Wheels: Smaller rims, taller sidewalls?

[CapriRacer]

Just an FYI:

There's been a lot of work about measuring RR in car tires in advance of regulations requiring publication of said RR values. One of those things is the difference between testing on a wheel vs a flat surface (rolling road). The result was that there was a very good correlation between the values. I can't seem to find the study on the internet, but I have notes from a conference I attended.

In other words, when it comes to testing RR in car tires, it doesn't matter whether the tires are tested on a flat surface or a large diameter wheel, the values are proportional.

[MeteorGray]

The pothole factor is one of the reasons I went to 65 aspect tires v the OEM-supplied 60 tires on my Mazda3. I'm now riding on 20565R16 Ecopias. They're working well.

[cRiPpLe_rOoStEr]

Originally Posted by basjoos

Going to a taller sidewall means you are less likely to dent your rims when you hit a pothole.

This, and the fact that 13" tyres used to be considerably cheaper than the 14" ones, were the main reasons why my mom lurked about it a few months ago.

[litesong]

Originally Posted by hat_man

I believe mine are 5x114mm but I'm not sure about the center hub.

That's where I messed up. Got lots of used tires & wheels & they all fit nicely. Saw one spare, but never used tire mounted on a 5 by 114.3 mm bolt pattern wheel & 40mm offset, just like I needed. Got it for $30. A week later, I REMEMBERED that I FORGOT to measure the center hole. Needed a 67mm center hole, but the wheel was 62mm. Oh, well. I can still use the tire, if I can't find a Lexus buyer, who needs a spare wheel/tire combo.

[litesong]

Originally Posted by Ecky

....BMW i3 tires: 175/55r20 - tall, narrow, use LRR compounds.....

From another thread, but more appropriate here, with additions:
Years ago, I uprated my 175x70x14 inch short wheels/tires to used 205x65x15 wheels/tires, which are about 8% taller than the 14's. Tho the aspect ratio(middle number) of the tires is "less", the 205 tire width, coupled with the aspect ratio, still gives an 11mm longer sidewall length, which handles the potholes better. My ride is wonderful with the 205s.
However, influenced by this thread in part, I continued to look for used 14 inch tires that were as tall as my 205x65x15 inch wheels/tires, because I kept the 14inch wheels.
Hey, I finally found a used 195x75x14 inch tire that is as tall as my 205x65x15 wheel/tires. The aspect ratio gives an additional 13mm sidewall length to really help on the potholes. Hope to find another 195x75x14 inch tire, but now I can use a 15 inch wheel/tire with the 14 inch wheel/tire, if necessary.

[Vekke]

In the ID3 155/70R19 were about 4% better in efficiency than stock 215/55r18 tires. Both were with fully blocked air cooling holes. 215 were A on rolling resistance, but the narrow ones ony C.

Actually difference was higher as the tire deflectors were 60mm too wide for these tires and still the first test showed 4% improvement. After I tuned the deflector size to match the narrow wheels it ofcourse got even better results.

In this case I would say it comes from aerodynamic drag. As the RR of that tire is said to be higher than the oem tire size.

On the tests 215 were with 3,5 bar and 155 with 4,0bar tire pressures. On tire pressure tests done to the 215 size it did not help much with those tires at least to boost the pressure, but I wanted to compensate the worse RR figure with little bit higher pressure.

The 155 have 0,84% bigger diameter, that was not taken into account in the tests. Meaning savings are that much more better.
https://www.willtheyfit.com/index.ph...h=5&offset2=40

I had also spacers in the car to bring the more out where oem tire is.

[CapriRacer]

Originally Posted by Vekke

In the ID3 155/70R19 were about 4% better than stock 215/55r18 tires. Both were with fully blocked air cooling holes. 215 were A on rolling resistance, but the narrow ones one C.

OK, where did that 4% info come from?

If I use my RR by size calculator (Barry's Tire Tech), I get a 2.02% difference in favor of the 18".

[California98Civic]

Originally Posted by CapriRacer

OK, where did that 4% info come from?

If I use my RR by size calculator (Barry's Tire Tech), I get a 2.02% difference in favor of the 18".

I think he means 4% better and fuel economy, not 4% difference in RPMs. That's why he references blanking out the ventilation holes on the rims.

[cRiPpLe_rOoStEr]

Sidewall difference between the 155/70 R19 and the 215/55 R18 being less than one inch, it may eventually be worth to consider the lower sidewall could lead to fewer deformations at the exact instant of acceleration. But I still value the enhanced smoothness a taller sidewall may lead while driving in a harsher environment.

[CapriRacer]

Originally Posted by California98Civic

I think he means 4% better and fuel economy, not 4% difference in RPMs. That's why he references blanking out the ventilation holes on the rims.

I suspect this was a personal measurement, and I am wondering how valid it is. I asked the question to get confirmation.