Video: Is smaller better when it comes to wheel size?

https://www.youtube.com/embed/1aEX5dD1IT0

Bigger might be better when it comes to fast food combo sizes, but can the same be said of wheels?

Here’s why we downsized the wheels on our 997 Porsche 911 project car from 19 inches to 18 inches.

Presented by CRC Industries.

MadScientistMatt
MadScientistMatt UltimaDork
4/2/23 7:58 p.m.

This seems like a category where there should be a just right size, and either bigger or smaller would slow you down. Older cars often had wheels that were too small for maximum performance, but it wouldn't surprise me if a lot of newer cars made their wheels too big.

LanEvo
LanEvo GRM+ Memberand Dork
4/3/23 12:42 a.m.

I've tested 15-, 16-, and 17-inch wheels on my racecar (Mercedes 190E 2.3-16) and found 15" was clearly faster. This was mainly down to a smaller overall tire diameter, which was a better match to the trans/diff ratios. There's also a significant savings in weight and tire costs. 

wspohn
wspohn SuperDork
4/3/23 10:14 a.m.

Adding unsprung weight is never the best way to go in terms of handling. The big wheel movement is style driven, not performance oriented.

Older cars had some odd choices - V8 powered cars with 13" wheels that didn't have room for adequate brakes and such.  Today we go overboard the other way .  Is there an ideal compromise size? Maybe 15", maybe a bit larger, but no one needs some of the huge wheels chosen for fashion rather than performance that we see today.

AngryCorvair (Forum Supporter)
AngryCorvair (Forum Supporter) GRM+ Memberand MegaDork
4/3/23 10:27 a.m.

brakes should be sized for vehicle weight, intended usage, and maximum speed.

wheels should be just big enough to clear the brakes.

fight me.

MauryH
MauryH GRM+ Memberand New Reader
8/11/23 1:55 p.m.

Another advantage of 18s vs 19s I found on my Cayman is the car is at least a half inch lower with the 18s which would lower the center of gravity a bit and thus seems to improve cornering. Partly tires since the 19s are 40 and the 18s 35 aspect ratio, but mainly wheel diameter...I think.

PT_SHO
PT_SHO New Reader
8/11/23 3:05 p.m.

If you aren't tied up in PCA events where they demand exact rim and tire of the as-delivered vehicle, then changing the tire / wheel size to improve your final drive gearing is one way to go. But your car may seem faster only because a smaller total height improves torque while it increases highway RPM. 

Changing total tire+wheel height and/or final drive ratio can actually muck with the car's computer as it senses the speed isn't "right" from comparing GPS speed with wheel RPM's, that can be a nasty surprise.

The rim protectors being sold as tires in 20, 22, etc are solely style driven.  And the tires are so short that they don't even do a good job of rim protecting.  C&D long term tests regularly show wheel replacements due to road damage.  I could tell the ride difference when I did back to back tests of an SUV with 17 vs. 18.  Now they are mostly 19 or larger. frown

A shorter tire height, all else equal, will usually mean quicker response though not necessarily better cornering.  That depends on camber control not allowing the shorter, stiffer side wall to roll so far that the tire footprint is compromised.  If a competitive tire in the same model is sized to retain the same total height and tread width, then compliance will be improved, weight of total assembly will be reduced, and results will usually improve.  But as tested here people usually _also_ change wheel widths so that's not an apples to apples comparison.

84FSP
84FSP UberDork
8/11/23 4:47 p.m.

Relevant factors are always weight, rolling diameter to move gearing or maintain, and width.  A smaller heavier wheel is not better in general.  A wider, taller, and lighter wheel could actually be better.  Generally the lightest, widest, smallest setup is best if this is autox.

VolvoHeretic
VolvoHeretic GRM+ Memberand Dork
8/11/23 5:55 p.m.

Taller no, wider YES!laugh

CrustyRedXpress
CrustyRedXpress GRM+ Memberand Dork
8/12/23 8:09 p.m.
LanEvo said:

I've tested 15-, 16-, and 17-inch wheels on my racecar (Mercedes 190E 2.3-16) and found 15" was clearly faster. This was mainly down to a smaller overall tire diameter, which was a better match to the trans/diff ratios. There's also a significant savings in weight and tire costs. 

Not surprised at all, but awesome to see it tested.

I remember the 2.3-16v's power band being relatively high in the revs and peaky...but also that the stock gearing allowed something like 145mph top speed.

Did you ever test a 14" wheel? Alternatively, can you swap in "shorter" gearing either for the Getrag or the rear diff?

DavyZ
DavyZ New Reader
11/16/23 7:17 p.m.
wspohn said:

Adding unsprung weight is never the best way to go in terms of handling. The big wheel movement is style driven, not performance oriented.

Older cars had some odd choices - V8 powered cars with 13" wheels that didn't have room for adequate brakes and such.  Today we go overboard the other way .  Is there an ideal compromise size? Maybe 15", maybe a bit larger, but no one needs some of the huge wheels chosen for fashion rather than performance that we see today.

Well said. Agreed.

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