What's the performance difference between 15 inch, 16 inch and 17 inch tires (all else equal)?

What's the *performance* difference between 15 inch, 16 inch and 17 inch tires (all else being equal)?

Let's say that the stock wheel is 16 inch and let's ignore sheer looks, and the fact the speedometer will read differently, and let's ignore obvious non-performance wheel-well fitment issue since they're obviously not performance changes.

What *performance* changes will the one inch larger or smaller tire cause?

Basically, I'm wondering why people almost universally want larger wheels, where all I'm asking about are what the performance tradeoffs are.

Reply to
Mad Roger
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Bigger wheel = less gasoline for a given distance and less tire wear.

Reply to
dadiOH

Folks might like to know that just putting the question as posed into google will get results like this:

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Reply to
Frank

The main reason is appearance. In the late 50's auto makers went to 14" wheels to make cars lower. Decades later, that is not as important as big flashy wheels.

The average driver will notice little difference in everyday driving, most cars are designed with the wheel size in mind. Larger diameter tires will last a but longer as there is more distance per rotation.

Tire profile will also affect performance. The low profile look sleeker, but the balloons are better on the bumps.

You will find some actual test results here

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Reply to
Ed Pawlowski

On 07/19/2017 1:00 AM, Mad Roger wrote: ...

Ed posted link to good evaluation of acceleration effect owing to the torque effect; what that article doesn't address is net effect of highway driving on mileage wherein the larger diameter equates to lower rpm at a given speed, as it assumes in the article, all else being kept constant. I've not seen actual data, so don't really know where the net result would be...

One other thing I'd note on the size and relative cost -- got a program car Enclave a few years ago and didn't think about the specific wheel size albeit noticed they were large. It actually is a real benefit for us as it gives some additional ground clearance so that plus the AWD it has been a good field car for SWMBO as she's so short the 4WD K2500 is a real bear for her to get in/out of. The larger diameter also smooths out gravel road washboard effects by the larger footprint noticeably.

The big disadvantage is that these are 19", not 18 or 20 and there's a tremendous premium(+) on the 19" tire cost relative to either of the others owing, I guess, simply to the relative number of vehicles using them...so, if one is considering a vehicle and such details as future maintenance costs, keep the 19" wheels on the "don't go there!" list...

(+) I'll note I've not researched this for a while now; the observation is based on that ruined one shortly after we got the vehicle and it was like $100 more expensive than a 20-incher for the same tire (Michelin iirc, altho don't know series otomh).

Reply to
dpb

Thank you for that article, where the 3 main takeaways are...

"If the wheel diameter increases by one inch, the height of the tire should decrease accordingly to compensate, in order to keep the overall diameter the same."

"With larger wheels and lower profile tires ?X and the resultant shorter sidewalls ?X they??re stiffer and there??s less of an air and rubber cushion than before, increasing the chances that hitting a large pothole could damage the tire, wheel or both."

"An 18-inch tire, for example, will probably weigh at least a couple of pounds more than a 16- or 17-inch tire. That could also be true of a larger wheel."

To summarize what the article said for moving to larger-diameter wheels...

  • The overall vehicle suspension remains at the same ride height
  • Tire air "cushioning" is greatly reduced
  • Unsprung weight goes up appreciably
Reply to
Mad Roger

Thank you for that performance-related test article,

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Where the 3 main performance-related takeaways are... "the force can be calculated to be around 460 Newtons. Now, increase that wheel diameter to a set of 19-inch ... Run the calculation through again and that driving force will decrease to 360 Newtons... which will culminate in a decrease in acceleration of said wheels."

"Fuel economy will inevitably suffer as well due to the engine having to work harder to rotate the wheels"

"Smaller diameter wheels will make for more concise handling as each rotation of the wheel covers a shorter distance, meaning more acute adjustments can be made during cornering compared to a larger diameter tyre"

To summarize what the article said for moving to larger-diameter wheels...

  • The engine delivers less driving force to the wheel contact patch
  • Which results in a decrease in acceleration & decrease in fuel economy
  • And there will be a decrease in handling (all else being equal)
Reply to
Mad Roger

I was surprised that everything performance related that larger wheels buy you as noted in those two articles was negative, including fuel economy.

Their argument on fuel economy was that the engine has to work harder to result in the same amount of torque at the contact patch.

Using their numbers, 360 Newtons is 78% of 460 Newtons, all else equal. Looked at the other way, 460 Newtons is 128% of 360 Newtons.

It seems that a 1/4 loss of torque at the contact patch is astoundingly huge, is it not?

Given that steady highway speeds still must overcome the force of friction (where wind resistances are appreciable at speed), that ~25% loss of available torque would still be missing highway speeds - would it not?

Reply to
Mad Roger

I would intuitively agree with you but the two referenced articles do not agree with our intuition.

Combined, the two articles said (for a one-inch difference)...

  • The engine delivers ~25% less driving force to the wheel contact patch
  • Which results in a decrease in acceleration & decrease in fuel economy
  • And there will be a decrease in handling (mostly in cornering)
  • And that unsprung weight goes up appreciably
  • In addition to tire air "cushioning" being reduced
  • While the overall vehicle suspension remains at the same ride height
Reply to
Mad Roger

I think in those calculations they are assuming the diameter of the whole wheel increases by the amount of the wheel increase. That isn't usually the case. With a larger diameter wheel, you typically do to a lower profile tire, so that the overall diameter doesn't change nearly as much, maybe not at all. I'd also be skeptical of theoretical numbers on things like fuel economy, as opposed to test data.

Reply to
trader_4

That's a fair assessment that the overall diameter of the wheel is a function of both the rim diameter and the tire aspect ratio.

Given that, you bring up a good point that we have two separate situations when we change the wheel size.

  • We change just the wheel size (and nothing else)
  • We lower the profile at the same time (which keeps diameter the same)

I had not thought of that situation when I first asked the question. I was just trying to figure out why people seem to love bigger wheels. (I already knew about looks but I was seeking performance implications.)

Since I'm not the one who puts 20-inch wheels on a Honda Civic, I have to ask here whether most people who oversize their wheels from stock aim to keep the overall diameter the same as stock, or if they allow the overall diameter to increase?

Reply to
Mad Roger

I found it interesting and first sentence says it, "They look cool."

Reply to
Frank

I need to correct the summary based on a distinction trader_4 brought up that there may or may not be an increase in overall diameter.

Since I'm not the one putting 20 inch wheels on a Honda Civic, I have to ask here whether the general trend is to maintain the overall diameter of the wheel-and-tire assembly, or if most people increase the overall diameter?

Reply to
Mad Roger

I agree that people do things for looks alone, but what is strange is that there doesn't seem to be a single beneficial performance impact of an overall larger diameter "tire-and-wheel assembly".

I wasn't expecting huge performance gains, but I would have expected at least one or two benefits - and not all negatives based on the two articles noted.

If the diameter of the wheel and tire assembly increases by one inch overall due to the one-inch increase in rim size - and assuming everything else is kept equal in materials and aspect ratio and tread width - then the two articles stated...

  • The engine delivers ~25% less driving force to the wheel contact patch
  • Which results in a decrease in acceleration
  • And which decrease in fuel economy (presumably at all times)
  • And unsprung weight goes up by a few pounds

The main astounding number is the fact the torque felt at the wheels is astoundingly less for a single inch in overall diameter change.

Presumably that torque loss happens at all speeds (why would it not?) so that denies us the one intuitive performance advantage of highway MPG.

Reply to
Mad Roger

Bling. This topic was beaten to death a month or two ago. When someone says larger diameter wheels must be effective because they are used on race cars ask them what size wheels are mandated for F1 or NASCAR and what sort of racing they had in mind outside of the Fast & Furious franchise.

Reply to
rbowman

For something like a Honda Civic the overall diameter is probably close to the OEM setup. There's only so much you can stuff into a wheel well.

Reply to
rbowman

I would tend to look at the drivers who over-size their wheels and conclude that it is _not strange at all_ that the mods are based solely on image .. John T.

Reply to
hubops

I'm having a hard time fathoming that there are zero performance benefits from putting a one-inch larger diameter tire-and-wheel assembly.

Most things done for "looks" have a semblance in reality, I thought.

For example, low-profile tires give better steering response, so, that's why (I presume) I see SUVs with super low profile tires (because they want to look like a better steering vehicle).

Likewise a wing in the rear has a genesis in actual aeordynamic theory so I understand that people want the look of a fast car (although at 60mph, a wing is probably just for looks).

Same with dual exhaust, or a hood scoop, both of which allow the engine to bring in and shove air out easily (which is essentially what an engine does).

So the whole performance-look thing is a bit confusing to me.

Unlike the examples above where the look is to replicate situations where there is actually a performance gain, if there are no performance gains to larger wheels, then how does the *look* of larger wheels look like you get performance gains?

Reply to
Mad Roger

But you can almost always add a wheel-and-tire assembly with a one-inch difference in overall diameter, can't you?

Reply to
Mad Roger

The psychological problem I'm having with "bling" with respect to race cars is that there seem to be zero performance benefits of larger wheels, even for race cars.

What race car benefits from 25% less torque at the driving wheel contact patch for example?

Reply to
Mad Roger

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