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Discussion Starter · #1 ·
Our modern classics, at least mine, has a bias ply tire on the front, and a radial tire on the rear. That has been verboten for cars, motorcycles, RVs etc everywhere but at Triumph as far as I can tell.:cool:

My Bonnie's handling seems just fine, but I'm wondering what riders are doing when it's tire replacement time? And at what point the stock tires need replacing? On my BMW I typically replace the tires with Michelin PR2, but I think they might not be appropriate for the lighter weight Bonnie.

Thanks for your input!
 

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When my Z2 wore out, I replaced it with a Metzeler Lasertec rear tire. They match the front tire perfectly.
 

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One of our fine British friends had posted that the practice of mixed bias ply and radial tires on a bike was illegal in the UK. Given that every new Bonneville I have seen in the USA has come from the factory with a radial rear and bias ply front I just don't know what to make of it... except as a rule I'm filing it into the 'old wives tale' category. My '05 rode fine with that combo and so did my son's '07 Bonnie.
Another thing I'm filing into the 'old wives tale' category is the "don't ever mix brands of tires front and rear". I'm not going to question that there may be SOME types of tires that negatively affect handling when different brands or different profiles are mixed - front to rear. I had to change the Metzeler ME88 on the rear with a new tire but did not want to change a perfectly good Metzeler ME880 on the front. Now I have a Bridgestone Sptifire on the rear along with the Metzeler ME880 on the front. So far I've had over 300 miles of very good handling with this combo... but they are now both bias ply tires too :-0)
 

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One of our fine British friends had posted that the practice of mixed bias ply and radial tires on a bike was illegal in the UK. Given that every new Bonneville I have seen in the USA has come from the factory with a radial rear and bias ply front I just don't know what to make of it
I think (but I'm not 100% sure) that it is only illegal to have radial front mixed with bias rear. I think the other way round is legal.

Clearly a radial rear and bias front works fine - lots of us have tried that now.

Presumeably the opposite can lead to some handling issues. I very vaguely remember a lot of discussion about it on TV in the seventies. But I was a kid so I wasn't paying much attention.
 

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I think (but I'm not 100% sure) that it is only illegal to have radial front mixed with bias rear. I think the other way round is legal.
That's correct. The UK law states that it is illegal to mix tyres of different types on the same axle (irrelevant to us) and illegal to have radial tyres on the front axle and cross-ply on the rear axle. (Bias-ply tyres are considered to be a subset of cross-plies for this purpose).

This regulation was introduced in the 1970s or thereabouts when radial tyres began to be popular, and people would not consider the suitability of mixing tyres, but just fit them as and when. I think the theory is that radial front/x-ply rear would oversteer at the handling limit, whereas x-ply front/radial rear would understeer. Understeering is considered to be the safer behaviour of the two. The rule is irrelevant to bikes as far as I know, as motorcycle's handling dynamics are a world away from a car's, but since when did the lawmakers ever consider the needs of bikes?

So the radial rear and bias front are legal and correct.

ADDED: The UK government don't put the vehicle Construction and Use Regulations online, which is a pity, but this is the nearest I could get. (Local authority guidance.)
 

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Discussion Starter · #6 ·
....... My '05 rode fine with that combo and so did my son's '07 Bonnie.
Another thing I'm filing into the 'old wives tale' category is the "don't ever mix brands of tires front and rear". I'm not going to question that there may be SOME types of tires that negatively affect handling when different brands or different profiles are mixed - front to rear.................... :-0)

Yeah, I have no complaints on my Bonnie's handling at all. My other motorcycle is a BMW R1200RT, which came with Bridgestone tires, I think BT020s. Handling was fine. However, when the rear got iffy I replaced it with a Michelin PR2, which I've had on my last two RTs. So I'm a miss-matched set on the Beemer. I have not noticed anything this, but then I'm still getting the new rear "settled", it has only 75 miles on it right now.
 
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