Tireman9 wrote:
CHD Dad wrote:
He is using the analogy of an engines redline to driving a tire above 65mph. If you are on the highway, you will likely be driving 65mph. On my local highways the speed limit is 70, meaning cars go 80+ and big rigs are all 70-75. Driving at 65 in the right lane makes me a road hazard to others at times. I get cars and rigs flying up to my bumper or just plain flying by me.
It is the redline = tire max speed I have issue with. Redline is the absolute of an engine. That is where the engineers have decided the mechanical limits of the engine are met. It is normally past the engines peak HP/TQ numbers and is also normally the physical limitations of the drivetrain. If 65mph is the MAX physical limitations of the tire then the actual speed rating should be far below that. You dont drive an engine at redline for hours on end and tire engineers shouldnt expect a tire to be driven at its Max for hours on end.
I do plan on contacting the engineer with above questions and how its worded on his site. I need to contact my friend as well, he works in the test dept for Michelin. He may not know the answers but I am sure he knows who will.
FYI - I am not an engineer, far from it. I am a gearhead and have been racing for over 2 decades. I am anal about my road and track tires. I used to own a Longacre tire pyrometer to make sure my alignment specs and pressures were spot on for given course conditions. I have since stopped racing other than an occasional karting sprint just to get the juices going but I do take tires very seriously!
Hi, Tire Engineer here. The analogy of Redline is mine. I was trying to come up with some way to let people know they should not drive above 65 and in fact should drive slower. The Load/Inflation tables for ST type tires go back to the days of 55 mph National Speed limit and have not and probably will never be adjusted as the load limits would probably be decreased which of course the RV mfg does not want.
Just as redline in an engine can probably be exceeded momentarily there will probably be cumulative permanent damage done to the engine and its life will be cut drastically, exceeding the 65 speed limit for tires can be momentarily be exceeded but the tire will be damaged and its life shortened. It may be possible that some tires are slightly more tolerant of exceeding the redline than others but I know of no way to pre-determine which individual tires can tolerate over speed. Also if a tire has ever been run low on air there will be internal damage which may make a single mile at 66 too much.
There is another problem that causes damage to ST tires and that is the basic multi-axle suspension used by most trailers made today. This set-up forces some of the 4 or 6 tires to be dragged around the corner with the result be very high internal structural strain that tires on cars or motorhomes or single axle trailers do not see.
See my post of November 20, 2013 on that specific topic.
My post of March 23, 2011 mentions my racing experience.
Hi Roger - thanks for replying to my questions. You and I are from the same area - I lived in Firestone Park for years before moving to SC. I have relatives that work at GY and one left BFG a long while back. Did some reading up on you and we ran at some of the same tracks. I did way too many laps at Nelson, ran at Mid-O quite a bit and liked the new BeaveRun facility (now Pitts Int of course). I did many years of AutoX with NeOhio and surrounding SCCA clubs and quite a few track events but nothing up to Indy Car level like you worked with! Also worked for Fred Baker for a few years and did hot lap demos for clients of ours in various Audi and Porsche's. Would love to read more about your race history but it was hard to find much, I did find a very old Pop Mech article from the late 80's!
I cant believe that tire companies havent made a better ST tire. 65mph makes sense with a 55mph speed limit. I would happily drive 55mph if it were the limit and I would have a nice safety margin in my tires. The fact that all major highways here are 70mph makes that difficult at best. I lost count of how many times we were almost rear-ended driving under 65mph. I have witnessed too many vehicles swerving to avoid me to comfortably tow at that speed in moderate traffic. If traffic is light and there is plenty of visibility and planning ahead then I can fine with it. In fact I just witnessed a bad accident on 95 where a camper was totaled and it appeared a car ran into it.
Sort of puts me in a bind - drive 65mph and put family in danger of being hit by another driver. Drive over 65mph and put family in danger due to inferior tire technology.
Not sure if this is the right thread, but would like to know your thoughts on running non-ST tires on campers. I see a lot of suggestions for upgrading to LT tires (I cant, I can only fit 14" tires on mine). I have to think LT tires are not meant for the side stress forces put on a tandem axle design of a camper. Big rigs have tandem axles to deal with but their tires are huge and heavy!
