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by simon8201 - 09/09/26 01:46 PM
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Wales
by Joske Vermeule, September 1
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Jun 14th, 2026
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Joined: May 2011
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Drive on the Wild Side Part of the Furniture
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Drive on the Wild Side Part of the Furniture
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If you wish to go uber techy apply thermal imaging to your tyres and adjust accordingly until you have even heat pattern for each wheel under each circumstance.
Probably a bit much on a Mog?
You could always drive sportingly for 10 miles or so, stop and jump out the car and do a touch test to see if all the same an d evenly warmed up. 
Adrian
Buggered Off, to a modern none leaky car, heart's still ticking
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Talk Morgan Guru
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Talk Morgan Guru
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Morgan state 22psi all round. For a normal load it is probably OK, but for a heavily loaded car it is worryingly low at the back.
I’ve set Aldermog at 22 front and 27.5 rear as 2 up with stuff we run at about 1250kg. It wil be interesting to see if there is any difference…..!!
Surely having much higher pressure in the rear tyres than the front will give you bad understeer Peter? Brian
Brian
1970 Morgan Plus 8 - Moss Box (Indigo Blue)
2014 Morgan SP1 (Rocket Red)
2015 Morgan Plus 8 (Rocket Blue)
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Tricky Dicky Member of the Inner Circle
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Tricky Dicky Member of the Inner Circle
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On my recent acquisition an 1999 Plus 8 with 7" x 16" 55 Section Centre Lock lightweight Alloys 20psi all round as recommended by Roger and Steve at Harpers is spot on for one up driving. She also has Konis at each corner and these are certainly playing their part.
She is a very settled car and soiled underpants will definitely be needed before she lets go.
Very interesting and exhaustive research Alderberry....
Last edited by 4/4sportsfun; 16/08/14 03:09 AM.
2009 4/4 Sport Henrietta
1999 Indigo Blue +8
2009 4/4 Sport Green prev
1993 Con Green +8 prev
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Interesting stuff; thanks Peter.
Richard
1976 4/4 4 Seater
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Formerly known as Aldermog Member of the Inner Circle
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OP
Formerly known as Aldermog Member of the Inner Circle
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Having opened a can or worms I felt more research is needed so I started looking at "recommended" pressures for a range of cars.
Findings:
1. Almost every modern car has different pressure recommendations for normal and loaded driving and these are further modified for normal and high speed driving. On my BMW the pressures for loaded high speed are higher than normal and fully loaded.
2. The difference between front and rear pressures seems to be linked to weight distribution, with a bigger difference for cars with a rear weight bias.
3. Manufacturers increasingly fit wider tyres to the rear wheels on powerful rear drive cars.
4. Aldermog's original 2009 rear Avons lasted less than 20,000 miles. The fronts look good for 40,000 but will be replaced next year when they are 6.
5. Properly inflated tyres should be 3 to 4psi harder when hot than cold. If more than 4psi they are overheating which is accepted as meaning under inflation or over loading and if less than 3 psi they are over inflated or under loaded, or both.
So Milligoons thermal imaging test can be replaced by a tyre pressure gauge. But I like his logic!
Where does this lead?
I believe that in the absence of evidence to justify the MMC recommendation of 22psi all round for the S2 Roadster a front rear bias makes sense. Aldermog has 4 leaf springs that need all the help they can get.
I do wonder if MMC under inflates tyres so they warm up a lot as the supplied tyres are working way under their recommended load. As mentioned previously the Avons fitted are Code 91 when based on the car weight they should be 81 at the rear and 75 at the front. Such tyres don't exist in the sizes needed.
I think handling would be improved if the front wheels carried 195 section tyres, not 205 section. Difficult to do without new front wheels.
I need more information: tyre pressure settings seem to be something of a "black art" and whilst I'm not sure that MMC are right I'm not sure they are wrong!!
Peter,
66, 2016 Porsche Boxster S
No longer driving Tarka, the 2014 Plus 8...
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Charter Member
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Some of the best knowledge (black art) about tyre pressure is held with the Motor racing fraternity. Whilst I'm sure Morgan have not calculated what pressures the should be, they do have a wealth of competition experience.
Martin (Deano)
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Talk Morgan Addict
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Peter, how do you calibrate your tyre pressure gauge to measure 0.5psi and what were the tyre temperatures when you measure it and was the temperature sensor calibrated? Get my point? Fascinating stuff and great research but I doubt most of us have the equipment to measure our tyre pressures accurately, it's good to be aware though. I remember years ago talking to a race mechanic in the pits who was throwing talcum powder on a sheet of smooth side up hardboard on the pit garage floor. I was intrigued and he said he was checking the tyre pressures, he rolled the car backwards and the rear slicks (from a Formula 5000) went over the talc and looked to see how much and where the tyre had picked up. I was open jawed and he said its a very old trick and shows how much of the tyre is in contact. He was not messing about and as the car was driven by Mike Hailwood (I think it was Matchbox sponsored?) it was a serious team. I like your methodology but know I have 3 gauges and not cheap ones and they are all +/- a couple of PSI and the thought of 0.5 PSI is outside my kits scope.
BR Colin
Who used to be a Spanner Juggler
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OP
Formerly known as Aldermog Member of the Inner Circle
Joined: Aug 2013
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Good point.
I think the important thing is to use one gauge.
Gauges at garages are supposed to be calibrated and checked, like the pumps. They used to be, wonder if they still are. Something I need to check.
Peter,
66, 2016 Porsche Boxster S
No longer driving Tarka, the 2014 Plus 8...
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Fascinating stuff and having been round this bouy a few times myself, I'll add my experiences. Firstly picking up on Colin's (S-J's) post, over the years I've accumulated a number of pressure gauges. I've two of the old stick gauges with the extending scale (which are roundly criticised as being inaccurate), two newer supposedly high accuracy digital gauges, two gauges on compressor based tyre inflators, and finally a Race Tech analogue gauge from my racings days. First thing to say is that the old stick gauges are calibrated in 1psi or 0.1bar increments, though you can "read" to 0.5psi or less. They both routinely show the same pressure and more over they offer repeatable results (i.e. the same pressure on multiple checks on the same tyre) though what they measure in absolute terms I'll come back to. For the newer digital gauges, one measures in 0.5psi and the other 0.1bar increments. However, despite them both claiming high accuracy and zero calibration at each use, they are both incapable of giving repeated results at the 0.5psi level, often varying by as much as 1or 2psi. All very frustrating, and completely undermining confidence for me personally. The Race Tech gauge is very clear, and gives very accurate repeatable results, and you can "read" the pressure to 0.25psi, but it was bought for racing slicks and wets operated at 12 to 15psi depending on conditions and has a full scale deflection (FSD) of 40psi. Best practice suggests that mechanical (i.e. Bourdon Tube) gauges are at their most accurate in the range of 40 to 60% of FSD. So, this is fine for the Plus 4 at ~22psi, but for the BMW tin top running 2.2 or 2.6bar (front) and 2.3 or 3.0 bar (rear) depending on load, it's outside its operable range. Going back to the absolutes, surprisingly the two old stick gauges and the two compressor tyre inflators all read the same pressure for a given pressure setting on a tyre in the normal 25 to 35psi range. Only as the pressures are increased to 45psi (3bar) or over is there any marked separation in the readings, and then only by say 0.1bar or 1.5psi. However, when compared to the Race Tech gauge at the 20 to 25psi range they all tend to read about 1.0 to 1.5psi low. So which is right in absolute terms? Well in truth I don't know, so I use the Race Tech gauge for the Plus 4 and the stick gauges for the BMW... I've given up on the digital gauges because of the poor repeatability issues. In the Mog, for 99.9% of the time we are two up in the car and I set them at 22psi all round. I've tried all combinations of 20 to 26psi settings all round at 1psi increments and with up to a +4psi rear bias over a period of time. For my taste >22psi is too hard, bouncy and uncomfortable, <22 psi is too soft with too much sidewall deflection. I also check my tyre temperatures (admittedly only by hand rather than an infrared thermometer) and find that at 22psi they are, as far as I can detect, evenly warm across the tread front and rear. In absolute terms, assuming the Race tech gauge is the most accurate, you could say that this equates to 23 to 23.5psi on the stick gauges. Now, who was is that said it's a black art...  P.S. My post was in response to S-J... Slow typing!
Last edited by MonteZooma; 16/08/14 11:32 AM. Reason: Editing iPads auto "corrections"!
Philip.
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Fascinating stuff and having been round this bouy a few times myself, I'll add my experiences. Firstly picking up on Colin's (S-J's) post, over the years I've accumulated a number of pressure gauges. I've two of the old stick gauges with the extending scale (which are roundly criticised as being inaccurate), two newer supposedly high accuracy digital gauges, two gauges on compressor based tyre inflators, and finally a Race Tech analogue gauge from my racings days. First thing to say is that the old stick gauges are calibrated in 1psi or 0.1bar increments, though you can "read" to 0.5psi or less. They both routinely show the same pressure and more over they offer repeatable results (i.e. the same pressure on multiple checks on the same tyre) though what they measure in absolute terms I'll come back to. For the newer digital gauges, one measures in 0.5psi and the other 0.1bar increments. However, despite them both claiming high accuracy and zero calibration at each use, they are both incapable of giving repeated results at the 0.5psi level, often varying by as much as 1or 2psi. All very frustrating, and completely undermining confidence for me personally. The Race Tech gauge is very clear, and gives very accurate repeatable results, and you can "read" the pressure to 0.25psi, but it was bought for racing slicks and wets operated at 12 to 15psi depending on conditions and has a full scale selection (FSD) of 40psi. Best practice suggests that mechanical (i.e. Bourdon Tube) gauges are at their most accurate in the range of 40 to 60% of FSD. So, this is fine for the Plus 4 at ~22psi, but for the BMW tin top running 2.2 or 2.6bar (front) and 2.3 or 3.0 bar (rear) depending on load, it's outside it's operable range. Going back to the absolutes, surprisingly the two old stick gauges and the two compressor tyre inflators all read the same pressure for a given pressure setting on a tyre in the normal 25 to 35psi range. Only as the pressures are increased to 45psi (3bar) or over is there any marked separation in the readings, and then only by say 0.1bar or 1.5psi. However, when compared to the Race Tech gauge at the 20 to 25psi range they all tend to read about 1.0 to 1.5psi low. So which is right in absolute terms? Well in truth I don't know, so I use the Race Tech gauge for the Plus 4 and the stick gauges for the BMW... I've given up on the digital gauges because of the poor repeatability issues. In the Mog, for 99.9% of the time we are two up in the car and I set them at 22psi all round. I've tried all combinations of 20 to 26psi settings all round at 1psi increments and with up to a +4psi rear bias over a period of time. For my taste >22psi is too hard, bouncy and uncomfortable, <22 psi is too soft with too much sidewall deflection. I also check my tyre temperatures (admittedly only by hand rather than an infrared thermometer) and find that at 22psi they are, as far as I can detect, evenly warm across the tread front and rear. In absolute terms, assuming the Race tech gauge is the most accurate, you could say that this equates to 23 to 23.5psi on the stick gauges. Now, who was is that said it's a black art... P.S. My post was in response to S-J... Slow typing! Hi Philip & Peter Strangely I tend to use my tatty old stick gauge most of the time as well, I think (just think don't know) that it's probably best to stick to one and then use it as a comparator if that's the right word? What I mean is a base data and if I set at 22 as you say Philip if it feels too hard or too soft I can adjust up and down a little, the accurate reading being not as important as knowing I am +/- from a baseline. I must say I have never owned a car that is so sensitive to tyre pressures and where just a pound or two up or down makes a noticeable difference. I really like Peters logical process to analysis and wish I could do it, I can follow and understand it totally but tend to jump in and change one thing and then decide if it's better or worse and then move on to the next thing, pre analysis is a discipline I still need to work on  All the best Colin (I would change the sign off but can't figure it out)
Last edited by Spanner Juggler; 16/08/14 11:28 AM.
BR Colin
Who used to be a Spanner Juggler
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