Mikeylomond

Hi


is mb australia replacing the knuckle to correct the crabbing or tyre skipping issue even the car is out of warranty. My car is 2016 glc 250d 4matic. I fitted 21 inch amg rims and tyres from glc43. Thanks

Teckno

Do you still have original rims, 20” ?
MB may invoke their own modification clause to avoid knuckle replacement. Yes important to have correct rims and ET offset for diameter.
There is no knuckle fix for GLC43 models.
21” rims will amplify judder I think. Increase cold tyre pressure to around 38-40psi to minimise effect. When were tyres balanced and wheel alignment done ?
Have you had car since new ? If not you can check via VIN details with Dealer as to service history, get a free print out and specifically see if knuckles changed by owner or dealer.
Good luck.

decorily

As mentioned above, this issue is possibly accentuated by the 21" rims. Also if you are in a cold climate it probably doesn't help. My 2016 GLC250d had the problem and it was more pronounced in winter. MB replaced the 'knuckles ' on mine and this did improve the situation somewhat. Also I found that when tyres were worn the issue was worse.
I'm not in Australia.

Mikeylomond

Hi decorily

some say to change the tyre to continental conti seal 5 star do you think it will help fix the crabbing issue? Or i change it back to 20 inch tyre?

Teckno

This will be a game of cat and mouse.
My approach would be :
1. Contact a MB Dealer, quote VIN and ask for a digital print of all servicing and service bulletin work, including specifically if the knuckles were ever changed by MB for original owner - you may have to provide proof of ownership if records still in previous owner name or MB Aust not advised you are new owner.
2. If no knuckle work done, refit old 19” rims and book it into MB Dealer for free knuckle conversion, incl free wheel align and ask for print out of wheel settings, before and after specs.
3. Once knuckle work done, fit your 21” rims , run at 40psi and pay tyre store to re align based on 21” settings, they may have changed from default 19” ???
4. Try driving in wet, cold roads, high rise car parks with finished concrete floors (coated) and round-a-bouts with high camber, try doing hard, slow right hand u-turns. Judder will show if there is any.
5. You are assumed to be running summer tyres. Book says change to winter tyres when 7 degrees !! Not practical.
6. MB fitted All season, mud & snow Goodyear tyres to cure this before knuckle replacement - it helped a lot, but not perfect.
7. Tyre wear still an issue with front left tyre on outer edge with ‘feathering’ - a ring and pulling of tyre compound, easily seen and felt running fingers against the tyre grain.
8. Yes some owners fitted Continental “Star” marked tyres, fine tuned for BMW and Rolls Royce and had some success, but juddering never went away, nor did tyre wear, getting 18,000 to 25,000km from fronts. Rotation helps, not sure if your rear rims are bigger - if so you can only rotate side to side, not front to rear.
If all else fails, go back to 19” and decide if you want run flats, conventional or all season, M&S tyres, then enjoy !!

Hope this helps.

Mikeylomond

Hi guys! Good news. I just changed my michellin ps4s 265 40 21 front tyres to atturo az 850 which totally fixed the crabbing / skipping issues in glc 43 or 250. I cant believed what an amazing tyre. Smooth and quiet on the road. Made in taiwan .

Teckno

Did you get normal or run flat tyres ?
You might consider replacing rears too.
change of tyre characteristics could play havoc with sensors and traction control - there has been discussions re having all 4 tyres same brand and tread depth with MB 4Matic system to avoid transmission issues.
Thanks for the update.
Did you ever find out if your knuckles were changed in the past ?

Mikeylomond

Hi .techno

I bought normal tyres non run flat on that size 265 40 21 atturo tyres. My rear is dunlop sport maxx gt run flat tyres 285 35 21. Do i really nead to change it to same brand in normal tyres. To prevent damage to transmission? I found out from Mb local dealer in northshore history of car from previous owner. No claims for changed of front knuckle records so far. Maybe because 19 inch was the original tyres and rim installed and didnt exhibit crabbing issues before i changed to 21 inch now that i bought second hand from glc 43 2020 model. Thanks

Teckno

Mercedes probably spent $ millions in designing, testing and replacing knuckles for RHD models from 2015 through to 2019. All 220 and 250 models in petrol and diesel.
It applied to all rim sizes from 17” through to 20” standard rims avail for the models.
The issue of mixing different brand tyres, different compounds and different construction, such as non run flats and run flats is well documented. Tyre brand advice is usually do not.
MB in their online manual and printed manual talk about replacing all 4 tyres at the same time due to sensor activity.
I have replaced just 2 front tyres with same brand as rear and not suffered any error or fault issues.
You might have comprehensive insurance cover issues if you have not informed your insurer re increasing to 21” if they were not MB offered rims for the GLC250 ??
You might also have an insurance assessor void an accident claim for mixing tyre types, etc - still a grey area, different tread, different brand, different characteristics as to braking and grip, different tyre construction in mixing run flats with conventional.
I am starting to sound very negative, but you need to do some due diligence research and make sure you have ins coverage, not to mention handling safety.
Happy researching.

Mikeylomond

Thanks techno you have a point. I will informed my insurance about the 21 inch size and probably change the rear tyres same brand with the front. Is 285 35 21 rear right size to match with 265 40 21? Or i need to match it with 295 35 21? Thanks

Teckno

I am no expert, so I suggest you visit some MB official sites, both in Oz, UK and USA to get official info that may assist, look at ordering options and at accessories, such as rim options.

My quick look suggests the following :
20” front 255,45,20 with ET 40 and overall rim & tyre diam 29.04”. Overall diam is important for correct speed, distance travelled and safety calculations by car ECU.
Rear 285,40,20 with ET22 and overall diam of 28.98”.

21” front 255/40/21 with ET40 and overall diam of 29.03”
Rear 285/35/21 with ET22 and overall diam of 28.85”

Another consideration is power distribution to front and rear axles with your 4Matic.
250 series is 45% to front and 55% to rear.
43 series is 35% to front and 65% to rear.
Not sure why, maybe AMG performance and drive for wider tyres ?
20” staggered in 250 series is 45/55 split, so not sure what if any impact.

Look at tyre sizes recommended by Mercedes if going 21”, may affect OEM alignment settings and correct inflation.
You will have a harder ride and increase possibility of tyre damage or worse due to low profile tyre and rough Oz roads.

You have some decisions to make after you do a deep dive into facts.
Good luck.