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

[CapriRacer]

Originally Posted by arcosine

Are the low RR tires using steel or kevlar belts or does it matter?

Pretty much everyone uses steel in the belts. There may be a few tires out there with Kevlar belts - but the operative word would be "few".

LRR is pretty much all about tread compound and the amount of tread compound used.

[roflwaffle]

Originally Posted by CapriRacer

You are right. It would be nice if someone would duplicate the study in another brand/model. That would verify the effect.

But there are laws of physics involved here, and even though I have reservations about the exact tires that were selected to be tested, I do not think there was any attempt to by-pass those laws. In other words, I think the effect demonstrated is real and reproducible. Until such time as we have additional data that contradicts the Smithers report, I don't think there is any reason to doubt the validity of the effect for every tire.

-- An Insider's Insight --

Since the study was presented to a government entity in public view, if there were any dissenting opinions, they could have been expressed at subsequent meetings. To date, there haven't been.

Further, tire manufacturers would have access to a lot of data. They may not have enough to data to confirm the results, but at the very least they would have data to contradict the results. They would not be afraid to publish the results if there was some advantage to do so - and so far they haven't.

There are 2 possibilities:

1) That the effect demonstrated is real
- OR -
2) That the results would have some positive affect on selling tires

I also know that NHTSA has been very active in testing tires for RR. If there was any reason to doubt the data, they would have published their data. In conversations with one of their test engineers, he acts like the effect is accurately described, but disagrees with the tire industry's position about what regulations should be put in place as a result. (THAT is a whole 'nother discussion)

So not only do I think the effect is as described, others must think so as well - and some of those are sure to have access to data that would contradict.

Someone would need more than just another brand/model. Many brands/models for many years would be needed. Even then, no where in the paper is the relationship bigger = better mentioned, you were the only one who mentioned it.

In the end the author states...

The lack of quality linear correlations between rolling resistances and the basic parameters investigated suggested that if the researcher is investigating manufacturer/tire design differences within a tire size, other more complex aspects of the tire will need to be considered.

So what they are stating is entirely reasonable given the data, and there were no objections because of that. You were the one who stated bigger = better, and that is where the debate is.

Originally Posted by CapriRacer

Doesn't this depend on what your definition of "bigger" is?

If 16" tires are larger than 15", then there is a problem - there are only 2 16" data points: 215/60R16 and 225/60R16. To be consistent, then these should be compared to 215/60R15 and 225/60R15 - but that data doesn't exist!

By contrast, the 15" data has 8 data points - ranging in size from 195/65R15 to 235/75R15. There are a number of ways to look at "bigger", but every way I know about would say a 235/75R15 is "bigger" than a 225/60R16 (with the exception of rim diameter).

That's why I did a regression analysis. That would factor out the effects the other parameters would have on the data and allow one to look purely at the effect one parameter has.

And the regression analysis says that going up in width has a positive affect, going up in aspect ratio has a positive effect, and going up in rim diameter has a positive effect. By any stretch of the imagination, all 3 of these results in "bigger".

I gotcha! I didn't bother to check the outside radius, so that's my bad.

In terms of a regression analysis, that's not exactly kosher. One of the assumptions of a regression analysis is that...

Originally Posted by Wikipedia

The sample is representative of the population for the inference prediction

So w/o data for larger sizes you still can't reasonably state that bigger = better even for goodyear integritys, and certainly not for tires in general.

[Ryland]

As I understand it the reason for a wider tire offering less rolling resistance would be that the weight is spread out over a wider area the contact area is shorter, or more so the flat spot made in the tire by it pressing on the road is smaller.
Now most cars that call for 155mm wide tires are pretty light in weight (less then 2,000 pounds) so you have about 400-600 pounds resting on each tire, the point then would be to figure out how wide you could go before you no longer see a return on reduced rolling resistance, right? and for say a 1,800 pound geo metro that for years were sold with 145mm wide tires it seems like 155mm wide tires are going to be about the right size if you can find them in LRR and that seems to be the original topic.
Am I mistaken that the idea is to keep the flat foot print of the tire as short as possible?

[Roman]

What i would like to know wil a smaller rim make effect.

For example i now have 185/60R14. I need to replace my tyres, so i will look voor some smaller like 155 and maybe even LRR type (when not much more expensife).

The problem i have now is that my tachometer (or how do you call that thing) give's to much. Like 10% to high. When i drove 100 km there will be 110 on my dayteller. So i need 10% less measure. (correct me if im wrong)

I found a site to calculate it (it's a dutch site) TECHNIEK - BANDENMAAT / TELLERAFWIJKING

So when i go from 185/60R14 to 155/60R13 than it should be ok.

But i could also use 155/50R14.

But which one would better for FE? Lets assume it's the same brand tyre and same type/brand rim.

But the measure wil increase from 71,5 inch to 63,8 inch. So the wheel has to make more rotations for the same distance. When i traveling whit the same speed as used to is it that the engine runs on more RPM (making also more noise) or not? When it makes more RPM for the same speed will it use more fuel?

Good is also that the hight will increase from 57,76 cm to 51,62. That is 6,14 cm zo 3,07 cm / 1,21 inch lower car, think that this would also pritty good for FE.

[CapriRacer]

Originally Posted by roflwaffle

Someone would need more than just another brand/model. Many brands/models for many years would be needed. Even then, no where in the paper is the relationship bigger = better mentioned, you were the only one who mentioned it...........

It is true that the presentation doesn't say larger = better, and it is also true that I have drawn that conculusion, but I am not the only person to have done so.

Originally Posted by roflwaffle

.......In the end the author states...

So what they are stating is entirely reasonable given the data, and there were no objections because of that. You were the one who stated bigger = better, and that is where the debate is.......

True - and perhaps I've overstated this. However, I think it is painfully obvious that larger sized tires give better RRC values than smaller sized tires - and if that were wrong, I feel confident someone would have pointed this out, particularly considering that there are regulations being written and this would be a very important thing to get right.

Originally Posted by roflwaffle

.......In terms of a regression analysis, that's not exactly kosher. One of the assumptions of a regression analysis is that......

So w/o data for larger sizes you still can't reasonably state that bigger = better even for Goodyear Integritys, and certainly not for tires in general.

But the data IS representative. They are all the same make and model - and you don't have to have EVERY data point to draw a conclusion.

But you are right to point out that there are risks associated with extrapolating data.

Side note: The way science works is that a phenomenon is observed and reported and some conclusions are drawn from those observations - just like I did. Then the data is examined, the analysis critiqued, other studies run, etc. - all with the idea of trying to refute the conclusion. If the conclusion stands up to scrutiny, then it is accepted - until further data comes along. We are in the critique phase - and I have no problem with anyone critiquing, questioning, etc.

[CapriRacer]

Originally Posted by Ryland

As I understand it the reason for a wider tire offering less rolling resistance would be that the weight is spread out over a wider area the contact area is shorter, or more so the flat spot made in the tire by it pressing on the road is smaller.
Now most cars that call for 155mm wide tires are pretty light in weight (less then 2,000 pounds) so you have about 400-600 pounds resting on each tire, the point then would be to figure out how wide you could go before you no longer see a return on reduced rolling resistance, right? and for say a 1,800 pound geo metro that for years were sold with 145mm wide tires it seems like 155mm wide tires are going to be about the right size if you can find them in LRR and that seems to be the original topic.
Am I mistaken that the idea is to keep the flat foot print of the tire as short as possible?

I think the right way to look at this is that RR is stongly related to deflection.

In the same way that more inflation pressure improves RR, less load also improves RR. It's not a stretch to say that decresing the percentage of rated load also decreases deflection - ergo RR - so using a tire with a larger load carrying capacity, but at the same load and inflation pressure, would also decrease the RR.

And the fact that the footprint gets smaller is an artifact of reducing the deflection.

[CapriRacer]

Originally Posted by Roman

What i would like to know wil a smaller rim make effect.

For example i now have 185/60R14. I need to replace my tyres, so i will look voor some smaller like 155 and maybe even LRR type (when not much more expensife).

The problem i have now is that my tachometer (or how do you call that thing) give's to much. Like 10% to high. When i drove 100 km there will be 110 on my dayteller. So i need 10% less measure. (correct me if im wrong)

I found a site to calculate it (it's a dutch site) TECHNIEK - BANDENMAAT / TELLERAFWIJKING

So when i go from 185/60R14 to 155/60R13 than it should be ok.

But i could also use 155/50R14.

But which one would better for FE? Lets assume it's the same brand tyre and same type/brand rim.

But the measure wil increase from 71,5 inch to 63,8 inch. So the wheel has to make more rotations for the same distance. When i traveling whit the same speed as used to is it that the engine runs on more RPM (making also more noise) or not? When it makes more RPM for the same speed will it use more fuel?

Good is also that the hight will increase from 57,76 cm to 51,62. That is 6,14 cm zo 3,07 cm / 1,21 inch lower car, think that this would also pritty good for FE.

This is exactly why I did the regression - to be able to answer such questions. I am disappointed that the OP didn't calculate it for hinslef, but there is a language issue.

So here goes (relatively speaking):

185/60R14 = 0.001191 RRC

155/80R13 (I think there is a typo in the OP) = 0.01223 RRC(103%)

So that would appear to be the wrong direction.

What about a 165/80R13? 0.001202 RRC (101%)

A couple of thoughts: These are pretty small differences considering the accuracy of the regression equation (Opps! I noticed I didn't say on the web page how good the regression equation was! r squared = 66% - which honestly isn't very good - but it is what it is.)

[roflwaffle]

Originally Posted by CapriRacer

It is true that the presentation doesn't say larger = better, and it is also true that I have drawn that conculusion, but I am not the only person to have done so.

Many people thought the world was flat! It's probably true that, all things being equal, a wheel with a larger radius tire will have slightly less rolling resistance due to less bearing drag, but there's no restriction that all things be equal in tire construction, so stating bigger = better is too broad a statement to make given the data. The safest thing to say would be that the tire w/ the lowest RRC is the best one in the context of rolling resistance.

Originally Posted by CapriRacer

True - and perhaps I've overstated this. However, I think it is painfully obvious that larger sized tires give better RRC values than smaller sized tires - and if that were wrong, I feel confident someone would have pointed this out, particularly considering that there are regulations being written and this would be a very important thing to get right.

It's a bit too general. It's true that for Goodyear Integrity tires, excluding most 16 inchers and all 17 inch tires, larger sizes tend to have better RRCs, but that's way more restricted than any statement you've made.

Originally Posted by CapriRacer

But the data IS representative. They are all the same make and model - and you don't have to have EVERY data point to draw a conclusion.

But you are right to point out that there are risks associated with extrapolating data.

Side note: The way science works is that a phenomenon is observed and reported and some conclusions are drawn from those observations - just like I did. Then the data is examined, the analysis critiqued, other studies run, etc. - all with the idea of trying to refute the conclusion. If the conclusion stands up to scrutiny, then it is accepted - until further data comes along. We are in the critique phase - and I have no problem with anyone critiquing, questioning, etc.

You don't need any data to draw a conclusion!

However for a regression analysis the sample needs to be representative of the population for the inference prediction. If a lot of 16" tires and all of the 17" tires are excluded, then you can't include those larger tires in any statement made, and you would be restricted to a statement about most Goodyear Integrity tires less than 16 inches. Science works because the people that draw conclusions also test those conclusions. You drew the conclusion that bigger = better, so in order for it to be scientific you would need to test it rigorously, not just cite data on one tire brand/type that excludes some of the larger sizes. Citing the data is sufficient for a hypothesis, essentially an educated WAG, but the scientific method is more than just a hypothesis.

[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

[CapriRacer]

Originally Posted by roflwaffle

Many people thought the world was flat! ........

ROFLOL! Thanks for the chuckle.

Originally Posted by roflwaffle

.......... It's probably true that, all things being equal, a wheel with a larger radius tire will have slightly less rolling resistance due to less bearing drag...........

RR testing of tires is designed to test only the RR of the tire. In other words, the tests are designed to factor out bearing drag and other extraneous stuff.

Originally Posted by roflwaffle

............ but there's no restriction that all things be equal in tire construction, so stating bigger = better is too broad a statement to make given the data. The safest thing to say would be that the tire w/ the lowest RRC is the best one in the context of rolling resistance. ........

I'm not sure but I think you just said the best RR is obtained from the tire with the best RR. If true, that isn't really very helpful for the guy trying to figure out if changing tire size is going to have an effect.

Originally Posted by roflwaffle

........It's a bit too general. It's true that for Goodyear Integrity tires, excluding most 16 inchers and all 17 inch tires, larger sizes tend to have better RRCs, but that's way more restricted than any statement you've made........

Yes, the data does not include larger 16" and 17" - it would be nice if it did. However, this is all we have to work with. Since we don't have that data - and have no reason to believe that other tires - or tires in other sizes - behave any differently, this is the best guess we can make. Once we have more data, we can add that to the mix and see what we get. But for now - it seems to be true.

Originally Posted by roflwaffle

......However for a regression analysis the sample needs to be representative of the population for the inference prediction. If a lot of 16" tires and all of the 17" tires are excluded, then you can't include those larger tires in any statement made, and you would be restricted to a statement about most Goodyear Integrity tires less than 16 inches. Science works because the people that draw conclusions also test those conclusions. You drew the conclusion that bigger = better, so in order for it to be scientific you would need to test it rigorously, not just cite data on one tire brand/type that excludes some of the larger sizes. Citing the data is sufficient for a hypothesis, essentially an educated WAG, but the scientific method is more than just a hypothesis.

I can appreciate the skepticism, but I think you're being a bit harsh.

Let's take the example above: Roman wanted to know if changing from a 185/60R14 to a 155/80R13 was a good move. How can we answer that question? The data doesn't include a 185/60R14 in the data set.

Some would say that narrower is better - based on ???

But having the regression equation gives us a tool to at least attempt a reasonable answer. If you consider that Roman would have to buy wheels to make this changeover, then we can tell him that the differences are small and he would be further ahead - cost wise - to continue to use the 185/60R14 - and perhaps a move to a larger tire might be directionally better - larger meaning wider, higher aspect ratio - all based on real data.