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Old 04-10-2017, 11:23 PM   #16
250ptm
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Looks like you got it right OZ. The wheels Jsouroufis appears to be using may have a PCD of 100 and not the usual mini 101.6. I can see that using a wheel of 100 pcd could easily occur, especially if it has countersunk stud holes, 1/16 th of an inch difference between a 100PCD and a minis 101.6PCD is not much.
Other option i see is you could bore out the wheel stud holes and fit sleeved bolts. Has anyone tried this?
Im interested to see the vids when they are available!
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Old 05-10-2017, 07:42 AM   #17
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Quote:
Originally Posted by jsouroufis View Post
Apologies for the late reply, caught up with the work..

So, the wheels are ET33, they were almost a year in the storage room and didn't remember exactly.

Anyway, had them repaired, fit them a few houres ago and just got back from a quick test drive.

It's true, they handle so much better! I even went WOT in a road I knew the Mini will bounce between two lanes a couple of times and I could keep it straight with one hand! Completely different handling!

Also, the steering seems easier to turn at a stop.

How can I say this, it just doesn't transfer any force to the wheel and rip it out of your hands!
I'll try to record a video and make a comparison in the same roads with some of the videos I already have that you can actually see the effort needed to keep it straight and how easy it is now!

I'm gonna need new arches as well as it look silly now..
In very simplistic terms, if you extend the KPI line downwards from the top ball joint through the bottom ball joint and continue until it hits the ground, this point is the point around which the wheels/tyres actually pivot around when the steering is turned. Theoretically the ideal situation is for the centre line of the wheel/tyre to meet that point so the wheel/tyre pivot around its centre.

The further away the centre line of the wheel is from the point on the ground where the KPI line meets it the more you have to drag the wheel and tyre around an arc when turning the steering wheel causing heavier steering. Also the larger the radius of the arc you have to drag the wheels through, the larger the lever effect the wheels/tyres exert back in to the suspension meaning that any bumps etc in the road can pull on the steering causing the car to weave around.

That's all in theory and I am sure much cleverer people with maths, physics and geometry can show that you can get better results doing something different again but that is my basic understanding of why large offsets cause poor handling in a Mini
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Old 05-10-2017, 08:46 AM   #18
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Originally Posted by 250ptm View Post
Looks like you got it right OZ. The wheels Jsouroufis appears to be using may have a PCD of 100 and not the usual mini 101.6. I can see that using a wheel of 100 pcd could easily occur, especially if it has countersunk stud holes, 1/16 th of an inch difference between a 100PCD and a minis 101.6PCD is not much.
Other option i see is you could bore out the wheel stud holes and fit sleeved bolts. Has anyone tried this?
Im interested to see the vids when they are available!
Yes I have done this. Its how I run 6 x 13 Revolution original 4 spoke wheels with 185x 55 x 13 tyres and the skinniest arches that suit the car. Be aware though that the original revolutions use a full sleeve bolt from standard. I wouldn't do it with a stud and nut combo. Wheels needed a little reaming. I don't know if I can post a pic on here now.
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Old 05-10-2017, 07:26 PM   #19
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my 2 cents: with a positive scrub radius, when accelerating the steering arms see tension as the wheel tries to scribe an arc around the kpi in the toe in direction , the greater the scrub radius the greater the tension. Transversely, with a negative scrub radius the steering arms will experience compression. Hypothetically, on a smooth track these forces left and right cancel each other out and all is happy is straight line world, the problem arises when one wheel gets more traction, on +ve scrub radius cars if the front right experiences more torque than the left for whatever reason, the steering will pull left. We do need a little tension or compression in the steering arms, so neutral scrub radius is not advisable either, +/-10-15mm was quoted to me as the sweet spot but i cant confirm this. 7x13's produce a 50-60mm scrub radius. I can put some simplified numbers together if it would be beneficial to understand the magnitude of the prblem.
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Old 06-10-2017, 07:41 AM   #20
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Thanks mikko, I knew someone with more knowledge would know better

I did a quick bit of Googling and found this from a Pistonheads thread

Quote:
It's difficult to offer any definitive advice on just one aspect of steering geometry, because the overall result is a balance between a large number of different factors (KPI, Ackerman, scrub radius, caster, toe, tyre pressure, tyre sidewall stiffness, etc., etc...), but some general pointers/observations:

• The main effect of scrub radius is to introduce a turning moment between the centre of the tyre contact patch and the point where the steering axis hits the ground. Obviously, the bigger the scrub radius, the bigger this moment will be. Since scrub radii tend to have quite small measurements, 10mm is proportionately quite a large change, so will almost certainly have an appreciable influence.
• On a RWD car, even if the tyre loads are equal, tyre drag will tend to load the wheels toward toe-out with a positive scrub radius (usual) or toe-in with a negative scrub radius.
• If there is more drag on one side of the car than the other (whether from braking or just as result of variations in the road surface), the effect will be to pull the steering around. This means that bigger scrub radii tend to lead to more tramlining and kickback.
• When a car goes round a bend, it transfers weight laterally, with the outside tyre becoming more heavily loaded. With positive offset, this means that the greater 'drag' from the scrub radius on that side will be fighting te driver trying to turn the steering into the bend... hence bigger scrub radius = heavier steering. Not always a bad thing, because since the resultant steering weight builds up in proportion to the amount the outside front tyre is being 'worked', it gives feedback on what is happening at the contact patch. Too much, though, and the steering can load up excessively in bends and/or start causing those problems with tramlining and kickback (if you want a masterclass in how not to do it, drive a non-PAS TVR Griffith, then drive an Elise to see how the experts do it. wink). The disclaimer here is that caster and KPI have a big influence, too.
• Negative scrub radius tends to give a very stable, but dead feel (ask Audi), so for that reason we can rule it out for a lightweight RWD kit car, 'cos no doubt you'll be wanting something that feels nimble and lively.
• Zero (or too little) scrub radius can cause the car to feel vague and 'wandery', because the slightest variation in load from one side to another can reverse the direction in which the steering is being pulled (often just by taking up the slack in the joints and bushes). Since positive scrub radius tends to cause toe-out, you have to think about this in conjunction with the static toe settings (it may be acting to cancel out some toe-in, for example, or to add to toe-out).
So... the bottom line is to think about your steering behaviour as it is at present.

• If it's just right, you're probably best off maintaining the same scrub radius as you have at present.
• If its a bit vague and wandery and doesn't load up as much as you'd like to give you feedback in corners, increasing the scrub radius might help.
• If it's heavy in bends, tends to kick the steering wheel about a bit in your hands and/or tends to tramlineon ruts and cambers, you might want to try decreasing the scrub radius a bit.
...but since you can balance changes in the scrub radius against other factors (some as simple as varying the tyre pressures by a couple of PSI), you can juggle other settings so that they tend towards cancelling out (or magnifying, of course) the effects of the scrub radius: there's always more than one way to skin a cat.

Sorry if that's all a bit woolly and undefinitive... best advice I can give is to start from how the car steers at the moment and think 'where do I want to go from here and how do I use the physics behind the scrub radius to nudge things in the right direction'.
https://www.pistonheads.com/gassing/topic.asp?t=1004532 for the whole thread

https://en.wikipedia.org/wiki/Scrub_radius

Also Wikipedia shows that I know nothing
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Old 06-10-2017, 07:52 AM   #21
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Depends on some other factors as well. For example, my rims are 6x13 ET33. If I went to 7x13 chances are that the extra 1 inch would be to the outside of the rim (or most of it).

If though that 1 inch was equally applied on both sides then the ET would remain the same because the center of the wheel didn't change.

However, this doesn't happen in our minis due to clearance reason to the inside.
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Old 06-10-2017, 04:59 PM   #22
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Quote:
Originally Posted by jsouroufis View Post

It's true, they handle so much better! I even went WOT in a road I knew the Mini will bounce between two lanes a couple of times and I could keep it straight with one hand! Completely different handling!
Also, the steering seems easier to turn at a stop.
How can I say this, it just doesn't transfer any force to the wheel and rip it out of your hands!
I'll try to record a video and make a comparison in the same roads with some of the videos I already have that you can actually see the effort needed to keep it straight and how easy it is now!
.
nice to hear your story, i realy struggle to understand in a clever modern world with all its clever improvements that some still fit big fat wheels and rubber, this aplys for snappy easy handeling and not drag race,
the vids you will do will be good to see,
and on the note of alloy wheel holes if re drilling to 4 inch look close because many alloy wheels have a steel insert pressed into a bigger hole,
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Old 07-10-2017, 11:33 PM   #23
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Reducing scrub radius was one of the main motivation for my change from a-series metro hubs to k series metro hubs. The difference is staggering in the cars manners. It's the reason most folk with metro based frames find the handling less troublesome under throttle.
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Old 09-10-2017, 02:49 PM   #24
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It's the reason most folk with metro based frames find the handling less troublesome under throttle.
Totally agree. Very stable and predictable, and with no LSD fitted
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Old 15-11-2017, 02:56 PM   #25
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I made a split screen side by side video on the same road going from 2nd gear WOT.
Although the road is not ideal because it happens to be one of the smoothest highways so it does not magnify the effort I need to keep it straight, but its enough to notice..If only I had two similar videos on a more ordinary road.

The problem is that I made the video on the macbook and for some reason iMovie keeps crashing when I try to export it. Been trying to find a solution for more than 2 weeks. I'm searching forums and trying various fixes but no luck

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Old 20-11-2017, 07:58 PM   #26
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Quote:
Originally Posted by Minicooper View Post
I wonder if they are 4 x 100 pcd which is can be forced to appear to fit the mini 101.6mm pcd flange
Does that mean what I think it means, you put the 100 pcd wheel on and tighten the wheel nuts up until the wheel 'fits'.
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Old 21-11-2017, 12:20 PM   #27
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Does that mean what I think it means, you put the 100 pcd wheel on and tighten the wheel nuts up until the wheel 'fits'.
Yes that's exactly what I'm saying

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Old 02-12-2017, 05:41 PM   #28
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Alright, an update came from apple for the iMovie and it fixed the bug, so I managed to export the video and uploading right now.

Should be ready in half an hour.
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Old 02-12-2017, 06:14 PM   #29
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There you go, just keep in mind that it's in a smooth road so not ideal but they were the best to compare the difference the offset makes excluding other parameters that could affect the steering effort.

Left side is with ET10, right with ET33

https://youtu.be/06rbljgwfng
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Old 02-12-2017, 07:39 PM   #30
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nice compare. Any +7 folks out there, take note and stop chasing your tails.
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