Stock tires give good fuel economy

[Erci]

Originally Posted by reeves

Any fuel economy I lost switching to AS/3's were negligible and more than compensated by the confidence I feel going around curves, braking, and accelerating.. all of which are amplified when it's raining.

Agree 100%. Worth it for the minor $ hit.

[sluflyer06]

Originally Posted by reeves

Any fuel economy I lost switching to AS/3's were negligible and more than compensated by the confidence I feel going around curves, braking, and accelerating.. all of which are amplified when it's raining.

how's the sidewall stiffness compared to the primacy? I've only had my car for about a month now but will have to get some all seasons for winter. Been dreading the soft sidewalls of all seasons

[Erci]

Originally Posted by sluflyer06

how's the sidewall stiffness compared to the primacy? I've only had my car for about a month now but will have to get some all seasons for winter. Been dreading the soft sidewalls of all seasons

Typically, any non-LRR tire will have SOFTER sidewalls. One way to achive LRR is to use stiffer sidewalls, which equates to less deformation as the tire rolls, which in return equates to less resistance. This also equates to harsher ride.

Newer LRR tires have gotten better.. they're using different compounds to not have to go too crazy with overly stiff sidewalls. I don't know how Prius tires compare to other LRR rubber, but I'm pretty sure any high performance non-LRR will have softer sidewalls.

[ZionsWrath]

Yea I got like 31 mpg driving ~70, AC on full trunk of gear for track event.

It is one of the main reasons I bought this car. Decent fuel economy, fold flat rear seat, coupe, RWD, good handling.

Now to see how it handles also carry a set of wheels/tires when I buy a track dedicated set soon.

[reeves]

Originally Posted by sluflyer06

how's the sidewall stiffness compared to the primacy? I've only had my car for about a month now but will have to get some all seasons for winter. Been dreading the soft sidewalls of all seasons

It's stiffer than stock, but still not as stiff as other summer tires. I don't race or track, but it definitely inspires more confidence than the stock tires, and I plan to keep them on throughout winter too to see how they perform.

[Iand518]

Originally Posted by reeves

Any fuel economy I lost switching to AS/3's were negligible and more than compensated by the confidence I feel going around curves, braking, and accelerating.. all of which are amplified when it's raining.

I noticed no fuel economy change. AS/3s best all-season tire I've ever put on a car. Wet traction is stupid good.


Sent from my iPhone using Tapatalk

[sluflyer06]

Originally Posted by reeves

It's stiffer than stock, but still not as stiff as other summer tires. I don't race or track, but it definitely inspires more confidence than the stock tires, and I plan to keep them on throughout winter too to see how they perform.

on my 135i I ran DWS which were pretty good in the snow but the sidewalls killed the front end feel, swapped out for Bridgestone RE970AS and steering was much better, would like to somehow not have to endure 4+ months of poor front end feel if I can.

[ZDan]

Originally Posted by Philly758

Rolling resistance aside, wider tires also have more surface area which creates more wind resistance and a decrease in fuel economy.

Wider tires don't add much to frontal area or drag coefficient. Going from 215 to 245 is a 30mm increase in width, 1.18", .1'. Assuming a general 6" ground clearance, 0.5', you're adding 2x 0.1' x 0.5' or 0.1 ft^2 to the car's ~20 ft^2 frontal area. Half a percent. Cd might also go up, but I seriously doubt by more than 0.005, or ~1.5%. Pessimistically, going from 215/45-17 to 245/40-17s might mean the difference between getting 31mpg and 30.5mpg on the highway, all else equal.

I ran the numbers when I was buying street wheels/tires for the FD. I was seriously considering getting skinny 7"/8" wheels and 205/225 tires to maximize my Texas Mile run. But the numbers just weren't in it. I went with 245/275 on 8.5/9.5" so they could make decent backup track wheels/tires. Spreadsheet that predicted my mph within 1mph suggests the wider wheels and tires might have cost me 0.5mph max.

Actually looking at the frontal area of a 245/40-17 vs. a 215/45-17 tire shows just how little frontal area you're adding:
http://willtheyfit.com/index.php?wid...et2=40#content

[wparsons]

I noticed VERY little change in mileage going from stock tires to 225/45 Dunlop ZII's under the same driving conditions, AND that includes them being slightly taller than stock. As a bonus, since lowering it 1" and adding more negative camber I've actually gotten better mileage

[Ubersuber]

Originally Posted by wparsons

I noticed VERY little change in mileage going from stock tires to 225/45 Dunlop ZII's under the same driving conditions, AND that includes them being slightly taller than stock. As a bonus, since lowering it 1" and adding more negative camber I've actually gotten better mileage

Noticed or measured?

Lowering the car and adding negative camber won't improve mileage.

[wparsons]

Measured. I track every single tank with an app on my phone, and the differences are outside the typical variance tank to tank.

More negative camber slightly decreases tire contact patch at rest, so if running a wider tire can decrease mileage I don't see how more negative camber couldn't increase it.

[Ubersuber]

Tire contact patch size is independent of camber, for practical purposes.

Tire contact patch shape may change but the area remains constant for a given tire, tire pressure and vehicle weight. The tire deforms by a fixed amount for any given tire construction, tire pressure and weight.

Anyway, you measured your fuel economy and it was "the same" or nearly so. This casts doubt on the claim by Michelin that their Primacy is LRR. Or, your maths may be bogus. I let my dash display do the maths and it was significantly different with the Primacy and with the new Pilots. The difference was around 10% which translated would be in the 7-8% range worse for the Pilots.

[wparsons]

IMO the contact patch will change size, only slightly, from camber simply because of how the sidewalls come into play.

The dash showed the same, but the dash is less accurate than tracking based on km's driven and fuel taken to fill up.