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Tyre Tips

Tyre Manufacturers Technical Helplines

General Rules for Tyre Safety

Worn Tyres

Legal Tyre Fitments

Tyre Repairs 1

Tyre Pressures 1

Tyre Speed Ratings

Tyre Load Ratings

Date your Tyres

Tyre Fitting 1

New Tyres 1

Tubed Tyre Repairs 1

Tyre Pressures 2

Tyre Manufacturers Technical Helplines

All tyre manufacturers have a technical department, essentially set up to support their Dealers. However, we've found they willingly advise individual owners (and they're good).

If you're unsure of your tyres; or want the recommended fitment, pressures etc. for your bike, ring them and ask ! It's that easy.

Remember, the sizes and pressures quoted in your handbook are for the Original Fitment, OEM tyres only. Change your tyres from OEM and you'll need to know the right sizes and pressures, or even if they're allowed (tested) for your bike.

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General Rules for Tyre Safety

Whatever your bike the first rule has to be fit the right tyres; they're the single most important part of your bike.

Make sure they're fitted properly check the direction of rotation arrow on the tyre, bike shops have been known to fit them the wrong way round !

Have them balanced they're big heavy and go round, so they should be balanced. If your fitter disagrees, it's because they don't have a balancer or can't be bothered.

Make sure the pressures are right. More about this later, this is crucial stuff.

Fit the right sizes (that fat oversize rear is upsetting the steering geometry and won't really give more grip). Oversizing the front can be even worse.

Match your tyres not all tyres work together. Radial and cross-ply mixes can be downright dangerous. Different tyre constructions won't always work together. Only follow recommended combinations and, whatever else, keep the best / stickiest tyre on the front.
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Worn Tyres

Motorcycle tyres must legally have at least 1mm of tread depth, continuously across 75% of the tyre. That's pretty silly though; the minimum recommended is 2mm. Would you believe that there is no minimum tread for a moped tyre, only that it's visible ! Shall we just say that's a health risk.

So what's the tread for? It's not for grip; after all racers have slicks (but watch them dive into the pits at even a hint of moisture), tread clears the water away. Think about a tyre with a contact patch say 75mm wide, doing 60mph (say 27 metres per second) over only 3mm of water.
That's 7.5cm x 2700cm x 0.3cm per second. (6075cc). Hold on, over 6 litres, nearly I ½ gallons per second has to be moved away by the tyre! It can't come out of a bath tap that fast (it's more alike to quickly emptying a bucket). Your tyres have to clear all that through a few grooves (and they do, look at the dry strip a modern tyre leaves on a wet road).

A nice new tyre with, say 5mm of tread does that, when you're down to 2mm then (logically) it can't clear half as much water. So what chance do you have with 1mm., let alone "visible" tread. Don't go there. Oz.
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Legal Tyre Fitments

There've been a few arguments with bike shops over this, so lets set this straight.

Front Rear  
Cross ply Cross ply GREAT
Bias belted Bias belted  
Radial Radial  
     
Cross ply Bias belted These may be legal
Cross ply Radial but please don't do it
Bias belted Radial  
     
Bias belted Cross ply ILLEGAL DO NOT FIT
Radial Cross ply  
Radial Bias belted  
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Tyre Repairs 1

There seems to be a bit of confusion about what can and can't be repaired. Overall I'd back the dealers, if its arguable then err on the side of caution. However, if you think you're being seen off here's an extract of BS. AU 159

No tyre may be repaired if it has any of the following :-
Damage larger than 6mm in tyres up to J speed rating; 3mm in tyres above J, up to and including V and not at all if the speed rating is above V.
Damage not reasonably perpendicular to the casing.
Ply separation or local removal of the inner lining and/or ply cutting by penetrating object.
Tread separation.
Broken or damaged bead.
Damage due to under inflation in service.
Sidewall damage.
A penetration occurring outside the central 50% area of the tread.

Tyres up to J rating can have a max 2 repairs, which mustn't overlap. Only 1 repair in tyres above J up to V rating (and none in tyres above V). Oz
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Tyre Pressures 1 most of this applies to cars too!

Only you can check your tyre pressures because they have to be cold when you do. As the tyre warms up, so does the air inside and tries to expand, which it can't so the pressure rises instead. A tyre that's been run up to temperature will increase pressure by up to 10 psi !

The pressures in your manual are for the original fitment (OEM) tyres, are you still running on those? If not then your new choice will probably need different pressures. Your dealer will have books listing pressures for different tyres, or try the tyre manufacturer's own help lines. Even a couple of pounds out can make a big difference to handling and stability, use a good quality gauge and don't trust the petrol station's, they're notoriously inaccurate. Oz
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Tyre Speed Ratings

Your tyres have loads of info on the sidewall; one of the most important is the speed rating. Interestingly, it seems that even though you typically only do 60mph, you legally still need V rubber if that's what your bike is rated for !

Rating Mph km/h
L 75 120
M 81 130
P 93 150
Q 100 160
R 106 170
S 113 180
T 118 190
U 124 200
H 130 210
V 149 210
W 168 270
Y 186 300
Z 150 240

V rated tyres are now usually, but not always, rated to 150 mph
HB or VB rated are biased belted construction
HR, VR or ZR are radial construction
The speed ratings for these are the same as H, V & Z rated tyres as above.
Thanks to Cambrian Tyres
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Tyre Load Ratings

If you look at a tyre sidewall, you will find something like 120/90-18 65H. The "65" is the load index.

By looking at the chart below you can see that this tyre can carry 290 kgs. That's this rear tyre only. If the front is a 100/90-19 57H, the front can carry 230 kgs. Play with your calculator (don't forget the weight distribution of your bike) and you'll see that you'd need a big bike with two riders in need of a weight watchers programme and some serious luggage to overload this pair of tyres. But anyway :-

Load Index (L.I)
Weight (kg)
L.I
kg
L.I
kg

L.I

kg

15

69
33
115
51
195
69
325
16
71
34
118
52
200
70
335
17
73
35
121
53
206
71
345
18
75
36
125
54
212
72
355
19
77
37
128
55
218
73
365
20
80
38
132
56
224
74
375
21
82
39
136
57
230
75
387
22
85
40
140
58
236
76
400
23
87
41
145
59
243
77
412
24
90
42
150
60
250
78
425
25
92
43
156
61
257
79
437
26
95
44
160
62
265
80
450
27
97
45
165
63
272
81
462
28
100
46
170
64
280
82
475
29
103
47
175
65
290
83
487
30
106
48
180
66
300
84
500
31
109
49
185
67
307
85
515
32
112
50
190
68
315
86
530

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