tyre on backwards

[fool on the hill]

I have just bought a second hand caterham with 13inch wheels and Yokohoma A021 tyres.

close inspection shows that three have the little arrows (direction of rotation) pointing the right way and one (offside rear) is pointing the wrong way.

OK so I need to get the tyre off, turned around, put on and rebalanced.

I just wondered how critical all this was. The tyre does not look asymmetric (unlike a A032R for example) and I have had bad experiences with tyre outlets getting the balance right. It looks like it could be a fair bit of hassle for little benefit.

just wondered

james

[Nick Green]

Last time I checked on a Yoko web site (www.yokohama.co.uk ?), the advice was to run rear tyres in the direction of the arrows (or "allows" as it said!) and the fronts backwards. This was for rwd applications. Apparently, if you ring them, they say run them all in the same (arrowed) direction. Not sure it is worth the hassle. Depends how much tread is left ?

[R2D2]

I used to run kleber slicks with direction arrows in the late seventies on a tarmac rally car and was told that the arrow was important because of the way the rubber was laid on the carcass of the tyre. I think that the band of rubber from which the tread is moulded from was joined at 45 degrees. I don' know if this is true or bulls**t. It seemed plausible at the time as it certainly had nothing to do with tread pattern!

 

Is it a good idea to trun tyres or swap them front to back with modern tyres as the wear pattern is different? (My tyre dealer won't swap my road car tyres from front to rear these days.)

 

 

[Tazio]

When the A21s came out some of the racing teams ran the rears tyyes with the correct rotation and the fronts with the arrow pointing backwards. The suggestion was that this improved braking performance on the fronts....

 

Alan

[CHRIS CLARK]

I think the important point here is that even race/rally teams etc will run the tyres as matched pairs whether backwards or forwards; not one tyre one way & one tyre the other on the same 'axle' line!!!

I had this problem when I collected my 7 and was admiring it in the drive.It had brand new tyres all around. I found that the spare wheel was set such that I could use it & get all four tyres showing the direction arrows pointing forward. This means that the (now) spare is technically only good for the offside!

[Graham Sewell]

When I spoke to George Polley, he said that in an ideal world they should match and be correct for the back and reversed for trhe front. He then added that for road use where you are not on the limit of adhesion that it almost certainly doesn't matter a damn.

 

Otherwise you need to carry two spare tyres.

 

This was backed up, when I needed to use my spare, and sod's finest laws dictated that it would always be the wrong way round. I noticed no difference in handling. The fact that they can be run in reverse shows that there is nothing structural to go wrong - so I wouldn't worry about it as you'll probably do more damage getting it fixed.

 

Cheers,

 

Graham

 

[GasMan]

I recently replaced slicks for hillclimbing with ACB10's. The poeple at BMTR's motorsport division told me that with any treaded competition tyre they should all go on and rotate according to the arrows. Only with slicks do you need to have the driven tyre rotate per arrows and the freewheeling tyres reversed.

[Simos]

Mr Fool,

 

Do you want to know whether you should change it, or why you should change it...? Ah hell, why keep it simple smile.gif

 

Ok here's my dose of bull**** for the day... the importance of the rotational direction depends on the type of tyre and it's use (surprise surprise).

 

I was given to understand by Dunlop (when racing Dunlop crossply slicks in another life) that it was because of the way the plys were built-up and attached to the bead (hub). You want the primary mode of the bands to be tension rather than compression FOR THE PRIMARY ROLE OF THAT TYRE - BRAKING OR ACCELERATING.

 

In a rear wheel drive car, accelerating (rotational) is the primary role of the rear tyres (braking secondary) so the arrows should be in the direction of rotation.

The front wheels however never accelerate but they do brake so their primary role is braking (rotational decceleration), and thus the tyre should be reversed as rotational forces are applied to the tyre in the opposite direction (primarily) to the rears.

 

/granny mode on

 

Think of the outside (tread) of the tyre with respect to the inside (bead/hub) and how they're connected with the bands of nylon/steel cording etc like the spokes of a bike. Unlike spokes, the cording does not necessarily run perpendicular to the rim and hub, but at an angle like a bandage wrapped around (and along) an arm. Each layer (ply) is at a different angle or direction, some forward, some backward some perpendicular.

 

As you accelerate the rim is trying to travel faster than the tread, as you brake the rim is trying to rotate slower. so whether the plys run forward or backward or perpendicular between tread and hub makes a huge difference to how the sidewall will behave - stiffen, flex, accept slip angle etc

 

The number of plys is written on the side of the tyre and whether it is perpendicular and steel (radial) or laid at different angles and nylon (crossply) or with a skew between the number of pys running forward rather than backward (bias ply or directional).

 

This is the basis of tyre types and why they behave differently. Radials are more forgiving over bumps because tensioning or compressing the tyre on bumps just squishes the steel cords (at the bottom, tension a bit more at the top) and transmits a thump. A crossply (especially a biased ply ACB-10) will tension a ply running at an angle betwixt hub and rim which will move the hub with respect to the tread (which you'll feel through the steering... and how!) tramlining here I come...

 

More importantly for us geeky types (and why F1 uses crossplys not radials) crossplys provide a gradual build-up of cornering forces with slip angle as you enter a corner and likewise release of forces as you exit (because the plys start off under some directional tension because of the design).

 

Radial plys do not have a natural directional tension and only start to build up tension as the sidewall comes under cornering forces. If you change direction in a radial, the tyre will flop (?) from one side to another (honest) which on the (F1) edge can upset the balance of the car. But I doubt any of us will feel it though unless Schumi's logged on right now..?

 

The net result is radials are far superior for Joe Public's driving which is why all road tyres are radials. I doubt even the carpark warriors with their anodised ashtrays would want an actual crossply, I certainly wouldn't have them on my family car.

But us wierdo's, sorry, ethusiasts might want a biased crossply with supersticky compound because... because... ... well if F1 uses them, I should have them on my Seven, stands to reason, or something.

 

/granny mode off

 

So where does that leave us ?

 

Radials are not directional, crossplys ain't necessarily but bias crossplys always are 'cos they have more plys skewed forward or backward (can't remember which)

 

The main reason for running the arrows correctly for my slicks was that running the wrong way around caused more cord and thus tyre flexing which heats it up quicker and then over-heats it. I tested this accidentally in several races and can confirm it ain't bollocks, I cooked several tyres this way.

 

But when did you last overheat a road tyre.... exactly.

 

The next reason is that for directional tyres, as explained (sort of) above, the skew of the plys dictates how the sidewalls will work and forces be transmitted from tread to bead and thus car. You don't want your two tyres behaving differently (remember the old govt safety tv ad with the old codger mixing radials and cross plys on a morris 1100 and ending in a ditch ?) A point put forward sucinctly by Chris.

 

So to answer the original question, yes, the offside rear needs changing, for safety rather than performance reasons.

 

(and if they were slicks on a track, or you wanted to be a purist, the fronts do too)

 

I'll shut up now. Does Peter know about tyres or just engines and chassis ?

 

Cheers, Simon.

 

[Graham Sewell]

Swapping the fronts is easy... just swap them over smile.gif. Sorry, long lunch...

[PACR]

The pattern of tread will govern how well it expells water from the roaad surface / under the tyre. I had my fronts on backwards (Avon ZR-1s) and noticed no difference at a trackday or on the road at all. However I swapped them round before driving in the rain after looking at the pattern - would have forced water into the centre of the tyre instead of to the side - might cause aquaplaning (earlier). I'd be concerned about the insurance refusing to pay out in such a case - they won't if you've got bald tyres... I've been advised against changing the rotational direction of the tyres - ie side to side swaps are a no-no.

 

Piers

[Graham Sewell]

A021Rs are large block pattern treads and have no obvious direction other than the little arrows and location of red dots. Personally, I have mine all pointing the same way (not reversed at the front) as the local MOT man might get confused.

 

Cheers,

 

Graham

[Paul Ranson]

and why F1 uses crossplys not radials

 

Unfortunately for your hypothesis F1 uses radials.....

 

Although I very much doubt that they have steel belts.

 

If you look at the Avon web site (here) you'll see a wide range of race tyres in both crossply and radial constructions.

 

Hillclimbers use crossply, it would be interesting to know about other areas of motorsport.

 

For reference to F1 and radials, I recall there was an article in Motorsport recently. An 'innovation' of Michelin or Pirelli back in the 1980s, IIRC.

 

Paul

[elie boone]

Do not forget to look at the tech. spec. on the Avon website there is all you need to now about the correct rotational fitment.

 

 

[Peter Carmichael]

GasMan,

 

Avon Racing will tell you to set ACB10s according to the product code and ignore the arrows. This is because the arrows only relate to the original application. With 6in ACB10s this was on the front of a formula ford.

 

The ACB10s are a hand built tyre with exactly the construction method that Chris Flavell describes. With 6in ACB10s all round on a RWD car it turns out that the arrows run the right way on the front and the wrong way on the back - this is because they are "front tyres".

[fool on the hill]

Wow - thirteen replies to a fairly footling

question in 24 hours.

Thanks to all you guys who contributed-

as the QC said to the judge who complained

that he was no wiser now than he had been before

"No melud, but far better informed".

 

My decision (for what it is worth) is to end up with all the arrows pointing in the normal direction of rotation although i have to accept that the logic of having the front ones pointing backwards is impeccable.

However it looks like it can wait until I have

time to visit somewhere "seven-friendly"

 

many thanks again to all the postings