Tire Size Question

[240DJunkie]

What would be the tallest and widest tire that I can mount on stock 240D wheels without any suspension modifications? I prefer the look of a car that sits tall and has tires that fill the wheel wells. I would welcome the slight improvement in MPG, and would not be troubled by a speedo and odo that were a little "off". When I drive, I enjoy the ride in the right hand lane, and let the high blood pressure crazies just whiz on by on their way to their next accident. Thanks for any input!

[ForcedInduction]

I use 205/60R15 tires on my 15x6" wheels. The ground travel distance is about 0.3% more than the stock 14" wheels.

Here is a fancy tire size calculator: http://www.miata.net/garage/tirecalc.html It will show you the difference in tire sizes and how far off the speedo will be.

[Maxbumpo]

MB only offered 14 inch and 15 inch wheels on that car. 15 wheels from a 126 have the correct offset.

[lkchris]

One would think that with the small amount of power available with the 240D, one would avoid mounting bigger, heavier tires.

There is no performance advantage to installing larger tires (they're all disadvantages), but as you've noted you're in it for the looks.

[aquablau]

If your 240D is a 115 with 14X5.5 wheels, I would go with a decent set of195/75/14. Anything larger really won't give you any benefits. Let's face it, you are not going to be cornering at high speed with the kind of hp that a non-turbo MB can put out. I will defer to others on size if you're 240D is newer than a 115.

[dropnosky]

Im not sure I understand what everyone seems to have against big tires. I too like the full wheel well look, and the slight disadvantages like poorer cornering are outweighed by the slight advantages of more ground travel per revolution and increased fuel economy. anyone who is driving a 240 is not really going to be concerned with acceleration, topspeed will be the only issue to worry about.

[Maxbumpo]

If you can provide objective documentation or studies to back up the idea of increased MPG, do it, otherwise this is just a bunch of talk.

I agree that the stock 14 inch tires look small and that a bigger tire will look better, but I only know of one 'study' if it could be called that. Car & Driver modified a 123 turbo diesel wagon when that model was introduced, adding 15 inch tires on custom rims (I think they were wider profile tires as well) and an air dam. The car looked great; if I recall correctly, performance in every category measured was worse than with the stock wheels/tires (acceleration, braking, grip). I don't think that they provided MPG numbers.

If adding bigger tires increased MPG without seriously compromising braking and cornering, we'd all be riding around on 22's!

[Maxbumpo]

I would welcome the slight improvement in MPG, and would not be troubled by a speedo and odo that were a little "off".
How will you measure MPG if your odometer is off?

[lkchris]

... outweighed by the slight advantages of more ground travel per revolution and increased fuel economy.

Yes, once again the laws of physics are repealed by ignorance.

No way adding weight and rolling resistance increases fuel economy.

It (larger tires) does, of course, create odometer error.

[dropnosky]

I am talking the difference between a 195 and 205 height ratio. yes, you are both right in that any real measurements are so minute that the issue is not even worth arguing about.

I feel the 205 height looks a little better in the wheel well, and if you stay with the same width, what new rolling resistance? Plus, I can personally tell you that the same brand tires of those two different heights and same widths, are nearly identical in weight after 5 years of throwing the things around.

but, as you say, there is no study of any kind worth mentioning, because its a pointless argument.

when I say increased fuel economy, I am thinking over hundreds of miles. Probably in the thousandths places increase in economy, any further increase would involve me once again repealing the laws of physics

[Dusty-NZ]

I have 205's on noddy , looks good I think , plus w123 springs , great ground clearance for the dirt tracks etc.

Others laugh at it for being so tall.

I dont care.

[doofwop]

I had 205s on my w123, and the profile wanted to roll under the wheels with heavy cornering at higher speeds. Made the car look like it could traverse some nasty terrain, high ground clearance and all, and rode very smooth. Just got some new 195 Michelins and the car is much faster and corners like its on rails. However it looks like a linebacker wearing ballet slippers. Ride is a smidge harsher, nothing to complain about. Function over aesthetics is my motto, with this car.

[OliverB]

The "205" refers to tire WIDTH, not sidewall height. The other number - 55, 60, 65, 70, 75, etc. - refers to sidewall height (actually the first 2 munbers refer to an "aspect ratio"). A 195 X 65 X 15 will have about the same total height as a 205 X 60 X 15, thus the revs/mile will be about the same and no appreciable change to speedo/odo accuracy. What you will get with the 250 is a lower profile sidewall and a slightly wider tire. This may result in a slight improvement in handling but the trade-off could be more rubber contact and resistance with the road and lower mpg. It could also result in reduced grip on wet roads because, on a wider tire, there are fewer pounds/sq. inch of contact pressure and the tire may hydroplane or slip easier - all other things being equal.

As others have said, even a small increase in total height and width can have a major impact on power and mpg, especially in an underpowered car. I understand the desire for a different "look" and that is OK as long as you are aware of the potential disadvantages.

[dropnosky]

The "205" refers to tire WIDTH, not sidewall height. The other number - 55, 60, 65, 70, 75, etc. - refers to sidewall height (actually the first 2 munbers refer to an "aspect ratio"). A 195 X 65 X 15 will have about the same total height as a 205 X 60 X 15, thus the revs/mile will be about the same and no appreciable change to speedo/odo accuracy. What you will get with the 250 is a lower profile sidewall and a slightly wider tire. This may result in a slight improvement in handling but the trade-off could be more rubber contact and resistance with the road and lower mpg. It could also result in reduced grip on wet roads because, on a wider tire, there are fewer pounds/sq. inch of contact pressure and the tire may hydroplane or slip easier - all other things being equal.

As others have said, even a small increase in total height and width can have a major impact on power and mpg, especially in an underpowered car. I understand the desire for a different "look" and that is OK as long as you are aware of the potential disadvantages.

My god, hes right! I had them backwards! oh well, what I should have been saying is between 65 and 70. pretty sad after selling and installing them for so long. I am going to face the wall with a dunce cap on for the rest of the night.