I put w210 16's on the w126 SD made no difference in speed. the only thing i noticed was that when i go around sharp bends at high speeds the car seems to stick on the road better and i dont get as bad of "tire squeal". could be due to one of two things. A: less side wall means less sidewall flex = better handling B: wider tires provide better traction because of increased tire surface area gripping road.

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1987 300D 180k
1985 300SD 330k Helga
1992 300D Lola 269k- Sold
1986 325 coupe Bessie >300k Original engine(ODO Broke) sold
2006 2500HD Druamax Linda- Tows boat and looks pretty in garage thats about it

I would add make sure the shop balances your tires with a Hunter brand road force machine. I have twice had brand new tires mounted without one being used and had to pay again for the job to be redone with a Hunter. They are freaking magic. No affiliation.

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1986 300 SDL - rolling parts car and test bed.
1987 300 SDL - semi daily driver.
1977 U1000 Unimog
2007 Ram 2500 6.7l

I work at a mercedes dealer that has a hunter balancer and i am not impressed. the thing is always out of calibration and this is not uncommon i know several other shops with this problem. often i can guess the weight and get it right more than the machine can. currently it is about +10g on its readings but luckily it will tell you the correct location.

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1987 300D 180k
1985 300SD 330k Helga
1992 300D Lola 269k- Sold
1986 325 coupe Bessie >300k Original engine(ODO Broke) sold
2006 2500HD Druamax Linda- Tows boat and looks pretty in garage thats about it

There is a miata tire calculator that will come up easily and let you know the effect of different tire sizes.

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85SD 240K & stopped counting painted, putting bac together. 84SD 180,000. sold to a neighbor and member here but I forget his handle. The 84 is much improved from when I had it. 85TD beginning to repair to DD status. Lots of stuff to do.

It makes sense that changing tire size would affect car speed as related to engine RPM. It also makes sense that there may have been some speedometer error that has changed now.

But I'm more worried about the statement in the original post that "About a month ago I cruised down to Tuscon on my 83 sd and I couldn't get it above 65 comfortably." Does this mean that it was just an uncomfortable RIDE at that speed, or does that mean that the engine/car wouldn't perform any faster?

A 300SD ought to be able to go faster than 65 with square tires, Fred Flintstone tires, or go-kart tires if it's working otherwise. So if the car was hitting 65 and refusing to go faster, then there's some other issue at work.

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~Michael S.~
Past cars:

1986 300SDL
1987 300SDL
1982 240D
1982 300SD


Current:

1987 300SDL

I went to 15's felt more stable and looked better IMHO

15" vs 14" is a minor change in rpm's/speed. MY dad's SD has 15" wheels with 215/60/R15 tires.....and the only real difference is about 100rpms less in 4th gear.....and a bit better handling due to the wider tires. 90% of my driving is 60 or below....so there's no point/advantage for me....and even so, it cruises just fine at 75.....

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-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)

Tire Size Calculator

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1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!

Sometimes I think I'm the only person on here who thinks the "Bundt cake" 14" wheels look more attractive on a w126 than the holes-around-the-edge 15" from the 86-91 w126 years.

w123, it's up in the air. I think I prefer the painted hubcaps but the bundts don't look "Bad" to me.

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~Michael S.~
Past cars:

1986 300SDL
1987 300SDL
1982 240D
1982 300SD


Current:

1987 300SDL

ya know, there are 15" and 16" bunts available EXTREMELY rare, but they do exist...

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

Well, if you went from the standard 195 all the way to the 215s, it would feel a lot more stable. Also . . did you go from a kelly, to a michelin? And when you did the change, did you have them align the car, as well as balance the tires? Just because your old tires were overdue for balancing/rotation, and skinny, doesn't mean that the upsize is "kind." Also . . . if your speedo is closer, is it possible that car was sold with 15' tires/wheels, originally?

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1983 300D, the "Avocado"
1976 240D, 4-spd the "Pumpkin", SOLD to Pierre
1984 190D, 2.2L, 5-spd, my intro to MBZ diesels, crashed into in 2002

I doubt changing wheel size made much difference in the ride comfort.
I had 8 year old tires on my 84 300SD with very little wear, and no weather checking to speak of. Older tires get a little stiff and less pliable
with time even if they have low miles.
I replaced them and it made a world of difference in the ride and handling.


A larger wheel will decrease the relative odometer reading just a bit because you
are traveling just a bit farther on each wheel revolution.

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85 300TD

88 560SL

05 SL65 AMG

Same here Tony.

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http://farm8.staticflickr.com/7271/7...144c3fc1dc.jpg

I would disagree with both and say that it may be tire compound or construction.
Any good experiment requires a number of 'constants'. In order for this test to be accurate, ie: wheel size benefiting performance, it is best to use the same tires, same age, noting tire pressure and alignment settings. Also important to note for handling comparison is if the offset is different from one wheel to another.
I drive many cars around a race track on every type of tire. Some squeal, some dont. This is a function of the tire. Also do not rule out tire pressure, as it has a great effect on traction and performance.

I just installed new tires on the stock bundts on my W123. Ride is awesome handling is great.

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83 300TD (need rear wiper assembly dead or alive)
84 300SD Daily driver
85 300TD almost 400k miles and driven daily.
98 E300D *sold
86 300SDL *sold and made flawless 10 hour journey to new home.

Now that you have 15" on there you should upgrade the brakes to 2nd gen w126. Wider tires and bigger brakes will certainly make you stop faster.

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http://superturbodiesel.com/images/sig.04.10.jpg
1995 E420 Schwarz
1995 E300 Weiss
#1987 300D Sturmmachine
#1991 300D Nearly Perfect
#1994 E320 Cabriolet
#1995 E320 Touring
#1985 300D Sedan
OBK #42