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Old 02-12-2017, 08:14 PM   #31
GEORDIE SP1
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Default Offset, KPI/KPO and handling

Good stuff, Iím on -7 ET and itís evil under acceleration, bought a set of +28 ET a few months ago to change over the winter.


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Old 02-12-2017, 11:20 PM   #32
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The single negative I've notice is the slight increase in turning radius..Not much, but enough to notice lock to lock on tight manoeuvres..
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Old 14-12-2017, 03:29 PM   #33
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Thought I'd share this great site I found while looking for some calculations in order to trade the 13's (ET10) with some 12's.

It has a nice visual aid to check the difference in fenders clearance, suspension, scrub radius etc.

https://www.wheel-size.com/calc/
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Old 15-12-2017, 08:26 AM   #34
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Cool site. I wonder if they can be persuaded to go down to 10 inch rims.
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Old 15-12-2017, 12:36 PM   #35
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we miss one thing, "i beleave" the position of the wheel within the balanced square will matter!
the tyre is also the problem! maybe the tyre is a bigger problem that the wheel.
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Old 15-12-2017, 01:53 PM   #36
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Quote:
Originally Posted by ardonfast View Post
we miss one thing, "i beleave" the position of the wheel within the balanced square will matter!
the tyre is also the problem! maybe the tyre is a bigger problem that the wheel.
Two major parameters, wheel offset and tire profile.

You are right but it's actually the angle of the virtual line from the upper and lower ball joints - aka kingpin inclination (KPI)- we don't know.

The KPI is part of the hub design so remains unchanged to the vertical axis.
If someone knew the scrub radius -KPO- with a specific wheel and tire combination on A series hubs, then you can put that on the parameters on the site and see that it alters the inclination.

You can set it to zero though to check whether your new wheel/tire will have a negative or positive affect on the scrub radius.

In my case, I had 175/50/13x6 ET10 and returned to my old rims with the same tires, so 175/50/13x6 ET33. Its obvious that I reduced the kingpin offset(scrub radius) by 23mm just from the rims offset. Still, I don't know if the actual scrub radius is positive, negative or zero, only that I reduced the original offset.

And since I'm looking to trade the ET10's with some 12inch rims, it helps me know what ET to look to keep the KPO I have now with the ET33.
With A539 165/60/12x5 ET31 I add 2mm offset while with semi A048 165/55/12x5 ET31 I add 5mm just with tire profile!

Sounds confusing but like you said, the closer the wheels to the body the better.
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Old 15-12-2017, 02:15 PM   #37
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yes , lets kill the confustion! > when we try to understand whats going on by looking at paper and complex numbers we are looking into a pointless aria!
thats only my words to help us!
now in my way i have learnt this> regardless of what the ET, KPO, is this will happen!!
bolt a set of 12 inch wheels on and your mini will totaly change its feel!
it will take time to get used to, but now you will feel 50% more controll,
you will have to ajust your driveing style and get more confident with movement,
you will have to use power more caifully out of tight turns but you will be as happy as a dog with a fat bone,
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Last edited by ardonfast; 15-12-2017 at 02:17 PM.
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Old 15-12-2017, 06:11 PM   #38
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Don't you need to know both the scrub radius and the KPI? There is nowhere to enter the KPI information on the site, unless I am missing something.
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Old 15-12-2017, 08:11 PM   #39
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Quote:
Originally Posted by Pete649 View Post
Don't you need to know both the scrub radius and the KPI? There is nowhere to enter the KPI information on the site, unless I am missing something.
why do you need to know? sorry but i could not ask any other way?
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Old 15-12-2017, 08:23 PM   #40
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From my understanding, the KPI depends on the hub design so it varies. Scrub radius or KPO change depending on your tire/rim combination. Rim offset and tire width mostly.
Found an old post from here with a good visual comparing the same wheel on different hubs.(re-uploaded the image)

Quote:
Originally Posted by evolotion View Post
the term is scrub radius, and no, "0" offset wheels will not achieve what you desire as its not that simple if you use the term scrub angle it just confuses things

heres a pic from my build where my main aim was to reduce scrub radius and therefore torque steer, kind of explains it well. as you can see scrub radius is reduced with a k-series metro hub setup.

[IMG][/IMG]
We can roughly estimate from the above pic that as evolution said he was using 13x7 starmags, which they have ET-7. The tyre is Dunlop 195/45/13 and the red line meets the patch contact at about 80mm from the centre.(total tyre width 195, divided by 2 is 97.5 of the tyre edge). In this case the KPO or scrub radius is 80mm.

If we take this as a reference number and put it in the calculator, each can estimate his KPO.
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Old 15-12-2017, 10:05 PM   #41
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yes a suspected, thats why all the standard cars i see on the highway have sensible wheels and tyres,
well most do lol,
some big exspencive cars are fat but they must have the worked out formaular,
the other small cars i see with fat wheels and stupid cambers cant drive in a streght line! and are fun to follow at speed lol
back to the kpi, this is usefull if any guys want to fit awkward size wheels, good luck to them.
i lernt my 1st lesson in apox 1994, i had a lovely pick up on 145/10,s
i was week and couldent resist the look of 13,s, it was new at the time so i did it,
it was a terible thing to do!!! i cant say how bad it made my mini drive,,
it did look brilliant thats true but i dont plan to make the same mistake again,
well even now i have a set on my mini but im going to change and if i run them i only exspect the same old problems,
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Old 16-12-2017, 08:50 AM   #42
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The bottom line is, try to keep the offset as close as possible to the figure that's right for your hub - but this only works if you're using the same size tyres as the car / hub was intended for.
You can juggle it with different size wheels (as those of us with Rover 100 frames have done with 14" rims), but the important bit is to keep the scrub radius within limits.

As an example, a Metro GTi uses 185/55-13 tyres, and rims are ET52
My car uses a Rover 100 hub with GTi lower balljoints - the same setup as a Metro Gti, but I'm using 14" rims and 185/50-14 tyres. These lift the front (and hence the hub) about 4mm from the road.
This moves the KPI contact point about 2-3mm outboard in relation to the tyre centre line.
To get this back, I need ET49 / ET50 rims, but have to run ET48 rims (in truth because of clearance issues) - I'm close enough, though, to give good stability

Last edited by fynnbar; 16-12-2017 at 09:07 AM.
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Old 16-12-2017, 08:54 AM   #43
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Quote:
Originally Posted by ardonfast View Post
why do you need to know? sorry but i could not ask any other way?
Time to back pedal. All you are doing is comparing so you would only need a known scrub radius for one setup as has been mentioned earlier. As an aside, the KPI for a mini is listed as 9 degrees 30 minutes in my workshop manual but I don't think that this gets us anywhere.
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Old 16-12-2017, 10:25 AM   #44
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i feel the need not to get baffled/confused by infinite precaculos,algorithems in our case!
leave that to richard bransons visit into outer space, my humer seems to be improveing after 7 days without whiskey!
i admit that i dont even understand the word you are useing "scrub radiouce"
my understanding of it is this,
> we have a wheel thats held by arms at a set point)
if the wheel is 10 inch or even 50 inch it makes no diferance to the vertical plane
provideing we have ajustable arm length at the bottom or the top. also the correct mesureing tool to put it where we want it,(in my case that tool is normaly my eyes and test drive,
all standerd fit tyers are made a proper size for the wheel,
if we use other tyers that are to wide, our problems start!
all tyres with a hard square edge amplify the problem by 90% dont use them,
well if you want to go around bends smoothly that is,
the o,p jsouroufs has proven a way to long overdue point,!! roll on the 12,s
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Old 16-12-2017, 10:37 AM   #45
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Quote:
Originally Posted by jsouroufis View Post
Two major parameters, wheel offset and tire profile.

You are right but it's actually the angle of the virtual line from the upper and lower ball joints - aka kingpin inclination (KPI)- we don't know.

The KPI is part of the hub design so remains unchanged to the vertical axis.
If someone knew the scrub radius -KPO- with a specific wheel and tire combination on A series hubs, then you can put that on the parameters on the site and see that it alters the inclination.

You can set it to zero though to check whether your new wheel/tire will have a negative or positive affect on the scrub radius.

In my case, I had 175/50/13x6 ET10 and returned to my old rims with the same tires, so 175/50/13x6 ET33. Its obvious that I reduced the kingpin offset(scrub radius) by 23mm just from the rims offset. Still, I don't know if the actual scrub radius is positive, negative or zero, only that I reduced the original offset.

And since I'm looking to trade the ET10's with some 12inch rims, it helps me know what ET to look to keep the KPO I have now with the ET33.
With A539 165/60/12x5 ET31 I add 2mm offset while with semi A048 165/55/12x5 ET31 I add 5mm just with tire profile!

Sounds confusing but like you said, the closer the wheels to the body the better.
i have 2 corrections to the above, kpi is a function of wishbone design and not hub design and as such is variable throughout suspension travel, with increased kpi during bump. Profile does does have a small effect, but without kpi angle cant be accurately calculated . I dont think the numbers are essential as much as knowing that reducing scrub radii as much as possible is preffered.
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