Coopers STT

[Izak]

Hello

I got my Coopers STT 305/70/16 from the Cape, and they are brand new. Had them fitted and they really look very nice and are not as noisy as I thought they were going to be. The one negative is the spare that is so big that it has to be pulled so tight against the rear door that there is space at all and it chafes the paint off the door. In afrikaans, ek moet die spaarwiel teen die deur vastrek en daar is geen speling tussen die deur en die band nie.

Jaco gave me one of his old Coopers that I fitted to the second spare and he made 2 very professional spacers of 32 mm each that I could fit to the spare wheel holder. (Will place a photo of that later today)

I have 2 questions, it seems the EGT is indicating that the car is running hotter after the new tyres have been fitted. I understand that they are wider with more wind resistance and they are substantially heavier than the BFG's. I am a little worried that with the Cooper's, the roof rack, RTT and a trailer, driving to Botswana in Des and in the sandy roads that the temp might cause a problem. It could be that the car is close to a service but I doubt that.

The second question is regarding the pressure of the tyres. The sales person at Tigre wheel and tyre recommended 1.8 bar because they are big, Jaco is at about 2 bar and on the internet a suggestion on a forum was 40PSi (2.7bar). I am running them now at 2.6 bar and they seem to be running down evenly. Bumpy and the ride is hard.


Regards

[Tinus lotz]

Ek ry my 33 teen 2.5 en dan gaan hulle naa 2.7 op as. Ek hiway ry
Ek dink 2.7 is te hard vir dag tot dag net wanneer jy swaar gelaai is die EGT kan dalk te doen wees met die wrywing maar ek is nie seker nie miskien omtrek wat verskil ?

[ricster]

305/70's.... what is the outside diameter of those. The bigger tyre will increase your EGT's a bit. You will find that on the uphills you will be going slower due to having to monitor the EGT gauge. When cruising on the highway though, your speedo will be reading more accurate to the GPS, your fuel consumption will be a bit better ( 3.0 diesel is already fantastic consumption ). Also due to the tyre being a M/T the tread pattern is quite aggressive which again causes your motor to labour harder, in turn increasing the EGT's.

Suggestion, feather the throttle according to the EGT's... so what if you climb a hill at 80Km/h..... the cars passing you will still be jealous . Play with the tyre pressure, the harder the tyre pressure the less the motor works.... but the bumpier the ride. But when loaded the bumps may not be felt too much........

[Gerrit Loubser]

The 305/70R16 tyres has a nominal OD of 32.8" (same as 285/75R16 tyres). The standard tyre size is 265/70R16 (nominal OD 30.6"), so going to 305/70R16 means that you have effectively made the gearing 7% taller. In turn this means that you are actually going 7% faster than before when the speedo indicates the same speed reading. Going faster needs more power and the power requirement varies roughly as the square of speed, so going 7% faster requires almost 15% more power. Generating more power requires that more fuel be burned in the same time and this generated more heat. All of this is beside any differences due to tread pattern, etc.

[ricster]

Wow.... now that is an excellent explanation !! 15% is quite a bit, I never realised it was that much !!!

But..... have you heard about the constipated mathematician??..... he worked it out with a pencil...

[Izak]

Thanx Gerrit/ Rickster

On my GPS the true speed is now 98 km when the GPS reads 100. Less than 2% out. On the 265/75/16 that I had, it was out by more than 12%. I used to travel at about 110 on the old tyres and she loved it EGT and Consumption wise.

I will just have to keep all this in mind, because I get nervous when the EGT gets to around 500. I know that is not to hot but still I do not like it.

With a PENCIL, RICK?????

[Jorrie]

Thanx Gerrit/ Rickster

On my GPS the true speed is now 98 km when the GPS reads 100. Less than 2% out. On the 265/75/16 that I had, it was out by more than 12%. I used to travel at about 110 on the old tyres and she loved it EGT and Consumption wise.

I will just have to keep all this in mind, because I get nervous when the EGT gets to around 500. I know that is not to hot but still I do not like it.

With a PENCIL, RICK?????

I am getting the same result after fitting 285/75R16 Cooper SSTs.

[Tinus lotz]

Jorrie die buite grote van die band is dieselfde net die breedte verskil ,het julle gekyk wat se verskil die km wat gery word teenoor gps afstand is ?

[Jorrie]

Jorrie die buite grote van die band is dieselfde net die breedte verskil ,het julle gekyk wat se verskil die km wat gery word teenoor gps afstand is ?

Tinus, nog nie. Volgens wat ek verstaan hou die twee nie verband met mekaar nie. Iemand anders het dit elders op die forum verduidelik.

[Tinus lotz]

jorrie ek doen bietjie navorsing as n mens 10% groter tires opsit behoort mens 10% veandering in trip meter te he .
ek dink dit verkil van patrol tot patrol maw auto 4.5 manaul of tiptronic probeer nou net kyk