Fitting Wide Aftermarket Wheels
- Thread starter Eastep
- Start date
Hi Mike,
8.25" wide? Are you planning to roll your wheel arches? Or cut them off and go with some type of fender flares? Check out the description on these 15x8 wheels with a zero offset that Vick's offers. I think you are going to find that you have some serious interference at that wheel width without modifying you car. I could be wrong I guess.
8.25" wide? Are you planning to roll your wheel arches? Or cut them off and go with some type of fender flares? Check out the description on these 15x8 wheels with a zero offset that Vick's offers. I think you are going to find that you have some serious interference at that wheel width without modifying you car. I could be wrong I guess.
Eastep
True Classic
Thanks Jim. I can roll my fenders, no problem. Im also a Vee dubber, so I don't mind if tires rub a little on lock to lock. "If it ain't rubbin; you ain't dubbin". My main concern is whether or not there will be a constant rub on the springs or if that offset will require a spacer/adapter? If no spacer is required to clear the suspension, then Ill simply use wobble bolts and centric rings but Im unsure how the wheels will atcully look mounted in those specs. Tires will be 195/45 or possibly 195/40 if available.
If you look at the specs for the two 195/45/15 offerings on Tirerack, you will find that the maximum rim width for both tires is 7.5". You are planning to to use a rim that is 8.25 wide. I am certainly no wheel/tire combo expert, so I will sit back and see what advice other folks have to offer.
Eastep
True Classic
They have to be stretched. Here are a cpuple shots of 195/45's on one of my old GTi (before it went "low") the wheels were 8in. Like you, though; I too would like to hear from some wheel/tire & suspension gurus. If it were a VW I know what would and wouldnt work. Since Ive never lowered, stanced and went wide on an X1/9, its new territory for me.
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Rupunzell
Bernice Loui
Simply picking a wheel & tire without consideration for how the chassis with suspension functions is not a good idea. More often than not, wheel and tire choices are made for visual considerations and the belief a wider-"bigger" tire produces more traction. Wider-bigger tires alone does not produce more traction as the actual contact patch remains much the same due to the weight loading the inflated tire being fixed, thus the contact patch on a pneumatic tire will remain much the same. Think of this effect as a inflated balloon and pressing a hand upon it.
Altering the shape of the tire contact patch alters how the tire is loaded, this is part of the reason why tire & wheel sized affects mechanical grip of a suspension and chassis. There is not more contact patch, the contact patch and tire loading changes.
Real race cars that use aero to convert power to down force with vehicle speed effectively increases the weight loading on it's tires producing more grip. This is where a wider-bigger tire can actually produce more traction and grip. Few road cars are designed this way or could produce the aero down force loading pure track race cars can produce (think F1) or similar.
Tire design and tread compound has a MUCH more significant effect on grip-tracion produced by a tire than size alone.
Change the wheel offset, changes the scrub radius which affects steering, stability under braking and stability when the chassis-suspension is traveling forward. To quote From here and there in Race Car Vehicle Dynamics:
Why negative scrub radius can be good for a FWD car:
"If one wheel has more traction than the other while accelerating or braking, it would tend to yaw the car, but the difference in tractive force turns the front wheels slightly to compensate."
If you had positive scrub radius, (towards the inside of the wheel center) and you had different braking in the two wheels, it would jerk the wheel out of a straight line, making the car unstable.
All that said, it sounds like 0 scrub radius is never bad
Do not simply pick what is visually appearing and make it fit the exxe chassis, choose a tire and whee combo that works properly with the exxe chassis-suspension-power train-road conditions-driver needs and many other factors. Simply making a wheel-tire fit often does not produce good overall results. Realistically, how much mechanical grip does a road car really need and what is the duration of that mechanical grip needed? Vehicle traveling in a straight line does not require a lot of mechanical grip, tire loading in cornering can, accelerating and braking does too.
Bernice
Altering the shape of the tire contact patch alters how the tire is loaded, this is part of the reason why tire & wheel sized affects mechanical grip of a suspension and chassis. There is not more contact patch, the contact patch and tire loading changes.
Real race cars that use aero to convert power to down force with vehicle speed effectively increases the weight loading on it's tires producing more grip. This is where a wider-bigger tire can actually produce more traction and grip. Few road cars are designed this way or could produce the aero down force loading pure track race cars can produce (think F1) or similar.
Tire design and tread compound has a MUCH more significant effect on grip-tracion produced by a tire than size alone.
Change the wheel offset, changes the scrub radius which affects steering, stability under braking and stability when the chassis-suspension is traveling forward. To quote From here and there in Race Car Vehicle Dynamics:
- Scrub radius will give you bump steer in one-wheel bumps
- For high-speed stability in the presence of road disturbances, zero or slight negative scrub radius is desirable (negative is outside the wheel center plane)
- Braking forces introduce steer torques proportional to the scrub radius. (This is actually more important for FWD cars as there are also forces induced by the wheels driving)
- There are some good stabilizing effects scrub has on front wheel drive cars.
Why negative scrub radius can be good for a FWD car:
"If one wheel has more traction than the other while accelerating or braking, it would tend to yaw the car, but the difference in tractive force turns the front wheels slightly to compensate."
If you had positive scrub radius, (towards the inside of the wheel center) and you had different braking in the two wheels, it would jerk the wheel out of a straight line, making the car unstable.
All that said, it sounds like 0 scrub radius is never bad
Do not simply pick what is visually appearing and make it fit the exxe chassis, choose a tire and whee combo that works properly with the exxe chassis-suspension-power train-road conditions-driver needs and many other factors. Simply making a wheel-tire fit often does not produce good overall results. Realistically, how much mechanical grip does a road car really need and what is the duration of that mechanical grip needed? Vehicle traveling in a straight line does not require a lot of mechanical grip, tire loading in cornering can, accelerating and braking does too.
Bernice
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My old GTI was stock. I think it had wheels very similar to "Phone Dials" on it. Of course this picture is so small, it is hard to tell.
I loved that car. Another one I regret getting rid of. I traded it in on a full size Chevy Blazer because my wife said I could buy a boat. Next thing I know, I have no boat, but I have a lovely little baby girl. That is life, right? So my wife let me trade the Blazer in and get a Mitsubishi Starion. That car was awesome and scary fast in its day.
I had that Starion for a few years. Then, as you can see, I had to sell it to get a full size van when my son came along. A Starion with one baby seat was doable, two was not going to happen.
I had that Starion for a few years. Then, as you can see, I had to sell it to get a full size van when my son came along. A Starion with one baby seat was doable, two was not going to happen.
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A set of the most common X wheel was the 13x5 CD91 which has an offset of 24 and a back space of 102mm (or 4.02"). The 13x5.5 CD31 wheels I have on my 85 are stamped "Offset 18".
You will have 2mm more "stick out" when comparing an offset of 20 to 22. Here is the Tirerack definition with a diagram. Offset is measured from the center line of the wheel to the mounting surface. I believe a 20 offset in a 8.25" wheel will translate differently on a given car compared to a narrower wheel.
Eastep
True Classic
Thanks Jim. Unfortunately I cant find the style of wheel I want in a negative offset, which is what appears to be ideal. The lowest Im coming across is a +0 offset. If Im understanding correctly: zero is dead center, with + offset= left of center and - offset= right of center. By this logic a +20 offset would equal 20% of the rim (regardless of width) being left of center. At 8.25in or 209.55mm wide, that leaves 80% or a huge (in this case) 167.64mm (6.6in) of wheel right of center!
Are these numbers correct? Is my understanding and math accurate?
Are these numbers correct? Is my understanding and math accurate?
kmead
Old enough to know better
Use this calculator:
http://www.rimsntires.com/specspro.jsp
OE wheels were CD91 5" wide with 25-27mm positive offset and the widest factory rim was the 5.5" wide "iron cross" CD16 with positive offset of 25
What you will find is that to go with a rim of this width that you need to have an offset of 0, an offset of 20 will have the rim occupying the same space as the strut on an X. You can fiddle around with the dimensions to your hearts content.
http://www.rimsntires.com/specspro.jsp
OE wheels were CD91 5" wide with 25-27mm positive offset and the widest factory rim was the 5.5" wide "iron cross" CD16 with positive offset of 25
What you will find is that to go with a rim of this width that you need to have an offset of 0, an offset of 20 will have the rim occupying the same space as the strut on an X. You can fiddle around with the dimensions to your hearts content.