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Skinners Sprint Micra

Definitely recommend a complete coil over reset chief. Rather than spending small amounts on guesses. Long run it'll work out cheaper. Plus you can then dictate your spring rates and damping style :)

Stiffer front springs combined with softening the rear will generally allow understeer to properly rear it's ugly head. The changes you've listed are oversteer corrections, but starting with a softer rear to find the correct ratio and share the resistive work is a good start :)

Shame you can't change track width :(
 
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SuperUno

Buy & Sell Member
Those rear tyre temps seem very odd to me.... ?

Agreed Manx tarmac is very bumpy, my hire car from my visit last year needed quite a few new suspension bits when i handed it back after 'testing' the TT course and some of the stages... ;) Also some new brakes.... ;)

You could add some rear wheel spacers and stay in class ?
 
Yeah figures, but having huge amounts is avoidable with correct shocks and arbs blah blah lol. Science. When you corner weighting my car?
Didn't realise I was

Not necessarily as its just not that simple. You usually tweak the shocks you use to the travel you require. Chances are the panhard rod vs the tie bars will max out before long travelled shocks :)
That's why K10 axles are better in my opinion. Better for long travel without sideways movement.

You need the car to use up its entire roll resistance just before you run out of lateral grip. Regardless of what you do you will always cock a wheel or it may appear on the ground but it's fully extended and providing no lateral grip
 
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Skinner_87

Skinner_87

Club Member
Those rear tyre temps seem very odd to me.... ?

Agreed Manx tarmac is very bumpy, my hire car from my visit last year needed quite a few new suspension bits when i handed it back after 'testing' the TT course and some of the stages... ;) Also some new brakes.... ;)

You could add some rear wheel spacers and stay in class ?
Glad you had a good run on the manx roads mate. Nothing handles like a hire car eh!
 
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Skinner_87

Skinner_87

Club Member
Surely a correct shock which allows droop would stop the cocking of a leg? Still can't imagine it's going to be perfect whatever happens.
I'm with you there Chris, I know kit cars have a lot gone into there geometry etc but there rear lift is very minimal, the quicker all 4 wheels are on the floor the better in my eyes
 

SirChris

Educated Bodger
I'm with you there Chris, I know kit cars have a lot gone into there geometry etc but there rear lift is very minimal, the quicker all 4 wheels are on the floor the better in my eyes
Don't see McLaren tripoding lol. But it's a Micra never going to be perfect.
 

SirChris

Educated Bodger
Didn't realise I was

Not necessarily. You usually tweak the shocks you use to the travel you require. Chances are the panhard rod vs the tie bars will max out before long shocks :)
That's why K10 axles are better in my opinion. Better for long travel with sideways movement
Ages ago lol.

Well you can drop a fair amount with spax. Like silly amounts compared to other variants. Either way can only do so much eh
 
Ages ago lol.

Well you can drop a fair amount with spax. Like silly amounts compared to other variants. Either way can only do so much eh
I can't remember last week

Chances are its not the length of his shock thats the issue. You're currently thinking of the rear wheels as independent, sure they can drop when equally jacked up etc on a solid axle, but jack one side up and one isn't far behind.

In cornering, if the rear springs are too hard which I suspect they are here for this particular car, then the outside wheel can't compress equally and leaves the axle very little travel when tied to an ARB, and the front is forced to roll more hence wheel lift

Cocking a wheel means its offloading its weight onto the front outside tyre, which doesn't seem to want to let go which is no bad thing (more vertical load = more potential "grip"). But all 4 in contact is better, but the 4th is useless without vertical load

Its a problem many light car owners have with an ff layout is we have very little weight at the rear to do anything productive our roll centre generally raises, spring rates and damping ratios start getting quite funky. A corner weighting session, and a chassis tech's assessment would highlight some issues and solutions, f/r balance, roll centre height etc :)
 
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SirChris

Educated Bodger
Poly rear ain't going to be lending any favours. I think 100/150 spring is ideal given we have piss all weight in the back for road race use. Possibly up the damping from the settings we discussed a while back Skinner. However a softer arse seems to stable the car and promote a tad of over steer. Better than the other .
 

SirChris

Educated Bodger
True on the independent, but its still a factor which will effect the travel of the axle. All of the ideas here should be considered.
 
For road rallying I had 120/90 so we're soft overall. It was a tad roly poly but without spending the money on the correct dampers it was something I had to live with
Generalist terms
Softer rear is understeer prone
Softer front is oversteer prone
Remember the weights between front n rear are different so while 100lb rear spring may seem soft or a 275 may seem hard
If you've twice as much weight up front than rear you need twice as much spring to cope but you can go too far, so finding each cars unique balance is key
 
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SuperUno

Buy & Sell Member
I have never worried about lifting an inside rear, at the point it almost lifts then its doing no work anyway.

The rear wheels just need to go where the fronts tell it to and control bump / rebound.
 
I have no practical experience with this but minis do the same cocking of the rear inner wheel through corners, minis run a trailing arm set up which means the rear roll centre is at ground level whereas the front is a fair bit higher, as a consequence the rear is trying to twist the front, if you like... This loads up the front outside tyre and suspension and results in tricycle action. The solution in a mini tends to be a beam axle like the micra has but it does little if the roll centre isn't the same as the front...
So where is the front and rear roll centre on a micra? and is it possible to move the roll centre? upward?
As I said no practical experience, so may be nice in theory but impractical and I was looking at the theory with minis in mind.
Sounds daft tying to make a roll centre higher but I look at it like the roll centre is the pivot for a lever trying to flip the car the centre of mass is the other end of the lever, the closer you can get the two the less the cars weight has on body roll, you might be able to get rid of one or both of those A.R.B?

Edit:
This thing has been lowered right? (duh, it's a track car) but AFAIK that lowers the front roll centre, as well which increases the leverage the front centre of mass has on the cars body roll as well...
Is it possible to lower the car with shorter springs and the use of a spacer between the lower ball joint and the hub leaving the front suspension geometry / roll centre unchanged? (\end silly brain dump) again not sure it's practical or I understand what's going on correctly.
 
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You're spot on with the ideas, but if we simplify the K11 rear axle roll centre as being in the centre of its pan hard rod when viewed from behind, lowering the car effectively raises the roll centre in respect to the chassis, but leaves less travel to fully extend a wheel.
Whats going on at the mo is rear inside wheel lift is occurring and the owner rather it didn't, at the same time he wishes to have good travel to absorb bumps/dips but without the body roll.
I've spent a couple of days with Paul (@pollyp) where he was still getting inside wheel lift, but a very consistent and strong road holding capability. Every drivers different but to generalise the setup, stiffer damping rear, and higher rear tyre pressures are a good baseline
 
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Skinner_87

Skinner_87

Club Member
Reading back through some notes and the original spring/shock Tarmac setup for the rear was 175lb so a set of 180lb will be here in the week :)

New decals are on & the car got it's annual wash and wax



 
Thanks Paul, an interesting read :)

Softening the rear seems like the most cost effective thing to do for now then! Glad in heading in the right direction allowing the rear to take more of the transfer
In cornering, if the rear springs are too hard which I suspect they are here for this particular car, then the outside wheel can't compress equally and leaves the axle very little travel when tied to an ARB, and the front is forced to roll more hence wheel lift
There was some sense in my waffle Paul :)
 
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Skinner_87

Skinner_87

Club Member
Nice run, what diff are you running? Certainly you now have plenty of power!
Funny you should ask Matt, it's a standard diff just a 5.1 final drive. Will be a 4.4 box and gripper diff for next year :)

The bodie really need the appropriate trumpets so the bulkhead will be for the chop as well!
 
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Skinner_87

Skinner_87

Club Member
5.1 makes sense with the gears you were using. Proper diff is great fun :)
It pulls really well but getting it off the line well in first is near impossible, I'm losing a second or so there so I'm hoping the slightly longer 4.4 will help.

Even if I only use 1 -4 on most events.

Do you run a plate or ATB diff Matt?
 

SuperUno

Buy & Sell Member
Its a SureTrac diff, I am never quite sure what type it is, but here is a video of 'how it works'. Either way it is something I should have fitted much sooner!


For a slipper diff it isn't too aggressive in use.
 

pollyp

Club Member
I'm using a gripper lsd (that's actually working now), mine's only a one-sided clutch pack cos need to use the speedo gear so it may be abit biased.
but now that it's fitted with double preload springs, it's able to withstand the 160ftlb turbo setup rather than shattering all the time.

the original dual-sided LSD will be stronger & stabler of course.

when I used the fixed lsd in blyton recently, I discovered that I could now simply apply WOT (or before both tyres spin) before the apex, point steering and I could feel the front end gain traction and PULL the front into the corner. certainly required a confident driving style to make it work.
obviously pushing too much torque and/or too much steering will overwhelm the slip angle and make it power understeer.
this is very dependant on the tyre too.

for static launches, yea it'll improve low gear traction upto a point. beyond that point is the limitation of fwd.
tyre temps, pressures, tread depth, tread pattern, compound, suspension setup, weight distrib & hundreds more variables will also affact ur launches.
 
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Skinner_87

Skinner_87

Club Member
Manx Classic 2015

Well April has been an gone again & was the usual fun 3 days. Person best times set again which I was very happy with however I carnt help think the ITB's do need trumpets to get the best from them. A few pics below & a few more to follow. Day 3 started very wet which was fun to say the least :)

Maybe big changes inset for next year , im not sure but with a view to rebuild the 4.4 : 1 gearbox up with a suitable diff to be able to attend a few track days in the UK it might be a busy year.
Heres a vid of the fastest run from day one, lost a lot of time with fluffed gear changes & a 4 wheel lock up into the chicane haha (see if you can spot it)

 

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pollyp

Club Member
Manx Classic 2015

Well April has been an gone again & was the usual fun 3 days. Person best times set again which I was very happy with however I carnt help think the ITB's do need trumpets to get the best from them. A few pics below & a few more to follow. Day 3 started very wet which was fun to say the least :)

Maybe big changes inset for next year , im not sure but with a view to rebuild the 4.4 : 1 gearbox up with a suitable diff to be able to attend a few track days in the UK it might be a busy year.
Heres a vid of the fastest run from day one, lost a lot of time with fluffed gear changes & a 4 wheel lock up into the chicane haha (see if you can spot it)

bedroom wallpaper pics there :cool:
 
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