Safe to mix bias & radial tires?

[Duck-Stew]

I'm already leaning towards a resounding 'NO WAY' on this, but would it be safe to run a biased front and a radial rear on a motorcycle?

I'm shooting for ~200mph this year which is a borderline for available motorcycle tires.

[sabat]

Is there a bias tire with a Z rating? What size do you need?

[Duck-Stew]

Front is either a 17x3.5 (which radials are readily available for and I can't find a biased ply), or a 17x1.85 (which is a biased ply only (top-fuel front runner 22x2.5x17).

Rear is a 17x4.5 for which I can only find a radial road-racing tire (160/60/17 or there-abouts).

[sabat]

Why not just go with the wider front rim? You could mount a relatively skinny 17" radial tire. Like from a 125cc road racer.

[Duck-Stew]

Why not just go with the wider front rim? You could mount a relatively skinny 17" radial tire. Like from a 125cc road racer.

I couldn't find an appropriately speed rated radial for the front.  There's a soft-compound radial Bridgestone road-racing slick that only fits a minimum rim width of 2.15".  That's all I could find.

We're planning on running the 3.5" this year and graduate to the 1.85" for 2014.

I did find this blurb on the Avon motorcycle tire website:
"TIRES: RADIAL VERSUS BIAS
While running a bias ply front tire and a radial rear tire can be acceptable in certain applications, you should never run radial front and bias rear as this can create an instability issue."

If that's the case, then we can run this 1.85" front rim this year coupled with a radial rear tire (medium compound road-race slick...)

[wobblywalrus]

Some of the Triumph Bonnevilles were equipped from the factory with radials on the rear and bias plies on the front.  It worked OK on the street, sort of.

Racing on the salt was a different matter.  The bike could easily, and did, go into horrible speed wobbles.  A radial on the front was a part of a big package of different things that cured the problem.

Probably the best thing is to talk to someone like John Noonan.  He has gone over 200 mph more times than almost everyone and he has done it on many different tracks and surfaces. 

[saltwheels262]

not a good idea to mix bias and radial tires - even @ 50 mph. imo.

[dw230]

When I was in the service I needed a pair of tires for my car. I went to the Goodyear store outside the base and wanted a pair of radials. The store owner, Indy car driver the late Chuck Hulse, would not let me do it. Sold me four radials, fair price because he drove one of my Dad's cars in the 50s/60s.

DW

[maj]

get the bt003's in whichever combo suits your rims ,class legal and they seem reliable to 250mph and slightly above

[fastman614]

It looks as if you are talking motorcycles here..... In years gone by, we ran Z rated shaved radials on the back of our Vega with bis ply front tires..... We had 60+psi in the rear tires. I was told by a tie engineer that the rear tires, with that much air pressure, would not really be "acting" like the were radial tires....

IMO about doing so on a motorcycle though, I would NOT try it as motorcycles and cars are not the "same animals"....

[Duck-Stew]

get the bt003's in whichever combo suits your rims ,class legal and they seem reliable to 250mph and slightly above

Ok.  For this year's rim widths, we just got confirmation that the BT003's will be legal for the speeds we'll be capable of (at least so far we're capable of them on paper...)

Thanks all. 

[Seldom Seen Slim]

"...for the speeds we'll be capable of (at least so far we're capable of them on paper...)..."


This reminds me of one of Jack Dolan's comments - which was something like theoretical speeds yield theoretical records - or something.  Jack, in case you're lurking -- howdy.  We do miss you here.  I think I may have finally surpassed your humongous number of posts.  Come back and say hi when you can.

Edit added a few minutes later on:  Well, maybe he's not watching.  I just checked -- he hasn't been "active" (for whatever that means to the SMF people that wrote the Forum software) since November of 2010.

[fredvance]

And we have missed him!!

[maj]

   Yep  his dry comments always made an impression

 

[hotrod]

On cars mixing bias and radial tires can be a deadly mix and is very strongly discouraged!

Their cornering behavior is very different when you are steering and or turning and putting side loads on the tires.
They also have very different characteristics when they break away and near the point that they start sliding.
This could make a high speed wobble much much more violent than it would be on matched tires.

The two tires (at normal pressures) behave very differently when it comes to the tendency to follow undulations and ruts in the surface and as a result the car gets very spooky.
I bought a used car from a guy (Plymouth Road Runner) and at low speed at city street speeds was well mannered but at highway speeds it behaved absolutely evil on uneven surfaces.
When you crossed a diagonal rail road track or seam in the road like where an off ramp comes off the main road it wanted to dart sideways violently as it crossed that seam or rut.

It took me a couple days to diagnose it, but it was because he had mixed radial and bias tires, the bias tires wanted to follow the rut, and the radials never even noticed the rut or ridge.
I don't recall for certain which end had the bias tires but was a real handful to drive on a road that was not smooth and flat over about 45 mph until I figured out what was going on.

I would not recommend it!

Larry