metroracerjim Posted March 22, 2010 Report Share Posted March 22, 2010 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. Quote Link to comment Share on other sites More sharing options...
Tony Posted March 22, 2010 Report Share Posted March 22, 2010 Hello Jim and welcome to wim. Why are you running such deep camber? Quote Link to comment Share on other sites More sharing options...
metroracerjim Posted March 22, 2010 Author Report Share Posted March 22, 2010 Hello Jim and welcome to wim.Why are you running such deep camber? 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. Quote Link to comment Share on other sites More sharing options...
Tony Posted March 22, 2010 Report Share Posted March 22, 2010 It's all to deep in my opinion.... On track we are talking grip limits -V- all the other aspects going on. Lets start at the beginning. The ideal situation is that the steer axis has maximum traction during the steering lock on lock transition. As the camber positions migrate lock the inner wheel needs a near vertical profile whilst the outer wheels position aids transition due to the inertia and grip gains and an obvious suspension "compression position". An aggressive camber position violates the tyres contact patch during transition, the gains simply distort the grip limits and off you go....... Half your current camber position would gain much more grip since the contact patch is less distorted and the tyres less distressed, the holy grail of racing is "grip -V- saturation".... Increase the grip first and learn the saturation limits. Quote Link to comment Share on other sites More sharing options...
metroracerjim Posted March 23, 2010 Author Report Share Posted March 23, 2010 It's all to deep in my opinion.... On track we are talking grip limits -V- all the other aspects going on. Lets start at the beginning. The ideal situation is that the steer axis has maximum traction during the steering lock on lock transition. As the camber positions migrate lock the inner wheel needs a near vertical profile whilst the outer wheels position aids transition due to the inertia and grip gains and an obvious suspension "compression position". An aggressive camber position violates the tyres contact patch during transition, the gains simply distort the grip limits and off you go....... Half your current camber position would gain much more grip since the contact patch is less distorted and the tyres less distressed, the holy grail of racing is "grip -V- saturation".... Increase the grip first and learn the saturation limits. 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. Quote Link to comment Share on other sites More sharing options...
Tony Posted March 23, 2010 Report Share Posted March 23, 2010 No.... The tyres contact patch needs to be undistorted in straight line travel to maximize grip, corner in the the front cambers will migrate from negative to positive and positive to negative inner/ outer wheels respectively. The missing link here is the castor position? Knowing this we could assume a migration path/ rate. At -3d front there's no way the contact patch at the front inner will be at the optimum contact and the car will push. Best advice "back it off". Quote Link to comment Share on other sites More sharing options...
metroracerjim Posted March 25, 2010 Author Report Share Posted March 25, 2010 No.... The tyres contact patch needs to be undistorted in straight line travel to maximize grip, corner in the the front cambers will migrate from negative to positive and positive to negative inner/ outer wheels respectively. The missing link here is the castor position? Knowing this we could assume a migration path/ rate. At -3d front there's no way the contact patch at the front inner will be at the optimum contact and the car will push. Best advice "back it off". 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. Quote Link to comment Share on other sites More sharing options...
Tony Posted March 26, 2010 Report Share Posted March 26, 2010 No.... The tyres contact patch needs to be undistorted in straight line travel to maximize grip, corner in the the front cambers will migrate from negative to positive and positive to negative inner/ outer wheels respectively. The missing link here is the castor position? Knowing this we could assume a migration path/ rate. At -3d front there's no way the contact patch at the front inner will be at the optimum contact and the car will push. Best advice "back it off". 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. Quote Link to comment Share on other sites More sharing options...
metroracerjim Posted April 2, 2010 Author Report Share Posted April 2, 2010 No.... The tyres contact patch needs to be undistorted in straight line travel to maximize grip, corner in the the front cambers will migrate from negative to positive and positive to negative inner/ outer wheels respectively. The missing link here is the castor position? Knowing this we could assume a migration path/ rate. At -3d front there's no way the contact patch at the front inner will be at the optimum contact and the car will push. Best advice "back it off". 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. Quote Link to comment Share on other sites More sharing options...
Tony Posted April 2, 2010 Report Share Posted April 2, 2010 Best i can offer> http://www.nigellangsgarage.co.uk/profile.htm Quote Link to comment Share on other sites More sharing options...
metroracerjim Posted April 2, 2010 Author Report Share Posted April 2, 2010 Best i can offer> http://www.nigellangsgarage.co.uk/profile.htm 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. Quote Link to comment Share on other sites More sharing options...
metroracerjim Posted April 16, 2010 Author Report Share Posted April 16, 2010 Best i can offer> http://www.nigellangsgarage.co.uk/profile.htm 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. Quote Link to comment Share on other sites More sharing options...
Tony Posted April 16, 2010 Report Share Posted April 16, 2010 Front toe is adjustable so there's no reason for such an aggressive negative position, -30' total is more than enough, the current positions are dangerous. The rest of the positions look ok. Quote Link to comment Share on other sites More sharing options...
metroracerjim Posted April 16, 2010 Author Report Share Posted April 16, 2010 Front toe is adjustable so there's no reason for such an aggressive negative position, -30' total is more than enough, the current positions are dangerous. The rest of the positions look ok. 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. Quote Link to comment Share on other sites More sharing options...
Tony Posted April 16, 2010 Report Share Posted April 16, 2010 Rear toe is lovely..... Front camber/ castor disparity is negligible so don't be to concerned about that....... But where did the front toe position come from? There horrible. Quote Link to comment Share on other sites More sharing options...
metroracerjim Posted April 16, 2010 Author Report Share Posted April 16, 2010 Rear toe is lovely..... Front camber/ castor disparity is negligible so don't be to concerned about that....... But where did the front toe position come from? There horrible. 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. Quote Link to comment Share on other sites More sharing options...
Tony Posted April 17, 2010 Report Share Posted April 17, 2010 -30' front toe out ( total ) is all you need...... Go for it tiger! Quote Link to comment Share on other sites More sharing options...
metroracerjim Posted April 20, 2010 Author Report Share Posted April 20, 2010 -30' front toe out ( total ) is all you need...... Go for it tiger! That's the sort of encouragement I need, stop worrying it and just drive it! Jim. Quote Link to comment Share on other sites More sharing options...
Tony Posted April 20, 2010 Report Share Posted April 20, 2010 Quote Link to comment Share on other sites More sharing options...
metroracerjim Posted May 12, 2010 Author Report Share Posted May 12, 2010 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. Quote Link to comment Share on other sites More sharing options...
Tony Posted May 12, 2010 Report Share Posted May 12, 2010 Other than the accidents ( that's racing ) i reads like things are greatly improved..... How did she feel corner in? Quote Link to comment Share on other sites More sharing options...
metroracerjim Posted May 12, 2010 Author Report Share Posted May 12, 2010 Other than the accidents ( that's racing ) i reads like things are greatly improved..... How did she feel corner in? 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. Quote Link to comment Share on other sites More sharing options...
Tony Posted May 12, 2010 Report Share Posted May 12, 2010 Can see a few issues there..... 1: When filming can you include the steering wheel, the yaw plays a great visual clue to the handling. 2: Corner out she's oversteering like a bugger. 3: Have you checked the body height before and after the race? Quote Link to comment Share on other sites More sharing options...
metroracerjim Posted May 12, 2010 Author Report Share Posted May 12, 2010 Can see a few issues there.....1: When filming can you include the steering wheel, the yaw plays a great visual clue to the handling. 2: Corner out she's oversteering like a bugger. 3: Have you checked the body height before and after the race? 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. Quote Link to comment Share on other sites More sharing options...
Tony Posted May 12, 2010 Report Share Posted May 12, 2010 Some work and research to do then, is there a race grade of hydrolastic fluid because i think it's getting mighty hot. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.