- My model of MX-5 is: ND BBR220
- I’m based near: South Lakes
- I’m looking for technical help or recommendations on: Tyre mixing pros and cons
My car is presently fitted with the original Bridgestone Potenza S001s. The tyres have been rotated and the fronts now have about 3 mm of tread left and the rears about 5 mm. However, I have a small bleb on the front nearside tyre, so it needs replacing (and off course the offside front will also be replaced).
The Potenzas are very expensive at £137 each and they also do not have the best reputation from what I have read on this forum. Many people seem to like Kumhos (Ecsta PS71 I think?) which are much cheaper at £85 each, a major saving. 
My conundrum is: I don’t really want to throw away two perfectly good tyres with 5 mm of tread remaining and buy four Kumhos. Neither do I want to buy two more Bridgestones which will be much more expensive and delay a trial of the Kumhos. I am thinking of getting two Kumhos for the rear and fitting the good Bridgestones to the front with the intention of replacing them with Kumhos, when their life has expired.
Would doing this seriously impact the handling of the car? The Kumhos have apparently better grip in the wet. Any advice would be gratefully received.
If the Bridgestones are approaching or over 5 years old I’d ditch the lot and go with the Kumho.
I’ve had Kumho on my last two NC’s and now the daily driver, can recommend them.
Just to add, mixing two different brands isn’t a bad thing just keep them as you intend in pairs. Apart from that I can’t say how the car will perform doing the swap only the pair, suck it and see I suppose.
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I was in a similar situation. Bridgestones down to 3mm at the front and around 6mm at the back. No blebs or damage though.
Considered just replacing the front and wanted to go with The Kumho PS71s after having the KU39s on my NC and loving them.
Decided to go with a full set at a great price through Black Circles. Fitted at a local tyre fitter booked through Black Circles and brought the two part worn Bridgestones home and got £30 for them on Facebook from another MX5 owners.
I love the PS71s. They really suit the car. It may be that there are better tyres available but you can pay double the money and only get a very small gain in performance.
I’ll replace like for like in pairs when they are around 3mm.
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Thanks for the reply. The tyres are only 3 years old but as you say I can just put the Khumos on the rear and get a feel for the balance. If I don’t like it I shall just have to bite the bullet and get another pair of Khumos for the front. Unless that is, I can get four Khumos for a better price than for two off (as Roadie did) from Black Circles. I can only ask!
Personally I would do 2 at a time and get the best value out of the tyres you have, but I am a Yorkshire man. Money is hard enough to come by so there seems no point in squandering it!
I always put my best tyres on the front, if I can get the front going where I want then it is up to me to get the rears to follow.
However, best practice is to put the better tyres on the rear as understeer is considered to be a safer option. It is up to you which end you put the new tyres on.
To me it is a matter of getting to understand how the car behaves differently when you have changed the two tyres and just get on with it. If your mid corner speed drops by a few miles per hour it is not going to change the world.
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For my daily driver I did a Black Circles price check on the PS71’s, delivered to my address and get the local garage to fit.
Armed with the price I went to my local garage (they had previously quoted £14 per corner to fit) they looked up prices of Kumho and we agreed an all in price for them to supply and fit. It was only £12 more than the BC price to supply only and the garage did a free tracking check/adjust.
Highly delighted with the car now, I’d suffered Bridgestones on that for over 5 years, took some wearing out but went hard and not very grippy in the wet.
So its worth throwing a few prices around at your local tyre fitters or garage see if they can compete or get close enough.
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I’d be tending to agree with the above and replace in pairs , although depending on the age of the rears ( and your confidence in them !) I’d be half tempted with changing the entire lot.
While I haven’t put any fresh rubber on my 5 yet, in my last car ( mini cooper s) I replaced all 4 tyres with Goodyear eagle F1 asymetric 5s all round for a ‘reasonable’ ( under £100) price per corner and found the provided both solid grip and feel vs the previous nackered tyres on the mini, along with a generous curb protector for added peace of mind. Not to give you too many options, but could be worth a look too if others agree with my assessment of the tyre ?
Recently replaced all four on my euro box, I found Asda tyres to be a couple of quid a corner cheaper than Black Circles but luckily we have a Costco card and their price was a no brainier! £15 a corner cheaper than Black Circles for identical tyre…
The reason using same type tyres is to have the same progressive behaviour. if you just use it to cruise on the roads I wouldn’t worry too much (unless you initiate spirited driving mode).
Old tyres, I would replace them… they just don’t work as they would if new.
New tyres. I use Michelin ps5 on road and track. very sticky and I like them a lot, (the ps4 are also great from owner reports). Mates using Kumho PS71 and love them as well…
I’m going to fly in the face of opinion and say change them all, based on personal experience of the car pulling one way or the other above 40 mph depending on which pair was on which axle with a new PS71 and part-worn Potenza mixed set.
Last year I needed new rears (<3mm tread) but the fronts were at ~5mm. Original Potenza’s fitted, about 15/16k miles on them. At the time it was my daily driver on a 94 mile round-trip commute.
PS71’s fitted to the rear, original Potenza’s on the front. Above 40 mph I noticed the car was pulling badly to the left.
Assuming pothole induced dunting of alignment, booked into local specialist. Pretty much in spec, but adjusted anyway to ideal.
Still pulling to left, I returned to the specialist and spent another hour investigating possible causes. Nothing found, so fronts and rears swapped diagonally to see what happened.
Car now pulled to right above 40 mph. Only difference now is which tyre is where.
Ran like that for a couple of months before replacing the Potenza’s with another set of PS71’s.
Instantly sorted the pulling. The steering wheel stayed straight at all speeds as it should have.
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Hmmm that’s interesting. I just can’t follow the logic of that. If the Potenzas were to blame then why did it not pull to one side before you fitted the Kumhos. If you just swapped the front tyres round side to side and it pulled the other way I could understand that it may be a fault with one of the Potenzas. However the pulling appeared only when you fitted the Khumos to the rear, which would be one hell of a coincidence.
I will try just fitting new Khumos at the back and see how I get on. I cannot bring myself to bin two tyres with 5mm of tread left for financial and environmental reasons. If I do suffer anything like what you have experienced I will bite the bullet and certainly report my experiences on here.
Neither could I. That’s why I sold my part worn good pair of Bridgestones when I fitted the full set of Kumhos.
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Bridgestones don’t age well. Bin them.
When I bought my NC the four OEM fitted Potenzas (date codes matched the car) had done 17,000 miles and were equally evenly worn with about 5-6mm tread.
However, at six years old, the grip was non-existent with DSC light flickering frequently, and they might as well have been made of Bakelite.
The Dunlops I replaced them with have aged infinitely better over eight (!) years and 20,000 miles, with grip still so good (no complaints from DSC) I am reluctant to replace them simply because of age.
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I didn’t understand it either, but the pulling was only ever a problem during the brief period of the car having a mixed set of new Kumho’s and part-worn Potenza’s.
The balance of all four wheels was checked & confirmed to be ok when I went back in after the alignment didn’t solve the pulling. We also checked for unusual wear and play of all suspension/hub/bearing components and made sure tyre pressures were correct and equal. Nothing abnormal was found.
Thinking about it the only difference was the wear between the Potenza’s. Off the top of my head one was maybe 1mm less worn as it’d been replaced after the active bonnet went off (new alloy because the estimator deciced the kerb mark was caused by the lamb I’d hit).
I don’t believe that uneven wear was causing the pulling because it wasn’t apparent when I had four Potenza’s on the car, and I’d run it that way for about 9 months before the rears needed changing. The problem only ever arose with the mixed Kumho/Potenza set fitted.
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The reason is because the two makes have a different construction and rubber makeup which makes for different handling traits.
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Well, Kumhos fitted to back. The garage had put the wrong pressure in them, 36 psi even though I told them 29 psi and I subsequently corrected before any evaluation of their performance. No constant pulling to either side but the car feels awful. It seems to feel very unsettled and constantly squirming around at the rear end and suffering from camber and bump steer making the car very nervous and nowhere near as stable as it was. When I corner the back end seems to sit down on the outside wheel and lurch around. So to me the Khumos seem a retrograde step. I will see if fitting them to the front improves things at all.
I think you need to bite the bullet and fit Kumho on all four corners.
I always go for a full set whatever car, just wear them out evenly front to back swap periodically then it wont feel like you’re scrapping two part worn tyres.
I’d want rid of the Potenza’s asap anyway, had them before on my daily driver😒
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What I can’t understand is why the car would feel fine before with a full set of Potenzas and feel awful when two Kumhos fitted to rear. I would expect the car to be the same if not slightly better. I understand a change in grip caused by fitting the Kumhos may upset the handling balance but to introduce squirming and instability does not really make sense. I will give them a bit longer and even try putting them on the front but if that doesn’t improve things I shall buy some more Kumhos when I have the reddies.I just hope the Kumhos are as good as many people on here say that they are.
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They’re a budget tyre giving excellent performance. I have various wheel sets with Michelin Pilots and Toyo’s and the Kumho’s are a very good tyre IMHO. No grumbles
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Different tyres have different characteristics. The MX-5 is beautifully designed to be a well balanced car. By putting tyres with different characteristics front and back it is bound to upset that balance that Mazda dialled in.
My ND feels so much better on a full set of PS71s than it did on the original Bridgestones.
My NC felt so much better on a full set of Kumho KU39s than the original Continentals.
Bridgestones and Continentals were both OK but Kumhos were better.
The only time I really had a handling problem was when due to a puncture on a Sunday in the wilds of Scotland. I ended up with a Hankook Ventis on the back of the NC with three Kumhos. Pulled left on acceleration and right under braking. Felt awful. Replaced it with another Kumho as soon as I could and perfection restored.
Always have a matched pair with equal tread on the back or it can destroy an LSD.
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