15x7 wheels - what offset?

[75coupe]

Dear All,

I am planning on fitting 15x7 wheels to my Beta Coupe, but after scouring several articles on the forum cannot find a definitive answer to the required offset.

I have seen some 4x98 PCD Rota alloy wheels which have an offset of 15 - would these be any good? Does anyone have experience of these wheels. I will be using them with semi slick tyres for sprints and hillclimbs.

Any advice greatly appreciated

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=280575615256&viewitem=&sspagename=STRK%3AMEWAX%3AIT

[MattNoVAT]

The offset should be cast into the inside of each wheel, When it comes to standard Lancia alloys Cromadora didn't seem to bother about stating the offset, not sure about FPS, but I don't have an FPS wheel to check.  

An example would be stamped/cast "ET15" for a 15mm offset.

For those who are wondering about the ET thing.....its German prefix "ET", meaning "Einpresstiefe" translating into "Press Depth", its fairly easy to work it out for yourself using attached diagram.



Offset (ET): Distance in mm from center (C) of rim to mounting plane (M)

[droptop]

The offset of the wheel is the distance from the point of contact between the wheel and car's hub to the centre line of the wheel. An offset of 15 means a lot of the wheel will be under the car which will mean gerat arch clearence, but is likely to foul brake calipers and steering and suspension components. Stay with an offset as close as possible to the factory original to avoid needing wheel spacers and other issues. A very big offset will result in "deep dish" look setups, but these can seriously shorten the life of your wheel bearings as the load point is way outside of what the designers had intended. Also the arches will catch the wheels when the car is loaded and/or during cornering.
It's a minefield so if you do want the 15mm wheels, go and fit one on the front and with the wheel off the ground, (use an axle stand or some other solid support. NEVER DEPEND ON A JACK WHEN WORKING ON THE CAR! I nearly lost a leg from the knee down many years ago while using just a jack.) first see if you can rotate the wheel by hand without fouling anything and then rotate it while steering the car left and right. Finally, remove the jack and try the steering with the wheel on the ground as the geometry changes when the car is on a jack. Repeat for the back on the side of the fuel filler hose as the hose can sometimes be fouled ba an incorrect rear wheel. If all is well, then enjoy and maybe post a picture.

[75coupe]

Thanks guys, can anyone tell me what the standard ET is for Beta alloys - is it around 35?

Obviously the ET will have to change as the rim gets wider, so from what I can work out from the drawing above an ET of 15 will have more rim to the outside than the standard rim (if ET is 35) which is what I need to compensate for the increase rim width - 1.5 inches wider than std. Fouling arches is not a problem as I can flare if necessary.

Will do some maths and work this out properly - I was being lazy and looking for a quick answer!!

Any one heard of Rota as a manufacturer?

[MattNoVAT]

The "ET" / Offset is always in measured in millimeters!

Not heard of Rota myself.

[hongkongphooey]

Standard offset is 34. I've put et20 7x15 on mine without the 6mm standard spacers on a spyder and it's tight,but it is lowered a lot. I've used 185 tyres too to keep the width down. The rear,i've took the standard spacers off and added 15mm hubicentric ones.....you've got bags of room on a spyder!

I think you might struggle with et15s unless you have standard ride height?

I know rota wheels pretty well,i've had 3 sets before,and they're pretty good quality.

[75coupe]

Thanks for the info.

I have found a useful online calculator and have come up with the following:

A 7" rim with a 15mm offset will give the same inner clearance as the standard wheel, but will protude 38mm more outwards.

A 7" rim with a 20mm offset will give 5mm less inner clearance than std, and will protude 33mm more outwards.

[MattNoVAT]

75Coupe,

Those Rota wheels remind me of Mini-lites!

Also, could you post up the Web URL of the wheel off-set calculator or PM it to me, as its a frequent question that crops up so would be a useful link to add to the forum. Thx

[75coupe]

Matt,

I agree they are very much a minilite copy and just about the right period for my mid '70's coupe, although 15 x 7" would have been massive back then....

the URL for the calculator:  http://www.1010tires.com/wheeloffsetcalculator.asp

Has anyone fitted 205/50 x 15 semi slick tyres? such as Toyo R888, Dunlop DZ03G, Khumo V70A etc, these tend to be wider than you average road tyre of the same dimensions, or do I have to be the guinea pig? My current 185/60 x 14 Toyo R888's are near the end of their life and want to go wider for more front end grip.

Cheers Ian

[MattNoVAT]

I've used the Dunlop 205/50/15's but not on a Beta but a highly modified HF4WD.

Stuck to the track like s**t to a blanket! 

[rossocorsa]

Matt,

I agree they are very much a minilite copy and just about the right period for my mid '70's coupe, although 15 x 7" would have been massive back then....

the URL for the calculator:  http://www.1010tires.com/wheeloffsetcalculator.asp

Has anyone fitted 205/50 x 15 semi slick tyres? such as Toyo R888, Dunlop DZ03G, Khumo V70A etc, these tend to be wider than you average road tyre of the same dimensions, or do I have to be the guinea pig? My current 185/60 x 14 Toyo R888's are near the end of their life and want to go wider for more front end grip.

Cheers Ian

I think 195 is the sensible max on a Beta

[MattNoVAT]

Forgot to say..thanks for posting up the link Ian

[andybeta]

Standard offset is 34. I've put et20 7x15 on mine without the 6mm standard spacers on a spyder and it's tight,but it is lowered a lot. I've used 185 tyres too to keep the width down. The rear,i've took the standard spacers off and added 15mm hubicentric ones.....you've got bags of room on a spyder!

I think you might struggle with et15s unless you have standard ride height?

I know rota wheels pretty well,i've had 3 sets before,and they're pretty good quality.

Correct.

I have got some 7x17" wheels to go on my HPE at some time with 215/40 tyres. I know of an HPE that had 7.5x17" Team Dynamic rims with 215/40 Michelin F1s on that went around Goodwood extremely quickly and there were no rubbing issues. The car, a bright yellow in your face HPE VX with Weber DCOE 45, was quicker than the Integrales on the day iirc.

Iirc I calculated the thickness of the spacers I needed on the rear was 18mm as the 17"x7 wheels have offset 38ET. Front didn't need any spacers. They are 4x98PCD.

HTH.

[mangocrazy]

This is another site that I use when needing an answer to wheel/tyre related questions:

http://www.carbibles.com/tyre_bible.html

[75coupe]

Well here they are 15x7 Rota ET15 wheels with Toyo R888 205/50x15 semi slick tyres. I removed the standard Lancia spacers to fit. An ET of 20 would probably fit better. There is plenty of clearance to strut, and no problem lock to lock on the front.

Yet to be tested in anger!!

[markwast]

Now Im JEALOUS .

Well done Iain.

[75coupe]

Thanks Mark, but I think I'm still jealous of your nice vented disc set up, and the GRP bonnet and the alloy crank pulley and nice exhaust !!!.....

[lanciamad]

Looks amazing Iain! and your be able to fit a vented disc setup behind them

[WestonE]

Off Topic I know, but what indicator units are those on the front panel?

The wheels look amazing.

Eric

[75coupe]

Eric,

They are LED side indicator repeater lights used normally on semi trailers and trucks etc. They are Narva brand, not sure if they are available and/or legal in the UK.

http://www.narva.com.au/products/browse/side-direction-indicator-3