Difference between 35-inch and 315 Tires (Metric vs Standard mm)

When comparing a 35-inch tire to a 315 wide tire, you are basically comparing two completely different measurements. The 35” is a metric value and refers to the width of the tire multiplied by the aspect ratio, which is the height of the sidewall, x2 because there are two sidewalls per tire, divided by the wheel inch, plus the wheel size… Phew!!! That’s a mouthful and a lot to digest at once so let’s break it down into a simple formula.

YES, 315 wide tires are the same as 35” tires although 315 is the tread width in millimeters and 35″ is the tire diameter. 315/70/17 is usually the accepted metric equivalent size for standard/imperial 35-inch tires.

Let’s see what that looks like in a formula form

Tire Size: 315/70R17 (35”)

  • 315 = the metric width of the tire measured in mm
  • 70 = the height percentage (Aspect Ratio) of the sidewall
  • (315 width x .70 = 220.5mm)
  • Divide mm by 25.4 to get inches
  • So….. 220.50 x 2 sidewalls = 441mm (divided by 25.4 = 17.36″)
  • 17.36″ + 17″ wheel = 34.36″ approximate tire diameter.

Let’s now look into this in a bit more detail

Are 35-Inch Tires the same as 315’s (Metric Vs Imperial MM)

Metric tire sizes can be a bit more complicated when it comes to understanding what size they really are.

Let’s see what that means.

Metric vs Imperial Millimeters

Understanding the difference between metric and imperial is handy when it comes to tire sizes because you can get really specific. There are so many different tire sizes available today so knowing the difference can mean finding that perfect fit for your truck. A simple way to differentiate is Metric is measured in milliliters and imperial/standard is measured in inches. That’s it!

So when it comes to tire production there’s no official mold which each tire manufacturer uses, however they use their own which basically means there’s no set industry pattern. So the 315/70/17 is usually the accepted metric size for 35” tires, even though the physical diameter of the tire can vary from manufacturer to manufacturer. Two different 35” tire brands can easily vary in true diameter.

This means certain tires are smaller than 35″ like a 34.6” and some will be slightly larger, depending on the brand and overall construction. So, this means a particular 35-inch tire can be somewhat wider in width than another. They are similar in metric size but there are slight differences in construction, weight, pattern, load rating, ply ratings, tread depth, etc.  

One way to find out the exact diameter of a tire is by going to the tire manufacturer’s website and checking the manufacturing specs on that specific tire and then comparing “apples with apples”.

What Size Lift for 35” Tires – Ford F150

The minimum requirements necessary to fit 35x.5 to a Ford F150 is a 4” lift kit and an aftermarket wheel with a more negative offset for improved UCA (Upper Control Arm) clearance. A more affordable option is a 2.5”-3” leveling kit with wheel spacers on the stock wheels combined with fender, body, wheel well and bumper plastic trimming

Read more here

Fitting 35” Tires with no lift – Jeep Wrangler

Fitting 35” tires on a Jeep Wrangler JK with a stock suspension requires the following:

  1. Removal of splash guards
  2. Fit a Rear Spare Wheel Spacer/Extender
  3. Fit Wider Aftermarket Wheel Flairs
  4. Leave the front sway bar connected
  5. Fitting larger bump-stops

So basically, yes it can be done but not without some additional modifications first. If your intention is to go off-road, it is highly recommended to fit a minimum of 2-3” lift to be able to disconnect the front sway bar to take advantage of the Wrangler’s legendary articulation. Don’t forget the larger bump stops or you’ll be picking up fenders on the trail. When flexing, the wheels will scrub heavily against the wheel arches and possibly rip off some plastic if you don’t take it slow. It won’t be a pleasant experience off-road – believe me!

Fitting 35-inch Tires On Your Truck

Bigger tires is the single most effective method of gaining improved ground clearance. This is especially important for overcoming obstacles in an off-road situation. There are however a few limitations, especially when it comes to IFS (Independent Front Suspension) 4WD vehicles.

Let’s now look at a few factors to consider when fitting 33” tires on your truck.

Lift Kit

Before you even consider fitting 35” tires on your IFS truck, you’ll need to have a minimum 4” lift kit installed. Depending on your truck, sometimes this isn’t enough, since you’ll still need to make additional modifications to prevent scrubbing at full lock. This is especially true if you want to retain full functionality and articulation which is important for off-road. If you decide to go 4” or higher, beware there are serious implications to any IFS suspension, but more on that later.

Who should fit 35” tires? There are mixed opinions when it comes to large tire upgrades, and depending who you ask, you’ll get differing opinions. I give it a Hell YES! If you can – why not? In fact I am currently planning a 35” tire upgrade on my truck! The added clearance, aggressive look, and improved traction and stability in my opinion is well worth it. It comes at a price of course.  

Click here for more info on fitting 33” to your truck

Wheel Offset

Wheel offset or backspacing is a factor that gets little consideration, and it can create complications if you’re not sure exactly how much brake caliper clearance is required. The problem here is, you don’t want to go too negative offset on the wheels else you risk to much wheel “poke”.

What is the difference/meaning of backspacing vs Offset?

Backspacing is the distance measured from the hub mounting surface to the inside edge of the wheel. When you decrease backspacing, you gain more inside wheel clearance. There is a fine line between keeping the tires in the guards and preventing scrub on arches, UCA, Brake calipers, etc.

Offset is measured in mm and generally refers to how your wheels sit inside the wheel wells. You get positive and negative offset wheels. When it’s positive the imaginary line is more towards the front and negative means the mounting surface is more towards the rear of the rim creating a deep dish effect.

Fender & Arch Trimming to fit 35’s

Usually there are a few plastic liners on the inner fender guards that needs to be massaged since they will scrub at full articulation. So get comfortable with your Stanley knife and cutter and do some trimming of those wheel arch/guards where they are making contact. You might even have to do some arch rolling, depending on which truck you have and how much space you’re working with.

Be mindful of the inner guard pinch weld and the inside of the fender flare. They usually need some trimming, depending on the tire and vehicle. Fender clearance and backspacing go hand-in-hand with tire width. A wider and taller tires will require more wheel arch clearance and room to move when flexing off-road and when turning at full lock. Don’t forget about your bumpstops. Manufactures seldom mention anything about bumpstops when selling you suspension components and its vital.  

When you squeeze oversized tires into a wheel arch without lifting the truck, you’ll need to trim away a lot of the inside fender and arch plastic to allow the tire to tuck behind the arch when turning and flexing off-road.

Will the 35’s throw out your speedo?

When you upgrade from a stock tire to one with a taller aspect ratio (Sidewall), increasing the wheel circumference, your speedo can be thrown out. In the case of 35” tires, the diameter will be larger and have an increase in the aspect ratio. This might throw out your speedometers reading quite a bit. The increase in tire circumference means the actual speed you are traveling will be higher than your speed reading and get worse the faster you travel.  

The below table will give you an indication of how the speedometer reading is affected from a 32” (275/70R17) to a 35” (315/70R17).

Speedo reading20mph30mph40mph50mph60mph70mph80mph90mph
Actual Speed21.43242.753.464.174.885.596.1

Below are the actual differences between the stock 32” tire and the upgraded 35”

MeasurementStock Tire (275/70/17)Upgrade (315/70/17)Differences
Diameter32.2″34.4″ (874mm)+6.8%
Width10.8″12.4″ (315mm)+14.8%
Sidewall7.6″8.7″ (221mm)+14.5%
Circumference101″107.9″ (2741mm)+6.8%
Revs/Mile627587 (365mm)-25

Conclusion

We have mentioned quite a few variables to consider before dropping a load on expensive oversized tires. You should first determine what the primary application for the upgrade is. Is it purely for aesthetics or will you need maximum practicality, off-road ability, while maintaining maximum articulation?

Jade C.

4-Wheel drives and off-road driving techniques has been my passion for over 20 years. Here we strive to provide the most accurate, up-to-date, information about the functionality, common faults and latest technology built into most 4 Wheel Drives.

Recent Content

link to 35x12.5R17 vs 315/70R17 – SIZE/WEIGHT/HEIGHT/LOAD Difference

35x12.5R17 vs 315/70R17 – SIZE/WEIGHT/HEIGHT/LOAD Difference

Understanding tire measurements can be very tricky and complicated, especially when tires are similar in size but described using different measurements. There is the metric measurement and the imperial or standard measurements and these can become confusing very quickly. So what is the main difference between 35×12.5R17 vs 315/70R17 tire? The 35” tire represents the […]