Tire questions..would this be a possibility?

Got 2 older vehicles,one is a 92 Caravan and one is a 92 Buick Century.Both vehicles have 14 " rims for the tires.The tires on the Caravan are P195/75R14 and they are worn down already.Going to park the Buick Century probably for good,but had brand new Goodyear Allegra tires installed last fall.They are hardly even used and they are P185/75R14 tires.They are slightly smaller in diameter.Was thinking of putting them on the Caravan rims and running them.Wouldn't have to put out over $500 for new tires and trying to sell the Goodyears for maybe half the amount I paid for them.
Being that the tire may be about 1/2" less in diameter,that means when the speedometer is showing 100km/h ,you may be going 5 or 10 km/h slower.That is no problem.Not really sure how much difference there would be.Does anyone have an idea how much difference.
One way is to run my truck at 100km/h and have the Caravan ride along side and see what the speedometer reads.At least I will not be going over the speedlimit.
The Caravan will be for my wife to use for work.It is actually her dads van.It only has 111,000 km's on it and no rust at 15 years of age.
Another question also.Is there an adapter you can buy that will convert side posts on a battery to accept cables that are used on the top posts.Battery is new in the Buick,but with side posts for the cables.The Caravan needs a new battery,but it has cables to go on the top posts of a battery.Must be a way,maybe a splice and connector.

yes they do make screw in battery posts, napa here in the states has them. Run the tires, they won't be off but maybe 2 to 3 mph. Paul

maxdlx said:

yes they do make screw in battery posts, napa here in the states has them. Run the tires, they won't be off but maybe 2 to 3 mph. Paul

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Just curious Paul why would the tires run 2-3mph off???? I always thought the first # was just the width of the tire, second # is height tire from rim to top of tire, then third # was rim size. What am missing, cause Im curious.

the reason the tires will be off is because the sidewall or aspect ratio of the tire goes off the tread width , so just because they are both 75 series tires the 195 series will be slightly taller then the 185 series is.
Another way to explain it is this, the 195 series tire has a sidewall height thats 75% of the tread width(195mm), so the tire that only has 75% of 185mm would be shorter.

The first number is your tread width

The second number is your sidewall aspect ratio, so a 50 series tire is shorter then a 75 series tire.

The third number is rim diameter.

I can still use the new tires then,they will be about .59 " smaller in diameter and about 1.86" less in circumference.
Check this out:
www.car-videos.com/info/tirespecs.asp

Yep mrviper you are correct,2nd # is a pecentage of the width which is the 1st number.In my case the 195/R75/14 sidewall height is 146.25mm.The 185/R75/14 sidewall height is 138.75 mm.That is a difference of 7.5mm or about a good 1/2".Could someone on here maybe figure how to calculate what the speed difference would be between the 2 tire.On the site I mentioned above ,there is a formula,but I can't figure it out.

go ahead and use them. the spedo will be out about 5kph. just do not tell the wife. will stop her from getting speeding tickets.

mrviper700 said:

the reason the tires will be off is because the sidewall or aspect ratio of the tire goes off the tread width , so just because they are both 75 series tires the 195 series will be slightly taller then the 185 series is.
Another way to explain it is this, the 195 series tire has a sidewall height thats 75% of the tread width(195mm), so the tire that only has 75% of 185mm would be shorter.

The first number is your tread width

The second number is your sidewall aspect ratio, so a 50 series tire is shorter then a 75 series tire.

The third number is rim diameter.

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Thanks for clearing that up for me Don.

I didn't think it would be an issue.Wife will have a better holeshot now...LOL

The speedo with be off by the same percent as the reduction in tire od. Buick tire od/Caravan tire od * speed

So that should work out to about 2 mph roughly then.

Well guys,got my tires switched from the Buick to the Caravan.Bought a tire changer for $60.00.Works like a charm.Dismounted 8 tires from the rims and installed eight tires back on to the rims.Swiching from a Buick to Caravan rims.Took me about 4 hours to complete everything.When I got time I will take the Caravan to a construction area(Hwy Project) on the perimeter of the city where they have one of those radar speed moniters that tells you your speed.Will check to see how much I really am off with that and that is it.

bluemonster1 said:

Well guys,got my tires switched from the Buick to the Caravan.Bought a tire changer for $60.00.Works like a charm.Dismounted 8 tires from the rims and installed eight tires back on to the rims.Swiching from a Buick to Caravan rims.Took me about 4 hours to complete everything.When I got time I will take the Caravan to a construction area(Hwy Project) on the perimeter of the city where they have one of those radar speed moniters that tells you your speed.Will check to see how much I really am off with that and that is it.

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Look this is very, very simple. Just think about it. Here are the facts.

# 1 (MOST important) The wifes going to be driving it right?

# 2 If you put smaller diameter tires on a car than what it came with it will actually be going SLOWER than what the speedometer is reading. (reread this one untill you get it)

# 3 The wifes going to be driving it right?

# 4 Women have no idea what the relationship is between tire diameter, speed and speedometer readings.

# 5 The wifes going to be driving it right?

# 6 Women have a tendency to push the limits on everything and NEVER see cops untill it's to late.

# 7 The wifes going to be driving it right.

# 8 When she thinks she is pushing the limits she will probably only be doing the speed limit. (you lucky dog)

The bottom line is put them on, DON'T check the odometer, tell her little tires get better traction in bad weather and are safer but everything else will be EXACTLEY!!! the same and count your blessings.

"I just saved alot of money down at the court house by switching my wifes tires to LITTLER ones AND my insurance went down TOO"
Phil (opsled)

smaller or bigger...what do women care..lol

The thing is ,my wife never speeds,she always drives under the speed.So maybe I should have put on bigger diameter tires....to keep her on par with the speed limit...LOL

bluemonster1 said:

The thing is ,my wife never speeds,she always drives under the speed.So maybe I should have put on bigger diameter tires....to keep her on par with the speed limit...LOL

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Congradulations, You got a rare one. Hang onto her!!!

Good Luck, Phil (opsled)