Tyre pressures for reducing understeer

[Iain]

Everywhere on the Internet seems to say that increasing tyre pressure on the front and reducing tyre pressure on the rear will help reduce understeer.

Surely higher pressure on the front means less contact area = less grip on the front = more understeer? Can anybody explain this please?!

[Mike]

Over and under-inflation can significantly decrease tyre life; while under-inflation increases fuel consumption by some 4% per 0.6 bar of pressure. Tyres that are 50% under-inflated increase a vehicle's braking distance by up to 10 metres in wet conditions when travelling at 60mph and using ABS.

Underinfl ated tyres also involve a serious risk of aquaplaning; low front tyre pressure results in understeer, and low rear tyre pressure in oversteer.

On another note...

Cross-ply and radial tyres should never be mixed on the same vehicle. Where a mix is necessary, radial tyres MUST only ever be used on the rear axle and cross-ply tyres on the front.

This mix of tyres will produce understeer whereas the opposite will produce oversteer. (Oversteer refers to the car turning more tightly into a corner than it is steered; understeer indicates that the vehicle turns at less of an angle than it is steered). Of the two conditions, understeer is generally accepted to be easier to control

[Iain]

That didn't answer my question?

[Ste L]

too hight presure's also make your car understeer mike...

[burgo]

i thought lowering your front pressure would induce oversteer. obviously i mean reducing it by a sensible amount

[Mike]

too hight presure's also make your car understeer mike...

Dont blame me, blame www.google.co.uk (http://www.google.co.uk) lol lol twas the first thing that came up regarding understeer

[Iain]

i thought lowering your front pressure would induce oversteer. obviously i mean reducing it by a sensible amount

So would I, everywhere else I read says differently though. Which is why I'm after an explanation. lol

[Mike]

I have a mathematic formulea (posh version of formula lol) for this too -

15" wheels, 195/45/15's, ET38, 38psi. Handled a dream. No over steer, no understeer.

Incidently, above formula was used on my BMX when i was 10, but 32 psi, the numerical psi related to the amount of spokey dokies I could fit on my wheels before they got annoying :D

[Edwin]

Everywhere on the Internet seems to say that increasing tyre pressure on the front and reducing tyre pressure on the rear will help reduce understeer.

Surely higher pressure on the front means less contact area = less grip on the front = more understeer? Can anybody explain this please?!

People that do this are trying to compensate te lack of good alignment! by increasing the front tyre pressure they creat a faster steering responce of the front wheels. by reducing te rear tyer pressure, the rear tyers will easer roll over it's side walls. When this happends de bodyroll will increase and therefor center of graviti will shift more while steering in to a sharp corner. While te back end of the car is stepping sideways, the driver thinks that has solved the problem! in most cases the cornering speeds will drop like ****!
The biggest problems of understeer with a nova, begins when they put in a bigblock egine like a 2.0. these engines are so heavy that the sheer weight of the engine will force the noose out of the corner!
Good alignement can solve a lot of thoose problems! After yaers of experimenting i found out how to make a nova with a normal caracter or, if nessesary with a oversteer caracter.

[meritlover]

i am with the agreement with Edwin!!

understeer is not a function of the tyres if the pressures are within the limits set by car/tyre manufacturers.
Iainel im guessing that you are one of these small boys that drive your car on the bump stops to impress ladies/other young boys and therefor upset your camber so much that out of a 195 tyre you will only be using approx 1.5" of the inside of the tyre anyway :(

get the geo and the alignment sorted...when it is you can experiment with the pressurisation of the tyres (rolling my eyes lots)

[craig green]

I agree. Its all about decent tyres, tyre width (to a degree) & good geometry.

I lowered my last daily driver (1.2) -60mm on GMAX suspension (if you can call it that). The camber was effected so bad that fr end gripo almost vanished. The car was understeering & losing grip so easily at low speeds. This was partly due to the std 165 tyres & improved with the 195/45 I later fitted. But it just proves the importance of good camber &/or geometry.

[to add] having the rear ride height slightly higher in relation to the front puts a little extra bias on the front grip.

[SRlew]

understeering is gay

but tbh i used to mess around with my tyre pressure on the nova, some times it made a bit of difference etc. my car was on a full suspension set up, aligned and every thing

also when i lowerd my rear more the car had a nice equal feel of grip, it just stuck to the road!? i thought it wpuld of madfe it worse but infact it made it better for understeer for some reason.

[meritlover]

well lowering the rear would make the front lighter as the weight would be transferring back.
there is no doubt that lowering a car would make it handle better. but there is a line.
when you say 'aligned and everything' what did that include? being that camber adjusting is not available on std front shocks, topmounts without filing the holes. and rear camber movement is not possible without shimming the hubs. but i dont know why you would like to do that.

[Iain]

Iainel im guessing that you are one of these small boys that drive your car on the bump stops to impress ladies/other young boys and therefor upset your camber so much that out of a 195 tyre you will only be using approx 1.5" of the inside of the tyre anyway :(
Talk about throwing wild accusations. :tosser: It was just a fcuking question regarding something I've read.

And for the record my car's not lowered stupid amounts, and it's not to impress anybody (it's not even styled). It has the best suspension I can afford on it, and I just want the best out of what I've got! And if simple things like playing with adjustable shocks and changing tyre pressure can help then that's all good.

[meritlover]

Mr Iainel it is not a 'wild accusation' as i said, it was a GUESS.:tosser:

[Iain]

Mr Meritlover it sounded like you were saying you thought I was some little chav.

[Stoo]

right

get camber adjustment via bolts on the front
get it tracked and aligned

rear, slightly higher than the front, gives it added 'point' and allows for beter turn in

stiffen the rear up a bit too, and fit strut braces

[Iain]

stiffen the rear up a bit too, and fit strut braces

I was playing with my rear shocks last night actually. :thumb: It did seem to feel a bit better with the rear stiffer.

[meritlover]

Mr Meritlover it sounded like you were saying you thought I was some little chav.

i accept your appology

as Mr Stoo states. it will cost virtually nothing to make a difference to your handling. if you can use a round file you can perform camber alignment. you can make a plumb line with a protractor a weight and some string. i have never done it with string. but with a stick the width of the car and make a metal bracket with 2 screws at the top so it can be set to touch the rim. then move the stick until the screws touch the top rim and measure the gap. then use some pythagorus (famous dinosaur) to calculate the angle.

alternatively i think that some ebay magnetic gauges can be bought that have a ball that rolls to the angle. but i think these are pants.

[mikey14sr]

My set-up was, -40 jamex kit (rear sat at standard height due to weight loss from removing rear seats and trim), 195/50x15 firestone tyres, pressures at 27psi front, 26psi rear, no front anti-roll-bar (bushes were knackered anyway), poly TCA and tie-rod bushes, GTE rear ARB.

That all handled quite well, had a good bit of understeer before I removed the front ARB, afterwards turn-in was sharper, it felt a lot more planted on bumpy bends, and the occasional (ahem, every morning on one particular roundabout going to work) slide from the back was more controlable. It did have a touch more roll than before, but it felt good to me.

EDIT: this was with a stitch welded front end, No strut braces and a little 1400 8v.

Also found this, http://www.frost.co.uk/item_Detail.asp?productID=9139&frostProductName=Camber%20Gauge&catID=64&frostCat=Suspension&frostSubCat=&subCatID= , not a bad price.

[Edwin]

Talk about throwing wild accusations. :tosser: It was just a fcuking question regarding something I've read.

And for the record my car's not lowered stupid amounts, and it's not to impress anybody (it's not even styled). It has the best suspension I can afford on it, and I just want the best out of what I've got! And if simple things like playing with adjustable shocks and changing tyre pressure can help then that's all good.

I understand that you just try to get the best out of it! Let me give you some tips!
Front camber CAN be adjust by camberbolts! The best ones can be found by a company called "special products" it wil give you a adjust range off aproxx 1,75 degrees.
Caster is big problem with ALL nova's! The bigger the caster the better! In standerd suspensions you can only try to get left en rightside even! to do so you have to work with shims on your TCA(radiator side) you can also try to machine the TCA to shorten de lenght of the TCA witch will give you more caster! Many people do not understand te need of a big caster angle! To understand me, you have to look at the front wheels of a mercedes-benz that is making a very short U-turn. these cars show a big camber change in cornes! and that's the secret to loose the understeer!!
About the rear! Alignement can be changed! again the company "special products" has beautifull shims witch allows you to change camber and toe, all in te same time!

For road use, try to get caster arround 2 degrees
and camber front -1 to -1,5 degrees
camber rear -1,0 degrees
Front toe, -0? 03' per side

About lowering the car i bit more on the backside. This is a very good thing!! because the body will be completly level at heavy breaking!! therefor you will be less confronted with sudden shifting of the centre of grafity! this wil give a more restfull carbody whille entering corners at high speeds! car becomes more smoother!

If you need some more tips, just say so!

cheers mate

[CP]

I experimented with a std pug 1.0l 106 with std skinny steelies and I found that although the ride got harsher and the noise increased, running all the tyres way above normal settings ( >50 psi at front and 40 on the rear) showed a marked improvement on handling. Simple as that. I think commonly used tyre settings are more to do with a soft ride etc than anything else.

Having reasonably high tyre pressures helps the tyre wall resistance to rolling over, increases ground pressure, improves sensitivity and steering response all of which will help stop understeer.
Select tyres with a lower profile & softer compounds specially formulated for performance and fit wider ones on wider rims if you can afford it.

Other things that really help- fit a performance suspension set-up, throw away antiroll bar, fit lowered front tie bar mounts, lower the car alround, reduce the weight of the car etc - the list goes on. This stops the body roll transferring weight during braking.

[Edwin]

50 psi??? did you every read the text on the sidewall of the tyer? should sound like "never exeed tyer presure above 44 psi" and do you think that the presure stays the same while the tyers heat up? well if it works for you, its ok with me! As a mannager of a tyer company i see lots of tyer faliurs due to presure problems. every time it scares the s**t out of me.

[CP]

Having reasonably high tyre pressures.

I'm not suggesting everyone driving around with pressures in the 50'slol - I increased the pressures incrementally to see as an experiment with minimal mileage involved

Also I drive a nova round race tracks on slicks so i'm well aware of the effects of heat