.... A car tire on a Spyder isn't even breaking a sweat...
You can check this for yourself - just take your (fully loaded) Spyder in to your nearest Garden Center or Weigh Station, anywhere with a Weigh bridge, & ask if you can weigh each end of your Spyder!! It might cost you a couple of bucks, but generally the operator will be laughing too hard to charge you anything! :dontknow: Find out what the front weighs, then divide that by 2 (cos the load is shared by 2 tires up front) & then what the rear weighs (only one tire there!) - then you'll know pretty closely what weight each of your tires is REALLY carrying....
Then look at the sidewall on your tires, somewhere on there will be printed the Maximum load @ Maximum pressure info for that specific brand/type/size of tire (nb, the 'Maximum' bit means the '
Never to be Exceeded in operation' Load &/or Pressure) & compare that to the actual load you now know that you are placing on them!! It's gonna be somewhat different to the Max Load, particularly since most car tires are somewhat over-engineered for the average CAR they expect to carry, let alone something like our Spyders that might be lucky to weigh 1/3rd as much as the average car running that size tire!! But luckily, as Mike has mentioned, there is a fairly simple formula (altho it's definitely not mine, it comes from the tire manufacturers; I've just learnt that it's smart to use it!) which you can use to work out what pressures to run in your (capable of carrying much heavier loads) car tires when they are only carrying your (relatively lightweight) Spyder!!
Just divide the weight your Spyder actually puts on each tire by the Max Load that tire can carry (taken off the printed info) - that will (almost certainly) give you a fraction, ie 0.294 or something similar, reflecting what percentage or fraction your Spyder's actual load is of the Max Load the tire is capable of carrying; so you can then multiply the Max Pressure by the same decimal/fraction to get the
Static Load Pressure necessary for your tire to carry the load the Spyder imposes on it while it's standing still; then just add (up to) 4psi to cater for the added loads that driving, cornering, moving, & speed, etc will impose on the tire during use. Written out 'properly':
(Max stated Pressure x (Actual Spyder Tire load/Max stated Tire Load)) + <4psi = the Pressure needed in that tire to carry the actual load your Spyder puts on it while you are riding...
There are 'fine tuning' methods available to check & adjust or confirm how correct/close to the optimal for that tire under your Spyder with your loads etc you've got, but I'm not going to go into that here/now (look up 'The 4psi Rule' if you wish - Cooper tires, Michelin, Goodyear, & others publish it every now & then) Besides, you are going to be a lot closer to the correct pressure for THAT tire under YOUR Spyder loaded the way YOU load it & how YOU ride it than you will by choosing pressures by almost any other means short of getting the tire manufacturer to do the calcs for you - especially if the only alternative is for you to go by the 'compromise' one-size-fits-all-potential-users pressure that's stated on the tire placard - a pressure which in the case of our Spyders is meant to enable a poor quality lightly constructed rubbish tire to work somewhere near marginally well anyway! :shocked:
Sorry for the epic post (again
) but some people did specifically ask! Enjoy! :thumbup:
