TKC80s not legal!?
 

In preparation for a trip to Latin America, I recently had TKC80s fitted to my BMW F650GS twin. When double-checking the recommended pressures with Continental they sent me this slightly disturbing reply:

....
Slight problem with fitting TKC80's on your machine; the 110/80 B19 is bias
ply construction and the 140/80 -17 is cross ply construction.

UK law does not allow this combination however it may be acceptable in other countries, but I would check before you go.

The only recommended fitment for your machine is the ContiTrailAttack
Continental Tyres UK
....

Anyone know what the difference between bias and cross ply is?

Thanks!

Well, here is the short answer.

Radial tire - Wikipedia, the free encyclopedia

Bias ply are also known as cross ply, and, yes these constructions of tyres are not supposed to be mixed on a vehicle. The wiki article explains something about this.

"bias" is a word used in textiles for the "cut of the cloth" so I can see how that terminology is used here, but "cross ply" is the more common term for the UK.

You can use 110/80B19(TL) and 150/70B17(TL) or 100/90-19(TT) and 130/80-17(TL/TT).
If you go for 150/80B17 you have to see that there is enough room.

The main thing remember for cross plys and radials is never to mix them on the same axle as each style of tyre acts slightly differently under applied loads. Not a problem on a bike. Apart from that theres' no worry. As long as you get a feel that you like there is no other defining logic.
As for some police force jumping on you for a mix of tyre compositions is beyond the realm of well.......... Though I have known a group of Germans being done for not wearing seat belts on their bikes down in C.A.R back in '92 !!

When I ran a mix on my Land Rover, besides not mixing cross plies and radials on the same axle, the other rule was if you are mixing them then run the radials on the back and the cross plies on the front. This was so your arse didn't overtake you.
The handling affects on a bike would be very different to a seventies Landy.

...will the police check the tires, or will they simply check that the tires are in good condition?...
Common sense applicable?

Thanks for all the thoughts guys. I feel educated now :innocent:

And yes indeed, common sense - I like the tyres and I wasn't about to ditch them or anything, just curious.

Well, just to set your mind at reat, I rode the PanAm throughout north/central/south America with TKC80's on the front, and a few different tyres on the rear, NO ONE CARES down that way ;)

I was stopped many times by Police, Army, whatever and no one even looked at my tyres.

A lot wanted photos of me and them with the bike though :)

Cheers
TS