Tire size vs lean burn, gear ratios, etc. What tire size am I after?

[phyregod]

The taller tires are being considered to lower the RPM at my planned cruising speed of 75mph and (hopefully) keep the motor in lean burn.

[elhigh]

In that case I'd consider something that was the height of the 195s but narrower than that.

Coker Tire in Chattanooga carries tall/skinny tires that give you the rolling circumference you're looking for. For instance: https://www.cokertire.com/tires/styl...wall-tire.html

That's not as tall as the 195 but taller than the stockers. NOTE: the tire specs call for a 3" wide rim! SUPER skinny. Also very useful in extremely wet conditions, ultra-skinny tires don't hydroplane much.

[Baltothewolf]

I can maintain lean burn on the highway as high as 80mph in my insight. I'm going to say this once, and I'm not going to try to argue my point past this.

You will regret not going insight rims/HX rims w/Re92's. Any tire that is 'taller' that will decrease cruising speed RPM is going to be minimum 5lbs heavier that an Re92. All MPG gains from that will be negated by increased surface contact, higher rolling resistance and increased rotational mass. The laws of physics don't allow a tire with more mass made of the same material to weigh less. That's just the way it is.

[CapriRacer]

First, your issue to going to be mostly about steady state fuel economy - parasitic drag and rolling resistance. A larger diameter tires is going to be a very worthwhile addition - and more importantly, you need to up in tire size and select a tire with good rolling resistance.

[BabyDiesel]

Check these out: 175/65R15 Toyo Versado Eco

They are 24.2" tall, which would lower your revs more than you wanted. They are light, thin and LRR though.

[GreenHornet]

Insight rims and RE92 would be a very solid choice! Yes unsprung weight is important but you will see wayyyyyyyy more bang for your buck paying attention to the body aero work since you will be commuting at 75mph. Do everything you can in this area and you should be sitting pretty good. Talk to the owner of the Aerocivic he can guide you in the right direction.

GH

[phyregod]

I'm doing way too much research. I've found the smart Fortwo's front tires are Continental contiecontact EP 145/65-15. 12 pounds tires. LRR design. The only wheels on the planet I've found that will fit them and the Crx are Toyota Yaris 15x5 steelies at 16 pounds.

That is +~6 pounds per corner vs. the insight combo. And another 2.5? Pounds per corner for spun aluminum moon discs. Total guess at the weight of the disks.

They are also only 1.5% taller. 900 revs/mile vs the stock 913.

But the kicker is, they're 20mm skinnier per corner. That is 80mm less contact patch width total vs. both stock and the insight.

Stop and go would suffer, but I would, in theory, gain mpg at cruising speed. But if +1.5% isn't big enough to keep me in lean burn, it's all for naught.

[beneuan88]

I'd be reluctant to go too extreme on tyre sizes, you still want your car to look good and be fun in the corners and havehdecent wheel well clearence don't you? 165/65 or 175/65 on a light weight stock off set 14x5 or5.5 alloy would be my choice, i rekon your gears are tall enough as is.

[CapriRacer]

With that commute, weight is hardly a factor in fuel economy. Improvements in F/E will be all about wind resistance and rolling resistance.

So you want to get the largest possible tire under the fenders - and the best way to measure that is by load carrying capacity (Load Index). Then select a tire line with very low RR (That will be difficult as there is very little published comparing different tire lines.)

You will have to be very careful in tire selection as parts of Texas use asphalt that gets extremely slippery when wet - reported to be similar to ice.

[gafhj]

Originally Posted by CapriRacer

With that commute, weight is hardly a factor in fuel economy. Improvements in F/E will be all about wind resistance and rolling resistance.

So you want to get the largest possible tire under the fenders - and the best way to measure that is by load carrying capacity (Load Index). Then select a tire line with very low RR (That will be difficult as there is very little published comparing different tire lines.)

You will have to be very careful in tire selection as parts of Texas use asphalt that gets extremely slippery when wet - reported to be similar to ice.

EU has new tire labels that mention rolling resistance, so this is a good source of information.
Example site that allows comparisons:
geizhals*eu/?cat=aumrf&xf=2984_1