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CorollaMaster 04-27-2008 03:51 PM

Wheels - Large or Small Diameter? Width?
Hey all,

I'm new to this, but I was wondering what is better:

- Larger diameters or smaller diameters?
- Larger or smaller tire widths?

My first guess is that a larger rim with smaller tires and smaller width would be best for rotational inertia of the wheels. But then again are you losing more energy trying to get the larger diameter accelerating in the first place? :confused:

I was also wondering if anyone knew of a company that makes good light weight rims that might make a difference? or is it better to go with the run of the mill black and some flat hub caps? :cool:

I'm also considering wheel skirts. My friend works in autobody and is willing to help me out so that they look somewhat professional. One step at a time I guess. Thanks in advance for the help!

toomuch 04-27-2008 04:31 PM

By better, I assume you mean more efficient. The smaller the width of the contact patch (tire), the more efficient.

When I had 175 MM contact patches at each corner, I had better average fuel economy than my current 185 MM width tires. (I do a lot of highway driving)

My technical knowledge regarding about diameter not impressive, but big tires take more energy to get moving. Smaller tires take less. Think of those little go kart tires. Easy to get them moving, but you are more limited in speed and are more dependent upon changing gears.

Forged rims are very lightweight, but cost a lot of money. If you are lucky, maybe you can find some small, discontinued set for $100 per rim. Usually the aerodynamic profile of these rims are the complete opposite of aero hubcap covers. These rims will be much stronger than steel rims. Good brands that i know of are BBS & SSR.
Use google for more. (not entirely sure those links will work)
Hope that helped :)

guitarterry 04-27-2008 04:37 PM

Some general rules?
Contact patch is derermined by air preasure A 22" tire at 32 psi has the same contact patch as a 12" tire at 32 psi
Reciprical weight weighs 10 more. i know this sounds funny. but it takes alot more to stop or start a tire than to say just lift it. Sprung weight is also more than non sprung weight. but that difference is for handling as opposed to mpg
So I guess tires have four variables, weight, aero, rolling resistance, and final drive ratio. those little 12" tires make weight and aero go down. rolling resistance is a smaller variable. then a person can use gears to make the final drive ratio back up. The best tire would be an extremely skinny and big around tire, like a bike tire. unfortunately as the diameter gets bigger, the width and weight gets bigger, and those two overly outweigh the diameter advantages

CorollaMaster 04-27-2008 04:53 PM

Thanks for your replies!

So it looks like trying to lower the contact patch is the best way to go with the tires.
I've also been doing some googling after toomuch's post and it seems like finding low RR tires is the way to do that. Another question that popped into my mind on the same topic is:

If I were to keep the same overall diameter of my current wheel base, which would be more efficient - larger diameter or smaller diameter lightweight rims?

I'll obviously try to keep the width as small as possible with low RR tires and correct pressure, but I'm trying to figure out what size rims would be the most beneficial efficiency-wise?

My hunch is that if you have something that has a good rotational inertia then it would be bad for starting and stopping but really good for steady highway driving.

Guitarterry - what did you mean by the reciprocal weight?

guitarterry 04-27-2008 05:12 PM

rotational weight. again the width of the tire and also the diameter of the the do not affect the contact patch. weight and air presure do. for an example, if you had a 3000 lb car and 30 psi in your tires the contact patch will be the same size no matter what tire u use 22" down to 12". Actually its an old racers trick. You can weigh your car by going out and using paper and a ruler. here is a link

toomuch 04-27-2008 05:12 PM

skinnier tires certainly have a disadvantage, less traction! Traction is also related to the tire compund and tread pattern, but the less of it you have on the road, the less traction you are going to have. So I wouldn't go too skinny, its better to not loose control of your car.
I definitely don't know everything or close to it about this subject, so keep on your quest!
As for your diameter question, I don't know. You could get the weight measures for a certain tire and wheel setup and see which weighs the least. Let us know, I am curious. I have done a little of that myself, but I forget what the result was.
Not sure about your hunch other, maybe someone else is.

Good luck!:D

toomuch 04-27-2008 05:13 PM


Originally Posted by guitarterry (Post 21848)
You can weigh your car by going out and using paper and a ruler. here is a link


guitarterry 04-27-2008 05:30 PM

see toomuch, its a common mistake to think tire size affects tire patch. and some of your statements are wrong. Its a common mistake. But hard to fix once people get it in there head.

toomuch 04-27-2008 05:42 PM

GuitarTerry, thank you for keeping the forums straight. You are right, I do not fully understand all of the workings of the tire and wheel. I understand that the tire pressure affects the form of the tire, and is what holds up the vehicle. But shouldn't a Corvette tire, with a 245MM width have a larger contact area than my 185MM wide tire corolla within reasonable pressure amounts? (& maybe i am still wrong, & still am not getting something!) could it just be that the patch is wider and not as long?
My experience with tire width and pressure is that at 175mm i could get 39mpg, and now with the 185mm s i get 35 mpg. There must be some other factor. Pumping up the PSI on the 185s from 33 to 35 has netted me about 1-2 mpg on average. the 175s were kept between 33 and 34.

Maybe you might want to check this out:
I love that site, but I haven't read that article lately. Don't have time to now either. Cya

guitarterry 04-27-2008 06:12 PM

the contact patch of the two tires u mentioned would be the same on the same car, with the same psi. how the tire reacts is where the difference is. eg, the 245 tire would be more stable because it is wider. There are lots of other factors. but Thats for a different thread. Now for your mpg statement. did you factor the different diameters of the tire into your mpg figures. if you dont adjust the figures the 175mm at 39mpg is probably the same as the 185mm at 35mpg

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