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I always use the same size tires so I am just asking this question to learn what is allowed by MB . 2013 Glk 350 4 matic, manual pg 358 - or 360, states “Always equip vehicle with the same size ON A GIVEN AXLE (left/right) “
I’m not thinking of doing this , can front to rear be different ? Could this be for Non 4matic? It does not say so. I’m just learning about AWD and tire size and don’t believe what car tire Salesman Say. Tire shops want to sell tires.
I am not a proponent of radical tire size changes. Oversizing your wheels to get a skinny sidewall look, and going as wide as you can fit into a wheel well both have consequences. More directly to your questions, AWD vehicles are sometimes equipped with "staggered" tire setups where the front set and rear set have different dimensions. But if you plug the dimensions into a tire calculator, you'll find that the tire circumferences are identical, so both front and rear axles are turning identical revolutions per distance traveled. If you change this, the difference has to be compensated for in the transfer case, which hasn't been designed for this. Regarding wheel/tire size on the same axle, different sizes have to be compensated for in the differential, which can briefly tolerate some difference (hence compact spare tires), but limited speed and distance need to be observed. Changing tire dimensions that change circumference also results in speedometer and odometer errors unless you reprogram the vehicle for this change.
If your car isn't AWD, front to back dimensions aren't critical (except for possible handling issues), but side to side remains so.
There might be some AWD vehicles that are designed for different circumference tires front to rear. In any case, IMO, stick with the OE tire dimensions or a deviation that introduces minimal circumference difference.
Last edited by streborx; Nov 19, 2024 at 09:09 AM.
2014 GLK350 base model (active) ; 2001 E320 base (retired); 2001 Wrangler soft-top
Well, in my manual, it does go into a bit more detail, to include a matrix (below).
There are folks who will, let's say, install 18" wheels (rim/tire) at the front and 20" wheel at the rear. I'd say a lot of folks change wheel sizes for looks alone.
Wheel "size" can also be altered by changing the tire dimensions. For example, a 245x45x18 tire is different compared to a 245x60x18 tire (diameter), or a 265x45x18 tire (width), or 265x55x18 (width and diameter).
For an AWD vehicle, I wouldn't mess around with different size wheels.
I guess I did not ask the question right . Will it damage transfer case , I’m not even thinking of this . But MB manual says it’s ok front /rear different size . Just not right/left. I think
tire shops push the rules -requirement to sell you 4 tires , when replacement One tire of SAME size is ok.
But MB manual says it’s ok front /rear different size . Just not right/left
I don't that's a valid inference. If you check, you will see the circumference of the only tires listed that are different front to rear is almost identical. I would never use significantly different size tires on an AWD car unless the car was specifically geared for that (like my tractor is). (Size meaning diameter, or circumference. Width differences don't matter as far as the AWD is concerned.)
I guess I did not ask the question right . Will it damage transfer case , I’m not even thinking of this . But MB manual says it’s ok front /rear different size . Just not right/left. I think
tire shops push the rules -requirement to sell you 4 tires , when replacement One tire of SAME size is ok.
Never use tires of different diameter front/rear on an AWD vehicle. The center differential is always engaged on an AWD vehicle. It is compromised of clutches and latches that will engage if the F/R rotational difference is more than a few percent. Different diameter front/rear tires will eventually damage it.
AWD is different from 4WD. 4WD disengages front wheels when not in use. 4WD should not be used on pavement because all 4 wheels are locked to rotate together. Use on pavement causes excess tire wear and poor wet traction. AWD is designed to enhance wet traction and not affect tire wear.
Last edited by Odd Piggy; Nov 20, 2024 at 12:05 AM.
Reason: Clarity
Then why in the manual does it say infer it’s ok? Doesn’t the manual say “not right /left” ? Thats what I see. I’m not going to do it , I’m trying to figure out what MB is saying
Comparing the first 2 tires listed in the manual, in #3 above, 235/50R19 and 255/45R19, there's a 0.3" diameter difference, 0.7" circumference difference and 6 revolutions/mile difference -- about 1%. That's as far as I'd push a staggered setup. I don't think the looks outweigh the tradeoffs. A square setup in 235 width will allow rotation and longer life. The tire calculator at tiresize.com provides a full perspective on tire alternate sizes.
Then why in the manual does it say infer it’s ok? Doesn’t the manual say “not right /left” ? Thats what I see. I’m not going to do it , I’m trying to figure out what MB is saying
I suppose that some of us interpret the manual text differently. Good that you don’t plan on doing it.
Let me give you an example from our family fleet. One of the drivers assumed that a small domestic SUV was like our 4WD same brand pick ups. Bigger rear tires (NBD on pickups) were put on first not to spend the cost of changing all 4 at once. Our regular tire supplier wouldn’t do that, but someone was found who would. A few thousand miles later, it began making a clunking noise on right hand turns. Like usual, it wasn’t brought to me until the “AWD, ESP, TC, ABS Inoperative” warning came on. A few thousand repair dollars later we traded it for a 4WD pick up.
2014 GLK350 base model (active) ; 2001 E320 base (retired); 2001 Wrangler soft-top
Originally Posted by John CC
Out of curiosity, does the model that comes with the staggered front and rear tires also come with a spare?
I can't speak (cough, "write") on behalf of @Odd Piggy , but I'd rather have an oddball size spare to get somewhere, rather than being stranded with no spare. (our Jeep is like that - spare much smaller than wheels).
However, it's worth mentioning, for over 20 years, we've experienced a flat ... but I keep a plug kit and mini compressor in each vehicle and have used that to "fix and go". (even with motorcycle!) ... have yet to use a spare, but glad it's there!
Last edited by calder-cay; Nov 22, 2024 at 05:13 PM.
The example was about switching to larger diameter tires, not spares.
I think I would have to agree on the small spare vs no spare. It took a few thousand miles for tires 2” larger diameter to destroy the AWD unit.
But GLKs were not equipped with mini spares as far as I know. Some, like mine, had a compressor and collapsible spare that inflated to the 28½” diameter of the tires. Others had a compressor and tire sealant kit. There might have been some that came with MOE run flat tires.
There might have been some that came with MOE run flat tires.
Yeah, all the Diesels. No room for a spare of any size. The DEF tank is where the spare would be.
OTOH, I can't remember the last time I had a flat. I don't have run-flat tires, but I carry a Slime tire compressor and leak stop kit, a cell phone and a AAA card.
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