Praga truck trial

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Rob Reznik
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Praga truck trial

Post by Rob Reznik » Mon Sep 07, 2009 12:43 pm

OK before anyone else mentions it I have others to finish but here goes.

The Praga is still located near Sleaford and yesterday we took the rear body off - looks like the whole thing has been rewired in the past at some expense but 99% of it will be ripped out as it is no longer required and could lead to other problems later on. It also looks as though it has been converted to negative earth at some stage as it should be Positive. Its located close to 'blacksmiff' and I'm going over for a day to work with him to separate and rejoin the two rear axles so that I can get some bigger aggresive Zil wheels and tyres on. Question here and bearing in mind it will be purely for trialing - do we reduce the number of springs as we will need to add a couple of very long ones on the bottom when the axles move apart? My thinking is that I want the axles to move easily so that the tyres are in contact with the ground more - fortunatly the Zil wheels PCDs are identical and better still the nut threads are also the same (John different to the Zetor) -the issue here was the Praga nuts were to small and would have nearly gone through the Zil wheel holes but now I can use the original Zil wheel nuts which are needed to locate the wheel - because the standard Praga front wheels are inset I dont think there will be a problem with tyres on full lock but I will probably need to cut the front wings and bumper back - sorry forgot to take photos - will also need bucket seats and harnesses if anyone has some spare? - there are solid straps reducing the drop on the axles - would they be OK removed? any advice would be appreciated.
Rob

Eastblock

Re: Praga truck trial

Post by Eastblock » Mon Sep 07, 2009 12:56 pm

If you make the springs longer but keep the number of leafs the same then they will be softer. Because you are running without a box this may not be a bad idea.

Wont the straps be there to protect the shocks from being ripped apart? IKBA applies.

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Re: Praga truck trial

Post by haymish » Mon Sep 07, 2009 5:00 pm

from memory of the one and only praga i have seen in the flesh-which was on a scottish estate-and all stripped down as if a trialer.it had only one set of shocks for the two back axles.they went right to the back of the chassis and were long reach things,not standard.it had no check straps-they were always standard on landrovers and they work fine without them.[it wasnt actually a trialer-it was for log hauling but didn't have the twin wheel set up anymore].definitely try and soften the back end for more traction[and as eastblock says -the lack of weight being carried.]

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Re: Praga truck trial

Post by Abrs » Mon Sep 07, 2009 5:21 pm

Good news on the wheel nuts then :wink:
will also need bucket seats and harnesses if anyone has some spare?
Never mind those; you're gonna need a roll cage first if you're planning to do any serious off roading :D , I don't think I would trust the flimsy standard pressed steel cab in a roll situation :? - you could end up with a flat head :lol:
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Ditch
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Re: Praga truck trial

Post by Ditch » Mon Sep 07, 2009 5:51 pm

What about those lovely comfortable Volvo seats I gave you. :)
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Eastblock

Re: Praga truck trial

Post by Eastblock » Mon Sep 07, 2009 6:00 pm

He's not THAT old! :mrgreen:

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Rob Reznik
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Re: Praga truck trial

Post by Rob Reznik » Mon Sep 07, 2009 6:39 pm

I need safety not falling asleep at the wheel :roll:

no shocks fitted and yes a roll cage is on the cards but will need to complete the rest of the mechanicals first
Rob

Eastblock

Re: Praga truck trial

Post by Eastblock » Mon Sep 07, 2009 6:44 pm

I'll get you one of those bead mats :wink:

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Re: Praga truck trial

Post by Ditch » Mon Sep 07, 2009 6:48 pm

Right Reznik! That's the last time I give you any of my unwanted, scrap, broken Volvo parts. Even if you beg me. :D
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Re: Praga truck trial

Post by Rob Reznik » Mon Sep 07, 2009 6:50 pm

:lol: :lol:
Rob

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Re: Praga truck trial

Post by Abrs » Tue Sep 08, 2009 12:35 pm

Sorry I forgot to say; I would imagine the straps are probably there to stop an axle dropping too far and over articulating the prop UJ's ?

Rob just a thought, I know you already have the Zil wheels but wouldn't it be better to find wider wheels/tyres that fit the Praga as it is, rather than having the hassle of cutting/welding props and link bars and then trying to find longer leaf springs to put in? - Just thinking that the wider wheels/tyres would also have an advantage over the Zil ones.


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Re: Praga truck trial

Post by haymish » Tue Sep 08, 2009 2:33 pm

oh abrs-you could create an argument that runs for an eternity :lol: wider small tyres over skinny taller ones.i've run both and for me tall and skinny are best offroad -better ground clearance but more importantly better bite from the tyres cos contact patch more concentrated.-the rally boys probably the best indicator of what is best-the worse the conditions the thinner the tyres they use :D
unless you are in a swamp :D

Eastblock

Re: Praga truck trial

Post by Eastblock » Tue Sep 08, 2009 3:07 pm

My Gaz69 on its very skinny tyres faired well in the mud of the forum meet.

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Re: Praga truck trial

Post by haymish » Tue Sep 08, 2009 3:19 pm

:D but of course they did cos only logical :lol:

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Re: Praga truck trial

Post by Abrs » Tue Sep 08, 2009 3:25 pm

haymish wrote:oh abrs-you could create an argument that runs for an eternity :lol: wider small tyres over skinny taller ones.i've run both and for me tall and skinny are best offroad -better ground clearance but more importantly better bite from the tyres cos contact patch more concentrated.-the rally boys probably the best indicator of what is best-the worse the conditions the thinner the tyres they use :D
unless you are in a swamp :D
:lol: - I think we are going to disagree again :D - No point having all that ground clearance if you are just going to sink straight up to your ass as soon as you go in the wet stuff :wink: - which constitutes most of the off road courses in the U.K. I think a wider tyre with an agri tread pattern is also going to give you the most traction - look at any modern agri vehicle and you will notice wide tyres are the norm, you will also notice some of the trials trucks are using agri tyres which offers them an obvious advantage over those without, the only disadvantage I can see with the smaller diameter tyre is that it may not overcome solid obstacles as easily i.e. rocks, but for more traction it's worth the trade off.

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Re: Praga truck trial

Post by haymish » Tue Sep 08, 2009 3:59 pm

:D no doubt agri pattern tyres get traction but i'd use a slim tall one not a fat low one-having spent countless hours watching idiots playing offroad and having recovered loads of them[in normal off road conditions-in reality not that deep mud rocks tree roots etc]its often the skinny tyred ones that make the most progress.and a relevant point for the praga-to run fatties effectively you need more bhp than if running skinny ones.i'd only go for fatties if on deep snow all the time or lived on melting permafrost.another down side to fatties is they float around more so steering much more of an issue.-its strange that most motorsport involving mud uses thin tyres :)
p.s in all seriousness two completely different philosophies at work here.an agri vehicle is designed to float over the top of the ground at reasoneably slow speeds-doing minimal damage,compression of the soil etc and has the right tyres for the job.an offroader be it truck or 4x4 couldn't give a monkeys about leaving a trail of destruction behind it and grip is the key.in the truck trials i have seen they dont float over the top of the mud-give it loud pedal till something solid is found and forward progress resumed-none that i have seen were wearing what i would call particularily fat tyres-agri tread good yes but tyre width depends on the application required

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Re: Praga truck trial

Post by Abrs » Tue Sep 08, 2009 9:00 pm

Sorry Haymish but I think your logic is a little flawed :wink: - agri tyres are usually of a floatation design which helps keep a vehicle from sinking like it would with a narrow tyre, they also have a self cleaning thin bar type tread which is very aggressive and bites into the ground, it offers the best traction you can get from a tyre (in most conditions) without using chains, lugs, bands etc. I do however agree that they require a little more hp to turn them but this is partially because you are getting better traction.

As far as speed is concerned, how fast is a trials truck going to go anyhow? Pretty slow most of the time I would think :shock: :lol:

Haymish I'm not trying to offend you here - in fact it's good conversing with someone on these issues without them throwing all the toys out of the pram :P
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Re: Praga truck trial

Post by haymish » Tue Sep 08, 2009 11:44 pm

have no arguements over the use of agri type tyres for grip but the argument that wider is better doesn't work for me.i've got basically agri tyyres on my gaz-just road legal :) -and they are brilliant off road-but i wouldn't expect more traction just by getting a wider fitment-nor would i want my gaz to float over mud if it had them.i want a tyre to bite through the slime to hit something more solid when i am offroad-the slimmer tyre has more grip and bite cos it has a smaller contact area whilst the big wide tyres spread the load more so its harder to get the tyres to bite.-watched a video of the paris dakar rally a bit ago-not one single vehicle had what i would call wide tyres.bikes,trucks,and cars all had slim tyres compared to what most people would expect.dune buggy's are the only competitive offroad motorsport that i can think off at the moment that wears wide rubber.rally cross,rallying,quad racing,4x4trialing,-never mind all the m'cycle assorted offroad antics where they all use slim tyres speedway ,trials,motocross,enduro etc.
if you need to float they are brilliant-used an ex mod landrover on morecambe bay with nearly 21/2 foot wide tyres and was astonished where it could get to but it would be horrible to drive round my local offroad extreme route[it steered like a drunken barge ]cos it slide allover the place on side slopes cos just too much rubber to bite through the slime-but awesome on soft sand :D [but lr definitely bit underpowered with them on]-find me a video of a truck trial with a truck using big tyres floating instead of applying the loud pedal to cut through the slime and get traction that way and i'll be amazed.-and if you can i'll be surprised if same truck on a sideslope isn't going sideways instead of where its pointing. :D -as said at beginning love agri tyres offroad just not tooooooobig please cos then the advantage receedingp.s. not all tractor tyres flotation :D just found a vid of yanks swamp racing on tractor tyre about 5 inches wide and 6 foot tall with insane v8's :shock:[i rekon about 14 inches wide enough for most medium sized trucks and going up to about 18 max for something like your tonka toy to get the best out of it offroad haymish

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Re: Praga truck trial

Post by Abrs » Wed Sep 09, 2009 12:35 am

I didn't mean massivly wide tyres - just an inch or two wider than a Zil tyre, by all means though if the tyres are too wide for the vehicle; as they are on many modified 4x4s then they can't make proper use of them due to the vehicle being too light - however agri tyres are a little different in this respect, they are wide but have a relatively thin section of tread which is pressed into the earth which acts like a lug - you can tell this design works very efficiently by the amount of earth one of these tyres can dig up when it is in a wheel spin situation - they don't just slip on the surface like the design of tyre you normally find on our trucks. the agri tyres are wide but they concentrate most of the weight onto the thin tread giving unparalleled traction - i.e. tractor tyres are designed for a vehicle which is expected to haul heavy equipment across rough and sometimes boggy ground so maximum traction/floatation is required from the tyres for these tasks.

find me a video of a truck trial with a truck using big tyres floating instead of applying the loud pedal to cut through the slime and get traction that way and i'll be amazed
The gauntlet has been laid and the challenge has been answered :lol:

[youtube]http://www.youtube.com/watch?v=a6_5KxeVEr0[/youtube]

[youtube]http://www.youtube.com/watch?v=uIwPoSR9u5E[/youtube]

Just let me know when you are ready to admit defeat :D
“There is something fascinating about science. One gets such wholesale returns of conjecture out of such a trifling investment of fact.”

Mark Twain

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Re: Praga truck trial

Post by haymish » Wed Sep 09, 2009 12:51 am

the first video had me dying laughing-now who mentioned falling off sideslopes :lol: that red truck impressive-but those tyres within my limits of sensible tyres-not wide boys.that first truck left me speechless.i didn't know if i should admire his courage or condon his stupidity-it was magic to watch :D