Does increasing rim size affect the acceleration?

[Jack Yak]

I have yaris sedan 1.3 , 07

the original wheel size is

185/60/R15

i wanna upgrade it to 195/50/R16

dose it affect the performance of the car ? especially the acceleration ?

someone told me if i increased the rim size from 15 to 16 it will decrease the car acceleration

and if you wanna performance use 15 if you wanna look use 16

is that true ?

[Flipper_1938]

On my old echo, I went from 14's to 17's and it sucked the life out of the car. You might not notice one inch difference, but I'm sure it hurts performance a little. If you are going for looks, it is probably worth it.

I have 20's on my rat rod truck. I know the truck would be faster on 15's, but I love the look of the big smoothies.
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[fnkngrv]

Moving to a bigger wheel will affect acceleration. It is a fact, but you might not notice it too badly only moving to a 16. The tire choices will make a big difference as well.

[kimona]

I went from 185/60/15's to 205/50/16's... and I don't notice any difference in acceleration whatsoever.

[YarisSedan]

Well rotational mass is going to be a big factor. The larger the rim typically the heavier it will be. Especially if you are not going with a good quality rim. All the cheaper rims are really heavy. I know from experience i bought some nice tires and put them on my stock steel wheels. They were wider and a little heavier. My car handled better but seemed ever so slightly more sluggish on takeoff. I then a month later swapped the same tires onto some konig heliums. My car handled completely different. Id say its a equivalent feeling when you first put on the trd swaybar. Its that dramatic. a few pounds heavier or lighter on each wheel you will feel it.

[403RS]

Originally Posted by Flipper_1938

You might not notice one inch difference, but I'm sure it hurts performance a little.

The wife might notice too.

[CrankyOldMan]

Originally Posted by YarisSedan

Well rotational mass is going to be a big factor. The larger the rim typically the heavier it will be.

This is moving in the right direction, but misses out on the other key factor: distribution of mass.

Caution, physics ahead! This is a very general overview of the effects of diameter and mass on rotational acceleration. The numbers aren't terribly accurate, but it's meant to give an impression of why larger/wider/heavier tires and wheels hurt acceleration.

Two cylindrical shapes of equal mass but different distributions will exhibit very different acceleration, due to different moments of inertia. For simplicity's sake, it's easier to evaluate a thin-walled cylinder, whose moment of inertia is its mass times the radius squared.

I = mr^2

Going from a 7.5" to 8" radius results in a pretty significant change in moment of inertia, assuming that the mass stays the same. I.e. 0.391*m lb*ft^2 vs 0.444*m lb*ft^2. In reality, a larger diameter (and typically larger width too) means an increase in mass as well, further increasing the moment of inertia. If we assume that half of the mass of the rim is in the outer ring, that a typical low end 15" rim weighs 14 lbs, and that a low end 16" rim weighs 15 lbs, the difference becomes even more pronounced. The 15" rim then has a moment of inertia of 2.73 lb*in^2 and the 16" rim is 3.33 lb*ft^2.

The real kick in the huevos comes from the calculation of acceleration, which is the torque divided by the moment of inertia (for constant acceleration only).

a = T/I

Assuming that torque is fixed (and it has to be for this equation) and our moment of inertia I changes from 2.73 to 3.33, the acceleration has to decrease to keep the equation balanced. I.e. 1/2.73 is larger than 1/3.33, meaning a larger acceleration value for the smaller/lighter rim.

"But Cranky," you say, "what if I get some super light weight rims?" Well, look back at the moment of inertia formula. Changing the weight has a very small effect on moment, but changing the radius has a huge impact. Even assuming that the distribution is the same, going from a 14 lb to a 12 lb wheel makes a very small dent in the numbers.

So having bored/scared/enlightened everyone, let me conclude by saying that ultimately, it comes down to what you're trying to achieve. If you want to show off how much you spent on them, go for some 18" rims. If you want bigger contact patches, get wider tires/rims. If you want firmer cornering, get lower profile tires. If you want better acceleration, get smaller diameter wheels. If you want higher top end speed, get bigger diameter tires. Mixing up these combinations can give interesting results: Jason@sportscar uses some crazy 13x10" rims with racing slicks on the track--huge contact patches, better acceleration, but at the cost of top end speed.

[thebarber]

it'll depend on the weight of the 16" rim/tire combo vs the 15's.

[MadMax]

Doesn't matter, bigger tires look cooler!

Cheers! M2

[YarisSedan]

Originally Posted by MadMax

Doesn't matter, bigger tires look cooler!

Cheers! M2

I think thats the ultimate answer

[CrankyOldMan]

Originally Posted by thebarber

it'll depend on the weight of the 16" rim/tire combo vs the 15's.

To some extent, yes, but even if you get a 16" combo that matches the weight and diameter of the stock tires on stock steelies, the distribution will be different. The distance from the axis of rotation has a much larger impact on acceleration than overall mass alone. In most cases, going with a 16" rim means a wider rim and tire, increasing the amount of mass at the outer radius of the tire and wheel.

If we move away from the thin-walled (read: zero thickness and width) cylinder to a thick-walled model with a height (width), the width and radius become even more significant:




Where p is the density of the material, h is the axial length of the cylinder, r2 is the outer radius and r1 is the inner radius. The width is a linear scalar quantity, but the radius is "quad-ed", meaning that even a small increase makes a big difference in the moment of inertia.

I do recognize that we may be talking about fractional quantities of torque or acceleration in all cases, but the principle stands: radius changes the values faster than width or even weight. That said, the same diameter wheels/tires with lower weight will of course have less negative impact on acceleration.

Just watch a figure skater do a spinny-thing where they start with their arms out and then bring them in to their chest. No change in mass, only radius. Makes me queasy just thinking about spinning that fast.

I've been meaning to try and get some wheel manufacturers to cough up actual numbers, but I suspect that their engineers will be guarding that kind of information very closely.

[thebarber]

i noticed a HUGE difference going from my summer setup of 15x7 rpf1's and proxes4's in 205-50-15 to my winter setup of 14x6 with 185-65-14 winterforce tires last year.

i couldnt wait to get my ultra light summer setup back on.

frankly, im not looking forward to tossing on the snows again at the end of the month...

[CrankyOldMan]

Hmm, once again, real world experience trumps academic theory =) Perhaps some details on your winter rims could help sort out the differences?

[bzinn 1]

Cranky has a valid point.....where the mass is located does effect the ability of the energy to rotate it.

My teacher in school actually used the formulas and the example of tire and wheels that he explained.....

general rule of thumb is larger rims are gonna weigh more,short of a few manufactures out there who make high end wheels that are light.strangely tires vary by brand as well,who would of guess a same size tire could be 1-5 lbs in differance by brand and style.

Try to stay with a wheel and tire combo that is close to the same weight as the stockies if you can,it can be done....my 17s were only 2lbs heavier than the stock 14s with hubcaps,but they made car feel sluggish,we have so little HP that every bit will count.

[thebarber]

Originally Posted by CrankyOldMan

Hmm, once again, real world experience trumps academic theory =) Perhaps some details on your winter rims could help sort out the differences?

summers are 15x7 enkei rpf1's @ 9.4lbs/wheel and 205-50-15 toyo proxes4's @ ~19lbs/tire. about 28lbs/corner

winter setup is 14x6 alloys from a 1987 supercharged mr2 with 185-65-14 winterforce tires. complete setup is likely about 35lbs/corner

weight IS the enemy

[TOUGEghost]

Weight isn't the only thing to worry about either. I've never really paid attention to the weight specs for any of my tires.

My stock 185/60/15's were 23.7" in diameter.

My 205/40/16 KDW2's were 22.4" in diameter, roughly a 5.5% difference. There aren't too many other tires for any size wheel that are shorter than this.

Not sure what the stock wheels weigh but my OZ's were about 13lbs each. Noticeable improvement in acceleration with the 16's vs the stocks, mostly due to the shorter tire diameter which effectively shortens the final drive ratio.

My 23.5" diameter 205/40/17's on 14.6 lbs RPF1 still accelerated better than stock, but not as good as the 16's.

Anyway, to sum it up, you can still get better acceleration with bigger wheels if you get light wheels and short tires.

[ilikerice]

Toughghost makes a good point. I was using 185/65/15 tires on my rota GT3's 15x7. Car seemed normal. When I just switched to 225/45/15 my acceleration increased a significant amount. I think the diameter of the tires made the most impact.

[ljming99]

Originally Posted by ilikerice

Toughghost makes a good point. I was using 185/65/15 tires on my rota GT3's 15x7. Car seemed normal. When I just switched to 225/45/15 my acceleration increased a significant amount. I think the diameter of the tires made the most impact.

The little yaris is light, even on a stock engine it can make the tires slip and loose grip on a hard launch. With 225 tires u get more grip, hence u lose lesser power on a hard launch which gives u better acceleration.