Tire spec question 70 vs. 75 - PeachParts Mercedes-Benz Forum

diesel don · #1 01-24-2003, 01:19 PM

Hey Tire Experts:

What is the difference between 195 70R14's and 195 75R14's?

Seems like my 240 had 75's but my 300's (123's) have 70's.

Are they interchangable or should I just stick with 70's on my 300's?

Thanks

Don

JHZR2 · #2 01-24-2003, 02:02 PM

the difference is 5% bigger aspect ratio on the 75s... i.e. the sidewall is a bigger percentage of the tread width and therefore a little higher. The difference? Maybe a tiny bit on your speedometer, which if already not too great, may be worse.
The 70s may handle a bit better than the 75s, but tire quality and design are a bigger factor. Neither should rub or act different from one or another, should be very interchangable, if you wish.

If your speedometer has been calibrated for 195/70 R 14 tires, replacing them with 195/75 R 14's would result in the speedometer reading low by 3.01%. Same as with the speedometer, if your odometer has been calibrated for 195/70 R 14 tires, replacing them with 195/75 R 14's would result in the odometer reading low by 3.01%.

JMH

diesel don · #3 01-24-2003, 02:05 PM

Thanks for the info. Much appreciated.

Would mileage increase or decrease as well by 3%

dp

JHZR2 · #4 01-24-2003, 02:11 PM

I believe that 'observed' mileage would be less, as the odometer wouldnt turn as much, and it would seem that the MPG was less. However, you would still be travelling the same actual distance, so your 'actual' MPG would remain the same.

The contact area of the tires should be essentially the same, and so rolling resistance (assuming the same exact tire in the two sizes) should be about the same.

It would be one thing if you went from 195s to 205s or something like this, but since the treadwidth is the same, I think all should be aboout the same, except for the measurement issue...

JMH

#5 01-24-2003, 04:39 PM

The actual fuel mileage will be negligible as will the speedo difference. After well over a half million miles of driving and putting tires on 123's, I firmly believe that it's difficult to beat 195/75's.

They carry the weight of the car well, there is no significant handling difference because these are not sports cars anyway, and the 75 series tires have harder compounds and last longer. The added benefit is that even though they last longer, they are less expensive than wider profile, performance tires.

My preference over the years has been 195/75-14, Michelin XH. I have not seen the XH in many years, so I'm not sure what is the current Michelin equivalent.

In this size they are not terribly expensive, but they are round, smooth, balance out very easily and will outlast about any tire you can put on it. In the long run, you will get more miles per dollar than anything else you can put on these cars. That has been my experience.

Good luck,

diesel don · #6 01-24-2003, 04:59 PM

Wow:

This is very helpful information from both of you. I'm headed off to get them tonight on the new (85 D) one. So the information was timely.

Thank you,

Don

JimSmith · #7 01-24-2003, 05:26 PM

diesel don,

Your 240D was more than likely equipped with 175/78-14's from the factory and in my opinion that size sucks on a W123. Too wimpy to maintain proper margins for strength and safety if the car is loaded. I never understood the technical justification for the 240D to 300D difference in rating. Fully loaded the two cars do not weight significantly differently, and coming down a windy mountain road those 175/78-14's (actually they have no aspect ratio number listed, and in that case the standard if no aspect ratio is specified, is 78) (edit-got distracted and left the sentence incomplete) is not confidence inspiring.

Since you are not fitting your 240D today, I guess all that is moot. Good luck though, Jim

psfred · #8 01-24-2003, 11:16 PM

Tire size specs have changed over the years, and radial tires were a new thing back then....

The 70 or 75 is the height of the tire, expressed in percent of tire width (so a 75 tire is taller than a 70).

You need to find a tire guy who is old enough and is knowledgeable enough to determine which current tire will have the same rolling diameter as the original spec tire -- this will give you correct gear ratio and speedo/odometer readings.

The tire size required may not spec out much like the original -- for instance, the "correct" tire for the 72 280 SE 4.5 is a 205/70, original tires are a 185/75 spec, but not radials, so they were taller for the same "height" -- radials squash down more that bias belt tires.

Peter

diesel don · #9 01-24-2003, 11:46 PM

Jim:

I felt the same thing when I purchased my 240D awhile back. There were either 175's or 185 75R14's on it. Seemed skinny and didn't hold the road as well.
Tonight I put the 195 75R14's on the 300 and went for a test drive. Ran about 40 miles and up pretty high. I thought they did very well.
I'm with you on the skinnier ones.

Psfred:

Wow, never thought of the impact of radials and different measuring standards.

Thanks for the input.

Don

#10 01-24-2003, 11:50 PM

I too had this question when buying a new set of tires. I asked many a mechanic, but when the decision came in, I stuck with the 70. The 75s, while okay for the car, look too tall to my calibrated eye. Some may tell the difference, I really can tell. Another word of advice came from my dealer, they also said stick with the 70's... Why? Mercedes Benz put a lot of research in designing suspensions, etc. If they fit 70s, they did so for a reason. What, I really don't know. But I like my brand new Michelin MXV4s. I HIGHLY suggest you buy Michelins. For having Coopers and Avons in the past, Michelins are quite the tires! Rubber strengths and compounds depend on tires, not sizes...

240 Ed · #11 01-25-2003, 07:51 AM

You will find a larger variety of tires in the 70 size than 75.

Tire developement has been going along with tire size.
IOW, when 70 series became the rage the tire companies spent millions on development; rain, grip, noise, etc. Then it was 60 series and the 70 series were not concentrated on much, but received some trickle down from the 60s. Now it is on to the ridiculous series, i.e. 45 and 55...

So, 75s are really old and 70s are sorta old.
Go with the 70s.
Buy Michelin or Dunlop. I happen to think that Dunlop D2 are very good on these cars.

Palangi · #12 01-25-2003, 11:39 AM

The difference between these two sizes is minimal. As long as all 4 tires are the same size, you won't notice any difference. The 75's will probably cost less, mainly because that is the more common size. My only advice would be that these are heavy cars on fairly small tires, therefore they don't tolerate cheap tires very well. Go with a premium brand tire like Michelin, Bridgestone, Dunlop, etc. Avoid the domestic brands as even their top of the line tires do not do well on these cars.

zbenz · #13 01-25-2003, 09:39 PM

I have had Michelin's on both my Benz when I bought them

. On both I found them quite inferior to the Goodyear Aquatread 3's I replaced them with. Just my $0.02

JHZR2 · #14 01-25-2003, 09:48 PM

good to know... I am set to use aquatred 3s on the 300D, because due to minor alignment/suspension problems, the fronts wear funny, and my dunlop SP Sport A2s are a bit soft...

The Warden · #15 01-25-2003, 09:58 PM

FWIW, I have BFG tires on my 300D right now; they came with the car. There's still a decent amount of tread on them, so I can't justify replacing them, but I'm not happy with 'em...

What do you all think about Big-O tires? I've used them on my trucks in the past, with great success...excellent warranty, good on- and off-road handling capabilities

but I've never bought a car tire from 'em...