[LITEMUP]

first: whats the best way to describe to uneducated people the difference in the weight and viscosity of motor oil. i work at a "tire and lube" and half way know the diff. but not all the way. for example 15W-50 vs. 10W30. i know they have different heat ranges, and they have a different weight, but doesn't the combination of numbers mean that the 30 weight oil will act like 10 weight when its cold or something?

second: i know that the way you read a passenger car tire....ie: 205/55R16...means the width is 205 cm, 55% of the width is the sidewall, and 16 is the rim size. however, i had a 205/55R16 and a 205/60R16 sitting right next to each other today, and the 55 series was wider. i thought the second number had nothing to do with the width. isn't the technical name for it called the aspect ratio?...im confused.

[neuralyser]

I was always under the impression that "205/55 R16" for example spelt a low profile, and that related to the 55 bit and that number as you say had no relevance to width...but I'm no expert.

[dave-r]

Both tires should have a tread width of 205mm. One should not have a wider tread than the other.

You are also right that the '55' means that the sidewall height is 55% of the tread width.

So that 60R should be slightly taller than the 55R but that is all. They should be the same width.
If they are different makes of tire it could be that they measure the tread width from a different starting point? Some tires have a tread that extends around onto the sidewall.

[dave-r]

Forgot about the oil question.

Originally oils had one grade each. That is you used a light oil (say a 10w) in some applications (usually light delicate machinery with fine tollerences) and a heavy oil (say a 50w) in a more crude, heavy engine with greater mechanical tollerences and clearences.

Multi-grade oils were developed so that the different properties of light and heavy oils could be used together in the same engine. For a start the light oil is better at protecting an engine when it is cold. A heavy oil would be too thick. When the engine gets hot the light oil would be too thin to prevent metal to metal contact so the heavy oil is better.

I don't know enough about it to go into it but I can say that a 10w-30w oil is still a lot lighter than a 20w-50w oil. The lighter oil would be better in a cooler engine or one with tight clearences. A heavy oil is better in a hotter engine with loose or worn tolerences.

In general our american V8 engines from the 1960s and 70s are pretty crude and when modified get rather hot. A heavier oil is better for them unless you live in a cold area.

[LITEMUP]

i will take a picture of the tires. i swear one is wider than the other and they are both 205. both 16 inch rims, same model of tire and everything. so we'll see whats goin on.

[insuranceguy]

205/55/16

Sidewall=4.4 inches
Radius= 12.4 inches
Diameter = 24.9 inches
Circumf=78.2 inches
Revs/mile = 811.00

205/60/16
Sidewall=4.8 inches
Radius=12.8 inches
Diameter=25.7 inches
Circumf=80.7 inches
Revs/mile=785.0

If your speedo was set exactly for the 205/55/16 and you put the 205/60/16 on, your speedo would be 3.2% too slow. i.e. if it reads 60mph you would be going 61.9 mph.

Sorry I don't have the metric conversion..

Todd