Scammell Explorer fixes and workarounds

[antarmike]

Ha, think I see a flaw in all this. Now most of us run on bargrip, trackgrip or other cross country type tyres. They are not flat across the tread, so circumference is measured around the centre ( mould line ), OK all well and good, but.....because of the heavily radiused profiles, when running at lower pressures you get the outer flanks of the tread profile in contact with the road, when this happens, the centre of the tread actually inverts as sidewalls bulge out, therefore the maximum circumference is reducing to the smaller circumference of the outside of the treads.

 

No matter how much theory and calculations you can come up with, there is nothing better than practise to prove a point.

 

:yawn:

 

Exept the radials I am familiar with are Michelin XL/ XCL and these are not half as rounded as Bargrips. They are really pretty flat across the width of he tread, but I am into a virtual ale now, and am starting to loose the plot!!!

Edited March 14, 2010 by antarmike

[Richard Farrant]

Exept the radials I am familiar with arew Michelin XL/ XCL and these are not half as rounded as Bargrips. They are really pretty flat across the width of he tread, but I am into a virtual ale now, and am strting to loose the plot!!!

 

 

Oh I was going on cross plys, hence ref. to bargrips and trackgrips..........anyway getting tyred ( :sleep:) of the subject now, so might join you with a virtual whisky :beer:

[abn deuce]

Anyone tending bar now ? I d like a cherry cola [_]) in my mug .

[N.O.S.]

I didn't stay long abn - the beer was FLAT and the barman was dressed in rubber. Not my scene.

[antarmike]

One last thought, 15.00 radials can give almost the same speedo reading as 14.00 crossplies if the radials are Michelin Pilot's these tyres , unlike XC/ XCL have an 80/85 % aspect ratio (can't remember the exact figure,but at the ratio they are the circumference is actually a pretty close match to 14.00 crossplies. I concidered buying some that came up at a good price,and I checked their size against 14.00's

Edited March 14, 2010 by antarmike

[Steifbear]

it is my understanding that the circumference of a tyre does not change if you let them down. Is this what the general answer is?

 

Pete Stevens

 

P.s went to Sainsbury's Last night in the Explorer vid's to come

[gritineye]

Mike, often bad maths can appear to be quite inflexible, unlike rubber which can tolerate a fair amount of wind-up...

 

http://www.tut.fi/plastics/vert/11_t...ling_input.htm

 

http://www.tut.fi/plastics/vert/11_tyre_as_car_component/handling_input_rolling_radius.htm

[antarmike]

it is my understanding that the circumference of a tyre does not change if you let them down. Is this what the general answer is?

 

Pete Stevens

 

P.s went to Sainsbury's Last night in the Explorer vid's to come

 

For all practical purposes, yes. (i think so, still get a virtual hangover!)

[gritineye]

You have missed what I am trying to say, Artificially altering the rolling radius by letting air out of the tyre will not alter the speedo reading of a 1500 tyre. If the same tyre is properly inflated or deliberately under inflated, the ride height will alter, (and the rolling radius) but for that size tyre the Speedo reads will stay the same.

 

Read on..

 

 

For all practical purposes, yes. (i think so, still get a virtual hangover!)

 

But totally irrelevant when it comes to the question of rolling radius, which you still say does not affect the speedo reading:

The detection of an underinflated tire is based on the detection of an increase in speed of the wheel carrying that underinflated tire, considering that when the tire is underinflated it will have a smaller rolling radius and will therefore rotate faster than a wheel with a normally inflated tire. In the following specification the term "rolling radius" means the distance between the wheel support surface and the wheel axis of rotation. The term "rolling circumference" is the effective tire circumference related to the rolling radius. The detection system must be quite sensitive considering that most modern high capacity aircraft are equipped with landing gear structures which involve a multiplicity of inflated tires arranged in sets or "bogies" associated with different ones of several main struts, and these sets include side-by-side pairs of tires. The difference in rolling radius of the underinflated tire then will be affected by the fact that a substantial portion of the load is carried by the adjacent tire.[quoute]

 

http://www.freepatentsonline.com/4224597.html

 

As the links I posted earlier show, there are many references to this effect written by learned and respected engineers and designers, I only chose this last quote from the many because it was the easiest for a layman to understand.

 

The fact that the speedo reading hadn't changed should alert one to consider how this came about, if your theory was correct then the reading would have changed. Strangely, you seem to have disregarded this anomaly,

[antarmike]

Read on..

 

 

 

But totally irrelevant when it comes to the question of rolling radius, which you still say does not affect the speedo reading:

The detection of an underinflated tire is based on the detection of an increase in speed of the wheel carrying that underinflated tire, considering that when the tire is underinflated it will have a smaller rolling radius and will therefore rotate faster than a wheel with a normally inflated tire. In the following specification the term "rolling radius" means the distance between the wheel support surface and the wheel axis of rotation. The term "rolling circumference" is the effective tire circumference related to the rolling radius. The detection system must be quite sensitive considering that most modern high capacity aircraft are equipped with landing gear structures which involve a multiplicity of inflated tires arranged in sets or "bogies" associated with different ones of several main struts, and these sets include side-by-side pairs of tires. The difference in rolling radius of the underinflated tire then will be affected by the fact that a substantial portion of the load is carried by the adjacent tire.[quoute]

 

http://www.freepatentsonline.com/4224597.html

 

As the links I posted earlier show, there are many references to this effect written by learned and respected engineers and designers, I only chose this last quote from the many because it was the easiest for a layman to understand.

 

The fact that the speedo reading hadn't changed should alert one to consider how this came about, if your theory was correct then the reading would have changed. Strangely, you seem to have disregarded this anomaly,

 

I have never known a sixty year old speedo where you can gat an accurate enough reading to know whether it has changed or not.

 

The quote you have given above is in direct contradiction you an earlier post. Previously you have put a link on the board that says that the wheel rolls around a point below the surface of the road, and that the rolling radius is therefore greater than the distance from road to hub. The quote above equates the rolling radius to the distance from ground to hub.

 

Clealy one of you learned sources has got something wrong!

 

And as I understand it the 15.00 tyres are actually correctly inflated, as were the 14.00. It has been suggested that even when correctly inflated the side walls deflect more on a radial than a crossply. ( I am not sure that is so).

 

So if we have a fully inflated 15.00 and compare it to a fully inflated 14.00 are you suggesting that the sidewalls deflect so far as to bring the two tyres to the same rolling radius. As I say the 14.00 radials I have on my Matador lift the axles to the same height as the 14.00 Crossplies on my Douglas.

 

If we concider what is actually happening, not theoretical stuff, if as you say side wall flex on radials is significantly greater, why do I get the same ride height?

 

Also I know the radials on the Mat are vitually the same size as the cross plies on the Douglas, yet the Douglas speedo shows 29MPH at max governed speed. The Matador on the radials shows 33-34 MPH at the same governed speed.

 

Which is why I say don't believe what the speedo is telling you. The "Radials side wall flex significantly more than the Cross ply" theory would dictate the Douglas went faster, but according to the Speedo the Matador is faster on the flat.

 

The original post that started this discussion said that the speedo remains accurate despite the change in tyre size. It is not recorded how that was determined. Was the Explorer followed by a car?, was the time taken over a given distanceand this time used as a basis for working out speed, (such as kilometer posts on a motorway or over a measured mile of a Police Vascar speed trap.) I know that having used a Tom Tom in various cars and vans that in none of them has the speed given by the SatNav matched the indicated speed on the Speedo. Was the speed of the Explorer on both sets of tyres taken from a Sat Nav, in the Explorer? Until we have some way of determining the accuracy or otherwise of the claims that "speedo remained accurate" after tyre size change, this whole discussion is rather pointless, if everthing is based on "it must be true because that is what a speedo says.

Edited March 14, 2010 by antarmike

[antarmike]

Got the brake shoes drilled and rivetted on for the last rear bogey wheel station. The end casing went on this morning, and the new hub oil seals are in place. At present waiting for paint to dry. The good news if I don't say it is the drum from this station was complely soaked in oil from the leaking fulcrum pin, so hasn't got the bad pitting that forced me to bore out the last two drums I looked at.

 

I view this week-end as good progress.

[gritineye]

Forceful has new boots! New 12 plies, tubes and flaps, in place of the old and stiff 18 ply ones, saving 150 kg and improving the ride and reducing the noise beyond all recognition. :yay:

 

No more bouncing along for the first few miles waiting for the flat spots to go away either, smooth as silk.:drive:

[N.O.S.]

I can see the mileage going up a fair bit this year!! :cool2: Makes Forceful look almost........new!

[younggun]

u have been busy bernard i like the new boots how did the job go ???

 

nick

Edited April 3, 2010 by younggun

[gritineye]

I can see the mileage going up a fair bit this year!! :cool2: Makes Forceful look almost........new!

 

And the fuel usage going down!

 

u have been buesy bernard i like the new boots how did the job go ???

 

nick

 

Easy Peezy with my new air bead breaker, tyre inflator and air wrench, even with lots of flakey rust in them, just a few minutes to remove each tyre. You can see the shiney marks bottom right where the tyre was pushed off.

 

Made it a one man job, not like the last time I had a flat, three of us ended up cream crackered.

 

Haven't got a needle gun so used an SDS drill with a blunt chisel in it, worked for me! Not much pitting, despite what it looks like.

[Steifbear]

Are they 1400 or 1500? They look awesome.

[gritineye]

Are they 1400 or 1500? They look awesome.

 

1400s, but quite a bit taller, the shoulders are more rounded than the old ones, probably helps the ride and steering feel as they run on about 2/3 of the tread, which means they might not scollop out so much.

 

The chassis is level with the concrete here but the walking beam is sloping which sort of exaggerates the difference between old and new a bit.

 

Don't mention the rolling radius.......

[NickAbbott]

Where did you get the 1400 tyres from, as I'm after 5 new or good 1400 x 20 tyres for my Matador?

[gritineye]

Where did you get the 1400 tyres from, as I'm after 5 new or good 1400 x 20 tyres for my Matador?

 

I bought them from a dealer at Beltring a couple of years ago, I think they came via Germany, not sure though.

[radiomike7]

Bad news Bernard, the deal you struck has broken the camel's back and your warrantee has just evaporated::shocked:

 

Denman Tire LLC has filed for Chapter 7 bankruptcy, and will liquidate due to poor economic conditions, particularly in the automotive sector. The move will put some 260 employees out of work. Since November, more than 250 workers have already been laid off at the US company.

 

Denman tried but failed to find a buyer who could reopen the plant or secure help from the government. As a result, Sanford Pensler, Denman Tire CEO, began Chapter 7 proceedings.

 

The company said in its bankruptcy filing that on 31 March it will provide the court with a list of its creditors.

[N.O.S.]

:rotfl: These are U.S. pattern tyres - quite a few suppliers, just look at any REO for a nice selection of brand names. So any major ex. military Reo stockist should be able to supply them, though 14.00s will be not as easy as 12.00s. I might be after some more 12.00s myself.

[antarmike]

:rotfl: These are U.S. pattern tyres - quite a few suppliers, just look at any REO for a nice selection of brand names. So any major ex. military Reo stockist should be able to supply them, though 14.00s will be not as easy as 12.00s. I might be after some more 12.00s myself.

 

I have one oddball American Bridgestone 14.00 that is to big to go on Andi's scammell. It is partworn but a bit scabby, but still has life in it, epescially as a spare, anyone interested?

[gritineye]

Bad news Bernard, the deal you struck has broken the camel's back and your warrantee has just evaporated:

 

Just like Sainsburys, as soon as you find something nice they stop selling it...........or is it just me?

[radiomike7]

Just like Sainsburys, as soon as you find something nice they stop selling it...........or is it just me?

 

No, it is the same with all the major supermarkets. A supplier will come up with a new product which is trialed for a short period after which the bean counters get involved to maximise the profits. This results in either a lower quality/quantity product or removal of the product in cases where the supplier cannot produce at the price level demanded. I see it all the time as I am involved with supplier collections for a large chain.

[AndyFowler]

Looking good Bernard ! Lot to be said for retirement ! Look forward to seeing you both out and about this year ! Happy Scammelling mate !