Tires on Chevy Class B's: Load and Speed Rating Spec

[peteco]

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.

[booster]

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.

[Bud]

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.

Bud

[Roadtrek Adventuous RS1]

Originally Posted by peteco

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 … 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.

[peteco]

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/

[peteco]

Originally Posted by peteco

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/

New link to Brown's speed rating discussion:

https://brownsalignment.com/tire-wea...speed-ratings/

[jjrbus]

I find the speed rating confusing as according to people who study these things has more to do with sidewall construction than MPH. The Bridgestone V-steel has nylon wrapped sidewall cords which makes the walls stiffer and more resistant to curb rash. A stiff sidewall on a 4 ton vehicle sounds like a good thing.

I am of the mindset that TPMS, compressor and being anal about pressure is more important than brand. I never drive anywhere, not even 10 feet on a low tire! Low Pressure ie 15% under recommended pressure.

https://www.rvtiresafety.net/

[booster]

The whole speed rating thing if kind of a black hole of confusing things to me.

What is missing is that I have never seen any article explain just WHAT is used to determine it.

Is it heat?

Is is centrifugal force and tread separation?

Is it really only for the rated tire when turning at that speed (sidewall rollover)?

Maybe someplace has that information, it would nice to know the logic behind it.


Or, it could be a obscure as being related to the vehicle the tires are on. Maybe. Do they want to limit the corner holding ability of a tire to prevent a rollover of a van at high speed cornering by limiting the top speed vs traction ratio?

Tire rack gives this speed chart vs typical application which is what sent me thinking about the vehicle really being the limiting factor, or at least a part of it.


No typical van or truck use beyond speed range R.

[booster]

I just looked at the PCM factory settings that I have saved for our 07 Chevy 3500 Roadtrek that were read by my HPtuner programmer.


The factory sets the speed limiter (fuel cutoff) at 90 mph and that is for a normal height van, not a top heavy Roadtrek.


Does this make the tire speed rating of R vs S less important? I have no idea. GM could have just picked the V-steels because of price or availability or even spiffs from the vendors to purchasing agent

On edit:

I just looked at the programming for a members 2009 Express 3500 Roadtrek and that one has the limit at 98mph. I think by 2009 they all had Dynamic Handling so that might explain the change. If so it points a bit more to it being more vehicle related than tires and the R vs S may not have anything to do with the actual risk factors of the tires.

[CapriRacer]

Hi Guys!

I was asked a question at another website and a link to this thread was provided, so I decided to join and try to answer that question here.

Who am I? I'm a retired tire engineer. I have a website where I address a lot of issues related to tires: Barry's Tire Tech:
Main Page

I have a page on Speed Ratings: Barry's Tire Tech:
Speed Ratings

Short Version: Speed Ratings are more about centrifugal forces rather than heat. That's why higher speed rated tires have more cap plies.

Are higher speed rated tires better? Kind of!

Ya' see, there are different approaches a tire manufacturer can take: They can rate a tire such that it barely passes the speed rating - OR - they can take a more conservative approach and rate the tire a couple of steps lower than what it is capable of.

What about the issue of a stiffer sidewall on higher speed rated tires? Not necessarily true. What makes for a higher speed rating doesn't translate to a stiffer sidewall. Those 2 things are independent of each other. But higher speed rated tires tend to ride ever so slightly worse, but this varies a lot from brand to brand.

What I think is important are cap plies. The more the better. Higher speed rated tires will have more cap plies, but that doesn't necessarily mean lower speed rated tires won't have multiple cap plies.

Cap plies are usually made out of nylon. Polyamide is another name for the group of fibers than includes nylon, but it also includes kevlar, so I suspect that any tire manufacturer that specifies polyamide might be looking at possibly changing the nylon for kelvar.

And just so everyone understands, speed ratings are a compliance kind of thing - meaning the tire manufacturer is certifying that the tire passes the specified speed rating, but it might actually be capable of a higher speed than indicated.

So do I think the fact that GM specifies an S speed rating meaning you should use an S speed rating? Sort of! It's just a bit more complicated than that!

Hope this helps. Feel free to ask me more questions.

[peteco]

Originally Posted by CapriRacer

Hi Guys!

I was asked a question at another website and a link to this thread was provided, so I decided to join and try to answer that question here.

Who am I? I'm a retired tire engineer. I have a website where I address a lot of issues related to tires: Barry's Tire Tech:
Main Page

I have a page on Speed Ratings: Barry's Tire Tech:
Speed Ratings

Short Version: Speed Ratings are more about centrifugal forces rather than heat. That's why higher speed rated tires have more cap plies.

Are higher speed rated tires better? Kind of!

Ya' see, there are different approaches a tire manufacturer can take: They can rate a tire such that it barely passes the speed rating - OR - they can take a more conservative approach and rate the tire a couple of steps lower than what it is capable of.

What about the issue of a stiffer sidewall on higher speed rated tires? Not necessarily true. What makes for a higher speed rating doesn't translate to a stiffer sidewall. Those 2 things are independent of each other. But higher speed rated tires tend to ride ever so slightly worse, but this varies a lot from brand to brand.

What I think is important are cap plies. The more the better. Higher speed rated tires will have more cap plies, but that doesn't necessarily mean lower speed rated tires won't have multiple cap plies.

Cap plies are usually made out of nylon. Polyamide is another name for the group of fibers than includes nylon, but it also includes kevlar, so I suspect that any tire manufacturer that specifies polyamide might be looking at possibly changing the nylon for kelvar.

And just so everyone understands, speed ratings are a compliance kind of thing - meaning the tire manufacturer is certifying that the tire passes the specified speed rating, but it might actually be capable of a higher speed than indicated.

So do I think the fact that GM specifies an S speed rating meaning you should use an S speed rating? Sort of! It's just a bit more complicated than that!

Hope this helps. Feel free to ask me more questions.

Hey CapriRacer, thanks for posting here for the benefit of all. Just an FYI, this forum (like most) has a range of ability levels, and usually we all get along as we try to learn to make our Class B vehicles better and safer. There are some quite capable folks on here and they are so generous of their time and knowledge. Sometimes the discussion goes to a very deep technical level and that's great. So don't shy away from giving us more detail.

Regarding the tire discussion here, please go ahead and take it to the next level of detail on the GM spec, particularly regarding our heavy near max GVWR vans.

[booster]

Originally Posted by peteco

Hey CapriRacer, thanks for posting here for the benefit of all. Just an FYI, this forum (like most) has a range of ability levels, and usually we all get along as we try to learn to make our Class B vehicles better and safer. There are some quite capable folks on here and they are so generous of their time and knowledge. Sometimes the discussion goes to a very deep technical level and that's great. So don't shy away from giving us more detail.

Regarding the tire discussion here, please go ahead and take it to the next level of detail on the GM spec, particularly regarding our heavy near max GVWR vans.

I agree, and I certainly am one of geeks referred to above


If it is centrifugal force that is the issue, that would help explain the lower tread depth I seem to see on higher speed rated tires, I think, and lower speed ratings on the off road tires with lots of heavy tread.


I think the big question is if, as a tire engineer and not a lawyer, what relative risk would you put on putting an R rated tire on one that factory was S rated if that vehicle was speed limited at under 100 miles an hour?


I would think the only time you could be going faster than the limiter allows would be if you were careening down a mountain with failed brakes or something and that makes for a lot more problems than just tires.

[peteco]

Originally Posted by booster

I agree, and I certainly am one of geeks referred to above


If it is centrifugal force that is the issue, that would help explain the lower tread depth I seem to see on higher speed rated tires, I think, and lower speed ratings on the off road tires with lots of heavy tread.


I think the big question is if, as a tire engineer and not a lawyer, what relative risk would you put on putting an R rated tire on one that factory was S rated if that vehicle was speed limited at under 100 miles an hour?


I would think the only time you could be going faster than the limiter allows would be if you were careening down a mountain with failed brakes or something and that makes for a lot more problems than just tires.

My thinking is that handling is the reason for the GM S spec, not speed. Also maybe extra margin for temperature capability. Hopefully Capri can provide insight.

[booster]

Originally Posted by peteco

My thinking is that handling is the reason for the GM S spec, not speed. Also maybe extra margin for temperature capability. Hopefully Capri can provide insight.

I agree and as I mentioned the increase in the limiter with Dynamic control would back that up. Of course, with our van you would want to decrease the limiter speed to allow for higher center of gravity than stock.

[jjrbus]

Originally Posted by CapriRacer

Hi Guys!

I was asked a question at another website and a link to this thread was provided, so I decided to join and try to answer that question here.

Who am I? I'm a retired tire engineer. I have a website where I address a lot of issues related to tires: Barry's Tire Tech:
Main Page

I have a page on Speed Ratings: Barry's Tire Tech:
Speed Ratings
.

Thanks for joining and chipping in, greatly appreciated and I will be checking your website. I often reference another retired tire engineer Roger Marble who is also an RV'er.

https://www.rvtiresafety.net/

[Doneworking]

We bought our 2007 RT 210P and took delivery in September 2006. The first time I replaced the tires the local tire guy recommended a certain brand and a R rated tire. Now, I am not very technical but a bit savvy.

Back then, the family that started RT still owned it and so I called the company. I don't remember all the details but the RT originally came with S rated Bridgestones. The RT guy told me then that they had spent a lot of time and effort on determining which tire to put on their product and they recommended that I stick with the Bridgestones because they liked the stiffer side wall and the S rating. I don't remember details of the conversation because it was many years ago and lunch yesterday is a bit of a mystery . I do recall the conversation and the content I have relayed herein.

[TX-Trek]

All good tires mentioned here. We have Cooper Discoverer HTP S rated LT tires and I really like them. About 10k miles on them so far.
They replaced Bridgestone R rated tires. As I recall both were 10 ply.

My take on the ratings is not about mph difference, more about heat resistance. Speed increases heat/pressure in the tire especially on higher temp pavements. IMO this is important driving this almost 10k lb tubby around.

I always check pressures via the dash TPMS and I've found that the S rated tires didn't increase pressures quite as much as the R rated tires after a period of time. I also verify with a manual air pressure gauge. This was on the same type of pavement in pretty close ambient temps. Driving 65-70, the R rated pressures could increase by almost 10 psi on a hot day, the S rated increased about half as much. I run 65F/80R pressures.

Not totally done in a scientific environment but good enough for me - if I have a choice I'll get the S rated tires.

[booster]

Originally Posted by TX-Trek

All good tires mentioned here. We have Cooper Discoverer HTP S rated LT tires and I really like them. About 10k miles on them so far.
They replaced Bridgestone R rated tires. As I recall both were 10 ply.

My take on the ratings is not about mph difference, more about heat resistance. Speed increases heat/pressure in the tire especially on higher temp pavements. IMO this is important driving this almost 10k lb tubby around.

I always check pressures via the dash TPMS and I've found that the S rated tires didn't increase pressures quite as much as the R rated tires after a period of time. I also verify with a manual air pressure gauge. This was on the same type of pavement in pretty close ambient temps. Driving 65-70, the R rated pressures could increase by almost 10 psi on a hot day, the S rated increased about half as much. I run 65F/80R pressures.

Not totally done in a scientific environment but good enough for me - if I have a choice I'll get the S rated tires.

The temp increase with lower speed rated tires has been a go to point for a long time, but CapriRacer says it is not the defining point, and he has more real knowledge, I assume, than any of the rest of us.


We have first hand information in our going from Michelin MS2 tires to Agilis that the temp can increase that much just from a model change, same manufacturer, same R speed rating. Others have seen similar.


As they say, It's complicated.

[CapriRacer]

Wow, it's exciting to see so much activity! So allow me to try to address all the issues brought up. If I miss one or more in depth is needed, let me know. Here goes:

• The risk of using an R rated on a vehicle spec'd with S rated tires.

The original spec isn't the issue. It's the risk of a tire failure - R rated being more risky than an S rated. But like I said, this issue is clouded by the way tire manufacturers view the speed rating. It isn't a clear bright line - it's a broadly fuzzy line - meaning that sometimes people will have success with R rated tires, but others won't and there won't be obvious differences.

• The handling of an S rated tire vs an R rated tire?

Speed ratings are generally determined by the belt package, and nylon cap plies make for higher speed ratings.

But handling is all about sidewall stiffness. A stiffer sidewall reacts faster to steering input and that just feels more comfortable and reassuring. Unfortunately, making the sidewall stiffer adversely affects the ride quality. It's a tradeoff!

So those 2 items are separate and can be manipulated separately. So it is quite possible to create a passenger car tire with a very high speed rating (say a Y or W speed rating) that also rides softly - and those do exist. But normally high speed rated tires are designed for high performance cars and in that application the desire is for a quick steering response. As a result, many people think that higher speed ratings mean better handling and harsher rides - and that isn't a cause/effect kind of thing.

• Why did GM spec an S rated tire?

Probably to get a more robust tire - one less prone to failure. Since the handling issue is separate from the speed rating, they might want to have soft riding tires for this vehicle. Of course, the tradeoff is a sloppier handling - and given that these vans could use some cornering stability, it's going to be like walking a tightrope.

[peteco]

Originally Posted by CapriRacer

• Why did GM spec an S rated tire?

Probably to get a more robust tire - one less prone to failure. Since the handling issue is separate from the speed rating, they might want to have soft riding tires for this vehicle. Of course, the tradeoff is a sloppier handling - and given that these vans could use some cornering stability, it's going to be like walking a tightrope.

Is handling completely separate from speed rating, or only somewhat separate? My thinking is that a less stiff sidewall means the sidewall flexes more, and that more flexing will result in a tire temperature increase, which then reduces the speed for safe operation, and thus a lower tire speed rating. You indicate both can be designed for separately, but it seems like they are somewhat tied together. Is my logic incorrect here?