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Thread: Trials Marlins

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  1. #21 Re: Trials Marlins 
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    Its 35psi, I've copied the following from the Regs

    Tyre Pressures for all classes 1–6 cars will be 25PSI / class 7 will be 35psi

    I'd agree 35psi is high for road use on a lightweight car like the Marlin, but its that high on the trial to handicap it against the other classes apparently according to the organiser. The car was advertised as having had a 12V socket installed specifically for inflating purposes, but I think "proper trialists" very often use compressed air cylinders. I was intending to inflate to 35psi once I'd driven there.

    And the event is supposed to be a very gentle introduction to trialing - hence the higher tyre pressures than those quoted by Mark

    I'll certainly feedback how it goes.

    To Liz's point, what are the recommended road tyre pressures for a SWB Roadster. I used to run a Caterham 1600VX at the recommended 20psi but they are quite a bit wider and I can't remember what I ran my Pilgrim Bulldog mk3 at 30 years ago (that's the last Marina based car I drove!)
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  2. #22 Re: Trials Marlins 
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    We use a 12v compressor on our marlin .Cars like the Austin 7s use compressed air .Once again good luck and enjoy your trial
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  3. #23 Re: Trials Marlins 
    frequent forum contributor Club Member David's Avatar
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    Quote Originally Posted by acbluemarlin View Post

    To Liz's point, what are the recommended road tyre pressures for a SWB Roadster. I used to run a Caterham 1600VX at the recommended 20psi but they are quite a bit wider and I can't remember what I ran my Pilgrim Bulldog mk3 at 30 years ago (that's the last Marina based car I drove!)
    I use 20psi as do a fair few others, so I suppose experiment around that to see what works best for your car, wheel and tyre combination.
    - 9th Custodian of JRR 929D, the Triumph Vitesse based special Paul Moorehouse built prior to the Triumph based Roadster kits.
    - 8th owner of Roadster chassis number 2395. Kit manufactured 1983, first registered in 1987. Now owned by Barry!
    - Builder of chassis number 2325 (PKK 989M) in the mid 80's. Now owned by Eric & Lynne in the NE of England.
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  4. #24 Re: Trials Marlins 
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    Depending on age and make of tyres around 18 -20psi, I found 22psi was too high when cornering. Liz
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  5. #25 Re: Trials Marlins 
    frequent forum contributor Club Member Alan c's Avatar
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    This is how you wor it out for caravans - whe I get time will see what marlin number is

    You first need to be able to decipher the code on the tyre wall… this is a typical code:
    205 / 65 R 15 94 H
    The first part of the number is the tread width, in this case 205 mm wide. The second number is the Aspect Ratio which means in this case the tyre wall height is 65% of the width of the tread. The next letter “R” is the construction, in this case Radial, the following number “15” is the rim diameter (in inches). The next number “94” is the load rating – more of this in a moment and finally the last letter “H” is the speed rating for the tyre.Load RatingThe load rating for the tyre can range from 60 to 130 which equates to a maximum load per tyre of between 250 Kgs to 1900 Kgs. The first thing to check is the tyres are rated for the MTPLM of your caravan, so we need to know the load index ratings.From the table above, you will be able to cross reference the load rating code number to the actual maximum permissible load the tyre is rated for. So in our tyre data example from above, we can see that a load index of “94” means the maximum load for the tyre is 670 Kg’s. Remember that is the load for ONE TYRE… so on a single axle those two tyres could carry a maximum load of 1340 Kg’s. The recommendation from the tyre industry though is you should never exceed 90% of the tyre’s load index, so in this case the maximum axle weight would be 1251 Kg’sThe other bit of information we need to know from the tyre is the Maximum Tyre Inflation Pressure and Load. This is usually located on the side wall below the tyre data in smaller text. It will say something like “MAXIMUM LOAD 720 Kg’s MAXIMUM PRESSURE 52 PSI” it might have the pressure given in Bar.Once you have the MTPLM of your caravan and the maximum pressure for your tyre we can now work out the correct tyre pressure.Take the figure for the maximum pressure for the tyre and divide it by the maximum weight from the table above. Now multiply this figure by the actual load you are going to put on the tyre – so half the MTPLM for a single axle caravan or a quarter of the MTPLM for a twin axle caravan. The resulting figure should be the correct inflation pressure for each tyre.Lets look at an example for a single axle caravan:Tyre Details: 205 / 65 R 15 94 H – Maximum Inflation Pressure 60 PSIWeight of caravan: 1200 Kg’s
    60 / 670 = 0.08955 (Max Pressure for tyre divided by load rating)0.08955 x (1200 / 2) = 53.7 PSI (inflation factor times half the weight of the caravan)
    So the correct tyre pressure is 54 PSIWorking out for a twin axle caravan:Tyre Details: 205 / 65 R 15 94 H – Maximum Inflation Pressure 60 PSI
    Weight of caravan: 1800 Kg’s
    60 / 670 = 0.08955 (Max Pressure for tyre divided by load rating)0.08955 x (1800 / 4) = 40.29 PSI (inflation factor times one-quarter of the weight of the caravan)
    So the correct tyre pressure is 41 PSI
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  6. #26 Re: Trials Marlins 
    frequent forum contributor Club Member stevejgreen's Avatar
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    Quote Originally Posted by Alan c View Post
    This is how you wor it out for caravans - whe I get time will see what marlin number is

    You first need to be able to decipher the code on the tyre wall… this is a typical code:
    205 / 65 R 15 94 H
    The first part of the number is the tread width, in this case 205 mm wide. The second number is the Aspect Ratio which means in this case the tyre wall height is 65% of the width of the tread. The next letter “R” is the construction, in this case Radial, the following number “15” is the rim diameter (in inches). The next number “94” is the load rating – more of this in a moment and finally the last letter “H” is the speed rating for the tyre.Load RatingThe load rating for the tyre can range from 60 to 130 which equates to a maximum load per tyre of between 250 Kgs to 1900 Kgs. The first thing to check is the tyres are rated for the MTPLM of your caravan, so we need to know the load index ratings.From the table above, you will be able to cross reference the load rating code number to the actual maximum permissible load the tyre is rated for. So in our tyre data example from above, we can see that a load index of “94” means the maximum load for the tyre is 670 Kg’s. Remember that is the load for ONE TYRE… so on a single axle those two tyres could carry a maximum load of 1340 Kg’s. The recommendation from the tyre industry though is you should never exceed 90% of the tyre’s load index, so in this case the maximum axle weight would be 1251 Kg’sThe other bit of information we need to know from the tyre is the Maximum Tyre Inflation Pressure and Load. This is usually located on the side wall below the tyre data in smaller text. It will say something like “MAXIMUM LOAD 720 Kg’s MAXIMUM PRESSURE 52 PSI” it might have the pressure given in Bar.Once you have the MTPLM of your caravan and the maximum pressure for your tyre we can now work out the correct tyre pressure.Take the figure for the maximum pressure for the tyre and divide it by the maximum weight from the table above. Now multiply this figure by the actual load you are going to put on the tyre – so half the MTPLM for a single axle caravan or a quarter of the MTPLM for a twin axle caravan. The resulting figure should be the correct inflation pressure for each tyre.Lets look at an example for a single axle caravan:Tyre Details: 205 / 65 R 15 94 H – Maximum Inflation Pressure 60 PSIWeight of caravan: 1200 Kg’s
    60 / 670 = 0.08955 (Max Pressure for tyre divided by load rating)0.08955 x (1200 / 2) = 53.7 PSI (inflation factor times half the weight of the caravan)
    So the correct tyre pressure is 54 PSIWorking out for a twin axle caravan:Tyre Details: 205 / 65 R 15 94 H – Maximum Inflation Pressure 60 PSI
    Weight of caravan: 1800 Kg’s
    60 / 670 = 0.08955 (Max Pressure for tyre divided by load rating)0.08955 x (1800 / 4) = 40.29 PSI (inflation factor times one-quarter of the weight of the caravan.
    So the correct tyre pressure is 41 PSI

    Interesting chart and calculation, but theory and practice don’t always match.

    In reality, the handling characteristics and suspension of a road going Roadster is more to do with the deflection of a tyres sidewall, primarily because the torsion bars and leaf springs are designed for a Marina weight distribution, where the weight of the engine is essentially directly above the front axle, and the rear axle, immediately behind the drivers seat.
    There was no change in spring rates when crossply were phased out to the far more complient radial tyres.

    Consequently preferred tyre pressures for street use are more a function of the tyres sidewall flexibility and the enthusiasm of the driver.

    It would be more interesting to find the lowest reccomended tyre pressure for a given profile, I dare say that every manufacturer would have a slightly different idea as to what that might be.
    MOC member since 05/97
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    The reasonable man adapts himself to the world; the unreasonable one persists in trying to adapt the world to himself. Therefore all progress depends on the unreasonable man.

    Loads of Marlin Reference can be found documents here or there.
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  7. #27 Re: Trials Marlins 
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    It’s still unusual for trial to run such high psi they normally let the class 1-6 run 2 or 3 psi lower than the class 7-8s
    I don’t know what your regs say but we must have two throttle return springs fitted plus a spare in the car and spill kit
    And fire extinguisher min 1.5kg
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  8. #28 Re: Trials Marlins 
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    The trial is off unfortunately - the farmer who owns the site says its too wet
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  9. #29 Re: Trials Marlins 
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    That’s a pity we had the same problem at the start of the year with snow then later rain better luck next time
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  10. #30 Re: Trials Marlins 
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    A few comments.
    Long wheel base Marlins do compete successfully in trials. Murray Montgomery-Smith being a very successful exponent.
    35psi seems a punitive handicap and one I have yet to encounter on any of the trials I have competed in.
    If you fancy a really good days trialling you could try the Northern Classic trial http://www.fellsideac.co.uk/ the event is 23rd February. The competitors and officials are all friendly and keen to help novices. It’s an easy run up the M6 from Chester.
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