Munchkin:
I can’t say to much about this due to the government secrets act… but I was delivering to a secure military installation, it can’t say anything about the load but it did have a yellow glow. When I got there the security guards couldn’t check my background as my identity had to be protected due to my SAS history. The Sargent came along and waved me threw as i had more security clearence than him… anyway I got to the office and walked in on two female officers lessing off. They panicked when I caught them and let me join in so I would keep there secret.
True story
Hah, if you hadn’t spelt sargeant wrongly you’d have had us there!
I did record it on my mobile, but that night half a dozen balaclava wearing men rappeld threw my bedroom window and deleted it.
Evil8Beezle:
I’m young in the game, and I’ve obviously got a lot of bollox to yet hear, but I wondered if people would like to give their experiences of the ultimate load or rollox they’ve been told by another driver… The spark of this thread came a little while back when another driver said, he really liked the 26t rigid with a tag he was driving, as with them, if you drop the tag during overtaking, you can get a couple more K’s out of em!
I just agreed with him!
It’s certainly plausible. Putting the tag axle down would reduce the weight on the drive axle. As a result, the tyre on the drive axle would deform less as it rotates, and therefore have a larger effective rolling diameter, resulting in a larger effective rolling circumference. So, for each revolution of the wheel, you cover slightly more distance. The tacho (and limiter) would still think you were travelling at the same speed as the axle is still rotating at the same rate (so it wouldn’t show up on the speedo), but your actual road speed is slightly higher.
Now, whether this effect is large enough to make an appreciable difference, I don’t know…
Maybe I`m biting at a dangling line & hook here, but,
Yes with less load the distance from wheel center to road surface will be increased, but due to smaller footprint, (less tread on road ) any section of tyre will be on the road a shorter time. So to get past all the complicated maths etc just think that:
The circumference of the tyre stays (effectively) the same, independent of loading. The speedo reads the number of revs of the prop shaft. So wheel load etc won`t make any difference.
Evil8Beezle:
I’m young in the game, and I’ve obviously got a lot of bollox to yet hear, but I wondered if people would like to give their experiences of the ultimate load or rollox they’ve been told by another driver… The spark of this thread came a little while back when another driver said, he really liked the 26t rigid with a tag he was driving, as with them, if you drop the tag during overtaking, you can get a couple more K’s out of em!
I just agreed with him!
It’s certainly plausible. Putting the tag axle down would reduce the weight on the drive axle. As a result, the tyre on the drive axle would deform less as it rotates, and therefore have a larger effective rolling diameter, resulting in a larger effective rolling circumference. So, for each revolution of the wheel, you cover slightly more distance. The tacho (and limiter) would still think you were travelling at the same speed as the axle is still rotating at the same rate (so it wouldn’t show up on the speedo), but your actual road speed is slightly higher.
Now, whether this effect is large enough to make an appreciable difference, I don’t know…
Maybe I`m biting at a dangling line & hook here, but,
Yes with less load the distance from wheel center to road surface will be increased, but due to smaller footprint, (less tread on road ) any section of tyre will be on the road a shorter time. So to get past all the complicated maths etc just think that:
The circumference of the tyre stays (effectively) the same, independent of loading. The speedo reads the number of revs of the prop shaft. So wheel load etc won`t make any difference.
No, I think you’ll find that the effective diameter is indeed reduced when heavily loaded (and increased if you reduce the load). Not by much though, and the speedo would continue to show exactly the same speed.
Evil8Beezle:
I’m young in the game, and I’ve obviously got a lot of bollox to yet hear, but I wondered if people would like to give their experiences of the ultimate load or rollox they’ve been told by another driver… The spark of this thread came a little while back when another driver said, he really liked the 26t rigid with a tag he was driving, as with them, if you drop the tag during overtaking, you can get a couple more K’s out of em!
I just agreed with him!
It’s certainly plausible. Putting the tag axle down would reduce the weight on the drive axle. As a result, the tyre on the drive axle would deform less as it rotates, and therefore have a larger effective rolling diameter, resulting in a larger effective rolling circumference. So, for each revolution of the wheel, you cover slightly more distance. The tacho (and limiter) would still think you were travelling at the same speed as the axle is still rotating at the same rate (so it wouldn’t show up on the speedo), but your actual road speed is slightly higher.
Now, whether this effect is large enough to make an appreciable difference, I don’t know…
Maybe I`m biting at a dangling line & hook here, but,
Yes with less load the distance from wheel center to road surface will be increased, but due to smaller footprint, (less tread on road ) any section of tyre will be on the road a shorter time. So to get past all the complicated maths etc just think that:
The circumference of the tyre stays (effectively) the same, independent of loading. The speedo reads the number of revs of the prop shaft. So wheel load etc won`t make any difference.
No, I think you’ll find that the effective diameter is indeed reduced when heavily loaded (and increased if you reduce the load). Not by much though, and the speedo would continue to show exactly the same speed.
We are also assuming that you are able to drop the tag while on the limiter!
I don’t know for sure (as I’ve never tried) but I didn’t think it operated at high speed.
OK. Ignore the tag axle bit. Some of you are saying that because of tyre distortion, a loaded truck will be slower than an empty one, due to the effective diameter being reduced? Try it with your speed display on sat-navs compared to speedo readings m/t and loaded. Sorted.
Franglais:
OK. Ignore the tag axle bit. Some of you are saying that because of tyre distortion, a loaded truck will be slower than an empty one, due to the effective diameter being reduced? Try it with your speed display on sat-navs compared to speedo readings m/t and loaded. Sorted.
I have - I see about 1mph higher speed on the satnag when empty, which is pretty much what I’d expect if the effective diameter of the tyre was increased by an inch or so.
Franglais:
OK. Ignore the tag axle bit. Some of you are saying that because of tyre distortion, a loaded truck will be slower than an empty one, due to the effective diameter being reduced? Try it with your speed display on sat-navs compared to speedo readings m/t and loaded. Sorted.
I have - I see about 1mph higher speed on the satnag when empty, which is pretty much what I’d expect if the effective diameter of the tyre was increased by an inch or so.
could even be a little more than that although I suspect an inch of flattening with load would be excessive.
295/80R22.5 would have a radius of 20.5inches, so if that was reduced by an inch with load, then that would represent a 4.9% change, so at 50mph the speedo could read 52.5mph, Although I suspect it will be more complex than that, as at 50mph the centrifugal forces within the tyre will tend to increase its diameter.
Roymondo:
I was talking about reducing effective diameter by an inch - not the radius…
as the turning point of the wheel would no longer be in the centre of the tyre, I suspect the relevant figure would be the distance between the centre of the rim and the ground, and that is why I would calculate the percentage change from the reduced radius.
billybigrig:
“Everyone give me a fiver and I’ll sort out all your work problems”
Narh…give me a fiver and you can join my gang… not gonna tell you what I’m using the fiver for,direction of the gang… if you get arsey then I’ll spit my dummy out…
The-Snowman:
About 8 posts there took on a sort of “carryfast” feel
Nope, not verbose enough!
Sparked my interest seeing the words ‘inch’ and ‘rim’ in the same post but lost it when I realised its about speed weight differential due to a circumference distortion calculation. Think we all know its some form of magic anyway that fluctuates slightly due to the earths gravitational pull and stuff…
This reminds me, I was talking to an agency driver in an rdc waiting room just last week who was telling me about the newest vosa ploy to get money off us so from next year on the gantrys on the m25 will be able to remotely download the tachos of hgvs as they pass under and then a fine will be sent to the vehicle owner for any infringement(s) how stupid are some people!!
raymundo:
I heard to counteract this all you need to do is line out the complete cab with lead and have a couple of CD’s in the windscreen (behind the lead)
You’ve been talking to the moaster again haven’t you?
so from next year on the gantrys on the m25 will be able to remotely download the tachos of hgvs as they pass under and then a fine will be sent to the vehicle owner for any infringement(s)