HIGH MILEAGE TYRES 325TDS

Hi to all Members - I have a 325tds and I wonder if anyone can advise me on a tyre purchase. I am doing about 1000 miles a month minimum, mainly on motorway and A roads at higher speeds.

I have had the car some years and always used Goodyear NCT3's - HOWEVER - the last set I had have lasted under 8500 miles on the back and are down to the wear limits already. The front ones fitted the same time look like new.

Goodyear say this is possible as they feel this model puts lots of power down on the road at the back!!

Has anyone had experiences with something that will last longer ?

Thanks - Mark

-I've had several hondas with proper double-wishbones all round and compliant (but not underdamped) relatively long-travel suspension, on good quality dampers with sophisticated valving. Each of these has laid down about 130-160bhp (all of which would be used on a regular basis) through 195-215 section 65 profile tyres on the front wheels.

-despite 'enthusiastic' driving I've got about 30K miles out of fronts, which with tyre rotation equates to about 45K miles for a full set. OK, these were not especially grippy tyres, or very soft compound, but the least mileage I got was 40K miles for a set of NCT2's. I threw a set of Michelin MXVs away when they were only 2/3rds worn because they had gone hard and had lost what little grip they ever had. This set would have done over 60K miles had I bothered to carry on with them. 

-I have never got anything like that mileage out of fronts on any vehicle (front or rear wheel drive)  that was fitted with MacPherson struts; so I strongly believe that there is something fundamental (like stiction, geometry, forced selection of damper rates through effect of brake/suspension forces on loading) that causes the suspension to work the tyres much harder, especially on the brakes. I have no idea why BMW continue to use the MacPherson strut when something genuinely better is readily available.

-on RWD cars (which I believe are a fundamentally better idea in terms of handling dynamics) I have likewise got through tyres on the driven wheels in about half the time  as I have done on a typical Honda FWD car. My only explanation for this (esp on a BMW which has essentially well designed rear suspension, leaving aside the vexed question of camber angles for the moment) is that the spring and damper rates on the driven wheels are more compromised (in relation to the road loads) than on a typical FWD car.

- I think this is because the rear springs and dampers typically have to be designed to cope with the extreme case of an extra ~400Kg (about eight hundredweight!) of people and luggage, poised right over the rear wheels. And the suspension still has to work, without sagging too much and/or bottoming out too easily. The net result of this is that for 'normal' driving (i.e. without this load) the back end is liable to be both oversprung and overdamped by ~30-50%. Note that similar loads in the vehicle will not cause such a large increase in the proportion of weight over the front wheels, (especially on a FWD car which likely will be front-heavy anyway).  The result of the overdamped and oversprung RWD rear end is that the tyres are worked very hard especially during acceleration on bumpy roads and thus tend to wear out rather quickly.

- Add into this cocktail even stiffer, shorter springs with even higher damper rates (as many BMW owners fit aftermarket, and I suspect feel slightly disappointed with if the car is actually still comfortable to drive after they have done so, thus damper rates are often overcooked) and the result can be extremely short tyre life indeed.

- note that, by contrast, some race cars and race motorbikes actually have quite 'soft' suspension (unless attitude changes are not tolerated for aerodynamic reasons in which case the springs are kept artificially stiff), using high quality dampers. The result is that for example, on the road, the same race-bike suspension can increase rear tyre life by over 50% over the conventional road suspension set-up which  is compromised in exactly the same way as it is on a typical RWD road car.  

- I would be SO much happier if motor manufacturers put effort into giving us truly better suspension, that adapted better to changing loads etc. A second set of springs that could be locked out when not required, plus adjustable dampers would do the job nicely; however, air suspension promises much but ultimately disappoints.

- As it is, they don't see a need to genuinely improve the suspension action in this way, and they do other things instead. The result is that we end up with cars that weigh too much and are filled with all sorts of daft gadgets that many owners never get any real use out of.

cheers

Brucey wrote: -- As it is, they don't see a need to genuinely improve the suspension action in this way, and they do other things instead. The result is that we end up with cars that weigh too much and are filled with all sorts of daft gadgets that many owners never get any real use out of. cheers

Thanks for that detailed analasis ! Mark

-thanks for your comments;

- I agree the proportional increase in rear axle load on a FWD car is far greater. But in practice this doesn't really matter, as the rear wheels don't have to do much in the way of dealing with big loads. There are obviously no driving loads, braking loads are mostly on the front, and the cornering loads are limited by the sanity of the driver and the complaints and threats of physical violence from any passengers.....In practice damping rates are typically set on FWD cars so that the rear end is a bit underdamped when the car is fully loaded; this probably gives the best overall compromise, and is unlikely to cause rapid tyre wear. Note you don't really have this choice on a RWD car.

- if the springs and dampers are correct on a RWD when the car is loaded, then I agree in terms of controlling the wheel over road irregularities (high speed damping) the damping rate will strictly still be matched to the spring (relatively stiff though it might be) even without the load on the car. However, the low speed damping (controlling gross body movements) won't be. Therefore yes, the back end will be overdamped, as well as oversprung.

-I agree stock BMW suspensions are not overly stiff (for the laden condition), but they are still subject to the inherent compromises described, so at the rear in particular are typically oversprung etc for the unladen condition.

-I likewise agree re. many lowering kits, and if there is to be no bottoming, the 'short spring' type must be either a steep rising rate, or just stiffer all round. Either way I agree there is a mismatch somewhere to the dampers. However I have also seen plenty of cars with 'uprated' dampers and OK, this might (or might not) make for lower lap times on a smooth racetrack. However, this can give such horrendous suspension for normal road conditions they would be better off going back to stock parts than trying to make the best of this bad job.

-I agree the camber thing is (for the road) a bit of problem, exacerbated  by lowering.

-I agree saloon cars (and any racing car with a relatively high c of g) are a bit odd as the importance of the anti-roll bars is greatly magnified, and even with little bodyroll, there is still a lot of weight transfer to the outside wheels during cornering. These factors can force the use of low profile tyres, and spring and damper rates that work the tyres a bit (or a lot) harder than one would ideally like during acceleration and braking. However by comparison, both some other race car types and motorcycles can have surprisingly soft suspension.  

-finally I couldn't agree more re. tyre pressures; they are frequently all over the place.

cheers