:agree: with Blueknight911 on this! The
other thing to bear in mind is that most cars are a lot heavier than Spyders, and their tires generally have a Maximum Load @ Maximum pressure placard stamped on the side. This means that if your local tire supplier can't get the Load/Pressure table for that particular tire from the manufacturer &
show you on that table what pressure you need to run in the tire to carry the load your Spyder imposes on it, you can fairly easily weigh each end of your Spyder (any weigh-bridge or garden mulch centre etc will have a weigh-bridge) and do the math yourself!! :thumbup:
Quickly looking at the OE Spec Kendas first, I have a recently failed front Kenda in the workshop that's a few years old now, and it's marked Maximum Load 175 kgs @ Maximum Pressure 30 psi. The front end of my 2013 Spyder RT Ltd at its 'Rider & Pillion plus all our travelling gear' heaviest weighs in at 230kgs, so each front tire carries a static load of about 115kgs (and I believe that's pretty damn heavy for a 2013 Spyder :shocked: ) which (if I do the math) means that my Spyder imposed load is just 0.66 of the tires Max load so it only
NEEDS 0.66 of the Max pressure or about 19-20 psi to carry the load I place upon it, and that's pretty close to what the BRP Recommended Tire Pressure is for those OE Spec lightly constructed tires (btw, this particular Kenda, which admittedly is
not one of the latest versions from the factory, shows that it has 3 polyester tread plies and only 1 (yep, just
ONE!) Sidewall ply... and
all those plies are made up of 'thread' which is only 66% as thick or if you like, approx 1/3 thinner/weaker than the 'threads' used by most Automotive tire manufacturers as plies in their tires - some go even heavier again!! So the Kendas are clearly quite lightly constructed, even before you add in the poor quality control & lack of consistency in their construction! :shocked
Moving on to the tires that I actually run and explaining the calculation needed in more detail, the sidewall Max Load/Max Pressure placard on my 175/60R15 Kumhos state Max Load = 495kgs @ 50psi... So my front tires would require 50 psi in them to carry 495 kgs, but they only need to carry 115 kgs when fitted to my Spyder and I want to know what pressure I should run in them?! What follows is admittedly a little bit of a 'ready reckoner', but it's pretty close and far better than just whacking whatever pressure your bum tells you feels good in there!!
Here's the calc - the tires Max Load is 495 kgs but it only needs to carry 115 kgs, so 115 ÷ 495 = 0.2323 repeating, but anything beyond 2 decimal points really isn't important, so I'll round that off at 0.23... The tires Max Pressure is 50psi & that's only required to carry 495 kgs, and we now know that the Spyder load is only 0.23 of the Tire's Max, so applying that to the Max pressure 50 × 0.23 = 11.5...... which means that my front tires will be quite safe carrying my loaded Spyder if I run them at 11.5 psi.... Now be aware that presuure is, strictly speaking, just that required for a static load. For ease of explanation & minimal additional confusing calculations, there is a way to work out how much more pressure you need to add to cater for dynamic loads, altho I usually just round it all out and simply add 4psi to that static load value, to cater for how hard I ryde my Spyder (largely because 4psi is the same value used by the '4psi Rule' to confirm that the tire is at it's optimum traction pressure and not over heating thru use & it's handy to remember just the one number - 4psi!) so even tho I now
KNOW the tire will likely be safe at 11.5 psi because I've done the calcs to show me the pressure the tire needs for the less than Max load, adding the extra 4psi to cater for dynamic loading increases gives me a working pressure of 15.5 psi up front.... and I usually run between 14 & 16 psi. :clap: The same sort of calc will work for your rear tire, and it'll give you a 'very close to ideal' pressure to run in your Auto tires when they are only carrying a light load instead of something more than 3 times as heavy!
hyea:
It's fine by me if you knowingly choose to run higher pressures than what ^^ that type of calc indicates should be necessary in your 'normal' Auto tire, but please, know that when/if you do run higher pressures, you
ARE compromising the ride, handling, traction, and the potential longevity of your tires, and don't complain if you hydroplane at the first sign of water on the road, or can't avoid some obstacle because your dry &/or wet braking distance has been extended significantly due to the lack of grip your tires have on the road! Get your Auto tire pressures
right and they can work with your suspension to give you a safe & comfortable ride with far better traction, handling, cornering, and braking than whatever you got from the OE spec Kendas.... fail to set them right &/or run them too high for the lighter than expected load your Spyder imposes on them, and your steering might
feel direct &/or crisp to the `less aware`, but you`ll actually be scrubbing tires thru corners, riding harshly & bouncing the tire off of the road surface, risking punctures, and you
will be getting less than ideal traction, ride, & handling, with compromised wet & dry braking too.... it's your choice tho!
![IMG_0616[1].jpg](https://www.spyderlovers.com/data/attachments/93/93561-97d50462e268eb143526704f194b6ef7.jpg?hash=0xF3RD8vd5 "IMG_0616[1].jpg")
![IMG_0617[1].jpg](https://www.spyderlovers.com/data/attachments/93/93562-69ee398329344e74d9fa93b71f06e341.jpg?hash=lFLS2_KeM0 "IMG_0617[1].jpg")
