Custom wheels for 928 for sale
04-10-2009, 05:17 PM
#17
Rennlist Member
Thread Starter
Ive fitted wheels and large tires that fit, both inside and outside with no rubbing. Now, to do this, you have a limit of 8" backspacing of a 9.5 and 11" rim. changing those dimensions changes the backspacing requirements.
Since we are talking about rim width. (bead to bead) that number cant vary much, even with different lip styles. however, on the inside where the lip is measured to the mounting surface, sure, .5" can be a variance I would imagine.
Bottom line, if you use an 8" backspacing with the dimensions I've used and convert it, it will more than likely work.. In otherwords, you will get the same safe fit as I have, by using an 8.5" rim with 7" of backspacing and so on (vs the 8" i use on a 9.5" rim) this will keep the rim face and tire at the same position near the fender lip with a little saftey margin. run a 275, less safety margin. run a 255, and you have good amount of margin.
I was using the total wheel width for my calculation for offset and that is not right. its only the bead to bead distance of the.
mk
If you have a 9.5" front rim for example . thats 241mm. half of that is
Since we are talking about rim width. (bead to bead) that number cant vary much, even with different lip styles. however, on the inside where the lip is measured to the mounting surface, sure, .5" can be a variance I would imagine.
Bottom line, if you use an 8" backspacing with the dimensions I've used and convert it, it will more than likely work.. In otherwords, you will get the same safe fit as I have, by using an 8.5" rim with 7" of backspacing and so on (vs the 8" i use on a 9.5" rim) this will keep the rim face and tire at the same position near the fender lip with a little saftey margin. run a 275, less safety margin. run a 255, and you have good amount of margin.
I was using the total wheel width for my calculation for offset and that is not right. its only the bead to bead distance of the.
mk
If you have a 9.5" front rim for example . thats 241mm. half of that is
Using backspacing to determine wheel fit sucks. There is no standard on backspacing. Some calculators factor in wheel lip and some don't. And the ones that do factor it in just put in a generic 1" or something. It's very inaccurate because not every wheel has the same lip. ET on the other hand is always accurate.
Dan
'91 928GT S/C
475hp/460lb.ft
Dan
'91 928GT S/C
475hp/460lb.ft
04-10-2009, 05:19 PM
#19
Rennlist Member
Thread Starter
04-10-2009, 05:39 PM
#20
Rennlist Member
Thread Starter
Backspacing – (Wheel Width + 1)/2 * 25.4 = offset
so, from the site formula these wheels would be:
FRONT-
7" -( 8.5+1)/2 x 25.4= 57mm offset
REAR-
8" - (11+1)/2 X 25.4 = 50.8mm
Or my Holbert 928 Fronts with the 9.5" rim and 8" backspacing-
8"- (9.5+1)/2 x 25.4 =69.8mm offset
how about 10" front rims with 8.5" backspacing-
8.5-(10 +1)/2 x 25.4 = 76.2.
So, it looks like the offset changes even though the position of the rim to the fender edge is the same?? confusing. Thats why i stick to what works. I know if you give me a 8" backspacing rim of 9.5 f or 11 rear, it will work.
(or 8.5' backspacing 10" wide front )
mk
so, from the site formula these wheels would be:
FRONT-
7" -( 8.5+1)/2 x 25.4= 57mm offset
REAR-
8" - (11+1)/2 X 25.4 = 50.8mm
Or my Holbert 928 Fronts with the 9.5" rim and 8" backspacing-
8"- (9.5+1)/2 x 25.4 =69.8mm offset
how about 10" front rims with 8.5" backspacing-
8.5-(10 +1)/2 x 25.4 = 76.2.
So, it looks like the offset changes even though the position of the rim to the fender edge is the same?? confusing. Thats why i stick to what works. I know if you give me a 8" backspacing rim of 9.5 f or 11 rear, it will work.
(or 8.5' backspacing 10" wide front
)mk
Backspace and offset are two ways of describing where the wheel sits in relationship to the hub. As such, there is a relationship between the two making - it possible to convert from one to the other.
Backspacing is the easiest to understand. It is simply the distance from the back of the mounting pad to the back lip of the wheel. It is measured by laying the wheel on its face, placing a straight edge across the wheel, and then measuring down to mounting face. The higher this measurement the more the wheel is pushed inboard towards the car’s centerline, as shown in the illustration above.
Offset is the distance from the mounting surface to the centerline of the wheel, expressed in millimeters. Positive offset means that the wheels are pushed inboard towards the centerline of the car like a car with front wheel drive. Negative means that the wheels are moved outboard towards the fenders, widening the track.
TO CONVERT OFFSET TO BACKSPACING:
For positive offset wheels: (Wheel Width +1)/2 + (offset * .03937)
For negative offset wheels: (Wheel Width +1)/2 - (offset * .03937)
TO CONVERT BACKSPACING TO OFFSET:
Backspacing – (Wheel Width + 1)/2 * 25.4 = offset
Round this result to the nearest milimeter. If the answer is a negative number the wheel has negative offset, if positive then a positive offset.
http://www.mickeythompsontires.com/t...p?bulletin=s10
Backspacing is the easiest to understand. It is simply the distance from the back of the mounting pad to the back lip of the wheel. It is measured by laying the wheel on its face, placing a straight edge across the wheel, and then measuring down to mounting face. The higher this measurement the more the wheel is pushed inboard towards the car’s centerline, as shown in the illustration above.
Offset is the distance from the mounting surface to the centerline of the wheel, expressed in millimeters. Positive offset means that the wheels are pushed inboard towards the centerline of the car like a car with front wheel drive. Negative means that the wheels are moved outboard towards the fenders, widening the track.
TO CONVERT OFFSET TO BACKSPACING:
For positive offset wheels: (Wheel Width +1)/2 + (offset * .03937)
For negative offset wheels: (Wheel Width +1)/2 - (offset * .03937)
TO CONVERT BACKSPACING TO OFFSET:
Backspacing – (Wheel Width + 1)/2 * 25.4 = offset
Round this result to the nearest milimeter. If the answer is a negative number the wheel has negative offset, if positive then a positive offset.
http://www.mickeythompsontires.com/t...p?bulletin=s10
04-10-2009, 06:48 PM
#21
Race Car
Yes, in order to keep the edge of the fender and the wheel the same distance as you increase the width of the wheel, the offset required will go up. There was some pretty nasty looking tire/fender smoking going on at one point in your last video on the passenger front Mark...
Dan
'91 928GT S/C 475hp/460lb.ft
Dan
'91 928GT S/C
475hp/460lb.ft
04-10-2009, 07:22 PM
#22
Rennlist Member
Thread Starter
Did you not hear what happened???? I got HIT badly in the front and rear wheels and the fender was crushed and rubbing on the tire in the rear and even worse on the front. notice the other video on the fender cam, no rubbing. I have never had rubbing of the tires on the fenders with the 275s, even with the fender lip 1" below the top of the tire!!
MK
MK
Yes, in order to keep the edge of the fender and the wheel the same distance as you increase the width of the wheel, the offset required will go up. There was some pretty nasty looking tire/fender smoking going on at one point in your last video on the passenger front Mark...
Dan
'91 928GT S/C 475hp/460lb.ft
Dan
'91 928GT S/C
475hp/460lb.ft
04-10-2009, 07:23 PM
#23
Rennlist Member
Thread Starter
OH, that was not my car if you are talking about the fender cam. notice the color is gold and it is the tire hitting the fender about 1" in. thats my buddies vet . those tires are WAY out. they have more clearance upward, so all he needs is stiffer springs. he has a set of rims that are farther in though.
mk
thats my buddies vet . those tires are WAY out. they have more clearance upward, so all he needs is stiffer springs. he has a set of rims that are farther in though.mk
Yes, in order to keep the edge of the fender and the wheel the same distance as you increase the width of the wheel, the offset required will go up. There was some pretty nasty looking tire/fender smoking going on at one point in your last video on the passenger front Mark...
Dan
'91 928GT S/C 475hp/460lb.ft
Dan
'91 928GT S/C
475hp/460lb.ft
04-10-2009, 11:17 PM
#24
Race Car
OH, that was not my car if you are talking about the fender cam. notice the color is gold and it is the tire hitting the fender about 1" in. thats my buddies vet . those tires are WAY out. they have more clearance upward, so all he needs is stiffer springs. he has a set of rims that are farther in though.
mk
thats my buddies vet . those tires are WAY out. they have more clearance upward, so all he needs is stiffer springs. he has a set of rims that are farther in though.mk
Dan
'91 928GT S/C
475hp/460lb.ft
04-11-2009, 02:33 AM
#27
Rennlist Member
Thread Starter
I wish my kinesis were chrome on the rim outers. the polished area just gets torched by the brake dust and I am pretty **** about keeping them clean and polished, inside and out.
