Studded tires, which pair should go on the rear? - PeachParts Mercedes-Benz Forum

lietuviai · #1 11-04-2003, 07:06 PM

I have a set of four studded tires for my '85 300D of which one pair has better studs than the other. I have never mounted them since I have owned the car and I was wondering which pair should I mount on the rear drive axle? I do plan on mounting all four tires this Winter.

Luke@tirerack · #2 11-05-2003, 09:54 AM

it doesn't matter if you are talking about a summer tire, winter tire, studded tire, front wheel drive car, rear wheel drive car or all wheel drive car .... the better tires always go on the rear !!!

lietuviai · #3 11-05-2003, 08:51 PM

In this case that's what I thought and that's what I did, because the studs were in better shape on the rears and I wanted to have better traction.
I had always heard that if you were only installing one pair of regular tires, they ALWAYS went on the front since if there was a chance of a blow out it would usually be the old pair and you don't want to have a blow out on the front tires since that's were all your steering stability is. I've had a rear tire go out on me before and I could still control the car very easily. I've seen incidents where a front tire would blow, the driver was all over the place.
THANKS
~DJ

jcantor · #4 11-06-2003, 09:08 AM

Luke,

I've seen the statement about always putting the better tires on the rear regardless of drivetrain before but I've never seen a full explaination. Can you offer one?

It would seem to me that on a front driver with all steering, acceleration, and 75% + of the braking on the front, that this would be the better place for better tires. Not having driven a front driver much, I don't really understand the driving dynamics of them - which of course is why I stay away from them :-)

jlc

DavidB29 · #5 11-11-2003, 07:14 PM

The Car Talk show on National Public Radio had a segment on this question, a couple of weeks ago. What they said was this:
*Tire guys used to say that the better tires should go on the front, because the front does most of the braking and turning (as well as traction on a front drive car).
*Some time ago (I think they said 20 or more years ago), the US govt (NHTSA perhaps, not sure) issued a rule that the better tires should always go on the REAR because of the risk of a blowout. The agency said, and the Car Talk guys seemed to agree, that a blowout on the front end could be controlled, but a blowout on the rear wheels is very difficult to control. Hence, keep the best tires on the rear to reduce the risk of loosing control in a rear wheel blowout.
Now as for my own opinion, I have driven for about 40 years and have only one blowout in that time. And it was a long time ago, and I'd guess tires are better now. (I frankly do not recall whaich wheel the blowout was on.) But I have had lots of occasions when I had to brake hard or needed to rely on front wheel traction for steering, especially under wet conditions. If I had a choice, I'd always have good tires on every corner. But if I had to choose to put better ones on one end of the other, I would certainly prefer to put them on the front. And I have done so many times.
Can the Tire God confirm the Car Talk explanation that it is blowout prevention that is the basis for the "best on the rear" rule? And is it a rule or regulation, or is it just advice? If it is advice, I don't think I agree with it.

#6 11-11-2003, 09:05 PM

Being an old codger, I would still assert that if I'm driving my daughter's '83 Toyota or my '91 Ford F-150, or any other car with a live axle at the back end, I'd much rather have a blowout on the live axle, because its weight will dampen most of the shaking and if you have enough experience to stay off the brakes and steer gently, the vehicle stays under control easily. BUT, in the same vehicle I want the best traction tires on the back, too, especially in bad weather, to avoid sudden final oversteer of a Corvair/Old Beetle sort. The trouble is, tires with a little more wear often have better traction in the dry (that's why Luke sells tires with most of their tread ground off to the autocrossers). So it becomes a really complex dilemma, avoidable only by putting the best bad weather tires on the back and checking all four for any potential cracks, bulges, and of course, air pressure, etc, at least once a week.

Luke@tirerack · #7 11-12-2003, 10:23 AM

Most vehicles are equipped with the same size tire at every wheel position. Ideally all of these tires should also be of the same type and design, have the same tread depth and be inflated to the pressures specified by the vehicle placard or owner’s manual. This combination best retains the handling balance engineered into the vehicle by its manufacturer.

However due to the front tires’ responsibility for transmitting acceleration, steering and most of the braking forces on front-wheel-drive vehicles, it’s normal for front tires to wear faster than rear tires. If the tires aren’t rotated on a regular basis, it’s also common for pairs of tires to wear out rather than sets. And if the tires aren’t rotated at all, it’s likely that the rear tires will still have about 1/2 of their original tread depth when the front tires are completely worn out.

Intuition suggests that since the front tires wore out first and because there is still about half-tread remaining on the rear tires, the new tires should be installed on the front axle. This will provide more traction, and by the time the front tires have worn out for the second time, the rear tires will be worn out too. However in this case, intuition isn’t right...and following it can be downright dangerous.

When tires are replaced in pairs in situations like these, the new tires should always be installed on the rear axle and the worn tires moved to the front. The reason is because new tires on the rear axle help the driver more easily maintain control on wet roads because new, deeper treaded tires are more capable of resisting hydroplaning.

Hydroplaning occurs when the tire cannot process enough water through its tread design to maintain effective contact with the road. In moderate to heavy rain, water can pool up in road ruts, depressions and pockets adjacent to pavement expansion joints. At higher speeds, the standing water often found in these pools challenge a tire's ability to resist hydroplaning.

Exactly when hydroplaning occurs is the result of a combination of elements including water depth, vehicle weight and speed, as well as tire size, air pressure, tread design and tread depth. A lightweight vehicle with wide, worn, underinflated tires will hydroplane at lower speeds in a heavy downpour than a heavyweight vehicle equipped with new, narrow, properly inflated tires in drizzling rain.

If the rear tires have more tread depth than the front tires, the front tires will begin to hydroplane and lose traction on wet roads before the rears. This will cause the vehicle to begin to understeer (the vehicle wants to continue driving straight ahead). Understeer is relatively easy to control because releasing the gas pedal will slow the vehicle and help the driver maintain control.

However, if the front tires have more tread depth than the rear tires, the rear tires will begin to hydroplane and lose traction on wet roads before the fronts. This will cause the vehicle to begin to oversteer in which the vehicle wants to spin. Oversteer is far more difficult to control, and in addition to the initial distress felt when the rear of the car starts sliding, quickly releasing the gas pedal in an attempt to slow down may actually make it more difficult for the driver to regain control, possibly causing a complete spinout.

Members of The Tire Rack team had the chance to experience this phenomenon at Michelin’s Laurens Proving Grounds. Participants were allowed to drive around a large radius, wet curve in vehicles fitted with tires of different tread depths — one vehicle with new tires on the rear and half-worn tires on the front, and the other with the new tires in the front and half-worn tires on the rear.

It didn’t take long for this hands-on experience to confirm that the “proving grounds” name for the facility was correct. The ability to sense and control predictable understeer with the new tires on the rear, and the helplessness in trying to control the surprising oversteer with the new tires on the front was emphatically proven.

And even though our drivers had the advantage of knowing we were going to be challenged to maintain car control, spinouts became common during our laps in the car with the new tires on the front. Michelin advises us that almost everyone spins out at least once!

Experiencing this phenomenon in the safe, controlled conditions of Michelin’s Laurens Proving Grounds rather than in traffic on an Interstate ramp in a rainstorm is definitely preferred!

In case there is any doubt, when tires are replaced in pairs, the new tires should always be installed on the rear axle and the worn tires moved to the front.

Luke@tirerack · #8 11-12-2003, 10:24 AM

The term “blowout” is generally used by drivers to describe a bursting tire accompanied by a rapid loss of air pressure. While one might assume that all blowouts are caused by too much internal pressure bursting a weak spot in the tire, the main reason for them is just the opposite. Most blowouts are caused by too little air pressure allowing the tire to flex beyond its elastic limits until it overheats to the point where the rubber loses its bond to the internal fabric and steel cord reinforcement.

Tire blowouts are usually the result of overloading the vehicle, impact damage (either immediate or delayed depending on severity of the impact), a massive cut that causes rapid air loss, or an unnoticed small puncture that allows the tire to slowly lose air over time until it fails. Blowouts are typically caused by anything that allows air to escape and prevents the tire from supporting the weight of the vehicle.

While tires have become so reliable that “blowouts” are an uncommon occurrence today, their lack of frequency only makes them more surprising and potentially more dangerous when they do occur. Regardless of the cause, what a driver does following a blowout can be the difference between a simple inconvenience or ending up in-the-ditch.

BANG…whoosh…flap…flap…flap…flap! In less than a quarter of a second your drive has gone from cruising to cursing.

Reacting to the surprise of the loud noise and a jerk of the steering wheel, many drivers’ first reactions are to lift off of the accelerator, hit the brakes and quickly steer the vehicle to the side of the road. Unfortunately these typical reactions have been shown to be dangerous, and may make it more difficult for the driver to maintain control.

However, preparation begins before the blowout occurs. You will not be ready to respond if you drive with one hand holding a cup of coffee and the other arm resting on the top of the steering wheel. Proper seat and hand position will give you better odds of dealing with any driving situation.

If you experience a blowout, it doesn’t make any difference if you are driving a sports car, sporty coupe or sport utility vehicle; the same procedures are appropriate. The driver should step on the accelerator for an instant to preserve vehicle momentum (or at least maintain constant accelerator pedal pressure), and offset the pulling caused by the blown tire by gently counter steering to keep the vehicle in its lane. Once the vehicle has stabilized, the driver can gently slow down and begin to carefully pull over to the side of the road.

Members of The Tire Rack team had the chance to experience tire blowouts at highway speeds at Michelin’s Laurens Proving Grounds. Tire after tire was sacrificed as participants were allowed to drive vehicles fitted with tires rigged with explosives attached to their sidewalls (a rear tire on a full-size SUV and a front tire on a full-size sedan). These tires were literally “blown out” with all of the accompanying noises.

While our drivers faced the initial intimidation of knowing they might be challenged to maintain vehicle control, we found that following the recommended procedures allowed us to easily continue in our original lane and gently slow down. Essentially our drivers learned you should continue to drive “through” tire blowouts to maintain vehicle control and worry about determining the cause of the problem later.

Remember: These are techniques, not guarantees. Please drive safely.

jcantor · #9 11-12-2003, 12:24 PM

Luke,

Thanks for the excellent and very well detailed answers to our questions.

BTW, is there anyway short of getting a job with TireRack to be able to participate in some of the proving grounds trials that you refer to?

jlc

Luke@tirerack · #10 11-12-2003, 12:26 PM

$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$