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Daninplymouth

mixing tyre sizes

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Hi,

can i ask is it ok to have slightly different tyres front to rear? i would be putting the same size on each axle but i wondered whether it would throw any issues with the abs etc.

only reason for asking is i have my first trackday coming up, i currently run 225/40R18 but was going to take 2 of my standard wheels as a spare incase anything went wrong 

thanks

dan 

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I'd argue that 215/45 versus 225/40 is very close in circumference. Nothing to worry about.

You have to expect a change in the handling balance in the corners near the limits, especially if your spares haven't taken a beating on track.

I don't know how picky VSC is compared with other stability systems, but I presume it doesn't care about differences between axles, otherwise it wouldn't allow tyre slip in straight lines like it does.

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I'd take just one, and spacesaver one at that, to not rob any boot space and reduce excess stuff i have to bring long way from home till parking, as often bring enough crap along already, like toolboxes, helmet, jack, stands and so on.

If i got flat tire mid track day i'd probably put spacesaver on and call it a day. No matter if flat will be front or rear, after all, as all wheels/tires for me are same, i can put from front one to replace punctured rear one and put spacesaver in front. But if it's because of wear or to switch to dedicated track tire set, then i'd rather bring all four, not just two. Maybe less so because of size, more so due tire model/compound/wear grip may noticeably differ and i wouldn't want to change much grip bias more to understeer or to oversteer. To even out wear from existing set if there is square wheel/tire setup, one can always do tire rotation of existing set anyway, and i doubt that wear will "arrive" unexpectedly mid track day, usually it's obvious, if tires with observable wear level will last or not.

Whichever you do, always try to put as similar as possible tires in rear, due LSD. More then advised, same wheel, same tire model & sizing and preferably even wear.

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I can't see why you'd bother. As long as you have at least 4mm of tread on your tyres you'll be fine on the day. Grip levels this time of year are pretty low anyway so you will get far less wear than you would on a clean track in warmer temperatures. If you put the stock tyres on the front then you will increase understeer particularly so if mixing Primacy tyres with grippier tyres. In summary, it would be shite. Don't worry about it, just enjoy with the same size tyres all round. 

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I’m not planning on using the primacys for any track time. I was more thinking if I wore them out or got a puncture would it be ok to put 2 on for the drive home as living in the good old southwest its a 200mile trip back from oulton park 

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Nothing wrong with using primacies on track either. Yes, maximum speed/maximum cornering grip will be a bit limited a bit, but more then sufficient to get fun and learning car/track.

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14 hours ago, Daninplymouth said:

I was more thinking if I wore them out or got a puncture would it be ok to put 2 on for the drive home as living in the good old southwest its a 200mile trip back from oulton park 

You'll probably be fine. If it's a concern, just drive a little more cautiously. A long time ago I got stuck in Sheffield, heading to Middlesborough. Eventually drove home on a mixture of 14 / 15 and 16 inch wheels. No bother, and that was a Ford!

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If you have over 4mm of tread you won't be under the legal limit by the time you drive home. Expect to lose a couple of millimetres off the tread if it's dry, warm and sunny. If it's wet you'll hardly get any wear. At this time of year I would be suprised if you go through more than a millimetre of tread. I've been driving on track for 20 years, never have I thought to take another pair of wheels with me whether it was 30 miles away in Oulton or 400 in Spa. As long as you have adequate tread to start with you'll be fine. 

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Lauren: is 4mm min thread legal requirement for both winter and summer tires @UK? Here in LV it's same for winters, but for summer tires 1.6mm is minimum required to pass MOT.

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29 minutes ago, Church said:

Lauren: is 4mm min thread legal requirement for both winter and summer tires @UK? Here in LV it's same for winters, but for summer tires 1.6mm is minimum required to pass MOT.

1.6mm is the legal minimum whatever the tyres. No requirement to run winter tyres in UK. I only said 4mm so that he would have plenty left to drive home on. 3mm or more is better when it comes to clearing water as a wet trackday is likely this time of year. 

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1.6mm isn't great in winter .. ok that was with an Alfa 156 (155bhp fwd) but I spent more time spinning the tyres than driving in a forward motion for a couple of days ... and the understeer was horrific!

My tyre dealer was calling them "Dunlop Kojaks" for good reason ... 

220px-Telly_Savalas_Kojak_1973.JPG.jpg

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