Tire Size Questions

The stock tire size on my 1996 RMS is 235/70R15. The tire calculator tells me that the tires are 28" tall, 9.25" wide, and the sidewall is 6.48".

The stock tire size on my 1996 RMW is 225/75R15. The tire calculator tells me that the tires are 28.3" tall, 8.86" wide, and the sidewall is 6.64".

The stock wheels look identical. Are they?

Why are the stock tire sizes different between the wagon and sedan?

Are they interchangeable?

My new wagon with stock wheels actually has P205/70R15 tires. The tire calculator tells me that the tires are 26.3" tall, 8.07" wide, and the sidewall is 5.65". The speedometer reads faster as one would expect.

If I were to swap these tires with my sedan would they all fit? Would the longer taller sidewalls and tires from the sedan give an even better ride?

My son will soon be commuting 100 miles/day in the sedan and I would like to put the mileage on the tires from the wagon. Is a tire swap a good idea?

Thanks,

Russ

Those 205 70 15s are too small. They are FWD minivan tires. They will work, of course, but at the expense of higher revs, worse fuel economy, harsher ride, and degraded handling. I'd sell them on craigslist, and go with some larger tires. 235 75 15s are slightly larger than stock, fit perfect, ride great, and are available readily at many price points. I ran 235s on my wagons for over ten years.

The 75 series is narrower than a 70 series of the same Psize but the sidewall height is taller than 70 series. The engineers used different sizes to adjust weight carrying capacity and ride comfort vs handling, most people with wagons cared less about the handling hence the narrower tire size. Just use the tire sites calculators to keep the overall tire diameter the same when comparing different size tires if you want the speedometer to read correctly. Slightly wider than  stock wheels won't affect speedometer reading much but much wider wheels will lower the sidewall height enough to notice a small difference in mph. The lower the sidewall height, the harsher the ride is the usual result.

see correction in post below.

jayoldschool wrote:

Those 205 70 15s are too small.  They are FWD minivan tires.  They will work, of course, but at the expense of higher revs, worse fuel economy, harsher ride, and degraded handling.  I'd sell them on craigslist, and go with some larger tires.  235 75 15s are slightly larger than stock, fit perfect, ride great, and are available readily at many price points.  I ran 235s on my wagons for over ten years.

Would you use 235 75 R15's on a wagon with a 2.56 rear end?

Thanks,

Russ

just me wrote:

The 75 series is narrower than a 70 series of the same Psize but the sidewall height is taller than 70 series. The engineers used different sizes to adjust weight carrying capacity and ride comfort vs handling, most people with wagons cared less about the handling hence the narrower tire size. Just use the tire sites calculators to keep the overall tire diameter the same when comparing different size tires if you want the speedometer to read correctly. Slightly wider than  stock wheels won't affect speedometer reading much but much wider wheels will lower the sidewall height enough to notice a small difference in mph. The lower the sidewall height, the harsher the ride is the usual result.

A 75 and 70 aspect ratio in the same size tire are the same width. A 235/75R15 and a 235/70R15 are both 235 mm wide. The 75 and 70 are the aspect ratio, 75% of the width and 70% of the width = height so it does appear narrower but it is because of the height difference causing a optical illusion. If you are stretching a tire out far enough on too wide of a rim to cause it to lower sidewall height you are going to be disappointed in the ride and life of any tire from a $50 independent company or a $200 Michelin tire. Not to mention what it is doing to the integrity of the tire itself.
Not trying to offend you but I think you just got bad info on tires.

1tireman wrote:

just me wrote:

The 75 series is narrower than a 70 series of the same Psize but the sidewall height is taller than 70 series. The engineers used different sizes to adjust weight carrying capacity and ride comfort vs handling, most people with wagons cared less about the handling hence the narrower tire size. Just use the tire sites calculators to keep the overall tire diameter the same when comparing different size tires if you want the speedometer to read correctly. Slightly wider than  stock wheels won't affect speedometer reading much but much wider wheels will lower the sidewall height enough to notice a small difference in mph. The lower the sidewall height, the harsher the ride is the usual result.

A 75 and 70 aspect ratio in the same size tire are the same width. A 235/75R15 and a 235/70R15 are both 235 mm wide. The 75 and 70 are the aspect ratio, 75% of the width and 70% of the width = height so it does appear narrower but it is because of the height difference causing a optical illusion. If you are stretching a tire out far enough on too wide of a rim to cause it to lower sidewall height you are going to be disappointed in the ride and life of any tire from a $50 independent company or a $200 Michelin tire. Not to mention what it is doing to the integrity of the tire itself.
Not trying to offend you but I think you just got bad info on tires.

Thank you for your response. What size of tire do you recommend?

Thanks,

Russ

Are you wanting a white wall or does it matter? If I was to run a 15" I would choose 1 of the 3, a 225/75R15, 235/70R15 or the 235/75R15. The 235/75R15 is about a 1/2" taller than the 225/75R15 so if it does throw off the speedometer it wouldn't be but 1 or 2 miles per hour at most. The 235/70R15 is not quite 1/2" shorter. Hope that is helpful in your search and good luck.

1tireman wrote:

just me wrote:

The 75 series is narrower than a 70 series of the same Psize but the sidewall height is taller than 70 series. The engineers used different sizes to adjust weight carrying capacity and ride comfort vs handling, most people with wagons cared less about the handling hence the narrower tire size. Just use the tire sites calculators to keep the overall tire diameter the same when comparing different size tires if you want the speedometer to read correctly. Slightly wider than  stock wheels won't affect speedometer reading much but much wider wheels will lower the sidewall height enough to notice a small difference in mph. The lower the sidewall height, the harsher the ride is the usual result.

A 75 and 70 aspect ratio in the same size tire are the same width. A 235/75R15 and a 235/70R15 are both 235 mm wide. The 75 and 70 are the aspect ratio, 75% of the width and 70% of the width = height so it does appear narrower but it is because of the height difference causing a optical illusion. If you are stretching a tire out far enough on too wide of a rim to cause it to lower sidewall height you are going to be disappointed in the ride and life of any tire from a $50 independent company or a $200 Michelin tire. Not to mention what it is doing to the integrity of the tire itself.
Not trying to offend you but I think you just got bad info on tires.

You are correct, my mind was still on the diff between the 225 and 235 he had been referring to and didn't do the switch correctly to 'same Psize'. Kinda like mouth running and brain in neutral. As for 'much wider wheel' I was thinking in terms of what happens when lowriders put a 185/75 or 80 on a 7 or 8 inch wide rim. When I worked at a tire store over a decade ago we refused to install those tiny tires on wide rims, I remember seeing a few of those cars on the side of the road on rims because the tire came off when they took a turn too fast, didn't know a bead could break off like that but it did.

I know what you mean about the brain switch thing. I think that happens somewhere in your 30's! Yes,I am amazed at some of the stuff we see people do and ride around on!

I'd ditch the factory wheels. Rock some after market rims or a set of Impala SS wheels. Best mod for our rides. IMO

rjathon wrote:

jayoldschool wrote:

Those 205 70 15s are too small.  They are FWD minivan tires.  They will work, of course, but at the expense of higher revs, worse fuel economy, harsher ride, and degraded handling.  I'd sell them on craigslist, and go with some larger tires.  235 75 15s are slightly larger than stock, fit perfect, ride great, and are available readily at many price points.  I ran 235s on my wagons for over ten years.

Would you use 235 75 R15's on a wagon with a 2.56 rear end?

Thanks,

Russ

I didn't. I used them on a non-tow 92 (2.73) and a tow pack 94 (2.93). However, I would still use them on a 2.56 car. They are available, and inexpensive. If I wanted more performance from a 2.56 car, I would do gears.

I'm 1000 miles from home with a bad tire. At Costo they don't have anything in car tires for my wagon but they do have Michelin LTX M/S2 truck/suv tires in the 235-75-R15 size so I'm going with them.

I hope that it is a wise choice as they will most likely last a long time.

Russ

They would make decent winter tires I bet.

rjathon wrote:

I'm 1000 miles from home with a bad tire.  At Costo they don't have anything in car tires for my wagon but they do have Michelin LTX M/S2 truck/suv tires in the 235-75-R15 size so I'm going with them.

I hope that it is a wise choice as they will most likely last a long time.

Russ

Good choice of tire Russ,with proper care they will give you a smooth ride and a long life.