NOTE: Trike tire load ratings NOT the same for all models & all model years!
There has been a fair bit of discussion lately on the trike forum about TPMS and recommended tire pressures. Some of the comments posted, including some by myself, have assumed that the rear tires that have size designations identical to car tires have the same load ratings. But today, I discovered they do NOT. Furthermore, it is important to remember that low profile tires like those on my 2023 RG3 do not flex in the same way that the higher profile tires on a Tri-Glide do. Here's what I found today:
I took a photo of the sidewall of the tire used as the rear tire on my 2023 RG3:
Now this is a 215/45-18R tire, which is a SIZE commonly used on cars, but the load rating on this trike tire is lower than the load ratings typically found on car tires. This is probably because Harley-Davidson, whose name by the way is engraved on the tire sidewall in addition to "Dunlop", evidently gave Dunliop a unique set of specifications, designed to work on a 2023 RG3, not a car, and not a Tri-Glide.
The load rating in the photo is only 1074 lb at 36 psi.
My RG3 apaprently weighs 1160 lb, and apparently 380 is on the front tire leaving 780 for the TWO rear tires to handle.
But, I myself weigh 168 lb, but my dressed for riding weight (including heavy leather jacket, full face convertible helmet, heavy HD boots, gloves, and emergency supplies in the pockets soemtimes totals to more than 20 lb when wearing winter riding gear. So, let's say I add a total of 190 lb. Maybe I will also carry a passenger (say 175 lb) and touring gear (60 lb max since that is all my RG3 trunk is rated for I believe.
My 190 lb goes about 70% on the rear tires, so 70% of 190 = 133 lb
My passneger's 175 lb goes about 90% on the rear tires, so 90% of 175 = 158
The luggage goes 100% on the rear tires, so = 60 lb
Total STATIC (not dynamic) weight on the rear tires = 351 lb.
So, now the 2 rear tires have to carry 780 lb + 351 lb = 1131 lb shared between them. That's 1131 / 2 = 566 lb per trear tire.
That's only 566 / 1074 = 53% of each tire's laod capacity.
BUT, when I corner "aggressively", it is easy to see that a significant portion of that weight will shift to the outside tire. Plus, if I hit a bump while cornering, or even hit a bad bump when going straight, each tire could have to absorb a much larger load spike, and I'd rather not have it blow out as a result.
So, the 1074 lb weight limit does not seem so generous anymore.
But also notice that the 1074 lb load limit requires 36 psi of pressure. HD recommends "only" 26 psi. That sounds very high for a "car-SIZED" tire on a trike carrying only maybe half of the statis and dynamic loads a car would subject it to. But if 36 psi is needed to support 1074 lb, than 26 psi might be good for only 26/36 x 1074 = 776 lb. THAT number is only 776 / 566 = 37% higher than the actual STATIC load. Is that getting your attention?
Plus, remember, this is a very low profile tire. The wheel is an 18 incher, and the total diametr of wheel and tire is only about 25.5 inches. Taking off the wheel diameter, and dividing the remainder of tire sidewall by 2, you see that I have only 3.8 inches of tire sidewall that can flex. If I hit a bad bump hard enough, it is conceivable that I could bend the wheel rim. Don't pooh-pooh that: My neighbour runs a Street Glide. He recently hit a freeway pothole SO bad that it DID bend the rim on his front aluminum wheel AND also took out the wheel bearings and the steering head bearings. No kidding. His bike was still rideable, but it acquired a severe vibration that required slow speed home, and then to a motorcycle shop where the crew diagnosed all the above listed damage. He's looking for a replacement wheel right now, and apparently a brand new one from HD is close to a $1000 here in Canada = $730 US at the current exchange rate.
In another thread, I recently mentioned that at least some tire experts believe that optimal tire traction and performance occur when the HOT tire pressure is about 10% higher than the cold tire pressure (This does NOT apply to dragracing!). Let's examine that a bit:
HD recommends 26 psi for my RG3. Applying that 10% psi increase theory, ideally my tires would go from 26 psi when cold to 28.6 psi when hot. I had success using this formula a couple of years ago on a Kawasaki 600 high performance sportbike (with an engine whoe rev limit was 16,500 rpm!).
Here in "metric" Canada, we use Kilopascals ("Kpa"s) instead of psi, and it takes 6.88 Kpa to amke 1 psi. So 26 psi = 179 Kpa. Per the onboard TPMS, my dealer set my right rear tire pressure at about 184 Kpa and my left rear tire pressure at about 180 Kpa.
Tomorrow, I am going to do a tire test where I will note the hot psi, and see exactly how high it gets. I'll let you all know what I discover.
Jim G
Last edited by JimGnitecki; 08-22-2024 at 06:58 PM.
Add some confusion. My Hannigan tires are 205/55R16. 1350 lbs @51 PSI. Hannigan calls for 28 PSI.
Bike weight is about 950 ready to ride, Trike kit is 320 LBS.
Add some confusion. My Hannigan tires are 205/55R16. 1350 lbs @51 PSI. Hannigan calls for 28 PSI.
Bike weight is about 950 ready to ride, Trike kit is 320 LBS.
Yes! See what I mean about tires that have similar nominal sizes and that LOOK similar being dramatically different? I know that many trike forum members here think the HD OEM rear suspension is way too stiff, and with "car" tires, maybe it is. But I rode my brand new "leftover' 2023 Road Glide 3 home from the HD dealership just yesterday, a distance of 173 km = 107 miles, on a variety of road types and surfaces, and I realized after the trip that I had not felt any symptoms of a too stiff suspension. MAYBE HD really did, at least recently (2023 and later??) work with a tire manufacturer (Dunlop) to spec out rear tires that might LOOK like car tires but that are very specifically tuned to the RG3??
Are the comments here in the forum about the suspension being too stiff UNIVERSAL to all 3 HD trike models and all model years, or have more recent buyers gotten suspension performance a little closer to what they want?
Have some trike owners replaced their rear tires with CAR tires of the same nominal size? If they did, how did they ensure that they got the right sidewall stiffness suited for an HD trike versus a car?
Go by the vehicle manufacturers recommendation not the maximum rating on the tires.
I think most of us know and agree with that statement, but a significant number of trike forum members say that some of the HD recommendations seem to produce undesirably stiff ride results.
There has been a fair bit of discussion lately on the trike forum about TPMS and recommended tire pressures. Some of the comments posted, including some by myself, have assumed that the rear tires that have size designations identical to car tires have the same load ratings. But today, I discovered they do NOT. Furthermore, it is important to remember that low profile tires like those on my 2023 RG3 do not flex in the same way that the higher profile tires on a Tri-Glide do. Here's what I found today:
I took a photo of the sidewall of the tire used as the rear tire on my 2023 RG3:
Now this is a 215/45-18R tire, which is a SIZE commonly used on cars, but the load rating on this trike tire is lower than the load ratings typically found on car tires. This is probably because Harley-Davidson, whose name by the way is engraved on the tire sidewall in addition to "Dunlop", evidently gave Dunliop a unique set of specifications, designed to work on a 2023 RG3, not a car, and not a Tri-Glide.
The load rating in the photo is only 1074 lb at 36 psi.
My RG3 apaprently weighs 1160 lb, and apparently 380 is on the front tire leaving 780 for the TWO rear tires to handle.
But, I myself weigh 168 lb, but my dressed for riding weight (including heavy leather jacket, full face convertible helmet, heavy HD boots, gloves, and emergency supplies in the pockets soemtimes totals to more than 20 lb when wearing winter riding gear. So, let's say I add a total of 190 lb. Maybe I will also carry a passenger (say 175 lb) and touring gear (60 lb max since that is all my RG3 trunk is rated for I believe.
My 190 lb goes about 70% on the rear tires, so 70% of 190 = 133 lb
My passneger's 175 lb goes about 90% on the rear tires, so 90% of 175 = 158
The luggage goes 100% on the rear tires, so = 60 lb
Total STATIC (not dynamic) weight on the rear tires = 351 lb.
So, now the 2 rear tires have to carry 780 lb + 351 lb = 1131 lb shared between them. That's 1131 / 2 = 566 lb per trear tire.
That's only 566 / 1074 = 53% of each tire's laod capacity.
BUT, when I corner "aggressively", it is easy to see that a significant portion of that weight will shift to the outside tire. Plus, if I hit a bump while cornering, or even hit a bad bump when going straight, each tire could have to absorb a much larger load spike, and I'd rather not have it blow out as a result.
So, the 1074 lb weight limit does not seem so generous anymore.
But also notice that the 1074 lb load limit requires 36 psi of pressure. HD recommends "only" 26 psi. That sounds very high for a "car-SIZED" tire on a trike carrying only maybe half of the statis and dynamic loads a car would subject it to. But if 36 psi is needed to support 1074 lb, than 26 psi might be good for only 26/36 x 1074 = 776 lb. THAT number is only 776 / 566 = 37% higher than the actual STATIC load. Is that getting your attention?
Plus, remember, this is a very low profile tire. The wheel is an 18 incher, and the total diametr of wheel and tire is only about 25.5 inches. Taking off the wheel diameter, and dividing the remainder of tire sidewall by 2, you see that I have only 3.8 inches of tire sidewall that can flex. If I hit a bad bump hard enough, it is conceivable that I could bend the wheel rim. Don't pooh-pooh that: My neighbour runs a Street Glide. He recently hit a freeway pothole SO bad that it DID bend the rim on his front aluminum wheel AND also took out the wheel bearings and the steering head bearings. No kidding. His bike was still rideable, but it acquired a severe vibration that required slow speed home, and then to a motorcycle shop where the crew diagnosed all the above listed damage. He's looking for a replacement wheel right now, and apparently a brand new one from HD is close to a $1000 here in Canada = $730 US at the current exchange rate.
In another thread, I recently mentioned that at least some tire experts believe that optimal tire traction and performance occur when the HOT tire pressure is about 10% higher than the cold tire pressure (This does NOT apply to dragracing!). Let's examine that a bit:
HD recommends 26 psi for my RG3. Applying that 10% psi increase theory, ideally my tires would go from 26 psi when cold to 28.6 psi when hot. I had success using this formula a couple of years ago on a Kawasaki 600 high performance sportbike (with an engine whoe rev limit was 16,500 rpm!).
Here in "metric" Canada, we use Kilopascals ("Kpa"s) instead of psi, and it takes 6.88 Kpa to amke 1 psi. So 26 psi = 179 Kpa. Per the onboard TPMS, my dealer set my right rear tire pressure at about 184 Kpa and my left rear tire pressure at about 180 Kpa.
Tomorrow, I am going to do a tire test where I will note the hot psi, and see exactly how high it gets. I'll let you all know what I discover.
Jim G
Sorry, my attention span does not allow me to read all of this.
08-22-2024, 06:56 PM
NOTE: Trike tire load ratings NOT the same for all models & all model years!
