Tires - How Narrow Should I Go?

[Vladi]

I have an 89 integra, it is pretty light (around 2300 pounds) I picked up some 13" wheels and I am trying to decide on what size tires to go with. I don't want to lose much gearing. Currently the tires are 195/65-14, so if I go with an 80 series I can retain most of the diameter. I was looking at 175 and 165 widths, 155 seems really narrow. How narrow can I go without severly comprimising the cars ability to corner with speed? I don't want to hurt my coasting ability! Those of you who have switched to narrower tires, did you see much improvement?

[theholycow]

Congratulations, you're the first recipient of my new tire width canned post...

Tire Width vs. Rolling Resistance
A canned post by theholycow

It is commonly thought that narrower tires have less rolling resistance and a smaller contact patch. This is not entirely true. They do offer weight and aerodynamic advantages, though.

Given that everything else is equal (construction, materials, tread pattern, air pressure), the wider tire will have LESS rolling resistance. Rolling resistance comes mainly from sidewall deformation -- look at where the tire meets the road, it's partially flattened instead of perfectly round, and the sidewall bulges to make that happen. Comparing most car tires, tread squirm should not make much difference in RR, though knobby off-road truck tires might have more.

Now, on to why wider tires have less RR. The contact patch size is determined by the weight on the tire and the pressure in it. At 50psi (pounds per square inch) with a 500 pound load, that's a 10 square inch contact patch. If that tire is 5 inches wide, it will have a 2 inch long contact patch -- so only 2 inches of sidewall must deform. If the tire is 2 inches wide, it will have a 5 inch long contact patch -- so 5 inches of sidewall must deform. The narrower tire in that extreme example will have far more RR.

How and why did I learn this? I was an avid member of rec.bicycles.tech and a bicyclist with tired, achy legs. When it's your own legs, sweat, and pain on the line, it becomes much more important to really understand and reduce losses than when it's just fuel economy. There's some very knowledgable folks on that newsgroup who have done the in-depth scientific research about things like this. On a bicycle the narrower tire is usually rated for higher pressure, so it ends up with equal or better RR anyway. On a car, that's not usually the case.

The other advantage for wider tires is better cornering, so you can carry more of your momentum through the corner.

Also of interest when choosing tires: http://www.miata.net/garage/tirecalc.html

[FLAteam]

so you're looking for 13 inch tires? I just got some kumho power stars 155/80R13 for $30 each at Discount Tire/America's Tire Co. (they're currently on sale) and I had a coupon for $25 off. I put them on my 13 inch Civic VX wheels.

I guess I woulda went with the 175/70R13, but they were $10 more, so $40 more all around. Also, the 175's weigh 2 lbs more than the 155s each, so it helps on that front.

[civic94]

my 94 coupe weighs about 100 pounds lighter than your teg, and used to have 175 series on them, the brakes were great. then i bought vx wheels that had the 165 series on it, and it felt very different. i was in traffic and i slam on the breaks, but this time the tires were screeching the road alot faster than the 175 series, and the stopping distance felt alot farther.

i then replaced the tires to 175 series on the vx rims.


the good thing about the 165 was that my car felt i had power steering on a dead stop

[theholycow]

Originally Posted by civic94

used to have 175 series on them, the brakes were great. then i bought vx wheels that had the 165 series on it, and it felt very different. i was in traffic and i slam on the breaks, but this time the tires were screeching the road alot faster than the 175 series, and the stopping distance felt alot farther.

10mm, that's less than half an inch difference in width. If you stopping power was strongly affected, it was most likely due to different tread, different pressure, different compound, and/or different wear...not different width.

Actually, among those, it was most likely the different compound at fault.

[fumesucker]

Originally Posted by theholycow

Congratulations, you're the first recipient of my new tire width canned post...

Somehow I had already read that on the forum but I do want to say that it is a very nice and informative post.

I had never thought of tires that way before but what you say makes eminent sense, it has "The Ring of Truth"..

[theholycow]

Originally Posted by fumesucker

Somehow I had already read that on the forum

I canned it from components found in other posts I've made on the subject. It's still a little rough around the edges; for example, the bit about tread squirm needs to be moved or re-written, it doesn't quite fit where it is.

Thanks for the compliments.

[GasSavers_BEEF]

so lets say someone (like myself) wanted to purchase some LRR tires. is there a rating for that? how would you go about asking a sales man about it?

new to the LRR thing so sorry if it is a stupid question.

[Vladi]

Thanks for all the response! I guess the next logical question when it comes to fuel mileage is - LRR tires vs more aero friendly narrow tires, and how much does rolling resistance still come into play at high inflation, 50 - 60 PSI?