| Wheel size... - Click HERE for Original Thread |
| ManHunter |
I was just thinking... putting bigger wheels on your car will slow down your acceleration, of course, but it will also make your top speed higher, right? I wonder what the equation is to figure out how much your top speed will be?
MH |
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| JDMBoi |
| gives u better gas milage :bigthumbup: |
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| Lll_J |
It will barely affect it.
Figuring out change in speed with new wheels,
( original diamater - new diameter ) / original diameter = percent difference
You can apply that to top speed, Bigger wheels obviously you add the percentage, smaller wheels than stock, you subtract the percentage.
Jordan |
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| TheNeonEdge |
so then if you go from stockl 15's to 20's
15-20/ 15 = -.3333333 33% loss in acceleration, and gain in top speed? Somehow I dont think so, I bet its an exponential equation.
--ThE EdGe |
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| Lll_J |
Well it seems right to me. It applys to speedo corrections. Remember its overall wheel diameter as well, that includes rubber. And this is theoretical.
I could be wrong.
Jordan |
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| Lll_J |
To elaborte, you have to take into consideration OVERALL wheel size.
First, get the size of the tire. Say it's a 225/50/16 for shits and giggles. The first number is the tread width in millimeters. The second number is the percentage of the tread width that makes up the sidewall, and the last is obviously the rim size in inches.
So take your first number and multiply it by the percentage (that's 225 * .5), take that number and multiply it by two (since there are two sidewalls, above and below the rim). Then take this and divide by 25.4 mm/in (converts it to inches). Now add in the rim size (16 in) and voila, you have an overall diameter.
So
225x0.5= 112.5
112.5x2= 225
225/25.4=8.858
8.858+16 (in this case) = 24.9" overal Diameter.
Now compare that to a 20" wheel, which you have to remember, you wont find large rubber for, your probobly going to go with somethin like a 225/35/20
So
225x.35= 78.75
78.75x2= 157.5
157.5/25.4= 6.2
6.2+20= 26.2" overal Diameter.
Now apply these to the Speed correction equation.
24.9-26.2/24.9 = 0.05x100 = about 5.2% difference.
Just to give it a more practical real life comparison. Shit my head hurts, I thought School ended a few hours ago. ;)
Jordan |
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| curtis_rak |
I got an idea!
Who not just keep the OEM aspect ratio and buy a lightweight rim. Problem solved.
Besides, having huge ass wheels and a bunked up speedo/odometer isnt all that cool.
....and....Huge rims=small penis. :P |
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| 1mns13 |
| Weight does not effect top speed, which is why larger rims create less horsepower. |
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| ChromeDragon |
| Call me crazy, but wouldn't circumference of the wheel be the issue, not diameter? :bigthumbup: |
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| curtis_rak |
| bigger diameter = bigger circumference |
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| ChromeDragon |
quote:
Originally posted by curtis_rak
bigger diameter = bigger circumference
I realize that, but it's exponential, so a straight factor equation like the one stated above would not factor in the exponent.
Chromey |
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| scooby_dooby |
the formula is:
km/h = (RPM / Gear Ratio / Final Drive) x 60 x Wheel Size in Km x Pi
so on my car:
a 14" wheel(36cm) + 195/60rubber(23.4cm) = 59.4cm
or
.000594km |
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| Inzane |
quote:
Originally posted by ChromeDragon
quote:
Originally posted by curtis_rak
bigger diameter = bigger circumference
I realize that, but it's exponential, so a straight factor equation like the one stated above would not factor in the exponent.
Chromey
Circumference = Pi x Diameter.
Therefore Circumference and Diameter are DIRECTLY proportional to each other.
If you increase your overall rolling diameter by 5%, you affect your circumference by 5%.
BTW on this general thread topic, increasing your overall rolling diameter will mean a theoretical higher top speed, gearing wise. But that doesn't mean your car has the horsepower to get there. |
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| Transporter |
what it comes down to ...you should not exceed 18" rim on sport compact cars.
it will adversely affect ride quality, performance and safety(abs, brakes)
and also the clearance of the wheels from the wheel well will be compromised by going any thing bigger than 18" on a sport compact car. |
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| SplineZ |
http://www.miata.net/garage/tirecalc.html
You can have 18" rims, and have the same outside diamter as a 205/60/15 quite easily.. its called "Plus sizing"
if you keep things in sync your outside diameter will not change.. however unsprung weight will, and larger wheels weigh more.. more power sapped spinning heavier wheels.
James Z |
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| Mekanik22 |
| If you change the size of your wheel, you have to adjust the speedometer gear on the transmission or you'll get a false reading when you look at it. This could lead to tickets that could have been prevented :) |
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| scooby_dooby |
quote:
Originally posted by Mekanik22
If you change the size of your wheel, you have to adjust the speedometer gear on the transmission or you'll get a false reading when you look at it. This could lead to tickets that could have been prevented :)
if you change your wheel size and get the incorrect size rubber ya, if you get the right rubber the overall diameter of your wheel will remain the same. |
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| Mekanik22 |
quote:
Originally posted by scooby_dooby
quote:
Originally posted by Mekanik22
If you change the size of your wheel, you have to adjust the speedometer gear on the transmission or you'll get a false reading when you look at it. This could lead to tickets that could have been prevented_ :)
if you change your wheel size and get the incorrect size rubber ya, if you get the right rubber the overall diameter of your wheel will remain the same.
I don't get it? Because your increasing your rim size, so it takes longer for your wheel to make a full rotation which effects the speed. The maker set the gear for that size of rim and when you change that, your altering that gear's reading as well. The speedometer is reading less than the wheel is acually going. |
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| turbomike |
| GEEKS................................. |
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| MrHeavyFoot |
quote:
Originally posted by Mekanik22
quote:
Originally posted by scooby_dooby
if you change your wheel size and get the incorrect size rubber ya, if you get the right rubber the overall diameter of your wheel will remain the same.
I don't get it? Because your increasing your rim size, so it takes longer for your wheel to make a full rotation which effects the speed. The maker set the gear for that size of rim and when you change that, your altering that gear's reading as well. The speedometer is reading less than the wheel is acually going.
As scooby_dooby said, it is the diameter of the tire that matters. It does not take any more distance for a bigger wheel to make a full rotation if the outer diameter of the tire used is the same. Go to the miata.net link on the previous page and you'll see. All bets are off however if you drive a train. |
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| Inzane |
quote:
Originally posted by Mekanik22
I don't get it? Because your increasing your rim size, so it takes longer for your wheel to make a full rotation which effects the speed. The maker set the gear for that size of rim and when you change that, your altering that gear's reading as well. The speedometer is reading less than the wheel is acually going.
small rim + high profile tire = big rim + low profile tire
(if you select your wheel sizes and tire sizes carefully you can keep the two sides of my silly equation roughly equal). |
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| Lll_J |
All the questons people are asking are answered in this post, read up people! haha. Spline said it along time ago..."plus sizing". You can keep the same overall diameter, your tire sizes decrease as your wheel size increasese, get it?
quote:
Circumference = Pi x Diameter.
Therefore Circumference and Diameter are DIRECTLY proportional to each other.
If you increase your overall rolling diameter by 5%, you affect your circumference by 5%.
BTW on this general thread topic, increasing your overall rolling diameter will mean a theoretical higher top speed, gearing wise. But that doesn't mean your car has the horsepower to get there.
Exactly, couldnt have put it better myself. As I mentioned earlier this is theory guys. Essentially if your really concerned about performance, you should not be going much bigger than your stock OVERALL diameter.
And if your concerned about your speedo being incorrect if you do change the size of your wheel/tire combo. Thats what the equation I stated is for. And besides, you should be able to feel how fast your going in your car! :D
Jordan |
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| Dr. Lightspeed |
| It depends on how much larger you go in total diameter. The ultimate effect is the overall effect it has on gear ratio if you increase your outside diameter of your wheel by say 10% this has the same effect as raising your gear ratio by 10 percent. so if you had a gear ratio of 3.51 :1 you would be effctively changing it to 3.15 :1 which would severley affect your accelleration for the other wheels you had. Now the second factor comes in if your wheels weigh more than the stock ones it is going to take more horsepower to turn them. Another factor is 1:100 unsprung weight factor. Add more weight to your wheels it will take more to slow and to go. Just my 2 cents |
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| mwdguy |
| not sure if it has been said yet but the weight is the biggest factor in increasingyour wheel sizes. Since 1 lb of rotational mass is roughly equivalent to 10 lbs of static mass, that is where the biggest difference is. If you can knock off 3 lbs a wheel, thats 12 total ... roughtly close to 120 lbs static mass you have dropped. |
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| Nightstalker |
| I wonder if eric is even reading this.. way to much math involved here.. its like a thinking man's thread or something :unsure: |
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| ManHunter |
I'm reading this. It's all interesting. My original question was answered a long time ago. :)
MH |
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| Lll_J |
Its like grade 6 Math. I hope everyone passed grade 6. Haha.
Jordan |
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| ChromeDragon |
quote:
Originally posted by Lll_J
Its like grade 6 Math. I hope everyone passed grade 6. Haha.
Jordan
There's that many grades? DAMMIT!!!
And I though grade two was hard!!!! :blink: |
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| SplineZ |
i got held back..
James Z |
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| ChromeDragon |
quote:
Originally posted by SplineZ
i got held back..
James Z
Is it possible to NOT be held back? :wacko: |
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| Nightstalker |
quote:
Originally posted by ChromeDragon
quote:
Originally posted by Lll_J
Its like grade 6 Math. I hope everyone passed grade 6. Haha.
Jordan
There's that many grades? DAMMIT!!!
And I though grade two was hard!!!! :blink:
:werd: I guess thats why were still going to the same school ;) |
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| MightyMidget |
quote:
Originally posted by SplineZ
http://www.miata.net/garage/tirecalc.html
god damnit ppl keep it simple.....use the calculator that James provided!!!!! it gives you all the answers without all the grade 6.5 math.......and yes plus sizing is great IF you do it right!!!
S |
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| TheNeonEdge |
K im a little confused.
According to that calculator If i went from my original tire size to 20's my spedo will read 100 when i am really going 109, does this mean that it just can't read the speed the same but it will still be slower or what?!
Specification Sidewall Radius Diameter Circumference Revs/Mile Difference
225/55-15 4.9in 12.4in 24.7in 77.7in 815 0.0%
225/40-20 3.5in 13.5in 27.1in 85.1in 745 9.5%
--ThE EdGe |
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| 2000z |
Revolutions Per Minute, if something is bigger does it take longer to make a full rotation? *cue nodding head smilie that I can't find right now"
It can't read the same when the overall diameter is a different size. It will also change your theoretical top speed. |
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| SplineZ |
if the diameter of your tire changes, than the ammount of ground it travels per revolution will change as well.
For example, if your regular tire is a 205/60/15, and the tire you want to put on is a 265/40/18, the outside diameters will be 24.7, and 26.3 inches repectively. That means that the original tire will cover 24.7 inches per revolution, and the other one will cover 26.7.
I know that my car uses "VSS" pulses to calculate how fast Im going. If I change the outside diameter of my tire, the pulses will not be as fast, and it wont have the proper signal to drive the VSS with. It will register slow, because your tire doesnt have to revolve as much to cover the same distance.
James Z |
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| SplineZ |
quote:
Originally posted by 2000z
Revolutions Per Minute, if something is bigger does it take longer to make a full rotation? *cue nodding head smilie that I can't find right now"
It can't read the same when the overall diameter is a different size. It will also change your theoretical top speed.
Back to grade 9 science, unit simple machines :D
Take a CD, and put a dot on the outside near the edge, and the inside near the edge. They take the same time to rotate, but the velocity on the outside dot is much higher.
James Z |
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