metroracerjim

The sphere's have an chamber at the top filled with Nitrogen, then there are two chambers below filled with fluid. As the suspension compresses the fluid is forced from the bottom chamber into the top chamber. There are valves to control the flow of fluid, and hence the damping. As the fluid enters the second chamber it compresses the Nitrogen, which is acting as the spring. Nitrogen is used for it's greater temperature stability. The rules state the sphere's can't be modified, as it's easy to mess up and hurt yourself, or make something that fails in short order. It is possible to drill through the top and burst the air spring (300PSI!). By welding or braizing a schraeder valve on top you can control the pressure in the spring and stiffen the suspension. Just need to be careful not overheat the rubber diaphragms. To make it really stiff you need a low pressure, as this makes the spring volume much smaller, but again you might have to add some fluid in there to prevent the diaphragm being overstretched. Coilovers would be much simpler. Jim. Jim.

I've not heard of anything. I've never measured the temperature of the spheres after racing, I've never heard anyone mention it. I'll have to have a feel next time I'm out. One of the drawbacks of the suspension is the variability with the ambient temperature. Summer to winter it can drop about 10mm. It would be nice if there was something thicker, as it would increase the damping at the rear (I can't fit rear external dampers in my class). The mixture is basically the same as anti freeze. People have tried using oil, but it rots the rubber diaphragms. Jim.

I'm still getting the camera position sorted, I wanted it to show what I'm doing, so I can see all my mistakes. I had it set up in a great position, but the scrutineer wasn't too keen, so I had to mount it differently. I usually set the suspension with a low fuel load, and some ballast in the car. I've not specifically done it before and after. After Brands it was visually wrong, the car had the rear passenger side about 12mm lower than the drivers. By fiddling with the rod lengths, and increasing the pressure slightly on one side it got it fairly close. It will be interesting to see what it's like when I get it back. It can take a while for the rear to settle. Looking at the car from behind it looks a little soft. Jim.

She was better than at Brands, but my I think I still need a little more work on the rear end. The ride heights just wouldn't settle right despite spending a day playing with them, and correcting a couple of problems. Hydrogas can be a pain like that, it would be much simpler if I could fit coilovers. I think with the corrected front toe the cars turn in is more consistent, and the car seemed slightly tidier to drive. Without the extra drag from the toe, the front tyres seemed to last better as well. The grip and turn in still drops off after a few laps, but the balance was still adjustable. Since I've made the rear camber and toe adjustable the cars become alot more interactive. I found myself delibately provoking the car at times to get the rear end helping. Not quite mastered it, but I'm getting better. Once I get the car straightened I'll take another look at the rear suspension, then leave it all as is for a while, and just get used to it. It's probably the best it's been. My driving can definately improve to take make better use of what's there, and then I'll see where I am. My 'onboard's on Youtube, Link below: or from behind: http://www.youtube.com/watch?v=uYoI-4crUz8 Jim.

I had an interesting weekend at Oulton. I did a test day on Friday, which helped learn the track. The car seemed to have more mid corner front end grip than before, which is alway's nice. I didn't find myself understeering like I was in Clearway's at Brands. Previously I'd noticed the outside fronty tyre seemed to be wearing it's outside edge round, which it doesn't appear to have done to the tyre I'd fitted for qualifying and the race. I'd improved massively over my times from last year, when I had no confidence. My qualifying time was about 11 seconds faster than last year. My best in the race is about a second off the lap record, which I was chuffed with. The race was going pretty well, I was getting ready to challenge for third in class, when I made a couple of mistakes and let three cars by. I caught them back up, but as I was overtaking one of them, the car in front span on some oil. I didn't have too much choice but to drive into him. Luckily it wasn't too much of an accident, but both car's going to need a little straightening. Just when you think you've nearly got things sorted! Ta, Jim.

That's the sort of encouragement I need, stop worrying it and just drive it! Jim.

I'm not sure!! Decreasing the camber should have reduced the toe out, as the steering arms are at the back of the wishbones, and the bottom of the wheels was pushed in around 2 mm. It was a bit of a head scratcher when I saw it, as last season it was only slight toe out (about 2mm). If it was only one side I'd expect that it was from whacking a kerb, or one of my occasional off roading sessions. The good news is there's an improvement to be had, and I don't have to spend as long in the garage. Thanks for the help and guidance, next race is Oulton, so I'll see what the effects are. Jim.

Thanks for that, I'll get that front toe adjusted, and try to even the cambers up. I was suprised my rear wheel toe was perfectly even, as I'd got the new brackets I'd had made on. What are the maximum allowable variances in the wheelbase and caster? At first glance they look pretty far off, but when I was talking to the operator he said they'd be within tolerance for a standard car. How close should you aim to be with some of these settings? Where does it become chasing perfection rather than a tangible benifit? Jim.

That's a good trek. I'll have a look round locally and see if there's anyone decent, it's a struggle to get the time off work at the moment. Ta, Jim. Well I managed to get a geometry done, which brought up a few more questions. I'd adjusted the front camber to reduce to around 1.5 degrees. There seems to be load of toe out present 0.8 degrees, and a bit of a camber disparity at the front. There's also some difference in the castor angle, about 0.5 degrees. There's some camber difference at the rear which I should be able to sort. Front Toe -.48 -.47 Camber -1.26 -.1.48 Caster +4.25 +3.54 King Pin +12.46 +12.42 Inc Ang +11.20 +10.54 Rear Toe +0.06 +0.06 Camber -1.51 -2.13 Thrust Angle +0.07 Front drivers side 3.06mm set back -0.06 Rear divers 1.71mm set back -.04 wheelbase -1.35mm Dg-0.02 Would post the print outs, but I need to work out how to do it. What do you think? Jim.

That's a good trek. I'll have a look round locally and see if there's anyone decent, it's a struggle to get the time off work at the moment. Ta, Jim.

I'll try and get the castor measured to be sure, I think as standard a metro GTi is approximately 3 degree's. I'm hopefully getting some work done at the weekend so I'll try and get the castor altered, and the tracking reset. Jim. Get a printout so we can see the full picture. I've talked to the guy's I usually use for work on my car, they're snowed under, and they just do a wheel alignment. Can anybody recommend a good place near York? Thanks, Jim.

I'll try and get the castor measured to be sure, I think as standard a metro GTi is approximately 3 degree's. I'm hopefully getting some work done at the weekend so I'll try and get the castor altered, and the tracking reset. Jim.

Thanks for that, I think I get it. Basically as you increase the negative camber (from zero) you increase the cornering grip as you're putting the wheel and tyre in a more appropriate position for cornering , however once the optimum is reached, then any increases are offset by conflicting losses. A bit like continually upping the boost on a turbo. It sounds like I'll have to do some experimenting (good excuse for some track time). I'll have to try and get hold of some tracking gauges to play with. Are there any clues to the tyre performance I can pick up from the tyres, such as even temperatures, or wear patterns? Jim.

The front settings come roughly from when I got the car. The previous owner had said the additional front camber made a big difference to the turn in. As last season was my first full season I was concentrating more on racing, and some of the more basic setup issues I hadn't really questioned it. From talking to other people I think they're running similiar values. When I had the front geometry checked recently the OSF front only had about 2 degree's, and the NSF had about 2.8 degrees. I altered the OSF to make it the same as the NSF. The biggest difference I noticed was the tyre seemed to be wearing better, as previously the outer edge had rounded off, as if the tyre was folding right over during cornering. With the increase in camber the shoulder of the tyre remained intact. When I've looked at the tyre, the inside doesn't seem to be wearing excessively. I'm trying to aim for about 30 PSI when the tyres are hot. Jim.

Hi, I've just registered on the forum, and it looks a pretty good site. I've started to get interested in suspension matters, as I've got a metro GTi that I race in the Drayton Manor series. We're allowed to do a bit of playing with the suspension, but unfortunately we have to run list 1A tyres, which means Yokohama A539's. The big problem with the tyres is they tend to go off after a few laps. I was wondering if there are setup hints anyone can offer on helping to save the tyres. At the moment I'm running 3 degree's negative camber at the front, with about 1mm toe out. I've made up some custom brackets for the rear so I can alter the rear toe and camber. At the moment this is approximately 2 degree's negative, and parallel. I think part of the solution is getting the rear more 'mobile' so that the front doesn't have to do as much work. Has anybody got any suggestions? Thanks, Jim.