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Timetrapper
11-04-2014, 01:39 AM
Hi all,

How much better performance, say on a 0 to 60 and quarter mile will the 17 inches provide vs. the 16 inches?
are they worth getting? It looks like around an extra 900 bucks.

jguerdat
11-04-2014, 08:36 AM
I haven't thought it all the way through but on the surface the 16s should be better since they're shorter, giving you ~4% better gearing for acceleration. Either tire would need you to shift to 3rd before 60. 1/4 mile might be different depending on having one final shift before the lights. Launch traction is an issue either way so using appropriate sticky tires would be mandatory.

doverosx
11-04-2014, 09:00 AM
Hi all,

How much better performance, say on a 0 to 60 and quarter mile will the 17 inches provide vs. the 16 inches?
are they worth getting? It looks like around an extra 900 bucks.

I went with the stock 16s since I could build a better 17" package on my own....having said that, I'm sticking with the 16s and just getting stickier rubber since I love the look of the hyper blacks. My original plan was to just sell the P7s and the wheels to put against a "better" 17" package.

Timetrapper
11-04-2014, 10:51 AM
why would someone get the 17s vs the 16s then? if not for a performance boost? just because they think bigger tires look cooler? could it be that simple?

skunkman
11-04-2014, 04:58 PM
For most racing situation smaller wheels are better - they are lighter and that helps you maintain speed in autocross. I have 17" wheels because I think they look better. If I were to autocross I would get a smaller wheel with sticky track tires and swap them out as needed.

Timetrapper
11-04-2014, 08:33 PM
ok so i could buy an abarth that has 16s, then when i want to replace them after they wear out, i could replace them with 17s and not have to mod the car though?

Tweak
11-04-2014, 10:21 PM
I haven't thought it all the way through but on the surface the 16s should be better since they're shorter, giving you ~4% better gearing for acceleration. Either tire would need you to shift to 3rd before 60. 1/4 mile might be different depending on having one final shift before the lights. Launch traction is an issue either way so using appropriate sticky tires would be mandatory.

Shift to 3rd before 60? I know I can easily hit 65MPH+ in 3rd w/o issue so just curious why you stated that? (I always like to learn more so thanks in advance for whatever explanation you might have).

jguerdat
11-05-2014, 08:22 AM
Shift to 3rd before 60? I know I can easily hit 65MPH+ in 3rd w/o issue so just curious why you stated that? (I always like to learn more so thanks in advance for whatever explanation you might have).

65? You must have larger than OEM tire sizes on the car or something is miscalculated. A top speed in gear calculator shows 59 MPH with the 16s and 61 for the 17s - before tire deformation (the tire loses diameter due to the weight on them flattening them out a tad) and the ability to accurately shift at redline (ignoring the possibility that shifting earlier is faster, as reported by various folks here). I've traditionally shifted before 60 to 3rd but I don't have an exact number.

doverosx
11-05-2014, 10:30 AM
ok so i could buy an abarth that has 16s, then when i want to replace them after they wear out, i could replace them with 17s and not have to mod the car though?

Yes sir!

IIRC, the 17s are only available with Pzeros so you do get a better tire out of the gate...buuut you could get better rubber for less money on 16s ;).

ophidia31
11-05-2014, 11:50 AM
So, with the cars havinig the 16's stock and 17" option, with the tires given for the 16" wheels, they are smaller in diameter than the 17". How does the vehicle make up for the difference in size on the speedo? A reflash at the dealer?

This is the question Ive had in my mind when i was looking at new wheels and the tires that would be going on them. I settled on 16's with a 205/45 to be close to the 17" diameter so theyd be the same between my winter and summer setup next year.

skunkman
11-05-2014, 01:55 PM
So, with the cars havinig the 16's stock and 17" option, with the tires given for the 16" wheels, they are smaller in diameter than the 17". How does the vehicle make up for the difference in size on the speedo? A reflash at the dealer?

This is the question Ive had in my mind when i was looking at new wheels and the tires that would be going on them. I settled on 16's with a 205/45 to be close to the 17" diameter so theyd be the same between my winter and summer setup next year.

You are very close compared to the 205/40 R 17 - my guess is within 5% at the speedo.

jguerdat
11-05-2014, 02:19 PM
It's simple math - divide the smaller diameter by the bigger. I get just over 2% error using the published diameters of 23.8 inches for the 205/40-17 vs 23.3 for 205/45-16.

And to follow up on my earlier comment to Tweak about speeds in 2nd, I just used the GPS to calibrate my speedometer using nearly new OEM 16 inch wheels and tires. I saw 58 MPH on the GPS while the digital readout said 60. I also hit the rev limiter at an indicated 59 MPH so true speed would have been more like 57 MPH. I don't understand 65 without taller tires or higher redline.

MemoryFoam
11-05-2014, 04:27 PM
It's simple math - divide the smaller diameter by the bigger. I get just over 2% error using the published diameters of 23.8 inches for the 205/40-17 vs 23.3 for 205/45-16.

And to follow up on my earlier comment to Tweak about speeds in 2nd, I just used the GPS to calibrate my speedometer using nearly new OEM 16 inch wheels and tires. I saw 58 MPH on the GPS while the digital readout said 60. I also hit the rev limiter at an indicated 59 MPH so true speed would have been more like 57 MPH. I don't understand 65 without taller tires or higher redline.

Actually, I think it's more accurate to use the published revolutions/mile figures instead of diameters. (tirerack.com has those figures for the tires it sells.)

In my case, switching from the original Pirelli 205/40R17 (886 r/mi.) to Michelin 205/45R17 (858 r/mi.) resulted in an error factor of 3.3%.

jguerdat
11-05-2014, 04:47 PM
I'd have to strongly agree with you. The diameter isn't as precise. Good call!

Tweak
11-06-2014, 12:52 AM
65? You must have larger than OEM tire sizes on the car or something is miscalculated. A top speed in gear calculator shows 59 MPH with the 16s and 61 for the 17s - before tire deformation (the tire loses diameter due to the weight on them flattening them out a tad) and the ability to accurately shift at redline (ignoring the possibility that shifting earlier is faster, as reported by various folks here). I've traditionally shifted before 60 to 3rd but I don't have an exact number.


It's simple math - divide the smaller diameter by the bigger. I get just over 2% error using the published diameters of 23.8 inches for the 205/40-17 vs 23.3 for 205/45-16.

And to follow up on my earlier comment to Tweak about speeds in 2nd, I just used the GPS to calibrate my speedometer using nearly new OEM 16 inch wheels and tires. I saw 58 MPH on the GPS while the digital readout said 60. I also hit the rev limiter at an indicated 59 MPH so true speed would have been more like 57 MPH. I don't understand 65 without taller tires or higher redline.

Stock 17in or the same sized replacement 17in tires by another manufacturer and same results. Car is modded and reaches higher speeds in every gear than in stock form. I should someday do some acceleration videos or something I guess. For the record there is a MAX of 1MPH variance between the Analog, digital and GPS in my car fortunately.