Tire stretching is very popular among the members of the car modding community because of the unique look it brings to the vehicle. With lowered suspension and oversized rims, stretched tires complete the “stance”, a term used by the Japanese modders.
In this article, I’ll explain the basic method of how to stretch tires, but more importantly, explain in depth the safety and legal issues that come with them.
The short answer is that stretched tires are not safe, and while technically not illegal, they can be used as an argument against you in case of an accident, shifting responsibility on you and voiding your insurance.
Tire stretching is exactly what it sounds like – it’s a process of taking a tire too small for the rim and making it fit. I’m aware that rim and wheel are used interchangeably, but I consider the wheel to be the tire and rim combined as it clears a lot of confusion.
The degree of stretching isn’t standardized, but there are some widely-accepted measures of knowing just how far you can stretch a tire. Before we get into it, I should give you a quick breakdown of tire and rim dimensions.
The size of a rim is determined by the following measurements: diameter, width, and offset. Bolt pattern is also important, but let’s assume the rim is a perfect fit for your vehicle.
The diameter is self-explanatory and represents the overall size of the rim when looked at from the side. Every vehicle comes with an acceptable rim diameter range, and going above it without compensating with thinner tires can cause problems with steering articulation and suspension.
The width of the rim is also quite simple – it determines the width of the tire and therefore the entire wheel. Wheels that are too wide may not even fit or will stick out on the sides, which is illegal in some states where wheels have to be fully shrouded.
The offset determines the distances from the hub-mounting to the centerline of the rim. A rim with no offset will be mounted perfectly in the middle, so half of the width is facing towards the vehicle, and half is facing outwards.
The negative offset pushes the rim away from the vehicle and is necessary to mount wider rims without creating massive wheel arches. The positive offset puts more of the wheel towards the vehicle, which affects the steering angle in a negative way.
The dimensions of the rim are displayed as follows: diameter x width ±offset, followed by the number of bolts x bolt spacing diameter. Diameter and width are measured in inches, while offset and bolt displacement is measured in millimeters.
This will be more clear if I provide a couple of examples:
We will ignore the bolt displacement as it doesn’t matter for stretching, and use the 18×10 (+0) as the base rim dimensions in the following sections.
Tire measurements are a bit more complicated. There’s the tire type, width, aspect ratio, construction type, wheel (rim) diameter, load index, speed rating, as well as weather rating.
Tire type determines the suitable application – P for passenger vehicles, LT for light trucks, and ST for special trailers.
Tire width is measured in millimeters and doesn’t have to be a perfect match for rim width, but it’s generally very close.
Aspect ratio represents the height/profile/sidewall of the tire in relation to the tire width. A 225mm wide tire with a 60 aspect ratio has a height of 135mm – 60% of the width.
You might be thinking that the aspect ratio doesn’t make sense and it should just be a number – and you’re right, it should. However, the first tires had a 100% aspect ratio, where the width and height were always the same. When the lower-profile tires came around, manufacturers created the tradition of using a percentage ratio instead of a number in millimeters, which stuck to this day.
Wheel diameter indicates the compatible rim size, measured in inches.
Load index represents the amount of weight each tire can support.
Speed rating tells you what the maximum speed is considered safe for the tires in question.
Let’s break down an example of the complete tire markings: P 215/65 R 15 89 H, M+S
Now that we know how tires and rims are measured, we can put the numbers together to create the wheel size.
Every vehicle comes with factory-recommended wheel and rim sizes. This information can be displayed on the back of the fuel tank cover, on the B-column behind the driver’s door, and in the owner’s manual.
You can go beyond the manufacturer’s recommendation and stay within the limitations of the stock setup by adjusting rim and wheel size.
The bigger the rim, the smaller the aspect ratio of the tire needs to be to maintain the same overall diameter. Greater the tire height, the smaller the rim has to be to compensate. You get the idea.
With the basics covered, we now know that a larger rim requires a tire with a smaller aspect ratio to maintain the same overall diameter. However, there is a lower limit to the aspect ratio, and 45-35 is already considered low-profile.
Stretching takes the aspect ratio to the extreme by placing a tire on a rim that is too wide.
To illustrate this point, let us take a setup of a 205/55 16 tire on a 16×8 rim. If we were to increase the rim width to 9″, the tire would have to compensate for extra 0.5 inches on both sides.
If the tire wall is positioned at a 90° angle, by stretching on a 9″ rim, the aspect ratio drops to 51, and the overall height decrease by 0.2 inches. This math is far from exact and depends a lot on how the tire will deform under stretch, but it should give you an idea of what to expect.
The modding community has come up to categorize stretches in stages to make it easier to create an ideal setup.
Stage zero is the neutral, stock setup. Increasing the stage also increases the risks involves, so the maximum that’s still considered reasonably safe is stage 3.
The stretch stage can be increased by:
The stretch stage can be reduced by:
This might seem confusing at first, but it’s actually not that complicated. You can mix and match the values and as long as you stay within the first 3 stages, your setup is going to work out.
The 255/35 tire on an 18×10 rim is in a stage 0 stretch as it’s perfectly squared. In the following stretch configurations, I’ll bold the values that have an impact on the stage.
As you can see, it’s all about allocating values. You can compensate for a decrease in one value by increasing the other two until you create an ideal setup. Naturally, the adjustments have to be within reason.
You can also stretch tires in the opposite direction – placing wider tires on a narrower rim. The same measuring rules apply, you just need to factor them in reverse. The reverse stretch works best for track-ready vehicles, and for that reason, stage 2 is considered the maximum.
The negative connotations regarding stretched tires come from the obvious damage and wear risks. However, the two should not be equated. I’ll also cover the legality of stretching the tires, and why that’s a complex subject.
It’s obvious that a stretched setup comes with certain drawbacks in terms of tire wheel wear. The tire will wear out more quickly and be prone to blowing a cord. This happens when the metal wires inside the tire become exposed and further damage will rupture the tire.
Debeading is also quite common, a situation where the tire loses contact with the bead of the rim and deflates. Lastly, the outer edge of the rim is exposed to damage as it will make the first contact with any surface.
By stretching the tire, you’re changing its geometry which has an impact on performance. Tires flex in corners to remain in contact with the asphalt, and this is achieved by proper sidewall geometry, which is lost through more severe stretching.
The more severe problem with stretched tires is hydroplaning. When it’s raining, tires have to force out the water they come in contact with to maintain a solid connection with the road.
Stretched tires are not as effective at pushing the water out, so a small layer of water will form between the tire and asphalt and cause hydroplaning – an occurrence where the vehicle has no grip on the road and loses control.
Stretched tires fall into a gray legal area. They’re not illegal, but excessive stretching may cause a police officer to pull you over. What I’m most concerned about is what happens if a vehicle with stretched tires is involved in an accident.
The insurance company might decline to pay the coverage if their inspector determines that the tires had a part in why the accident happened. I cannot give you a solid answer to this question, so I would advise you to do your research before deciding whether to stretch the tires or not.
The risks and dangers involved in tire stretching have been blown way out of proportion. It doesn’t take an expert to realize what the negative connotations of stretching tires are, but that doesn’t mean it’s all that serious.
Tire stretching is far more common than people realize. The stretching guide has shown you just how little it takes to achieve a stage 1 stretch, which is barely noticeable.
The stage 1 or stage 2 stretch is still highly usable even if you’re driving your car daily. If you understand that this modification is done for looks and not for performance, you can adjust your driving style and habits accordingly.
To be on the safe side, I would recommend the stage 3 stretch for the weekend and show cars only. Going beyond stretch 3 is really dangerous, but is still done for show cars that don’t see a lot of mileage on them.
I have to disappoint you, but I’m not going to give you a step-by-step guide on how to stretch tires. The process is quite dangerous and I don’t feel like following a written guide will help.
If there’s a tire shop nearby willing to do the mounting for you, don’t hesitate to use their service. Otherwise, take a look at the video below to get a better understanding of what the process involves.
The answer depends on the level of stretching, but the more sensible stretches are fairly safe. You can think of it as the difference in safety between brand new tires, and those that are half-worn.
The primary reason you’d want to stretch tires is to get a better-looking vehicle. This modification has been popular for decades across the globe and allows the vehicle to sit even lower to the ground. A minor stretch can slightly improve performance, but a stock performance-oriented tire will do a better job.
No, stretching tires is based on the width of the rim, not its diameter. You need to take into account the width of the rim (second dimension) where an increase of half an inch results in 1 stage of stretch.
The answer depends on how the car is configured. A professional drift car has over 500 horsepower and needs wider tires to reign in all that power, while a slightly modified hobby car can well enough on its stock tire width.
By increasing the size of the wheel, you will increase ground clearance. To calculate the increase in clearance, take the difference between the overall diameter of the old and the new wheel and divide by 2. Keep in mind that larger wheels increase turn radius and reduce the length of travel of the suspension.
Because stretching affects the tire geometry and reduces its ability to flex, stretched tires will cause a rougher ride.
Stretching tires is not as dramatic as people set it out to be. The process of stretching is dangerous, but if you pick the right tire and rim, you shouldn’t have any issues with it. Follow the rules of stretching provided in this article, and you can create a setup that is both good-looking and practical!
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