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Smaller Tires Or Bigger Tires?


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#1 Brendon

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Posted 16 October 2007 - 11:54 AM

I've been reading up on this debate across various sites, mostly through google. The basic question I'm posting is which is better for performance, having smaller diameter tires or bigger tires?

Now as we all know, a tire/wheel combo which weighs more will accelerate slower for obvious reasons of weight and rotational inertia to overcome. That's why everyone laughs at the people who put huge bling-bling 40 lbs monster 18" wheels on a Corolla. But my question has to do with mechanical advantage through the overall diameter of the tire. Here's the senario I'm looking at for myself:

Corolla A: Has 14" wheels with 185/65R14 Yokohama AVID HS4 tires. Overall diameter is 23.47", circumference is 73.73", and it revolves 859.3 times per mile.

Corolla B: Is the exact same car as Corolla A except the driven front wheels use 185/60R14 tires. Overall diameter is 22.74", circumference is 71.44", and it revolves 886.9 times per mile.

For control purposes, let's pretend that both tires are the exact same in terms of weight, design, treadwear, etc. The only difference is the diameter. So which car will accelerate faster? From what I've read online, most people say that a smaller wheeled/tired car will accelerate faster, but have a lower top speed and its top end acceleration will be reduced. At the same time, some people argue larger tires are better for acceleration because they have less rolling resistence and can produce more rolling inertia to maintain the speed. I'm looking to get the opinion here on the Corolland community.

I'm wondering how would smaller tires on the driven wheels (front wheels) affect my Corolla overall? 0-60 acceleration? 60+ acceleration? Top speed? Cornering and handling? Braking distance? Fuel efficiency? Engine working harder?

Edited by Brendon, 16 October 2007 - 02:12 PM.

#2 fishexpo101

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Posted 16 October 2007 - 11:22 PM

A popular question - problem is, there are too many variables that you are not directly in control to come to a good, precise result. I could spew into all kinds of equations, theories, and some simulations (by profession, I'm a scientist - physics, math, and computer sims are my specialities) - but I'll leave those details out for right now and just give a gross overview of what "could" happen. A short answer - most performance gains are picked up running a lightweight, larger contact area, stiff sidewalled, and traction oriented tire. But that same tire will also return the worst fuel efficiency and generally ask the most from the car's engine.

For the performance oriented group - reducing overall weight, is the Holy Grail to performance, as you don't change any of the existing powertrain - plus mods of more of less free to very low cost (at least initially). In that regard - having a smaller tire/wheel will help with achieving those goals. Good example is the GM Sunraycer (solar powered race vehicle) in the late 1980s. That had low rolling resistance, bicycles tires. Doesn't look like much, in the way of contact patch size and overall traction, but that vehicle could take a 90 degree turn - flatout at 70MPH, no braking at all, just the go pedal all the way. The keys were a lightweight vehicle, lightweight components. There is no arguing that given identical tires - the lighter one (generally the smaller one) will have more performance potential.

But that's not the whole story - other factors you have to consider. Smaller (diameter) tires generally means the tire will have to make more revolutions to cover a set distance. Assuming the gearing of the car will not change. What this means is that the car will have to do more work to cover the same distance. If it will make a difference in performance - depends on the car and the desired performance. Off the line acceleration may or may not be better with a smaller tire - depends on the powerband and the gearing. You might gain some with better acceleration, but if you need shift sooner (say a run from 0-60MPH) - you might end up on the losing side of that battle. Since gearing will not change, your top speed will definitely suffer, assuming that the engine is sufficiently powerful enough to get you up there. That's because the tire has to be turning more to cover the same distance, you may end up just "run out of revs".

Handling is also a tough one to approach. You have to balance traction, sidewall stiffness, rolling resistance, and contact patch size. If we look at the extremes - say a 14" tire vs a 18" tire, keeping the overall diameter the same, both filled to max cold tire pressure. Traction is more a function of tire design - assuming that they are of the same material and if possible, the same tire - the 18" tire will definitely be better that the 14" tire on the stiffness, low rolling resistance, and contact patch size. But does that make it a better tire - all depends. If the combination turned out to be the same weight, then maybe the bigger tire will be the better choice. But currently, I've yet to personally run a larger diameter tire that weights less than a smaller tire (assuming they are the same series, type) - eventually we may see them get closer in weight, but I've yet to run into that situation. Hard part is matching the tire to the car - just because a tire is better in certain aspects, doesn't mean it will translate to better performance on the car.

Moment of Inertia - I wouldn't even worry about this. Difference is so minute, given the dynamic road conditions that people run into everyday, I wouldn't waste too much of my time worrying about this. If your running it on a prescribed track against identical cars - then that is a different story.

Best way to approach this problem is to run two identical tire sets. Then experiment with parameters that you can control - like wheel types, tire pressure, tire temperature, tread depth, etc. Even buying tires of two different sizes from the same series and make of tire will not always mean an apples to apples comparison (tire construction can vary wildly with even slight tire size differences). A little extra belt material here, difference tire casting process, difference in QC could turn out a hugely different performing tire. Even tire testing machines - loading with identical tires from difference batchs and running the tire to failure can turn up vacillating results from tire to tire. I've seen tires that were so-so in performance turn into some decent tires, once you shaved a few tenths off of them. Others actually became worse the more then wore down. Some respond well to heat cycling, others don't care.

Personally, I saw nearly no differences between running a 205/45R16 tire vs a 195/60R14 tire - in terms of handling, cornering, and acceleration. Basically it boiled down to that the tire's capabilities entended much further than what the point in which the chassis was capable of pushing the tires. Fuel economy on those tires flipped flopped between them - initially I was getting better fuel economy with the 16" tires than the 14" tires - but after about the same distance traveled (~20K miles) on the sets - the 14" is starting to get better numbers than what the 16" tire was able to put up. Weight wasn't that much different between the two sets - maybe 5-10lbs per tire/wheel.

#3 Brendon

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Posted 17 October 2007 - 02:35 AM

I know what you mean about weight. I recently purchased some ultra light wheels that weigh in at about 9 lbs each. From my old 20 lbs steel ones, these have reduced about 44 lbs at the wheels and improved my acceleration significantly, at least from a dead stop. I don't know how accurate my stopwatch is, but I was able to drop my 0-60 time down to 9.2 seconds from its previous 9.6-9.7 seconds. Not bad for an automatic.

The reason why I got interested in this subject was because I was originally thinking about going to a lower profile on the front wheels for cosmetic lookings (having a slightly higher back end and lower front end). The difference isn't much between 60% profile and 65% on 185s (about 1/3 " in height). Then I started to worrying about what reducing a tire's diameter might do to my car's overall performance. I've recently begun looking at eletric bicycle conversion kits. One site that I visited did testing between bicycles with 20" and 26". The results were that the 20" bikes produced more torque and had more off-the-line punch, but couldn't make it to as high a top speed as the 26" bikes and drained the batteries faster on control runs because it had to work harder to spin the tire at a same speed. Of course, there is a huge difference between 26" and 20". The difference in my car application is less than 1" diameter change. I just don't want anything adversely affecting my car's performance.

#4 Accent 1ZZFE

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Posted 17 October 2007 - 06:45 AM

In general if you run a smaller tyre/rim, the car should feel punchier from a stand still and roll on.

The weight savings made in the rims and tyres and the altered rolling diameter of the wheel/tyre combo contribute to improved throttle response.

The performance wont be drastically altered by going to a lower profile tyre, expect more stiffness in the sidewall and you may experience a harsher ride but be rewarded with better handling and turning.

Not sure of the legalities where you live, here our tyres must abide by the mimimum load index and speed ratings as specified by Toyota.

Edited by Accent 1ZZFE, 17 October 2007 - 06:49 AM.

#5 fishexpo101

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Posted 17 October 2007 - 10:41 AM

Good point about load ratings - generally the tires available within a reasonable range should be fine. For the difference in ~3/4" in overall height - won't be much of an issue. But generally speaking, you should keep the tires the same all around. Don't try and get some weird staggering or tire sizes for this particular chassis, unless you made some significant changes to the suspension or plan on running the car only in a straight line. Just like mixing winter tires with all-season tires - can make for unpredictable handling in some situations. Plus having the same tires all around makes for easy tire rotations.

#6 Bikeman982

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Posted 28 October 2007 - 12:09 AM

I have 195/70R 14 on the back and 185/70R 14 on the front.
The larger tire on the back makes it feel a little more solid and the front end seems pretty nimble.
I can't rotate the tires around, like they were all the same size.
I also like the slightly raised look of the back end, it seems a little sportier.
Posted Image

Edited by Bikeman982, 28 October 2007 - 12:13 AM.

#7 robbieboy333

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Posted 05 November 2007 - 10:36 PM

Good point about load ratings - generally the tires available within a reasonable range should be fine. For the difference in ~3/4" in overall height - won't be much of an issue. But generally speaking, you should keep the tires the same all around. Don't try and get some weird staggering or tire sizes for this particular chassis, unless you made some significant changes to the suspension or plan on running the car only in a straight line. Just like mixing winter tires with all-season tires - can make for unpredictable handling in some situations. Plus having the same tires all around makes for easy tire rotations.

In regards to mixing tire sizes on most vechicles these days one should use caution, most of your sensors for your vechicle are calibrated to the revolutions of your tires, if a real drastic mix is used you could damage or cause problems with many different aspects of your car. The recommended change of tire size is plus / minus 3 % with-out causing any problems with your vechicles comp sys/ sensors. Now when down sizing the overall circumference from the original size ensure you maintain the GVW of the vechicle to prevent over heating of the tire with a full load. I honestly feel if one feels they will accelerate faster with a lighter tire/rim combo alone with-out any other modifications to the vechicle to decrease the over-all weight of the vechicle you will be dissappointed. Just a point to ponder if one increases the circumference greater than 15% over your original tire size you will find your ABS system with no pulsations...

#8 Bikeman982

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Posted 05 November 2007 - 10:44 PM

In some states if you put on wheels with tires that extend beyond the wheel well, it is illegal.
Unless you add wheel well trims that will cover the tires.
If you change rims and tires to lower the body, you risk hitting the car on bumps when you go over them,
as well as high points (speed bumps) on some roads.

Edited by Bikeman982, 05 November 2007 - 10:46 PM.

#9 robbieboy333

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Posted 06 November 2007 - 10:05 PM

Check out this link, we use it daily in our shop, it,s a tire size comparator and its free. it will give you all info you need when changing sizes.. cat.cc/tiresize.htm -

#10 gvr4ever

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Posted 07 November 2007 - 02:20 PM

I've been reading up on this debate across various sites, mostly through google. The basic question I'm posting is which is better for performance, having smaller diameter tires or bigger tires?

Now as we all know, a tire/wheel combo which weighs more will accelerate slower for obvious reasons of weight and rotational inertia to overcome. That's why everyone laughs at the people who put huge bling-bling 40 lbs monster 18" wheels on a Corolla. But my question has to do with mechanical advantage through the overall diameter of the tire. Here's the senario I'm looking at for myself:

Corolla A: Has 14" wheels with 185/65R14 Yokohama AVID HS4 tires. Overall diameter is 23.47", circumference is 73.73", and it revolves 859.3 times per mile.

Corolla B: Is the exact same car as Corolla A except the driven front wheels use 185/60R14 tires. Overall diameter is 22.74", circumference is 71.44", and it revolves 886.9 times per mile.

For control purposes, let's pretend that both tires are the exact same in terms of weight, design, treadwear, etc. The only difference is the diameter. So which car will accelerate faster? From what I've read online, most people say that a smaller wheeled/tired car will accelerate faster, but have a lower top speed and its top end acceleration will be reduced. At the same time, some people argue larger tires are better for acceleration because they have less rolling resistence and can produce more rolling inertia to maintain the speed. I'm looking to get the opinion here on the Corolland community.

I'm wondering how would smaller tires on the driven wheels (front wheels) affect my Corolla overall? 0-60 acceleration? 60+ acceleration? Top speed? Cornering and handling? Braking distance? Fuel efficiency? Engine working harder?



With the size different your giving, I doubt that you would even tell. Technically the smaller tire will accelerate faster. The 185/60 would most likely have less rubber contacting the road, so cornering and braking might be effected a little. For the corners, usually stiffer side walls and rubber compound make the most difference, but larger rims can too because it is easier to make a shorter side wall stiffer.

One of the major car magazines did a long term test on a WRX and it came with 16" wheels. During the test, they changed to optional 17" rims. The effect was slower 0-60 times, but better corner capability.

I have the stock XRS rims and tires on my LE corolla. I don't notice any difference in acceleration, but the new tire setup corners tons better. If you do want to upgrade, I would find the lightest 16" wheels and do a plus size tire, so the overall diameter is as close to stock as possible.

Light weight rims might be able to counteract a slightly larger wheel. Go as light as possible. Tire rack has 16" rims that are under 13lbs each. Not the cheapest, but if you want performance and not bling, you gotta pay a little more.

BTW, in the case of 16" wheels on my car, I have not notice a loss in fuel economy. The alloy wheels seemed lighter then the stock steel wheels, so that could be why.