Got Another Tire Size Question

[rico05]

Did a search, no real luck in finding relevent info. I am looking at Falkein Azeins, and I misread the available sizes. WOuld 205-50R-15 be too small of a sidewall? I will have a decent amount of suspension modifications to the car (if that matters to anyone)

[SmithSR]

205/50-15 OD is 23.07"

factory OD is either 195/60-15 (24.21")or205/60-15(24.69")

link for Falken Azenis available sizes....http://www.falkentire.com/html...s.htm

Is it too short a sidewall? That's up to you. It's do-able, but not "ideal" for keeping OEM axle ratio, speedometer and odometer readings...

I say go for it, and enjoy the sticky tire. Falken is supposed to be broadening it's sizes in that model anyways...

[rico05]

how much will the speedo be off?

[krazy skwerel]

check the guide posted on his forum got all the info you need.http://gs.tolan-hoechst.com/tirecalc.htm just plug in all your info and it does the rest for you.

[rico05]

Link no workie

[SmithSR]

Rico, I cannot recall the exact % variations, when you deviate from OEM tire diameters...suffice to say, the difference is noticeable but not overwhelming. I do remember seeing an equation, or some very simple test to gauge actual speed vs indicated speed. (other than a radar to clock you) I'll look this up and post it soon as I locate it.

[SmithSR]

PS: and I don't mean, drive next to your buddy and see what his speedo reads... believe it or not, there is a formula...

[rico05]

Thank you for your help! My mom is super cool and said she might actually buy my tires for me, so I need to figure out what brand/size I want so that she can get them.

[SmithSR]

Speedometer Error Formula

original tire revs per mile / new tire revs per mile X indicated speed = actual speed

To find our answer, we need to first find out tire Overall Diameter(OD), then find "tire revolutions per mile"

original tire is 205/60-15(OD 24.69")new tire is 205/50-15(OD 23.07")

Finding revs per mile is easy: 20,800 / overall tire diameter = tire revolutions per mile

...so..

revs per mile for 205/60-15 is 842.4205/50-15 is 901.6

.. now assume you're cruising at an indicated speed of 60mph, and put those revolutions per mile into the original formula...

842.4 / 901.6 X 60(this is your indicated speed) = 56.06 actual mph.

842.4 / 901.6 X 70 = 65.4actual mph

All the work is done for you now, just plug in whatever tire sizes you choose, and find your actual vs. indicated speed.

A given tire's overall diameter can be found on most all manufacturer websites...

To my knowledge, the above formula is correct, but it's getting late....

Remember there is a percentage of error in speedometers, and in measuring tire OD, so this is not absolute spot on exact to a decimal perfect, but it's close, and it's an excellent tool to clue you in to what's going on with the car, when you alter from OE sizes.

PHIL:)

[rico05]

Ok, Last and final question on this subject: Anyone think 50 series tires on 15s will look tiny and dumb?

[rico05]

Bump to the Izzo

[SmithSR]

the 50-series will not look tiny and dumb, just smaller. It only really matters how it looks to you. Have a local shop mount one up and install it on the car so you can see how it looks.

[rico05]

Yeah...it's only 10mm so no biggie. And with the silly drop that I can get with my super secret final suspension setup I have planned (for this week) the wheel gap will not be a big problem.

[krazy skwerel]

I had no problem with the link. It is a really helpful calculator.

[rico05]

Well, when I first tried it a few days ago it didn't work, but now it does. You linking to it may have given a lot more traffic to the site and took it down for a little while.