Wheel Spacing, how much is too much?

Looks like i’ve been given a handy template to fill out so i’ll start there…

  1. My model of MX-5 is: NC1 2006
  2. I’m based near: South West
  3. I’m looking for technical help or recommendations on: How much wheel spacing to add improve handling without pushing the wheel outside the line of the body work.

Hi all, as suggested above, for our track focused NC we’re looking to add some spacing to the rear hubs to widen the track a bit and hopefully provide a bit more traction at the back end on the power out of the corners. We followed this principle in Karts back in the day, increasing the width of the rear axle on the dry days to carry more speed through the corners without losing the back end, so i can’t see why applying the same principles to an MX5 shouldn’t work?!

I’ve found a number of spacing kits on the internet that range from 20 - 60mm in width, I suppose the questions i’m asking are;

  • Has anyone any experience of adding wheel spacing and the scale of the benefit?
  • What amount of spacing is it realistic to try to get away with without pushing the wheel too far out of the body work?

Thanks in advance, and apologies if this is in the wrong area and/or has been discussed before.

This is a huge topic. Geometry of suspension is a rabbit hole best left to experienced people. There’s rules of thumb but some times you can try to make things better only to ruin them. You’ll not notice a huge difference with 20-30mm spacers but it’s there. Maybe better. Maybe not. Hard to say.
The extra leverage makes the unsprung weight harder to control regardless, and you will be adding unsprung weight in the form of spacers. And it exasperates bump steer. You will alter droop due to leverage against the shocks and dampers too. You are altering the moment of inertia in a negative way making the suspension react more slowly. The wider track will give greater mechanical grip, but mechanical grip is static, dynamic grip will be reduced. It’s a trade off.

Imagine holding a bag of sugar close to you and swooping it around quickly, now try it at arms length. Every increment between the two divides the difference between the two but always in the same way. That’s unsprung weight.

Be aware if you go into competition narrow can be your friend too, clipping a cone carries a penalty, if the wheel is 30mm further from centre you may clip it where you would have missed as standard. Narrow, windy circuits favour nimble narrow cars. Imagine a motorbike thru a slalom, it may be possible to straight line it on a bike, a car would be swerving like mad on the same course.

If you only do the rear axel also bare in mind that’s like a dart flight, the rear wheels are not dead ahead they are set to create very slight drag in order to keep you stable and looking where you’re going not where you’ve been at high speed. You need to test and adjust to suit as you alter wheel track.

If you’re doing it just to say you have or because you heard you should then don’t bother. You’ve heard of ‘the scientific method’, well it’s the only answer. Design a practical experiment to test a hypothesis and check to see if the results agree with the theory. Seat of the pants can feel good some times even when things get worse.

Just from a practical point of view regarding spacers, 25mm will get standard offset wheels, right to the edges of the bodywork. More will have the wheels sticking out beyond, less will mean cutting studs down so they don’t hit the back face of the wheel. Out of 20 studs, when I fitted 25mm hubcentric spacers, only one, IIRC, protruded and that couple of mm was accommodated by the slight recess cast into the rear of the OEM wheels. My car (2010 Sport Tech) is lowered on Meister club race coilovers and no arch rubbing or clearance issues at 25mm. You could get the same measurements with a 30mm offset aftermarket wheel too.
Barrie

Not sure if both posts above are by the same person or its just a co-incidence that you’re both called Barry. The second post kind of feels like a continuation of the thought process of the first post too! Either way, i’m very grateful for the thoughts given so far. :grin:

Point taken on keeping the car nimble and not having anything sticking out. I learnt this lesson the hard way in Karts many years ago, clipping a concrete block at 60mph with the extended rear axle, flipping the kart and falling out in the process. This was my motivation in wanting to find out how much I could get away with without having anything protruding past the limits of the body work! :crazy_face:

Points also taken on how increasing spacing will effect the demands of the suspension geometry. Will ask the old man to talk to the people who’ve set the car up for us about that.

Ultimately, I feel like I’ve got two limiting factors in the car at the moment, which are more prevalent the faster the corner gets (fairly obviously I suppose). The first, and most scary issue, is turn-in oversteer. I’m aware I need to manage this better with a bit of trail braking and generally being smoother transferring the weight coming off the brakes. Its quite tricky to catch the car when it steps out on the way in to the corner and I’ve had a few seriously near misses on this one which is denting my confidence in the car. The second is the car stepping when loaded up half way through a corner trying to get back on the power. We’ve played with dampening and roll bar stiffness on this one and i’m generally happy with the balance of the car in terms of over/under steer, but I feel like there’s more to be found. Perhaps i’m being a bit naive, but I just remember adding spacing to the rear axle on the kart making a huge difference to the amount of speed I could carry through corners and was hoping to re-create that in the MX5. Perhaps we’ll pick up a set of 25mm spacers and stick them on and see how it goes.

Point also taken on the scientific approach. If I ever get a day of running in consistent weather it would be good to run the car with and without the spacers on the same track in subsequent sessions and then measure the time difference, if any, on the video footage after the event. Even if there’s not a great deal of difference in time, if the extra spacers make the car feel more stable i’d take that just for the additional confidence that would bring.

Interested to hear your thoughts on this. Thanks again.

:grinning: one is Barry and I’m Barrie! I’m the non science guy! :rofl:
Barrie

Cool, thanks Barrie, I’ve got it all sussed now! :innocent:

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What tyres are you using and what pressures are you running at? As an old kart driver myself, who was a rubbish driver but successfully compensated with a good setup. My advice is start timing laps and recording everything you do or change to the car. Start with improving the standard just small adjustments and drive slightly slower to give you consistent results. The 2 Barries (sounds like a comedy show) are right, just don’t get bogged down with unsprung weight until you can afford magnesium wheels! :wink:

Reading my post back it sounds a bit negative. Wasn’t intentional. For cosmetic reasons they do look better. I had a GBS zero and ran 15mm hubcentric spacers on the rear purely for cosmetics. It did make the car snap a tiny tiny bit more on oversteer but noting dramatic. Don’t be put off using them, just don’t expect them to change the laws of physics :rofl::rofl:.

The two Barrie’s! Now there’s a thing! :rofl::rofl:

Anyone remember Barryokie? There was a bit of a thing on the name a few years ago.

No. I’ve not heard of that :thinking: just done a quick Google and there seems to be guys doing Manilow medleys, is that it? :grin:
Barrie

It was a radio one thing iirc. All sorts of shout outs to people called Barry. People called Barry encouraged to call up and sing on air. You know the sort of thing.

A well set up MX-5 should not be a desperate handfull. If you are getting corner entry oversteer I would look to your suspension set up, tyre grip or the fact you are carrying too much braking effort into the corner unloading the rear, so very much over “trail braking”
Again for mid corner oversteer, if you have the car rotated you would be hoping the power would squat the back and control any slide and so again look at set up or tyres or driving style. Pushing the wheels out a further 20mm or so is going to make as much difference as fitting a Chrome gear knob. The common set up would be 7.5" wide rims with a 10mm lower offset and 215 tyres.

Interesting.
I have been wondering about how slightly larger tyres or subtle spacers on the rear only would affect the stance of the car, for cosmetic reasons only.

@Bettabuilda I just googled the lyrics for Copacabana in an effort to make up some play on words for comedy effect (geometry and spacing are crucial in racing?!) but have instead been shocked by the drama in that track. Poor Lola, shes just trying to be a star and then Rico shoots Tony and she ends up losing her mind! I had no idea that song was so dark. :grimacing:

@Mrbarry To be honest, i’m not really interested in the cosmetic effect (I just want to go faster through the corners) so I was on board with your original response. :+1: Thanks for clearing that up, though :grin:

@NickD Thanks for your reply. We’re still learning about the car and i’m trying to improve in the seat so i’ll take on all of what you’ve said. I’ve found so far that a balance of +5 stiffness in the rear dampers gives me the best balance of Turn in Vs controllable oversteer on the corner exit. Generally i’m happy with that but the consequence of having a responsive front end appears to be the snap coming off the brakes on the way into the corner. I’ve watched my footage back countless times and everytime i lose the back end on the way into a corner it appears to be because i’ve come up off the brakes way too sharply to get back onto the power. Hence me getting the impression that i need to trail the brakes a bit more and transfer the weight back a bit more gently. It’s interesting that you don’t think spacing will make any difference here so before we try spacing i think i’ll work a bit harder on trying to push the limits of the damper settings to see if i can solve it with that. Looks like this will be what i’ll be working on at Oulton on the 13th. :grin:

@Enjoyabull We’re running Toyo R888R’s. I don’t know the pressures (the old man is the mechanic) but I know he’s taken a lot of advice on that and we alter the pressures after a few laps of hot running to make sure they’re consistent and specific to the layout when the tyre is at a working temperature. Obviously can’t use timing equipment on track days but I do record all the runs and watch them back after and yes we keep a journal of the set up changes we make through the day for cross reference. Good tips across the board here thanks :+1:

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I spent £65,000 modifying my track car for time attack, it was a fast car but there was a piece missing. I had a few lessons (not cheap if I remember correctly around £800 a day) and practiced what I was shown. It was hands down the best money I spent for my lap times.

I lacked god given talent, all men seem to think we have it but it’s quite rare, so had to practice and take instruction. I always revelled in testing days after that, javelin testing days are often timed, where as normally timing on track will see you banned for life from that track and with that organiser if it’s not a competition event). Most people would either turn up for 15 minutes and go home, true testers of race cars, or hammer around all day because testing days are cheap track days. I fell into the latter normally and could generally be seconds ahead of the field :rofl:. Best being the day my track car was unfinished so I tracked my old diesel estate car in standard road form and took a minimum of 3 seconds a lap out of a group of guys in Evo’s, they had a support van and all sorts. All the gear but no idea.
So, if you’ve had no instruction and want to get faster don’t rule it out :+1:

Thanks Barry, great stories there. We most definitely have NOT spent £65,000 on our MX5! We have had occasional good results against faster cars in the Javelin/Japanese Sprint Series, though, when I keep it on the track. :sweat_smile:

RE: Tuition. I rely heavily on my experience from Karting where we raced at a relatively decent level but the introduction of suspension amongst lots of other things in cars obviously changes a lot! I’ve had a session with Rodders in the car on a soaking wet track at Brands Hatch last year and he gave me some great tips. I think i’d have gone for a few more of those this year but of course Covid has put pay to a lot of that. So all i’m left with is YouTube and the likes of the Driver-61 channel. I appreciate there’s a lot left to learn and nothing replaces in car-tuition but i’m trying to make the most of what i’ve got at the moment. Not sure if any of you guys will be at Oulton on the 13th but it would be good to catch-up there and follow you round a bit to see where i can improve. :+1:

Thanks to everyone for the replies and guidance here, we ended up going on a bit of a journey from where the thread started but its been enjoyable! :smiley:

Hi Nick that’s the exact set up I’ve got on my Sport Black and I have to say that it drives very well with a good set of lightweight wheels and Hankook evo tyres.

Plus 1 for tuition.
You will at very least get an opinion if your car is set up well or not.
The solid rear axle of karts means you tend to have to be aggressive on the steering to get the back to come round to kill understeer. You need to be more subtle in a car.
If you say you are getting oversteer at the point of coming off the brakes it suggests the driving style is a bit too digital.

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@NickD
Bang on the money, the transition from kart means finding your zen with the car and driving softly. I still struggle with holding the steering wheel too tight! and I stopped Karting nearly 30 years ago.