4 or 2 Conti DWS?

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This is for the wife's C300 AWD. Here's what's on there now: Conti Pro Contact, tread depth: front: 8/32" rear left: 4/32" rear right: 6/32" Since this car is used during winter, I'm inclined to get her some new tires before the first snow hits. From what I've read, snow traction really diminishes once the tread goes below 6/32". AWD and DSC help, but they don't perform miracles. I've decided on Conti DWS. The only question is, do I just get her 2 of them for now for the rear axle since the fronts still have plenty of tread left? Or is the winter traction of DWS so vastly superior that it would be too big of a mismatch and I should just buy 4 DWS and maybe try to sell the two CPCs that have good tread left? For the record, she drove on the CPC last winter and didn't have any issues, but obviously there was a lot more tread on them last year. Thanks!
 
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I'd go four new on separate wheels. Save the good tread for winter use and wear the others down in the summer. Once the DWS is worn down to 8/32 or so, make those the summer tires and get a new winter set. If you don't want to get new wheels, I'd probably just replace all four. I hate driving in winter on poor tires, and I love driving in winter on good tires. I'd much rather have two new DWS on the back than none though. Which tires tend to wear more on that car; front or back?
 

JRed

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I have Conti DWS tires on my Subaru and they are very good in the snow, but they're not "night and day" different from any other tire I've had on my Subaru. They've worn VERY well, however. This set has about 1/2 the treadlife left and they're going on 25k miles. If you're that worried about snow, how about getting another set of wheels and a set of real "winter tires"?
 
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Quattro Pete

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Originally Posted By: rpn453
Which tires tend to wear more on that car; front or back?
The back ones wear quicker. 80% of the power goes to the back. It's a staggered setup: 225/45/17 front, 245/40/17 back. Not ideal winter tire sizes, I know, but like I said, the car did just fine last winter with all-season tires and I'm not planning to have a second set of rims/tires for it.
 

Quattro Pete

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Originally Posted By: JRed
If you're that worried about snow, how about getting another set of wheels and a set of real "winter tires"?
Not all that worried. I was more interested in hearing about how different the DWS is from CPC in terms of winter traction. From what you're describing, it doesn't sound like there is that much difference between them, so I may be OK with nearly new CPC up front and brand new DWS in the back.
 

JRed

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Is your C300's AWD system not affected by different size tires? I think that'd be the real issue to consider...
 
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I may mentioned this before, overall diameter of 225/45-17 is about 0.3" larger than 245/40-17. The better match diameter are: 215/45-17 front to 245/40-17 rear 225/45-17 front to 255/40-17 rear To get more traction with snow and ice, narrower tires will be better. When I was in Minnesota, I downed size summer wheel/tire of the Toyota Supra by 2, from 16" to 14" and using all-season 195/70-14 I could go almost anywhere in winter. If I was you I would look into buying 2 wheels and install 2 DWS in size 225/45-17 for the rear.
 
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With a staggered setup, it's a lot more likely that I'd just replace tires in pairs. If you don't feel it's worth getting a second set of wheels for your winter driving conditions, and those Contis have provided adequate performance in previous winters, then I'd just go with two right now. My father used studded winter tires on the rear with all-seasons in the front of his RWD vehicles for many years. I also drove a Chevette in high school with that setup. It works pretty good. Very stable on snow and ice!
 
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With the AWD setup, you're almost obligated to replace all 4. If you only do 2 and the AWD setup fails, it is incredibly expensive to fix. Plus many tire dealers won't do 2 on an AWD.
 

Quattro Pete

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Originally Posted By: JRed
Is your C300's AWD system not affected by different size tires? I think that'd be the real issue to consider...
The OEM setup includes 225/45/17 front and 245/40/17 rear, which is already somewhat different in terms of the overall diameter. I'm assuming it's not an issue then, or else the factory wouldn't have put that on.
 

Quattro Pete

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Originally Posted By: Quattro Pete
80% of the power goes to the back.
I may have goofed up on this. I think only 55% of the power goes to the rear.
 
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I can't see them using a staggered setup if variations in tire diameter could harm the AWD system. According to the Wikipedia Page, the modern 4Matic system uses an open center diff, so small variations in tire size would be a non-issue. Brakes provide all the slip control. Prior to 1998, 4Matic used a complex electronic clutch system and would likely be sensitive to variations in tire diameter.
 
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if you use the tire calc its only about .1" sidewall difference or 1% difference ie speedo reads 60 you are going 59.4mph 245/40r17 vs 255/40r17 is 1.3% difference .. a bigger difference than the stock size. So I think your tire calc is faulty HTSS_TR The 1% difference in stock size between front and back is very small.. tires that are worn differently could easy be 3/32 off also. That all said with AWD I'd buy 4 and sell the old ones.
 
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Quattro Pete

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Originally Posted By: Rand
245/40r17 vs 255/40r17 is 1.3% difference .. a bigger difference than the stock size. So I think your tire calc is faulty HTSS_TR
I think his calculations are correct. Difference between 225/45/17 front and 245/40/17 rear is 1.0%. Difference between 225/45/17 front and 255/40/17 rear is 0.2%. So, if you assume that 225/45/17 is the stock diameter, then technically 255/40/17 would be a closer match. I agree though that we're splitting hair here. Thanks for the feedback, everyone.
 
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Originally Posted By: CapriRacer
With the AWD setup, you're almost obligated to replace all 4. If you only do 2 and the AWD setup fails, it is incredibly expensive to fix. Plus many tire dealers won't do 2 on an AWD.
I noticed my Acura MDX with SH-AWD* has no mention of matching tires. Yet at the same time the service manual mentions mismatched tires potential causes to overheating that causes SH-AWD shut downs. *SH(super handling)-AWD is front biased AWD with ability to not kick power to rear wheels, but an individual rear wheel to enhance handling.
 
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Originally Posted By: rjundi
I noticed my Acura MDX with SH-AWD* has no mention of matching tires. Yet at the same time the service manual mentions mismatched tires potential causes to overheating that causes SH-AWD shut downs.........
I've noticed that many AWD systems that have problems with different tire diameters fail to mention a tolerance - and worse, fail to mention tire diameter at all. I had a long conversation with a Volvo service manager about this. He was trying to get us (the tire manufacturer) to pay for the second replacement of the center coupling, because of a difference in tire diameter between two different speed ratings of the same design (an usual situation to be sure). I pointed out to him that he was citing a service bulletin from Volvo that stated the tires had to be within "X" circumference and that tires should be replaced in sets of 4, but this is never communicated to consumers. I also pointed out that the tires were on the vehicle the first time the unit was replaced.
 
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Originally Posted By: Quattro Pete
Originally Posted By: Rand
245/40r17 vs 255/40r17 is 1.3% difference .. a bigger difference than the stock size. So I think your tire calc is faulty HTSS_TR
I think his calculations are correct. Difference between 225/45/17 front and 245/40/17 rear is 1.0%. Difference between 225/45/17 front and 255/40/17 rear is 0.2%. So, if you assume that 225/45/17 is the stock diameter, then technically 255/40/17 would be a closer match. I agree though that we're splitting hair here. Thanks for the feedback, everyone.
wow fail.. I apparently cross read the sizes.. approved .. twice. That makes more sense If I read them straight across... Also: interesting story capriracer. So the dealer put 2 different speed rating tires on the car??
 
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Before everybody gets too confused pondering suitable tire sizes, please take note that MB originally offered both uniform and staggered fitment options in three different rim diameters. My first step in figuring out what size to use would be to get in writing from a Mercedes service department (or preferably a regional service rep.) a get-out-of-jail-free card that says that there's no difference in the gearing of the car based on the tire size that was originally fitted. Of course I'm guessing about there being no difference - if there is, then they would tell you so, and you're clear on your way to fit a staggered setup for winter. ...but Tire Rack has no issue with fitting a uniform winter setup to the car, regardless of whether it had a uniform or staggered setup when it was new.
 
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Originally Posted By: Rand
.....Also: interesting story capriracer. So the dealer put 2 different speed rating tires on the car??
Actually, the story is even more complicated than that. The consumer replaced a pair of tires as suggested by the Volvo dealer, but the first time the consumer did all the leg work himself. The car got the same exact speed rating. Then later, the Volvo dealer got a set of tires from a local tire dealer and mounted them himself. When he specified the tires, he neglected to mention the speed rating, so the local tire dealer supplied him with what he thought the correct tire was - and got it wrong. The Volvo dealer didn't notice. What made it really bad was that the Volvo dealer was at the middle of this in every instance. But for some reason, the Volvo service manager was trying to stick it to the local tire dealer - who in turn was asking for help from us - the tire manufacturer. I was all prepared to go to court and had all my ducks lined up. Interestingly, all the documents were supplied by the Volvo dealer - the service bulletin, the maintenance records. To my mind it was pretty open and closed, but the Volvo service manager was not convinced it was his fault. But we never heard anymore about it, so I guess it was resolved.
 

Quattro Pete

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Update: I ended up pulling the trigger on 4 Conti DWS. I couldn't pass up the deal I was getting. They'll be mounted before the snow hits, which may be fairly soon judging by this crazy weather...
 
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