Rear inside wheel off the ground!!

Jak Fuller

Jak Fuller

Hi everyone! As some of you may know, me and Mikey (my K11) have been doing some autotests for a couple of years now. He's perfect and can pretty much beat anything from Westfield's to MX5's, except for one particular Mini Clubman, which is extremely flat around every corner!
I think the reason that I don't beat him (apart from less power) is that since having the SPAX fast road kit fitted in October last year, the car has been on three (and sometimes two) wheels around every corner (I actually went OVER a cone on the inside rear wheel because it was so high in the air!). Because of this, i can't push him any further or he will tip over!! Is this because the rear of the car is still to high (lowered 35mm but no weight at all), because I don't have ARB's or because the car is too stiff? Like I say, the car feels perfect apart from this, but I just can't push him all the way.
Many thanks, Jak.
 
I remember discussing a similar thing with pollyp after seeing some photos of his on an autotest.
It seems to be what k11s do without swaybars when pushed hard, not that I'm a fan of swaybars as they control body roll but detract from overall grip, that said if the inside tyre is in the air it's not gripping much.
Minis use rear swaybars because rear roll can unweight the inside front wheel loosing traction on corner exit particularly, the loss of rear end grip is more than compensated by the increased grip @ the front. The mini's rear roll centre is at ground level whereas the micra's is about half way along the panhard rod. Mini's have been converted to solid rear axles in the past for more grip and a higher rear roll centre.
I think what causes the rear inside to lift is jacking forces, if you imagine all the lateral turning forces being pushed through the rear roll centre on a lowered car half way along the panhard rod might be just above the axle, this sideways force is resisted by the tyres or in your case the outside tyre, if you draw a line between the roll centre and the middle of the outside tyre then this line has a vertical and horizontal component, in my head it's this vertical component that is trying to twist the axle around and therefore lifts the inside wheel.

Again in my mind there's 2 options to help ;
  • Widen the effective rear axle
  • Lower the roll centre
  • Both
Widen the rear axle might be large negative offset rear wheels or cut up an axle and extend it.
Lowering the roll centre might be further lower the car at the back (may not be much more to do here) or (don't hate me here) for the lowest diameter wheels and tyres you can find.

Older cars like beetles and triumphs tamed thier jacking by limiting the extension of the suspension, I remember ebbdude or something like that doing straps for similar Motorsport to achieve this, I'm not sure how much is recommend it either way but it could be an option?

What's the car's balance like do you tend to oversteer or understeer? When? Does the cars body roll much or just lift the inside wheel? So you have pictures?

All this is just thoughts, I have read a bit but not had much chance to apply it in practice so make of it what you will.
 
Wow!! That's alot of writing!! Thanks for that!
I don't tend to understeer at all, really. I get a bit of lift-off oversteer but it's usually pretty planted. I just can't push to the limit!!? The body feels quite rigid. There is a noticeable bit of roll but not so much as expected. Unfortunately I don't have photos as the locations for the autotests are all on MoD land, so no photos are allowed.
I am thinking of going lower, as I can get the Humphris 60mm drop or 80mm, but unsure which yet.
Thanks again! Jak.
 
I'm only 16 still so I'm on a budget at the moment. Alloy roof is out of the question!!?? would keeping the spare wheel in the car help, then?
 
perspex rear windows are easy and cheap to do, and there is a lot of strengthening metal that can be removed from the C pillars and t/gate.
i think pauls main problem was the front corner diving, which he addressed with his lowered b/balljoint,
mine handled very flat with liftoff oversteer like yours, i span at 70mph at donnington and had a mad tankslapper there too (which was very scary)
i think you need to remove topend weight and/or widen the track if you are lifting 2 wheels
 

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MSA Spec plastic windows are same weight (if not a bit more) than normal nissan glass which is naturally thin. So not worth the hassle.

Lifting a inside rear wheel isn't really an issue though, it is part of FWD driving. Never caused me an issue I run OEM ARB's for good turn in grip, has won me class wins in autotests (some outright), autosolos, stage rallies, targa rallies etc... Reduce weight where you can and get seat time, this is where performance will come from.
 
SuperUno said:
MSA Spec plastic windows are same weight (if not a bit more) than normal nissan glass which is naturally thin. So not worth the hassle.

Lifting a inside rear wheel isn't really an issue though, it is part of FWD driving. Never caused me an issue I run OEM ARB's for good turn in grip, has won me class wins in autotests (some outright), autosolos, stage rallies, targa rallies etc... Reduce weight where you can and get seat time, this is where performance will come from.
Click to expand...
Thanks. I know that lifting the inside rear wheel is normal, but as I said I have quite easily flicked it on to 2 wheels before. I could not take a corner faster or it would go over! I've driven many other prepped up fwd cars and Mikey is the only one to do this so easily.

Sent from my SM-J330FN using Micra Sports Club mobile app
 
I recently came across this youtube channel and this video on caster which explains that the inside rear wheel can be unweighted by large caster settings as you head into a turn, this is not necessarily a bad thing as it applies this weight to the front inside wheel where the steering effort is being applied and grip is more valuable... There's a balance to it though as steering feel and effort are also changed by caster, positive caster can create other positive effects as it can increase negative camber on the outside wheel and increase camber on the inside wheel (both moving in the correct direction) which could be particularly important for the micra with macpherson struts which typically don't have any negative camber gain under load (cornering).

Anyway see what you make of it.
 
fuzzy-hair-man said:
I recently came across this youtube channel and this video on caster which explains that the inside rear wheel can be unweighted by large caster settings as you head into a turn, this is not necessarily a bad thing as it applies this weight to the front inside wheel where the steering effort is being applied and grip is more valuable... There's a balance to it though as steering feel and effort are also changed by caster, positive caster can create other positive effects as it can increase negative camber on the outside wheel and increase camber on the inside wheel (both moving in the correct direction) which could be particularly important for the micra with macpherson struts which typically don't have any negative camber gain under load (cornering).

Anyway see what you make of it.
Click to expand...
Fantastic video, learnt something new

Sent from my Nexus 7 using Micra Sports Club mobile app
 
fuzzy-hair-man said:
I recently came across this youtube channel and this video on caster which explains that the inside rear wheel can be unweighted by large caster settings as you head into a turn, this is not necessarily a bad thing as it applies this weight to the front inside wheel where the steering effort is being applied and grip is more valuable... There's a balance to it though as steering feel and effort are also changed by caster, positive caster can create other positive effects as it can increase negative camber on the outside wheel and increase camber on the inside wheel (both moving in the correct direction) which could be particularly important for the micra with macpherson struts which typically don't have any negative camber gain under load (cornering).

Anyway see what you make of it.
Click to expand...

That's awesome, thank you very much!
 
fuzzy-hair-man said:
I remember discussing a similar thing with pollyp after seeing some photos of his on an autotest.
It seems to be what k11s do without swaybars when pushed hard, not that I'm a fan of swaybars as they control body roll but detract from overall grip, that said if the inside tyre is in the air it's not gripping much.
Minis use rear swaybars because rear roll can unweight the inside front wheel loosing traction on corner exit particularly, the loss of rear end grip is more than compensated by the increased grip @ the front. The mini's rear roll centre is at ground level whereas the micra's is about half way along the panhard rod. Mini's have been converted to solid rear axles in the past for more grip and a higher rear roll centre.
I think what causes the rear inside to lift is jacking forces, if you imagine all the lateral turning forces being pushed through the rear roll centre on a lowered car half way along the panhard rod might be just above the axle, this sideways force is resisted by the tyres or in your case the outside tyre, if you draw a line between the roll centre and the middle of the outside tyre then this line has a vertical and horizontal component, in my head it's this vertical component that is trying to twist the axle around and therefore lifts the inside wheel.

Again in my mind there's 2 options to help ;
  • Widen the effective rear axle
  • Lower the roll centre
  • Both
Widen the rear axle might be large negative offset rear wheels or cut up an axle and extend it.
Lowering the roll centre might be further lower the car at the back (may not be much more to do here) or (don't hate me here) for the lowest diameter wheels and tyres you can find.

Older cars like beetles and triumphs tamed thier jacking by limiting the extension of the suspension, I remember ebbdude or something like that doing straps for similar Motorsport to achieve this, I'm not sure how much is recommend it either way but it could be an option?

What's the car's balance like do you tend to oversteer or understeer? When? Does the cars body roll much or just lift the inside wheel? So you have pictures?

All this is just thoughts, I have read a bit but not had much chance to apply it in practice so make of it what you will.
Click to expand...
Lowering your roll center will increase the distance between your center of gravity and the roll center. This results in a bigger rolling moment that causes more load on the outside tyres and less load on the inside tyres.

I would recomend trying the oem anti roll bars or aftermarket stiffer ones if you prefer those. They should keep your inside tyres closer to the ground.

Roll center adjusters to raise the rollcenter in the front would be nice alltough I'm not sure if these are available aftermarket for the micra. If they are please let me know.

Sorry for the bump
 

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