3 pounds per corner heavyer, acceleration difference?

[yellowmp5]

i j/ swapped out my 18" MS6 wheels + 215/45/18 Pirelli P Nero Zero M+S with powdercoated 18" RX-8 + 235/40/18 Falken ZE912
accordin' to my research:

MS6 wheels = 23.5 lbs
215/45/18 Pirelli = 23 lbs
net total = +/-46.5 lbs

RX=8 Wheels = 22.6 lbs
235/40/18 ZE912 = 26.8 lbs
net total = +/-49.4 lbs

roughly 3lbs gained per corner...


i found accelerating is j/ a bit slugglish.....so is it j/ me, or that 3lbs/corner does make a different....
will i see a significant sign of MPG decrease? Pre-mature brake pads? etc?

[GGG]

Could have sworn that the RX-8 wheels were 2lbs lighter (per rim) - would be about the same with the wider/heavier tyres...

i j/ swapped out my 18" MS6 wheels + 215/45/18 Pirelli P Nero Zero M+S with powdercoated 18" RX-8 + 235/40/18 Falken ZE912
accordin' to my research:

MS6 wheels = 23.5 lbs
215/45/18 Pirelli = 23 lbs
net total = +/-46.5 lbs

RX=8 Wheels = 22.6 lbs
235/40/18 ZE912 = 26.8 lbs
net total = +/-49.4 lbs

roughly 3lbs gained per corner...
i found accelerating is j/ a bit slugglish.....so is it j/ me, or that 3lbs/corner does make a different....
will i see a significant sign of MPG decrease? Pre-mature brake pads? etc?[/b]

[HawaiianEagle]

i would imagine, as with any additional weight, your accel will dimish.. overall though, you kinda have to decide what you want... i mean your giving up 12 pounds but gaining 20mm of rubber per corner.. if you auto-x this might mean alot. I'm not an avid auto-x'er so I wont begin to get into how 235's are better than 215's and so on and so forth. i'll leave that for one of the experts...

you could always keep the 235's and run some forged 18x8's rims. that would give you the advantage of the 235's and some weight reduction over the stock rims...

good luck

[posttosh]

your giving up 12 pounds but gaining 20mm of rubber per corner.. if you auto-x this might mean alot.[/b]

Assuming that the tires are inflated to the same pressure, the size of the contact patch of a 235/40R18 tire is the same as the size of the contact patch of a 215/45R18 tire. The only way to increase the size of the contact patch is to decrease the pressure, but that has other effects, not all of them desirable.

[HawaiianEagle]

Assuming that the tires are inflated to the same pressure, the size of the contact patch of a 235/40R18 tire is the same as the size of the contact patch of a 215/45R18 tire. The only way to increase the size of the contact patch is to decrease the pressure, but that has other effects, not all of them desirable.[/b]

how is that possible... a 215mm wide tire having the same size contact patch as a 235mm wide tire..... so does a 195mm tire have the same contact patch as a 335mm tire? given the same air pressure of course...

[posttosh]

how is that possible... a 215mm wide tire having the same size contact patch as a 235mm wide tire..... so does a 195mm tire have the same contact patch as a 335mm tire? given the same air pressure of course...[/b]

Yes. The shape of the contact patch is different for the different width tires, but the effective area is the same size. (This assumes that there is relatively even pressure across the area of the contact patch, which is never fully achieved, but which all tire designers strive for.)

[Owen Birch]

Yes. The shape of the contact patch is different for the different width tires, but the effective area is the same size. (This assumes that there is relatively even pressure across the area of the contact patch, which is never fully achieved, but which all tire designers strive for.)[/b]

duh, what?!?

so a 215 VS a 235 has the same contact area? Oh, please do explain this one in great detail...

[posttosh]

duh, what?!?

so a 215 VS a 235 has the same contact area? Oh, please do explain this one in great detail...[/b]

I'll let Chris Longhurst, author of the Wheel and Tire Bible, do it for me. (Scroll down, or use text search, to the subsection headed: "Fat or thin? The question of contact patches and grip.")
Or, if you would rather get your information from Mazda6tech.com, see here.

[HawaiianEagle]

i've yet to read the technical babble, but before i do i'm going to write to john force and tell him to run 15x5's out back instead of the usual 15x16's... since it's the same contact patch as long as the air pressure is the same


ok i read the brain smokin techie talk and i've gathered that the contact patch is the same in widths close in size (215 vs 235) but at some point the wide and skinny patch of the wider tire will over come the narrow and fat patch of the more narrow tire... good info post...

[posttosh]

i've yet to read the technical babble, but before i do i'm going to write to john force and tell him to run 15x5's out back instead of the usual 15x16's... since it's the same contact patch as long as the air pressure is the same [/b]

Actually controlled tests of that nature (not that extreme, obviously) have been done, and the results were not what you might expect: Big wheels and tires vs. smaller wheels and tires

ok i read the brain smokin techie talk and i've gathered that the contact patch is the same in widths close in size (215 vs 235) but at some point the wide and skinny patch of the wider tire will over come the narrow and fat patch of the more narrow tire.[/b]

I don't see where you got the last part. The area where a wider tire may have a performance advantage usually relates to the behavior of the sidewall (and transition zone between the sidewall and tread) rather than in the contact patch. For the same reason that high-end phonograph stylii had (have) elliptical rather than round diamond tips where the stylus meets the groove, a wider-but-shorter contact patch has less resistance to being deflected from a straight line rotation than a narrower but longer contact patch does. That means that -- everything else being equal -- a wider tire will feel lighter and quicker through the steering wheel (at speed) than a narrower tire, but it also means that the wider tire is more subject to deflection by small road irregularities, requiring more micro steering adjustments, than a narrower tire.