155/80-13 tires (looking for LRR options)

[roflwaffle]

I didn't know about RR testing accounting for bearing drag, do you have a link to the equipment/procedure behind this? While you don't have any more data, and you have no reason to believe that other tires behave any differently, you also have no reason to believe that other tires don't behave any differently. For one, your sample data set is way too small to draw conclusions about a larger population, and two, even with the small set that you used to validate your assumption, the author of the data you're using came to a different conclusion, that simple physical characteristics are not enough to predict the RRC. You just don't have enough data to make any definitive statements about how tires in general behave. You can assume they behave in a certain way, but that's not scientific. It would be like assuming that everywhere in the world is above 100F in the summer, going to death valley for your first data point, then assuming that everyplace else is like death valley in the summer. Not that you're wrong about your assumption per say, you could be right, just that you don't know, and saying bigger = better as a quantitative statement is wrong in the sense that you can't know that w/o a lot more data. It's fine as an assumption, but presenting it as anything other than that is not scientific. I'm not saying this to be harsh, just to illustrate the difference between what someone can reasonably assume and what they can't reasonably assume in the scientific sense.

[Roman]

Originally Posted by arcosine

According to this site 165/60HR14 is the stock tire size for a 83 Golf. 155/50R14 tires would decrease your mileage.

1983 Volkswagen Golf GTi car technical specifications from Carfolio.com - 3 door 1.8 litre (1781 cc) Inline 4 111.5 PS, 5 speed manual

That's for the GTI. I have a Golf Diesel, that one had 145/80R13 as default. At least that is what i have found. The prevorius owner has replaced them by 185/60R14. I think he did this because of the replacing of the engine. Default is 1.6 liter and i have a 1.9 Turbo Diesel.

I'll try to get some 13inch rim from the scrapyard for testing.

[CapriRacer]

Originally Posted by roflwaffle

I didn't know about RR testing accounting for bearing drag, do you have a link to the equipment/procedure behind this?........

I don't have a specific link - and I know there are different techniques. I would suggest you look up the SAE procedures. I'm reasonably sure those procedures outline factoring out the bearing loss. Just be aware that they may not specifically delineate what part of the procedure is correction factors and which parts are actual testing.

Originally Posted by roflwaffle

......While you don't have any more data, and you have no reason to believe that other tires behave any differently, you also have no reason to believe that other tires don't behave any differently.......

Actually I do. The important factors in rolling resistance are deflection, the amount of material being deflected, and the properties of the material being deflected.

The load tables are based on the same amount of deflection, so regardless of the tire size, I have a pretty good handle on the deflection.

When it comes to the 2 materials questions - amount and properties - there wouldn't be any fundamental differences that would depend on size. While it is true that as the tire size increases the amount of ply cord increases, those increases also occur within the data range. Plus, there is nothing peculiar that happens in the design of a tire that would distinguish one tire from another that would cause a break in the logic.

The only one that comes to mind is the change from a single ply to a 2 ply - and that change is also included within the data range.

In the end, it becomes extremely important to use the same make and model to assure that the construction is consistent with the tires selected for testing. That is probably where the data set is the weakest. I know there are OE tires in that mix - and I think that accounts for low r[sup]2[/sup] value.

Originally Posted by roflwaffle

.......... For one, your sample data set is way too small to draw conclusions about a larger population............

I disagree

Originally Posted by roflwaffle

.......... and two, even with the small set that you used to validate your assumption, the author of the data you're using came to a different conclusion, that simple physical characteristics are not enough to predict the RRC..........

Actually the author didn't highlight ANY conclusions regarding the affect tire size has on RR - and that makes sense given the context. He was contracted by the CEC to get data to help write regulations. As I explained before the tid bit we are discussing was not important for writing regulations. What was important was that there was a difference - and that would complicate writing a regulation.

Originally Posted by roflwaffle

.............You just don't have enough data to make any definitive statements about how tires in general behave........

Again, I disagree

Originally Posted by roflwaffle

..........You can assume they behave in a certain way, but that's not scientific.........It's fine as an assumption, but presenting it as anything other than that is not scientific. I'm not saying this to be harsh, just to illustrate the difference between what someone can reasonably assume and what they can't reasonably assume in the scientific sense.

We have traversed this territory before. I understand your reservations about drawing conclusions on a limited amount of data. I have pointed this out in other situations where I have been on your side of the fence, so I appreciate your sentiment.

Perhaps the best way to say this is: Based on the Smithers data, Bigger is Better.

And unless there are new thoughts, I'm going to discontinue commenting on this as we seem to rehashing the same points.

[arcosine]

I wouldn't worry about bearing drag... its infinitesimal. The main concern would be pumping losses and engine/drive friction.


Roman, what RPM is the engine when at 100 kph?

[Ryland]

Originally Posted by Roman

That's for the GTI. I have a Golf Diesel, that one had 145/80R13 as default. At least that is what i have found. The prevorius owner has replaced them by 185/60R14. I think he did this because of the replacing of the engine. Default is 1.6 liter and i have a 1.9 Turbo Diesel.

I'll try to get some 13inch rim from the scrapyard for testing.

If you have the GTI alloy wheels I know that the GTI wheels in the USA are really heavy, they might be hard to find but VW made some 13" alloy wheels, otherwise the stock steel 13" wheels are even lighter then the GTI alloy wheels.
145R13 were stock for alot of the early Diesel VW's 155/80R13 were common as well, but you will notice in this thread that no one seems to make a low rolling resistance tire in the 155/80R13 size so you might have to go with 165/70R13 or 175/70R13 to find a low rolling resistance tire.

[Roman]

I don't think i wil use LRR. What is see is that it's good for 0.3 liter on 100 km(according the Michelin Energy Saver). And the smalest energy saver (165/60R14) cost about 100 euro each. A normal tyre 155/60R13 cost about 40 euro. So 240 euro's less. And i don't think that a 165/60R14 LLR has a better FE than a normal 155/60R13.

Lets say it saves 0.3 liter on 100km like Michelin says. Lifetime is 40.000 (also according Michelin) saving 120 liter. 240 euro diverence is 185 liter diesel. So i have to make at least 55.000 km before saving money.

Originally Posted by arcosine

I wouldn't worry about bearing drag... its infinitesimal. The main concern would be pumping losses and engine/drive friction.


Roman, what RPM is the engine when at 100 kph?

I don't know. My RPM meter is broken. Have to fix that first. But i think it's a bit high. The transference is a bit wrong. The gears are very short.

[roflwaffle]

Originally Posted by CapriRacer

I don't have a specific link - and I know there are different techniques. I would suggest you look up the SAE procedures. I'm reasonably sure those procedures outline factoring out the bearing loss. Just be aware that they may not specifically delineate what part of the procedure is correction factors and which parts are actual testing.



Actually I do. The important factors in rolling resistance are deflection, the amount of material being deflected, and the properties of the material being deflected.

The load tables are based on the same amount of deflection, so regardless of the tire size, I have a pretty good handle on the deflection.

When it comes to the 2 materials questions - amount and properties - there wouldn't be any fundamental differences that would depend on size. While it is true that as the tire size increases the amount of ply cord increases, those increases also occur within the data range. Plus, there is nothing peculiar that happens in the design of a tire that would distinguish one tire from another that would cause a break in the logic.

The only one that comes to mind is the change from a single ply to a 2 ply - and that change is also included within the data range.

In the end, it becomes extremely important to use the same make and model to assure that the construction is consistent with the tires selected for testing. That is probably where the data set is the weakest. I know there are OE tires in that mix - and I think that accounts for low r[sup]2[/sup] value.



I disagree



Actually the author didn't highlight ANY conclusions regarding the affect tire size has on RR - and that makes sense given the context. He was contracted by the CEC to get data to help write regulations. As I explained before the tid bit we are discussing was not important for writing regulations. What was important was that there was a difference - and that would complicate writing a regulation.



Again, I disagree



We have traversed this territory before. I understand your reservations about drawing conclusions on a limited amount of data. I have pointed this out in other situations where I have been on your side of the fence, so I appreciate your sentiment.

Perhaps the best way to say this is: Based on the Smithers data, Bigger is Better.

And unless there are new thoughts, I'm going to discontinue commenting on this as we seem to rehashing the same points.

Arg, the quote sniping! *No!!!!!!11!!!1!

Um, lesse, starting from the back and going forward, saying it's based on the Smithers data isn't inaccurate, but it would be better IMO to describe what the Smithers data entailed so that someone could get a good idea what exactly the data set was restricted to.

The author didn't come to any conclusions, while you did, which is different AFAIK. I mean, if I say some data set points to some trend, and someone else says the data set doesn't point to any trends, then those are differing conclusions given the same data.

You can disagree with the author about whether the data indicates anything or me about whether or not the sample size is too small to draw any conclusions about all the different tire sizes/models from different manufacturers made over different years, but in order to do so in a logical fashion you need to support your case with evidence by saying that all tires are made with so and so manufacturing process and all use a type of construction and compound where whatever values are going to be restricted such that the variation between them is not going to be large enough to throw off your assumption that larger tires = less Crr or whatever. For instance you mentioned the important factors, so provide data on the materials used indicating how that doesn't change a whole lot, how deflection is quantified, and so on. At least if you want to provide a logical/scientific statement. If you qualify your statement by saying it's your opinion then you really don't need anything else to satisfy most statements.



*It's considered kind of a pain because breaking something up into little chunks can loose context, and especially on boards that don't nest quotes because then the person responding has to go back and forth between the reply and the thread to figure out what they were quoted on as opposed to just discussing the different things in one big chunk.

[euromodder]

Originally Posted by Roman

I don't think i wil use LRR.

Lets say it saves 0.3 liter on 100km like Michelin says. Lifetime is 40.000 (also according Michelin) saving 120 liter. 240 euro diverence is 185 liter diesel. So i have to make at least 55.000 km before saving money.

I have gotten 51.000 km out of my Energy Savers already, and the front tyres should be good for at least another 15.000 km or thereabout.

On the rear axle the tyres will last a lot longer.
With 51.000 km they're only just broken in
About 1/3 of the usefull thread life is gone, so they should get 150.000km.
Or 100.000km average.

But I plan to switch the rear tyres to the front when the front tyres wear out - otherwise the rear tyres will get too old before they'll wear down.

Starting from 41.56 mpg - 5.66 L/100km, I got a 7% reduction in my fuel consumption, or almost 0,4L/100km.

I'm using 205/55/16 91H W-rated Energy Savers on a 1400 kg vehicle.

[Roman]

Originally Posted by euromodder

I have gotten 51.000 km out of my Energy Savers already, and the front tyres should be good for at least another 15.000 km or thereabout.

On the rear axle the tyres will last a lot longer.
With 51.000 km they're only just broken in
About 1/3 of the usefull thread life is gone, so they should get 150.000km.
Or 100.000km average.

But I plan to switch the rear tyres to the front when the front tyres wear out - otherwise the rear tyres will get too old before they'll wear down.

Starting from 41.56 mpg - 5.66 L/100km, I got a 7% reduction in my fuel consumption, or almost 0,4L/100km.

I'm using 205/55/16 91H W-rated Energy Savers on a 1400 kg vehicle.

That is interesting indeed. But what would be the difference between a 165/60R14 Energy saver and a normal 155/60R13? That's the question....

[Crazyrabbit]

I can't say the Ohtsu Negotiator 155/80-13 tires are LRR because I changed several variables at once, but I did just have a personal best tank at 64.6 MPG. NICE! Yeah at over 50 psi they feel like rocks, but what are you going to do?