185/65/15 88Q on a 124 300D 2.5? - PeachParts Mercedes-Benz Forum

JamesDean · #1 11-12-2012, 11:19 AM

Hello everyone,

I've got a set of snow tires that I was previously using on my 190E. They're General Altimax Arctic's mounted on a set of 126 rims. They are 185/65/88Q size and rated.

I know the wheels wont bolt up but assuming I get a set of stock 124 rims. Will I be OK running that size and weight rating on my 300D in the winter?

I will be driving mostly highway (turnpike)...

97 SL320 · #2 11-13-2012, 06:03 PM

Need more information.

What is the stock size?

What is the weight rating for the tire you want to use? ( 88 is the load range but using the actual weight on the tire is a better measure for what you want to do.)

What are the axle weights on the target car?

My first impression is that they are a bit too light in weight rating for highway driving. What size tires are on the front? Narrow tires on the rear and wide in the front will lead to oversteer under power ( tail out ). Narrow tires are much better for snow driving as they bite in to the snow rather than float over it so in the snow I'd expect the car to understeer ( car won't turn ).

JamesDean · #3 11-13-2012, 07:22 PM

Well these would be going on my 300D 2.5.

Stock tire size is 195/65/15.

Going to TireRack, they picked a 195/65/15 91Q variant of the snow tire that I have.

I am not sure what the axle weights are... I know the curb weight of the car is about 3390 Lbs or so. All tires would be the same size.

88 = 1235lbs per tire.
91 = 1356lbs per tire.

3390/4 = ~850 if equally balanced.

My alternative is to buy a new set @ $320.

97 SL320 · #4 11-14-2012, 08:28 PM

The weights and tire size are close enough that I'd run it but not load the car with lead bricks and drive to Nevada then run the Silver State Classic.

Technically, in some states with safety inspections tire sizes under the label on the door are not approved.

Realistically, if you had stock tires on a fully loaded car Vs -1 size on a driver only car , the -1 tire setup might not be as deep in to the limit as the stock setup.

neanderthal · #5 11-14-2012, 11:03 PM

Size is what came as the base model size (if it wasn't a 195/70R14) but the load range is all wrong. You didn't specify if its a P185/65R15 or a 185/65R5.

You'll basically have to pump those tires up to their maximum air pressure (as noted on the sidewall) and not have more than the driver in the vehicle.

Don't look at the tables, multiply the max capacity by 4 and say "oh, i'm fine, the W124 doesn't weigh 4800lbs." The weight is not a static thing; it shifts and moves with acceleration, braking and turning. It's very possible to have more than half the weight of the vehicle on two tires in the right circumstances.

JamesDean · #6 11-15-2012, 08:36 AM

Quote:

Originally Posted by neanderthal

Size is what came as the base model size (if it wasn't a 195/70R14) but the load range is all wrong. You didn't specify if its a P185/65R15 or a 185/65R5.

You'll basically have to pump those tires up to their maximum air pressure (as noted on the sidewall) and not have more than the driver in the vehicle.

Don't look at the tables, multiply the max capacity by 4 and say "oh, i'm fine, the W124 doesn't weigh 4800lbs." The weight is not a static thing; it shifts and moves with acceleration, braking and turning. It's very possible to have more than half the weight of the vehicle on two tires in the right circumstances.

The tires that are on it now are 195/65/R15 91Q i believe. The snow tires are 185/65R15 88Q.

Thats a good point about dynamic loading.

If I were to buy a new set (same General Altimax Arctic's) just for the 300D, TireRack says I would use a 195/65/15 91Q.

Hmm and what about studding the tires?

Evidently is legal in Ohio from November to April (http://codes.ohio.gov/orc/5589.081). I've never driven with studded tires. Not entirely sure how that would do on the freeway or anything like that.

97 SL320 · #7 11-16-2012, 07:34 PM

Quote:

Originally Posted by neanderthal

It's very possible to have more than half the weight of the vehicle on two tires in the right circumstances.

EDIT : I have not proof read all of this as I need to run but, you will get the idea of what I'm pitching. The goal is to determine how deep a stock tire car at max weight is against the tires rating vs a small tire car running light payload.

While it's possible to have weight move around, that condition is intermittent ( unless you are road or oval track racing ) And likely taken into consideration when a tire is rated.

Going to the tire makers web site should net real answers on the weight rating. Some sites also have a chart what inflation pressure is required for what corner weight.

So, look at the tire label on the car door / jamb. It will show max gross axle weight rating ( GAWR ) and max gross vehicle weight rating ( GVWR ) . Sometimes it will also show max vehicle payload.

Divide front GAWR by 2, divide that result by the stock tire weight rating. This percentage is how heavily you are loading the tire in a static mode. ( Do this for the rear also. )

( Axle weight / 2 ) / stock weight rating = % of weight rating used. ( A )

Now do the same with your target tire.

Next individually divide front and rear GAWR into curb weight to generate F / R weight distribution. Use this to generate empty axle weights.

Max F GAWR / max weight % = Front distribution %

Front distribution % * curb weight = curb front axle weight

( Payload you will be running with / 4 ) + curb front axle weight= front loaded weight.

Target tire weight rating / front loaded weight = % of weight rating used for target tire. ( B )

Compare result A and B to determine if a stock tired car fully loaded has more / less reserve weight than a small tired car running with a driver only.