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"The thinnest adapters they offer are 19mm thick, you have to factor that into the equation for the new wheel offset. I chose the 19mm adapters which puts the total offset at 43mm or 44mm depending upon which source you use for the original offset. I have seen both 24mm and 25mm listed. I ended up going to 16x7 wheels with a 4x100 bolt pattern and 42mm offset. Using 205/45R16 tires and on the 16x7 wheels............."

Hi,

 read the above on:

http://tr7triumph.com/forum/viewtopic.php?t=13458

Should the offset now be 5mm or 6mm? not 43mm or 44mm?

This is of course assuming we are talking positive offset/ET. 

Edited by spitfire6

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it may be me but your question doesn't seem to tie in with the link about a TR7 on v wide rims using pcd adaptor plates? i know from having some standard 5.5 TR7 rims that fitting on the Vitesse that will happily take other 5.5 rims i had to use 5mm spacers to avoid fouling.

Alan

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Have just gone through this with my Amazon, there is a differences between offset and back spacing. A narrow wheel with 0 offset will have less backspacing than a wide wheel with 0 offset. An back spacing determines if the wheels will physically fit on the hub/brake/ suspension.. The diameter of the hole in the rim and the nose of the hub must be compatible or made to be. Also will the rims center on the hub or by the lug nut tapper. 16x7 Toyota rims replacing 15x5.5

002.JPG

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17 hours ago, oldtuckunder said:

it may be me but your question doesn't seem to tie in with the link about a TR7 on v wide rims using pcd adaptor plates? i know from having some standard 5.5 TR7 rims that fitting on the Vitesse that will happily take other 5.5 rims i had to use 5mm spacers to avoid fouling.

Alan

Hi Alan,

 Just checked the link & is correct.

He was saying that a spacer or adaptor in this case increases ET. It does not. It reduces it. The new offset is 5mm or 6mm not 43mm or 44mm.

I spent hours last night checking and checking. Loads of wrong advice out there.

Back space and ET are related. I will stick with the German metric ET. Whats an inch? LOL.

http://www.gtsparkplugs.com/Offset-to-Backspace.html

Cheers,

Iain.

 

 

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OK lets agree to stick to ET as the term to measure between the inside of the wheel mounting flange and the centre-line of the wheel, so we can have Negative, Zero or Positive ET, which if we agree means that we can say Zero ET means the flange is directly in line with the centre of the wheel, A Positive ET means that flange face is outboard the centre line of the wheel, and a Negative ET means that flange face is inboard the centre line of the wheel. 

As I understand it (but stand by to be corrected) ET is entirely a wheel measurement it has nothing to do with suspension geometry, offset of the hub face etc. it is entirely a wheel measurement ( and if correctly stated should be  ET0, ET+mm or ET-mm, but as usual we assume that if some says or writes ET30 they mean ET+30, however it would easy for someone when measuring what they know to be a negative ET to just say "its got an ET of 30"  and in such ways Beagle Lander Parachutes fail to deploy)

So lets look at an example, lets say a wheel has an ET0 which puts the centre line of the rim inline with the outer face of the hub,  now if I put a 20mm spacer between the hub and the mounting face of the rim, the centre line of the rim moves outboard of the outer face of the hub by 20mm. To get the centre line of the wheel  back in-line with the outer face of the hub I now need a wheel with an ET+20.   

So if you look at the TR7 example he is actually using ET correctly and I think he has the math correct, in that if a wheel originally had an ET+25, and you add in a 19mm spacer, then a replacement wheel to have its centre line in line with where the centre line of the original wheel was will need to have an ET of 25 + 19 = ET+44.

Spacers cannot alter the ET of a wheel, in fact nothing can its cast in, well yes you could machine a bit of the mounting face but we will take that as the case that proves the rule.

Alan

Offsets are an entirely different topic!

 

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3 hours ago, oldtuckunder said:

Hi Alan,

"OK lets agree to stick to ET as the term to measure between the inside of the wheel mounting flange and the centre-line of the wheel, so we can have Negative, Zero or Positive ET, which if we agree means that we can say Zero ET means the flange is directly in line with the centre of the wheel, A Positive ET means that flange face is outboard the centre line of the wheel, and a Negative ET means that flange face is inboard the centre line of the wheel."

I agree but visualise it the same but differently; -ve ET moves the wheel out and +ve ET moves the wheel in.

 

"As I understand it (but stand by to be corrected) ET is entirely a wheel measurement it has nothing to do with suspension geometry, offset of the hub face etc. it is entirely a wheel measurement ( and if correctly stated should be  ET0, ET+mm or ET-mm, but as usual we assume that if some says or writes ET30 they mean ET+30, however it would easy for someone when measuring what they know to be a negative ET to just say "its got an ET of 30"  and in such ways Beagle Lander Parachutes fail to deploy)"

Space stations & metric/imperial.

"So lets look at an example, lets say a wheel has an ET0 which puts the centre line of the rim inline with the outer face of the hub,  now if I put a 20mm spacer between the hub and the mounting face of the rim, the centre line of the rim moves outboard of the outer face of the hub by 20mm. To get the centre line of the wheel  back in-line with the outer face of the hub I now need a wheel with an ET+20.

So if you look at the TR7 example he is actually using ET correctly and I think he has the math correct, in that if a wheel originally had an ET+25, and you add in a 19mm spacer, then a replacement wheel to have its centre line in line with where the centre line of the original wheel was will need to have an ET of 25 + 19 = ET+44.

Spacers cannot alter the ET of a wheel, in fact nothing can its cast in, well yes you could machine a bit of the mounting face but we will take that as the case that proves the rule."

If you have a wheel with an ET+25 & you add a 19mm spacer to the wheel, the "new" wheel becomes ET+6mm.

You could machine the wheel to increase the ET or add material to the mounting service to decrease the ET?

Make sense to me I'm afraid. Maybe we are talking about the same thing?

Cheers,

Iain

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Quote

 

 

 

 

Edited by spitfire6

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Hi Alan,

 Offset and ET are not the same thing? I understand that ET and backspacing are not the same but mathematically related.

Cheers,

Iain.

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1 hour ago, spitfire6 said:

If you have a wheel with an ET+25 & you add a 19mm spacer to the wheel, the "new" wheel becomes ET+6mm.

I think this highlights where the problem is.

You don't add a spacer to the wheel, you add a spacer on to the hub or between the hub and the wheel.

A wheel that has an ET+25 will have at ET+25 when its was first made and an ET+25 when it is thrown into the smelter at the end of its life. What ever you do spacer wise can't make the slightest difference to the ET of a wheel fitted to it, however it will alter the required ET of a wheel fitted to it if you wished to retain the centre line of a wheel in relation to a part of the suspension.

ET is a fixed attribute of the wheel.

If you really want to argue the point if you welded the spacer to the wheel, then yes a wheel with ET+25 having a 19mm spacer welded to it does become a wheel that is ET+6, and the effect would be the same as buying a wheel with an ET+6  i.e the centre line of the wheel is going to move 19mm outwards. However if you want to fit a 19mm spacer and retain the centre line of the wheel in the same place instead of needing a wheel with a ET+25 you need a wheel with a ET+44

Alan

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If you want to install different wheels to your TR7 determine the space in the rear wheel opening between the inner body and the rear axle flange. Minus a little clearance that is your max back space. The front will have plenty of room. The offset is where the wheel mounting flange is in relation to the rim center. Most modern production wheels are 35 to 45 mm off center. A 7 inch rim is 178 mm. With a center at 89mm plus 43mm offset equals 132mm backspace plus about 12mm for the rim lip. Wheel spacers/ adapters  have their own studs and can be a different bolt circle diameter than the axle flange. Don't forget the wheel center hole compatibility . 4x100 use to be a common Japanese bolt circle diameter.

 

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Hi Alan,

 I disagree that you can not change the ET of a wheel.

Machine the hub mounting surface of the wheel and you will increase the ET of that wheel when fitted. Add a spacer and you will reduce the ET of the wheel when fitted.

That's appears to be a fact?

.Cheers,

Iain.

PS. 122344, Thanks for the extra info.

 

 

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23 hours ago, spitfire6 said:

Hi Alan,

 I disagree that you can not change the ET of a wheel.

Machine the hub mounting surface of the wheel and you will increase the ET of that wheel when fitted. Add a spacer and you will reduce the ET of the wheel when fitted.

 

I agree with you on the first, but as I said earlier in the thread you only have a few mm to play with doing that, which is why I said its the exception that proves the rule.  On the second I would disagree the ET of the wheel hasn't changed, the spacer has moved the whole wheel outwards (altering offsets) but the wheel itself hasn't changed.  Its a bit like putting on 6" Stiletto Heals and claiming that you have grown 6" true the top of your head may be 6" higher, but you haven't physically grown at all you are the same height you were before!

Apart from machining the hub you cannot alter the physical ET of a wheel, you can add/remove spacers, machine the hub on the axle and generally move the reference point that the wheel bolts to in or out, but none of those actually alter the physical ET of a wheel.

Alan

Edited by oldtuckunder
correction of has to hasn't (line 2)

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Hi Alan,

 It's Unfortunate we disagree.

The original post was made in my search of KPI/SAI & castor information & some conflicting information.

Cheers,

Iain.

Edited by spitfire6
/

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Hi Iain

Well here is a wheel we can both agree has had its ET altered! :biggrin:

Been done properly the big lump of alloy has 4 tapped fixings with the wheel, and then top hat steel inserts that go through the wheel and the block, this alters the ET of the wheel from +35 to +5 (block being 30mm thick). I think it legally isn't a spacer but rather an altered wheel, as the MSA prohibit spacers of greater than 20mm, and this would have been through scrutineering many times

1051336658_wheels_studs010(Large).thumb.jpg.0b2c48283a4714cfedf76e134280a430.jpg

934875564_wheels_studs014(Large).thumb.jpg.1550988b5a924c2c3aefc6179f458bec.jpg

Of course as I alluded it does have the ability to confuse as anyone looking at the wheel may well think the cast dimensions are correct.

566262194_wheels_studs016(Large).thumb.jpg.85319ef766135a47a74711f4338e7410.jpg

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Hi Alan,

Thanks for the post.

I have just found out my wheels are +28ET. That's after I changed the front tyres to 185's today. I had thought they were 35mm.

Confused as to why they seem very close to the wheel arch. I have had 195's on the front before with clearance issues only at low v speed manoeuvring.
 

Reason for tyre change was to make my scrub radius go negative.

Because of what I read on the internet:

https://www.racingaspirations.com/scrub-radius/

I then used this to calculate:

https://www.wheel-size.com/calc/?wheel1=155-80-13X4.5ET22&wheel2=185-55-15X6ET28&fcl=12mm&scl=40mm&wcl=12mm&sr=0mm

If you scroll down its better than:

https://www.willtheyfit.com/index.php?width=155&aspect=80&diameter=13&wheelwidth=4.5&offset=22&width2=185&aspect2=55&wheel_size=15&wheel_width=6&offset2=28

The app I always used previously.

 

I need to get ride height, castor, camber & tracking set. I need to measure my front rear track as well. KPI and scrub radius have become important. Going to 185/55/15's from 175/55/15's does feel better. 8mm tread on the T1R Toyos is far better than the 6mm tread I had from new on the Asian tyres. Passenger tyre was too worn in places, ie. outer edge.

Cheers,

Iain

 

 

Edited by spitfire6
url changed

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image.thumb.png.2fa9a36175aa565228fddc66aa34a1c7.png

 

Hi,

 I thought I have posted before, but can not locate.

Every setting seems to be wrong, incorect or just plain implausible?

Cheers,

Iain.

Edited by spitfire6

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