Yes I concede I mean the rolling diameter not the resistance
Bluey Circles:
the tread depth does not explain it to me.
315/80 - 22.5 tyre will have a radius of 538mm
increase speed 56 to 60 = a 7.1% increase
to achieve this through tread depth alone would need a depth of 38mm (is that posible even with a regroove ?)
Tyre sizes are an approximation to the nearest generic size, much like bhp. A 500 Volvo is actually a 496. The same with tyres, hence some being bigger than others. It’s the reason continental do Porsche, Audi and Mercedes only fitment tyres, as these tyres have been made to the exact measurements of said manufacturers rim sizes, although they are badged with the generic sizes. If you get a brand new conti, and a brand new bridgestone, mark the tread and roll them one revolution, you’d be surprised at the difference
OVLOV JAY:
Bluey Circles:
the tread depth does not explain it to me.
315/80 - 22.5 tyre will have a radius of 538mm
increase speed 56 to 60 = a 7.1% increase
to achieve this through tread depth alone would need a depth of 38mm (is that posible even with a regroove ?)Tyre sizes are an approximation to the nearest generic size, much like bhp. A 500 Volvo is actually a 496. The same with tyres, hence some being bigger than others. It’s the reason continental do Porsche, Audi and Mercedes only fitment tyres, as these tyres have been made to the exact measurements of said manufacturers rim sizes, although they are badged with the generic sizes. If you get a brand new conti, and a brand new bridgestone, mark the tread and roll them one revolution, you’d be surprised at the difference
No, the rims are made to the size specified (a 22.5" rim is a 22.5" rim regardless of who made it). The reasons for marque-specific car tyre fitments have nothing to do with rim sizes.
Well I’ll go back to ats and ask the manager why he refused to take my money, as he gave that reason why he wouldn’t put an Audi only tyre on my st, even though they’re the same tyres apart from the AO marking
Got overtaken recently on the '25 by a Daf 18t box on an 11 plate - he was easily cruising at a steady 65 mph no problem - anybody else seen it around - white with a roller shuttter door.
OVLOV JAY:
They set the k factor to the rolling resistance of the tyre, i.e.the amount of tread. To save time and measurements, the dealers have the measurements to hand for all the tyres. Some dealers just limit all to the lowest, some blanket to the highest and some bang in the middle. Upshot being some do 52, some do 60 and most do 55 in the middle ish. I’ve noticed crossroads set everything for the lowest amount of tread, as most brand new ones come out doing 60, while mc truck seem to set the highest, as all ours seem to do 53 on bridgestones, but the msc ones on contis do 55/56. Mercedes and man seem do be the only ones that set them up properly, as they all seem to be bang on 56. Volvo scania and daf seem to take the lazy route
I think you don’t fully understand tacho calibration
To get the L factor which is the rolling circumference of the tyre, now dealers do not have measurements to hand ,as how would we know how worn the tyre is ■■? The L is calculated on the rolling road ,that is why you will see the reflective tape on the tyre after a calibration…So I’m sat in the cab with the calibration tool plugged in to the tacho head ,There are generally 2 types of rolling road ones that require you to drive at 50kph ,and the style we use which you can drive at 5kph but measure over a distance ,So as I’m doing my 5kph the reflective tape passes a sensor the measure the circumference of the tyre and after the preset time the tyre measurement appears on the calibraton tool,it then finds the W and K factor which on a digi are the same ,it then puts the W / K factor on the screen .When you stop it sends the new details to the tacho…The only input I have is pressing the throttle …Yes it is possible to manually change the K/W factors …I cant speak for others ,but I would never mess with a tacho for a stranger or anyone for that matter ,why drop myself in the ■■■■ …At the end of the calibraton you have to do a speed for speed check at 50 kph So when the calibration tool say I’m doing 50 kph ,then that is what hopefully be on the tacho head .Tolrance for a INSTALLED digi that is in use …ie carrying out a post installation speed for speed check you are allowed +/- 6km/h…Which is where people will manually alter the K/W to take advantage of the tolerance …The only reason the tolerance exists on digis ,is that it was part of the analogue calibration and they had to allow it on digis
When I limped in and out of probably all the Renault Premium’s at my old firm, I found that they varied between 53 and 58 according my my SatNav. All were obviously serviced and calibrated at the same place…
Maybe my post wasn’t clear, I didn’t mean tyre measurements to hand in that way, I meant they physically had it to hand as in the tyre is in front of them. And you’ve agreed with my point that some go over and some go under, ie the tolerance
The AO marking doesn’t stand for “Audi Only”, it stands for “Audi Option” - It’s all down to a marketing agreement between the tyre company and the car manufacturer. In essence, the tyre company work with the car manufacturer to come up with a tyre that is well suited to a particular model. The tyre company agree to produce x thousand sets for OEM fitment, plus a larger number to be supplied as replacements during the lifetime of that particular model (it having been established that during the first few years, owners will be willing to pay a premium to keep the “designed” tyres on their cars). In later years, especially as the cars are passed onto their second and subsequent owners, brand/performance becomes less of an issue and price starts to take over. The fact that an ATS manager fails to understand (or quite possibly does understand but chooses for commercial reasons to follow the marketing bullshine) is no great surprise.
Whatever the reason it has nothing whatsoever to do with rim sizes (which are set out in industry standards).
OVLOV JAY:
Bluey Circles:
the tread depth does not explain it to me.
315/80 - 22.5 tyre will have a radius of 538mm
increase speed 56 to 60 = a 7.1% increase
to achieve this through tread depth alone would need a depth of 38mm (is that posible even with a regroove ?)Tyre sizes are an approximation to the nearest generic size, much like bhp. A 500 Volvo is actually a 496. The same with tyres, hence some being bigger than others. It’s the reason continental do Porsche, Audi and Mercedes only fitment tyres, as these tyres have been made to the exact measurements of said manufacturers rim sizes, although they are badged with the generic sizes. If you get a brand new conti, and a brand new bridgestone, mark the tread and roll them one revolution, you’d be surprised at the difference
I totally agree with you that there is differences in circumferences of tyres of the same spec from different manufacturers, I don’t know how greatly the tolerances vary.
the point of my earlier post was purely to dispel the tyre tread depth as having any significance on speed, typical truck tyre, an extra 1mm tread will only give 0.1mph increase at 56
Roymondo:
The AO marking doesn’t stand for “Audi Only”, it stands for “Audi Option” - It’s all down to a marketing agreement between the tyre company and the car manufacturer. In essence, the tyre company work with the car manufacturer to come up with a tyre that is well suited to a particular model. The tyre company agree to produce x thousand sets for OEM fitment, plus a larger number to be supplied as replacements during the lifetime of that particular model (it having been established that during the first few years, owners will be willing to pay a premium to keep the “designed” tyres on their cars). In later years, especially as the cars are passed onto their second and subsequent owners, brand/performance becomes less of an issue and price starts to take over. The fact that an ATS manager fails to understand (or quite possibly does understand but chooses for commercial reasons to follow the marketing bullshine) is no great surprise.Whatever the reason it has nothing whatsoever to do with rim sizes (which are set out in industry standards).
We had this crap with my wifes merc, it was in for a service and they phoned to say it needed two new tyres, £170 each, I said not to bother I could get the exact same Continental Sports Contacts for £80. They argued that that was an inferior tyre, I was then told the car could only be fitted with “MO” (Mercedes Original) and if I didn’t it would void my insurance, I argued it wouldn’t, they then told me it would void my warranty, I argued it wouldn’t. It’s a total rip off this special "original’ tyres crap. I went to my local tyre services and fitted P7s - it voided nothing!
The only way to really ensure a fair lick over other trucks is a ‘special’ set of drive axle tyres for the tacho calibration.
Wouldn’t surprise me if they don’t come from the factory from new well out then get their wings clipped on the first tacho calibration.