Need help buying tires , 55 to 50

I have no idea on your questions regarding tires.

Your '50' or '55' is an aspect ratio, not a diameter. If you knew the actual rollout (loaded circumference at proper pressure) you could know the difference between them for rotations per mile or per engine speed etc. But you don't.

1. Go to tirerack.com. They are honest, their prices are good. The customer reviews are doubtful because they are often made by people who have just changed from a failed tire to a new tire and are impressed with the improvement.
2. Tires with directional tread look like they have directional tread. If you see a V shape or you see a center rib, it's a directional tire. I like directional tread designs; they perform much better on wet roads. Yes, they limit your ability to easily rotate tires.
3. TPMS reset on many newer cars requires plugging in an OBD-II tool and telling the computer there is a new tire. Not a huge deal, but a thing worth billing for.
4. The difference in noise between different tires is substantial, but tires sold as "quiet" aren't necessarily quieter. If you drive a very quiet car where the tire noise is one of the worse noise sources then you might worry about trying different "quiet" tires. Note that the customer ratings about noise on tirerack bear no connection with how noisy the tire is.

--scott

There are online calculators where you can put in two tires of different aspect ratios and see what the effect on the speedometer is.

On 4/4/2020 6:14 AM, micky wrote: ...

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Aspect ratio gives profile and is ratio of sidewall section height to section width...but the overall diameter is

Doverall = Drim + 2*Hsection

So the ratio of the two tires is

(Drim + 2*Hsection)/(Drim + 2*Hsection*55/50)

Well, this is simple w/ MATLAB which is open in other window...

So there's only roughly a 3% difference in overall diameter instead of

All in all, it doesn't matter enough that you'll notice it other than, perhaps, the lower profile will drive and ride a little more stiffly. Whether you'll actually notice unless you drive the vehicle very hard is doubtful.

Why there's so much difference in price I've not looked at at all...more marketing than anything else one would suspect.

Nice drawing/explanation at

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On 4/4/2020 9:30 AM, dpb wrote: ...

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Sorry, missed a fixup on renaming the overall diameter anonymous function...in last section...

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On 4/4/2020 9:30 AM, dpb wrote: ...

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Just noticed was 215, not 225. Minimal difference but for the record...

Of course, but it helps you to calculate the nominal diameter. The formula is simple:

rim diameter + ((tire width * aspect ratio as a percentage) *2)

Converting the 17" rim diameter to mm, you get 431.8 ((215 * .50) * 2) = 215

((215 * .55)) * 2 = 236.5

Now you can compare 646.8 to 668.3.

All of those are nominal values. Production differences will cause some variation, not to mention wear as a tire is used.

In 1982, shortly after buying my first computer, a Commodore64, the first BASIC program I wrote was a tire size calculator. In that version, I used a lookup table to convert the letters that were used to indicate aspect ratios, but these days it's all just numbers so it's even easier.

You should be able to -

You really need to ask that question????

Not if you turn off your hearing aid or turn up the music.

Learn to read your speedometer??

No. it is an asymetric tread. Asymetric treads are NOT directional, generally speaking.

Actually he does - he gave you the math. they are both 215 section width, and both 17 inch diameter, so the difference is as he said

Nothing is going to be "quiet" in an old solara convertible - - --

most cars - so is produced inhnigher numbers. That is OFTEN how pricing works out. If a tire size is uncommon - used OEM on only a few models - particularly low selling models - the tire will be more expensive (and less likely to be in stock)

On 4/4/2020 3:38 PM, Clare Snyder wrote: ...

Ya think!!??

The Enclave has 19" -- didn't even think to look when purchased; it was a program car at a good discount so just took the one with the lower mileage. Ruined an almost new Michelin within a month; the replacement was >$400 almost 10 years ago now. The 17" comparable was about half...

I look carefully at what rims are on vehicles now!!!

The letter was carcass sise - you still had a number for aspect ratio. I remember L78 15, C60-13, and G70-14 being pretty common

And the 18" would likely have been a buck or 2 less than the 17.

Oh yeah, brain fart. Thanks for the correction. I remember L78's and G70's, and a friend had a '55 Chevy with N-something's on the rear. Quite wide.

I'll get back to you about individual replies but I see a tire store here advertising rim seals for $15/tire but I can't find anything about them with google.

They're closed now but do you know what rim seals are.

Actually, 20" were significantly less than the 19" as well...

Likely the seal dor 3 piece rims there is the inner rim, the outer rim, and the center - also called "modular " rims. they can be reconfigured for different widths and offsets.