Swapping tyres around, and scrutineering!

[G JONES]

Although it isn't a problem to run them in reverse the makers advise that they are fitted in a certain direction This is because it is the best way to fit them taking into account the forces excerted on the tyres during braking and accelerating.

No question that there is a "recommended" direction to fit the tyres - however - as you would agree Keith - if they are fitted the other way - they are not unsafe - just not fitted the "best" way... I would agree that they should be fitted the "best way" when possible - but see no reason not to turn them when they have worn on the one side - which some outfits will do at times. (having had advice from the maker's Tech rep to confirm whether it's safe to do so)

They are not going to say that you can fit them in a direction which is not the best direction.

No - and I think we know why...

[flexford]

I can only speak for myself. I am aware of the fitting guide. And I am aware tyre fitters will tell you it's OK to run them the other way round. However, no tyre fitter will put that in writing. So, the only official line I have to work with IS the fitting guide.

The way I see technical inspection is this. The rider is responsible for the safety of their machine, as per ACU handbook. But I have a duty of care to the rider. I cannot, therefore, pass something that goes against written instruction from the manufacturer.

Jo, please don't change 0.000001% of the way you scrutineer.

When our bike went through scrutineering at the TT, one of the other scrutineers said to me (looking in your direction), "she's good" which was a chap trying to say "she's is EXCELLENT" ... he commended you on your thoroughness and the fact that you never miss a thing .

Each year I take my car to a garage that is renowned for failing a lot of cars on their MOT (because they are SO thorough), I take my car their because I used to drive it too fast to miss any type of fault ..... people that are anti thorough scrutineer's are missing the point - they are their to make sure your bike is safe for you to ride. Diligent and thorough scrutineers are worth their weight in platinum!

Re the tyre direction, I would hope if a scrutineer was concerned about the tyre direction then they would point the fact out (if the competitor hadn't already realised) and ask that they be changed around, but not stop a competitor going out on circuit of they couldn't be changed at the meeting .... . We made sure that Avon were happy that the tyres would not let us down because of the wrong rotation and like I say they were worked pretty hard at EF with no detrimental effect .. however I complete understand your comments and where you are coming from on this

Please keep up the excellent work

[Jo Warriner]

I can only speak for myself. I am aware of the fitting guide. And I am aware tyre fitters will tell you it's OK to run them the other way round. However, no tyre fitter will put that in writing. So, the only official line I have to work with IS the fitting guide.

The way I see technical inspection is this. The rider is responsible for the safety of their machine, as per ACU handbook. But I have a duty of care to the rider. I cannot, therefore, pass something that goes against written instruction from the manufacturer.

Jo, please don't change 0.000001% of the way you scrutineer.

When our bike went through scrutineering at the TT, one of the other scrutineers said to me (looking in your direction), "she's good" which was a chap trying to say "she's is EXCELLENT" ... he commended you on your thoroughness and the fact that you never miss a thing .

Each year I take my car to a garage that is renowned for failing a lot of cars on their MOT (because they are SO thorough), I take my car their because I used to drive it too fast to miss any type of fault ..... people that are anti thorough scrutineer's are missing the point - they are their to make sure your bike is safe for you to ride. Diligent and thorough scrutineers are worth their weight in platinum!

Re the tyre direction, I would hope if a scrutineer was concerned about the tyre direction then they would point the fact out (if the competitor hadn't already realised) and ask that they be changed around, but not stop a competitor going out on circuit of they couldn't be changed at the meeting .... . We made sure that Avon were happy that the tyres would not let us down because of the wrong rotation and like I say they were worked pretty hard at EF with no detrimental effect .. however I complete understand your comments and where you are coming from on this

Please keep up the excellent work

Blushing lots!

Thank you Kelly! Don't know what else to say except I wonder who the scrut was that said that, lol!

Seriously, it is nice to be appreciated, thank you.

[tbrown57]

We have a 1996 Windle

We run the same tyres on the front and chair (160's) same compound, also front an chair reverse rotation. Always have done and will continue to. 1 set of old yokos £220 a set, lasted 2 meetings and a practice day so far an we've not been hanging around. They have been no problem what so ever .

[SlowPhil]

Been wearing the ‘boots’ on the wrong feet for many years and never had a problem. Should you get picked up just sand the arrow off and play dumb!

If you think about it the breaks have much more power than the engine so, in which direction should the front tire rotate?

[Whites]

We also fit the front and side in the reverse direction, the majority of forces on these two wheels are from the brakes.

This got me wondering though, the arrows on the front and side tyres, do they mean the best direction for grip (if driven) or the best direction for braking forces. i.e. this is a front/side wheel, for best brakng effect fit this direction.

More likely they make all they tyres, don't know what we are going to use them for and stick the arrows on the best direction for a driven wheel.

[SlowPhil]

But is that what Avon says?
When you have no money or time for a new rear boot and theres one race to go. what are you going to do? Haha
Never had a tire break up cos of that arrow, even when its been taken off

[Whites]

I've never experienced new tyres

We are still using Scud's old front F1 tyres on our rear (almost out now though )

As for sizes, we usually use same size on the side and front (6.2 I think). And 8.2 on the rear.

[speech]

started practice at the TT with a rear avon fitted the wrong way round, worked ok until thursday night , no sign of lamination line. Then it was spotted and was put on the right way round, after 2 laps on friday it had chunked and was FUBAR d . so i m not convinced a direction change half way through a tyres life is a good idea

[ChrisWells]

I can only speak for myself. I am aware of the fitting guide. And I am aware tyre fitters will tell you it's OK to run them the other way round. However, no tyre fitter will put that in writing. So, the only official line I have to work with IS the fitting guide.

The way I see technical inspection is this. The rider is responsible for the safety of their machine, as per ACU handbook. But I have a duty of care to the rider. I cannot, therefore, pass something that goes against written instruction from the manufacturer.

Hmm, so LCR's should be banned from the TT because Louis recommends them for closed circuits only? (Sorry feeling slightly mischievous today. Also I heard that rumor 3rd hand so there may be no basis in truth for it and I obviously don't agree with that conclusion, but it is logical.)

Chris

[Jo Warriner]

No apologies necessary but I will remind you that i don't make the rules...

[steve-e]

Louis hasn't said that, definitely not to me but then we don't talk much (once a year - "Louis would you like to support the site for a year again, it is very appreciated" Louis "Yes, thank you" ).
I've spoken to people close to Louis who reckon as far as he's concerned even the F1 would be fine for the mountain course. I would recommend giving it a thorough checking over after each session but then everyone does that with their f2s as well don't they?

The point is that the tyre companies have made a recommendation in writing, so that has to be complied with.. not a third hand story including my one!

[steve-e]

started practice at the TT with a rear avon fitted the wrong way round, worked ok until thursday night , no sign of lamination line. Then it was spotted and was put on the right way round, after 2 laps on friday it had chunked and was FUBAR d . so i m not convinced a direction change half way through a tyres life is a good idea

Now that IS interesting. I wonder why it happened.... cue DS the ex tyre man

[Jo Warriner]

But is that what Avon says?
When you have no money or time for a new rear boot and theres one race to go. what are you going to do? Haha
Never had a tire break up cos of that arrow, even when its been taken off

You keep on sanding off the arrows, there's another way to tell the direction apart from the arrows!!!

And yes, the front tyre should be fitted in the reverse direction.

Speech, I am not surprised! I don't think that's a good idea either!

[David Stewart]

The arrow on tyres used to be suffixed with "Drive", which somehow disappeared from most uni-directional stuff in the late 1990's. The very first tyre company to mark tyres in such a fashion was Michelin way back in the 1930s and what was actually written under the tyre arrow was the word "Force". Given that all of those tyre markings were in French, when India Tyres (later owned by Dunlop) introduced a uni-directional tyre, they put the word "Drive" under the arrow. Very British you see.

If you substitute the word "Drive" for the meaning "Maximum Force" when thinking about the correct application of a tyre, you won't go far wrong. Meaning the front tyre goes the other way round for correct fitment, even under the strictest interpretation of the manufacturers fitment guide.

The reason some bias-belted tyres destroy themselves when used in one direction and then the other, is due to carcass set. The twisting forces applied to the carcass when used the wrong way around - combined with the heat generated - set the tyre belts in a particular fashion. If you then reverse that whole process the tyre doesn't like it. The best way to think of it, is to consider bending a piece of plastic one way for a couple of minutes. It will reform "almost" to it's original shape when you let it go. However, if you do that and then bend it in the opposite direction, it will develop a white stress line (which is due to the cells being deformed and chemically changed) and that will be much weaker and more pliable than the rest of the material.
If you think of the tyre belts being able to wiggle around underneath the camelback tread layer when you have done this to a tyre, you will understand why the tyre will delaminate and chunk.

Radial tyres are much less prone to this, as they are designed with much more flex in them as standard (but they will still do it under very extreme conditions). I would class the Mountain Course as "very extreme conditions" on a hot lap.

Hope that helps.