Tire spec question 70 vs. 75 - Page 2 - PeachParts Mercedes-Benz Forum

rwthomas1 · #1 01-26-2003, 12:38 AM

Aren't 300D's supposed to have a T rated tire? I have found T ratings harder to find in 75 series tires but very easy to find in 70 series.... Just a thought. RT

#2 01-26-2003, 12:58 AM

I've used 205/70 and 205/75's on early 80's 300's and I don't like the 75's. The side wall is too tall and not stiff enough to prevent roll at highway speeds. With 75's the car feels like a old Caddy with their unresponsive steering. I do like 205's. The bigger foot print increases traction and reduces tread wear significantly and I don't have to run 32 psi tire pressure to keep the sidewall from flexing. I do not push my cars hard so the 70's work fine. Michelin's wear great, I got 80K from a set, but they have become too expensive for me. In fact they were on a car so long they began cracking. Now I target 50-60K tires and bought my last set from a newly scrapped 300SD with new tires ($80 with rims) in a junk yard .

#3 01-27-2003, 09:03 AM

Yes, because you are using 205's. These are too tall. Use a 195/75 or 185/75. They can carry the weight of the car and are not too tall. Trying to make a sports car out of a 123 MB is like trying to make a race horse out of a pig.

Quality 195 or 185 75's is the key.

Good luck,

240 Ed · #4 01-28-2003, 08:25 AM

Quote:

Quality 195 or 185 75's is the key

No, 70 series will give you better handling AND give you a more matched ride with the Bilsteins ....IMHO:p

#5 01-28-2003, 02:12 PM

If you are willing to give up tire life, the 70's will work for you. The 75's are typically harder compound passenger car tires rather than softer 70 series performance tires that cost more and have shorter life.

I have run about every size in both 70 AND 75 series tires on 123 cars and I can't tell the difference. These are not sports cars, they are solid, but somewhat squirmy handling passenger cars. Trying to make a sports car out of one by changing tires and shocks is like trying to make a race horse out of a pig IMHO.

If you want tire economy use a quality, preferably Michelin 195/75-14 tires, dynamically balanced. If you want shorter tire life, with immeasurable handling differences then knock yourself out with 70's, 65's or whatever. Maybe you can achieve what I have never been able to. Maybe you will be able to turn the pig into a Thorobred.

Best of luck,

lrg · #6 01-28-2003, 06:32 PM

As a more practical issue I choose to use 195/75-14 tires because my car, like lots of our old cars, has a wee bit of slop in the steering box. All the rest of the front end is sound but I still have some play at the steering wheel. Let's face it, the MBZ designed steering box is not the high point on these cars. IMHO going to a higher performance tire seemed pointless and potentially annoying if it was going to increase the tendancy to wander on the highway.

psfred · #7 01-28-2003, 11:49 PM

lrg:

If the steering wheel rattles on gravel or rough pavement, you probably need a new steering coupler -- goes between the gear box and the column. There are two rubber bushings that go in there, and when they disintegrate, the steering gets loose. On the W108/109 the bushings are replacable, but on the W115 and later, I think they are crimped on and you must replace the coupler. Fits the older cars, but if you can find the bushings, they are MUCH cheaper.....still looking for mine!

PEter

lrg · #8 01-29-2003, 12:40 AM

psfred,
My wheel doesn't rattle it's just that I have about +/- 1" of freeplay at center. The column seems solid, it appears to be the box that has the play. I have adjusted some of it out on the steering box adjustment nut but can't get it to completely tighten up without overtightening the steering adjustment. MBZ actually has a spec for freeplay so I assume even new the steering was not exactly razor sharp. In fairness though, back when these cars were designed the typical American car was much looser. We've all gotten a bit more critical as cars have gotten better. It's good to know about the coupler though, that may be the next item to need replacement. Thanks.

LRG

#9 01-29-2003, 07:01 AM

The problem with these boxes is that the worm shaft bearings loosen slightly. I have tightened them successfully in the past, but this can be a risky proposition. You risk getting them too tight.

Good luck,

psfred · #10 01-29-2003, 06:56 PM

lrg:

Check all the ball joints, too -- a loose upper one will cause excessive wandering. Will also wear the tire on both sides, makes it look like it has been underinflated or driven too hard.

The center is a big vague to prevent oversteering -- my Volvo has very tight rack and pinion, and I tend to drive all over the road in it, since any steering wheel movement changes the direction of the car. The 87 is much easier to drive, actually, since although the steering feels a bit vague at center, the car runs straight.

Peter

240 Ed · #11 02-05-2003, 05:48 AM

IRG,
It would be my guess that your idler bushings are worn. This is a cheap and easy fix for slop in the steering. You should have a bit less than an inch of play at rest. Worn idler bushings will show up more when you are on the move.