I have a distinct no-troll-feeding policy.Sure. Care to share the details of that statistical analysis with us?
I have a distinct no-troll-feeding policy.Sure. Care to share the details of that statistical analysis with us?
Yeah me too. I only asked because of what you posted:I have a distinct no-troll-feeding policy.
It's only after the datapoints converge on the new nominal that you can start to trust that your new nominal is truly different than the previous one. Think in terms of T-testing/Z-testing and sample size. At some point, the sample is large enough that the error terms shrink enough that you can justify concluding the new nominal is different than the prior.
I felt so. It was about 4# per wheel and 4# per tire.8lbs on such vehicle is BIG thing. There is no doubt major contribution to higher mpg is less unsprung weight. Toyota and Honda for example always went smaller rotors on family SUV’s, minivans to bump mpg.
On Atlas for example, I switch from 255/50R20 to 235/65R18 snow tires which hardly have better rolling resistance. But gain in is 2-3mpg’s.
That was to illustrate the phenomenon of convergence that seemed less intuitive to others and warranted explication.Yeah me too. I only asked because of what you posted:
Underwhelming for the vehicle in question. In any case rolling resistance is a type of friction btwUnderwhelming according to whom?
I would have gone with 185/70/16 if such a tire existed. But it doesn't that I could find, 205 is about as narrow as you can go in 16" wheels and have some options for profile and brand and overall design.
The narrower tire was a major point of the upgrade because it's hard to find narrower tires in larger wheel sizes. They should indeed have less rolling resistance.
What they will *not* have is less friction in terms of traction, at least not to the degree people mistakenly seem to believe. The formula for static friction has no term for surface area. It's just the coefficient of friction and the amount of force acting on it. In other words, larger contact patches do not translate to more traction automatically. Rather, the increased traction largely results from the softer compounds of "performance tires." So then you go to an all season-compound on a wide tire on a large wheel and you get 1) more weight 2) stiff sidewalls that are instable over rough sections 3) worse performance in terms of fluid dynamics-- passing through air, water, and snow.
Moreover, for a given amount of contact patch surface area, a longer narrower patch is preferable to a shorter wider one for my purposes. Short and wide is preferable on track days with high corner loads on a dry traction surface. For civilian car usage on public roads in varying weather conditions, tall and narrow is a better choice. As it is for straightline drag racing and it is for many offroad scenarios as well.
Absolutely. 205 is as narrow as one can go safely on IS250.Underwhelming for the vehicle in question. In any case rolling resistance is a type of friction btw
Darn it. I was hoping to to be the first to mention this.it affects the moment of inertia
The nice thing about being the owner and an engineer is getting to decide what *I* think is appropriate.
I would have gone with 185/70/16 if such a tire existed. But it doesn't that I could find, 205 is about as narrow as you can go in 16" wheels and have some options for profile and brand and overall design.
The narrower tire was a major point of the upgrade because it's hard to find narrower tires in larger wheel sizes. They should indeed have less rolling resistance.
Yes, but that is option on your car. 185/70 should never be considered for IS250.My car runs 195/60/16. The same engine size was available with 205/55/16 but the emissions and fuel consumption were higher which was enough to push the car up into the next tax bracket so the 195's save on fuel and tax every year.
And while reducing unsprung mass really helps with ride quality, it's the reduced polar MOI that is the relevant factor for MPG with respect to weight
The problem with braking is that the braking system is designed with tire size designed for weight, suspension performance etc. 205 is still an acceptable size for that car. Anything less than that would greatly affect braking, and handling.Reduced inertia helps braking and acceleration too. There is no better place to reduce weight than the wheels as you get a double contribution from reduced overall vehicle weight and reduced inertia.
Good topic @Hohn. I'll likely look into that as well. Any way you could post the picture of the IS250 with those wheels? A side profile, and maybe one from the front or rear, just for us to get an idea on what the width and sidewalls look like on there.
It is in the sense that all energy loss of motion is “friction.” But specifically it is the friction of the rubber deflecting within itself, analogous to shear friction in a fluid.Underwhelming for the vehicle in question. In any case rolling resistance is a type of friction btw
The offset of the replacement wheels is -41mm. The OEMs were 43MM from what I can gather from online resources. So a pretty tiny increase in scrub radius, but too small for my to notice any change to dynamics.I like the pic. Looks good. wheel/tire combo reminds me of a police cruiser.
question @Hohn: did this affect your scrub radius, if so how much, and can you tell a difference at the steering wheel?
my GS almost had too much contact patch inside of the tire’s pivot point, over-compensating when say the tire pressure was too low… it had excessive pull away from the wheel that dragging. Moving the wheel/tire 5mm outboard was helpful in my case and became more neutral. It probably could have come outboard another 2-3 as an improvement. one thing is for sure, preserving oem handling requires staying within bounds. it looks like yours probably is pretty close to the oem?