Given that the wheel diameter and width stay the same what is the impact on handling with different offset wheels? As an example the lower the offset a wheel has the wider the track would be. The engineers at MINI selected a 52mm offset on the GP wheels and because they were a special run could have specked any offset they may have wanted. I am sure that their decisions are made for the mass's and are not necessarily best for handling.
If you were to go from a 52m offset to say 40mm offset it would increase your track approximately 1" (1/2" per side). What could one expect from that type of change?
Thanks, Steve

 

cant believe no one touched this yet. So here goes. You steering will feel heavier, thats for sure. I believe it also lowers your
{center of gravity (in comparison to width anyway (some highly technical stuff i havnt fully warped my head around yet, but get the jist of it))this part is wrong, but leaving it in for schizers and giggles}. But it also lowers your active spring rates, because their is now more leverage, which means you will pick up more body roll (noticeable or not is another question, with 1 inch wider track, and all else being equal, than yeah, you'll probably notice...). It also decreases the tendency to understeer (assuming front track is wider than rear) but also cant really explain that either. Be aware tho, going with wider track "may" have adverse effects on wheel bearings. Im sure eventually it will, but you could be looking at 125k miles instead of 150k miles, who knows for sure. Lots of folks run them, and dont seem to be having wheel bearing issues yet, at least not on the grand scale.

Hope some of this helps, if nothing else, its a bump, and maybe meb or onasled will chime in.

Beecher

 

No offense Beecher but I disagree with most of your comments. I'm no expert but let me try to explain. I'm not trying to bash here so bear with me.

Assuming the only change is offset....

Steering may feel slightly heaving but probably not by much. I don't know if one would be able to feel the difference - unless you go way beyond the typical change of a few millimeters of offset so that ackerman and steering geometry is somehow changed. Two items that can sometimes increase the resistance required for steering to feel heavier, would be increased sprung weight and tire compound. Those are probably not the only two items. The gear ratio on the steering rack, amount of power assist and diameter of steering wheel (i.e. amount of leverage the driver can exert upon the steering gear) are also factors.

Center of Gravity has nothing to do with it. Center of Gravity is about the height of the car's center of gravity. This is again an exercise in geometry and advanced math to determine the car's center of gravity. Suspension changes to ride height is an obvious thing that can lower a car's center of gravity.

Understeer or general handling characteristics will likely not change assuming all 4 wheels received the same change in offset. Understeer can be changed by changing grip characteristics through things that affect roll - like suspension stiffness, suspension geometry.

You are correct on potential for wear on the wheel bearings - depending on the car and bearing design. The NSX is famous for wearing out wheel bearings when people switch to larger and often heavier wheels. Going out further on the offset can exert more leverage on the fixed axis of the wheel bearing (think breaker bar).

 

The offset for a lot of the Mini wheels of varying diameters are pretty close to 50 http://www.mini2.com/forum/faq.php?f...factory_wheels

I'm no expert here so hopefully someone will add more info to this thread. But from what I understand, increasing track within the parameters of the car's optimal suspension design (not stance) can have the effect of increasing overall grip levels. Might want to Google suspension design and track width to learn more.

Offset also plays a role in allowing one to run a particular width of tire and clear brakes and suspension components w/o interfering with body work.

At higher speed levels, overall track and wheel widths also has an affect on aerodynamics. Wheels that stick out further than others and wider tires can increase drag (and thereby decreasing MPG).

 

You will notice more torque steer. This will be the biggest difference when changing the offset. Stress on bearings is an issue depending how much you change things.

 

so we agree on all the center of gravity thing. I had exceptions in my posts that covered all your "except" parts. hahaha.

I have driven a mini with 3/8 spacers and more offset in the wheels (15x8 37 offset i think, with 225 tires (overall rim and tire weight about 30lbs, so quite light)), the steering was quite abit stiffer. It was nice tho. He also mentioned going 1 inch wider in the above post, that would quite definently
be noticeable ( so i guess it was more spacer than rim i felt maybe).

My remark about under steer, you are correct, if the track change was from rims, balance would not change, but overall grip would (my mind was on spacers). Thanks for clarifying that.

I will see if i can find the post that i "thought" said something about center of gravity. Sounded complicated, and i dont think i read it word for word, so...

Beecher

oh, and no offense taken

 

https://www.northamericanmotoring.co...center+gravity

ok, found that, not the post i read before tho, but i believe was the result of it (the one i read must have been the one meb refers to in the first post.

post 18 was what i think i was trying to say.

boy oh boy. hahaha

Beecher

 

I believe you may be correct on the c.o.g. thing. But you also may be thinking about Roll center?

 

maybe.....

I think im going to have to get out the puhn book. that thing gets pulled out alot on this forum. no doubt a good thing. Maybe i will find some on roll couple to thro in, just for good measure, hahaha.

I think your right. After reading the huge thread about it the other day, this discusion, and the one i linked above, i have no idea anymore, hahaha. Alls i know is wide track is good, and go wider in the front if you can, but that is getting into spacers, and now im kind of doubting that mild changes in track from offset, which is usually due to width changes, probably doesnt add up to diddly in the world of handling.

Ahhh, i love suspension discusions as much as i love discusions about how to build a cooper with more horsepower than an s. hahah.

Beecher

 

PenelopeG3
Thanks for the correction on stance vs track. I have made corrections to my post.
Steve

[quote=PenelopeG3;1922040]
I'm no expert here so hopefully someone will add more info to this thread. But from what I understand, increasing track within the parameters of the car's optimal suspension design (not stance) can have the effect of increasing overall grip levels.

 

I have written a lot about this.

CofG can only change if the car is lowered or if components or weight is shifted. Changing offset does not alter CofG

Spring and damping rates will be reduced - this is called motion ratio and any offset changes must be fogured into the motion ratio. These are linear equations but depend highly on the pickup point for the strut, the inner pivot point and obviously, the tire's center line

SAI or kingpin axis (angle) is not altered but because the tire is moved farther out, scrub is changed for the better. In simple terms, you must move the tire far enough out to avoid center point steering - the SAI meets the ground at the tire's center line. This is not good since this location does not cause the tread on either side to distort. Distortion is necessary if pneumatic trail, tire slip signals and load are to be telgraphed to the steering wheel - having the leverage point inside the tire's centerline is better for sport or track work. But beware, if you lose one brake up front or if one tire blows, this scrub location will leave all of the control within your hands as a driver - unstable with a car driven by its front wheels!

Roll center locations and therefore instantaneous centers will be moved both statically and dynamically. And therefore, camber curves will be altered.

Roll resistance will increase since the track is increased. But since the tires can perform more work because they now posses more mechanical leverage - more grip, there is a little washout. Essentially, the right and left tires perform a more equal role. The car will resist quick turn-in (assuming we are discussing the front being wider than the rear) even though the steer gear has not changed. But, the car will also bite with much more tenacity once it takes a set.

My total front and rear offsets were 23mm front and 33mm rear. you will need to add a littel more camber to the rear wheels if you use anything close to the above rear offset; the instant center moves farther away decreasing camber curver or camber gain during cornering.

There are a host of other muchy more subtle items that are affected, but these are the big ones. This was quickly written. FYI - the Mini's stock track is slightly more narrow up front and this aids that quick tuck-into corners.

 

all praise meb.

he knows what hes talking about. Maybe you should do a nice little write up about some of this stuff and have it stickeyed or something, that way you dont have to keep posting it. Or just type it up in word, and copy and paste it to post when required. hahaha.

Thanks

Beecher

 

If I knew how to get drawings on here I would prepare a few shematics. If someone???wants to figure how to get drawings on here, I'll fax them. I have to prepare them first.

 

id be willing, but have no idea how. i was trying to figure out how to post pics in a thread earlier, got tired of waiting for my dial up.

Might be able to fax them to me, and i would then scan them, and try posting them from a friends house, or at least email them to someone who could post them.

Beecher

 

i can host/post pictures for you, i don't have a fax machine, but i think my dad does, i will ask him and get back to you

 

I'm assuming you don't have a scanner. It can work well to simply take pictures with a regular digital camera, set to close-up (macro) focus mode. If the drawings are computer based, there are various ways to get an image file or print directly to a PDF. I can help with whatever may work for you (I also have a fax machine).

 

I have 15x6.5 (12 lbs) wheels with a 40 offset. Also I have 205/50/15 tires. What kind of charateristics will this give the car?

 

You have an 03' Cooper.

Stock wheels and tires are-
15x5.5" +45mm offset (stock rim weight 12 lbs or heavier)
175/65-15 Continental tires
Backspace is 5"

15x6.5" wheels +40 offset
205/50-15 tires are smaller than stock about 23.1" tire diameter
Better stock size would be 205/55-15 or 195/60-15
Backspace is 5.3"

Your rim is now 1" wider than stock. Due to the offset about 0.3" more rim faces the inside towards the suspension parts while 0.7" faces more to the outside of the car.

With a lowered suspension you have to keep at stock tire diameter or less so for you the 205/50-15 can be OK if lowered. For a stock suspension MINI you'd get more wheel gap and 205/55-15 would be a better size.

Since your new wheel position is only about 0.4" centered toward the outer side of the car I would not expect that +40mm offset would do much to change your handling as much as reducing weight in the rims or improved handling based on the exact tire model you selected to use. When using a wider rim it is common to have an offset that is less than stock offset.

 

My car did come stock with a 175/65/15 with 15x5.5 wheels. The tires I am running are 205/50/15 BfGoodrich G-force tires. I know that 15x6.5 rims are smaller and lighter than say 17x7.5, but would the 17x7.5 rims handle better do to the bigger size?

 

There are at least 6 BF Goodrich g-Force tires.

For street use-
In extreme performance Summer tires-
g-Force T/A KD
In ultra high performance Summer tires-
g-Force T/A KDW2
g-Force Sport
In ultra high performance All Season tires-
g-Force Super Sport A/S

17x7.5 are not by themselves going to allow for better handling per se. But 7.5" wide rims are wider so wider tires are possible and will fit. You may be gaining weight due to the larger diameter 17" rim, light rims are possible but very costly usually.

Tire sizes in 17" will be with much lower sidewalls that are stiff and ride quality will be not as comfortable depending on how your current tires are now. If you have KDW2 those are a little harder riding. 215/40-17 or 215/45-17 are possible sizes but if you have lowered suspension then there could be some rubbing with the taller 215/45-17.

Stock 205/45-17 will fit 17x7.5 rims but tire selection is less.

17x7.5" rims will need to be with less offset to fit any MINI whell well.
+40mm offset will put the wheel about the same position as stock.

The advantage in handling will come from the stiffer sidewalls of the tires that fit this sized rim and the tire model you choose since some tires have various sidewall contruction that could help handling vs comfort.

There is no great reason to move from 15" rims to 17" rims unless you like the appearance.

For comfort the 50 series sidewall should work for street driving.
Another option is to look at other size tires 195/60-15 or if you are lowered then even 195/55-15 (Bridgestone Potenza RE-01R Extreme Performance Summer tire handles well).

50 or 55 series sidewalls are not possible for 17" rims since they are much taller than stock MINI tire diameter.

 

Well I have 205/50/15 BfGoodrich GForce Sport summer tires. The problem is that I have wheelgap more than I want. Should I keep the 15's or get a larger size wheel. Here are some pics of the gap:

 

From the pictures your wheels and tires look fine.

To reduce wheel gap lower your MINI with lowering springs or coilovers or
get different sized tires like 205/55-15 or 195/60-15 or 185/65-15.

 

...15" wheels also weigh less than larger wheels.

...drawings...hopefully I can get to these. In addition to all of my comments above, increasing track without altering anything else, raises the static roll center. This is actually a good thing if we look at what lowering our cars will do to the relationship between RC and CofG. FYI

 

i sent you (meb) a PM about hosting the drawings for you with my fax number

 

Got it. I sent you my email address. If you can send me yours, I'll email the image to you, then follow up with a description here once you've posted the pic. Thanks for helping the computer illiterate