When tuning oversteer/understeer, tyre pressure is one aspect that can be used.
Traditionally the wisdom is that reducing understeer can be achieved by increasing front pressure a bit and vv. Same thing at the back.
However!
Read the info on the Nankang site for their track rubber:
If you are having handling issues, please see the table below which may resolve your issue, remember to do this in small increments at a time
To reduce Over steer
Reduce rear pressures or increase front pressures
To increase Over steer
Increase rear pressures or reduce front pressures
To reduce Under steer
Reduce front pressures or increase rear pressures
To increase Under steer
Increase front pressures or reduce rear pressures
Wow! :o
The thing is that there are two different drift angles aspects adressed here:
- On road tyres the drift angle is caused by creep due to deformation. Add air and you get less.
- Track tyres have stiff enough sidewalls so a bit less pressure hardly increases creep but it does raise the rubber temp, adding stickynes, reducing drift angle. Will, till you overdo it and cook the rubber.
With the AD08R I am in the doldrums. It bóth applies depending on use/condions so I have gone back to OEM values compensated for weight and size *.
I have gone from 185 SL82 to 195 SL85 meaning going from 26 to 24 psi to maintain status quo.
Here is a handy on-line calculator: https://tiresize.com/pressure-calculator/
To compensate for the about 15% lower weight thus less load I have dropped the pressure 2 psi front and 3 rear so to 22 and 29. Also the AD08R has a bit stiffer wall than the OEM fitted ones so though the pressures séém lowish, they are not.
All very interesting
Tyre pressures are a bit like tyre choice imo, you get such a variation of comments regarding them, coming from a Motorcycle background I can ASSURE you that the pressures the manufacturers give for "road tyres" are generally way off the mark for any kind of spirited riding, I always drop the pressures to suit the bike set up and tyre wear pattern
I am no expert on car tyre pressures but one ting I have found on the MR2 is a little similar, lots of posts on run 32 rear 26 front, its what the MR2 likes, must admit, I dropped my rear to 28 and the front to 24 and imo the car feels much more planted and thats with TR1 which are seam quite soft walled to me
Rob
I use tyre pressures to fine tune tyre temps. The aim being to have consistent temps across the whole tyre.
Quote from: JB21 on September 9, 2020, 11:00I use tyre pressures to fine tune tyre temps. The aim being to have consistent temps across the whole tyre.
I know you do track days so are pushing the boundaries far more than most who are probably just using their car for the odd spirited blast, there is a massive difference however and as you say, you will tune your tyres to the days and the conditions, I use tyre warmers on track, (bike) this helps gives you that
People should not be afraid to experiment with tyre pressures
Rob
Surprised you've lowered them.
I've found my various 2s to be very dicey with low pressures.
Obviously plenty of people up the pressure although I've not felt the need on anything other than T1Rs.
The newer TR1s do seem better from what people say.
Although I'm very much into AD08Rs.
Quote from: 1979scotte on September 9, 2020, 11:34Surprised you've lowered them.
I've found my various 2s to be very dicey with low pressures.
Can you expand on ´dicey´?
I have btw basically maintaíned the OEM spec pressure; compensated for size and weight.
Yes, AD08R it is. Shame they messed with it for eco sake. Fingers crossed they sort it with an AD08RS2 by the time I need a new set.
Not really just felt very unsafe.
Dont think i was referring to you anyway mate it was whoever was running toyos
The ´issue´ I have is that I lóath understeer. Not any slight wandering but the front starting to slide before than the rear. There is nothing that undermines my confidence as a front end sliding first.
The AD08Rs are as good as it gets on the road, so all that is left is negative camber and the tyre pressure.
Quote from: Petrus on September 11, 2020, 09:20all that is left is negative camber and the tyre pressure.
You can also increase roll stiffness or spring rate at the rear, or decrease it at the front. Toe adjustments also make a huge difference to the attitude of a car. Consider changing from toe out to toe in at the front end, for example, what effect that has at initial turn in, and through the middle of the corner.
Tyre pressure changes are a 'crutch' for other handling problems. The increase or decrease in pressure mainly changes how quickly the slip angle builds, so you only get a change in handling tendency in transitions. It is a valid tool, but generally better used as a tuning tweak when 'in the field'.
It's also worth considering the tyre is basically a spring - an air spring. More pressure makes the tyre stiffer. For tyres with soft sidewalls, more pressure can be beneficial to support them, especially if you are adding more load to the car (track use, 'spirited' driving). More pressure can be very useful here too.
When racing in the 24hr at Spa last year, we used 55 front and 70 rear in our C1. I've run race-winning MX-5s starting at 45psi cold.
Personally I don't enjoy a 'sloppy' feeling car, so always go up from recommended pressures in a 'performance' car.
Manufacturer stated pressures are a guideline and not a one size fits all, as
@Zxrob says we should not be scared of experimenting with this stuff, it is absolutely safe to do so.
Quote from: AdamR28 on September 11, 2020, 10:46You can also increase roll stiffness or spring rate at the rear, or decrease it at the front. Toe adjustments also make a huge difference to the attitude of a car. Consider changing from toe out to toe in at the front end, for example, what effect that has at initial turn in, and through the middle of the corner.
Spring rate is something which will affect the comfort (and ride hight) too. Also would need matching damping. Not going there yet.
Yes, increase toe in a mite is one I have on the list. At OEM now.
The tyre being air suspension I am véry conscious about. It also affects tyre conformation = traction. Not, or not much of, an issue on a smooth racing track but on real world roads it makes a massive difference.
Thank you for sharing btw!!
No problem, always good to discuss this sort of thing!
Technically yes you would need to change the damping - however only a small (say, 5%) change in wheel rate (through either ARB or spring) will make a noticeable effect on under / oversteer balance. The damper will be absolutely capable of dealing with this - and there is no reason that you 'have' to increase spring rate, it can always go down... And ride height doesn't need to be changed - one of the benefits of swapping the ARB, it's a much easier job and doesn't affect ride height or two wheel rolling bumps at all.
Try some front toe out, around 15 minutes / 2mm. It will make a huge difference from the stock setting of zero toe.
Regarding tyre conformation and traction... I do agree that a large increase in tyre pressure will have an adverse effect on a bumpy road all other aspects being equal, especially with the basic standard dampers. But 5 or 10 psi isn't all that much, and worth a try.
The spring rate of a tyre (approx 20kg/mm) is a LOT higher than that of the suspension components (approx 2kg/mm OE spring rate at the rear on an MR2) given the sort of tyres and pressures we use. My point here is that adding 5psi to the tyre will increase its spring rate a little, perhaps another 5kg/mm, but the overall effect on the car isn't that much when the tyre is already so much 'harder' than the suspension.
In terms of traction, if you reduce the surface area (footprint) of the tyre by increasing tyre pressure, you are then increasing the pressure upon said area (the weight of the car hasn't changed!), and the overall friction amount remains almost unaffected.
Quote from: AdamR28 on September 11, 2020, 12:25No problem, always good to discuss this sort of thing!
Technically yes you would need to change the damping - however only a small (say, 5%) change in wheel rate (through either ARB or spring) will make a noticeable effect on under / oversteer balance. The damper will be absolutely capable of dealing with this - and there is no reason that you 'have' to increase spring rate, it can always go down... And ride height doesn't need to be changed - one of the benefits of swapping the ARB, it's a much easier job and doesn't affect ride height or two wheel rolling bumps at all.
Try some front toe out, around 15 minutes / 2mm. It will make a huge difference from the stock setting of zero toe.
Regarding tyre conformation and traction... I do agree that a large increase in tyre pressure will have an adverse effect on a bumpy road all other aspects being equal, especially with the basic standard dampers. But 5 or 10 psi isn't all that much, and worth a try.
The spring rate of a tyre (approx 20kg/mm) is a LOT higher than that of the suspension components (approx 2kg/mm OE spring rate at the rear on an MR2) given the sort of tyres and pressures we use. My point here is that adding 5psi to the tyre will increase its spring rate a little, perhaps another 5kg/mm, but the overall effect on the car isn't that much when the tyre is already so much 'harder' than the suspension.
In terms of traction, if you reduce the surface area (footprint) of the tyre by increasing tyre pressure, you are then increasing the pressure upon said area (the weight of the car hasn't changed!), and the overall friction amount remains almost unaffected.
Toe out at the front helps massively with turn in and understeer, toe in on the rear helps oversteer. I currently run (total) 4mm out on the front and 4mm in on the rear. Front ARB full stiff (3 settings) rear ARB medium setting (4 settings). Not a hint of understeer, even in the wet but with just enough oversteer to rotate into corners, but does get a bit hairy in the wet at the rear.
Also running -3 camber front with -3.5 rear. Nice even temps across all 4 tyres.
Only thing I really need to adjust on a track days is damping and tyre pressures.
Quote from: AdamR28 on September 11, 2020, 12:25In terms of traction, if you reduce the surface area (footprint) of the tyre by increasing tyre pressure, you are then increasing the pressure upon said area (the weight of the car hasn't changed!), and the overall friction amount remains almost unaffected.
Well, yes and no.
Mathematically yes but this steps over the difference in conformation; a softer tyre will adjust better to unevenness.
That observed, the footprint will hárdly change as we are dealing with relatively stiff (radial) tread surface.
Thanks for the toe suggetstion. Will have a go next time I have it in the garage.
I have refrained from it because of the slight tendency to occasionally ´tram rail´. A bit more for less understeer would be worthwhile trade off though.
I already have just under -2 camber front and over - 2.5 rear.
Quote from: AdamR28 on September 11, 2020, 10:46Quote from: Petrus on September 11, 2020, 09:20all that is left is negative camber and the tyre pressure.
Tyre pressure changes are a 'crutch' for other handling problems. The increase or decrease in pressure mainly changes how quickly the slip angle builds, so you only get a change in handling tendency in transitions. It is a valid tool, but generally better used as a tuning tweak when 'in the field'.
I couldn't agree more and as I had this discussion multiple times in the past. If you have to tune by air pressures it shows the weakness of your set up. Air pressure tuning is for coarse correction of a bad handling car in the moment and usually a last resort not meant for a street driven car.
Factory tire pressures are mainly for the OEM tires based on the weight of the vehicle and the tire load rating. When you change the tires you need to take note of the load rating differences written on the sidewall and compare them to the OEM tires and make the adjustment based off a chart. If you plus size your tires and have to use reinforced tires you might have to run more tire pressure otherwise you will damage them. It is the air that holds most of the weight not the tires construction.
If you have to tune by tire pressure it is better to instead figure out what needs to be changed with the suspension and alignment first. The tire should be optimized for its contact patch not weakened.
Often times people chose the wrong components and then have to resort to extreme measures of changing tire pressures which is counterintuitive making the car handle well in one situation and worse in another.
Interesting how one ´faction´ sticks to OEM pressure whereas another sees it as a good point of departure.
I think OEM is in this case too the by far best researched compromise for the OEM car and intended use.
As are the suspension compenent and suspension set up spec.
The aforementioned toe in/out is a perfect example. The 0 degrees is a compromise to get a car with initially slight understeer and minimal tram-lining. With the FL Toyota went wider rubber at the rear to get more bland, oops predictable, oversteer, a bit more understeer. Tuning by tyre width illustrated ;-)
Imo the tyre pressure is just as ´unholy´ as any of the mentioned components and to some extend under investigation when the suspension or it´s set up are changed.
Indeed Dev, compensating the tyre pressure for tyre/load changes is still OEM yet álso tuning for the changed conditions, just back to OEM ;-)
It applies to a héavier load too. On the MR2 Spyder not an issue but a fully loaded SUV with a high max. load it probably is. Our previous family 4x4 had a max payload of 1 tonne with a curb weight of 1600. The instruction manual had simple table for matching tyre pressures.
By and large a forgotten adjustment to circumstances as who reads the effing manual??!!
Im not saying to run OEM tire pressure. OEM tire pressure is for OEM tires. As a guide you should base your tires pressures first on the load rating of the tires and the weight of the car. After that you should tune your tires by pyrometry if you want to get it to be optimum to have the right contact patch or you can use the chalk method.
Once that is done then you can make adjustments to the suspension and alignment. Many of these issues unfortunately are based on poor tire size choices and alignment.
Usually if you have a problem with oversteer or understeer the best course correction is to adjust the sway bar in the rear and that is why a four position adjustable is a good way but its still not ideal as addressing the foundation of the suspension system particularly the damping, springs and alignment.
This is why if you throw aftermarket suspension on the car you have now introduced a situation where the car is more likely to be unbalanced, unpredictable and most of all no longer confidence inspiring. Good suspension starts with good planing and researched components having adjustability to align the car for great handling as a complete system. This is not to say adjusting tire pressures doesn't have its place but it should be the last refuge of adjusting for handling behavior.
Quote from: Dev on September 11, 2020, 17:37Good suspension starts with good planing and researched components having adjustability to align the car for great handling as a complete system.
Quite.
QuoteThis is not to say adjusting tire pressures doesn't have its place but it should be the last refuge of adjusting for handling behavior.
Hence I have basically stuck to OEM, compensating for pr and load.
Next a whiff toe out.
Quote from: Petrus on September 12, 2020, 19:07Quote from: Dev on September 11, 2020, 17:37Good suspension starts with good planing and researched components having adjustability to align the car for great handling as a complete system.
Quite.
QuoteThis is not to say adjusting tire pressures doesn't have its place but it should be the last refuge of adjusting for handling behavior.
Hence I have basically stuck to OEM, compensating for pr and load.
Next a whiff toe out.
I do not run OEM air pressures for my tires. I have instead calculated what tires pressures I need.
The link you posted is what I have used along with a chart after I bought new tires in April and they work perfectly.
https://tiresize.com/pressure-calculator/
Simply adjusting alignment to tune the behavior of the car by introducing toe is not a one size fits all. It is a compromise between high speed stability vs low speed cornering. If you get it wrong you can compromise stability and easily lose control at higher speeds especially in the rain. Radical alignment is best for the track and not for the street. Just changing one variable will mess up another and that is why the entire system has to be tuned together conservatively if you go outside the scope of factory suspension. When we modify our suspensions there is a lot less forgiveness even though most feel like they can drive at higher speeds but for the demands of the road it's much easier to lose control.
@Petrus @Dev Just re-visiting this thread.
In particular the tire pressure calculator.
Having failed miserably to find an alternative, are you aware of any.
Only reason I ask, the load rating I want to enter is not provided.
Quote from: Ardent on February 20, 2021, 11:41@Petrus @Dev
Just re-visiting this thread.
In particular the tire pressure calculator.
Having failed miserably to find an alternative, are you aware of any.
Only reason I ask, the load rating I want to enter is not provided.
If you cannot find the rating Jason, it is not that complicated.
You want to compensate cahnge in tyre rigidity with air pressure
Starting from OEM a neat rule of thumb is 0.1 bar more/less for each rating down/up.
Quote from: Ardent on February 20, 2021, 11:41@Petrus @Dev
Just re-visiting this thread.
In particular the tire pressure calculator.
Having failed miserably to find an alternative, are you aware of any.
Only reason I ask, the load rating I want to enter is not provided.
We can use a chart. What is your the load ratings of the tires?
I did a write up on tire pressure and load index with the charts.
It explains in detail how to use the chart and the rational of why you have to match the load index.
https://www.mr2-spyder.com/community/diy-how-to/how-to-set-your-air-pressure-using-the-tire-load-rating-chart/ (https://www.mr2-spyder.com/community/diy-how-to/how-to-set-your-air-pressure-using-the-tire-load-rating-chart/)
Oem rear 86.
Fitted 90 xl.
Cheers for replies both.
Will have a read up after dinner.
@Dev refers to a "Chalk test" in the link.
The only chalk / tyre combination I can remember is the numbered marks a coach driver would put on the front tyre of the coach, iirc the passengers put a small coin ( before decimalisation) into a hat, when the coach stopped at the " Half Way House" the mark corresponding to 12 o'clock indicated the winning seat number.
My guess for Dev's version would be a chalk mark across the width of the tread to indicate over inflation/ chalk missing from middle of tyre, under inflation / chalk missing from each side of tyre and chalk evenly worn would be just right inflation.
The same way as gauging correct tyre inflation with tread wear but a lot quicker..
Quote from: Ardent on February 20, 2021, 18:19Oem rear 86.
Fitted 90 xl.
Ok so at 86 load rating for the OEM comes to 1058 pounds for 32 psi. This is taken from the standard load chart.
The new tire is 90XL so we need to look at the reinforced chart for what matches 1058 or closest to it for the new tire pressure. Surprise, surprise its 32psi.
Much of the confusion is SL and XL tires use different charts.
You cant simply go by some rule of thumb of adding and subtracting without knowing what kind of tires you are dealing with otherwise you can damage your tires or worse.
Quote from: Joesson on February 20, 2021, 18:28@Dev refers to a "Chalk test" in the link.
The only chalk / tyre combination I can remember is the numbered marks a coach driver would put on the front tyre of the coach, iirc the passengers put a small coin ( before decimalisation) into a hat, when the coach stopped at the " Half Way House" the mark corresponding to 12 o'clock indicated the winning seat number.
My guess for Dev's version would be a chalk mark across the width of the tread to indicate over inflation/ chalk missing from middle of tyre, under inflation / chalk missing from each side of tyre and chalk evenly worn would be just right inflation.
The same way as gauging correct tyre inflation with tread wear but a lot quicker..
Yes that is spot on. I would say doing the chalk test is not necessary for most people as long as the load ratings are matched however if someone wanted to confirm the chalk test can be a fast way of seeing it with your own eyes.
You can also do pyrometry using a cheap infrared thermometer. It doesn't have to be spot on but it should be within range.
For a lot of us including myself we have been conditioned to using factory air pressure but that is not how it should be done. It really depends on what tires being replaced and matching load ratings. I have heard in some countries they will not sell you tires unless they are matched and now in mine there is an effort by tire shops to be trained in setting air pressures by load ratings.
Quote from: Dev on February 20, 2021, 19:31Quote from: Joesson on February 20, 2021, 18:28@Dev refers to a "Chalk test" in the link.
The only chalk / tyre combination I can remember is the numbered marks a coach driver would put on the front tyre of the coach, iirc the passengers put a small coin ( before decimalisation) into a hat, when the coach stopped at the " Half Way House" the mark corresponding to 12 o'clock indicated the winning seat number.
My guess for Dev's version would be a chalk mark across the width of the tread to indicate over inflation/ chalk missing from middle of tyre, under inflation / chalk missing from each side of tyre and chalk evenly worn would be just right inflation.
The same way as gauging correct tyre inflation with tread wear but a lot quicker..
Yes that is spot on. I would say doing the chalk test is not necessary for most people as long as the load ratings are matched however if someone wanted to confirm the chalk test can be a fast way of seeing it with your own eyes.
You can also do pyrometry using a cheap infrared thermometer. It doesn't have to be spot on but it should be within range.
For a lot of us including myself we have been conditioned to using factory air pressure but that is not how it should be done. It really depends on what tires being replaced and matching load ratings. I have heard in some countries they will not sell you tires unless they are matched and now in mine there is an effort by tire shops to be trained in setting air pressures by load ratings.
In my experience tyre fitters put some arbitrary pressure into tyres. The get out being that the receipt says to check tyres/ pressures within n period.
( As I have mentioned in another thread) In a similar way how is it that the air gun used to fit the wheel nuts is automatically adjusted to suit each and every vehicle that the shop works on!
Don't start me on air guns. The answer is simple. They are all set to torque the living daylights out of everything. Unless it is hammered into next week, it's not tight enough.
First thing I do. Get home, crack the nuts and torque correctly.
Quote from: Joesson on February 20, 2021, 22:05Quote from: Dev on February 20, 2021, 19:31Quote from: Joesson on February 20, 2021, 18:28@Dev refers to a "Chalk test" in the link.
The only chalk / tyre combination I can remember is the numbered marks a coach driver would put on the front tyre of the coach, iirc the passengers put a small coin ( before decimalisation) into a hat, when the coach stopped at the " Half Way House" the mark corresponding to 12 o'clock indicated the winning seat number.
My guess for Dev's version would be a chalk mark across the width of the tread to indicate over inflation/ chalk missing from middle of tyre, under inflation / chalk missing from each side of tyre and chalk evenly worn would be just right inflation.
The same way as gauging correct tyre inflation with tread wear but a lot quicker..
Yes that is spot on. I would say doing the chalk test is not necessary for most people as long as the load ratings are matched however if someone wanted to confirm the chalk test can be a fast way of seeing it with your own eyes.
You can also do pyrometry using a cheap infrared thermometer. It doesn't have to be spot on but it should be within range.
For a lot of us including myself we have been conditioned to using factory air pressure but that is not how it should be done. It really depends on what tires being replaced and matching load ratings. I have heard in some countries they will not sell you tires unless they are matched and now in mine there is an effort by tire shops to be trained in setting air pressures by load ratings.
In my experience tyre fitters put some arbitrary pressure into tyres. The get out being that the receipt says to check tyres/ pressures within n period.
( As I have mentioned in another thread) In a similar way how is it that the air gun used to fit the wheel nuts is automatically adjusted to suit each and every vehicle that the shop works on!
I read an article long ago regarding the tire pressure monitor systems they put in cars at the turn of the century. They said that a large majority of vehicular accidents could have been avoided if people properly inflated their cars tires. Now its mandatory that manufactures have warnings but it still doesn't address proper pressures.
I use to take with me my torque wrench when fitting new tires at the shop. Now I take just the wheels.
Quote from: Dev on February 20, 2021, 19:18Quote from: Ardent on February 20, 2021, 18:19Oem rear 86.
Fitted 90 xl.
Ok so at 86 load rating for the OEM comes to 1058 pounds for 32 psi. This is taken from the standard load chart.
The new tire is 90XL so we need to look at the reinforced chart for what matches 1058 or closest to it for the new tire pressure. Surprise, surprise its 32psi.
Much of the confusion is SL and XL tires use different charts.
You cant simply go by some rule of thumb of adding and subtracting without knowing what kind of tires you are dealing with otherwise you can damage your tires or worse.
It is a curious game of many moving parts.
Load wise.
The fronts match the oem. But does not feel the same as as the yokos.
The rears are 90 vs 86 oem, but the rear feels great.
Have been running stock pressures. And with the info provided above. I will be leaving the rears well alone. They feel right and seemingly, they are.
Today, tried the fronts with 27. Cannot say that improved anything. Will return to 26. Drive again. And then try 25.
Probably down to construction characteristics. I am not lacking any grip that for sure.
More a feel/behavioral thing.
Quote from: Ardent on February 20, 2021, 23:03Quote from: Dev on February 20, 2021, 19:18Quote from: Ardent on February 20, 2021, 18:19Oem rear 86.
Fitted 90 xl.
Ok so at 86 load rating for the OEM comes to 1058 pounds for 32 psi. This is taken from the standard load chart.
The new tire is 90XL so we need to look at the reinforced chart for what matches 1058 or closest to it for the new tire pressure. Surprise, surprise its 32psi.
Much of the confusion is SL and XL tires use different charts.
You cant simply go by some rule of thumb of adding and subtracting without knowing what kind of tires you are dealing with otherwise you can damage your tires or worse.
The rears are 90 vs 86 oem, but the rear feels great.
I just want to highlight something you might be missing. 90XL is exactly the same as 86SL.
Two different numbers but the same load rating for the same PSI.
XL tires has its own chart.
This often confuses people and it has taken me awhile to figure out long ago until I asked a large tire distributer to clarify.
The main difference is the XL tires are reinforced to hold more air which supports higher loads but are weaker than SL tires for its respective load rating.
Quote from: Dev on February 20, 2021, 22:56I use to take with me my torque wrench when fitting new tires at the shop. Now I take just the wheels.
Then sort the pressures when you get home. :)
Quote from: Dev on February 20, 2021, 23:12I just want to highlight something you might be missing. 90XL is exactly the same as 86SL.
Two different numbers but the same load rating for the same PSI.
XL tires has its own chart.
This often confuses people and it has taken me awhile to figure out long ago until I asked a large tire distributer to clarify.
The main difference is the XL tires are reinforced to hold more air which supports higher loads but are weaker than SL tires for its respective load rating.
I love this place. everyday is a school day.
Until this thread, and the last few posts, no I did not know there were two charts/tables.
I just took load rating to be load rating. Did not treat XL vs non XL as having different values. (just construction)
Thanks for clearing that up.
Seems a bit like centigrade vs Fahrenheit. Same temp diff scale.
I will resist the temptation to be lazy and ask for a link to the tables. Little project for later.
Quote from: Ardent on February 21, 2021, 01:10Quote from: Dev on February 20, 2021, 22:56I use to take with me my torque wrench when fitting new tires at the shop. Now I take just the wheels.
Then sort the pressures when you get home. :)
Yes. Its a much better experience this way. My car is on jack stands in my garage with no chance of anyone messing with it or the dangers of having it improperly lifted.
I drop off wheels with new tires and the shop does the rest on their own time without having to wait for it in the lobby. I drive off and go to a friends house and get a call when they are ready to be picked up.
The guy doing the work knows I mean business and are going to do a good job with the mounting and balancing on my request because I am no ordinary customer that just hands over the keys and just drives away.
I recommend others to do the same if they have a second car, its much more convenient and less stressful.
I can post the charts. Although they are from Toyo tires they are universal. One chart is SL and the other is XL.
1111-IMG0339.png1112-IMG0340.png
Quote from: Ardent on February 21, 2021, 01:20Quote from: Dev on February 20, 2021, 23:12I just want to highlight something you might be missing. 90XL is exactly the same as 86SL.
Two different numbers but the same load rating for the same PSI.
XL tires has its own chart.
This often confuses people and it has taken me awhile to figure out long ago until I asked a large tire distributer to clarify.
The main difference is the XL tires are reinforced to hold more air which supports higher loads but are weaker than SL tires for its respective load rating.
Seems a bit like centigrade vs Fahrenheit. Same temp diff scale.
Almost the same analogy but not quite. There is a backwards rational for this if you want to get more confused.
It is because they try to match like for like between SL and XL for the consumer that is trying to match load rating blindly.
The difference is when you get the XL tire in the same load rating as an SL you have to put more air in it to carry the same load.
How is that for confusion and a backwards way of thinking because the guy that is clueless will not know that he needs a higher inflation.
So why do they do this thing with higher inflation of XL tires. It is because when people plus size their wheels (big wheel guys) they will need low profile tires that are weaker by nature and therefore need to be reinforced to hold more air to carry the load.
Its kind of like having to use low compression pistons to run more boost to gain more power without detonation. It doesn't make sense but it makes sense.
Quote from: Dev on February 21, 2021, 01:32I can post the charts. Although they are from Toyo tires they are universal. One chart is SL and the other is XL.
1111-IMG0339.png1112-IMG0340.png
much appreciated.
I have (had) a load table. Just the one. But no mention if it is SL or XL. Big help that is.
Quote from: Dev on February 21, 2021, 01:43Its kind of like having to use low compression pistons to run more boost to gain more power without detonation. It doesn't make sense but it makes sense.
Nice one Dev.
Lóve it!
Thank you!!!
So having printed out and looked over the tables kindly provided by
@Dev I arrive at the following.
As Dev identified earlier, The OEM SL load index of 86 is directly matched by the XL load index of 90. Pressure remains the same.
So what I thought might be the area to explore, isn't.
What has raised an eyebrow is the following.
OEM SL load index is 81. The tyres I have fitted are rated SL 82.
For the same 26 psi inflation. 81 = 783lbs 82 = 805lbs
That is a difference of +22.
Yesterday, I put 27psi in. And as noted above, did not improve things (handling) at all. The opposite in fact. Adding the 1psi now made a difference in load rating of +45. (783 vs 828)
But looking at the table. If I now go with the option I was going to take next and drop to 25. The difference is now -11. (783 vs 772) So perhaps 25.5. But will go 25 for a start just to see.
Quote from: Ardent on February 21, 2021, 11:16So having printed out and looked over the tables kindly provided by @Dev I arrive at the following.
As Dev identified earlier, The OEM SL load index of 86 is a directly matched by the XL load index of 90. Pressure remains the same.
So what I thought might be the area to explore, isn't.
What has raised an eyebrow is the following.
OEM SL load index is 81. The tyres I have fitted are rated SL 82.
For the same 26 psi inflation. 81 = 783lbs 82 = 805lbs
That is a difference of +22.
Yesterday, I put 27psi in. And as noted above, did not improve things at all. The opposite in fact. Adding the 1psi now made a difference in load rating of +45. (783 vs 828)
But looking at the table. If I now go with the option I was going to take next and drop to 25. The difference is now -11. (783 vs 772) So perhaps 25.5. But will go 25 for a start just to see.
I would certainly try 25psi. I bet it would feel right.
The interesting thing in your situation is you initially disregarded the what the SL chart was telling you for the 90XL on instincts alone which was a good move because you would have been under inflated and overtime you would have more heat in the tires and would have damaged them. Reading the chart the wrong way also has its consequences, the industry needs to fix this with a better rating system.
I have found when I used the charts exactly as intended for my new set of tires they were perfect.
Now that others that are reading this thread I hope the information will be disseminated to others that are asking about air pressure. We should no longer be quoting the factory air pressures without knowing what tires they have.
As it turns out. Tried this out on the daily.
Same sort of thing.
I fitted oem to the front. 100 sl.
Then checked the rears. 104 xl
X ref'd the tables and they balance out.
Happy days. Just good to know.
Quote from: Dev on February 21, 2021, 15:21I would certainly try 25psi. I bet it would feel right.
And I can now report. It does. For me, 25 is where it's at. Today. Conditions, atmospheric pressure, temp etc.
Best run I've had with this tyre combo.
Quote from: Ardent on February 21, 2021, 17:47Quote from: Dev on February 21, 2021, 15:21I would certainly try 25psi. I bet it would feel right.
And I can now report. It does. For me, 25 is where it's at. Today. Conditions, atmospheric pressure, temp etc.
Best run I've had with this tyre combo.
Warmest weather I would imagine
I just remembered one of the discussions I had with a tire engineer when I called one of the manufactures.
The reason why there is so much confusion and two charts is primarily because in some countries they have laws against fitting tires have a lower load index than what came with the car from the factory.
If the 90XL tire were to instead rate the tires on the SL scale which would be 86 load rating all would be fine in the world.
Its not done because you would be limited by the number of tires in the XL category that can cary the load if you were to inflate the tire to a higher pressure. Since they are reinforced they can take up to 6PSI more pressure than a comparable SL tire to carry more load.
In order to solve the confusion at tire shops and for inspection purposes they make it simple so they can clearly see that tire matches or exceeds the load rating of the OEM tires to be safe.
The problem is most people will not fill the XL tires to the correct air pressure to carry the load.
Duplicate
Quote from: 1979scotte on February 21, 2021, 17:59Quote from: Ardent on February 21, 2021, 17:47Quote from: Dev on February 21, 2021, 15:21I would certainly try 25psi. I bet it would feel right.
And I can now report. It does. For me, 25 is where it's at. Today. Conditions, atmospheric pressure, temp etc.
Best run I've had with this tyre combo.
Warmest weather I would imagine
I certainly acknowledge can have an influence. But temps have been consistent between yesterday and today here.
Car was just overall happier on 25 than 26 and much happier than at 27.
Which in away, sadly throws up the question. Did I previously spend unesseaesrily on the the AD08R's.
I am cornering the same on these as before. I do miss the ad08r. But one wonders just how far from their limit was I. Because I'm now where near the limit of the rainsports.
The context being road legal speeds on the public highway. I am still all over everything else like a rash in the twisties.
As a bonus, the rainsports are more usable, more of the time.
Have fully opened the torque taps and no fuss or nonsense from the rear. Just grip n go.
lets have some fun and see if anyone can answer this riddle based on what we have learned about load ratings.
You are a tire shop manager and a young rice boy comes to your shop asking to fit tires on his newly acquired 18" wheels.
His previous tires/wheels had the load rating of 86SL and now his new low profile tires that he brought for mounting on his new wheels have a load rating of 86XL.
A. Mount the tires.
B. You advise him that its unsafe.
C. Kick him out of the store for having too many stickers.
Your answer with the reason.
Quote from: Ardent on February 21, 2021, 20:51Which in away, sadly throws up the question. Did I previously spend unesseaesrily on the the AD08R's.
I am cornering the same on these as before. I do miss the ad08r. But one wonders just how far from their limit was I. Because I'm now where near the limit of the rainsports.
The context being road legal speeds on the public highway. I am still all over everything else like a rash in the twisties.
As a bonus, the rainsports are more usable, more of the time.
Have fully opened the torque taps and no fuss or nonsense from the rear. Just grip n go.
At legal speeds trough corners you will not come néar the limit of AD08Rs bar wintery conditions. You will thus have traction surplus for the unexpected or mistake. Oh and stop shorter if needed.
Assuming width/profile etc the same.
If the 86sl tyre had an oem inflation of 28psi. To obtain the same with the 86xl. The yoof should be advised to inflate to 32psi.
Dunce cap and flame retardant pants at the ready.
Quote from: Ardent on February 22, 2021, 18:22Assuming width/profile etc the same.
If the 86sl tyre had an oem inflation of 28psi. To obtain the same with the 86xl. The yoof should be advised to inflate to 32psi.
Dunce cap and flame retardant pants at the ready.
Without getting into tire widths , profile or inflation pressure. We need to assume that the OEM load rating is correct. But lets say for argument sake the inflation pressure for the OEM is 32 psi.
Try again.
A, B, or C
with the now added info of 32psi. Now fit and inflate to 37.
Quote from: Ardent on February 22, 2021, 22:36with the now added info of 32psi. Now fit and inflate to 37.
Correct. Basically as long as the load ratings numbers match or the new tires load reading is higher it's good.
The only difference is the XL tires need more air to hold the load. I think they do this so tire shops don't mess up but they eventually do because they fill it to factory air pressures.