225/40 front and 225/45 rear on a 4x4

[Cale1911]

So beeing a newbie here, and not founding the info i need here's my problem and hope for your help guys.

 

I have mk2 superb combi from 2010, that i bought used this summer. It's a 3,6fsi 4x4 with 4th gen haldex. Btw what a great car.

The car came with a set of 2 extra winter tyres. A few days back went and took 2 brand new winter tyres in the original dimension 225/40 R18

Gor them fitted today, and everything OK, came back home, parked, and...WTF noticed that rear look a bit larger.

And yes the difference is obvious. 

So the fronts are 225/40 R18, and in rear 225/45 R18 . Using a calculator it's 3.3% difference (22mm) 
And the idiot (like me) installing them didn't said a word, or warn me about it.

So i'm worried about a possibe damage to the haldex system, diffs, couplings, etc. I know it's mainly FWD and haldex system only activates when it should, but i stil think it's a NO-GO.

And the rear ones are in good state, used only one season, one year old with a lot of meat, so i would loose a lot.

 

So im in a doubt of getting rid of them, and buying 2 more, or keeping them just this season.

 

Yes i know, really stupid of me, i had to look before and eveything, but S..T happens. I really belived the winters ones were the same. They came in those white plastic bags,

and when i was looking i went for DOT mainly. I did see 225/4... but just didn't go all the way to make sure.

I'll be talking to the service tommorow, as they are all closed now but would also like to hear from you guys.

 

I know, crazy story

Cheers,

Cale

 

 

[Ootohere]

Is the haldex working OK still?   Good move to get matching tyres on size wise.

 

If the difference is obvious then why use a calculator,

you have the wheels / tyres use a measuring tape and measure the actual circumference & difference.

http://kouki.co.uk/utilities/visual-tyre-size-calculator 

[Cale1911]

Well, to tell the truth, i assume it's working fine.

However to my knowledge you can only test the proper function of haldex coupling and 4x4 system on a slippery surface with your foot on the throttle.

That is how is tested after haldex oil and filter change. This would of course induce stress to the drivetrain and that's what i'm trying to avoid until i know is it safe or not.

I think the car itself cannot know that the wheels on the front and rear axle are not same size, so only thing that comes to me are the ABS sensors that might read the actual turning speed of wheels, and to missinterpret it as a wheel slip  and to send more power to the rear trying to mend it...So the car would constantly be trying to fix "errors" received from sensors and that could cause damage?? I think.

So the actual circumference & difference is not that importanat as the damage that can be caused by it.

I just wanted someone experienced who knows what i'm talking about to say, "yes it's safe, just drive" or "OMG, don't do that you'll ruin it".

[Jeeves]

I don't profess to know the mechanical implications of what you've done, but it's been taboo since my first days of owning a quattro (Torsen not Haldex), so I only ever change all 4 and have even put a budget on the full-sized spare if I've done a size conversion.

 

I would see if you can get it on a 2-post lift or jacked up at all 4 corners and see if the Haldex drives both axles.  It'll simulate a an icy surface if you can't find one.  Try both First and Reverse. Then I'd consider replacing the free tyres for peace of mind.  As said above, measuring their used circumference might reveal their closer to the new ones than you think, but they're also like to have less tread depth.

[KenONeill]

@Cale1911 - That's exactly how ABS, Haldex, some tyre pressure monitors (and traction control systems if fitted) is by using the ABS sensors to measure wheel rotational speed and taking action if the front-rear differential (sometimes also across axle for ABS and traction control) exceeds a programmed level.

 

So your differential tyre sizes will affect systems other than just the Haldex. 

[Cale1911]

2 hours ago, KenONeill said:

@Cale1911 - That's exactly how ABS, Haldex, some tyre pressure monitors (and traction control systems if fitted) is by using the ABS sensors to measure wheel rotational speed and taking action if the front-rear differential (sometimes also across axle for ABS and traction control) exceeds a programmed level.

 

So your differential tyre sizes will affect systems other than just the Haldex. 

That's what i was afrraid of. I'm still waiting for an odficial response from skoda, but thinking i will have to get a set of propper tyres and loose trese.

[Cale1911]

Had a long conversation today with a authorised service. It got them puzzled and they had to do some brainstorming, manuals readindg etc.

They only had one case simmilar to mine, 2 years ago, when a guy came with Q7, huge tyres in the back. He drove 300km at highway speeds and nothing happened.

After they changed his tyres all errors from the dash went off.

 

According to them, NO warning lights from ABS, ESP and TPMS were lit because i only drove 1km from shop to home, so the time was too short, and the speed was so low that the

sensors didn't have sufficient data to figure that something was wrong.

 

They also said that if would go for a ride ie. longer than 1hr, more than 50km, with speed exceeding 80/90kmh it would definitely cause errors on ABS, ESP and TPMS.

Not so much on the drivetrain, Haldex and other mechanical components, at least that's what they THINK. So they are not sure.  

 

They strongly adviced me to change it ASAP, and NOT to drive long trips mentioned above to prevent any possible mechanical/electrical damage to the car.

So i went and ordered another set of new winter tyres to be mounted on monday. A company car will do next couple of days.

 

So how does BMW ships their X5 with different wheels/tyres size combo front/rear?

 

 

 

[KenONeill]

@Cale1911 - As I said on Friday morning, the rotational speed differentials that activate ABS and traction systems are programmable. BMW must deliberately program the systems in their cars for the differential rotational speeds.

[Ootohere]

x-drive a very different system from Haldex, and not just on the X5 available pretty much across the different series now.

 

As to the TPMS thing, that sets to what you set it at, and not all tyres front and rear need to be at the same pressure or size, (need to be same size tyres across the axles, but when a spare tyre a little different is fitted, the TPMS can be reset and then not give warning of a change of size.)

i sometimesrun bigger tyres on the front of Fabia, and no issues, no ABS / ESP issues either,

but then then they do not have haldex.

 

 

Edited 18 December, 2017 by AwaoffSki

[Cale1911]

1 hour ago, AwaoffSki said:

 

 

As to the TPMS thing, that sets to what you set it at, and not 

i sometimesrun bigger tyres on the front of Fabia, and no issues, no ABS / ESP issues either,

but then then they do not have haldex.

 

 

That is the case with most of "medium class"cars today. Assuming they have Asb/Esp sensors fitted front only.

Edited 18 December, 2017 by Cale1911
Wrong quote

[Ootohere]

Not since ESP became a legal requirement with EU type approval and before with manufacturers that had it as standard and not an option,  ie skoda,  greed.    So TPMS now as required,  ESP / ABS, ETC is only not there on older cars now.   Perfect on the likes of my Jimny where the least electronic interference the better,  and I decide when I want AWD.  On my 335d x-drive I am happy for it doing its thing,  and a proper TPMS that tells pressurws, temps, and at which tyre. 

[dg360]

My assumptions:

The rear tyres had a larger circumference than the fronts tyres?

The sensors would show that the rear wheels were turning faster than the fronts?

 

In this case, I think it's a terrible idea to continue but I can't see what damage you will have done.  My guess is that the Haldex system would assume that the rears were slipping more than the fronts even without power going to them, as a result it wouldn't send power back to the rear wheels.  All of the sensors might well be confused but I don't see what serious harm would have been done to them.  Different size wheels/tyres on the same axle would be asking for serious trouble as on top of all of the sensors being very unhappy the differential is going to extremely unhappy but even then small differences happen when people use space savers.

Here's something to consider - I'll bet putting snow chains on the front wheels has a similar effect on the size difference (other way around of course).

 

Just my view - I'm in no way qualified to pass official judgement!

[fatzy]

@Cale1911, did you get any solution about the staggered tyres?

 

Ideally, all tyres shall have the same circumference, like in the original setup of your car.

 

But, I have read somewhere (an official e-mail from Haldex) that the unit allows for constant 4% difference without problems. That is a built-safety margin. It is always speed differences in the drivetrain, when driving in turns all four wheels have different speed, tyres from different tyre makes have different circumferences (also within the same dimensions) and to allow for different tyre wear on the same car (which alone can give 1.5% difference). And for allowing some degree of staggered sizes fore/aft, which some cars has as their original setup.

 

Your difference is in the range of 3.3 - 3.5%. I wouldn't loose my sleep over it, nothing is broken. In fact, Haldex regulates more power to the rear axle when you hook up a heavy caravan and the front wheels have less grip, like in uphill driving. It is sole the purpose of the Haldex differential to regulate different power to the rear wheels, that's why it is there. And both Veyron and Aventador uses Haldexes, so it can handle a lot of power.....

 

I think dirty oil and clogged filter (for the ones which have that) is a bigger threat.

[Cale1911]

Well, the issue was sorted a couple of days after starting this topic. Got all 4 new winter tyres. I just didn't want to experiment.

BR, 

Cale