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Old 05-16-2018, 07:36 PM   #1
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Default Tires on Chevy Class B's: Load and Speed Rating Spec

I am starting this thread to get the thoughts of members here, whom I find are very knowledgeable. Frequently on other forums people ask for recommendations on tires for their Chevy Roadtrek 190 or 210, and this may apply to the Roadtrek 200 as well. Many times Michelins are recommended. Michelins are fine tires and probably have no issues 99% of the time. However GM specs the E load range AND an S speed rating. The reason the speed rating matters is because a higher speed rating has stiffer sidewalls, and GM specs the stiffer sidewall S spec over the R speed rating spec that Michelin and most tire manufacturers have. The OEM Bridgestone has the S speed rating, and yes it rides a bit rougher, but that is what is expected from the stiffer sidewall. The stiffer sidewall would have better handling due to lesser defelection of the sidewall when cornering or in a large side wind or gust condition. There are other manufacturers besides Bridgestone with the S speed rating spec. I am not suggesting that everyone with Michelins or other R spec tires run out and get new tires. But if you need new tires or your tires have some sidewall cracking or other signs of stress you should consider changing to an S spec tire.

The tire manufacturers are aware of this issue as well. I had contacted Yokohama a couple years ago with a question about their 245/75-16 tires. They asked me for the application, and when I told them it was for an Express 3500 based Class B conversion van, Yokohama said they would not recommend their tire and would not warranty it at all because it had an R rating and GM spec was for the S. Recently I noticed Yokohama's present GEOLANDAR H/T G056 tire now carries an S rating. I assume they designed this tire with a stiffer sidewall to meet the S spec.

Perhaps Yokohama was possibly concerned about liability issues. That is why some tire stores will not sell an R or lower speed rating spec tire for the Chevy Roadtrek. I assume this may be due to the tire seller possibly being named liable in an accident due to installing tires with a lower spec than the manufacturer requires. A lawyer could claim that the vehicle control was compromised due to sub-spec tires. In today's litigious society one needs to be cautious wherever possible.

I hope this thread will cover all thoughts, both in agreement or not with what I have presented. I will then point others to this discussion so they can hopefully be better informed when deciding on replacement tires.
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Old 05-16-2018, 09:01 PM   #2
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That was a fairly common discussion a few years ago IIRC. I don't think there was ever any hard core proof one way or the other on it.


Since the difference between R and S is the difference between 106mph and 112mph, the first question always has to be is if there is a chance to ever being to going that fast. I have found references to various top speed cutouts on the Express vans that varied from about 92mph up to 100mph in the past, mostly from old roadtest articles for various years. I just looked at the PCM programming for our 2007 and a 2010 van and didn't see any cutout setting, but that might be one they lock out, or it may not exist.



My choice was not to be concerned about the rating difference because there is essentially no way you would get me in a 9500# van going over 85mph anyway, so far under the tire rating. We have 265-75-16 Michelin MS2 tires on ours and the sidewalls certainly are a bit softer as evidenced from the smoother ride and profile when sitting. What we have found is that they actually handle better at speed than the Bridgestones did, so sidewall stiffness isn't everything, it appears. How the tread maintains contact shapet in sideloads is balancing act for the designers, I think, and well designed tires of both types manage to leave the tread very flat as the sidewalls move over due to sideload.



It very well may be that the speed rating has a more to do with heat buildup than handling, so the softer sidewalls with more flex would likely run a bit hotter at extended times at higher speeds.


When I talked to Michelin about it a number of years ago when we switched, they recommended the MS2 for Express vans up through the 3500 in the stock 245-75-16 size.


My bet would be there are lots more tire failures between brands than between R and S speed ratings, but that is just a guess, as we really haven't heard of lots of any tires enmass, except maybe the Hankooks that were put on the Fords.
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Old 05-16-2018, 09:31 PM   #3
Bud
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Hi booster,

Getting old I suppose because I might do it: Test the speed governor with my 04 Express Van chassis in 2018 vs 2007. I don't recall if it was 106 or 108 mph, then the engine just quits. How much throttle did that take? Less than a Sprinter makes. Down a mountain with no one it site, no potential for any large animal ............ maybe just a blowout was almost all of the risk.

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Old 05-16-2018, 10:35 PM   #4
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Default How fast are you thinking of going???

Quote:
Originally Posted by peteco View Post
I am starting this thread to get the thoughts of members here, whom I find are very knowledgeable. Frequently on other forums people ask for recommendations on tires for their Chevy Roadtrek 190 or 210, and this may apply to the Roadtrek 200 as well. Many times Michelins are recommended. Michelins are fine tires and probably have no issues 99% of the time. However GM specs the E load range AND an S speed rating. The reason the speed rating matters is because a higher speed rating has stiffer sidewalls, and GM specs the stiffer sidewall S spec over the R speed rating spec that Michelin and most tire manufacturers have. The OEM Bridgestone has the S speed rating, and yes it rides a bit rougher, but that is what is expected from the stiffer sidewall. The stiffer sidewall would have better handling due to lesser defelection of the sidewall when cornering or in a large side wind or gust condition. There are other manufacturers besides Bridgestone with the S speed rating spec. I am not suggesting that everyone with Michelins or other R spec tires run out and get new tires. But if you need new tires or your tires have some sidewall cracking or other signs of stress you should consider changing to an S spec tire.

The tire manufacturers are aware of this issue as well. I had contacted Yokohama a couple years ago with a question about their 245/75-16 tires. They asked me for the application, and when I told them it was for an Express 3500 based Class B conversion van, Yokohama said they would not recommend their tire and would not warranty it at all because it had an R rating and GM spec was for the S. Recently I noticed Yokohama's present GEOLANDAR H/T G056 tire now carries an S rating. I assume they designed this tire with a stiffer sidewall to meet the S spec.

Perhaps Yokohama was possibly concerned about liability issues. That is why some tire stores will not sell an R or lower speed rating spec tire for the Chevy Roadtrek. I assume this may be due to the tire seller possibly being named liable in an accident due to installing tires with a lower spec than the manufacturer requires. A lawyer could claim that the vehicle control was compromised due to sub-spec tires. In today's litigious society one needs to be cautious wherever possible.

I hope this thread will cover all thoughts, both in agreement or not with what I have presented. I will then point others to this discussion so they can hopefully be better informed when deciding on replacement tires.




For what's it's worth.... I'd be more concerned about getting the right tires than the speed Ö RV's are usually not speed demons... and the journey is the destination in this case..


I can tell you that Michelin Defender light truck tires are excellent and getting a tire pressure monitoring system... Truck System Technologies has a very good system... you'll be light years ahead...


Even though I've been up to 80 MPH... I don't recommend it... 60 to 65 is a much better cruising range for fuel economy...


My two cents.
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Old 05-17-2018, 12:11 AM   #5
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I think the term "speed rating" and the associated mph numbers are somewhat misleading. Of course no one is going to drive their vehicle at the limits. The following site covers the other points better than I can describe.

https://brownsalignment.com/tire-liability-policy/
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