Excuse the strange title and let me explain. My first MX-5 was a 1.6 Eunos. Had Avon ZV3s all round and I loved everything about the handling and grip. I replaced the rears with a pair of Barum Bravuris. I know it’s a budget brand but they get good reviews and I found they were really great on grip. There was a slight vagueness to the handling which was probably due to different tyres front and rear but nothing major and I was very happy with them. Now I have a Mk1 1.8 which has Pirelli P6000s all round. I know I’ve got a bit more power and a bit more weight but I just don’t seem to have quite the grip I had in the old 1.6. In the wet the 1.8 just doesn’t seem to be as predictable as I would expect. I don’t drive ‘on the edge’ particularly when conditions are poor. I expected a top end tyre such as the Pirellis to be the dogs whatsits. Is it me, is it the extra power, or is it that the tyres don’t suit the car. Would be interested to hear if anybody has experience of the difference in grip and handling between the 1.6 and 1.8.
I’m not an engineer and I appreciate that tyres, wheels, weight and power all play their part, I would guess it’s far more likely to be a difference in the chassis alignment between the two cars. MX-5s are extremely susceptible to changes in chassis set up, which is highly adjustable even with standard shocks and springs. When was the last time the car was aligned?
Pirelli P6000s are dreadful, and somehow not cheap either. I blame the production costs of their calendar.
While it could be alignment, or tyre pressures, or the extra few percent of power, or the tiny amount of additional weight, chances are it’s because 6000s are dreadful.
Find someone local with decent tyres and swap wheels. It’ll take less than an hour and you’ll find out whether you need to spend £200 on a new set of tyres or £100 on alignment.
It does remind me, though. I once stacked an E30 at 20mph (railings, 1 BMW 0 - thought it was a 0-0 draw, since the railings were still up and the car still drove, but actually the entire chassis was bent and the insurance company wrote it off), and if I recall correctly that was on P6000s. On the other hand it was at 6am on something like the December the 20th, and the road was so slick I didn’t even leave any skidmarks, despite ending up facing the wrong way down a dual carriageway. Remember, kids, always drive in a manner appropriate to the conditions…
It’s the tyres and/or the alignment, not the 1.8 engine. Mine doesn’t have enough power to unstick itself except on ice, even if severely provoked (e.g. by flooring it in 2nd on a wet corner). I have the now-unavailable Goodyear Eagle F1 GSD2 tyres, and they are very grippy.
What’s aligned? It’s had a service and MOT since I bought it but so far as I know it’s never had anything such as alignment checked. To be honest I wouldn’t even know where to go to have it checked out.
That’s what I was thinking. Looks like the concensus could be along those lines. The 1.6 would very occasionally stick it’s tail out if really provoked in the wet with the Avons or Barums. The Pirellis almost feel like they don’t want to get wet so are tiptoeing over the water. Think a bit of surfing at tyre.shopper.co.uk might be on the cards.
Ah. Where to start. The process of aligning a car basically means making sure the chassis/suspension geometry is as it should be - basically that all the wheels are pointing in the right direction. The MX-5 is adjustable in nearly every possible direction. This level of adjustment is both good and bad - good because it allows the car to be made to handle extremely well, and to suit a variety of driving styles, bad because the whole thing can be knocked out by a pot hole, changing one parameter changes all the others.
The above might sound a bit scary, but don’t worry about it. Any half decent tyre fitters should have alignment or ‘geo’ equipment that can check if there is something particularly wrong. For the very best job look for a local equivalent of Wheels In Motion - I’m sure your local area peeps can help you with this!
There will be plenty of further advice if you do a forum search for ‘alignment’.
Toyo T1R, is a fab tyre on these cars ( Camskill have a special offer on, or at least did have @ £29.56 each+ a couple of quid delivery) , don`t forget you probably have different diffs on the two cars Plate?/ Viscous/ Torsen? if it has a viscous type, is it shot?
Also beware of too much negative camber on the rear, on road tyres you dont need much at all, if the car is on coil-overs put the front ride height higher and the rear a bit lower to put more longitudinal weight biased to the rear.
Flyin` Miatas has some really good roadcar settings, check it out.
The last P6000s that I bought cost £60 per corner in 205/55R16 fitment for a Mondeo. That’s not a bad price for that size of tyre and the P6000s were adequate, but not outstanding on the Mondeo and also on a Focus before that.
Opinions abound that the P6000 is more suited to heavier cars and particularly FWD applications, and less suited to lighter cars with more even weight distribution like the MX5.
OK so assuming a mk1 MX5, wheelbase 2270mm, mass 940kg, front suspension swing axis parallel to the centreling of the car and that the weight distribution is 50:50 with the front and rear suspension at factory settings:
Raising the front suspension up 25mm moves the CofG rearwards 0.069mm, increases wheelbase by 0.138mm and adds 0.057kg to the rear tyre load.
Raising the front suspension up 50mm moves the CofG rearwards 0.275mm, increases wheelbase by 0.551mm and adds 0.228kg to the rear tyre load.
Raising the front suspension up 75mm moves the CofG rearwards 0.62mm, increases wheelbase by 1.239mm and adds 0.513kg to the rear tyre load.
So jacking the front suspension up nearly 3" is like putting half a bag of sugar in the boot. Not really an effective way of transfering weight. You’d be better off moving your seat back a notch.
Not quite correct, in fact quite wrong, if you have ever had an MX5 on corner weight scales you will know that an adjustment of 3mm in ride height on the spring seats will result in over 15kg difference on the scale. Ps. make sure the car is ballasted to your own weight on the drivers seat and has 1/2 tank of fuel if you want to set it up properly and remember the camber will alter as the ride height is varied due to geometry changes.
When it comes to good handling, theory must give way to experiance, set a car up by the book and you will never win a race.
Corner to corner the weight transfer is significant (and hugely dependant on spring rates), it’s why coil-overs have the adjustment. But raising one end or the other is exactly the same as parking on a tiny, tiny slope (0.076 degrees in the case of a 3mm adjustment). It’s o-level physics - look at the gravity load, look at the reaction loads at the tyres.
Using modesty and some more modelling I’ve added a CofG height component, because at larger angles the height of the CofG changes the load at the rear tyres more. Assuming a vehicle CofG height of 400mm the figures change to:
Raising the front suspension up 3mm moves the CofG rearwards 0.53mm, increases wheelbase by 0.002mm and adds 0.220kg to the rear tyre load.
Raising the front suspension up 25mm moves the CofG rearwards 4.474mm, increases wheelbase by 0.138mm and adds 1.881kg to the rear tyre load.
It also says that an MX5 will start to tip over at about 71 degrees.
Changing the height of the CofG to something stupid (1000mm) gives a 4.6kg additional tyre load at 25mm.
When it comes to everything theory and experience must match, otherwise everyone is wasting their time. Feel free to suggest other factors that affect CofG movement and I’ll model them. I would ask that you provide any data from practical experimentation, including when you increased ride height at both front dampers simultaneously by 3mm and the exact weight transfer you got.
I’ve set up cars using corner weights, fully adjustable suspension, the driver in the car and adjustable ballast, and they have won races. Not with me driving though, because I’m not that good. I’ve also set up 3D models with calculated inertias and got the same results as measurements from experimentation.
It annoys me greatly when the real world and simulation don’t match, whether the problems is with the simulation or the quality of the measured data. I can’t make the numbers add up to a 3mm ride height change on the front axle adding 15kg to the rear axle, not even with a 1100kg car and a CofG of several metres, or 60:40 weight distribution with the bias in either direction. More data doctor.
