Bigger wheel = Higher speeds?

[damir831]

Ok, I don't know if anyone's every brought this up before. Switching from 13s to 17s makes the car go 70 when it's really showing 60. Does that mean that you can trick the speed governor (sp?)??? If I did go 120 with 17 instead of 13, would I really be going 140?

[90CRXZCSi]

yes you will see a change in speed switching from 13's to 17's. It might show you are going 120, and you might really be doing 140 but im not sure exatly how that works..

[damir831]

So if i really wanna go high speeds, should i just leave the 17s on, and go 5 to 10 below what the speedometer tells me? Where can i get the speedometer adjusted to the right wheel size? Can I do it myself? How much does it cost? I don't have the 17s on yet, I just wanna know what to do once I do put them on.

[esp]

are u sure about the speed changing that much because if u switch from 14's to 17's the speed doesnt change.



edit: i just looked it up and if u are traveling 60 mph with 17's your car is only gonna show 56.5 mph. so there is your answer

[damir831]

Well, this is on a miata website, but I'm sure they're all the same.

http://www.miata.net/garage/tirecalc.html

I have the stock 13s right now, and I wanna switch to 17's. It says if the speedometer says you're going 60, you're really going 71.4 because of the bigger circumfierence per turn on the 17s.

Do I just go to a mechanic to adjust the speedometer to normal or can I do it myself?

Thanx

[esp]

i am assuming u have a civic right? what year and model?

[Marc-OS]

You got this all wrong, the speedo will only change +/- 1 or 2 MPH as long as you keep the same overall diameter as the stock tire. For instance, I switched to 16" wheels on 205/40/16's and according to the site, it's says when I'm going 59.3 mph my speedo will read 60. Since I kept the same overall diameter nothing was really changed.

[damir831]

Well, the diameter will change no matter what. Just the 17s are as big as the whole rim and tire on the civic, now add the tire on top of that and the diameter will change. There's a big difference between an inch or 2. If you're talking 15's then yes, you can get low profiles and it will end up being the same as stock, but just the rims themselves are as big as the whole rim and tire on my stock.

I have a 95 DX coupe. I'm kind of new at this, what kind of tires should i use for 17s?

[esp]

u should get 205/40/17 tires for 17 inch rims, and i checked again your speedometer will show 57.9 when going 60 mph in your car

[damir831]

Hmmm where did you get those numbers?? I know that the car will probably have a slower launch, but it doesn't make sense that the car's speedometer would show a higher speed than it is with a bigger diameter. Think about it this way - mark a point on a 13 inch rim with a tire on it and roll it once til u get back to the point that u marked, just one time around, see how far it will go. Do the same thing with a 17 and the 17 will go further because of the bigger circumfierence. That means that for each turn, the 17 will go further. Now let's say the 13 one goes 2 feet per turn, and the 17 one goes more, so let's say 2.5 feet per turn. I'm just making those numbers up. For every 10 turns, the 17 would go 25 feet, and the 13 would go 20 feet.

When the new tire turns, the computer doesn't know that I have a bigger tire now, so it still thinks that a turn is 2 feet, when it's really going 2.5 feet per turn.

Now back to my original question, since the computer thinks that I have 13 inch rims, I won't be able to go past 120 on the speedometer. If I have a bigger tire, I will be going more per turn, so if I use the numbers from the top, the 17 one goes .5 feet more per turn which is about 20 percent faster. Again, I'm just making these numbers up. The computer thinks that I'm going 120, when I really have a bigger tire and it goes more per turn, about 20 percent faster in that case.

Isn't this one of the many reason they use bigger tires for drag racing? One turn on a 13 and one turn on a 26, the 26 would go twice the distance per turn.

I'm not talking about the launch, I know it will be harder to turn bigger tires if the car is not in motion.

Did you check out the link that I posted? It says that switching from 13's to 17's will make the car go 10 miles faster than the speedometer is showing at 60 mph.

[esp]

u got the numbers from whalentire.com


u seem to not realize that u have a 13 inch rims with big tires, and when u get 17 inch rims the tire size goes down, i.e. low profile tires.

[damir831]

The link that I posted, u can pick whatever tire u wanna have on whatever rimsize. You would be right if if the rims and tires would all be the same, meaning 14 in rim plus 2 in tire, or 13 in rim plus 3 in tire, then yes, of course they will go the same distance per turn, but like I said before, just the 17 inch rim has the diameter of both, the rim and tire of a 13. No matter what I do, the 17s will go further per turn.

[esp]

Originally Posted by damir831

Did you check out the link that I posted? It says that switching from 13's to 17's will make the car go 10 miles faster than the speedometer is showing at 60 mph.

i doubt that this is true, most likely not possible, think about it, if i put 20 inch rims with the wrong size tires, and i throw my speedo off do u really think that i might magically somehow be able to go 170 in a stock civic???????

[matkg]

Anytime you change the diameter of your tires, you change the car's rollout. Meaning, for every turn of the wheel, your car covers more or less ground. You're probably cheating your odometer (a bit), but it still doesn't change the speed your going under a cop's radar gun.

Same principle applies to a kid and his dad walking. Same angle of motion but since the dad's taller, more distance is covered.

[damir831]

Originally Posted by matkg

Anytime you change the diameter of your tires, you change the car's rollout. Meaning, for every turn of the wheel, your car covers more or less ground. You're probably cheating your odometer (a bit), but it still doesn't change the speed your going under a cop's radar gun.

Same principle applies to a kid and his dad walking. Same angle of motion but since the dad's taller, more distance is covered.

Exactly what I was saying, the speed will increase even though the speedometer doesn't show it. By the time you reach 120, you will be going a lot faster because the tire covers more ground per turn, than it would with a smaller wheel.