Advice on wheel off-set's
Discussion
I'm putting some 8x17 five spoke compomotive wheels on the Griff,but as usual what starts as as what i presume is relatively straight forward has left me a little confused!.i have been advised that a 25ET all round will work but have seen on some other threads some people are running a 35ET on the rears?
I don't want the wheels to sit in to far from the arches and not so far out they foul the arch?
They have put the wheels on Hold so i would really appreciate some feedback as to anyones own experiance. Listed below is the measurments from compomotive
I know i can go for a wider wheel a 18x9 on the rear but not in the five spoke which has that authentic early griff look. Many thanks
I forgot to mention i'll be running Toyo 888
Mo1781 8x17 overall wheel width 225mm. Offset et25
Wheel backspace 138mm. Wheel outboard 87mm approx
If you were to change to et35 offset
Wheel backspace 148mm. Wheel outboard 77mm approx
I don't want the wheels to sit in to far from the arches and not so far out they foul the arch?
They have put the wheels on Hold so i would really appreciate some feedback as to anyones own experiance. Listed below is the measurments from compomotive
I know i can go for a wider wheel a 18x9 on the rear but not in the five spoke which has that authentic early griff look. Many thanks
I forgot to mention i'll be running Toyo 888
Mo1781 8x17 overall wheel width 225mm. Offset et25
Wheel backspace 138mm. Wheel outboard 87mm approx
If you were to change to et35 offset
Wheel backspace 148mm. Wheel outboard 77mm approx
- backspace measurement is taken from the wheel mounting face to outer edge of inner rim
- outboard measurement is taken from the wheel mounting face to outer edge of outer rim
8" wide wheels will not be nice on the front without PAS - you'll most likely need to adjust the rack end stops and the feel will be really heavy. 7.5" is as far as I would go, and 7" is my preference.
The offset for 7" wide wheels should be ET25 (as standard). If you go for wider, then you will need to increase the offset to maintain the position of the outer edge of the wheel relative to the body.
So if you have 8" wide on the back, you should have an offset of say ET40 to ET42. ET25 would be going the wrong way completely. The standard 7.5" wide wheels are ET35 on the back.
BTW good choice of wheel. I have the 6 spoke (MO6) on mine, and there should be a thread about it somewhere here.
The offset for 7" wide wheels should be ET25 (as standard). If you go for wider, then you will need to increase the offset to maintain the position of the outer edge of the wheel relative to the body.
So if you have 8" wide on the back, you should have an offset of say ET40 to ET42. ET25 would be going the wrong way completely. The standard 7.5" wide wheels are ET35 on the back.
BTW good choice of wheel. I have the 6 spoke (MO6) on mine, and there should be a thread about it somewhere here.
dnb said:
The offset for 7" wide wheels should be ET25 (as standard). If you go for wider, then you will need to increase the offset to maintain the position of the outer edge of the wheel relative to the body.
True but that's an odd requirement. Most people try to maintain the tyre in the same position.
7 TVR said:
I'm putting some 8x17 five spoke compomotive wheels on the Griff,but as usual what starts as as what i presume is relatively straight forward has left me a little confused!.
The front wheels on the Griff are not the same as the rear - different offset, diameter, width. You're trying to make f&r the same so one or the other will be compromised unless you order two pairs.
dnb said:
JR said:
dnb said:
The offset for 7" wide wheels should be ET25 (as standard). If you go for wider, then you will need to increase the offset to maintain the position of the outer edge of the wheel relative to the body.
True but that's an odd requirement. Most people try to maintain the tyre in the same position.The things that you do need to watch are the tyres rubbing and the wheels catching the mechanical bits of the car, quite different things.
If you stick ET25 8" wheels on the back of a Griff, they will rub on full suspension compression without arch mods. If you stick 8" ET25 wheels on the front, they also rub somewhere. Been there and done it with various Cossie wheels while I was working out what fitted best. (I have softer suspension than most, and use all the suspension travel available - roads are far from good here!)
The mechanical bits have lots more clearance than the body, so you can have the wheel insides closer to the mechanicals than standard, but there is less scope for moving outwards IYSWIM.
If you are buying direct from Compomotive, then they will sell you exactly what you ask for. They are good people to deal with and will not insist on selling "a set of 4". You could have 4 different wheels if you so desired, although I dread to think what the car would look like
The mechanical bits have lots more clearance than the body, so you can have the wheel insides closer to the mechanicals than standard, but there is less scope for moving outwards IYSWIM.
If you are buying direct from Compomotive, then they will sell you exactly what you ask for. They are good people to deal with and will not insist on selling "a set of 4". You could have 4 different wheels if you so desired, although I dread to think what the car would look like
Edited by dnb on Thursday 3rd June 23:00
They did just rub with the new suspension on and not running sufficient camber to clear (although too much for preserving the inside edge of the tyres!) Standard was 205 for non-PAS and 215 for PAS - at least in my hand book. (But the fuseboard diagram was wrong, so I take these things with a pinch of salt anyway...) Guess these things sometimes come down to TVR production tolerances...
The 225/xx/R15 would end up with a different tyre shape to 225/yy/R17 (or R18 as the OP suggests!) if you are trying to maintain the same overall rolling radius. This would work against you somewhat, even if the 15" rims were fine. On a different car that I own, 215/35/18 rubs slightly at the back, but 215/45/17 does not (for the same offset and width of wheels, but different brand of tyre). Your argument is good, but not quite infallible.
Besides, I have always maintained that 7" wide rims are fine on the front and on an early (most likely non-PAS) car 8" fronts would spoil the steering somewhat and create needless other issues, so the offset should be as standard, so the argument (while fun) is not the main issue. On the 500SE, the offset on the front was ET35 since they used the rear wheels on the front too. I am sure there were no spacers, but rack stops were fitted that mine does not have. This would give more clearance for the body and less for the mechanicals - so by your argument (and mine) it is wrong because it moves the tyres inboard by about 5mm compared to earlier cars. My argument would see the wheels with an offset of ET30ish and move the tyre centres back outboard as far as I would be comfortable with before horrible noises happened on compression.
The 225/xx/R15 would end up with a different tyre shape to 225/yy/R17 (or R18 as the OP suggests!) if you are trying to maintain the same overall rolling radius. This would work against you somewhat, even if the 15" rims were fine. On a different car that I own, 215/35/18 rubs slightly at the back, but 215/45/17 does not (for the same offset and width of wheels, but different brand of tyre). Your argument is good, but not quite infallible.
Besides, I have always maintained that 7" wide rims are fine on the front and on an early (most likely non-PAS) car 8" fronts would spoil the steering somewhat and create needless other issues, so the offset should be as standard, so the argument (while fun) is not the main issue. On the 500SE, the offset on the front was ET35 since they used the rear wheels on the front too. I am sure there were no spacers, but rack stops were fitted that mine does not have. This would give more clearance for the body and less for the mechanicals - so by your argument (and mine) it is wrong because it moves the tyres inboard by about 5mm compared to earlier cars. My argument would see the wheels with an offset of ET30ish and move the tyre centres back outboard as far as I would be comfortable with before horrible noises happened on compression.
Thanks for all the advice even if it is a little conflicting, in response to Jr i know the orig wheels are staggered front to back, but after speaking to people who have done complete race seasons with 17 all round and running an even wider wheel i did not feel this would compromise the handling, I guess the best option on the rear is to go for the higher off-set which leaves me with the option to run spacers if needed. The main reason for the wheel change being to get some more rubber on the road as the projected 480 Bhp LS3 conversion will turn the arse end into even more of a happy slapper than she is already, and also to facilitate the fitting of an AP Big brake conversion i've just purchased of a certain dutchman.[Thanks Hans]
Edited by 7 TVR on Friday 4th June 00:37
7 TVR said:
Thanks for all the advice even if it is a little conflicting, in response to Jr i know the orig wheels are staggered front to back, but after speaking to people who have done complete race seasons with 17 all round and running an even wider wheel i did not feel this would compromise the handling, I guess the best option on the rear is to go for the higher off-set which leaves me with the option to run spacers if needed.
The handling will be affected slightly but as mentioned above TVR did it when they fitted 16" all round - you'll need the geo resetting though. FWIW I'd think about say 32mm all round and use spacers or rackstops at the front, six of one and half..Good luck, J
dnb said:
They did just rub with the new suspension on and not running sufficient camber to clear (although too much for preserving the inside edge of the tyres!) Standard was 205 for non-PAS and 215 for PAS - at least in my hand book. (But the fuseboard diagram was wrong, so I take these things with a pinch of salt anyway...) Guess these things sometimes come down to TVR production tolerances...
OK so your car will not take 225 tyres at the front. Production tolerences in the size of the mould and the thickness of the fibreglass do come into it, as do accident repairs but you've got a very unusual car and I still don't see how the wheels would rub on the bodywork.dnb said:
The 225/xx/R15 would end up with a different tyre shape to 225/yy/R17 (or R18 as the OP suggests!) if you are trying to maintain the same overall rolling radius. This would work against you somewhat, even if the 15" rims were fine. On a different car that I own, 215/35/18 rubs slightly at the back, but 215/45/17 does not (for the same offset and width of wheels, but different brand of tyre). Your argument is good, but not quite infallible.
Well that's a very odd one - the tyre with 18mm extra clearance in height and which will not distort as much width ways rubs. Brand of tyre will be the reason, on tread depth for dia and tres shape and strength for width. That's still an extreme example since you must also have a car with very fine tolerances as well as the tyre differences.dnb said:
Besides, I have always maintained that 7" wide rims are fine on the front
but they are a bit of a joke with a 225 tyre. The problem with the wheels is that they were sized with 205f and 225r in mind (even though 215 was thrown on the front initially sine the wheel size can't go up 3/8") If you're changing the wheels and want wider tyres best to correct this production cost anomaly IMHO.dnb said:
8" fronts would spoil the steering somewhat and create needless other issues,
8" fronts, if with a 225 tyre would be better suited to the tyre than 7" holding the tyre better than the 7". Whilst this would be beneficial for feedback, esp on the move, parking would be a pain and extra stesses would be transferred onto the mechanical joints. 7.5" would be my choice.dnb said:
On the 500SE, the offset on the front was ET35 since they used the rear wheels on the front too. I am sure there were no spacers, but rack stops were fitted that mine does not have. This would give more clearance for the body and less for the mechanicals - so by your argument (and mine) it is wrong because it moves the tyres inboard by about 5mm compared to earlier cars.
Two points here: the tyre c/l moves in 10mm so if you compare the 205 tyre on most early cars to the 225 of the last cars yes it 5mm on the outer edge and 15mm on the inner edge but firstly your argument has now changed since you are now talking about the position of the tyres (as mentioned above I've always thought it odd that you have had problems with wheels rubbing on bodywork) secondly you find the above wrong because the position of the outside rim (and maybe tyre as well now) has changed, I would want to take into consideration many factors: inner and outer clearance to everything, track requirements, suspension set up, wear requirements, etc. before forming an opinion.dnb said:
My argument would see the wheels with an offset of ET30ish and move the tyre centres back outboard as far as I would be comfortable with before horrible noises happened on compression.
Your original statement would have moved to an offset of 31.6. This later one is better IMHO but I still like to consider as much as possible before making a choice.As I said at the beginning I find you single wheel outer rim requirement view odd. I now find your wheel and tyre outer edge view better but still prefer my attempt at a more comprehensive view.
It is of note that your rule(?) of thumb approach appears to give very similar conclusions to my approach at the front but not at the back:
dnb said:
So if you have 8" wide on the back, you should have an offset of say ET40 to ET42. ET25 would be going the wrong way completely. The standard 7.5" wide wheels are ET35 on the back.
I'd want to maintain the suspension geo and not introduce unnecessary offset forces by keeping the wheel in the same position with the same offset as standard, et 32/35 depending on which wheel you have, so with 225 tyres the wheel may be 1mm wider than the tyres but with 245 tyres, which most cars have, most people would even notice a difference and the wheels still at least 8mm more clearance than the tyres.The wheel offset / tyre conundrum really is a chicken and egg problem. You probably need to start with choosing the tyres you want to run and then find some rims that match the optimum size for the rubber. Then you need to check that the rubber will clear the bodywork and the wheels will clear the suspension.
All of the wheel combinations I have tried have been seeking grip rather than cosmetic benefits and to that aim I have where possible stuck as closely to the original offsets and rolling diameter as the original spec. Keeping them all the same has the additional benefit of allowing you to swap the wheels without resetting the geo each time.
If it is any help I currently run 9 x 17 et 30 on the rear with an 230/610 Avon slick which clears the body and the suspension. I also have 8 x 17 et 33 which clears OK with 245/45 Hoosier slick. Largest I have tried on the front is 7.5 x 17 with 225 slicks. Can’t think why you would need a wider rim or tyre on the front.
All of the wheel combinations I have tried have been seeking grip rather than cosmetic benefits and to that aim I have where possible stuck as closely to the original offsets and rolling diameter as the original spec. Keeping them all the same has the additional benefit of allowing you to swap the wheels without resetting the geo each time.
If it is any help I currently run 9 x 17 et 30 on the rear with an 230/610 Avon slick which clears the body and the suspension. I also have 8 x 17 et 33 which clears OK with 245/45 Hoosier slick. Largest I have tried on the front is 7.5 x 17 with 225 slicks. Can’t think why you would need a wider rim or tyre on the front.
steve-V8s said:
The wheel offset / tyre conundrum really is a chicken and egg problem. You probably need to start with choosing the tyres you want to run and then find some rims that match the optimum size for the rubber. Then you need to check that the rubber will clear the bodywork and the wheels will clear the suspension.
All of the wheel combinations I have tried have been seeking grip rather than cosmetic benefits and to that aim I have where possible stuck as closely to the original offsets and rolling diameter as the original spec. Keeping them all the same has the additional benefit of allowing you to swap the wheels without resetting the geo each time.
If it is any help I currently run 9 x 17 et 30 on the rear with an 230/610 Avon slick which clears the body and the suspension. I also have 8 x 17 et 33 which clears OK with 245/45 Hoosier slick. Largest I have tried on the front is 7.5 x 17 with 225 slicks. Can’t think why you would need a wider rim or tyre on the front.
Good stuff. As I understand it the OP is considering an 8" wide front wheel because the off the shelf style that he has chosen is not available in 7.5".All of the wheel combinations I have tried have been seeking grip rather than cosmetic benefits and to that aim I have where possible stuck as closely to the original offsets and rolling diameter as the original spec. Keeping them all the same has the additional benefit of allowing you to swap the wheels without resetting the geo each time.
If it is any help I currently run 9 x 17 et 30 on the rear with an 230/610 Avon slick which clears the body and the suspension. I also have 8 x 17 et 33 which clears OK with 245/45 Hoosier slick. Largest I have tried on the front is 7.5 x 17 with 225 slicks. Can’t think why you would need a wider rim or tyre on the front.
One other point for the OP: 888s are fairly wide for the nominal width compared to standard road tyres. It will be interesting to see how your car works out, sounds like a great project.
@ dnb
good afternoon dnb, i have a serious question about this subject;
why is 8 x 17 et 40 - 42 better for rear wheels?
i'm currently running 8 x 17 rear with offset 33 (no spacers which is about the same as 7,5 x 16) recommended by team dynamics!
my front wheels are 7 x 16 offset 25.
when i checked everything at www.willtheyfit.com i have found out that et33 puts
the rim / tyre more outside the body than et 40 which will put the wheels more inside,
close to chassis tube outrigger to main chassis so you have to use a spacer??
i'm also curious about this subject again so no offence!
reason for replying; i was looking for possibility to fit 9 x 17 et 30? i'm guessing?
cheers
mischa
good afternoon dnb, i have a serious question about this subject;
why is 8 x 17 et 40 - 42 better for rear wheels?
i'm currently running 8 x 17 rear with offset 33 (no spacers which is about the same as 7,5 x 16) recommended by team dynamics!
my front wheels are 7 x 16 offset 25.
when i checked everything at www.willtheyfit.com i have found out that et33 puts
the rim / tyre more outside the body than et 40 which will put the wheels more inside,
close to chassis tube outrigger to main chassis so you have to use a spacer??
i'm also curious about this subject again so no offence!
reason for replying; i was looking for possibility to fit 9 x 17 et 30? i'm guessing?
cheers
mischa
Edited by MischaVisserv8 on Friday 4th June 13:08
@ JR
I have 215 tyres on the front. I agree that 225 on 7" is silly - it's one reason why I changed them. My choice is 7", but this is one of those 6 of one 1/2 dozen of the other choices... It seems to suit what I do with the car better. Lots of things were considered for quite a while before I changed things, and broadly they worked out.
@ the last poster
Your fronts are standard, so no issue I can see...
The backs you have probably wouldn't fit on mine if I used certain tyres without a bit of work on the inner arches. Not a problem if say you have really stiff suspension or you don't intend to use full compression travel. (I do, so I have slightly different requirements - my car has been described as a "Rally Griff" several times...)
I tried spacing off my Estorils from the car to simulate the maximum "outwardness" I could have and then translated this into what this ET would be for an 8" rim. I can't remember the numbers, but it worked out to ET35 8" being OK provided I stuck to the standard width tyres. I went with ET40 - a common size - it gave me scope to not worry about the tyres, put the wheels about in the right place and I could easily get spares from off the shelf. The ET37-and-a-bit I worked out would be better, but aren't as available. If you have 17"+ rims then there is plenty of clearance at the back.
Thinking about it, ET42 is a bit too far (but will work). This came from me thinking about Focus RS wheels at one point, so should be ignored.
My theory was also to maintain the standard geometry as far as possible. It seems my car has more issues at doing this than most! When all said and done, TVRs have mostly Ford hubs, and these were designed for different offsets to TVRs, so changes in loadings should be designed to go back in the direction of what the hubs "expect", but given we are all talking about 1-2% of the total width I can't see it being too much of an issue - we can't be this close to the design limits...
It's interesting to see the huge prodiction tolerances TVRs have. Mine must be at one extreme. Or maybe I simply didn't get the body put back on right!
I have 215 tyres on the front. I agree that 225 on 7" is silly - it's one reason why I changed them. My choice is 7", but this is one of those 6 of one 1/2 dozen of the other choices... It seems to suit what I do with the car better. Lots of things were considered for quite a while before I changed things, and broadly they worked out.
@ the last poster
Your fronts are standard, so no issue I can see...
The backs you have probably wouldn't fit on mine if I used certain tyres without a bit of work on the inner arches. Not a problem if say you have really stiff suspension or you don't intend to use full compression travel. (I do, so I have slightly different requirements - my car has been described as a "Rally Griff" several times...)
I tried spacing off my Estorils from the car to simulate the maximum "outwardness" I could have and then translated this into what this ET would be for an 8" rim. I can't remember the numbers, but it worked out to ET35 8" being OK provided I stuck to the standard width tyres. I went with ET40 - a common size - it gave me scope to not worry about the tyres, put the wheels about in the right place and I could easily get spares from off the shelf. The ET37-and-a-bit I worked out would be better, but aren't as available. If you have 17"+ rims then there is plenty of clearance at the back.
Thinking about it, ET42 is a bit too far (but will work). This came from me thinking about Focus RS wheels at one point, so should be ignored.
My theory was also to maintain the standard geometry as far as possible. It seems my car has more issues at doing this than most! When all said and done, TVRs have mostly Ford hubs, and these were designed for different offsets to TVRs, so changes in loadings should be designed to go back in the direction of what the hubs "expect", but given we are all talking about 1-2% of the total width I can't see it being too much of an issue - we can't be this close to the design limits...
It's interesting to see the huge prodiction tolerances TVRs have. Mine must be at one extreme. Or maybe I simply didn't get the body put back on right!
Ok things have moved on a bit so here we go:
I have managed to get the front in a 17x7 now so am much happier and these will run an et28! wanted 25 but been told they cannot do on that size but presume 3m want make to much dif?
As for the rear i was going to stick to 17x8 with an ET35, i'd say the car will be 50% road 50% track and is currently running up-rated shocks and springs with 888 which i must say i love, as others have stated i would like to keep geo as close to standard as it's proved so good so far!
once again its great hearing everyone individual experiances??
I have managed to get the front in a 17x7 now so am much happier and these will run an et28! wanted 25 but been told they cannot do on that size but presume 3m want make to much dif?
As for the rear i was going to stick to 17x8 with an ET35, i'd say the car will be 50% road 50% track and is currently running up-rated shocks and springs with 888 which i must say i love, as others have stated i would like to keep geo as close to standard as it's proved so good so far!
once again its great hearing everyone individual experiances??
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