Tyres!

[yokotas13]

nah, i dont go to iraq

[rb26stagea]

Yep....Grant's definitely back

[Lil_Bobby_260]

technically, every time you turn a corner, all four wheels travel slightly different distances. How do the clutch packs deal with that? Sounds wierd that seeing as theyre going different speeds anyway that a difference in diameter would cause cornering issues...

For long term issues tho, i nutted this out - this is my reasoning as to why something that seems so inconsequential can cause dramas -

A difference of 10mm in rolling diameter (Say 660mm front and a 650mm) rolling diameter rear tyre is a different of 31.42mm difference in distance travelled per rotation. Given that each rotation of a 650mm diameter tyre is about 2050mm, your larger tyre would rotate about 65 times every time your smaller one does 66times. So your larger tyre will have rotated one less time than your smaller one every 133 metres. If you do 1000 km a month, so 12,000km a year, then its a matter of your clutch packs coping with a difference of 90225 rotation difference every year. Thats a lot of wear and tear on your clutch packs, from a difference of 10mm.

if you have 225 tyres with 40 section, and 225s with 45 section, your difference in diameter will be 22.5mm (45% of 225 - 40% of 225, then multipliy it by two as we're dealing with diameter, not radius), so double the above figure. More than 180,000 times is what ur gonna get.

Hope that A) that makes sense and that B) it is correct!!

Bobbeh

[rb26stagea]

*walks in to the room. Slaps bobby in the head. walks out*

[Lil_Bobby_260]

ok so my mum helped with the math....

[Sydneykid]

technically, every time you turn a corner, all four wheels travel slightly different distances. How do the clutch packs deal with that? Sounds wierd that seeing as theyre going different speeds anyway that a difference in diameter would cause cornering issues...

There are front and rear differentials that help with the corner turning differences. Plus it is a short term difference, corners don't last for kilometres. When I get the ATTESA shudder, from different diameter tyres, it is during a long straight'ish run (think freeway). Time for the ATTESA to "wind up", for the plates to get hot, for the hydraulic fluid to overheat etc.

Cheers

Gary

[RubyRS4]

Bobby, your thinking is along the lines of my thinking.

I'm trying to dig up info on the attesa system to understand it a bit better. This has been a topic of discussion between my friends and I (all of us not shy to modifying cars/bikes over the years) to nut out and understand a bit more.

You've also got to view it in a track sense. If you do laps at Mallala all day, what impact does that have on the system? And we're not just talking front to rear tyres, or left to right tyres, but the difference in distance from the front left and rear right during a right hand turn. I'm sure if the system is intelligent enough to deal with that all day on track, then it should handle different profile tyres (but not entirely difference circumferences).

Everyone is speculating on how it works and how their cars have behaved in a given situation, but we want to find some documented discussion on the matter. If anyone has a link to a journal or tech article on this, it would be greatly appreciated.

I find it interesting. Including everyone's view on the matter.

Edited April 10, 2008 by RubyRS4

[Sydneykid]

I'm not speculating, I know exactly how it works.

Track work, turn left, turn right, power on, power off, all of those transient things "unlock" the clutch pack under instructions from the ATTESA ECU. Driving along the freeway in straight line with power on does not. It's truly that simple.

The total tyre diameter is ALL that matters, width is irrelevant, profile is irrelevant, wheel diameter is irrelevant, tyre compound is irrelevant. As long as the tyres are the same circumference, that’s the ONLY thing that matters.

For circuit work with longer races, say over 1 hour, we run a pump and an oil cooler on the transfer case to keep the temperature of the clutch pack fluid under control. We also run the same on the rear diff and the gearbox.

Cheers

Gary

[RubyRS4]

I like to see it for myself, either in documented form from a reliable source or seen in practice.

I take what everyone says with a grian of salt, and then weigh it up against what I read about it. I'm having a few beers with some mates tonight (one of whom is an engineer) so it'll make for great conversation and debate tonight

[RubyRS4]

The total tyre diameter is ALL that matters, width is irrelevant, profile is irrelevant, wheel diameter is irrelevant, tyre compound is irrelevant. As long as the tyres are the same circumference, that's the ONLY thing that matters.

Don't you mean the overall "circumference"? Not tyre diameter? (although diameter is in the calculation for the circumference)

And don't you mean the overall wheel diameter? You say its not relevant but the wheel diameter is made up of the rim diameter and tyre profile.

Overall wheel diameter = rim diameter + tyre profile

Therefore wheel diameter together with rim diameter and tyre profile are relevant.

Which, as you say, so long as the circumference is the same is the only thing that matters. So you can mix and match rim sizes and tyre profiles to obtain the same circumference.

So rim diameter, tyre profile, and over wheel diameter does matter.

Edited April 11, 2008 by RubyRS4

[AlexCim]

Don't you mean the overall "circumference"? Not tyre diameter? (although diameter is in the calculation for the circumference)

And don't you mean the overall wheel diameter? You say its not relevant but the wheel diameter is made up of the rim diameter and tyre profile.

Overall wheel diameter = rim diameter + tyre profile

Therefore wheel diameter together with rim diameter and tyre profile are relevant.

Which, as you say, so long as the circumference is the same is the only thing that matters. So you can mix and match rim sizes and tyre profiles to obtain the same circumference.

So rim diameter, tyre profile, and over wheel diameter does matter.

He said circumference, read his reply again.

He said wheel diameter is irrelevant. The wheel is the metal part, the tyre is the rubber part. Hence, it doesn't matter about the size of the metal part as you adjust the size of the rubber part.

Keep them the same rolling diameter and then it is fine. You could run a 20 inch skinny wheel with a 20 profile tyre on the front and a 15 inch wide wheel on the rear with massive profile, they will be the same. Rim size, width, offset, NOTHING matters as long as you adjust the tyre profile to suit.

My stagea ran 18x10 with 235/45 on them and 18x9 225/45 and it was fine. Never shuddered, never burnt clutch packs whatever, it was fine.

In the end as well, its only a transfer case. Sure a rebuild will cost $2000 but shit, I have found series 1 auto gearboxes WITH transfer cases for $250. Add labour and materials to change it over, thats a grand total of under $500. Not only that, but its not like a shat transfer case will mean the car is un-driveable, it is just rwd without choice. However, maybe not everyone is like me an realizes that "its just a car" and that "its just money" and the most important thing is happiness (whether that comes from running mismatched/sized wheels or not)

Edited April 11, 2008 by AlexCim

[Sydneykid]

I like to see it for myself, either in documented form from a reliable source or seen in practice.

I take what everyone says with a grian of salt, and then weigh it up against what I read about it. I'm having a few beers with some mates tonight (one of whom is an engineer) so it'll make for great conversation and debate tonight

If he doesn't know how ATTESA really works, he will only confuse the issue. Most guys (even engineers) think that GTR 4WD is the same as WRX 4WD or EVO 4WD or Audi 4WD. Where as us ATTESA experienced guys are fully aware that it isn't even close to being the same.

But hey what would I know, I only have a diploma, a degree and a masters and have been involved in all levels of circuit racing for 35+ years.

Cheers

Gary

[RubyRS4]

Don't go getting touchy. I only said I wanted to read things for myself ... do my own sussing out. A guy is entitled to find out for himself.

Given that, and given you've been in the game for 35 years, surely you would have something in documented form (manual or tech article) that would cover the ATTESA? If you do, I wouldn't mind taking a look.

Edited April 11, 2008 by RubyRS4

[RubyRS4]

He said circumference, read his reply again.

He said wheel diameter is irrelevant. The wheel is the metal part, the tyre is the rubber part. Hence, it doesn't matter about the size of the metal part as you adjust the size of the rubber part.

I did read his reply. 'Circumference' was mentioned, so too was 'profile' and 'tyre diameter' and 'wheel diameter'.

A wheel is the rim and tyre. Thats my interpretation of it, as any normal person would.

And for the record, I have a few Diplomas and 2 Degrees and a Masters also.

[leetom]

I did read his reply. 'Circumference' was mentioned, so too was 'profile' and 'tyre diameter' and 'wheel diameter'.

A wheel is the rim and tyre. Thats my interpretation of it, as any normal person would.

And for the record, I have a few Diplomas and 2 Degrees and a Masters also.

rueben meet gary (i know your pretty new here) he knows a little bit about skylines, when he speaks we listen

[Lil_Bobby_260]

rueben meet gary (i know your pretty new here) he knows a little bit about skylines, when he speaks we listen

+1. Most of us have learnt at least a thing or two from him.

[rb26stagea]

And sacrificed the odd goat to him....

In all seriousness, he is an absolute Guru. Trust his word.

[RubyRS4]

rueben meet gary (i know your pretty new here) he knows a little bit about skylines, when he speaks we listen

I'm not saying he doesn't know his thing. I'm just questioning him a bit more than most people would I guess.

How else do we learn if we don't question and challenge things.

I'd be more than happy to meet him and discuss this over a few beers.

In the meantime, I'm just looking for something on paper. I do find this an interesting topic ... lots of variables!

And sacrificed the odd goat to him....

In all seriousness, he is an absolute Guru. Trust his word.

Well endorsements don't get much bette than that do they?

I'm serious about the beers Gary. If I'm ever in town or you're here PM me in all seriousness.

[GoldZilla]

rueben meet gary (i know your pretty new here) he knows a little bit about skylines, when he speaks we listen

+1. Most of us have learnt at least a thing or two from him.

And sacrificed the odd goat to him....

In all seriousness, he is an absolute Guru. Trust his word.

Agreed! The man is a wealth of information and a good guy to boot!

[Lil_Bobby_260]

I'm serious about the beers Gary. If I'm ever in town or you're here PM me in all seriousness.

haha lol @ beers and seriousness... cos thats a common combination... :-)