dubzi
Part of things
Posts: 711
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Since I put my Golf back on the road I've been finding that it handles really badly and dangerously in the wet, much worse than it did last year. It understeers quite easily. I have changed the suspension from coilovers to conventional struts, albiet lowered and uprated ones, I also have lower and upper strut braces. I was thinking that maybe one of these things had caused the problem. I checked the tyre pressures though and found them to be 30PSI (No idea why I pumped them up that high, faulty guage on the pump maybe!). The sticker on the car recommended 26 so I dropped them to that. It now seems to handle better and the ride is smoother, it feels less like it's bouncing around evne in the dry. Good result it seems. The pressures on the sticker are for the original 175/70/13 tyres. I'm running 175/60/14s at the moment. I will shortly be putting some 185/60/14s on, decent brand part worns to replace the Nankang ditchfinders that came with the wheels that I'm currently running. This should also help the handling! Now the questions: What would be the correct/optimum pressure to run these tyres at? Is the 26PSI more related to the weight of the car, regardless of tyre size or does that make a difference? Anyone know any good reference web sites on the matter? All I can find is "pressure guides" telling me my '83 Golf came with 195/60/15s as standard! Random 'Dub detail:       Thanks. |
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Last Edit: Jul 31, 2009 8:26:45 GMT by dubzi
Happiness ain't at the end of the road. Happiness is the road.
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MWF
Posted a lot
Posts: 2,945
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The tyres themselves should have pressure advice printed into the side wall.
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PhoenixCapri
West Midlands
Posts: 2,683
Club RR Member Number: 91
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Its based on axle weight vs. tyre size basically. For those tyres on that car I'd expect around 30psi in the fronts and 28psi in the rears (increase to 30psi rear fully loaded).
Then if you were going to do a lot of driving at over 80mph I'd put another 2psi on top of those values as this reduced the heat generation of the tyres thus stopping them going bang at constant high speed (autobahn driving).
Obviously you can play around with tyre pressures and see if it improves the 'feel', I'd say lowest 26/24 (front/rear) highest 36/34 - all unloaded.
If you can't find a happy balance you need to look at the;
Suspension geometry - check the toe in is correct, probably about minus half a degee (more castor/camber possibly if can be adjusted)
Tyre brand - toyos and yokos are good tyres at a good price, amazing the difference these will make over nankangs!
Tyre profile - 60 profiles a fairly high so can give boatish feel, get hold of some 15" wheels with some 50 profiles and see if its better.
My CRX had a similar problem to your Golf. It the toe was out which improved things a lot, then lowering springs, 15" wheels with 195/50/15 Toyos and a fiddle with the pressures to 30/28 transfored it. It now has steering feel to match my Escort which has fully adjustable everything and took a couple of years tuning to get right!
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The tyres themselves should have pressure advice printed into the side wall. That's be the maximums though....don't take any notice of that. 26psi will be a good starting point for your car regardless of tyre size. You can adjust up or down slightly from that and see what gives you the best results. |
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dubzi
Part of things
Posts: 711
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Yeah, the max is 44 psi! Don't really want to go that high, it'll never go round corners again! I set the camber up when I replaced the struts to 1/2 degree positive. The toe was done last year and there's no evidence of tyre scrubbing or pulling. It drove fine in the dry (although it was a bit "bouncy") just lethal in the wet. It "feels" much better with 26 psi all round, suspension is less harsh. It had 30 in the front and it was too hard, not only the understeer but the wheels had a tendency to lock up as soon as you touched the brake. That's what lead me to conclude it was tyres rather than suspension. Must have pumped them up too hard at some point as I can't see the fact I ditched coilovers causing all this. Might try 28 when I fit the 185s. Continental Premium Contacts for the front should improve things over the Nankangs.  |
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Last Edit: Jul 31, 2009 9:40:21 GMT by dubzi
Happiness ain't at the end of the road. Happiness is the road.
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PhoenixCapri
West Midlands
Posts: 2,683
Club RR Member Number: 91
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Well the coil overs would give you different spring rates and bound/rebound rates so they would have a pretty big effect on the handling!
1/2 deg posituve camber sounds a bit odd to me, would have though 1/2 degree negative was more normal. FWD cars don't tend to need much front camber, but then I run minus 3.5deg on the Escort!
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just play with the pressures till it feels right, and coilovers will feel different to standards...
and nankangs aint too bad, i replaced some proxes with nankangs once and it actually cornered better! although they went bald quicker
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bortaf
Posted a lot
Posts: 4,549
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Jul 31, 2009 10:30:57 GMT
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The tyres themselves should have pressure advice printed into the side wall. That's be the maximums though....don't take any notice of that. 26psi will be a good starting point for your car regardless of tyre size. You can adjust up or down slightly from that and see what gives you the best results. You'd be surprised how many numptys do that ! the amount of cars I get in that are handling wierd or the brakes are "funny" cos somone has looked at the tyre max pressure then used it  usually women but there you go ;D Have you had the tracking reset after playing with the front susspension ? that's probably the 2nd biggest reason I get to see cars with handling problems, that and knackerd wheel bearings? |
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Last Edit: Jul 31, 2009 10:31:42 GMT by bortaf
R.I.P photobucket
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Jul 31, 2009 13:53:06 GMT
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Some cars are very sensitive to tyres as well, worst thing i ever noticed it on were Sierra Xr4x4s, curse word tyres on them kill the handling, with good tyres on they'll out handle a scooby no bother, crappy ones will have em randomly under/oversteering and have the ABS kicking in all the time if the roads damp.
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Volvo back as my main squeeze, more boost and some interior goodies on the way.
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Jul 31, 2009 14:02:08 GMT
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In theory, a wider tyre should require lower pressure to take the same load, as pressure=force/area. Tyre carcasses don't actually work like that though, so I'd probably do as some others have mentioned, start at 26psi and experiment up and down in small increments to see what's best.
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MWF
Posted a lot
Posts: 2,945
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Jul 31, 2009 14:54:57 GMT
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The tyres themselves should have pressure advice printed into the side wall. That's be the maximums though....don't take any notice of that. Don't take any notice of it? I know a guy who destroyed two tyres and most an arch using the pressures stated in his cars manual, which was higher than the max pressure of his replacement tyres. All I am saying is the pressure vs load should be there and he can make judgement from that. |
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MWF
Posted a lot
Posts: 2,945
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Jul 31, 2009 14:55:56 GMT
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Sierra Xr4x4s, curse word tyres on them kill the handling, with good tyres on they'll out handle a scooby no bother, I'm embarrassed by that comment and even used to own an XR4x4 |
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Last Edit: Jul 31, 2009 14:56:12 GMT by MWF
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Jul 31, 2009 15:41:17 GMT
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Sierra Xr4x4s, curse word tyres on them kill the handling, with good tyres on they'll out handle a scooby no bother, I'm embarrassed by that comment and even used to own an XR4x4 tis true, i've had loads, going right back to the mk1 4x4 ghia estate and me mates a scoob fanatic, providing your brave enough to keep your foot on the gas the sierra will out corner an imprezza (well saying that i'm not talking about a brand new one, i'm going back to the 90's ones) i know it to be true, i used to chase him round and round roundabouts, the Scoobs understeer and have to lift off, keep your boot down and a 4x4 sierra will over steer and catch them up unless your on cheap tyres and then your off into the kerb same as the subaru. |
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Volvo back as my main squeeze, more boost and some interior goodies on the way.
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MWF
Posted a lot
Posts: 2,945
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Jul 31, 2009 16:44:24 GMT
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I appreciate the Sierra has the advantage of the rear bias power distribution, rather than the older Impreza's 50/50 split, and that helps in certain situations, but I don't agree an XR4x4 can 'out handle a scooby no bother'. I think there's lots of scenarios where an Impreza would be faster.
I loved my XR4x4 to bits, and mine handled a lot better than stock too, but I'm not going defend one over an Impreza.
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Jul 31, 2009 17:34:01 GMT
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My mates a loon and mine could hang with his no bother, i'm taking about the 2 litre ST ones (too many points on his license for a turbo one back then) not the WRX thingy if thats what your thinking about, rally weapon versions should be playing with the escort cossies not the XR4x4.
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Volvo back as my main squeeze, more boost and some interior goodies on the way.
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