Can radial tires be mixex with bias

[ernemats]

Can I put regular tires on the front of my tractor when I have radials on the rear ? It is four wheel drive and I don't want to damage the transmission or gear cases. Thanks

 

[Texasmark]

Opinionated reply: For a given tire size, being air pressure dependent, especially at lower air pressures, your main concern would be "rolling circumference". Since you said "I put", past tense, you already mixed them. I'd get on soft ground in 4wd and make some zippers. Tweak your radial air pressure (should be the most sensitive to this trial) until you don't see any squirming on either set of tire marks. That would be what I would do.

Fronts are auxillary power so main drive needs to be rears. Any differences should favor rears with no sliding marks. Course in turns you want the fronts pulling you around the turn rather than the rears pushing straight ahead and forcing the fronts to slide/being pushed through the turn.....analogous to a front wheel drive sedan pulling you through a turn vs a rear wheel drive pushing the fronts for an example.

I noticed European farming Utube videos where large 4wd, radial equipped, farm tractors pump up the tires for road use and once on the field deflate the tires. I would assume 2wd is used on the road and it's obvious 4wd was the necessity in the field. So pumping them up for road use may have been to reduce sidewall flexing for longer tire life, not an attempt to maintain the proper drive ratio between fronts and rears.

I have mixed the two on drive and driven vehicles on the road and with 4 ply type tires, the radials will squirm while the bias won't and makes for a funny feel, not unsafe, just different. I would prefer bias on the fronts with a FEL if mixing, unless the fronts are near the diameter of the rears, like older Fords, JD, and IH machines I have seen.

 

[PILOON]

On a tractor I'd not be overly concerned as long as sizes are OK.
BUT
Once they did that on a company car I once drove and that darn car squirmed all over the place.
I had to take serious measures to force them to change them out to a correct matching set as that car was looking for an accident.
That was back when folks only installed snows on rear driven wheels and kept all seasons up front.
Dang car would jump and leap whenever I changed lanes and dangerous at higher speeds.

 

[RNeumann]

No issue on a tractor......unless you are doing 40+ mph for hundreds of miles at a time.

 

[ernemats]

Have not done it yet just thinking about it. Rears are 16.9 x 30 fronts 11.2 x 24. I do very little road running and not over 15 mph if I do and if so no more than1/4 mile at a time.

 

[ernemats]

Talked to a tractor tire dealer yesterday and they do not recommend doing it as the radials have a tendency to squat where as bias do not do it as much and therefore changes the rolling circumfrence a little.

 

[PILOON]

Talked to a tractor tire dealer yesterday and they do not recommend doing it as the radials have a tendency to squat where as bias do not do it as much and therefore changes the rolling circumfrence a little.

Heck, why not simply use higher PSI then.
The whole idea is that the smaller fronts will wear faster than the rears so there will almost never be a real match hence they usually suggest a 5% oversize to start.
On 'non hard' surfaces slippage compensates anyway.

 

[kthompson]

Have you talked with a dealer? Radials do squat so to speak but it is rather common with tractor tires to bump up the pressure for side loads or for front end loader as has been pointed out. Just wondering, any chance the circumference of radials might be same as bias belt with same air pressure.

 

[AWSubie]

The reason why bias and radial tires should not be mixed applies to the difference in spring rates between the two types of tire construction. On a vehicle that is road driven at higher speeds, the handling of the vehicle is negatively effected when one tire reacts differently than another. For a tractor operating at slow speed, you don’t need to be concerned about mixing tires.

 

[Bird]

Once they did that on a company car I once drove and that darn car squirmed all over the place.
I had to take serious measures to force them to change them out to a correct matching set as that car was looking for an accident.
That was back when folks only installed snows on rear driven wheels and kept all seasons up front.
Dang car would jump and leap whenever I changed lanes and dangerous at higher speeds.

I had the same thing happen years ago. It was a city car that had been driven by someone else and I couldn't believe anyone could have driven it and not get that "fixed". It even had a radial on one front wheel and bias ply on the other front wheel.

 

[ovrszd]

Have not done it yet just thinking about it. Rears are 16.9 x 30 fronts 11.2 x 24. I do very little road running and not over 15 mph if I do and if so no more than1/4 mile at a time.

Yeah Mark assumed you already mixed them in that first post.

You'll have no problems as long as the rolling circumference is similar. They will be similar as long as you don't change sizes. I don't think you'll notice any difference.

 

[Warpspeed]

Its an interesting question, there are so many aspects to it depending on the type of vehicle, two wheel drive or four wheel drive, type of centre differential, and where and on what surface its driven especially with a locked centre diff.

One thing to think about is that most if not all radials these days have a steel belt to give vastly improved sideways stability to the tire. Now think about that for a moment. The steel belt cannot stretch or change length under high or low air pressure. The tire circumference does not change. It does look awfully flat at the bottom with less air, but the rolling circumference does not and cannot actually change.
On a low speed 4WD tractor I would think fitting the same sizes as the recommended factory originals would be all you need to worry about.

On a high speed road car, radials and cross plies have completely different handling characteristics.
Definitely the same type on the same axle, but you can mix fronts and rears, but its probably not a very good idea.
If you must mix front to rear, then always the radials must go on the back no matter which wheels are the driven wheels.

The reason for that is that at the limit of adhesion the radials will always grip better and hang on for longer assuming good tread and a dry road. The cross plies roll onto one shoulder and then let go suddenly.
If it breaks loose at the front you go off the road facing forwards, and may still have some limited control (understeer). You crap your pants, but at least you and the car probably survive the experience.
If it lets go at the back (oversteer) the car will spin and an inexperienced driver will immediately become disoriented traveling sideways or backwards off the road with absolutely no control at all.

A controlled crash is always better than an uncontrolled crash.
You might just be able to avoid the steel pole or concrete wall at the very last moment if you are still traveling forwards and can see ahead with some minimal control of direction.

 

[zzvyb6]

The reason for that is that at the limit of adhesion the radials will always grip better and hang on for longer assuming good tread and a dry road. The cross plies roll onto one shoulder and then let go suddenly.
If it breaks loose at the front you go off the road facing forwards, and may still have some limited control (understeer). You crap your pants, but at least you and the car probably survive the experience.
If it lets go at the back (oversteer) the car will spin and an inexperienced driver will immediately become disoriented traveling sideways or backwards off the road with absolutely no control at all.

Not exactly. Radial tires have much softer vertical spring rates and ride better as a result. They usually have quite a bit higher cornering stiffness because the sidewall, bead area and belt package [as we call it in the industry] structures are reinforced differently. Because of this they also have much less self aligning moment (like 10 times less). This is recognized by the lack of steering wheel returnability. Also because of the soft sidewall, they have very little camber stiffness. The end result is the dangerous practice of 'intermixing' the two types. A vehicle not designed for radials will have a very high steering gain and little steering feel, and a slow response initial response and settling time.

This is why tires named or referred to as 'racing radials' are not radial construction. To prove it, we burn them or slice them and examine the cord angles. Just the thin sidewall alone severely reduces the puncture and damage resistance of the tire. Not a good situation at 180+ mph.

Yes I worked in the industry.

BTW, this is also why a sidewall nick or cut repair is forbidden at all reputable tire shops. Too much flexing for a patch to contain and still be durable and not self destruct from strain and heat cycles.

 

[Warpspeed]

Yes they ride more softly with softer vertical rates because the sidewalls are made much thinner (much lower ply rating) than cross plies.

They have exceptionally higher cornering stiffness and much lower slip angles because the steel belt under the tread is exceptionally stiff in shear.

Self aligning torque (of the steering) comes from a built in deliberate front end caster in the front end geometry, not from the tires. A shopping trolley can have solid wheels, and all four wheels self steer and align themselves perfectly with whichever way you push the trolley. Bicycles self steer too, you can ride without touching the handle bars and the front wheel self aligns. Nothing to do with the type of tires.

Yes you are quite right about racing radials.

 

[zzvyb6]

Self aligning torque (of the steering) comes from a built in deliberate front end caster in the front end geometry, not from the tires.

That's not true, either. Self-aligning torque comes primarily from the twisting of the belt, sidewalls and beads. It's actually due to a fore/aft force distribution across the tire. Caster is added for several reasons. It adds a lateral force component to the tierod and steering rack which adds some effort/feel and returnability. It also aligns the tire's peak force from load and slip angle with the tire's peak aligning moment. Otherwise, at extreme sideforce/ cornering levels, the aligning torque starts to reverse and can go negative. That 'feel's all wrong to most drivers. I personally know that some race drivers can NOT trust their car's sidebite capability unless this is done. It does cut down the max grip level slightly but adds to a driver's confidence.

Your caster wheels are solid metal or plastic. Very little deformation possible to develop an aligning moment, hence the necessary high caster setting.

Here's my job in action: Tire Force Test - YouTube

The squeal is a high pressure supersonic air bearing under the roadway belt. This is a production SUV tire undergoing a simulated vehicle rollover maneuver. Doesn't even loose air, (as required ).

That's why we run tests, computer models and road measurements

 

[Warpspeed]

Feels all wrong to most drivers, definitely have to agree.... Its terrifying.

That is very interesting about aligning torque reversing at very high force levels. I may have personally experienced that on the race track a couple of times, and its a truly frightening effect. Never understood how or why until just now, but you can be cornering very hard, and suddenly the steering tries to go full lock with enormous force.

Anyhow, caster definitely effects straight line stability, braking stability, as well as off centre steering loads (and feel).
Under those conditions there is not a lot of cornering force, if any at all. And we still need sufficient self aligning torque, and the belts in the tires are not going to provide that when steering straight ahead.

 

[ovrszd]

Great stuff. If we were on an auto forum. Not sure what any piece of it has to do with a tractor?

 

[zzvyb6]

All that matters to tractoring is the effective rolling radius. But, the manufacturer may have already built in an optimum front/rear slip ratio to give the best traction for pulling taking into account the type and pressure. If you change this, then drivetrain strain and traction reduction is likely.

For loader work, since radials 'squish' more and the wheels may not have been designed for radial tire bead forces, there may be airouts, blowouts, and bent rims (outward) resulting. Some operators stretch the limits and those are usually the ones that are the loudest on forums complaining about 'bad' designs, quality, cost of parts and disappointment with their purchase. Foreseeable misuse of anything these days is a crisis in any product development cycle. That's another reason so many companies have left the States. You can't fight them overseas.

 

[DarkBlack]

The tire circumference does not change. It does look awfully flat at the bottom with less air, but the rolling circumference does not and cannot actually change.

Got to disagree with that statement.

 

[ovrszd]

Got to disagree with that statement.

This is much debated.

Warpspeed is correct in the sense that the distance around the outside of the tread does not and cannot change.

With that given, wouldn't it be logical to assume the distance traveled with each revolution remains the same? Even though the sidewall has bulged and shortened the tire height if measured from the ground up to the top of the tread?

This fact is what made Radial tires so popular. The radial design keeps the circumference from changing. This design makes the tire roll much easier because of a lack of distortion on the tread face. Thinner, softer sidewalls take care of the "squat" or "bulge". The sidewall requires much less HP to flex than the tread would.