LRR vs. Weight

[alexshock]

What is better for fuel economy: tire weight or LRR index?

Can those tires with bad LRR still be efficient if they are lightweight?

I'm asking this question, as I started some wheels modding.
I'm going to switch from 205x55x16 to 195x65x15 (more details here: https://ecomodder.com/forum/showthre...tml#post642248).

So average tire weight in that size aprox. 8.5-9 kg., most ecotires are 7.5 kg., but I found some Fulda EcoControl HP2 which are declared to be 6.3 kg. (I have not measured them yet, but specification is like that.)

So, total tire weight can be reduced by 2.2 kg. per corner, 8.8 kg. total!

While they are labeled as "EcoControl", EU LLR index is C-E WTF? Can that be considered as ECO?

[freebeard]

You need to get the attention of CapriRacer. ecomodder.com/forum/member-capriracer

I have no idea. Lighter tires should make more difference that lighter wheels, given the angular momentum.

[alexshock]

Originally Posted by freebeard

Lighter tires should make more difference that lighter wheels, given the angular momentum.

Yes, for sure. The farther weight from rotation center the more weight-effect.
But my concern is not between rims and tires, but more about different tires.
May light tires be more efficient than same-sized tires which are heavy but have low RR?

[Stubby79]

Unlikely, unless all you do when you drive is chronic stop and go from one set of lights to the next...the LRR would quickly outpace the benefit of lighter tires. IMO.

(Buy the lightest LRR's you can get)

[alexshock]

Originally Posted by Stubby79

... all you do when you drive is chronic stop and go from one set of lights to the next...

That is actually my case... Nearly 70% of my ride is a city traffic.

[Vekke]

Better LRR will give you better results than saving few kg even its rotating weigths.

Best way to test tires is to buy them used with the wheels. Try to find ones where you know their eu RR values. You can get sets even for 50euros or less.
Then just resell the ones which doesnt work well. In the end just put the best tires to your best wheels.

I would try 165/80R15 tires. Those I would install to 6,5" wide wheel
In most cases steel wheels with aerodynamic hubcaps is the best option.

You have the 1,8 hybrid so it can recharge batteries in braking so their weigth is even less important.

LRR helps in city and Cd helps in road. Narrow LRR wheels migth raise the max ev speed closer to 90 km/h. LRR gain also comes from higher tire pressures.

[CapriRacer]

Originally Posted by freebeard

You need to get the attention of CapriRacer. ecomodder.com/forum/member-capriracer .......

Read my webpage on the subject of fuel economy and tires: Barry's Tire Tech

and: Barry's Tire Tech

Then post back so we can discuss.

[IsaacCarlson]

LRR will do best in a highway setting. Low weight will do better in a stop and go setting. There are some cross over areas, but this is the general idea.

We got heavier tires this time and there is definitely a penalty for weight. Starting and stopping takes more power. It has gotten better as the tires have worn down, but it is still there. I do like having more rubber on the tire though, because we used to get all kinds of flats with those thin walled economy tires.

I might try a lighter tire next time, but I really like the tires we have.

As far as LRR tires, I don't like how stiff the tread area is. It's like a plastic ring and that will likely inhibit traction in off road or rough road scenarios.

[CapriRacer]

I am going to make the assumption that Alexshock (OP) hasn't read the 2 web pages I pointed out - and that's why he hasn't posted back. But I am going to continue the conversation anyway.

First, I think even in extreme cases of stop and go traffic, rolling resistance is better for fuel economy than weight - because tires are such a small portion of the weight of the vehicle.

Also, the European regulations on tire labeling have a peculiarity about them. Rolling resistance varies by tire size, but the regulations do not take that into account. That means that you can get a tire with an A rating in one size and a C rating in the same make and model, but in another size. This is one of the reasons why the US hasn't issued regulations yet.

Also, there is technology triangle involving RR, treadwear, and traction. To get good values in one area, you have to sacrifice one or both of the others. And that is where the term "LRR" comes in. It means "Better RR compared to other tires with similar wear and traction characteristics.".

I know that sounds like a contradiction, but there are ways to improve RR while minimizing the impact to wear and traction. Suffice it to say that the term "LRR" is a relative term, not an absolute - so it shouldn't be a surprise to find a tire labeled "LRR" that doesn't have a good RR value - it's just better than other similar tires.

[alexshock]

Thank you, CapriRacer!
I have read all your links. The biggest surprise for me was that wider tires are better for LRR.

I have even found a good article from EU commission (here) and a good calculator for those who are as lazy as me (https://ec.europa.eu/energy/sites/en...culator_en.xls).
In my case it predicts difference between A and C tires as 0.2 l/100km (1.7 mpg).
It even shows the difference between urban and highway (spoiler: LLR more affects highway), but in my case it is almost the same.

So, now I have doubts between Continental with "A" index and 7.8 kg weight vs. Fulda with "C" index and 6.5 kg weight.
(I don't have final decision as I still want to do experiments with lightest ever tires , In my conditions it is not only an aggressive stop-n-go, but also a lot of hills and ramps in the city.)

In the best case I will reduce 14.4kg with Fulda which is actually exactly 1% (!) of the car weight. (Not counting rim weight here.)
And only 8.3 kg with Continental difference between them should not cover FE gain from LRR...