Wide Tires: Do They Really Need More Power?

Hello,

In many car forums, discussions often revolve around the use of extra-wide tires on everyday cars and their effects compared to the "narrower" original equipment (OEM) tires: increased fuel consumption, reduced top speed, and sluggish acceleration.
Therefore, I find the roller cult ridiculous anyway, but I am still interested in the technical aspects.

When accelerating, the increased mass of the wheels, their rotational inertia, as well as air and rolling resistance naturally combine to create maximum braking force and increased fuel consumption. I can imagine that this is quite noticeable in the "butt meter" (feeling of acceleration) in cars with less powerful engines -> so far, so clear.

If, for example, I read that a 100 horsepower Polo 9N experiences a maximum speed loss of approximately 185 km/h to 180 km/h, then the wider tires (205 or 215) would consume about 8 horsepower, which is 8% more power, compared to the standard 185 or 195 tires - considering a 5-10% increase in tire width, as if these tires formed the entire frontal area of the car's aerodynamic profile ?
Instinctively, I would classify the increase in frontal area in the direction of the airflow, due to the few uncovered centimeters of tire height, as completely insignificant compared to the total frontal area of the car.

Does anyone here know the approximate real-world effects of changing air and rolling resistance when using wider tires?

Hello Ulf,

I use quite different tires: 205/55 16 in the winter and 235/45 17 in the summer (all from the factory).

Certainly, there will be the differences you described - but everyday life is different:

- In the summer, my BMR (Basal Metabolic Rate) slows down due to the temperature.
- In the winter, I experience a noticeably higher energy consumption, but this is due to cold starts, not rolling resistance.

These phenomena are exact opposites of the parameters related to maturity, and they are much more pronounced.

And the 1.5 tons of the Passat feels much more comfortable with 235 tires than with 205-profile tires.

m;

"I couldn't get along with the original 175/65 R14 fuel-efficient tires on the 5.5-inch steel rims on my daily driver. They were rock hard, but didn't offer proper straight-line stability, were extremely sensitive to crosswinds, and I was absolutely afraid of driving on wet road surfaces. I found that unacceptable! So, despite the eco-friendly model, I bought 6.5-inch alloy rims from a 307 and started thinking about wider tires. Since 185/55 R15 tires were significantly more expensive, I decided on 195/50 R15. And because I didn't drive with the fuel-efficient tires for very long, and mostly only within city limits, I don't have any fuel consumption data from that time."

"I can identify the loss in maximum speed. With the fuel-saving deflectors, I measured 185 km/h using GPS, but the engine overheated within minutes due to the lack of an intercooler. Then, after about 15-20 kilometers of continuous full throttle, a protective mechanism reduces the maximum speed to approximately the registered value of 168 km/h. At that time, I didn't have the ScanGauge II either, so I didn't know about the intake air temperatures caused by this. Now, with that knowledge, I rarely drive longer distances faster than 135 km/h. Most of the time, I drive around 105-115 km/h. The resulting increase in driving time on my daily 93-kilometer commute is in the single-digit minute range. It's not worth it to me."

Regarding the Tmax loss: Originally, with a still-cool engine, the car could achieve approximately 185 km/h. With the 195 tires, this was reduced to about 172 to 175 km/h. I can only speculate about the increase in power required by these tires. However, the appearance and handling of the factory-lowered vehicle are better suited to the wider wheels. The investment was worthwhile, and the increased fuel consumption seems to be manageable during my usual driving.

Hutfahrer wrote:

With the original 175/65 R14 fuel-efficient tires on 5.5 J steel rims... the GPS measured a value of 185. . . . Originally, with a still-cool engine, approximately 185 km/h could be achieved. With the 195 tires, this was reduced to about 172 to 175 km/h.

. . Although the 175 tires have a slightly larger rolling circumference, which makes them about 2 km/h faster than the 195 tires in terms of top speed - at the same engine RPM!

So, we would have at least a 12 km/h (approximately 7.5 mph) reduction in maximum speed due to the 195-size tires instead of 175-size tires: another striking case if the measurement conditions are "identical"!

...I had hoped that the smaller rolling circumference of the 195s wouldn't cause me to lose too much agility. It's just an air pump.

Seat Ibiza, 1998, 110 horsepower, AFN engine.
Reference section S6 towards Sebenstein (slightly downhill): according to the speedometer:
Summer tire: Maximum speed ~208 km/h with size 205/45/16 (Hankook Optimo).
Winter: Maximum speed ~215 km/h with tires size 195/55/15 (?).

Best regards.
peter

PS: Since I occasionally like to 'use' the AFN (presumably a road or track), and this section is approximately 5km long, perfectly straight, and slightly downhill, I have these values memorized.

I'm also interested in what you said about the tires.
Currently driving a 1.9 TDI Quattro A4 with original 235/45 R 17 tires on 7.5x17 alloy wheels.
These are coming to an end this summer, and I'm wondering if I should switch to different rims.
Then I should put on 205/50 R17 tires to be able to accelerate a little faster.

I have the impression that accelerating from 100 to 200 km/h on the highway consumes a significant amount of power, and I estimate that it results in an additional fuel consumption of about 0.5 liters. However, I'm not really brave enough to try it...

"Because the braking distance is clearly shorter with wider tires. The cornering speed will decrease slightly with the 205s. However, they are a bit more agile. I'm just having a hard time deciding whether to try them or stick with the 235s."

Steffarn wrote:

I have the impression that accelerating from 100 to 200 km/h on the highway consumes a significant amount of power, and I estimate that it results in an additional fuel consumption of about 0.5 liters. However, I'm not really brave enough to try it... Because the braking distance with wider tires is clearly shorter. The cornering speed will decrease slightly with the 205s. However, it will be a bit more agile. I simply can't decide whether I should try it or stick with the 235s.

Okay, you've described the expected outcomes well. Now you just need to prioritize. The 205s are 1% smaller in circumference. Personally, I would try the 205s and enjoy the lower fuel consumption and increased agility, unless you really drive a lot on winding roads.
haithamina