Does sidewall height affect performance? 40 vs 45 series.

[flatwerx]

Does sidewall height affect performance? 40 vs 45 series.
I’m getting the SQ ready for some wheels and tires. Lots of road trips, some dirt roads, all over the US/North America.
I’ve been looking at 20x10.5 wheels with some 295/40r20 tires but kinda like the idea of a 19x9.5 with a 285/45r19.

Does sidewall height between a 40 and 45 series tire affect performance in any kind of major way? I understand there is a bit more deflection but is it really a huge deal breaker?

[snolvr]

I would venture to say no, unless you really like to push the car through the twisties. That's where you might feel the difference as the tire deflects. But the nice thing about a 45 sidewall is more wheel protection and a slightly more comfortable ride.

[Smac770]

More wheel, less sidewall vs less wheel, more sidewall. Of course it'll impact the responsiveness, harshness, directness, whateverelseness. Enough that you'll notice? Who knows. I remember a Tyre Reviews video from a ways back where the less wheel, more sidewall config did better in the wet. But that's test results. In the real world, you're probably going to wreck or not wreck all the same.

[flatwerx]

Appreciate the info guys.
@snolvr I just left the Denver area to Montana. With the twisties we have in CO/MT, and some of the dirt roads we can camp on with the SQ5, how do you think a 45 series will be?

[Norskie]

If you're going off-pavement the taller sidewall will be appreciated and you'll likely not notice a difference on tarmac.

[Boldkitty]

Also, a tire/wheel that is taller slows acceleration and raises top speed. A shorter combo does the opposite.

[lumberwood]

Don't you need to maintain the same overall wheel diameter to ensure accurate speedo reading, regardless of wheel rim diameter or tire sidewall height? So if a 45 sidewall, you'd need a slightly narrower tire vs a 40 sidewall, to maintain exact overall wheel dia.
True or false?

[5000S]

Don't you need to maintain the same overall wheel diameter to ensure accurate speedo reading, regardless of wheel rim diameter or tire sidewall height? So if a 45 sidewall, you'd need a slightly narrower tire vs a 40 sidewall, to maintain exact overall wheel dia.
True or false?

You need to know the real tire diameter, not wheel diameter. It does not matter what wheel size, it could be 14" to 21", and it could have the same
diameter, tire, wheel combination.

A good site for this is Miata, the combos are all there. This is not rocket science.......

Audi speedos are commonly wrong, with the real world. I have found many can be approx. 3% off with a factory wheel tire size.
They usually read too high for the true ground speed, measured by GPS. ie. speedo shows 60 MPH, true speed is 58.
This is from my own experience.

[Norskie]

Don't you need to maintain the same overall wheel diameter to ensure accurate speedo reading, regardless of wheel rim diameter or tire sidewall height? So if a 45 sidewall, you'd need a slightly narrower tire vs a 40 sidewall, to maintain exact overall wheel dia.
True or false?

https://www.willtheyfit.com/ will show you how much the speedo will be off.

[lumberwood]

You need to know the real tire diameter, not wheel diameter. It does not matter what wheel size, it could be 14" to 21", and it could have the same
diameter, tire, wheel combination.

A good site for this is Miata, the combos are all there. This is not rocket science.......

Audi speedos are commonly wrong, with the real world. I have found many can be approx. 3% off with a factory wheel tire size.
They usually read too high for the true ground speed, measured by GPS. ie. speedo shows 60 MPH, true speed is 58.
This is from my own experience.

That's what I meant, we're saying the same thing. In my head, tire + rim = wheel. Thus, overall wheel dia. though overall tire works too since the tire is the outer most component in the measurement.

Thanks for the link, Norskie.

[mys4.org]

Something to keep in mind, there are few if any non-drifting races series that use extremely low profile tires. The construction of the tire is vastly more important than the tire profile height. In my mind if you have a really low profile tire it is unable to absorb road imperfections meaning it bounces and does not maintain good contact with the road. A taller profile tire to a point will absorb and keep better contact with the road. Obviously a extremely tall profile tire the sidewall will roll and that can creates another problem for responsiveness, but that comes down to the preference to the driver... . The point to all of this a lowest profile tire possible does not equal better performance on its own. I would always error on a taller tire simple to offer more protection to my wheels as long as the overall diameter is near oem spec.