Tire sizing on '87 300D

[Adenauer]

I've just noticed that the tires on the 300D are 205/60R15 and that the original spare (unused) is 195/65R15. That seems a pretty big jump in sizing from the original, no?

How would 205/60R15's impact off-the-line acceleration, highway cruise speed vs. rpm, and overall fuel economy?

There is still quite a lot of tread remaining on the 205's but if returning to the 195's would improve driveability across the board, I'll have a set mounted.

Thoughts?

[t walgamuth]

It is just one size up in width with a corresponding reduction in height aspect ratio. They should not impact your speedo/odo accuracy much if any. If they are good tires I would keep them and go back to stock when buying new. IMHO they ride and handle best with the size tires they were designed for.

Tom W

[Adenauer]

Will do.

My lack of tire sizing knowledge had me believing the 205's are quite a bit larger all around.

Thank you.

[Brian Carlton]

Originally Posted by t walgamuth

It is just one size up in width with a corresponding reduction in height aspect ratio. They should not impact your speedo/odo accuracy much if any. If they are good tires I would keep them and go back to stock when buying new. IMHO they ride and handle best with the size tires they were designed for.

Tom W

The argument that the OE tires are the tires that "handle best" must be taken with some skepticism.

The W126 was originally provided with 195-70-14 tires. Later in life, the identical chassis was offered with 205-65-15 tires. A rather significant difference for virtually no change in chassis design.

So, if the smaller 195-70-14's are preferred because they "handle best"..........you'd have to make the conclusion that the M/B engineers were clueless when they upsized the tires to 205-65-15's.

In general, a lower profile tire will handle better. The ride might be compromised, but, like all tire and wheel decisions, there is no panacea.

On the W-126, there is no argument. The 15" tires with a lower profile are clearly the better choice.

[Adenauer]

Given a suspension in otherwise excellent health, would the taller profile tires then, contibute to a somewhat vague feel in cornering at speed?

Idler arm kit has been installed, new damper, new stabilzer bushings, tie rod ends are tight as are ball joints and control arm bushings. Struts are roughly 25,000 miles since new.

[Brian Carlton]

Originally Posted by Adenauer

Given a suspension in otherwise excellent health, would the taller profile tires then, contibute to a somewhat vague feel in cornering at speed?

Idler arm kit has been installed, new damper, new stabilzer bushings, tie rod ends are tight as are ball joints and control arm bushings. Struts are roughly 25,000 miles since new.

Yep, the SD has 215-70-14's and it's a bit mushy in the corners.

The sidewall on the SDL's 215-65-15's is significantly shorter and it will easily outperform the SD on curves.

[Adenauer]

No wonder F1 cars are practically running on the rims!

So aside from the factory spec for tire size on the '87 300D, is there a recommended replacement size or is it best to stay with the 195/65R15's?

[Brian Carlton]

Originally Posted by Adenauer

No wonder F1 cars are practically running on the rims!

So aside from the factory spec for tire size on the '87 300D, is there a recommended replacement size or is it best to stay with the 195/65R15's?

It depends on your priorities. Do you want the best possible handling at the expense of ride? Or is ride quality of paramount concern?

Do you want to change wheels to 16"?

I don't have a W-124 so I can't recommend the best tire for it, however, lower profile tires with wider tread will improve handling.........as mentioned above.

[Adenauer]

Thanks, Brian. I think I'll run the 205's until they're ready for replacement. I'll go back to the original size at that point as I probably drive the car much as the engineers thought most people might - conservatively?

[t walgamuth]

Originally Posted by Brian Carlton

The argument that the OE tires are the tires that "handle best" must be taken with some skepticism.

The W126 was originally provided with 195-70-14 tires. Later in life, the identical chassis was offered with 205-65-15 tires. A rather significant difference for virtually no change in chassis design.

So, if the smaller 195-70-14's are preferred because they "handle best"..........you'd have to make the conclusion that the M/B engineers were clueless when they upsized the tires to 205-65-15's.

In general, a lower profile tire will handle better. The ride might be compromised, but, like all tire and wheel decisions, there is no panacea.

On the W-126, there is no argument. The 15" tires with a lower profile are clearly the better choice.

As you well know, the earlier 126s were short wheelbase cars with less weight. The later larger tires were a natural progression. Note also that the factory offered the 15" rims with 7" width and after a year or two went back to a 6.5" width for ride considerations.

And of course my comments are my opinion. Others have different opinions.

No worries.

Tom W

[Brian Carlton]

Originally Posted by t walgamuth

As you well know, the earlier 126s were short wheelbase cars with less weight. The later larger tires were a natural progression. Note also that the factory offered the 15" rims with 7" width and after a year or two went back to a 6.5" width for ride considerations.

And of course my comments are my opinion. Others have different opinions.

No worries.

Tom W

The difference in weight is about 200 lb...........hardly significant.

Additionally, there were short wheelbase models produced after 1986 that, presumably, used the larger 15" tires.

I'm simply noting that the factory doesn't have a magical size for a vehicle. The actual tire chosen by the factory is likely to be the smallest that they can possibly select to do the job. Why spend more money on larger tires if the market..........or the vehicle...........doesn't force you to do so?

Larger tires with shorter sidewalls have been proven to benefit handling of the W-126, and presumably the W-124 as well. The factory size is usually a conservative position for the beginning of a discussion........not a panacea.

[t walgamuth]

One tire size is not all that significant either.

Tom W

[Adenauer]

Did I understand correctly that 205 is one step up from 195? I guess I thought that sizing went 190, 195, 200, 205...and so on. Guess it's not like a pair of skis!

[Brian Carlton]

Originally Posted by Adenauer

Did I understand correctly that 205 is one step up from 195?

You did.

[Adenauer]

Roger that. Thanks for all the replies.