GPZ-Bob
Two Stroke Sniffer
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Nobby the Bastard
Harley Gaydar
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ThatDippyTwat
World Chat Champion
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Ste
Not Work Safe
Joined: 01 Sep 2002
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Teflon-Mike
tl;dr
Joined: 01 Jun 2010
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 Posted: 01:50 - 30 Dec 2018  Post subject: |
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On a YBR, I cant say.... but.... the 'old' as in before it was officially a DT, DT was specced to have regulation 2.75x21 front, 3.50x18 rear, (I think, from hazy memory). ACU/FIM regs for competition trials provide2.75x21 front, 4.00x18 rear, BUT with a limit on the tread pattern and depth, essentially defining a block-tread, rather than a full-on knobly. When the lads started to use these in clubman enduro, you could fit a 4.00 trials tyre on the back, no real problem, B-U-T.. if you wanted a more agresive scrambles knobly, then you would have to down-size back to 3.50 or maybe even 3.00 depending on how agressive the tread, in order to not foul on the swing-arm.... IE, its NOT just the tyre size that matters.
More from trials.... you want to put more rubber on the terra... let the tyres down...... tyre squashes, and you get a bigger foot-print....
Ever tried riding a motorbike with only 3psi of pressure in the rubber? Hmmm....
Off-Road, on the loose, it sort of works, because the flat tyre beneath the wheel, squirms about a bit less than the mud would, with properly inflated tyre squeezeeing it into ruts..... and the 'grip' is a perverse kind, that's as much viscouse as it is frictional....
ON road.... with a hard surface beneath the rubber, a flat tyre is a flat tyre, and it just wobbles around beneath you, and you dont get any extra grip... just the directional stability of a drunk lurching after another pint!
In pure friction, the 'grip' is the % of the weight force, clamping rubber to road, that the rubber can transmit side-ways. The critical factor here is the co-efficient of friction, how sticky the rubber be, NOT how much of it is squashed against the tar, which actually doesn't even factor in the sums....
A-N-D would likely be a constant anyway... you have 130Kg of bike, and 70Kg of rider weighing down two wheels, each pumped up to about 30 pounds per square inch.... 200Kg is just about 440Lb, divided by two wheels, means about 220lb per tyre, divided by 30lb per square inch, you get approx 7 square inches of rubber per tyre.
Don't matter what the carcas dimensions are; could be a skinny 2.25" front tyre, or a fat car tyre rivalling 400mm section hoop... it AINT gonna put any more rubber on the road for it, unless there's more wight squashing it, or less pressure resisting that squash!!!
Old rule of thumb, was as wide as you have to, as narrow as you can....
A narrower tyre, has to roll less from the center line for any angle of lean, so it tends to give a lot more neutral handling, with less geometry change as you steer. It also tends to offer less rolling resistance, the contact patch where its squashed out, pushed into an oblong along the length of the bike, rather than across its width, giving a smaller frontal area for 'drag', so more mph and more mpg for it NOT being so wide, AND better handling AND they tend to be cheaper to buy....
So why fit fat rubber?
Basically cos of the look.... pandering to the aesthetic, you spend more money, to get less speed, use more fuel, and worse handling, and NO more grip..... its rather a lot of negatives with almost no possitives...
And its a YBR..... its hardly going to win any medals on the cat walk to start with.....
It is what it is, a humble low cost ecconomy commuter bike, with few pretensions of being anything but bus-fare beating transport. It wont look any better than it did when it came out the factory, and anything changing the look, will, to any-one who has a clue what they are looking at, just look a bit daft, at best......
More Grip?
The YBR comes with rather concrete OE rubber that has about as much grip as I do on reality.... not a lot then.....
As said, this has naff all to do with the tyre sizing, but a heck of a lot to do withe the rock-hard rubber compound, speeced cos its cheapo, and likely to outlast the bike for wear.
You want more grip.... you want better... NOT wider.... and softer is better.
They have dropped my favourite lightweight rubber from the brochure, that was a Mitchelin M45... I think it has been superceded by the 'Pilot Sport' which comes in the same compound, but a slightly sportier and possibly not so great in the wet, tread patern.... got to be better than the OE crud though, or a budget ChengChit....
Aprox £80 a pair, 'Decent' rubber on a bike like this isn't 'cheap', but its far from expensive either..... and if you want to find any real 'upgrade' to the OE fit tyres, or cheap chit aftermarket rubber likely fitted if any-one has managed to ever wear out the OE fit before they have totalled the bike...... THAT is where you should be looking.... better make, better grade, NOT fatter carcass size.....
You know.... some of the pedal cycle psyco's get up to speeds of around 70mph, a YBR can only achieve with a hill, on the flat, on tyres that are barely 10mm wide, and when they go round corners, are scraping the pedal caps of the 'up' pedal, at that sport of speed.... and the bike STICKS to the tar..... Believe me, FAT TYRES is not what's making them stick, cos they are as far away from fat as a Sumo Wrestler is from a Paris Cat-Walk model after she's thrown up in the dressing room! That rubber, is, by comparison positively anorexic......
Fit the sized Yamaha recommend... it wont foul anything, and if you buy a decent brand, in a sticky compound you'll get ALL the extra grip you WONT from a wider tyre, and none of the handling quirks they can cause.....
If you want it to look fatter and meaner and beefiier? Lol!!!! It just wont! EVER! Its a YBR!!!!! But hey.... not my bike, nor arse on its saddle or the line.... go for it!
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Current Bikes:'Honda VF1000F' ;'CB750F2N' ;'CB125TD ( 6 3 of em!)'; 'Montesa Cota 248'. Learner FAQ's:= 'U want to Ride a Motorbike! Where Do U start?' |
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Northern Monkey
World Chat Champion
Joined: 17 Nov 2013
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ThatDippyTwat
World Chat Champion
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grr666
Super Spammer
Joined: 16 Jun 2014
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| Posted: 10:25 - 30 Dec 2018 Post subject: |
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I have Michelin city grips on my Yammy 125 scoot and they are centrestand grindingly good. I agree with some
of the others, stick to standard sizes and improve the quality of the tyre instead.
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Currently enjoying products from Ford, Mazda and Yamaha
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AdamEf
Nova Slayer
Joined: 19 Dec 2015
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