Discussion
The offset on the 15 x 7 fronts on a Griff is 25mm. The offset on the 16 x 7.5 rears is 40mm.
Is the difference in offset related to the different width (7.5 inches instead of 7)? Someone I spoke to suggested it was. I presume diameter makes no difference.
If so, what would the correct offset be for a 8 inch wide wheel? Mr. Branch, what width and offset did you say yours were (wheels we're talking about here
) and do they still rub the arches on full lock? Kerniki?
Ta,
Ian A.
Is the difference in offset related to the different width (7.5 inches instead of 7)? Someone I spoke to suggested it was. I presume diameter makes no difference.
If so, what would the correct offset be for a 8 inch wide wheel? Mr. Branch, what width and offset did you say yours were (wheels we're talking about here
) and do they still rub the arches on full lock? Kerniki? Ta,
Ian A.
quote:
The offset on the 15 x 7 fronts on a Griff is 25mm. The offset on the 16 x 7.5 rears is 40mm.
Is the difference in offset related to the different width (7.5 inches instead of 7)? Someone I spoke to suggested it was. I presume diameter makes no difference.
If so, what would the correct offset be for a 8 inch wide wheel? Mr. Branch, what width and offset did you say yours were (wheels we're talking about here
Ta,
Ian A.
You sure about those figures? The Chim wheels I measured were 1" (exactly) inset at the front (15x7"), and 1.25" (exactly) at the rear (16x7.5"). That would make the rear inset roughly 31mm rather than 40mm? Would have expected Griff wheels to be the same but never measured them.
The Chim wheel offsets mean that the extra 0.5" width is all in the inside; the outer edge of the tyre is in the same place wrt to the wheel arch, but the inner edge is half an inch closer to the suspension etc.
If you have unlimited space round the wheel I would suggest you stick to the standard inset (be that 1.25" or 40mm) with 8" rims. But I suspect that you will be constrained by the wheel clearance against the front suspension on lock, and the front and rear wheel arches on bump. If the wheel arches are close you would need to incrase the inset by 0.25 to stay clear of them, but this would make it even harder to clear the front suspension, possibly compromising the steering lock.
Think you need to take some careful measurements. BTW I wouldn't assume that it is the same for all cars or for all wheel types.
Cheers,
Peter Humphries (and a green V8S)
quote:
You sure about those figures? The Chim wheels I measured were 1" (exactly) inset at the front (15x7"), and 1.25" (exactly) at the rear (16x7.5"). That would make the rear inset roughly 31mm rather than 40mm? Would have expected Griff wheels to be the same but never measured them.
Pretty sure, the wheels have ET25 stamped on the front and ET40 on the rear which is supposed to signify the offset IIRC. I'm fairly confident I remember the figures correctly but no-ones perfect.
The reason for finding out is that I've just had yet another frustrating conversation with a wheel distributer.
Me: I need some alloys, 17 x 7.5, PCD 108mm, ET40
Distrib: What car are they for
Me: Err, well actually it's a TVR but that doesn't matter
Distrib: No, can't help you mate. Don't do TVRs.
Me: Why not, which particular measurement is not available?
Distrib: Don't know, just don't do TVRs.
Not the first time I've had this response. I smell a conspiracy! I'm going to try asking again with just the wheel measurements.
I will examine the car tonight to see where the wheels are closest to surrounding objects.
Ta,
Ian A.
My Griff, fitted with OZ Split rims, has a rear offset of 33mm stamped on the wheel. I have been looking at changing wheels, but struggled to find ones I like with bith front & rear offsets available. It is interesting if TVR themselves use a variety of different ones, as his may open up more possibilities for wheel choice.
Jon H
Jon H
quote:
My Griff, fitted with OZ Split rims, has a rear offset of 33mm stamped on the wheel. I have been looking at changing wheels, but struggled to find ones I like with bith front & rear offsets available. It is interesting if TVR themselves use a variety of different ones, as his may open up more possibilities for wheel choice.
Jon H
TVR probably changed the wheel arch when they changed the wheel design. Oh no wait, this is TVR not Mercedes. TVR probably hit the wheel arch with a large lump hammer when they changed the wheel design.
Given that some cars have a difference of about an inch between the wheel and the edge of the car, it can't be too critical.
Probably something you have to try before you buy.
Ian A.
quote:
You sure about those figures? The Chim wheels I measured were 1" (exactly) inset at the front (15x7"), and 1.25" (exactly) at the rear (16x7.5"). That would make the rear inset roughly 31mm rather than 40mm? ......
The Chim wheel offsets mean that the extra 0.5" width is all in the inside; the outer edge of the tyre is in the same place wrt to the wheel arch, but the inner edge is half an inch closer to the suspension etc.
If you have unlimited space round the wheel I would suggest you stick to the standard inset (be that 1.25" or 40mm) with 8" rims. But I suspect that you will be constrained by the wheel clearance against the front suspension on lock, and the front and rear wheel arches on bump. If the wheel arches are close you would need to incrase the inset by 0.25 to stay clear of them, but this would make it even harder to clear the front suspension, possibly compromising the steering lock.
...
Cheers,
Peter Humphries (and a green V8S)
Peter
I take it you changed the standard 15" chim wheels to 16" on your V8S, did you have to use spacers at all or was it a straight swap? also did it affect the wheel geometry?
Harry
quote:Ian, my wheels were marked ET25 front and ET35 rear, elsewhere they were also both stamped 30. I decided to accuratly measure the offset myself with a couple of straight edges and a steel rule and indeed the front was exactly 25mm (1") the rear was however 37mmm. Taking into account the spacers (because I was told the worng offset by the factory !!!) I have 34mm front and 37mm rear on 8" rims. The front still very slightly rubs the lower wishbone on full-lock (left turn only) but then my cars body is also approx 3-4mm offset to the left relative to the chassis! Working on the basis that an increase from 7" to 8" at the front is 25mm ideally you want to add 12mm to the offset to keep the centre line of the rim in the same place relative to the suspension. This would mean an offset of 37 but I reckon this would rub quite noticably... Mail me off-line if you want more details, or call Richard at Peninsula who has done a few of these by now... Rich...
The offset on the 15 x 7 fronts on a Griff is 25mm. The offset on the 16 x 7.5 rears is 40mm.
Is the difference in offset related to the different width (7.5 inches instead of 7)? Someone I spoke to suggested it was. I presume diameter makes no difference.
If so, what would the correct offset be for a 8 inch wide wheel? Mr. Branch, what width and offset did you say yours were (wheels we're talking about here
quote:
Working on the basis that an increase from 7" to 8" at the front is 25mm ideally you want to add 12mm to the offset to keep the centre line of the rim in the same place relative to the suspension.
The offset is the distance between the center of the rim, and the mounting face. If you want to keep the center in the same place wrt the suspension, you want to keep the offset the same. If you increase the offset as you suggest, this would keep the outer edge in the same place and move the inner edge in an inch. If you see what I mean! (How many times has this done my head in!)
Cheers,
Peter Humphries (and a green V8S)
heres a good explanation of all this confusion with pictures, thankfully.
www.usacomp.com/Offset.htm
heliox
quote:
Peter
I take it you changed the standard 15" chim wheels to 16" on your V8S, did you have to use spacers at all or was it a straight swap? also did it affect the wheel geometry?
Harry
Yes, thats right. The ones I used are the standard 16*7.5 Chimaera 4.0 five-spoke wheels, which have an offset of 1.25". Straight swap, no geometry problems, no spacers. Not much room to go wider than this on the back though, because of the trailing arm clearance. Reading about the different offsets people have found on other Chimaera and Griffith wheels, you might want to be careful about the other wheel styles though. Mine runs quite high camber so it suffers more tramlining and kickback than most, but this didn't increase noticeably when I changed the wheels. However, running lower profile and wider tyres did make the turn-in a little sharper.
Cheers,
Peter Humphries (and a green V8S)
quote:Pete my humble apologies, you are of course correct. In my defence it was 2 1/2 years ago I did it and I didn't have my back-of-a-fag-packet diagram to hand yesterday. However... I think my suggestion would keep the inner edge of the rim static relative to the suspoension/inner wheel arch (not the outer edge) but I agree with the help of a said fag packet it is possibl eto work it all out on paper first! Rich...
If you want to keep the center in the same place wrt the suspension, you want to keep the offset the same. If you increase the offset as you suggest, this would keep the outer edge in the same place and move the inner edge in an inch. If you see what I mean! (How many times has this done my head in!)
Cheers,
Peter Humphries (and a green V8S)
quote:
I think my suggestion would keep the inner edge of the rim static relative to the suspoension/inner wheel arch (not the outer edge) but I agree with the help of a said fag packet it is possibl eto work it all out on paper first! Rich...
It's an area that is ripe for misunderstanding because there's no standard definition for which direction the offset is measured. I prefer to use the terms inset or outset to avoid this potential confusion, but these aren't generally accepted terms. The TVR wheels are inset, obviously.
Cheers,
Peter Humphries (and a green V8S)
quote:Just re-read my last post
quote:
I think my suggestion would keep the inner edge of the rim static relative to the suspoension/inner wheel arch (not the outer edge) but I agree with the help of a said fag packet it is possibl eto work it all out on paper first! Rich...
It's an area that is ripe for misunderstanding because there's no standard definition for which direction the offset is measured. I prefer to use the terms inset or outset to avoid this potential confusion, but these aren't generally accepted terms. The TVR wheels are inset, obviously.
Cheers,
Peter Humphries (and a green V8S)
brain / hand co-ordination not good this morning eh? Thought for one moment Cambelt had hacked my User ID: ! Rich...Gassing Station | General TVR Stuff & Gossip | Top of Page | What's New | My Stuff