N-C is right.(He usually is).
If you fit a solid, non compressable wheel/tyre combination with an overall diameter of, say, 25 inches diameter and the speedometer is set to be accurate with this combination then it will overread if this combination is changed to a diameter of 20 inches.
The tyre footprint on the road is flat. Most of the rest of the tyre is round. In between these two states the tyre deforms from round to flat and reforms from flat to round. The lower the pressure in the tyre the more deformation takes place. If the pressure is low enough the tyre will, under certain conditions, roll off the rim.
The deformation of the tyre produces heat. This will ruin the structure of the tyre if the underinflation is severe enough for long enough.
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But the diameter does not change by 5 inched due to a pressure reduction of 50%. I doubt it would even change by even 10% Remember the rim is still connected to the tyres inner diameter and the outer is restricted by the the steel/canvas layers. One revolution of the rim still requires the circumference of the tyre to rotate one complete turn. and due the the stell reinforcement the circumference does noy actully change a great deal. Always good the exercise the grey cells. Regards Peter
Edited by Peter D on 13/10/2009 at 21:08
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The problem is visualisation. You may imaging the rim rotating on the rim which is just the outer carcass of a tyre. thus it would take much more than one revolution of the drive shaft to get the tyre outer carcass one complete revolution. But no the side wall if still attached and one revolution of the drive shaft in one revolution of the circumference of the tyre. When you go to the tyre store your tyre pwior to fitting does not look much smaller then the inflated tyre on your car, when they blow it up it grows a little in diameter thus circumference but the greatest change it the change in profile and the fact the bead get popped out. A tyre is not a balloon, it is a semi ridget flexible outer carcass held up by an inflated side wall. If you still can not get your head around this, then go to your car and make a mark on both tyre walls with chalk where the tyre meets the road. Now deflate one tyre 50% ( I assume you have a compessor ) then roll the car one full revolution of the inflated trye then go and look at he 1/2 deflated tyre. And there you are not a lot of difference is there. Regards Peter
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Sorry, not relevant as that refers to changing the tyre size and profile thus the circumference. not defalting a tyre with a known circumference. Regards Peter
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For information only relevant or not
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Sorry not relevant as that refers to changing the tyre size and profile thus the circumference. not defalting a tyre with a known circumference. Regards Peter
If the tyre is deflated then the profile has reduced. Instead of being say a 215/50/17 sized tyre, it would be a 215/x/17 sized tyre, where 'x' is whatever the profile of the tyre is when it is flat.
The wheel when the tyre is inflated will be indicating a lower speed than when the tyre is flat as the same wheel has to travel further because the profile is reduced.
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Hi Dave, I agree the profile has changed but the circumference has not changed as much and that is the point.
I have provided an example of a practicle test so if you are unsure then try it.
Regards Peter
Edited by Peter D on 13/10/2009 at 22:59
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Peter,
Here's something for your grey cells....
If you let a tyre down enough so the axle does drop a bit, where does the circumference of the tyre go to in that region?
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It goes on to the ground of course .I've been waiting for someone to suggest the chalk mark test.simple and effective try it nc.regards everyone.mrt.
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Someone mentioned visualistion and chalk marks.
Try and visualise a tyre on a wheel from the side, when not on the car it is perfectly round though when on a car it's not quite round, the bit that sits on the road is flattened a little, this is normal even if it is inflated correctly. The bit that has been flattened a little is displaced either side of the primary contact point so as to create a worthwhile contact patch. When the wheel rolls the carcus flexes maintaining the contact patch.
If you make a chalk mark on the circumferance of the tyre at the top and plot the path of the mark as the wheel rolls, say clockwise, (in relation to the car, not the ground, that is something else) then the mark follows a smooth path until around the 4 o'clock position where it starts to be displaced outwards, then by 5 o'clock ish it is coming back inwards to it's inner most point at 6 o'clock, back out at 7 o'clock and back in again at around 8 o'clock then following a smooth path around the top of the wheel back to 4 o'clock ish.
That irregular path accounts for the circumferance of the tyre being different in relation to the rolling radius when the wheel/tyre is on the car rather than off it.
Now if you lower the pressure you simply create a more irregular path for your chalk mark, it will be displaced outwards earlier and inwards further at 6 o'clock thus the rolling radius will reduce.
The conclusion is that reduced tyre pressures DO alter the speedo reading.
A side effect of this flexing of the carcus is heat build up, it is this that makes an under inflated tyre, that has to flex more as it rolls, more likely to blow out at speed.
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Pirelli explain it.
"Rolling radius
The radius of a rigid wheel which covers the same distance covered by a tyre, performing an equal number of turns. It has an intermediate value between the free radius and the load radius and varies for a given tyre according to the type of road and load, the pressure and the speed."
What they're saying is imagine replacing the wheel and tyre with a rigid wheel of a diameter such the the centre of the axle is at the same height from the ground as with the original. If you drive the car at a given road speed the rigid wheel will rotate at the same speed as would the original. The relevant dimension is the rolling radius which is the distance from the centre of the axle to the ground. Forget any part of the tyre's circumference which isn't in contact with the ground.
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Yes we know about the sidewall profile change but have you tried the chalk test. ? You are just visualising the problem Yes a 50% deflated tyre will alter the speedo reading but by far less than you think and way way less than any axle to road rolling radius calculation. Regards Peter
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Would centrifugal force not compensate for a percentage of under inflation rolling diameter?
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Yes a 50% deflated tyre will alter the speedo reading but by far less than you think and way way less than any axle to road rolling radius calculation. Regards Peter
No, the rolling radius calculation IS what determines the effect that deflating the tyre has had on the speedo reading - see my post above.
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I did read it with interest Cheddar. HAve you tried the chalk test. I suspect not or you would not hold that view or get it mixed up with Pirelli's example of establishing the correct rim/ tyre size for replacement combinations. Regards Peter
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Peter, no I have not tried the chalk test, I dont need to, I understand the maths.
Re the chalk test, one or two revolutions of the wheel on your drive will not prove anything though 100 revolutions across say a large flat car park with the car moving in a dead straight line, the same tyres with the same amout of wear and one tyre at 15 psi and another at 35 ... ...
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The percentage error is the same if the tyre revolves once or 100 times. If the error was dictated by the rolling radius approach then you would see a significant error in just one revolution. Using a 14/195/70 thus the 'rolling radius' method would give you 11.5" inflated and 9.25 at 16 psi 1/2 pressure. that is a 20% error in one rotation. Remember that one rotation of the rim is still one rotation of the outer of the tyre. The rim and the circumference of the rim and the circumerence of the out tyre canvas are not geared. Regards Peter
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The distance between the road and the center of the axle is the effective radius of the wheel. I'm sure that you'd agree that with a wheel of different radius the speedo is affected? Now with a reduction of 50% pressure maybe some low profile tyres wouldn't be affected too badly but I suspect that on a higher profile tyre the difference could be as much as an inch. That would have a noticable affect on speedo accuracy.
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I'm not going to stick a big oar in here, but it seems to me that there is some cross-purpose talk about what 'rolling radius' really means. Forgetting chalk-mark experiments, my reckoning is that as real-world tyres have an essentially unstretchable belt within the tread circumference, the only variation in the 'rolling distance' of a tyre (however hard or soft) will be limited to flexing or scuffing within the depth of the tread.
Edited by Andrew-T on 14/10/2009 at 16:53
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Spot on Andrew-T. Regards Peter
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Yes, but its the SHAPE of the steel bands which change. If the shape were to remain constant then there would be no effect on speedo
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OR think of it this way, would you expect a car running on just its rims to have an effect of the speedo? Take it one step further what would you then expect to happen on a completely deflated tyre fitted to the rim? In this case the rim is almost as close to the ground as when the rim was running without a tyre.
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But we are talking about a 50% deflated tyre, we are not running on the 'rims'. One revolution of the drive shaft equals one revolution of the entire circumference of the steel re-enforced carcass as it remain attached to the rim. Regards Peter
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Peter, that is simply not right, my earlier post explains that that irregular path of the carcass of the tyre accounts for the rolling radius being different when the tyre is deflated.
OK ..
Say the rolling radius of the tyre is 25 cm then the effective circumference is 157 cm so the wheel/tyre needs to turn 637 times to cover 1000m.
If the tyre is defleted so the rolling radius becomes 24.5 cm, only 5mm less, then the effective circumference is 154 cm so the wheel/tyre needs to turn 649 times to cover 1000m.
Perhaps think of the carcass of the tyre as like a bicycle chain when it moves onto a smaller sprocket causing slack in the chain, deflating the tyre causes slack in the carcass.
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No sorry, the cancass is directly attached to the rim, one turn of the rim equals one turn of the entire circumference of the tyre which has not changed more than a few %. There is no gearing involved. Have you done the chalk test yet. No, Didn't think so. Regards Peter
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Have you done the chalk test yet. No Didn't think so. Regards Peter
As I said before I have not tried the chalk test, I dont need to, I understand the maths. In which regard you have ignored the majority of my last post.
I give up!
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It is not a maths issue Cheddar it is a practical engineering issue and easily proved with a car and a peice of chalk. Pete D
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I don't need a piece of chalk to tell me that since fitting slightly smaller profile tyres, my speedo now over-reads by approx 3 mph, and traveling the same route with those slightly smaller tyres the odometer reads approx 1½ to 2 miles more than when it did with the larger profile tyres fitted.
I'm sure if I'd let the exact amount of air out of the tyres to mimick the lower profile, I would get the same results.
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Indeed Dave as you have fitted a tyre with a different circumference by selecting a different profile. This is not the same as a 50% deflation of a tyre. Regards Peter
Edited by Peter D on 14/10/2009 at 22:11
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I understand the maths ... I give up!
As Peter said, maths doesn't come into it. The belt in the tyre remains the same length (very nearly) whether the tyre is hard or soft. The hub may be nearer the ground, but the tread will roll the same distance (very nearly) as the wheel turns. The only way to get a different result would be for the tyre-bead to skid round the wheel rim.
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>>As Peter said, maths doesn't come into it.
Sorry, I'm afraid it does.
The truth is really quite complex, and lies somewhere between the extreme positions taken up by PeterD and Cheddar.
The vital point is included in the post by L'escargot, where Pirelli state that for a given tyre, rolling radius is affected by pressure.
The chalk marks will change as the tyre is deflated - not by quite as far as you might imagine from a radius based approach, but, they will change, which is contrary to the view held by those who believe or tend towards belief in a fixed circumference.
I hinted at the complexity in my question about where does the circumference go to as the tyre deforms into the road - you can't replace what was an arc of a circe with a straght line without any change in length.
In the question as posed by the OP, the engineer was right, the relationship between distance covered and how far the wheel turns will change - the engineer didn't say by how much it would change!
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The truth is really quite complex and lies somewhere between the extreme positions taken up by PeterD and Cheddar.
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I take umbrage at that NC!!!!!
The fact is that lower the pressure changes the rolling radius and thus affects the speedo, Peter D would not accept this so I attempted various ways to illustrate the point.
The vital point is included in the post by L'escargot where Pirelli state that for a given tyre rolling radius is affected by pressure.
We all know that though Peter D would not accept it.
Perhaps re-read my previous posts!
Edited by cheddar on 15/10/2009 at 08:36
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What we need is for an ardent disbeliever of the rolling radius hypothesis to get their car put on a rolling road and be given a speedometer readout with the tyres inflated hard and with them underinflated.
www.slarkraceengineering.co.uk/rollingroad.htm
"For those cars with non-standard gear ratios, wheels/tyres, (and pressures)* we have a very useful function for measuring actual road speed compared with speed displayed in car. This is also printed on an easy to read graph. ............. "
* I added "(and pressures)".
Edited by L'escargot on 15/10/2009 at 10:00
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Good morning guys. "The chalk marks will change as the tyre is deflated - not by quite as far as you might imagine from a radius based approach, but, they will change," Correct they do change slightly nobody has said otherwise but by no where near the % the the RR method changes, even on a 50% deflation. A 20% RR change makes about a 2.5% difference in the true distance travelled depending on tyre structure type nominal profile. With a difference of 8 to 1 if makes the RR method for a deflated tyre irrelevant. Regards Peter
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Imagine you could fit a tyre of twice the standard size to the wheel.Now deflate so that the distance from hub centre to ground is the same as with the original tyre.The circumferance would be twice what it was previously but it is no longer a circle,this is what is causing confusion amongst the 'x amount of tread = x distance travelled = 1 revolution of the driveshaft' faction.The rolling radius would be the same and the speedo reading would be the same.The circumferance has no bearing on the reading.So,technically,deflation will affect the speedo reading,however the 50% mentioned may well not make any noticable difference using an average sized wheel.
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For each complete revolution of your big tyre the axle travels the same distance as the circumference. If you deflated the tyre by 50% and rotated the drive shaft one complete turn the axle has still travelled a distance equal to the circumerfence of the tyre, yes there will be some compression in the section that is in contact with the road but it is very small. Regards Peter
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The mods are going to lock this thread unless someone goes out and performs the chalk-mark experiment ... :-)
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The mods are going to lock this thread unless someone goes out and performs the chalk-mark experiment ... :-)
........... or does the rolling road test.
......... or asks a tyre manufacture for an explanation.
Edited by L'escargot on 15/10/2009 at 19:34
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For each complete revolution of your big tyre the axle travels the same distance as the circumference.
For each complete revolution of your big tyre (or any other tyre) the axle travels 2 x pi x r where r is the distance of the axle from the ground and pi = 3.14159 approx.
However, just for fun ........... www.drinkfromthefurrycup.com/stories/045.shtml
Edited by L'escargot on 15/10/2009 at 19:31
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For each complete revolution of your big tyre (or any other tyre) the axle travels 2 x pi x r where r is the distance of the axle from the ground and pi = 3.14159 approx.
Yes, as per my post Wed 14 Oct 09 17:49.
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Yes as per my post Wed 14 Oct 09 17:49.
You and I (and Number_Cruncher and sierraman, to name but a few) are of one accord. Great minds think alike.
Edited by L'escargot on 15/10/2009 at 19:42
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You and I (and Number_Cruncher and sierraman to name but a few) are of one accord. Great minds think alike.
Perhaps not NC, he says the truth lies somewhere between Peter D and I, if he believes that then he is wrong.
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As posted by L'escargot, from Pirelli;
---------------8<-------------
"Rolling radius
The radius of a rigid wheel which covers the same distance covered by a tyre, performing an equal number of turns. It has an intermediate value between the free radius and the load radius and varies for a given tyre according to the type of road and load, the pressure and the speed."
---------------8<-------------
Note: "It has an intermediate value between the free radius and the load radius....."
My view of the situation is consistent with that as given on Pirelli's website, the truth lies somewhere between the two extremes.
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Been there done it. Mark both tyres with chalk perpendicular the the surface on which it rests and matk the surface. With an assitance role the car one full rotation then mark the surface again. Role the vehicle back and check the marking match. Now deflate one tyre by 50%, role the car one full rotation of the inflated tyre then check the deflated tyre markings. In the case of a 14/70/195 the rotation error was just less then 2.5% of the circumference. What elase can I say. Regards Peter
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>>What elase can I say
A complete set of information would also include how far the axle moved downwards as the tyre was deflated.
However, the 2.5% shows that in the OP's question, the engineer was right, and the plumber wrong.
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Even 50% will make little difference, remember the steel wire buried in the outer carcass does not change it's length. Was one of my very early replies. It will make lttle difference I did not say it would make do difference unlike the 'engineer' who was thinking of the gearing implications. I provided the change in RR ages ago 20% on the tyre and vehicle I tested it on. All good fun for the grey cells. Regards Peter
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Peter, why do you insist on harping on about the circumference of the tyre and whatever is inside it?
>Even 50% will make little difference, remember the steel wire buried in the outer carcass
>does not change it's length.
It might not change the length of the steel wire but that is irrelevant to the RR and effective circumference of the tyre.
To give an extreme example, imagine a tyre as it goes over something like a kerb perpedicular to it's direction of travel. The tread of the tyre is pushed inwards creating an indentation in the tyre. The length of your Holy steel wire hasn't changed but the circumference of the tyre has.
Now imagine that on a smaller scale.
Kevin...
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>>The radius of a rigid wheel which covers the same distance covered by a tyre, performing an equal number of turns. It has an intermediate value between the free radius and the load radius and varies for a given tyre according to the type of road and load, the pressure and the speed.">>
NC,
That is the difference between the load and dynamic rolling radius explained by hysteresis, the fact that the tyre material will not bend and flex at will, by increased pressure as the tyre warms at speed and by centrifugal force as the wheel spins.
However it is not explained by Peter D's assertion that as long as the circumference is constant in length the gearing (speedo reading) will be unaltered even though the rolling radius changes due to a reduction in static pressure.
Therefore the truth does not lie somewhere between the two extremes.
--
Edited by cheddar on 15/10/2009 at 22:37
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There's no need to complicate matters by considering dynamics, thermal issues or hysteresis - the mechanics of a slowly rolling tyre are clearly not as simple as either extreme grouping is making out.
When this thread began, I was firmly adherent to the radius [in terms of the height of the axle rather than the much more subtle concept of rolling radius] view, but, I have to confess, I had never given the matter as much thought as it deserved.
PeterD's posts have caused me to go away and rethink, which is what led to my question about where the circumference goes to - how can an arc be replaced by a straight line if there is no flexibility.
So, after more thought, I take up a position in between the extreme views, which does tally with Pirelli's definition of rolling radius.
Bear in mind that "rolling radius" is a theoretical radius - there is no physical dimension which you could measure from a tyre which would match it - it's a theoretical number obtained by doing a more scientific version of PeterD's chalk test.
There's an interesting outcome of this - even if you ignore the energy lost in deforming the sidewalls and tread, the hysteretic losses, even ignoring the kinematics of tread block engagement, you cannot roll a tyre which supports any load without friction, and hence wear - the incompatibility between the arc and straight line implies slip.
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Bear in mind that "rolling radius" is a theoretical radius - there is no physical dimension which you could measure from a tyre which would match it - it's a theoretical number obtained by doing a more scientific version of PeterD's chalk test.>>
I have to disagree, static rolling radius (load radius) is simply the axle centre line to the road surface and is good enough to determine the gearing changes caused by changes in wheel and tyre sizes and also by tyre PRESSURE changes. Dynamic rolling radius accounts for hysterisis etc and can surely be computer modeled.
PeterD's posts have caused me to go away and rethink which is what led to my question about where the circumference goes to - how can an arc be replaced by a straight line if there is no flexibility.
- the incompatibility between the arc and straight line implies slip. >>
No.
1/ because the arc is displaced a little outwards before being displaced inwards as it becomes a straight line thus maintaining the length of the circumference.
2/ The circumference is, when the tyre is under load, effectively running eccentrically the axle centre due to the elasticity in the tyre construction (side walls).
Edited by cheddar on 16/10/2009 at 07:24
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The road surface is tangential to the tyre at the point of contact, so all you need to do is consider the equation for tangential speed.
v=r x omega ................ equation 1
v is the tangential speed of the point on the tyre in contact with the road, and hence is the speed of the vehicle.
r is the distance of the axle from the road which, to make the calculation easier, we will consider to be constant.
omega is the rotational speed of the wheel in radians per unit of time.
One revolution (i.e. 360°) is 2 x pi radians, so RPM is omega/{(2 x pi)/360}, or omega = RPM X 2 x pi/360
Substitute for omega in equation 1 and you get ..........
v = 2 x pi x r² x RPM
In other words, the vehicle speed is proportional to r (which is the height of the axle from the road, aka the rolling radius) and the rotational speed of the wheel, and doesn't depend on any part of the tyre's circumference which is not in contact with the road.
Edited by L'escargot on 16/10/2009 at 09:00
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>>static rolling radius (load radius)
These are not one and the same thing.
Yes, it can form a baseline to allow the effect of CHANGES to be evaluated.
>>1/ because the arc is displaced a little outwards before being displaced inwards as it becomes a straight line thus maintaining the length of the circumference.
Can you point me towards a reference for this?
The sidewall stiffness will prevent the tyre from moving a long way from concentricity, but, yes, that will happen.
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>>r is the distance of the axle from the road
No, that and rolling radius are not one and the same dimension. (It's very close, but, not the same)
Edited by Number_Cruncher on 16/10/2009 at 10:51
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No that and rolling radius are not one and the same dimension. (It's very close but not the same) >>
>>static rolling radius (load radius)
>>These are not one and the same thing.>>
They are, it is dynamic rolling radius that differs.
I think the eccentricity is the key.
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>>They are
No - please read Pirelli's definition again.
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>>They are No - please read Pirelli's definition again.
Pirelli's definition is for dynamic rolling radius.
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In as much as they acknowledge that the rolling radius is a function of speed, yes.
"It has an intermediate value between the free radius and the load radius..."
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For each complete revolution of your big tyre the axle travels 2 x pi x r
Not necessarily. As a tyre becomes more deflated, the rolling becomes closer to a track-laying vehicle. You surely don't propose the same argument for one of those?
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>> For each complete revolution of your big tyre the axle travels 2 x pi x r Not necessarily. As a tyre becomes more deflated the rolling becomes closer to a track-laying vehicle. You surely don't propose the same argument for one of those?>>
The same principals apply however the track is in effect the surface that the wheel rolls upon so the rolling radius is the axle centre line to the point where the wheel engages with the track.
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A track vehicle does not have a 1 to 1 gearing between the circumference of the rim and the circumference of the tyre. Regards Peter
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Wow you guys I didn't expect a response like this to my post.When I asked this question I was adamant about my version.Now i'm not so sure . There is alot more involved than what meets the eye so I'm swayed slightly.Now er where did I put that piece of chalk?.regards everyone. Mrt.
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A tracked vehicle does not have a tyre(in the sense we are talking about).The track can be disregarded,it acts as the surface on which the vehicle moves.
The circumferance of a tyre may be of a fixed value regardless of inflation but the shape varies,with low pressure the bottom of the circle is squashed and this is what will vary the distance travelled per revolution and thus the speedo reading.
I'll be finding a piece of chalk and letting one of my bike tyres down soon.
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Peter D,
Imagine that the wheel/tyre assembly has no tyre but consists of an infinite number of spring-loaded spokes, to simulate a tyre. The spokes compress in length a pre-set amount under the weight of the car. Would the speedo reading be the same regardless of how much the spokes compressed?
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Les - not the same thing, as your proposed arrangement doesn't have the tyre's semi-rigid belt which keeps the circumference (almost) constant.
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Hi L'escargot, I like your spring analogy but it has completely different dynamics as you have removed the constant of the reinforced circumference of the tyre. I am off on vacation tomorrow but will try and log in somewhere to see how this thread is going. Have you found a piece of chalk yet. Regards Peter
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Thinking on that again what you describe is in fact a tracked vehicle with the actual road being the track and yes the distance travelled will be proportional the RR. But a tyre is not a tracked vehicle and there is no gearing ratio between the rim and the outer carcass. One rotation of the rim is one rotation of the circumference of the tyre, if not it would rip it apart. Regards Peter
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As it is Sunday morning I have carried out a test whilst drinking my second cup of coffee.
Test subject -front wheel of GT Talera(Halo Combat fitted withh Pirahna Pro).
Test location - kitchen floor
Test equipment- pressure guage,tape measure,yellow crayon from puncture repair kit.I used the valve as the marker so no discrepancies could be introduced through tyre slippage on the rim.One revolution of the rim has to equal one rev of the tyre,as P D has so consistantly pointed out.
Results - 50 p.s.i. one revolution 2078 mm
25 p.s.i. one rev 2065 mm
0 p.s.i. one rev 1939 mm
Note - no downward pressure was applied to the handlebars.
This would affect the speedo reading on the bike as the distance travelled by one revolution has to be programmed into it.
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Sierraman - brilliant to do all that while drinking a cup of coffee ...
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But a tyre is not a tracked vehicle and there is no gearing ratio between the rim and the outer carcass. One rotation of the rim is one rotation of the circumference of the tyre if not it would rip it apart. Regards Peter
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there is a gearing ratio due to the inflation pressure ,although not directly the flex of the tyre is a form of gearing .
if you look at an over inflated tyre from the front the contact point is convex but if you look at a seriously under inflated tyre it is concave at contact point which is why an over inflated tye wears in the middle and an under inflated tyre wears on the outside corners of the tread ,the exess size of the circumference in relation to diameter has to go somewhere and folds itself inwards altering the ratio with the sidewalls which as you rightly say would rip itself apart
will deflated tyres alter speedo reading ? no they wont
will that speedo reading be wrong ?yes it will read low on under inflated tyres
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Do deflated tyres alter the speedo reading?
>>>>>>>>>>
>>>>>>>>>>>>>probably not because there isnt as much resistance from the air on the tread pattern to slow the cooefficient of doobery watsname as car is sat upside down in a ditch
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At the end of the day, all other things being equal, thinking outside the box and hitting the ground running, together with the big picture of the 30,000 foot view of blocking and tackling, my two cents worth of paradigm shift suggests that we should take it to the next level at this point in time to get synergy on this action item.
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Underinflated tyres will make your car more comfortable around town if you don't go fast.
They will also change the speedometer reading slightly and increase the fuel consumption.
If they are seriously underinflated they will overheat at sustained high speeds, perhaps to the point of rupture.
Is there anyone in the world who doesn't know these things? If so they must have led a very sheltered life or be very confused.
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