The Triumph Dolomite Club - Discussion Forum

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 Post subject: Tyre pressures
PostPosted: Sat Feb 03, 2018 11:06 am 
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Googling my Fourtrak tyre pressure ("4 PSI rule"), as I had forgot what they are when using 31" tyres, came across this wild statement from Cooper Tires:
Quote:
"Beware of vehicle placards with recommendations below 30psi.
Some older vehicles may still show lower pressures which were
used to “enhance” ride but resulted in poor tyre life and in some
circumstances are dangerous."
https://www.coopertires.com.au/media/14 ... ssures.pdf

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Current fleet: Triumph Dolomite Sprint '75, Daihatsu Fourtrak, Honda CG125, Yamaha Fazer 600, Shetland 570

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 Post subject: Re: Tyre pressures
PostPosted: Tue May 15, 2018 12:30 pm 
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Having just bought new Falken tyres I asked them for a pressure recommendation and they have kindly supplied me with a certificate, which is good enough for me to supply to the insurance company if needed to explain why I've inflated them more than the 70s tyre pressures suggested by BL.

2 bar front/ 2.2 bar rear - Attached the PDF if anyone else wants it.

Edit: Better add that was for a Sprint, also attached a translation from the German!
Image


Attachments:
201805208.pdf [18.34 KiB]
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Current fleet: Triumph Dolomite Sprint '75, Daihatsu Fourtrak, Honda CG125, Yamaha Fazer 600, Shetland 570

Disposal fleet: Golf GTi 16v MK3 Anniversary

Past fleet: Triumph 2000, Lancia Beta Coupe, BL Mini Clubman, Austin Metro, Vauxhall Cavalier MK1 & MK2, Renault 18 D, Rover 216 GSI, Honda Accord (most expensive car purchase, hated it on pickup from dealer, was made out of magnetic metal as only car I've ever been crashed into, 4 times), Golf GTi MK3 16v x 3
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 Post subject: Re: Tyre pressures
PostPosted: Tue May 15, 2018 1:11 pm 
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Incredible,

I've been setting up 29f, 31r because it felt right.

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 Post subject: Re: Tyre pressures
PostPosted: Tue May 15, 2018 1:29 pm 
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I'm not surprised Mahesh, I put the new rubber on and it was like driving on flat tyres over the old ones, not a pleasant experience cornering. which is why I thought I'd ask the question,. Going to adjust upwards when I get home!

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Current fleet: Triumph Dolomite Sprint '75, Daihatsu Fourtrak, Honda CG125, Yamaha Fazer 600, Shetland 570

Disposal fleet: Golf GTi 16v MK3 Anniversary

Past fleet: Triumph 2000, Lancia Beta Coupe, BL Mini Clubman, Austin Metro, Vauxhall Cavalier MK1 & MK2, Renault 18 D, Rover 216 GSI, Honda Accord (most expensive car purchase, hated it on pickup from dealer, was made out of magnetic metal as only car I've ever been crashed into, 4 times), Golf GTi MK3 16v x 3


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 Post subject: Re: Tyre pressures
PostPosted: Tue May 15, 2018 1:57 pm 
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I put 30psi all round for as long as I can remember.

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 Post subject: Re: Tyre pressures
PostPosted: Tue May 15, 2018 3:36 pm 
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Seen a few old posts that you've been in Mart but everyone always comes on and says that we run the risk that the insurance would be invalid, so having paperwork to mitigate has put my mind at rest. It's good to hear that others like you and Mahesh's real world experience matches what the tyre supplier suggests, taking into account that the 2.2 bar for the rears is at maximum load.

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Current fleet: Triumph Dolomite Sprint '75, Daihatsu Fourtrak, Honda CG125, Yamaha Fazer 600, Shetland 570

Disposal fleet: Golf GTi 16v MK3 Anniversary

Past fleet: Triumph 2000, Lancia Beta Coupe, BL Mini Clubman, Austin Metro, Vauxhall Cavalier MK1 & MK2, Renault 18 D, Rover 216 GSI, Honda Accord (most expensive car purchase, hated it on pickup from dealer, was made out of magnetic metal as only car I've ever been crashed into, 4 times), Golf GTi MK3 16v x 3


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 Post subject: Re: Tyre pressures
PostPosted: Tue May 15, 2018 8:09 pm 
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ive always had 30 all round.

As for insurance for being invalid for incorrect pressure does anyone know anyone that had a claim refused for slightly incorrect pressure, the answer will be no as a claims assessors rarely check pressures unless they suspect the pressure is overly inflated or very flat then they would have to prove they were that pressure at the time of the incident.
Police do sometimes check pressures at an accident scene if it involves a life changing injury or death.
Most cars don't even get checked other than a repair value assessment.

(many years experience in the accident trade)

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 Post subject: Re: Tyre pressures
PostPosted: Tue May 15, 2018 8:40 pm 
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A couple of years back Falken recommended 26 all round on my 1850, 29 fully loaded, standard 4.5j dolly steel wheels.


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 Post subject: Re: Tyre pressures
PostPosted: Thu May 17, 2018 7:57 am 
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Yep I always used higher pressures similar to the folk on here.
On my kit cars however I use less because they weigh less.
Horses for courses old boy.

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 Post subject: Re: Tyre pressures
PostPosted: Thu May 17, 2018 12:50 pm 
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Quote:
Yep I always used higher pressures similar to the folk on here.
On my kit cars however I use less because they weigh less.
Horses for courses old boy.
Exactly! On the lightweight (760kg) Carledo I run my 195/50/15s at 28 front and 24 rear dropping the rears to 12psi on the dragstrip.

But I expect to be running the considerably heavier (and softer sprung) Dolomega with it's 185/60/14s at about 30 all round.

You have to go with what works best for the car, not what someone said 40 years ago about a tyre that is no longer available! Tyre technology, like every other sort, has moved on and so should we!

Also, Justin has the right of it! An insurance assessor will not check tyre pressures during an inspection. The Police WILL, in the event of a fatality but only insofar as to make sure (as far as possible on a damaged car) that the tyres were at a reasonable pressure at the time if the incident. A few pounds here or there would not bring their wrath down on you!

Steve

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 Post subject: Re: Tyre pressures
PostPosted: Thu May 17, 2018 3:10 pm 
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12psi front and rear on my Vindicator, because its near as dammit 100g per corner on Toyo T1Rs 195/50/15. i started out at 30psi all round and it handled like a very fast supermarket trolley

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 Post subject: Re: Tyre pressures
PostPosted: Thu May 17, 2018 8:13 pm 
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On the volvo 165r15 2.5 bar at the front and 3 at the rear. Makes it slide better in corners. Dollies about 2 bar and the ones with 205/60/13 2.2-2.5.

Jeroen

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 Post subject: Re: Tyre pressures
PostPosted: Wed Feb 13, 2019 4:10 pm 
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Quote:
12psi front and rear on my Vindicator, because its near as dammit 100g per corner on Toyo T1Rs 195/50/15. i started out at 30psi all round and it handled like a very fast supermarket trolley
At 100 g (i.e. 0·1 kg) per corner, that must be a light-weight small-scale model, with VERY large wheels & tyres!?! :shock: :roll:

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 Post subject: Re: Tyre pressures
PostPosted: Wed Feb 13, 2019 4:12 pm 
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Both the Triumph Toledo 1300 owners’ handbook and official BLMC Triumph Toledo 13/1500 workshop manual, specify tyre-inflation pressures of 22 psi & 26 psi for the front & rear tyres respectively, for the original factory-fitted 155 SR13 radial tyres, mounted on 4J x 13 inch steel wheels.

When my father bought the six-month old, ex-demonstrator 1974 four-door Triumph Toledo 1300 in May 1975, it had already been retro-fitted by Mann Egerton with 5½ x 13 inch Cosmic aluminium-alloy wheels and 175 SR13, Uniroyal Rallye 180, steel-braced radial tyres, but they hadn’t specified any alternative tyre pressures, for these substitute wheels & tyres.

Apart from a short period in the early-1980s, when I was experimenting with tyre pressures, my 1974 four-door Triumph Toledo 1300 has always been run with tyre-inflation pressures (as indicated on the hand-held PCL pencil-gauge or foot-pump gauge) of 22 psi & 26 psi in front & rear tyres respectively; in both 175 SR13 (aka 175/80 SR13 | Uniroyal Rallye 180 during 1975 to 1982 & Kelly-Springfield Steelmark from 1982 to 1987) and 185/70 SR13 tyres (Firestone S211 from 1987 to 1999), mounted on 5½ x 13 inch aluminium-alloy wheels.

Sometime in the early-1980s, whilst I was studying at Cranfield Institute of Technology, I learned from a fellow student who owned a Triumph Dolomite 1500, that the specified tyre-inflation pressures for the Triumph Dolomite 13/1500, were 26 psi & 30 psi for the front & rear tyres respectively; 4 psi more than for the slightly shorter and lighter-weight Triumph Toledo.

Knowing that increased tyre-inflation pressures confer more precise steering and reduced rolling resistance (i.e. reduce fuel consumption), but mindful of the uneven tyre wear associated with either under-inflation or over-inflation, I decided to try slightly increasing the inflation pressures of my Toledo’s front and rear 175 SR13, Kelly-Springfield tyres.

Not being as heavy as a Dolomite 13/1500, I opted for 24 psi & 28 psi for the front & rear tyres respectively. This certainly made the steering lighter and more responsive, but I didn’t run the car long enough with these increased inflation pressures, to discover whether they gave any statistically significant reduction in fuel consumption.

One undesirable side effect of increasing the inflation pressures, was that the car became noticeably skittish, when negotiating a particular bend (I rounded it twice a week for nearly 3½ years) whose road surface was uneven (i.e. bumps or corrugations), so I reverted to the original tyre-inflation pressures of 22 psi & 26 psi for the front & rear tyres respectively.

This skittishness was probably attributable to the increased vertical stiffness of the inflated tyres, which act as air-springs in series with the suspension’s helical coil springs, thus increasing the suspension’s overall stiffness. I also suspect that substituting ultra-low profile tyres such 185/55 R15, might similarly confer such skittishness, owing to the greater vertical stiffness of such tyres.

Each of the five 175 SR13 (aka 175/80 SR13) Kelly-Springfield Steelmark radial-ply tyres gave just over 35,000 miles of service during the period 1982 to 1987. Wherever possible, I have always tried to wear out a complete set of five tyres at approximately the same rate, by rotating the wheels around the car at each service interval.

Using tyre-inflation pressures (as indicated on the hand-held PCL pencil-gauge or foot-pump gauge) of 22 psi & 26 psi in front & rear tyres respectively, I observed no uneven tread-wear patterns which might otherwise have suggested over-inflation or under-inflation.

I was also running the front wheels at more negative camber than the factory-standard specifications, having completely removed the stacked pairs of camber-adjustment shims from between the front sub-frame and the upper portion of the front-suspension wishbone-brackets. Despite this, there was no indication of any noticeable tyre-shoulder wear.

I have also since become aware that increasing a tyre’s inflation-pressure decreases a tyre’s slip angle when subjected to a lateral force and vice versa. As a consequence of changing tyres’ slip angles, one can also change the degree of over-steer or under-steer characteristics. This is one reason why rear-engined, rear-wheel-drive vehicles have traditionally had substantially higher inflation-pressures in the rear tyres compared to those at the front, because decreasing a rear tyre’s slip angle relative to that at the front, reduces the tendency to over-steer.

At some time in the future, when I substitute 5½J x 15 inch MG Maestro aluminium-alloy wheels and either 185/65 R15, 185/60 R15 or 185/55 R15 radial-ply tyres on my 1974 Triumph Toledo 1300, I might need to reconsider what tyre inflation-pressures would be most appropriate!?!

Here's a test procedure I might try:

https://axleaddict.com/auto-repair/Chec ... ket-Wheels

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Nigel A. Skeet

Independent tutor of mathematics, physics, technology & engineering, for secondary, tertiary, further & higher education.

https://www.linkedin.com/profile/view?id=308177758

Upgraded 1974 Triumph Toledo 1300 (Toledo / Dolomite HL / Sprint hybrid)

Onetime member + magazine editor & technical editor of Volkswagen Type 2 Owners' Club


Last edited by naskeet on Fri Feb 15, 2019 4:41 pm, edited 2 times in total.

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 Post subject: Re: Tyre pressures
PostPosted: Wed Feb 13, 2019 6:18 pm 
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Quote:
Quote:
12psi front and rear on my Vindicator, because its near as dammit 100g per corner on Toyo T1Rs 195/50/15. i started out at 30psi all round and it handled like a very fast supermarket trolley
At 100 g (i.e. 0·1 kg) per corner, that must be a light-weight small-scale model, with VERY large wheels & tyres!?! :shock: :roll:
Helium filled tyres, great for increasing power to weight ratio.

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Vindicator Sprint, Honda Fireblade RRX 919cc, re-powered by AB Performance. Quick.
1995 Trusty Peugeot 306 XND, no turbine, 227K miles young.
1997 Trusty Peugeot 306 GLX TD, 90K miles and soon to ride again..
Alfa Romeo 147 1.9 JTD 150 Ti Lusso , no longer smoking.
Various other transient runners for selling.


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