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Twins Technical Talk Technical Talk for Hinckley Triumph Twins: Bonneville, T100, Speedmaster, America, Thruxton, and Scrambler.

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Old 04-13-2011, 01:30 PM   #1 (permalink)
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Mixing Bias belted and Radial tires

So what gives. Some newer HD's have stock Radials in back, Bias on front. Triumph has stock radials on front and Bias belted on back for the 2010/2011 Speedmaster.

My 07 Speedmaster rear Metzeler Bias belted stock marathons have plenty of miles remaining and I am looking to replace my front tire only. Do not want a stock Metzeler Lasertech, b/c i do not like the tracking irregularities character.
Thinking about a Michelin Pilot Road 2 Radial for experiment to replace front.

I am not a aggressive rider but want a better feel and look. I am aware of the Avon's, Pirelli's and other Bias front tire options.

Am i nuts? Easy now
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Old 04-14-2011, 10:36 AM   #2 (permalink)
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Everything I have read says "Don't do it!" My understanding is that radials have a lower profile and that the wheel width needs to be correct to acommodate it. Also, radials have a different handling characteristic than bias ply. The Harleys are likely engineered to take care of the performance difference (gratuitous slam - as if a Harley rider would notice!). My guess is that H-D is taking advantage of the lower profile offerred by the radials to go to a fat but short tire.

I'm a bit obsessive about my tires. I don't even like mixing tire models front/rear, much less brands. I would suggest going with a Metzler bias for the front. If you can't find one that fits IMHO you hould stay with a bias ply of a different brand.
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Old 04-14-2011, 01:12 PM   #3 (permalink)
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Not sure what they come stock with now, but T100s did come from the factory with a Lazertec on the front and a radial Metzler on back. Seemed as though it actually handled better with the mixed tires that it does now with matching Lazertecs front and rear... think I'm with ya on the 'tracking irregularities character'.
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Old 04-14-2011, 01:39 PM   #4 (permalink)
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Legal fitments must be both tyres the same , or radial rear with a crossply or bias belt front . Illegal fitments are radial front with a crossply or bias belt rear , or bias belt front and crossply rear . This is the law in the UK . Saying that , my 09 Bonny currently has a bias belt Avon distanzia rear and a metz Z4 radial on the front so while actually illegal , it handles fine . That and as the baffles for the arrow 2 into 1 have been on the bench in the garage for 8 months it is quite loud so I think any copper will be more interested in the noise rather than the tyres .
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Old 04-15-2011, 02:31 AM   #5 (permalink)
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I don't know of any laws here in the US regarding fitments of tire construction types on MC's. But if you look at the spec's for the US version of the Speedmaster and America, they use a stock metzeler radial up front.

I am beginning to believe that the common wisdom of NOT mixing Bias and Radials on a motorcycle is simply the result of decades of use on automobiles. Vehicle suspension, wide track tires, less firm sidewalls on car tires, 3000 lbs+ weights and the way it all reacts on a four wheeled vehicles.
Ideas that simply don't pan out generally on motorcycles because of narrower rims sizes along with the standard widths and air pressures on lesser vehicle weights, not having the same reaction of a four wheeled vehicle's suspension as it does on two.
Disclaimer:
I am not at all sayin to anybody or suggesting that mixing tire constructions for riding track or aggressive sport bike cornering is a good idea, its dangerous.
I am not a expert or engineer. DO NOT TAKE THIS SERIOUSLY. BE careful, use good judgement.
Matter of fact IMO, on wet surfaces a good tacky front radial and a hard rubber metzeler marathon in the rear may bite you if you get too confident in a hard turn on a Cruiser with Bias ply on back.
On the other hand the feel with a radial in front doing general cruising in sane speed zones may just be a good thing. But then if you think about it (just thinking as i write this)
Suppose you corner at a intersection and there are small pebble/stones in your turning path.....your front tire will instantly pass the feel to your grip, your first symptom telling ya whoa baby, the Radial may hold the line better than a Bias. So it may cause your rear to slide out, go down if your reaction times are slow.
May take some getting used to the feel.

Too bad there are not any radial options for a 15 inch rear wheel to match.

Last edited by mstrmac; 04-15-2011 at 02:39 AM.
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Old 04-15-2011, 03:35 AM   #6 (permalink)
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Quote:
Originally Posted by mstrmac View Post
Triumph has stock radials on front and Bias belted on back for the 2010/2011 Speedmaster.
Are you sure? As John pointed out, that would be illegal in the UK. The Metzeler Lasertec is a bias ply tyre (front and rear fitment versions). The 865cc T100, Bonnevilles and Thruxtons used to come from the factory with an ME33 or Lasertec bias ply front and an MEZ2 radial rear. Don't know what they put on them now.
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Old 04-15-2011, 12:06 PM   #7 (permalink)
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Originally Posted by PAAS View Post
Are you sure? As John pointed out, that would be illegal in the UK. The Metzeler Lasertec is a bias ply tyre (front and rear fitment versions). The 865cc T100, Bonnevilles and Thruxtons used to come from the factory with an ME33 or Lasertec bias ply front and an MEZ2 radial rear. Don't know what they put on them now.
i did not actually look at a 2010/2011 America or Speedmaster but you can google or bing it and here is what you get:
American Pricing : $TBA USD
Engine
Type Air-cooled, DOHC, parallel-twin, 270 degree firing interval
Capacity 865cc
Bore/Stroke 90 x 68 mm
Compression Ratio 9.2:1
Fuel System Multipoint sequential electonic fuel injection with SAI
Transmission
Final Drive X ring chain
Clutch Wet, multi-plate
Gearbox 5-speed
Cycle Parts
Frame Tubular steel cradle
Swingarm Twin-sided, tubular steel
Front Wheel Cast aluminium alloy 5-spoke 19 x 2.5in
Rear WheelCast aluminium alloy 5 spoke 15 x 4in
Front Tyre 100/90 R19
Rear Tyre 170/80 B15

Front Suspension Kayaba 41mm forks with polished lowers, 120mm travel
Rear Suspension Kayaba chromed spring twin shocks with adjustable preload, 96mm rear wheel travel
Front Brakes Twin 310mm discs, Nissin 2 piston floating calipers
Rear Brakes Single 285mm disc, Nissin 2-piston floating caliper
Dimensions
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Old 04-15-2011, 05:14 PM   #8 (permalink)
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According to Metzeler the fitment for the front wheel of a 2011 Speedmaster is a 100/90 - 19 M/C 57H TL ME 880 MARATHON and the 2011 America a 130/90 - 16 M/C 67H TL ME 880 MARATHON, both bias ply tyres I believe. It wouldn't be the first time that specs on Triumph's web site have been incorrect. If I get the chance to visit a dealer over the weekend I'll see what tyres are actually fitted and get back to you. I don't blame you for not wanting a Lasertec on your front wheel. I had a pair of Lasertecs on my T100 and the bike wobbled badly when crossing white lines and tar snakes.
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Old 04-15-2011, 07:56 PM   #9 (permalink)
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Old 04-15-2011, 08:19 PM   #10 (permalink)
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Yes, I've looked at Triumph's (UK) website and am aware of what it says. But again, it wouldn't be the first time it's had errors on it. In the UK we have annual government controlled inspections known as the MOT. I've checked again, and if you presented a bike fitted with a radial front tyre and either a bias ply or cross ply on the rear it would fail the test. Irrespective of whether that combination is actually dangerous in practice, it would be illegal to use it on UK roads. Therefore I find it impossible to believe Triumph actually fit this combination despite what it says on their website.
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Last edited by PAAS; 04-15-2011 at 08:22 PM.
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