Tire pressure and handling
Posted by Jose Pinto
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There was a chart here somewhere where one could see how tire pressures affects handling.
Something like: More pressure at the front >> less understeer Anyone recalls where it si? Thanks in advance! 
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That was in a previous BEN carnation. You'll have to try the way back machine. If I remember correctly it was produced by Ove or at least he had input to it. Edited 1 time(s). Last edit at 10/09/2013 09:58AM by Archeo-peteriX. |
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Hello. :-)
There is usually a pressure for optimum grip, and going either higher og lower will reduce the grip. If you have perfect pressure in all four tyres, you can go either higher or lower up front to induce understeer. To create oversteer, go higher or lower in the rear. If you go lower with the pressure at the back, the handling will be slightly more sluggish, but the traction is better that with too high pressure. I prefer lower rear pressure on E30s, but higher rear pressure on FWD cars. So in short, it is rather complicated! 
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Holy Smoke! Look who has reappeared
How are things with you Ove? Do you have a permanent cupholder now? Still steering the 318Ti around the tracks? Any little Oves yet? Sorry for all the questions but we've missed your august presence around here 
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Things are fine with me. I never had a 318ti, but rather a 323ti. It has now been replaced by a 2012 F20 116i. Neither of these cars exist in USA. The current 116i is a five door hatchback with a down tuned Mini Cooper S engine. That means 1.6L straight petrol four with turbo and 136 hp and rear wheel drive. No real LSD, but a fake electronic system using the ABS brakes. I am indeed married, but no kids. Still working with paint robots. Since last time I was here, I am spending some more time on fitness and photography than before. 
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Well congratulations on your marriage
Sorry about the 318Ti; I just remembered it was the Ti model which I would have liked as a replacement for my iX. Just haven't been in the financial position to afford another BMW :-( Your new ride looks really good. It really is a shame that North American never gets fuel efficient and good looking cars that offer performance as well. We are stuck with over weight, gas guzzling monstrosities that support the oil companies obscene profits. Fitness and exercise are admirable pursuits, particularly as we age. It's never too early to start but it can be almost impossible if we wait too long 
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I would love an electric car. My friend has two Teslas; one is the sedan that his wife drives and the other is the two seater sports job. I rode in the two seater...goes like the wind! He made millions in the dot com era so he can buy whatever he likes.
We don't get any considerations for electric vehicles here except a higher purchase price 
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Here in new york you get to drive in the HOV lane with just one person (the driver) in the car if you're driving an electric car. That's something.... Hi Ove, nice to see you again Buddy 
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Hey Ove, nice to hear you over here!
Short commute is a blessing! I do 120km round trip per day, and still the cost of most EV in diesel would leave the diesel option cheaper. ...Unless EV were subsidized or old diesel car heavily (even more) taxed. :/ Example: BMW i3 or activehybrid 3 against the "traditional" powered equivalents. The way to go is have a living arrangement with short commute to be done by bike or public transport. Wish I could get a job near home. |
In Norway, the cost of electricity is significantly lower than diesel, and many electric car owner charge for free. I have a 2 km commute to work, a 1 km commute to the gym, and a 400 meter commute to the local shops. I do however have a very long commute to the Nürburgring (1000+ km), which would be difficult for an electric car.
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Thanks Ove! From what I gather, the optimum grip will depend on tires also, and is way above what is stated on the fuel flap sticker. I am running the Continental premium contact 2 way above the sticker figure, 2,6 rear and 2.4 front. I experienced up to 3, but I fear damaging the tires and felt no advantage in doing so. No complains for grip in corners and braking, and there's no way the MB 250D could loose traction accelerating... 
Cornering fast and good braking is critical for me, as I do a lot of mountain roads in my commute. |
With my E30s, I usually ended up with something like 2.3-2.4 bar up front, and 2.2 in the rear. Tires with soft sidewalls will require higher pressures. The lowest I have used was a set of R-compounds where I started with a cold pressure of 1.3 bar in my front left (outside) tyre. If you have an agressive driving style, you might want higher pressures than if you drive very smoothly. High pressures is also good for low fuel consumption and less tramlining, and it will increase the speed were you start aquaplaning on wet roads. |
I drive an ex-Taxi Mercedes Benz 250D, how aggressive can that be?! 
But then again, I end up cornering a bit fast cause if I were to slow down much the car would take forever to pick up speed again, specially going uphill. Lower fuel consumption is good, so I will stick with slightly higher pressures. For the record, I am getting better consumption than my sister's BMW 318d 
Aquaplaning is not an issue on dry pavement, so I will be good for the next six months or so. I notice a bit less adhesion on stone paved streets or bad pavement with higher pressures, perhaps because more bump movement is transmitted to the suspension to deal whith, i don't know. |
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A bit late, but here is my zim 2c worth.
Jose, I have been looking into this for a very long time, there are as many tire pressure recommendations as there are opinions, ask six people, you will get six answers, the figures in the manual are a good compromise, and valid only for the tires as fitted standard OEM, many other factors come into play as well, driving style, road surface etc, etc. The system I have found which works the best and give the best compromise between handling and tire life is the 10% rule. Simply put, your tires should be 10% harder when hot than when cold. So for instance, let us take an arbitrary number like 2 bar, if you pump your tires 2 bar when cold, they should give you a reading of 2.2 bar once warmed up to temperature. If they read less than that, for instance 2.1bar, you are running them too hard, they are not generating enough heat, thus the air inside is not expanding enough with temperature. And vice versa, if they read high, 2.4 bar after warming up, you are running them too soft, and they are generating too much heat, causing the air inside to expand too much. Adjust accordingly, it will take a bit of trial and error to get the numbers right, but once you have found the right pressure that gives you that 10% increase from cold to hot, make a note of it, and that becomes your new tire pressure. Give it a try, it works extremely well, and I use it on both my car and my bike, only use the numbers in the manual as a baseline to start from. ---------------------------------------------------------------------------------------------------------------------------------- E30'S AREN'T BUILT, THEY'RE CAUGHT IN THE WILD!!! 
When in doubt, use full throttle, it may not improve the situation, but it will end the suspence. |
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Understood, obviously one can not compare it to track applications, realistically, road driving is generally within pretty much the same parameters, one is not going to go flat out around a traffic circle 10 times, navigating a traffic circle is no more than navigating a chicane or bend in the road in real terms, and yes I agree, driving through town in the rain is different to sitting on the super slab for 2 hrs at 80mph, no argument there.
There is no perfect system, even the published figures are subject to these same variations, it is a compromise, and one that I have found gives me the best tire life and handling without sacrificing one or the other. ---------------------------------------------------------------------------------------------------------------------------------- E30'S AREN'T BUILT, THEY'RE CAUGHT IN THE WILD!!!
When in doubt, use full throttle, it may not improve the situation, but it will end the suspence. |
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I settled for 2.4 Bar front and 2.6 rear at the Benz, the FWD citröen has 2.3 front and 2.1 rear.
The new shocks in the benz made it much more stable and soft than before, the old sachs shocks were completely wasted. During winter time, I believe the tires must run cool for most of the time, unless I would use the brakes a lot, and I don't pound the brakes much. Just installed the second brake pads in 80000km, and the old ones had about 1/3rd to go, just the sensors gone bad. I know when I arrive and touch the tires, there is no heat that I can sense, unlike in the summer. Also I think left and right temperatures must be equal, even when driving at a lot of roundabouts, because the round left portion is compensated by turning right to enter and leave the roundabout. Unless you would do the entire circle, to decide which way to go. Several times. And very fast. 
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I have heard that the taxis in my area have around 20 percent higher wear on the right side than left, due to all the roundabouts. The exit of a roundabout is usually not a right turn, but more of a track out (straightening of the left turn). |
My Benz is an ex-taxi, it came with both right side shocks completely shot, one wheel bearing, several suspension arms, etc... Bad suspension causes premature and uneven tire wear. I am inclined to believe it has to do with the hard life and neglect, more than the roundabouts... There are more bumps and holes at the right side of the road than in the middle, this is my experience over here.
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But taxis running outside the urban areas, with less roundabouts, have more even tire wear. Norwegian taxis are rather well maintained. |
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