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The great tire experiment continues - Volvo 850 Turbo

How to go faster, stop quicker, and turn harder. Chips, exhaust, larger turbos, bigger/slotted/drilled rotors, high performance brake pads, manual boost controllers, performance shocks/struts/springs, airbox mods and more! Also discussion on HID and Xenon lights, aftermarket foglights and other exterior lighting.
northernlights
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Volvo Repair Database The great tire experiment continues - Volvo 850 Turbo

Post by northernlights » Sat Nov 15, 2014 5:36 pm

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After 29k miles, and more tire rotations than any sane person would do, it was time to replace my used up set of 205/55R16 Conti DW's. So, against the recommendations of Moderators, Volvo USA, Attorneys, Preachers, the NSA, and my Mom, I decided it was time to try out a set of OEM 205/50R16's on my now certainly doomed 20 year old Columba (which is Portugese for 'Bends easier than public opinion in an election year') wheels.

I bought a set of 205/50R16 Bridgestone Potenza RE760's based on reviews and price. So far so good, as they ride much smoother than the worn out Conti's, and seem to handle fine in the dry.

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Why the change? Aside from the horrible wear marks in my poor wheel liners, a slightly inaccurate speedometer, and strange undulations during parking lot maneuvers, there weren't really any negatives to the 205/55R16 size. But, I wondered what Volvo had in mind way back in 1990-whatever when they were doing the design work. The original size was probably chosen for a good reason.

And based on my experience with Volvo to date, it seemed like they usually made good decisions, at least through the 60's and 70's, like seat belts, padded dash boards, copper-nickel brake lines that never rust, O2 sensors that reduce emissions 10x more than specified, etc, etc. So after some soul searching, I decided to take the plunge and try out the original size, deciding my results would depend on the answers to these three true/false questions:
  • 1) Sometime after 1980, Volvo engineers became idiots
    2) People drive on flat tires, and wonder why bad things happen
    3) Tires have gotten better in the past 20 years
As I have addressed #1, at least from a historic basis, allow me to elaborate on #2. I have observed that, in general, very few people ever bother checking their tire pressure. Find a random person with a car more than three model years old, and see how much air is in the spare. In the past several years, I've seen numerous temporary spares partly shredded, yet safely stowed back in the trunk, implying they were probably driven on with little to no air pressure, until they essentially exploded. Say, maybe like an unnameable vehicle with tires intentionally left underinflated to soften the ride? TPMS anyone?

I also came across an interesting paper which equated the effective spring rate of a tire with the inflation pressure. Most tires did not do so well below 25 psi, so driving around on low tire pressure with low profile tires is probably hard on the both the tires and the wheels.

Helping to seal the deal - note that many low profile tires now have material added as rim protectors. It is clearly visible on the top image of the RE760. Does it help? Who knows, but I bet it doesn't hurt.

My personal experience with Cam Sensors sums it up. Given the apparent nature of Volvo engineers (e.g. 'What do you mean you expect to start the car with a failed Cam Sensor - how will we know when to fire the plugs?') compared to, say a Ford engineer (e.g. 'The cam sensor failed - let's make our best guess and fire the plugs!') I suspect the early 850 Turbo testing did not involve crashing through potholes on flat tires, because who would do that? Perhaps it should have. I suspect they naively assumed that drivers would not do silly things. They clearly never drove in Florida.

In the end, I think the answers are F, T and T. We'll see how it goes in practice. I might be in the market for replacement wheels soon, but I'll chance it in the name of experimentation!

hausmeister
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Re: The great tire experiment continues - Volvo 850 Turbo

Post by hausmeister » Tue Apr 28, 2015 8:29 am

On my 2 cars I have 205/45R17 and I believe 205/50R16. No Issues really.
But the right pressure is important, I slowly ruined a set of tires by driving with to low pressure (I used the recommendation from volvo which is to low for these low profile tires).
Now I use 2.5 to 2.8 bar which is ~36 to 40 psi.
s70 '98 2L na manual Image || 850 T5-R '95 auto Image

shaker_chi
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Re: The great tire experiment continues - Volvo 850 Turbo

Post by shaker_chi » Mon May 04, 2015 2:03 pm

From what I've read Volvo went to the 55's from the 50's due to bent rims. Not sure how accurate that information is though.

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matthew1
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Re: The great tire experiment continues - Volvo 850 Turbo

Post by matthew1 » Mon May 04, 2015 3:12 pm

^ that's correct
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northernlights
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Re: The great tire experiment continues - Volvo 850 Turbo

Post by northernlights » Mon May 04, 2015 3:52 pm

shaker_chi wrote:From what I've read Volvo went to the 55's from the 50's due to bent rims. Not sure how accurate that information is though.
Although that may be true, so far I am having more problems with crappy 205/50R16 tires than bent rims!

precopster
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Re: The great tire experiment continues - Volvo 850 Turbo

Post by precopster » Mon May 04, 2015 11:54 pm

In the owner's manual of my 98 V70R it clearly states that I should be using 205/55 16s yet if I am priveleged enough to own the T5 or LPT variant I should run 205/50 16s.......What the??

All these variants run exactly the same final drive ratio so Volvo in their wisdom assume that R drivers are perfectly OK with getting speeding fines due to the 4% difference in rolling circumference. Well drivers of the R originally spent a few thousand more dollars on their steed so they could theoretically spare the cash for the fines! ! :roll:
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jrbettis
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Re: The great tire experiment continues - Volvo 850 Turbo

Post by jrbettis » Wed May 27, 2015 7:36 pm

Soft alloy compound may also be a reason for more sidewall. Stiffer sidewalk for turbos. Tire size per rolling resistance and inertia from a standstill. See wagons wheels after John Wayne goes Yah! Sweet spot for hp, torque reaching the ground. Liked my Potenzas, wrong tire pressure shortened lifespan.

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