More tire pressure stuff - a method for calculating tire pressure?!

[rjinaz86323]

Buttersmooth posted this in another thread. I wanted to bring this to the top to get some more opinions. I know this flies in the face of other suggestions so want to start a new thread to discuss.

Rear with a Yoko 92H (1400# rating @51psi) and 450# load (road scale weight for Spyder) calculates to ~16psi. 1400 / 51 = 27.45 #load per psi (per tire spec). Spyder 450# rear weight / 27.45 = 16.39psi.

Front Vredstein 980# rating @51# 980 / 51 = 19.21# (load per psi) 375# load (750# total on front) calculates to 19.5psi. 375# / 19.21 = 19.5psi.

[Little Blue]

....Not real sure about what you are talking about.
Peter Aawen is the go to guy for Tires and PSIs.

Maybe he will come on board and Post Up some things about your questions. I have been doing and following Peter's Tire Tips for a long time. It works for me.

Thank You and have a Blessed Day. .....

[FrogmanDave]

I'm not sure I see a question here.

[rjinaz86323]

Using the formula that Buttersmooth posted comes up with considerably different recommended PSI. Just wanting opinions either for or against this logic. I know all about Peter and Mikes recommendations, just looking for input on alternate viewpoints. Thx

[Fatcycledaddy]

I just got back from a 2 week trip from MI to CO and back towing my Aspen camper fully loaded and 2 up with bike fully loaded. We rode in rain 11 of the 14 days, not all day rain every day, but some rain, about 4 days were rain all day.
I have the factory tires on the front, and the Q5 on the rear. I am running 18 PSI in all tires and the wet traction of the Q5 was fantastic at that PSI. Front tires would go to 20 PSI and rear to 20.5 PSI when running down the dry road at 75MPH for hours at a time.
I pushed it a little in the rain with some hard braking and full throttle take offs up hill just to see what would happen, and the rear tire never broke lose in any way.

LOVE the Q5!!! Will be putting those on the front also for the next riding season I think.

Thanks Mike!!

[Woodaddict]

alot of figuring to come up with a certain pressure................one thing for sure and clear...............the Spyder weighs alot less that any 4 wheel vehicle that those tires would be on................so you can come up with deductions WHAT the pressure could / should be given weight factors. Whatever pressures feel best for your riding style. As well as reading what us owners do with car tire pressures

i run 20 in fronts and 18 in rear, car tires

[bigbadbrucie]

Buttersmooth posted this in another thread. I wanted to bring this to the top to get some more opinions. I know this flies in the face of other suggestions so want to start a new thread to discuss.

Rear with a Yoko 92H (1400# rating @51psi) and 450# load (road scale weight for Spyder) calculates to ~16psi. 1400 / 51 = 27.45 #load per psi (per tire spec). Spyder 450# rear weight / 27.45 = 16.39psi.

Front Vredstein 980# rating @51# 980 / 51 = 19.21# (load per psi) 375# load (750# total on front) calculates to 19.5psi. 375# / 19.21 = 19.5psi.

My opinion, for what it’s worth, is do what you want...you’ve already heard from the tire experts and are trying to second guess them so just don’t pay any attention and put whatever psi in and suffer the consequences. jmho

[rjinaz86323]

Sorry I brought this up. I am not second guessing anyone (I have mine set as Peter recommends), just trying to understand if Buttersmooths logic has any merit. I thought our sole purpose here was to educate. That is all I am trying to do, is learn.

[canamjhb]

I think I know what you're doing. You're reducing the PSI by the actual weight (percentage) of the Spyder based upon the tire mfg. maximums. You're coming up with 16.4 for the rear and 19.5 for the fronts. I don't think that is that far off from what Mike and Peter recommend. The one thing I think may affect the equation is that you are reducing both front tires equally on a straight-line formula. I'm not an expert but I believe that formula should be progressive. In other words, each tire is rated individually. If you reduce the pressure in 2 tires supporting a fixed load, I don't think that reduction would follow the same as it would if applying it to a single tire.....? Anyway, enough of my ranting. I followed the expert's advice with very good results. I modified slightly to accommodate my (much) heavier weight and simplified approach and ran 18 PSI in all three. And I "rode more and worried less"..... Jim

[rjinaz86323]

I am currently running 17 front and 18.5 rear as per Peter and Mike's recommendation. Just trying to broaden my knowledge.

[Navydad]

Sorry I brought this up. I am not second guessing anyone (I have mine set as Peter recommends), just trying to understand if Buttersmooths logic has any merit. I thought our sole purpose here was to educate. That is all I am trying to do, is learn.

I'm not sorry you brought it up. I find this sort of thinking interesting. We wouldn't have half of the stuff we have these days if someone hadn't had alternative viewpoints. Just because we have experts that guide us doesn't mean we have to fall in line with the rest of the sheep. I like to experiment and try different things and 90% of the time I end up back at what the experts suggest, but that other 10% where I found something better was worth it to me. I ride mostly two up and prefer twisty back roads. I run 19psi all the way around and that works for me. Maybe won't work for you, who knows unless you try.

[BLUEKNIGHT911]

I think I know what you're doing. You're reducing the PSI by the actual weight (percentage) of the Spyder based upon the tire mfg. maximums. You're coming up with 16.4 for the rear and 19.5 for the fronts. I don't think that is that far off from what Mike and Peter recommend. The one thing I think may affect the equation is that you are reducing both front tires equally on a straight-line formula. I'm not an expert but I believe that formula should be progressive. In other words, each tire is rated individually. If you reduce the pressure in 2 tires supporting a fixed load, I don't think that reduction would follow the same as it would if applying it to a single tire.....? Anyway, enough of my ranting. I followed the expert's advice with very good results. I modified slightly to accommodate my (much) heavier weight and simplified approach and ran 18 PSI in all three. And I "rode more and worried less"..... Jim

You are not ranting ...... I think you have a better understanding than most here on this Forum .... Peter and I have come up with similar PSI's .... however we took what you said into account and if ...... switched his psi's from rear to front & and the front to the rear we would be in total agreement. ...... JMHO .... Mike

[ButterSmooth]

I found (and subsequently lost) a very detailed webpage dedicated to setting initial tire pressures based on the manufacturer's rating and the actual load on the tire. It caught my attention because it confirmed and validated what Peter and Mike have been recommending for tire pressures. A second source confirmation of expert advise is a good thing.

The one interesting variance from Peter and Mike's recommendation is the higher pressures in the front that result from the front tires smaller cross section and lower load rating, while carrying a heavier load. Of course the 750# front weight is distributed on both tires, so each sees a 375# load.

This is a starting point for finding the 'right' pressure for you. I look for an increase of no more than 4# cold to hot on any tire. More increase than that and I increase the cold pressure. I won't go lower than the formula pressure, since that's what the manufactures says is the minimum for the given load.

I don't feel confident about the chalk method, since the tire has a different dynamic shape at ~800 rpm (60mph) than it does rolling in the driveway.

Anyway, I thought I posted a second source confirmation of the consensus pressures, Not a radically different proposal.

[Peter Aawen]

^^ Thanks ButterS.


And thanks to you too, rjinaz, . Altho I too am not sure I see a question, but the method outlined is basically the method I've posted a number of times here over the years as a fairly readily do-able method of working out the pressures you are likely to need to run in a given tire under a given vehicle/load; and like ButterS, I'll stress again, it's not 'mine' - it's just one tool that's been around for quite a while now that is supported by a whole lot of technical background bunf as being a handy method that most can manage to use if they wish! . I reckon it's somewhat better than the arbitrary choice of a blanket '18 psi all round'; it's waaaayyy better than simply following the tire placard on your Spyder if you are running a very differently constructed and more capable tires than the OE spec tire the placard's figures are aimed at; and it's definitely going to get you into the right ball park for your a/mkt tires/Spyder riding/load.[B][I]

That said, as I'm sure I've mentioned before when I've suggested using this method, it's best if you use it to derive a good 'cold start' pressure then move on to fine tuning your tire pressures to suit your actual specfic needs now by using another tool like the '4psi Rule' (which reacts to the riding that you actually just did & all the myriad of variables that produced any pressure changes! ) or you can use it to confirm the sort of pressures Mike & I have been suggesting for quite a while now! I believe that the results this particular 'rough guide' calculation will produce are a pretty good result for any given Spyder/load/tire combination to help you get better traction, ride, handling, suspension compliance, tire longevity, tread wear, et al from your tires! . Certainly it's better for all those things than simply following the 'one size meets most needs despite the vast range of variables' tire placard pressures, especially when you are running a/mkt tires. That's because it's a step further down the path of actually measuring at least some of the variables that apply (in this case, the various weights) & then calculating out the ideal pressure given any/all the measured inputs! And I believe that it does coincide pretty closely with the figures Mike & I have been suggesting for years.... maybe not exactly, but then again, how many of us are actually checking & adjusting our tire pressures in response to a change in any one of the major variables that can effect the 'ideal' tire pressure for your Spyder right now?? I do.... sometimes ..... well, occasionally anyway!

And if you are prepared to put in the effort to use this method to calculate your cold start pressures, so much the better, it's a good way to get a closer to the ideal cold start pressure for whatever particular tires you have fitted to your Spyder carrying the load that it generally carries! . And if you are so inclined & prepared to outlay juust a little more effort, you could even fine tune those cold start pressures in order to more specifically match your ACTUAL ryding by using the 4psi rule ButterS & I have mentioned above!

Over to you!