SP 12 wheels

[QBee]

I have a pair of 17 x 7J and a pair of 18 x 8J.....I think!
Does anyone know the offset? Cannot see the Offset stamped on them.
It says ET, then there is a blank square.
They were bought for a Chimaera

[PH430]

Then you have to measure it.

Google: measure offset

Good luck

[QBee]

Thanks, I understand what the offset is. Measuring it is the problem

[PH430]

Normal sp12 front offset 25 and rear offset 35 for the Chimaera

[SteveSPG]

QBee said:

Thanks, I understand what the offset is. Measuring it is the problem

put a bit of masking tape across the inside of the wheel front to back
using a straight edge across the mount face, drop a mark to the tape.
measure from the mark to the front of the rim, and again to the back of the rim. you know now where the mating face is within the wheel width, and adding the measurements together gets the wheel width.

halve the wheel width to get the centreline of the wheel. mark that point on the tape from the front or back

measure the distance between the centre point of the wheel, and the mating face, this will give you the offset.

ideally you would do this from the tyre bead faces, but unless you have a heavy bead protector rim or something, then this will get you pretty close.

sorry if this is already pretty obvious to you

[QBee]

That's a method, thanks. I will bring two wheels into the lounge and try it during Celebrity Mastershout, just to annoy the head chef and bed warmer.

Reason for the question is to try to understand the implication of the offset on my new road wheels. Car was geo'd on my SP12s, which house my track tyres.

The new road wheels, as adjusted by spacers, are offset 35 front and back. So if our friend above has supplied the correct info for my particular wheels, my rear looks good in them, but my front is 10 mm different.

We will see.....

[PH430]

Original TVR wheels:

Fronts are 7j offset 25
Rear are 7,5j offset 33
1j = 12mm

So if you want the same as standard 8j must go on. 33 + 6mm= offset 39
Because there is ennough space, the most mount the offset 35 on the 8j rim and it loooks better.

[QBee]

You understand better than me.

I want my new 7j wheels to have their centre line in the same position as my 8j wheels.......I think.
Or do I want the outside edge of the wheels to be the same distance from the centre line of the car?

Answer that question first please, and then tell me secondly what offset I need my new 7js to be to match the 8js in geo respects.

[SteveSPG]

offset is just the offset from the centreline. doesnt matter how wide you go so a 24 offset is still a 24 offset irrespective of wheel width.

so, 7, 8, 9 width or whatever you ought keep the offset from the centreline the same, however the wider you go you will induce other stresses and handling characteristics even though the offset remains the same. wider tyres and wheels tend to increase tram lining for example. perhaps more important for the fronts than rears, which you can move around a little more with no effect, but even a few mm movement on the fronts will be noticeable.

IIRC tvr used 33 offset spiders for some chimes, but ive no idea if the hubs were modified to suit??

I use 33 offset fronts and rears 8 inch rims rl7 on griff front, work fine.

Edited by SteveSPG on Tuesday 5th November 17:03

[QBee]

SteveSPG said:

offset is just the offset from the centreline. doesnt matter how wide you go so a 24 offset is still a 24 offset irrespective of wheel width.

so, 7, 8, 9 width or whatever you ought keep the offset from the centreline the same, however the wider you go you will induce other stresses and handling characteristics even though the offset remains the same. wider tyres and wheels tend to increase tram lining for example. perhaps more important for the fronts than rears, which you can move around a little more with no effect, but even a few mm movement on the fronts will be noticeable.

IIRC tvr used 33 offset spiders for some chimes, but ive no idea if the hubs were modified to suit??

I use 33 offset fronts and rears 8 inch rims rl7 on griff front, work fine.
Thanks Steve SPG (you any relation of Harry TSG?) I appreciate all your help on this.

I need thinking time on this, but you are leaving me thinking that ET 35 spacer-corrected offset all round on 7 inch wide wheels will be ok for road use. I will take it for a good drive when i am not flat out with work and see how it feels. I am not worried about having the widest wheels possible for road use, as i personally feel that i don't like tramlining, and with such a light car wider wheels can lead to less grip, not more, particularly in damp or wet conditions. I have another set of wheels and tyres, the SP12s for track use, the newly acquired wheels and tyres are my all year road wheels, and believe me, I drive the car at least twice a week every week. With three months to insurance renewal, I have done 10,000 miles since the last renewal, and there are no foreign cruises in there.