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Skinners Sprint Micra

4 days to go until the hill climb :)

5.1 gearbox has been fitted with a new release bearing on the clutch.(old one sounding like a bad taller skate!)

Suspension has settled nicely and I'm happy with the damping. Will soften the rear ARB to try and negate the slight under steer on cold tyres.

Done filter fitted as well, a sniff fit. Not revved above 5.5k yet but it's pulling great, maybe it's me but the extra cc seems torquey compared to the last

O any the shift lights fitted as well ready to go

 
Last edited:
Skinner_87 said:
4 days to go until the hill climb :)

Suspension has settled nicely and I'm happy with the damping. Will soften the rear ARB to try and negate the slight under steer on cold tyres.
Click to expand...

will have the opposite effect mate :)
A softer anti-roll bar on the rear means that the percentage of weight transfer at the rear will decrease so you will get more overall grip at the rear (more understeer).

Its important to note that total vehicle weight transfer is a function of geometry (CoG location, track width) not stiffness. The percentage of weight transfer front and rear can be adjusted by changing the roll resistance. if one end is allowed to roll, this results in less weight transfer (its kind of counter intuitive).

I would remove the front ARB and see how it handles then. (or stiffen the rear)
 
Noddie said:
Its important to note that total vehicle weight transfer is a function of geometry (CoG location, track width) not stiffness. The percentage of weight transfer front and rear can be adjusted by changing the roll resistance. if one end is allowed to roll, this results in less weight transfer (its kind of counter intuitive).
Click to expand...
Extremely well put Ed :)
Only thing I'd change is where you say its 'not stiffness'. Roll resistance is a combination of spring rate, anti roll bar stiffness and ride height as a whole which is effectively stiffness of the components as a whole :)
More roll = more weight transfer
Where the back cannot roll and the front can, weight transfers to the outside tyre increasing turn-in, reducing understeer

Looking at the 3 legged videos of Pauls his rear arb is stiff enough
I'd say reduce/remove the front arb :)
 
h701micra said:
Extremely well put Ed :)
Only thing I'd change is where you say its 'not stiffness'. Roll resistance is a combination of spring rate, anti roll bar stiffness and ride height as a whole which is effectively stiffness of the components as a whole :)
More roll = more weight transfer
Where the back cannot roll and the front can, weight transfers to the outside tyre increasing turn-in, reducing understeer

Looking at the 3 legged videos of Pauls his rear arb is stiff enough
I'd say reduce/remove the front arb :)
Click to expand...

I was saying that total weight transfer (WT) is not a function of any stiffness (only vehicle geometry and mass). it is purely the height of the CoG and the track (taking moments about the outer wheel) which results in a higher vertical reaction force from the outside tyre. the total amount of WT (force added to the two outer wheels) is constant no matter what you do to ARB and springs. only the percentage from and back can be adjusted. If you want to decrease WT then you need to lower the CoG or decrease total mass or make the vehicle track wider.

More roll = less percentage weight transfer at that end of the car (and more at the other end because the total is constant). This is the counter intuitive part, but it is just that if the car is allowed to roll at the rear, then the reaction force at the rear is lower and therefore the front wheel is obliged to react more to the WT.

In fact, more WT at one end of the car decreases overall grip at that end due to the non-linear nature of lateral force (sideways grip) generated by the tyre as a result of vertical force (weight).
This diagram might help (dont quickly but i think its gets the point across) :

with no weight transfer both wheels have a an equal weight force of 250 (red line) which results in a total lateral (grip) force from both tyres of 500+500 =1000
but with weight transfer the outside wheel has a weight of 400 and the inside is 150, this results in later grip of 700 + 150 = 850. there is more grip generated from the outside tyre but the total grip from both tyres is decreased.

tyre gip (Small).png


Hope this helps everyone :)
 
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Noddie said:
More roll = less percentage weight transfer at that end of the car (and more at the other end because the total is constant). This is the counter intuitive part, but it is just that if the car is allowed at the rear, then the reaction force at the rear is lower and therefore the front wheel is obliged to react more to the WT.

In fact, more WT at one end of the car decreases overall grip at that end due to the non-linear nature of lateral force (sideways grip) generated by the tyre as a result of vertical force (weight).
This diagram might help (dont quickly but i think its gets the point across) :

with no weight transfer both wheels have a an equal weight force of 250 (red line) which results in a total lateral (grip) force from both tyres of 500+500 =1000
but with weight transfer the outside wheel has a weight force of 400 and the inside is 150, this results in later grip of 700 + 150 = 850. there is more grip generated from the outside tyre but the total grip from both tyres is decreased.

View attachment 30485

Hope this helps everyone :)
Click to expand...
First bit fair enough :)

Next bit more roll is less weight transfer? Impossible? Body roll is a direct result of weight transfer from one side to the other.
More roll occurring from a higher weight transfer percentage
There's no constants on corner weights dynamically as speed, aerodynamics and G force will continually change our figures.
The percentage of weight transfer and overall loaded weight isn't what effects grip. Its the speed of weight transfer. We need to find tge right speed to load the tyre in such a manner we don't overload its peak grip. More weight over a tyre increases its lateral grip tolerance :)

Like the diagram :) it helps clear it up.
You've lost 150 from your figures which would suggest negative G, or vehicle is either going uphill or furiously accelerating transferring weight elsewhere Mass cannot be lost but weight can be gained. Unless I've misunderstood you ? :/
 
h701micra said:
First bit fair enough :)

Next bit more roll is less weight transfer? Impossible? Body roll is a direct result of weight transfer from one side to the other.
More roll occurring from a higher weight transfer percentage
There's no constants on corner weights dynamically as speed, aerodynamics and G force will continually change our figures.
The percentage of weight transfer and overall loaded weight isn't what effects grip. Its the speed of weight transfer. We need to find tge right speed to load the tyre in such a manner we don't overload its peak grip. More weight over a tyre increases its lateral grip tolerance :)

Like the diagram :) it helps clear it up.
You've lost 150 from your figures which would suggest negative G, or vehicle is either going uphill or furiously accelerating transferring weight elsewhere Mass cannot be lost but weight can be gained. Unless I've misunderstood you ? :/
Click to expand...
Just saying what I have been taught :)

The 150 loss is the decrease in total lateral grip as a result of the weight transfer. (the example is for a pair of wheels, either both front or both rear eh :) )
 
Noddie said:
Just saying what I have been taught :)

The 150 loss is the decrease in total lateral grip as a result of the weight transfer. (the example is for a pair of wheels, either both front or both rear eh :) )
Click to expand...
No not at all I love to hear other points of view :) its how we evolve
I just stick to my old school taught debate thing.
Your view, my view, etc etc, conclusion

I'll look into the lateral grip thing. See if I can produce a similar chart on real world data :)
 
I run 30/26psi (cold) on the rally car, which seems to work well, if it is v cold or wet, then i sometimes drop the rears to 24psi.
 
Skinner_87 said:
Also to have a play with the tyres pressures as I think 32/30 is a tad high for the weight
Click to expand...
30/28 here :)
Wouldn't wanna go much lower personally on tarmac especially uphill
You'll get no heat in the back at all. Mine are usually warm after 10mins or so.. but mine doesn't weigh much over 180kg on the back :/
 
I am getting pretty decent mpg tbf. But I got a bit of tyre pinch, any less pressure anf the tyres move not the suspension when I rock the car...
 
Skinner_87 said:
Thanks for the kind words guys!

Thursday went very well with what I think was a class win :) will be sure tomorrow when the final results are in.

Here a vid of the fastest run, bit of a missed down shift & some more bravery needed but good fun! New engines going strong
Click to expand...

I want to do this stuff so bad
 

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