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15" WHEELS ON 77mgb

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Mertbeebe77MGB Avatar
Mertbeebe77MGB Merton Beebe
Florence, Oregon, USA   USA
I am interested in putting 15" wheels in my 77 MGB. I now have 185/60R14
wheels on 5.0 wide rims. I also have a 3.4 liter Chevy V6 with a Tremec
T5 v8 transmission. With this combination I feel like I need lower gears
in my rear end. I have the stock 3.9 ratio. If I go to the 185/65R15 tire that will give about a 10% effective rear end reduction.

I woould like some feedback on the best wheel width and the amount of
positive offset that would fit without hitting the fender lip. I would like to hear from guys who have made this change and also what kind of alloy wheels that were used. (After market and older stock wheels that have the correct offset for '77 MGB.)

Thanks,

Mert



Edited 1 time(s). Last edit at 2011-10-11 04:53 PM by Mertbeebe77MGB.

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canuck Avatar
canuck David Ross
Tampa, USA   USA
1978 MG MGB V6 Conversion "New Baby"
15x6 Superlites from Hap Waldrop with Goodyear V rated Eagles 195/65/R15. No offset and fitment is not problem.


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mgv8glen Avatar
mgv8glen Glenn Towery
Dover, DE, USA   USA
I have run the 195 65 15s on the early Saab 900 wheel, that are 5.5 inckes wide. I do not know what the off set is but I do know that I have to use a 3/8 spacer for the wheel to sit just wright

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Duncan Avatar
Duncan Duncan Cowen
Delta, Vancouver, Canada   CAN
I've just posted about the relationship I've experienced between steering feel and excessive positive offset. I thought it was the tire width that made my A so heavy to steer... I was wrong! Something to consider as you choose your new rims.

Peter-Sherman Avatar
Peter-Sherman Peter Sherman
Melbourne, Australia   AUS
positive offset moves the center line of the tyres in, and makes the centers, where the bolts or spinner is, stick out more. It reduces the wheel track. The terms are counter intuitive, you'd think positive would make the track larger.
On an MGB 25mm pos offset with 15 by 6 inch wheels (that adds up to 4.5" backspacing) fits under the standard guards There are no clearance issues with 195 by 60's . I do not believe that there would be issues with larger tyres, but I can't be sure. Take some measurements off your current set.

1744 Avatar
1744 Gold Member Bill Guzman
CA, USA   USA
1973 MG MGB GT "Renegade I GT"
1974 MG MGB "Renegade"
The best to explain what happens with large offsets and bigger tires is with this picture.

The line from the upper ball joint or king pin through the steering and lower ball join or king pin should be as close as possible to the center of the tire or no further than 1" from the edge of the tire.

This makes a big difference in steering effort. Way the line is away from the tire it increases tire scrub, not a good thing.

Observe performance vehicles, they all have the offset to the inside and the rear to the outside, this reduces tire scrub.

The picture of the wheel and tires, both tires are of the same dia, the front is a bit narrower and the offset is to the inside, the rear tire and wheel is wider and the offset is to the outside.

225X50X15 rear and 205X55X15 front same diameter.



It is our attitude that will determine the outcome


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Jim Stabe Avatar
San Diego, CA, USA   USA
Thanks for the picture Bill. That is what I was trying to explain in the other thread about scrub radius. http://www.mgexperience.net/phorum/read.php?40,1877355



Jim

"If you want me to agree with you then we would both be wrong"

'66 MGB widened 11" with supercharged LT1 Chevy and 6 speed, C4 Corvette suspension
Pictures here Part 1 http://forum.britishv8.org/read.php?13,7581
Continued in Part 2 http://forum.britishv8.org/read.php?13,22422
Continued in Part 3 http://forum.britishv8.org/read.php?13,33108
Continued in Part 4 http://forum.britishv8.org/read.php?13,40751
Continued in Part 5 http://forum.britishv8.org/read.php?13,48698,48698#msg-48698

Mertbeebe77MGB Avatar
Mertbeebe77MGB Merton Beebe
Florence, Oregon, USA   USA
David;

Thanks for your setup info. The wheels look good! I have 3 other questions after looking at your pictures.

(1) Is your MGB lowered? It looks like it is from the picture. My car is about 9" from ground to the bottom of the
rocker panels.

(2) What is the dimension between the front side of the wheel rim and the mounting face of the wheel?

(3) When you changed from stock wheels to 15 x 6 wheel, did the steering effort stay the same or become easier?


Thanks,

Mert

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V8MGBV8 Avatar
V8MGBV8 Carl Floyd
Kinggsport, TN, USA   USA
In reply to a post by Mertbeebe77MGB My car is about 9" from ground to the bottom of the
rocker panels.

Yep, those stock height RB MGs look like 4 wheel drives. grinning smiley

Mertbeebe77MGB Avatar
Mertbeebe77MGB Merton Beebe
Florence, Oregon, USA   USA
Peter:

Thanks for your reply. I take it by your car photo that you are using an
after market wire wheel. I believe that my stock Rostyle wheel (14x5)has
a 25mm offset. It seems like a 6" wheel should have a little bit more
offset to keep the face of the wheel in the same place.

I have found a few sets of wheels on ebay that have 40mm to 55mm offset
that I like the looks of, but none with a 25mm offset. The dealers that
have Minilite style wheels guaranty they will fit, but they are very
pricy. ($650.00+)

Comments please!

Mert

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Peter-Sherman Avatar
Peter-Sherman Peter Sherman
Melbourne, Australia   AUS
Merton,
If you go up an inch in size you add half an inch either side. So in theory you are correct. However most people want the tyre filling the guard so aim at close to the edge, but not too close to rub on hard cornering. I have about half an inch on the outside (average of both sides, closest point) and slightly under an inch to the bump stop base on the inside. There is an offset to the left with MGB's, usually a quarter to one half of an inch.
The wire wheels you see there are Dayton dental drive.
http://www.britishv8.org/Articles/Dayton-Wire-Wheels.htm
Good article, however, not quite correct about the max size that will fit on an MGB. 15 by 6 with 195 by 60 tyres fit with no rubbing. With the adaptors these wheels have a 4.5 inch backspacing. Dayton measure that way. Backspacing is when you place a straight edge across the back of the wheel rim and measure from the centre of that to the bolt up face of the wheel centre. You have half of 6 inches, which is three, plus one inch pos offset, = 4 inches. Then you must take into account the thickness of one of the rims, which is usually about half an inch. Wheel width is measured from the inside of the rims so a 6 inch wheel measures 7 inches from the outside of the rims.
These are quite expensive, however, unlike the splined or rudge style wire wheels, those big teeth never wear out, never clunk and are very strong. So are worth it if you want wires. If in fact you really do want wires. The Wire wheels are about 4kg heavier than my performance superlight alloys. I contacted dayton and they said that the dental drive wheels are about 1 lb lighter than their splined drive wheels of the same dimensions and spoke count, however you need an adaptor, and spinner which weigh 4 kg. A splined hub and its spinner would be heavier than a non splined hub. In other words, close enough to the same weight.
40 to 55mm is allot of pos offset. The inside of the wheel would rub on the bumpstop base, unless you used massive spacers. A bit dangerous I feel.

V8MGBV8 Avatar
V8MGBV8 Carl Floyd
Kinggsport, TN, USA   USA
dcraddock43 Gold Member Dave Craddock
Redford (Detroit), Mi., USA   USA
Try Hap Waldrup, he's a Superlite wheel dealer,http://www.acmespeedshop.com/
Dave Craddock


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