Tire Diameter and Width Advice

[sgltrk]

I'm running 315-70-17's on my Dodge CTD. I know it's not even the same class of truck as yours but these are over 32" tall and work well for me on the highway and in the dirt and rock and occasional sandy washes in central Arizona...

Thanks Verdesardog,

Adding in your input the range I'm looking at seems to be from 32"-35". With that info I can add the other factors and move forward with gear calculations. Do you have many small to medium height ledges on the trails in your area? How tall of a ledge can you handle with your tires?

Lyle

 

[sgltrk]

You'll need to find the target RPM range for the motor you're using and take into account the output ratio of the transmission it'll be hooked to. Then, once you know your target RPM range, you can match the axle ratio to the tire size to achieve your ideal RPM.

If someone here says "I'm running XX tires with XX ratio gears", it won't necessarily mean it's right for your rig.

Excellent point Clandr1,

The idea behind this post is to determine what tire diameters are the best compromise for on road and for dealing with the off road obstacles in my local terrain.

My target RPM is around 1800. The eng. produces max torque (220 lb/ft) at 1600 RPM. The torque curve is fairly flat staying above 190 lb/ft out to about 2600-2800 RPM. If need be I can tweak injector timing and pump adjustments and approach the 300 lb/ft range. With slightly larger injectors I can exceed 300 lb/ft. That eng. output should let me run some fairly tall axle ratios if necessary.

The trans will be either a Toyota R150F or R151F. Both have OD ratios of .838:1. If I can find, big if, a set of 5th gears from an R452 trans they will swap directly into either the R150 or R151 producing an OD ratio of .69:1.

LOL, I'm getting my own post off topic and probably way too deep into the weeds.

Lyle

 

[clandr1]

Glad you already have the data on the ratios and RPM specs! Sorry if I overshot your question by overcomplicating my response.

Here's my bare bones, no nonsense recommendation: in my opinion, a 33x10.50 tire is as big as one should go for general overlanding purposes. If you're in a smaller vehicle (which you are), I think you'd probably be better off with 31"x10.5 to minimize the amount of weight due to the tires.

Best of luck with whatever you decide!

 

[moodywizard]

I am in socal and have a FJ Cruiser which I like to take everywhere (camping and wheeling). I currently run 305/70/16 MTR's on steel wheels, equates to about 33x12x16. This is the biggest I would suggest going if you actually want to drive some distances and still have nice road manners. But like others have said it all depends on what you plan on doing and the vehicle.

Also on another note my name is Lyle too, how weird...

 

[4x4junkie]

Thanks 4x4 Junkie,

I'm concerned about the front leafs for the long term. I'm picking up about 200 lbs. additional weight with the new engine so I hope that will help provide a little more supple ride. Regardless I will work with them for now as there are many other mods planned. I have been leaning toward the 33" to 35" range so your experience is moving me toward the taller tire. With the 37's currently on the truck it is quite a step up to the cab, something I want to reduce as much as I reasonably can. How are your MT's on the road in terms of handling, stopping, ride and noise?

Lyle

My KM2s are smooth and vibration-free up to about 75 MPH, but do vibrate a little bit above that speed. I have little reason to go that fast though, partly because my mileage tanks by 4-5 MPG (I usually just set the cruise somewhere between 60-65 or so, which additionally removes some of the aggravation of being stuck behind morons every few miles who text while driving 55 in the fast lane).
Noise is greater than would be with ATs, but isn't obnoxious (definitely not the deafening roar of Super Swampers). If the windows are up you can talk in a completely normal voice. There's some number of 35" ATs available if you want more quietness.

I can't say I've ever wished for smaller tires like some here are advocating though. Again, I think this has a lot more to do with how the rig is built.
I somewhat recently put on a set of Fox shocks, which made a dramatic improvement in the ride pleasantness over the Rancho shocks I had prior. The springs I have are also about the same stiffness as stock in the rear, and a slight bit softer than stock up front (most lifted springs tend to be significantly stiffer than stock).
If one doesn't include rockier, more technical trails in their ventures at all, then smaller tires can certainly suffice as they usually are much cheaper to buy (and require less lift and/or fender trimming).

 

[sgltrk]

Glad you already have the data on the ratios and RPM specs! Sorry if I overshot your question by overcomplicating my response.

Here's my bare bones, no nonsense recommendation: in my opinion, a 33x10.50 tire is as big as one should go for general overlanding purposes. If you're in a smaller vehicle (which you are), I think you'd probably be better off with 31"x10.5 to minimize the amount of weight due to the tires.

Best of luck with whatever you decide!

LOL! No sweat! Didn't mean to imply your input was off track just that I tend, strongly, to get deep into numbers crunching and research, and then put out more info than anyone really wants. Is your concern with tire weight due to off road shortcomings or suspension control issues on road? Did that question make sense? I guess I'm asking if tire weight in some way relates to off road performance and durability?

Lyle

Lyle

 

[sgltrk]

I am in socal and have a FJ Cruiser which I like to take everywhere (camping and wheeling). I currently run 305/70/16 MTR's on steel wheels, equates to about 33x12x16. This is the biggest I would suggest going if you actually want to drive some distances and still have nice road manners. But like others have said it all depends on what you plan on doing and the vehicle.

Also on another note my name is Lyle too, how weird...

Hello Lyle,

Not that many of us around. I think you are the third or fourth one I have run into in my life other than family. If you want weird my Grandfather and Father were also Lyle so, I'm the III.

Since you are in the area where I will spend the most time, do you feel there is an advantage to the wider 12/12.50 as opposed to a 10.50 tire? Have you ever felt the need for a 34" or 35" tire?

Lyle III

 

[sgltrk]

My KM2s are smooth and vibration-free up to about 75 MPH, but do vibrate a little bit above that speed. I have little reason to go that fast though, partly because my mileage tanks by 4-5 MPG (I usually just set the cruise somewhere between 60-65 or so, which additionally removes some of the aggravation of being stuck behind morons every few miles who text while driving 55 in the fast lane).
Noise is greater than would be with ATs, but isn't obnoxious (definitely not the deafening roar of Super Swampers). If the windows are up you can talk in a completely normal voice. There's some number of 35" ATs available if you want more quietness.

I can't say I've ever wished for smaller tires like some here are advocating though. Again, I think this has a lot more to do with how the rig is built.
I somewhat recently put on a set of Fox shocks, which made a dramatic improvement in the ride pleasantness over the Rancho shocks I had prior. The springs I have are also about the same stiffness as stock in the rear, and a slight bit softer than stock up front (most lifted springs tend to be significantly stiffer than stock).
If one doesn't include rockier, more technical trails in their ventures at all, then smaller tires can certainly suffice as they usually are much cheaper to buy (and require less lift and/or fender trimming).

Hey 4x4junkie,

The KM2's are more aggressive than I was planing on. I'm not so much worried about noise as I am about on road handling and stopping. Any thoughts in that regard? As to usage we'll start with trails and eventually hope to be able to run across the desert dealing with whatever presents itself in terms of terrain. I was originally thinking of 33's but recently have been considering 34's or 35's hence this post asking for advice. Good info about the Fox shocks, thanks. As I respond to everyone's input I find it is helping me better define my direction.

Lyle

 

[moodywizard]

Lol my great grandpa was named Lyle too!

I feel there is some times an advantage to the wider tire. As in sand, mud, and maybe helps stabilization being more wide on the fj as it's already wide. I think the only advantage for a skinny is less weight and more performance due to that. But then again this is a 4x4 vehicle not a sports car. BFG and hankook make a 34" tire, I was really contemplating those versus the Mtrs for that and they were cheaper ( hankooks especially). But I really feel like the Mtrs are in stoppable and in the end it's really only a 1 inch height difference from 33 to 35 so I don't know the height benefit out ways all the cons for a bigger tire in my case. Cons being heavy, more money, heavier tire means more stress on driveline, etc . Also I would for sure have to regear. I have full steel skids underneath so I'm not afraid to drag her along if need be over the rocks. Where abouts are you located? I'm in palmdale.


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[clandr1]

LOL! No sweat! Didn't mean to imply your input was off track just that I tend, strongly, to get deep into numbers crunching and research, and then put out more info than anyone really wants. Is your concern with tire weight due to off road shortcomings or suspension control issues on road? Did that question make sense? I guess I'm asking if tire weight in some way relates to off road performance and durability?

Lyle

Lyle

Typically the heavier the tire, the slower your truck will accelerate and decelerate, not to mention the suspension may not be able to handle heavier weight tires (depends on the truck and what shocks/springs/coils one has). I guess what I'm saying is, ultimately it's about ground clearance and fitting the tires in the wheel well. Personally, I'm a firm believer in keeping a truck stock when possible, including lift. So, if you have to put a 2.5" or 3" lift on your vehicle to go from 31" to 33" tires, just stick with the 31" tires if your ground clearance is satisfactory (which IMO the small Toyota 4x4 trucks have plenty of).

 

[sgltrk]

Lol my great grandpa was named Lyle too!

I feel there is some times an advantage to the wider tire. As in sand, mud, and maybe helps stabilization being more wide on the fj as it's already wide. I think the only advantage for a skinny is less weight and more performance due to that. But then again this is a 4x4 vehicle not a sports car. BFG and hankook make a 34" tire, I was really contemplating those versus the Mtrs for that and they were cheaper ( hankooks especially). But I really feel like the Mtrs are in stoppable and in the end it's really only a 1 inch height difference from 33 to 35 so I don't know the height benefit out ways all the cons for a bigger tire in my case. Cons being heavy, more money, heavier tire means more stress on driveline, etc . Also I would for sure have to regear. I have full steel skids underneath so I'm not afraid to drag her along if need be over the rocks. Where abouts are you located? I'm in palmdale.


Sent from my iPhone using Tapatalk

NOt surprised about your Great Granddad. Our name seems to run in families, kind of like cancer. LOL!

OK. More width on soft ground makes sense, better flotation. An inch in height one way or the other probably isn't that big a deal and I'm just over-thinking it.

I'm in Moreno Valley.

 

[sgltrk]

Typically the heavier the tire, the slower your truck will accelerate and decelerate, not to mention the suspension may not be able to handle heavier weight tires (depends on the truck and what shocks/springs/coils one has). I guess what I'm saying is, ultimately it's about ground clearance and fitting the tires in the wheel well. Personally, I'm a firm believer in keeping a truck stock when possible, including lift. So, if you have to put a 2.5" or 3" lift on your vehicle to go from 31" to 33" tires, just stick with the 31" tires if your ground clearance is satisfactory (which IMO the small Toyota 4x4 trucks have plenty of).

Clandr1,

The truck is currently a rock crawler so the "keeping it stock" ship has sailed I'm afraid. It has a 3" lift and is currently sitting on nearly new 37x12.50R15 Pitbull Rockers. I'll be selling those when I decide on new tires. Because clearance is not an issue I'm wide open on a replacement tire size. If clearance were not an issue for you would still stay with the 31"-33" range?

By the way I have family all around the Dallas area and was in Little Elm for several days about three weeks ago.

Lyle

 

[clandr1]

Clandr1,

The truck is currently a rock crawler so the "keeping it stock" ship has sailed I'm afraid. It has a 3" lift and is currently sitting on nearly new 37x12.50R15 Pitbull Rockers. I'll be selling those when I decide on new tires. Because clearance is not an issue I'm wide open on a replacement tire size. If clearance were not an issue for you would still stay with the 31"-33" range?

By the way I have family all around the Dallas area and was in Little Elm for several days about three weeks ago.

Lyle

Very cool! I grew up in the north dallas area and have no plans to move... As a side note, you might want to update your profile to include what city you're in/near since you never know who might be close by and PM you about wanting to take the 37" pitbulls off your hands.

As for your question, yes, I would still stay in the 31"-33" range. In my opinion, 35" and above makes the truck less street friendly. The two major trips I've taken in my Jimmy (Ouray, CO and Big Bend NP in TX) have been LOOOOONG highway jaunts to get to the destination, only to find out I could've accomplished the off road sections with a stock Land Cruiser and all terrain tires.

I guess it's all about what your goal is, and where you're going. If you plan on doing some crazy off roading and rock crawling, then stick with 35" tires. However, if you're more into mild off road adventures, go with 31-33" tires (along with stock suspension) and it'll make your ride there and back a little more bearable.

 

[4x4junkie]

Hey 4x4junkie,

The KM2's are more aggressive than I was planing on. I'm not so much worried about noise as I am about on road handling and stopping. Any thoughts in that regard? As to usage we'll start with trails and eventually hope to be able to run across the desert dealing with whatever presents itself in terms of terrain. I was originally thinking of 33's but recently have been considering 34's or 35's hence this post asking for advice. Good info about the Fox shocks, thanks. As I respond to everyone's input I find it is helping me better define my direction.

Lyle

No problems here with handling or stopping (it'll lock up the front wheels no problem if I step on it hard enough, the rears are kept in check by the rear ABS system). I also keep their pressure between 30-35 PSI for the road (closer to 35 for those long freeway hauls).
Every vehicle is different though... Stopping matters are largely determined by your brake system components and their proportioning. I recall the early Toyotas had non-vented rotors which is something you may want to upgrade to if it hasn't already been done.

Thing to remember is it's a 4x4 truck and not a sports car, and drive it accordingly.

 

[sgltrk]

Very cool! I grew up in the north dallas area and have no plans to move... As a side note, you might want to update your profile to include what city you're in/near since you never know who might be close by and PM you about wanting to take the 37" pitbulls off your hands.

As for your question, yes, I would still stay in the 31"-33" range. In my opinion, 35" and above makes the truck less street friendly. The two major trips I've taken in my Jimmy (Ouray, CO and Big Bend NP in TX) have been LOOOOONG highway jaunts to get to the destination, only to find out I could've accomplished the off road sections with a stock Land Cruiser and all terrain tires.

I guess it's all about what your goal is, and where you're going. If you plan on doing some crazy off roading and rock crawling, then stick with 35" tires. However, if you're more into mild off road adventures, go with 31-33" tires (along with stock suspension) and it'll make your ride there and back a little more bearable.

Next time I'm around Texas I'll try to let you know. Maybe we can get together for lunch or something.

Lyle