Radial & Bias

I just purchased a K1100LT from my friendly local(?) BMW dealer. I like the bike more than I thought I would. Had a superb R1100RS; but, it began exasperating
my back problems. Anyway, the dealer had installed a new front tire. Good. On close inspection I find the tire they installed is a bias ply and the rear tire is a radial ply. I thought you just don't mix tires. The bike does handle a little funky on the twisties. I thought it might be due to the added weight of top box and radio. Any thoughts or advice?

Used to be YellowBikeMike
Now Family Truckster Mike

I believe that those bikes all came with radial tires as standard, I may be wrong as I have never owned that new a bike. BUT, I do know that you should never mix Radials and Bias Ply tires on any vehicle. You are asking for a very bad accident.

If I was you, I would be back at the dealer demanding the proper tire be installed ASAP. Do NOT ride at any great speed nor do any "canyon carving" as it is presently equipped, unless your medical insurance is up to date, and you like to spend time in the company of nurses, or worse yet, enjoy being in a pine box underground.

shire2000 said:

I believe that those bikes all came with radial tires as standard, I may be wrong as I have never owned that new a bike. BUT, I do know that you should never mix Radials and Bias Ply tires on any vehicle. You are asking for a very bad accident.

Click to expand...

Why? Or perhaps the proper question is why not?

// marc

marchyman said:

Why? Or perhaps the proper question is why not?

// marc

Click to expand...

Radial tires have more sidewall flex than bias ply tires. that is why bias tires usually have a greater load capacity. With the tires flexing at different rates, that might be why the bike corners funky.

Ralph Sims

I haven't noticed any funkyness in cornering, but then I'm not the fastest rider in any given group, either. On my '05 GS I currently run a radial (Tourance) on the rear and a bias ply (TKC-80 knobby) on the front. It works for me.

// marc

Radial ply tires flex easier than a bias ply and have lesser roll resistance, but given front tires are different sizes, shapes, and treads than rear tires I doubt that you can identify any real issue with mixing. None-the-less, the dealer should have matched them. I would go back and demand matching ply tires.

I wonder if your owners manual might have some guidance in this situation?

Well folks I went back to the dealer yesterday. Their comment was "I can't believe we did that". They looked at the rear tire and said "this tire is cracking, so you'll need to replace this anyway. We can sell and mount a bias ply tire for you". Well the rear tire does show cracking - in the mold coating that is remaining high on the shoulder. I told them this but they hold to the rear tire needing replacing. This from a dealer I thought was one of the best. Yeah it's my fault for not being more observant before the purchase. Let the buyer beware.
Thanks for all your input.
Family Truckster Mike

Both the manufacturers of tires and vehicles along with the "so called" experts who test and engineer these things state that you should not mix types of tires, i.e. Bias Ply and Radial. They have completely different handling charateristics in different situations. Under normal low speed operating you may not notice the differences, but all you need is that one time in an emergency situation.

I can just imagine your insurance company stating that they won't cover the accident because you could have avoided the situation if you had the properly matched tires on the vehicle. You just know they are always looking for some way to deny a claim and therefore save themselves money.

Upon further investigation, BMW specs bias ply tires for this model (K1100LT). So the dealer was not wrong in installing the bias front tire, but, they sre should have noted otherwise. That being said, I'll install the proper bias ply tire on the rear as soon as it arrives. Anybody need a little used Avon Azaro 140/80 ZR17?
FamilyTrucksterMike

The H-D Rocker comes from the factory with one bias and one radial tire. The no mix policy came from long ago before adequate testing and just kinda hung around. Isn't true anymore.

PS, Just so I don't have to defend H-D, the Yamaha Star Raider also has a mix of bias and radial.

shire2000 said:

I can just imagine your insurance company stating that they won't cover the accident because you could have avoided the situation if you had the properly matched tires on the vehicle. You just know they are always looking for some way to deny a claim and therefore save themselves money.

Click to expand...

May I politely say: BS!

Your insurance company will pay off if you are DRUNK! [and then drop you like a hot coal] if you have the appropriate coverage. Now, if you show me a specific exclusion in your policy I'll certainly feel otherwise. Otherwise the fear of no insurance is just another internet urban legend.

// marc

If you think that your insurance company will not make a stink and may actually pay you out if you have an accident, if they can prove that the accident could have been avoided due to your negligence? Well, good luck with that.

Here in B.C. we have government run auto insurance and they are always looking for ways they can get out of paying. When they investigate an accident, they not only look at who was at fault, but also check to see if you vehicle was properly maintained. i.e. appropriate tires for the vehicle along with proper lighting, etc. There have been some cases where people were rear ended and the claim was denied because the brake lights were not working, or at night the running lights were not working. They have come out and stated that if you hit someone on a rainy day and they find you have bald tires - you are not getting paid out in full. If you are in an accident in winter on snow or ice covered roads, and you do not have snow tires on your vehicle, then you are not going to get paid out in full. They may pay out a lessor amount due to your negligence and the local police may actually charge you with negligent driving (yes, we do have that charge here).

Oh, and here in B.C., if you are drunk and have an accident, the insurance company will pay for the other person's damages, but will then sue you for reimbursement. You will get nothing for your damages.

Let's not get on our high horses about what the insurance companies will or will not do. We all know that they are in business to make money and therefore will try to limit the amount they pay out on claims any way they can.

The whole point of this thread was about mixed tires on a bike and my point is to keep your bike properly maintained.