se7enmad Posted June 14, 2004 Share Posted June 14, 2004 Are a couple of psi of tyre pressure on an ACB 10 enough to change a car's handling altogether? Though I am used to my car being twitchy now, during last weekend's blat she was @"@"@" dangerous. Had not checked tyres before run but on returning were 20psi hot. To be honest I am a fan of lower pressures on tyres as it feel the car is more 'planted'. My worry is that the car's handling is very variable, and I just cannot believe that a couple of psi and warm temperatures make the car go crazy. I always rant about the ACB's (and especially their square profile) not being suitable for my environment, so I would rather not go into the tyres merits, rather about the change in performance with temperature and pressure. Funny thing is that if I leave car as is she may well behave properly if environmental conditions are diffenent so blatting is always an unexpected. I know end resultant of this, as has been told to me over and over again is - change tyres - but should I be looking at what else in the setup? BTW other problem is my 55kgs of weight - when heavier drivers try car out, or I am passenger, car behaves much better because of added weight. How should I tackle this (apart from getting myself fat and heavy) 😳 ? Antonella 1998 Caterham Classic my site here more photos here Link to comment Share on other sites More sharing options...
Graham Sewell Posted June 14, 2004 Share Posted June 14, 2004 You could also carry Matthew as ballast! He'd probably enjoy it Low tech luddite - xflow and proud! Link to comment Share on other sites More sharing options...
Joe 90 Posted June 14, 2004 Share Posted June 14, 2004 I'm not sure how much I can help because feel is so subjective, but pressures do make a difference. 20 psi hot is low, so I would expect it to be a bit wobbly. If there is a really big diffference between hot and cold pressures, the air in your tyres could be too humid. As far as weight goes, I'm convinced Sevens (especially xflows) need more rearward weight balance. My cunning plan is to move the battery to the back of the car. SEP field working, not spotted in 101,000 miles. Some photos on webshots, updated 10 June Link to comment Share on other sites More sharing options...
thinfourth Posted June 14, 2004 Share Posted June 14, 2004 i find ACB-10s very pressure sensitive on the road Sod the heater wheres my shades Link to comment Share on other sites More sharing options...
se7enmad Posted June 14, 2004 Author Share Posted June 14, 2004 Graham, Matthew is always with me *cool*- the car is so twitchy I had a violent "left -right" loss of control last blat - thank God it was a major 4 lane road (marsa) on a Saturday afternoon and that Matt is used to misbehaviour in the 7 or he would have been frightened. I had difficulties everywhere else. thinfourth - very pressure sensitive - that is the point - but how much so? Oliver, this is not wobbles - this is railcar on road behaviour... Antonella 1998 Caterham Classic my site here more photos here Link to comment Share on other sites More sharing options...
se7enmad Posted June 14, 2004 Author Share Posted June 14, 2004 air in your tyres could be too humid now that is interesting - car is in a damp garage (they are all like that over here ) how do I get dry air into a tyre? Oliver - I am 20-25kg lighter than an average man - I jump in the seat with the potholes (not nice) - there is no way I could transfer all that weight rearward. Maybe a flatflooring setup could help but with a live axle and little adjustment except for ride height I doubt whether that means much. Probably more to gain with spring rates and shock changes but to be honest there is little local expertise available; the local (and effective) reasoning is to get cars to articulate as much as possible and get forces from the bad road surface absorbed as effectively as possible. How they do that is kept mostly secret. Some people throw antirollbars out of the window, and stiffen up the chassis instead. It is difficult for me to explain the car's behaviour as I said because when people try it out the car behaves better as the driver is heavier. I think I may stop going out in the car altogether for a while until I have clearer ideas on my long term plans for her. Antonella 1998 Caterham Classic my site here more photos here Link to comment Share on other sites More sharing options...
se7enmad Posted June 15, 2004 Author Share Posted June 15, 2004 ok, seeing no progress with queries, yet another query... would any sort of permanent distortion on the tyre contact patch result from keeping a car garaged on ACB 10's? Is there any comparison with a slick tyre in this respect? Should I be changing wheels or overinflating the tyres on long periods of non use? Antonella 1998 Caterham Classic my site here more photos here Link to comment Share on other sites More sharing options...
Alba 7 Posted June 15, 2004 Share Posted June 15, 2004 For long term storage (e.g. over winter) I was always told to put the car up on stands so that the tyres don't develop a flat spot. Not sure if it folklore or for real but several people now have all told me the same thing. Antonella, probably isn't what you wanted to hear as AFAIK it is permanent but should be considered next time the car is off the road for a while. Link to comment Share on other sites More sharing options...
Joe 90 Posted June 15, 2004 Share Posted June 15, 2004 Antonella, I don't weigh much more than you and the difference is less than the weight of a spare or a full tank of petrol. I have also damn near left the seat over potholes Re tyre pressures, the air supplied in garages is normally just compressed, and will have the same moisture content as when it was compressed. It doesn't have anything to do with how the car is kept. Moist air changed pressure a great deal more than dry air, which is why race teams have "air driers" for their tyres. SEP field working, not spotted in 101,000 miles. Some photos on webshots, updated 10 June Link to comment Share on other sites More sharing options...
Chris W Posted June 15, 2004 Share Posted June 15, 2004 Tyres will squash down until the pressure inside exactly balances the weight applied. To a first approximation 1/4 of the total car's weight is on each tyre in a static situation. So if for example the car weighs say 600kg (~1300lbs) there is approximately 325 lbs pushing each tyre down. If each tyre has say 20psi pressure inside it, the tyre's footprint on the road under static conditions will be simply 325/20 = 16.25 square inches. If you increase the tyre's pressure to say 24 psi the tyre's footprint will reduce proportionately to 325/24 = 13.5 square inches. Thus the footprint area will vary linearly with change of tyre pressure. Thus an increase of 4 psi per tyre (in this example) will reduce the area of the tyre available for grip by 17% ......a noticeable difference. Chris 2003 1.8K SV 140hp see it here Link to comment Share on other sites More sharing options...
se7enmad Posted June 16, 2004 Author Share Posted June 16, 2004 Oliver, Chris W - thanks for your replies Good to hear I am not the only one who occasionally loses contact with the seat when driving...!! Oliver - re the humid air - maybe I have to resign to the fact that I cannot change humidity in the tyre then. Air humidity is occasionally very high over here - 99% today for most of morning in fact ☹️ ☹️ Chris W, thanks for clarifying effects of localised tyre pressure. In practical terms - does it mean : a. I should overinflate tyres whenever I am leaving the 7 in the garage for longer periods of time b. actually throw the tyres away if the handling does not improve with alteration of pressure ie should I assume they have been permanently damaged? Antonella 1998 Caterham Classic my site here more photos here Link to comment Share on other sites More sharing options...
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