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new owner tire question
- Thread starter junior
- Start date
Hello Junior
I have an RT we run car tires because they are a better tire. Most run about 17 to 20 psi in all 3 tires.
I have an RT we run car tires because they are a better tire. Most run about 17 to 20 psi in all 3 tires.
BLUEKNIGHT911
Sadly Passed Oct 2024 - RIP
Hi junior, there are too many reasons to explain WHY you should run lower PSI's than normal .... However I have auto tires also and run 15 psi front 17 psi rear ..... I posted the WHY - Science, quite a few times ..... Mike 
hyea:
hyea:
It is true that the load the tire is carrying will make some difference, & the ST certainly is a touch lighter than an RT. Similarly, the 'brand' of tire will make some difference, but not so much as the load & speed rating (ie, the 'construction' of the tire) and even that would be nowhere near as much as the difference changes in load the tire is actually carrying will make; and at the load levels our various Spyders impose, any difference any &/or all of that will make is likely to be measured in fractions of just ONE psi anyway - and most readily available tire pressure gauges aren't anywhere near able to measure that small a difference really accurately, let alone display it; nor for that matter, would you be able to set your tire pressures that accurately without the appropriate gear!
So for all reasonable intents & purposes, the 'optimal pressure range' for most readily available car tires that will fit our various Spyders & the loads we can realistically impose upon them in the range of conditions that anyone is realistically likely to be riding in boils down to just a few psi either side of the oft suggested 14-18 or so up front & 14-20 or so for the rears! You might CHOOSE to vary from those guidelines for personal preference reasons, but if you do, just be aware that doing so will bring some compromise in the overall balance of ride, handling, traction, steering precision etc. as well as likely introducing some tire wear & longevity compromises - but doing that it is your choice after all! :thumbup:
BLUEKNIGHT911
Sadly Passed Oct 2024 - RIP
What Peter said is what I've said .... He types faster than I do:roflblack: .... Mike
hyea:
h0gr1der
New member
Peter Aawen and Bluenight911,
Kind of along the same line. I've installed the Vredestein 175/55R15's on the front, waiting on the rear. Trying to learn and implement the 4 PSI test. Then I stumbled across Finless Bob's video; https://youtu.be/rMO-ZNf05sk about the FOBO TPMS test. Interesting take on the rear. He's running a Yokohama S drive, says the rear gets hotter because it's a drive wheel. Pressure went from 28 PSI cold to 35 PSI hot in the video. From what I have read more than 4 PSI indicates under-pressure. At 28 PSI cold? Please help me understand this. Saw one article that used 10% front and 20% rear pressure increase as normal, but pertained to race bike I think. I'm confused.
Kind of along the same line. I've installed the Vredestein 175/55R15's on the front, waiting on the rear. Trying to learn and implement the 4 PSI test. Then I stumbled across Finless Bob's video; https://youtu.be/rMO-ZNf05sk about the FOBO TPMS test. Interesting take on the rear. He's running a Yokohama S drive, says the rear gets hotter because it's a drive wheel. Pressure went from 28 PSI cold to 35 PSI hot in the video. From what I have read more than 4 PSI indicates under-pressure. At 28 PSI cold? Please help me understand this. Saw one article that used 10% front and 20% rear pressure increase as normal, but pertained to race bike I think. I'm confused.
Those FOBO & other valve cap style TPMS sensors are fairly well known for returning odd pressures/temperatures at times - sometimes it's just due to the little 'o' ring inside jamming in the valve stem so they only report on the tiny volume of air trapped above the tire valve & actually in the sensor, other times it can be due to the sensor itself getting hot & reporting odd temps, maybe it can even be both.... don't laugh, it happens, I've personally experienced all of those scenarios & more!! :shocked: So, given the cold start pressures Bob mentioned he started out at, then unless his tire actually had a slow leak or an internal construction failure & was close to self immolation, then I suspect that the increase he reported had a whole lot more to do with the TPMS Sensor getting a spurious reading or otherwise getting hot than it did to the tire pressure increasing that much or the air inside the tire getting that hot, but I wasn't there so I really don't know that for sure! :dontknow:
Ideally, if you ever get that sort of 'suddenly markedly different from usual' report from your FOBO or any other TPMS, you should stop, get off, & check the tire pressure with a 'known to be recently reliable' tire pressure gauge just to check on the alarm & see if it really IS a spurious report. Still, I really can't see that Bob's rear tire just suddenly decided to defy the laws of physics & the vast amount of empirical evidence out there plus the millions of miles or more of repeated testing & checking to just suddenly decide that it'd increase its temp & pressure that much more than any other tire rolling under those sorts of loads & conditions has ever done before - UNLESS there was some other problem or the measuring device experienced a glitch! That said, if the tire WAS beginning to fail for whatever reason, OR if the pressure in the tire proper wasn't actually 28 psi but something considerably different & a heap lower, then maybe the 35psi alarm was valid?! The beginnings of de-lamination in a tire can show that sort of increase, but a healthy tire with the light load a Spyder imposes on it starting out at 28 psi cannot normally (or safely) show that much of an increase in pressure unless something else is happening!
Ideally, if you ever get that sort of 'suddenly markedly different from usual' report from your FOBO or any other TPMS, you should stop, get off, & check the tire pressure with a 'known to be recently reliable' tire pressure gauge just to check on the alarm & see if it really IS a spurious report. Still, I really can't see that Bob's rear tire just suddenly decided to defy the laws of physics & the vast amount of empirical evidence out there plus the millions of miles or more of repeated testing & checking to just suddenly decide that it'd increase its temp & pressure that much more than any other tire rolling under those sorts of loads & conditions has ever done before - UNLESS there was some other problem or the measuring device experienced a glitch! That said, if the tire WAS beginning to fail for whatever reason, OR if the pressure in the tire proper wasn't actually 28 psi but something considerably different & a heap lower, then maybe the 35psi alarm was valid?! The beginnings of de-lamination in a tire can show that sort of increase, but a healthy tire with the light load a Spyder imposes on it starting out at 28 psi cannot normally (or safely) show that much of an increase in pressure unless something else is happening!
h0gr1der
New member
That's why I'm confused. My truck has the internal TPMS things that actually display pressures. The truck's factory recommended pressures are obviously too high, because I never see more than 2 lbs increase. But I'm not going to change it, I know it's being recorded and if there's ever a warranty issue with the tires...
So the front Vredestein's are larger, but lighter by 2 lbs. 30 lb. max sidewall on the Kenda vs 51 lbs max sidewall on the Vredestein. I've corresponded with Vredestein to no avail for the load/pressure chart they used in the manufacture of this tire. No luck. So in an overabundance of caution I started out at the OEM pressure of 20 Lbs on the front. I'm down to 18 lbs, but it sure looks like the tire is low. Pressure increase and handling doesn't support this, so I've ordered one of those fancy high dollar tire gauges. I'll do the same for the rear, working my way down.
So the front Vredestein's are larger, but lighter by 2 lbs. 30 lb. max sidewall on the Kenda vs 51 lbs max sidewall on the Vredestein. I've corresponded with Vredestein to no avail for the load/pressure chart they used in the manufacture of this tire. No luck. So in an overabundance of caution I started out at the OEM pressure of 20 Lbs on the front. I'm down to 18 lbs, but it sure looks like the tire is low. Pressure increase and handling doesn't support this, so I've ordered one of those fancy high dollar tire gauges. I'll do the same for the rear, working my way down.
Can you take a pic of the info printed on the sidewall of those Vredstein tires that tells everyone all about the Max load is whatever lbs or kgs at whichever Max pressure in psi or kPa & then post it up, or at least print it out here for us all to see? That Max Load @ Max Pressure info can be very handy in working out what's a good cold start pressure if you have some idea of how much load each of your tires is carrying!? :thumbup:
Given that variance you get from the 'ideal' increase of 4psi with your truck tires, don't worry too much if it's only a little out - it's still within a couple of psi up or down, and now that you only know it's not quite the ideal starting pressure for you (because you've learnt a bit about how to fine tune your 'ideal cold start pressure') you can work out the sort of compromises that running pressures just a little too high to start with like that 2psi pressure increase indicates might bring. You can choose to live with it as is & comply strictly with the manufacturers recommendation, or you can make your own judgement call & adjust your starting pressures accordingly - but at least now you have SOME idea of the why's & wherefore's between what's good & what's not! And the truck or tire manufacturer isn't going looking for one or two pound variances, they are going to be looking for relatively quick changes in pressures & temps, especially leading to either in the extremities! There are measuable & once you've been trained properly, fairly readily identifiable differences between tires that have been looked after & tires that haven't, even (or maybe especially) if they have been running at noticeably different pressures to those on the tire placard! And sometimes those on the placard can be very wrong for what they are doing! Like any 'real' car tire under a Spyder.... :dontknow:
Another thing to remember about the tire placard info & its recommended pressure is that it is either the tire or the vehicle manufacturers 'educated best guess' at what will be a 'good for most' pressure given the OE Spec tire & the expected 'average users loading' for the vehicle.... Weasel wording a bit, isn't it? But it can only be an 'educated best guess' because it must be based upon a collection of assumptions about the variations in the range of different load & road surfaces & ambient temps & speeds & of a bucket load more variables besides that about what different owners might use/apply & how & why they drive etc - there's no way it can be anything much more! It might even be supported by a heap of actual testing in a wide range of those conditions encompassing many miles driven on tracks & skid pans & even actually on roads & tracks around the world (& I'm very thankful for all that testing on a number of levels, including financial!
) to provide the data sets that leads to all those assumptions becoming a 'best guess' & eventually an 'educated best guess' about loads & conditions etc, but there are still going to be a heap of assumptions made, generally those about you & your particular driving & your driving style on specific (or particular) roads with your own chosen loads aboard etc, so for that "recommended pressure" to be as close as it is means that everyone involved in arriving at that 'educated best guess' has done their job pretty well! (You can thank me later, they've already paid me the money! ) But because it's an 'educated best guess' that 'recommended pressure' is still very likely going to involve the final end user (or in other words, you!) having to accept that you might be working well out towards one end or extreme in a given range of variables or two so you may well end up having to make some compromises in achieving the best balance of all the wear & ride & handling & traction & noise & all those other things that might vary a little or a lot because YOUR particular set of loadings & speeds & driving style etc and the variances in the roads you drive on, the different ambient temps etc are all going to be just a little different to anyone else's - but the vehicle & tire manufacturers have looked at everything they can & given you that recomendation as being a reasonable 'educated best guess' given the range & variety of all those variables...... only now you know a way of checking to see how close their 'educated best guess' actually was to the driving you just did given all those different variables as covered in the last hour or so of your driving!! Amazing stuff, isn't it?! :shocked:
So don't sweat the small stuff too much! It's actually a pretty good thing that the manufacturer's recommendation got as close as just 2psi off your ideal!! Sure, you can fine tune things a little if you feel that way inclined, doing so might even mean you'll get better milage from that brand/make of tire than some, or better grip in the wet than the tire manufacturer expected, or maybe you really liked the ride & handling from your last set of tires better - but now you have some tools & maybe even the interest to take a little time & effort to actually try to get the best FOR YOU from those tires instead of just accepting whatever the 'educated best guess' of a manufacturers 'one size fits all' recommendation about the OE Spec tire might get you. And if you don't want to do that, then fine, just don't get upset if your tires don't perform exactly how you'd been led to expect them to - the manufacturers best guess was off a tad, or an assumption they made about any one of that fairly massive range of variables might have been wrong FOR YOU, or you may just be running a significantly different tire, but if you've made no effort to remedy that difference or the indicated departure from ideal pressure change &/or adjust your starting pressures accordingly, then what can you really expect! Over to you!:thumbup:
Sorry about this being yet another epic saga, but tires & pressures are not a simple & straight forward thing - there are lots of potential variables that apply to tires & their 'right pressure'...... and what's right for YOU might not be exactly right for ME, just like you might expect different things from your tires! But hopefully this saga has helped a little in raising the level of some readers understanding about what is really a fairly complex thing that does impact upon all of us who own &/or ride/drive vehicles! :2thumbs:
Given that variance you get from the 'ideal' increase of 4psi with your truck tires, don't worry too much if it's only a little out - it's still within a couple of psi up or down, and now that you only know it's not quite the ideal starting pressure for you (because you've learnt a bit about how to fine tune your 'ideal cold start pressure') you can work out the sort of compromises that running pressures just a little too high to start with like that 2psi pressure increase indicates might bring. You can choose to live with it as is & comply strictly with the manufacturers recommendation, or you can make your own judgement call & adjust your starting pressures accordingly - but at least now you have SOME idea of the why's & wherefore's between what's good & what's not! And the truck or tire manufacturer isn't going looking for one or two pound variances, they are going to be looking for relatively quick changes in pressures & temps, especially leading to either in the extremities! There are measuable & once you've been trained properly, fairly readily identifiable differences between tires that have been looked after & tires that haven't, even (or maybe especially) if they have been running at noticeably different pressures to those on the tire placard! And sometimes those on the placard can be very wrong for what they are doing! Like any 'real' car tire under a Spyder.... :dontknow:
Another thing to remember about the tire placard info & its recommended pressure is that it is either the tire or the vehicle manufacturers 'educated best guess' at what will be a 'good for most' pressure given the OE Spec tire & the expected 'average users loading' for the vehicle.... Weasel wording a bit, isn't it? But it can only be an 'educated best guess' because it must be based upon a collection of assumptions about the variations in the range of different load & road surfaces & ambient temps & speeds & of a bucket load more variables besides that about what different owners might use/apply & how & why they drive etc - there's no way it can be anything much more! It might even be supported by a heap of actual testing in a wide range of those conditions encompassing many miles driven on tracks & skid pans & even actually on roads & tracks around the world (& I'm very thankful for all that testing on a number of levels, including financial!
) to provide the data sets that leads to all those assumptions becoming a 'best guess' & eventually an 'educated best guess' about loads & conditions etc, but there are still going to be a heap of assumptions made, generally those about you & your particular driving & your driving style on specific (or particular) roads with your own chosen loads aboard etc, so for that "recommended pressure" to be as close as it is means that everyone involved in arriving at that 'educated best guess' has done their job pretty well! (You can thank me later, they've already paid me the money! ) But because it's an 'educated best guess' that 'recommended pressure' is still very likely going to involve the final end user (or in other words, you!) having to accept that you might be working well out towards one end or extreme in a given range of variables or two so you may well end up having to make some compromises in achieving the best balance of all the wear & ride & handling & traction & noise & all those other things that might vary a little or a lot because YOUR particular set of loadings & speeds & driving style etc and the variances in the roads you drive on, the different ambient temps etc are all going to be just a little different to anyone else's - but the vehicle & tire manufacturers have looked at everything they can & given you that recomendation as being a reasonable 'educated best guess' given the range & variety of all those variables...... only now you know a way of checking to see how close their 'educated best guess' actually was to the driving you just did given all those different variables as covered in the last hour or so of your driving!! Amazing stuff, isn't it?! :shocked: So don't sweat the small stuff too much! It's actually a pretty good thing that the manufacturer's recommendation got as close as just 2psi off your ideal!! Sure, you can fine tune things a little if you feel that way inclined, doing so might even mean you'll get better milage from that brand/make of tire than some, or better grip in the wet than the tire manufacturer expected, or maybe you really liked the ride & handling from your last set of tires better - but now you have some tools & maybe even the interest to take a little time & effort to actually try to get the best FOR YOU from those tires instead of just accepting whatever the 'educated best guess' of a manufacturers 'one size fits all' recommendation about the OE Spec tire might get you. And if you don't want to do that, then fine, just don't get upset if your tires don't perform exactly how you'd been led to expect them to - the manufacturers best guess was off a tad, or an assumption they made about any one of that fairly massive range of variables might have been wrong FOR YOU, or you may just be running a significantly different tire, but if you've made no effort to remedy that difference or the indicated departure from ideal pressure change &/or adjust your starting pressures accordingly, then what can you really expect! Over to you!:thumbup:
Sorry about this being yet another epic saga, but tires & pressures are not a simple & straight forward thing - there are lots of potential variables that apply to tires & their 'right pressure'...... and what's right for YOU might not be exactly right for ME, just like you might expect different things from your tires! But hopefully this saga has helped a little in raising the level of some readers understanding about what is really a fairly complex thing that does impact upon all of us who own &/or ride/drive vehicles! :2thumbs:
Last edited:
h0gr1der
New member
Vredestein, specs as requested
Mr. Aawen,
As requested. There's a lot of talk about pressures, but very little of load ratings. I learned of load ratings with my 3/4 ton Dodge truck tires. The tires are BFG Commercial Tractions with a load range of D, and a service description of 110/107Q @ 65 PSI. Long story short, the unladen rear axle pressure (I did get a load/pressure chart from them) was closer to 30 PSI. Unladen the rear axle weighs about 2400 Lbs, but the load range and service description say that the tire will support around 2300 Lbs each at 65 Lbs. If you don't use the correct pressure for load it will wipe out the center treads in pretty sporty fashion.
With all that blather, nonetheless, comparing the OEM pressure to the much recommended 16-18 PSI front, I have to wonder about each tires pressure ratings. Here's some very rough and unsubstantiated numbers to think about.
Spyder center of balance split on the tires. I've heard 60/40, but also 55/45. Some folks have actually weighed this.
Spyder maximum weight laden (GVWR) ; 1653 U.S. Lbs
Spyder front weight; 991.8 lbs @ 60%, 909.15 lbs @ 55%
Spyder tire individual load; 495.5 lbs @ 60%, 454.58 lbs @ 55%
So, with the Kenda running at roughly 2/3 of maximum sidewall rating, and only achieving it's full load rating of 55H (481 lbs) at max sidewall of 30 lbs, and the Vredestein acheiving it's load rating of 72T (908 Lbs) at 51 PSi max sidewall, running at roughly 39% of it's max sidewall, I wonder which one is actually closer to being out of it's official load/pressure ratings. I've read and tried to understand all the engineering terms associated with tire load, but my old gourd isn't smart enough to cipher some of it. I never did get Vredestein to answer me on the load/pressure charts.
Mr. Aawen,
As requested. There's a lot of talk about pressures, but very little of load ratings. I learned of load ratings with my 3/4 ton Dodge truck tires. The tires are BFG Commercial Tractions with a load range of D, and a service description of 110/107Q @ 65 PSI. Long story short, the unladen rear axle pressure (I did get a load/pressure chart from them) was closer to 30 PSI. Unladen the rear axle weighs about 2400 Lbs, but the load range and service description say that the tire will support around 2300 Lbs each at 65 Lbs. If you don't use the correct pressure for load it will wipe out the center treads in pretty sporty fashion.
With all that blather, nonetheless, comparing the OEM pressure to the much recommended 16-18 PSI front, I have to wonder about each tires pressure ratings. Here's some very rough and unsubstantiated numbers to think about.
Spyder center of balance split on the tires. I've heard 60/40, but also 55/45. Some folks have actually weighed this.
Spyder maximum weight laden (GVWR) ; 1653 U.S. Lbs
Spyder front weight; 991.8 lbs @ 60%, 909.15 lbs @ 55%
Spyder tire individual load; 495.5 lbs @ 60%, 454.58 lbs @ 55%
So, with the Kenda running at roughly 2/3 of maximum sidewall rating, and only achieving it's full load rating of 55H (481 lbs) at max sidewall of 30 lbs, and the Vredestein acheiving it's load rating of 72T (908 Lbs) at 51 PSi max sidewall, running at roughly 39% of it's max sidewall, I wonder which one is actually closer to being out of it's official load/pressure ratings. I've read and tried to understand all the engineering terms associated with tire load, but my old gourd isn't smart enough to cipher some of it. I never did get Vredestein to answer me on the load/pressure charts.
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