Rear tires, Is bigger slower?

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07-20-2010, 03:47 PM

#21

Z1 Performance

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Quote:

Originally Posted by J. Dub

Wait.... What?

I thought our speedo automatically calculates changes in tire size to show the correct speed we're going basically no matter what size tire we have.

Correct me if I'm wrong please.

Cause if I run a 295/35/19 rear tire and I am going the same speed as John Smith on the highway whom has stock tire sizes we will both show the same speed on our speedo... Correct?

your speedometer has no idea what size tire you're running- so no, it does not correct for anything.

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07-20-2010, 03:50 PM

#22

J. Dub

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Quote:

Originally Posted by Z1 Performance

your speedometer has no idea what size tire you're running- so no, it does not correct for anything.

So how do we get it to show the correct speed? Do you all change the speedo gear teeth count?

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07-20-2010, 04:05 PM

#23

Done Deal DR

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Quote:

Originally Posted by J. Dub

So how do we get it to show the correct speed? Do you all change the speedo gear teeth count?

I have not heard of anyway to correct this, at least with a reasonable cost.

You live with it, though of course I'd recommend the proper tire sizes if its an option.

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07-20-2010, 05:18 PM

#24

terrasmak

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Quote:

Originally Posted by youngh

lol I knew I kind of felt weird when I went from 245/45/18s to 245/40/18s.. same for fronts i also went 5mm smaller height and felt like I accelerated faster..

5mm? Thats not 5mm, that a full inch difference.

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07-20-2010, 05:39 PM

#25

youngh

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Quote:

Originally Posted by terrasmak

5mm? Thats not 5mm, that a full inch difference.

Inches sorry

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07-20-2010, 05:43 PM

#26

terrasmak

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Quote:

Originally Posted by youngh

Inches sorry

Do you know what aspect ratio is? Do you know how to apply it? Your tire is not 245mm x 45mm.

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07-20-2010, 05:55 PM

#27

youngh

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hmm, didnt know aspect ratio was the 2nd number, always thought it was a measurement hahaha

Last edited by youngh; 07-20-2010 at 06:30 PM.

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07-20-2010, 07:45 PM

#28

T_K

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Quote:

Originally Posted by youngh

hmm, didnt know aspect ratio was the 2nd number, always thought it was a measurement hahaha

Aspect ratio is a percentage applied to the width of the tire.

245/45 vs 255/45

The 2nd tire is taller since the same percentage off 255 is larger than off a 245.

245/45 vs 275/40

Smaller percentage on the 2nd tire, but it's much wider. Going off the top of my head, these 2 have very similar sidewall heights.

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07-20-2010, 07:54 PM

#29

J. Dub

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Quote:

Originally Posted by J. Dub

So how do we get it to show the correct speed? Do you all change the speedo gear teeth count?

Quote:

Originally Posted by Done Deal DR

I have not heard of anyway to correct this, at least with a reasonable cost.

You live with it, though of course I'd recommend the proper tire sizes if its an option.

Uh... So everyone I know running around on the boards with slightly larger diameter then stock tire sizes has their speedo off? And we can't correct it. That sucks.

Last edited by J. Dub; 07-21-2010 at 05:37 AM.

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07-20-2010, 11:18 PM

#30

youngh

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Quote:

Originally Posted by T_K

yeah did some research and found that out today

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07-26-2010, 11:41 AM

#31

Done Deal DR

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Quote:

Originally Posted by J. Dub

Uh... So everyone I know running around on the boards with slightly larger diameter then stock tire sizes has their speedo off? And we can't correct it. That sucks.

Yes, that's precisely correct.

As long as you know the difference you're fine. You can get the exact difference of your speedo @60MPH using a site like the 1010 tire calculator, or using basic math if you know the overall diameter of stock and your new tire.

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