Thread: Wheels

Hey Arthur me again. So are all the offsets positive, as in moves the wheels out towards the outside of the car away from the diff?

Originally Posted by matpoli

What a timely thread as I was considering changing my std series 2 272309 (are these for 109's I have them on my 88) 5.5 inch rims to either Disco 1's 7inch or defender rims 6.0-6.5inch in the hope that the wider rims will allow my Pirelli Dakar Scorpion 7.5 R16 to balloon more when I let them down.

At the moment I let them down to 12-10 psi for beach sand and I was disappointed that I wasn't able to climb a slope that a patrol went up easily. I didn't have much momentum only about 20m worth but I thought I would get further than half way up.

I tried in 1st 4H and then even in 2nd 4L and couldn't crest it, IF I had more surface area I my tyres would I make it??

I must say the little girl has never got me bogged on sand, I have needed help with in mud and if I get the wider rims I'll use my old rims for some muddies

Oh and sorry if this is considered hijacking a post Oh greyist of ghosts

Thanks for any comments

down to 4 PSI 2 low launch easy snig third and walk it up on the torque.

Originally Posted by Blknight.aus

down to 4 PSI 2 low launch easy snig third and walk it up on the torque.

I'm guessing that this would only be done if there was no other option and then you would pump back up to 10 or you run the risk of poping a tyre off the rim.

Originally Posted by matpoli

Hey Arthur me again. So are all the offsets positive, as in moves the wheels out towards the outside of the car away from the diff?

Hi Matpoli

They are a bit of a mixture of positive and negative offsets, have a look at this link of Diana's and you will see what they are.



Then have a look at what rick130 has put on his post, it does explain the difference in offset's.

Originally Posted by rick130

Diana, the current style 130 rim has an offset of 20.6mm positive.

It's stamped on the rims and I've measured it to confirm.
This means that the rim centreline is 20.6mm outside of the mounting face, or to put it another way, this particular rim has 103mm of backspace, ie. if you lay a straight edge across the back of the rim and measure to the mounting face it's 103mm.

standard 110 rims have a positive offset of 33mm (as does the Disco I) regardless of whether they are the 5.5" or 7" rim.
On the 5.5" rim the backspace should be 102.85mm, (I'll drag a 5.5" rim out of the shed and confirm this later) and the 7" rim should have 122mm of backspace.

Positive offset means the rim centreline is inside of the mounting face, negative offset is obviously the other way around. (it can get confusing)

Ah Found it! and I was the one that posted it

Originally Posted by wrinklearthur

To determine the correct offset of the rims, extend the line through the centre of the swivel pins, at a spot on the road under the tyre. At this point and the centre line of the tyre should coincide, but in practice these two points do often fall short, leaving a gap between the two points called a scrub radius. Changing the tyres from a small diameter to a larger diameter can work to close the scrub radius.

ref; Wheel options for the MGF

Originally Posted by matpoli

I'm guessing that this would only be done if there was no other option and then you would pump back up to 10 or you run the risk of poping a tyre off the rim.

depends on how slow you're willing to travel for straight up and down and gentle throttle applications if your carefull you can stay that low all day long.

Generally 16PSI is the lowest reccomended pressure for normalish driving.

the lower the tyre pressure goes the more spread you get and ignoring a lot of factors its exponential so as you go lower in the pressure range a smaller number makes a much bigger difference in contact patch. The typical limiting factors that work against this are.

1. construction stiffness. trying to lower the pressure on a heavy duty tyre built to handle multiple thousands of tons isnt going to help as much as it will on a canvas rag tyre designed to flex around and bag out while only supporting a couple of dozen kilos. Similarly cross ply rag tyres flex a lot better than most radial steel belts.

2. Tyre life. The more it flexes the more likely you are to pinch it or punch it in both cases, theres a flat.

3. Rim Spinning. Without enough pressure to hold the beads to the rim and transmit the drive the rim spins in the rubber and you get no go and a flat in the mix.

Thank you very much to Arthur for the great pictures and blknight for your advice as well.

I'll just keep an ear out for either some 6.5" or 7" rims and put new rubber on them when i need to and i will definitely be book marking this thread as I'll use it for future reference.

My current tyres are Pirelli scorpion 8 ply 7.5 x 16's and although tough they don't give me enough surface area on the beach and the damn things never wear out.

And thank you grey ghost for starting the thread.