Any advantage to taller wheels in the same width?

[CarlThompson]

I'm not a wheel / tire expert so sorry if this is a silly question.

Would there be any advantages to replacing a 235/45R18 setup with 235/40R19 with the same type of tire? Since they would be the same width I wouldn't expect any traction improvement because the contact patch would be the same, right? Would there be any handling improvement due to the stiffer sidewall? Since the contact patch would be the same size does the mean the energy efficiency would be the same? Since the overall diameter would be virtually identical there should be no issue with speedometer error or tire clearance, right?

I can think of a few disadvantages of the taller wheels

• 19s would be a bit heavier than 18s even in the same width so may / will negatively impact acceleration and handling
• Slightly harsher ride and slightly more prone to damage due to lower sidewall
• More epensive

I can think of only one advantage offhand

• Might be more attractive in side view

So if I were going to buy aftermarket 235/45R18 wheels would it even make any sense at all to consider upsizing to 235/40R19? I don't need the greatest traction as I don't push cars very hard so I don't think I'd want the efficiency disadvantages of going to a wider wheel like 245s. But what about going taller?

Thanks!

 

[tm1v2]

I've changed wheel diameter / tire sidewall height on three cars now, including two Teslas. What follows is all from my experience... (I'm not simply repeating things I've read)


Taller sidewall absorbs small bumps and road texture better. Especially with a soft sidewall tire, like a comfort-focused all-season, but even stiff sidewall performance tires ride better with some sidewall. Large bumps won't feel much different between 235/45 vs 235/40 based on my experience though. (Absorbing large bumps better is a job for the suspension or really tall offroad tires.)

Taller sidewalls also give more protection/cushion for your wheels over potholes and torn up roads. This is a very real difference and can be very important depending on the condition of the roads you drive on.

The main advantage of shorter sidewalls is the larger wheel diameter allows fitting larger brakes. If you're not fitting larger brakes then the bigger diameter wheels / skinny tires are mostly for looks.

There is also a theoretical advantage in steering response to a shorter sidewall. My experience is that's very true for soft sidewall tires - they accentuate the responsiveness difference between sidewall heights. However with very stiff sidewall performance tires, the steering response difference between, for example, 235/35R20 vs 245/45R18 is extremely minimal! You gain way more wheel protection and ride quality than you lose in steering response.

(Especially with stock Model 3 suspension/bushings...there's enough slop to hide small differences in wheel/tire responsiveness.)

Larger diameter wheels cost more, and skinnier sidewall tires for them also cost more! I've no idea why a 245/40R19 tire costs more than 245/45R18, it doesn't make sense to me, but it's very consistent across all tires and brands I've ever looked at.

Lastly, depending on the exact wheel and tire, you're more likely to end up with lower total wheel+tire weight with smaller diameter wheel and taller sidewall tire. I haven't done a ton of weight spec comparisons, that's just the trend I've seen, definitely check the numbers for any specific wheels and tires you're interested in (if you care about this).

 

[Sam1]

Larger diameter wheels cost more, and skinnier sidewall tires for them also cost more! I've no idea why a 245/40R19 tire costs more than 245/45R18, it doesn't make sense to me, but it's very consistent across all tires and brands I've ever looked at.

I believe it's because the tire manufacturers have to design the beads in a larger diameter which uses more materials, and have to use even more materials to stiffen the sidewalls since there is obviously less of it. I have quite a few sets of tires where the smaller 275/35/19 are 3 pounds heavier than 275/40/17 firehawk indy 500 tires even though it is a smaller tire.

 

[gearchruncher]

and have to use even more materials to stiffen the sidewalls since there is obviously less of it.

This is not how physics works.
If you only want 10 mm of deflection, the taller the sidewall, the stiffer the sidewall needs to be. A beam does not get smaller and lighter the longer you make it for a fixed deflection at the end of the beam.

The larger bead diameter is what drives cost, as well as simple supply/demand/marketing. Not everything in the world is priced at cost+fixed markup.

 

[Sam1]

This is not how physics works.
If you only want 10 mm of deflection, the taller the sidewall, the stiffer the sidewall needs to be. A beam does not get smaller and lighter the longer you make it for a fixed deflection at the end of the beam.

The larger bead diameter is what drives cost, as well as simple supply/demand/marketing. Not everything in the world is priced at cost+fixed markup.

Disclaimer: I'm absolutely not an engineer, but the sidewalls on the 17" tires I referenced are absolutely thinner than the 19" of the same brand. All of mine are currently mounted or I would gauge them out to get a specific number to show you. The beam you refer to, doesn't rely on an additional variable like tires do (compressed air) as well. If the tires did not require air, then yes, the beam analogy would be spot on.

 

[gearchruncher]

The beam you refer to, doesn't rely on an additional variable like tires do (compressed air) as well. If the tires did not require air, then yes, the beam analogy would be spot on.

A useful logic method can be to take things to extremes. If larger sidewalls require less material to achieve the identical stiffness and function as shorter, fatter sidewalls... At some point your sidewall can be infinitely thin, weigh infinitely little, and be infinitely long. I don't see a lot of high aspect ratio truck tires out there with super thin sidewalls.

Tires with higher aspect ratios are not trying to achieve the same goals as lower aspect ratio tires, even if they are the same brand or even model. Lower aspect ratios tend to be performance oriented, higher comfort. I'd expect less stiff sidewalls on those tires for that reason. Engineers tune tire designs to this. Tires of the same model don't even always have the same tread patterns at different widths or aspect ratios.

There's way too much going on here to be sure that the only reason sidewalls are thinner on higher aspect ratio tires is because it actually requires less material for the same stiffness.

Also, remember that PSI acts on area- and the hoop stress in a tire comes from circumference and width. These do not change with sidewall size. I don't yet see how air pressure acting on additional sidewall area makes the sidewall stiffer in lateral loads. The air pressure doesn't resist this motion at all as it does not change the volume of the tire.

 

[jackmott]

Moving up to larger diameter wheels, all else remaining constant (same tire model, same tire outter diameter etc) has a small performance improvement when cornering for reasons more complicated than "stiffer sidewall". This effect is barely even important when racing. In that it isn't the first thing you worry about. You first worry about which model of tire is stickiest, and then you worry about how much tire you can fit. It is kind of rare that you even have a lot of option on what wheel diameter you can use among the best tire compounds and widths you need.

For non competitive driving I would never consider it. It is just a looks thing with quite a few negatives. Easier to damage wheels, total package tends to be heavier, ride tends to be bumpier.

 

[Sam1]

Moving up to larger diameter wheels, all else remaining constant (same tire model, same tire outter diameter etc) has a small performance improvement when cornering for reasons more complicated than "stiffer sidewall". This effect is barely even important when racing. In that it isn't the first thing you worry about. You first worry about which model of tire is stickiest, and then you worry about how much tire you can fit. It is kind of rare that you even have a lot of option on what wheel diameter you can use among the best tire compounds and widths you need.

For non competitive driving I would never consider it. It is just a looks thing with quite a few negatives. Easier to damage wheels, total package tends to be heavier, ride tends to be bumpier.

The best way I've heard it described is that the taller sidewalls are more forgiving. The break point of traction is very acute on low profile tires, and taller tires has more of a buffer zone for lack of a better term. This is for course driving though, as on the strip it's completely different since you need taller tires with low pressure and the ability to wrinkle to increase the contact patch size even further.

 

[jackmott]

Fair point I didn't even think about drag racing, not that it seems like our cars are such that it matters it all for that.

A wider range of moderate slip could be more fun and safe for the street too.

 

[Sam1]

Fair point I didn't even think about drag racing, not that it seems like our cars are such that it matters it all for that.

A wider range of moderate slip could be more fun and safe for the street too.

it really doesn't matter on our cars. I've ran everything from 18" soft 200ta tires to 20" Pirellis and PS4S, and the fastest straight line times I clocked were on a set of 235/40/19 OEM all season continental contipro rx or tx (whatever they were).

 

[jackmott]

it really doesn't matter on our cars. I've ran everything from 18" soft 200ta tires to 20" Pirellis and PS4S, and the fastest straight line times I clocked were on a set of 235/40/19 OEM all season continental contipro rx or tx (whatever they were).

Yeah if I was going to the houston drag strip which is sticky as hell I'd look for some 205s with super low rolling resistance or something. Gain some aero and rolling resistance time once you get going fast.