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Old 04-13-2021, 08:32 AM   #1 (permalink)
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Tire model, size and pressure

I'm currently running rather inefficient tires (Toyo Proxxes T1R), wich have a fuel efficiency rating of F and are staggered.
I'm looking to buy a set of fuel efficient tires to replace them in the near future when they are worn out, but I'm not quite sure wich ones to buy.
As of now my tire sizes are:
185/55R15 front (1,6 bar reccomended, 2,0 bar currently)
205/50R15 rear (1,8 bar reccomended, 2,2 bar currently)
As my rear tires are wearing down about twice as fast as my front tires, I would prefer identical sizes front and rear.

As of now I'm considering the Conti EcoContact 6 XL because it is rated A for fuel efficiency and B for wet grip.
The size I'm looking at is 185/55R15 front and rear, getting them approved by the TÜV and increasing the pressure to 3 bar.

Any suggestions are appreciated.

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Old 04-14-2021, 09:23 AM   #2 (permalink)
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You didn't tell us what vehicle these would be going on. That's important because if the wheels are different widths, the tires might not fit and TUV might not approve such a change.

I did a quick check with the resources I have and they don't list a 205/50R15 as OE on anything, and a 185/55R15 is only the GM Spark and Fiat 500e, but my source is for US vehicles only.

And it appears that going from a 205/50R15 to an 185/55R15 is going DOWN in load carrying capacity - again, that might run afoul of TUV.

I assume you want to make this change so you can rotate tires, but if the wheels aren't that same, that would be ill advised and maybe even impossible.

So 2 questions:

What vehicle are we talking about? Does the vehicle have different wheels front to rear?

What process does TUV use for such a change?

(OK, that was 3 questions!)
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Old 04-14-2021, 10:37 AM   #3 (permalink)
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Quote:
Originally Posted by CapriRacer View Post
I assume you want to make this change so you can rotate tires, but if the wheels aren't that same, that would be ill advised and maybe even impossible.

So 2 questions:

What vehicle are we talking about? Does the vehicle have different wheels front to rear?

What process does TUV use for such a change?

(OK, that was 3 questions!)
My car is an MR2 Spyder, as it weights less than 1000kg the load rating is not an issue.
The tire in question has a load rating of 86, meaning 530 kg per tire, or 1060 kg per axle.
Beeing able to rotate the tires is indeed part of the reason for going down in rear tire size as my rear tires wear faster than my front tires, but so is the lower rolling resistance and slightly reduction of aerodynamic drag.
The main issue with the TÜV is them checking if the tire fits properly in there and the tire is suitable (speed, load rating and so on).
As neither fitment nor ratings are issues for my car, I see no issues there.

According to the EU label for efficiency I might be looking for fuel savings around 0,5L/100 km over my rather inefficient performance tires.
That's the difference between 40 mpg and 44 mpg, ignoring the difference in size and pressure.
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Old 04-14-2021, 01:00 PM   #4 (permalink)
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I suspect part of the rear tire wear is the inflation pressure. Going up to 3 bar is going to make that worse.

The other part of the wear picture is that it is a drive tire. Certainly rotating tires front to rear will extend their life.

Edit: Oh, and I looked up the MR2 in my books and found that a 2001 model did come with the tire sizes listed. But the wheels are indeed different. 6 front / 6.5 rear. I don't know how that may affect things, but you'll want to think about that and maybe even do a trial fit.
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Old 04-14-2021, 01:36 PM   #5 (permalink)
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The higher tire wear on the rear likely comes from the rear end beeing heavier and the car beeing RWD.
Rotating the tires would greatly increase their lifespan as the front tires experience nearly no wear at all.
The wheels I'm currently running are of identical size, sadly mine didn't come with the OEM wheels.
The facelift version even hat 15" front and 16" rear wheels...
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Old 04-15-2021, 01:36 PM   #6 (permalink)
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I've been fairly happy with Vredestein Quatracs. They don't really stand out in any category but strike a nice balance of inexpensive, availability in many sizes, reasonable rolling resistance, light weight, and decent tread life.
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Old 04-16-2021, 09:57 AM   #7 (permalink)
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In 50 years driving, I wear out the fronts first because of the camber change when turning trashes the edges. Pretty much can get two fronts sets to a set of rears since they are different sizes. On vehicles that freeway drive primarily,, all 4 tend to wear evenly with minor position rotation. My superbug with negative camber on the rear wore out all 4 really flat after up to 70,000 miles of use. If you're trashing tires you have a traction suspension or load problem
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Old 04-16-2021, 10:24 AM   #8 (permalink)
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My rear tires are both wearing evenly and at an expected rate, keep in mind they have to take more load than the front tires and the car is RWD.
There are only about 400 kg on the front axle and the brake ballance of my car is nowhere near as front heavy as it is in FR or FF cars, so even when braking the tiires aren't loaded as hard as they are in many FF cars, leading to rather low wear on the front axle.
Got an alignment to factory spec after doing the shocks, the car has rather low negative camber and next to no toe on the front and rear axle.
I'm running 280TW tires, wich means they last about half as long as regular economy tires with their 500-600TW ratings.

But I'll measure the exact tread depth later to seeexactly how much I've worn them down.

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