20 In Tires on 370Z
 

I have a few questions:

1. Going from 19 in to 20 in tires, wouldn't it make the car accelerate less fast since the radius of the 20 in is bigger?

2. What is going to be the % error of the speedometer with the increased radius?

Thanks for the help,

for the same wheel design/mfg/materials, 20's are going to be heavier and therfore hurt accelleration, but its not something to lose sleep over. Its more of a factor for a race car than a hobby car.

Yes regardless of the weight unless your talking about 40 lb wheels, it will slow the car a bit, but you will never notice honestly going from the sizes your saying. I think the speedo will probably be off about 5 mph from what I have seen before.

Thanks for the reply. The speedo will be about 5MPH too fast or slower?

What I did, Is looked up the Number of turns per mile that our wheels are spec'd at. This can be found on the tire-rack website. So with the sport package the number of turns front/rear per mile is 777/785 for the bridgestone tires (this varies on tire size and make).

Next you take the tires you want to replace it with and the size/make. Look up the specs on turns per mile.

For example: my replacement Pole Position Bridgestones at 255/30/20 is 772 revs per mile and 305/25/20 801 revs per mile.

So my new 772 will read "slower" and my new 801 will read "faster" on the speedo. Some say keep it less than 3% difference. Now you take the ratio and multiple the percentage. So, my fronts are 0.6% slower and my rears are 2.03% faster. (Revs/turns per mile is found on the tire-rack website under specs after you look up your tire make/model/size)

Example: If you are calculating 2.6% faster and your speedo is reading 60mph. You are actually doing 58.5 mph!

This website will give you an idea BUT you have to look up the tire specs (revs per mile) for each brand and make. It Is different!

Tire size calculator


If I said something wrong....sorry! and hopefully someone will correct me :)

1. Acceleration will vary if you change the overall wheel/tire combination diameter or if you change to a lighter or heavier wheel/tire combination. If you change your setup to a lighter 20" wheel for example, the rotational mass will be less. It will vary depending on the tires and wheels you choose.

2. The change in speedometer reading will be based on what size tires you end up putting on. 275/40R18 for example, has roughly the same diameter as 275/30R20 (with less then 1% difference).

Thank you all for your the detail and information it was very helpful.

What is considered one of the best tires out there? It seems that the Bridgestones that comes with the car are mediocre according to some reviews.

you're gonna get a lot of opnions on tires. From what i'm seeing, if you are talking about summer tires:

Hankook Ventus V12 EVO - Good all around street tire, fairly inexpensive, supposedly really good tread life, not great for the track.

Bridgestone RE-11 - Great for the track, expensive, really good handling, not the best treadlife.

Thers a lot of others, but thats juts two ends of the spectrum. if you just want a solid tire that wont break the bank, but isn't necessarily the BEST performing, i'd go with the hankook. IF you want mostly performance, and you dont' care about money or treadlife, go with the RE-11

RE-11 for the win!

http://www.the370z.com/wheels-tires/...ew-inside.html

The RE-11 seems like a great tire but that's basically $1200.00 every time you change tires. OUCH!!!!!