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  #1  
Old 06-09-2003, 05:55 PM
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Location: MINNEAPOLIS, MN
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85 MPH at 3500 rpm?

I tried looking for this fact using search but found no answers. If someone has a W124 260E or 300E (mine is a 1987) could you tell me whether 85Mph is at 3500rpm? I have a feeling that I am moving a lot slower than 85 but I might be wrong. If anyone knows what the stated factory figure for cruising in drive for each 1000rpm could you please post it? That would be an easy way of calculating the correct speed.

Thanks, Igor.
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  #2  
Old 06-09-2003, 07:11 PM
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Me again, but this time, my info may not apply.

My M103 motor does 70mph at 3400rpm, but my 126 weighs alot more than the 124. It's possible that at the same rpm, a 124 car would have greater ground speed?

Perhaps one of the 124 members will provide a better answer than mine.
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  #3  
Old 06-09-2003, 07:20 PM
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Location: Florida / N.H.
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If you want it Exact, take the ratio # of the differential and do the math [ using rolling circumference...]
RC is easily found by checking for proper air pressure and then mark the tire with the ground and push car one wheel revolution, - Measure ground distance covered..
This eliminates guessing on tire circumference and is accurate for each individual car/tire set up..
More accurate , of course, for stand trans [ no OD] vs auto/torque conv.
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  #4  
Old 06-09-2003, 07:35 PM
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Join Date: Mar 2003
Location: Southern California
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260E axle ratio = 3.27:1 (300E is 3.07:1)
195/65R-15 tires = 837 revs per mile

Speed at 60 (1:1 top gear assuming no torque converter slippage):

3.27 x 837 = 2737

Any other revs at speed can be determined by linear proportioning, e.g. at 85 MPH:

2737(85/60) = 3877

Speed per thousand RPM = 60/2.737 = 21.92

The speed/rev relationship is established by speedometer gearing and speedo head calibration and is independent of actual installed tire revs per mile or installed axle ratio. An axle ratio change or installation of tires with different revs per mile will affect speedometer accuracy, but not the speed/rev relationship.

Duke
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  #5  
Old 06-09-2003, 08:01 PM
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Location: Florida / N.H.
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The speed/rev relationship doesn't change.. the Actual ground speed does..
So, if one were check speed accuracy , tach rpm can be used .
Knowing ratio and tire size tells one what RPM will produce
Actual speed..
I drive 2 of my Vintage cars and monitor speed via tack [ per 1000 rpm] as one has had diff. gear change and the other is Km only...just by habit..
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  #6  
Old 06-09-2003, 09:27 PM
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Location: Grand Rapids, MI
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IZELJIC, the simplest way to check the accuracy of your speedometer (which I take to be at least part of your basic question) involves a stopwatch (cheap at Radio Shack) and a freeway with mile markers at a low-traffic time. Ideally, pick a stretch that's fairly straight and flat. Time yourself over two or three miles at a steady speed and do the math. Arithmetically convenient speeds are 60, 72 and 75 but any speed you can maintain consistently will do. For the most precise results, do several runs at different spots and take the average.

As a point of reference, my 560SL turns 2110RPM at 60 mph, according to the Road & Track test of the model in 1989. My speedo incidentally is spot-on at 80, both by stopwatch and GPS; most of my other cars have indicated anything from 77 to 81 at a true 75. Useful to know when maximizing time efficiency while minimizing ticket risk.
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'97 SL500, 40th anniversary edition

'04 Olds Bravada (SWMBO's)
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'89 560SL (sold)


SL--Anything else is just a Mercedes.
(Kudos to whoever said it first)
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  #7  
Old 06-10-2003, 03:09 AM
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my Euro 500 Se is only turning 1800 at 60 , lets see 120 at 3600 , speedo is right on the button so if it would pull 5400 in fourth that would be 180 ,something is wrong here? it has correct size tires,tach seems to function well? Tach must be off.....
William Rogers........
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  #8  
Old 06-10-2003, 07:57 AM
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Location: Grand Rapids, MI
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Quote:
Originally posted by william rogers
my Euro 500 Se is only turning 1800 at 60 , lets see 120 at 3600 , speedo is right on the button so if it would pull 5400 in fourth that would be 180 ,something is wrong here? it has correct size tires,tach seems to function well? Tach must be off.....
William Rogers........
Ah, for the dear dead days when cars were geared to actually hit redline in top gear--but then again, that nice loafing engine at cruise does have its points. Decisions, decisions.....
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Craig Bethune

'97 SL500, 40th anniversary edition

'04 Olds Bravada (SWMBO's)
'06 Lexus ES330
'89 560SL (sold)


SL--Anything else is just a Mercedes.
(Kudos to whoever said it first)
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  #9  
Old 06-11-2003, 03:06 PM
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Join Date: Apr 2003
Posts: 320
My 94 E320 is at 90 mph at 3500 RPM. You may be able to use speed displays found at the side of the road to make motorists aware of their speed, or you can have a friend follow and compare the speeds.
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