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-   -   Reduction in fuel efficiency after changing the tyres (https://www.team-bhp.com/forum/tyre-alloy-wheel-section/256899-reduction-fuel-efficiency-after-changing-tyres.html)

Hello guys,

I have a Skoda Octavia TDi AT (2019). The vehicle had come with 205/55 R16 tyres. After using the tyres for close to 43k kms I replaced them with Continental 205/60 R16 (note the difference in the ratio).

Now, I am facing a typical problem. After the replacement I was quick to observe that the on board computer was displaying a lesser mileage to a litre. Initially I thought that maybe it is because of a bigger contact patch with the road (since these are new tyres) I should get marginally lesser fuel consumption. But to my surprise I am getting a reduced average of nearly 2kmpl. I confronted the tyre seller for suggesting me to buy bigger sized tyres. He claimed that everyone goes for this upgrade and ideally there should be no deviation in average as more distance is covered per rotation by the bigger wheel.

Since I was not happy and not convinced, offered me a replacement of these tyres and gave me an option change them back to the stock size. But the question is does slightly changing the profile of the tyre cause so much deviation of around 15%? I love the overall feel with these new tyres as the ride height has increased and the bumps cannot be felt inside the cabin anymore after the change. But I am also not OK to compromise on the fuel efficiency of the vehicle by such a big margin. Please advise. Many Thanks.

You have upsized the tyres by 3.24 percent. Your original tyre circumference was 1985.17 mm against 2049.57 mm. In simple words when the speedometer is showing 100 kph the actual speed will be 103.24 kph and if the odometer is showing 100 kms travelled the car would have travelled 103.24 kms.

The above numbers should not make a huge difference in the average. It would be ideal to know what your milage numbers are but a reduction as per MID of 3 to 4 percent is acceptable. This is only on MID/Odometer, in reality there is no reduction.

I suggest you look elsewhere as well like due service / bad fuel / change in traffic conditions or change of driver.

The drop in fuel efficiency was pretty instant. I realized it in the first 20 mins of driving. I have got my vehicle serviced just a month back (2000 kms back) so the question of service issue etc doesn't arrive. To rule out the possibility of bad fuel, I have emptied the tank entirely and refueled at a renowned fuel station. Still no change.

As pointed out by tazman, the change in circumference is just a few procent. Shouldn’t even show up in your fuel efficiency.

There are two other factors that can be a major contribution to your fuel efficiency:
- tire pressure
- The tire itself (make, model)

On tire pressure, just 0.2 bar higher or lower than recommended can easily give you a 10-15% difference in fuel efficiency. One problem could also be the manometer accuracy they used to pressurise your tires, see below.

There can be substantial differences in fuel efficiency (again 10-15%) between different brands/models/thread tire. Not sure about India, here in Europe tires have an efficiency rating/indication.

So it's easy to see that these two factors, either one of them, or a combination of both could cause a difference in fuel economy.

As mentioned, there are other factors that could cause the fuel efficiency to get worst. It might just have coincided with getting the tires changed.

I would at least check the tire pressure, preferably get it checked at a few different places. See if you get a different reading. Most manometers, unless they get replaced every 12 months will be wildly off.

I usually keep the pressure on all my vehicles about 0.15 and 0.20 bar higher than the normal recommended pressure. That gives me better mileage and a little higher does not really affect performance, helps actually at high speed driving on the motorway, especially with passengers and luggage in the car.

It also provides a bit of a buffer margin as tires always slowly deflate.

Make sure your tires aren’t under inflated. It will affect your fuel efficiency negatively, and also your tires are likely to wear quicker as they warm up much more.

Good luck

Jeroen

Usually an increase in your tire diameter, results in a small power loss. Are you compensating the loss of power by accelerating more? This could result in lowered efficiency.

some times the newer softer tires have better grip and hence more friction compared to older hard/worn-out tires resulting in relatively lesser efficiency.

Compare the FE with your new tyres (when your car was new), not the old ones.

Considering the odo error, hardness difference and also the additional flex this tyre has, the difference of 2 km/l is not that huge. Your actual difference would be around 1 km/l.

Do a tankful to tankful check after sometime, with built in 3% error.

Contact patch size is same, if air pressure is same, section is still 205mm.
Also, 'wider' tyres usually lead to slightly more fuel consumption, and that is not because the size of the contact patch changes (area of contact patch depends only on vehicle weight and air pressure) , it is because the 'aspect ratio' of the contact patch (more rectangulary than before, if going for wider section tyres).

In your case, I can guess only three reasons :
1) something else has changed, coincidentally, independent of tyre change
2) air pressure filled in your new tyre is lower than what you had before
3) tyre compound is drastically different, your new tyres are more 'sticky' or 'grippy' - check the "TRACTION X" marking on your sidewall and compare it with old tyre. The X would be A/B/C

New tyres have a coating on them which needs to wear out before normal tyre behaviour is noticed. Grip till such time will be lesser, and hence above would not be the reason for the drop in FE.

This is the most likely cause: lower pressure in the tyres, either as set by the tyre shop, or if you have re-inflated later at a place which had a faulty measurement.

*

The pressure readings are not consistent across bunks. Suggest to go to Shell and get the tyres inflated to the same psi readings as recommended for the stock tyres. Check again after this.

Either your tyre pressure is too low or as Turbohead mentioned, you might be over compensating with the throttle due to the increased rotating mass on your axles (mind you, you have gone for a 10 percent increase in sidewall height :eek:). Either way there's really no way to know what drop in fuel efficiency you're experiencing unless you do a tank-to-tank calculation; fill up to auto-stop, set trip to 0, drive about, fill up again to auto-stop, calculate mileage based on number of kms on the trip readout vs number of liters of fuel filled :thumbs up

Ideally you ought to have gone with stock size itself perhaps if you mention which tryes your car had, the members can recommend specific models of tyres that will give you better ride quality without having to alter your tyre size like this.

Hi. Just a few observations.

What is the point of reference for the original fuel efficiency against which you say that it has reduced by 2 kmpl? Is it your vehicle's lifetime fuel efficiency? Or have you reset the meter anytime?

What is the time and distance covered by the new set-up of 205/60R16 tyres? Is it a sufficiently large sample space to factor in different driving behaviors and traffic patterns? like City/highway/bumper-to-bumper traffic, etc.?

Also if I'm not wrong, the stock tyres would have been GY Eagle NCT5s, which model of Conti have you fitted? Is it the UC6?

I swapped my 195/55R16s to 195/60R16s, a 3.1% circumference difference. This set off 3 calibration issues:
1. The speedometer error reduced, so while at an indicated 55 kmph I was doing 50 kmph by GPS, it now shows 52 kmph on the meter while GPS shows 50;

2. Known distances became a little shorter. What I've always known to be a 25.8 km round trip, became a 24.9 km round trip; and

3. The FE dropped from an usual tankful to tankful 18.5 kmpl on highways, to 17.2 kmpl (and the best average dropped from 21.2 kmpl to 19.3 kmpl).

So you're apparently burning more fuel per km, but you're also travelling lesser km between 2 points, which sort of evens things out! And you're riding more comfortably as an extra bonus. So why worry at all?

I moved from 245/75/R16 to 275/70/R16 on my Isuzu which is a decent upsize. The originals OEM were MRF's and the current ones at 30000 kms is Michelin. In my case the FE increased from 11.5 to 12.5 on highways. In the city it reduced from 10 to 9. If we calculate 2.5% upsize the highway milage is even better and city milage has not reduced drastically.

Personally always prefer to stick to original tyre dimensions as suggested by OEM, instead of upscaling. IMHO, experimentation is okay, but not at the cost of peace of mind.

This is easier said than done. For example, some sizes suffer from chronic cases of tyre impact failure - like 195/55R16 (Baleno/i20/Verna), 205/50R17 (EcoSport), 185/55R16 (Honda City), etc., 205/55R16 is also one of these sizes with short sidewalls and suffering from the same issue.

Note - When I say that these sizes suffer from chronic issues, it means the failure rate can be as high as 3%, while 1% or lower is still ok.

The above was a very indicative list off the top of my head. I'm listing down the common sizes where it is recommended to up-size :-

• 175/60R15 => 185/60R15 (Grand i10 Nios/Aura)
• 175/65R15 => 185/65R15 (Honda City/Ignis)
• 185/55R16 => 185/60R16 (Rarely available) / 195/55R16 / 205/55R16 (Honda City)
• 195/55R16 => 195/60R16 (Baleno/Verna/i20)
• 205/55R16 => 215/55R16 (Corolla, Octavia)
• 205/50R17 => 215/55R17 (EcoSport)
• 215/50R17 => 215/55R17 / 225/50R17 (MG ZS EV)
• 225/45R17 => 225/50R17 (Pre 2013 C-Class, Octavia vRS)

If you care to search around in the forum, you'll find entire threads dedicated to tyre issues on these particular sizes. THe brand/quality of tyres is not the issue, it has more to do with the size itself.