Attesa Question

[pintaline]

im trying to work out what wheels to get for my stag.....does anyone know how much tollerence the attesa system has for rolling diameters? the rolling diameter of a 205/55r16 (the stock 16" wheel) is 632mm and the standard RS4s mags are 215/50r17 with rolling diameter of 648mm... how much either way can we go without upsetting the attesa?

D.

[Lil_Bobby_260]

ahhh... the question that has been sked and answered a thousand times....

heres my answer from last time someone asked -

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. A differene of rotation of more than 180,000 times is what ur gonna get. How long do you think your clutch packs will last.....?

Hope that A) that makes sense and that B) my maths is correct!!

Bobbeh

[pintaline]

so you're saying that even 10mm can be fatal over time?

the RS4s wheels are already 16mm larger rolling diameter than the standard 16" wheels... would the manuals have been adjusted at factory to suit this or are all manuals running their standard 17" wheels going to burn through clutch packs quicker than autos?

and, should i be trying to match rolling diameter of the standard 16" with the factory 205/55r16 or the 17s that came on my manual?

D.

[Lil_Bobby_260]

it doesnt matter what the rolling diameter is - what matters is that is it the same rolling diameter front and back.

and yes, im saying it will be damaging over time. It is not the issue of changing the diameters, that doesnt hurt. Just make sure there is no difference between front and back.

[pintaline]

so you can garruntee that changing the diameter wont effect the system, as long as they're all the same? coz i've been told that it will cause problems

D.

[RubyRS4]

so you can garruntee that changing the diameter wont effect the system, as long as they're all the same? coz i've been told that it will cause problems

D.

As long as the front left, front right, rear left and rear right wheels (wheels = rim and tyre) equal the same diamater/circumference, then you're safe.

For example, I'm running 235/40 tyres on 18" rims all round = no problems.

Apparently the ATTESA system can't handle even the slightest differences in circumference ... something I'm reading about at the moment for myself.

Edited May 14, 2008 by RubyRS4

[munchstagea]

And the reason is... That's how ATTESA works: Differential between wheel speeds = a wheel must be losing traction -action- engage 4wd and try to rectify the issue...

[chook]

+1 just keep all 4 tyres identical, including same brand and model, no problem

[pintaline]

thanks all, i had been told otherwise but many voices beat just 1, any day.

it's big wheel time......

D.

[Lil_Bobby_260]

What happens when your 8mm deep tread wears down to the 1.5mm wear bars...? thats a 15mm change in rolling diameter. Doesnt matter. As long as front and rear is the same. The atessa system wont even know that the diameters have changed, as long as they are changed equally. only issue is that your speedo will be out. Bigger diameter means that your car will travel further with every rotation.

so you can garruntee that changing the diameter wont effect the system, as long as they're all the same? coz i've been told that it will cause problems

D.

[STAGE1]

Q

I have the same tires front and rear only the front are new and the rear are almost had it. Would this explain why I get a slight surging feel after about a half hour of cruising on the highway?

[Duncan]

yes that is very likely the reason. new rear tyres or just swap front to rear.

BTW it is difference front to rear that matters not the difference to stock wheels. I run 245/45/17 on mine which is pretty big - but no problems with attessa

[Lil_Bobby_260]

yeah agreed with duncan. if there is a large difference it will cause the problems. Hence, rotate your tyres every few thousand kays to keep the wear even.

[RubyRS4]

What happens when your 8mm deep tread wears down to the 1.5mm wear bars...? thats a 15mm change in rolling diameter.

If you're talking new tyres (8mm deep tread) front and worn tyres (1.5mm wear bar) rears then its:

8mm - 1.5mm = 6.5mm

6.5mm x 2 = 13mm

Thats a 13mm change (not 15mm) in diameter

Sorry couldn't help myself

[STAGE1]

So if I do a hard left the inside tires will do less distance than the outside tires then a km down the road I do a hard right everything will right itself (just kidding) I plan to get new tires for the rear very soon. LOL

I am going on a trip this weekend so I will swap front to rear and see how it goes.

Thanks for your help.