land Rovers and Land Cruisers. I still use them on my '84 Ford F250. However, I think that the theory that skinny tires "cut down through the mud or snow to whatever is solid underneath has pretty much been debunked. The popular belief is , I think, that flotation is preferable in all but a very few conditions.
Bill

[jeff@work]

Scott Brady did an excellent write up of the pros and cons of narrow vs wide tires. http://www.expeditionswest.com/research ... _rev1.html

I'm personally running 265/75r16s on a Quigley 4x4 and i've thought about going to a taller tire like a 255/85r16. I don't have a ton of room to work with but i think those might fit, I definitely do not want to go wider as it would probably hurt gas mileage a bit, the wider tires are heavier so more wear and tear on all the steering components, plus i don't like my tires sticking out past my wheelwells throwing crap all over the side of my van. (The only e load range 255/85r16 i know of is the toyo m-55, i haven't really looked at 285/75r16's)

Personally if i wanted to keep the warranty I wouldn't mess with the tire size. Going from a 265/75r16 to a 285/75r16 is usually about a 1" difference in overall tire height, which actually gives you only an extra .5" of ground clearance. Also if you look around and compare tires the actual heights will vary from brand to brand. I've seen 255/85r16's vary from 32.8" to 33.3" and 265/75r16's vary from 31.6" to 32.0".

From my reading it seems that the diesels with the super low torque are the ones that do a bit better on gas mileage when going up in tire size as compared to the gas powered vans.... granted that all really comes down to overall tire size, gearing, and the speeds you drive. Okay i'll stop rambling now

[Greg In Austin]

Jeff@work,

Make sure and look at the details of the writeup you referenced.

Most of the white paper talks in generalities, but at one point (in a small chart) he makes some recommendations.

Even though he mentioned tha is was talkng about heavy expedition vehciles, the vehicle he used is about half the weight of a SMB; it was 5k lbs.

For vehicles of the weight we are talking about, 255 is on the extreme edge of his recommendation, and falls outside recommendation for soft surfaces.

This chart represents the recommended tire width, based on the vehicles weight (GVWR).

Vehicle GVWR Mixed Terrain Typical Soft Surfaces Typical
3,000-4,000 8.5-9.5â€

[jage]

He lost me in the abstract- "While the coefficient of friction (Ff = Cf x Fv) is linear and not affected by width" that's a total BS statment in my view. He fails to note the coefficient of friction is simply the measurement of the friction between two surfaces (and there is one for static and one for dynamic calculations for any pair of surfaces).

What this means is that my pencil eraser may have the same coefficient of friction as a 20" wide racing slick for a particular surface (let's say smooth glass for my pencil and ice for the tire) but if they were both on the same surface it would be different, just like a 10" tire would be different from the 20" on the same surface.

[j.whitbread]

I've found a lot of info related to this topic. Nitto Terra Grappler makes a 285/75 17E. (33.8") Will that fit the Quigley 4x4?

[sdwindansea]

I just had a set of Nitto Terra Grapplers installed on my SMB today. They are 285/75/16 that replaced the stock 245/75/16. I will create a separate topic later, but one word of caution. You may have trouble fitting the spare tire. I'm not sure where your spare is now. I have the trojan tire carrier. The new wheel/tire does not really fit on it. The upper left corner of the tire carrier pushes the spare out so it doesn't sit flush on the bolts. I am driving over to Aluminess early next week to see what can be done. Also, this shouldn't be a problem on the newer trojan tire carries (2008).

[j.whitbread]

Since installing the new tires (see gallery) here are the speedo details. I went from Hankook 245/70 17 to Nitto 285/70 17.

With the original tires of 245/70 17 the GPS at 70 MPH the speedo read about 72 MPH.

Now with the 285/70 17 and the GPS at 70 MPH the speedo reads 66/67 MPH.

FYI: V10, 5R110, 4.10 gears. The V10 has no problem getting right on top of the truck and running it quickly through the gears. The tires aren't too big in other words.

[Rockman]

Ive got 285/70 17 on my Quigley and they rub really really bad. They look like they have plenty of room when straight, but I "think" that the American Racing Baja wheels are offset or something (they were put on by previous owner) and maybe they swing out when turned.

Anyone know how I can tell if they are offset? I really dont want to buy new rims (unless someone on here wants them), and I really dont want to downsize the height of the tire.

Anyone have any suggestions on "testing" to see if the rims I have need to go?

BTW, awesome tire coverage on this tread.

[BroncoHauler]

Rims are typically available in different backspacing. Maybe there's a product number hidden somewhere that will help you figure out which version of your particular rim you have. Or you or a tire shop can measure the backspacing and see if there's another rim with different backspacing that will work better.


Herb

[j.whitbread]

The wheels I have are the Ford Super Duty aluminum wheels. I also have the original wheels (same size and set back). It does sound like your wheels are the wrong setback.