Interesting mod to run wider tyres

[m1tch]

Hi all,

After asking around on the Facebook groups with regards to fitting wider wheels and tyres under stock arches, someone mentioned a very interesting mod which might massively help with fitment of wider wheels without modding the bodywork.

I will be looking to run 255 rear tyres on a 17x9 rim, the stock rear FL wheels are 16x7, so will be looking to fit 2" wider wheels to the car, the good news is that the rear quarter panels on our cars are bolt on rather than welded on. If we had welded on wings I would have needed to cut and then weld up the inner and modded outer arch however there is a really simple solution.

The solution is to simply space out/custom make a slightly wider support bracket that sits between the bodywork of the car and the wing (it sits in the front part of the arch and acts as support).

Extending/making a slightly wider bracket will mean that all the stock parts of the arch will bolt up as per OEM but the centre part of the wing is pushed out slightly more - this in turn will give additional clearance using the OEM rear quarter without needing to bolt on flares to the OEM arches.

I will be running coilovers with my project and can adjust the ET of the wheels I am getting so might only need an extra inch of 'push' to be able to fit the much wider wheels - might still look to roll the arches slightly anyway to avoid any issues with rubbing.

Just thought I would share this - seems like a very simply solution and can be done fairly easily as our bodywork panels are bolt on rather than welded on like many other cars.

[J03]

Fitting a longer bracket won't really do anything unless you modify the lower & rear fixing points also. Then you're going to have some funky panel gaps.

Best to do away with the bracket completely & just simply roll the arches to the desired flare.

[s12vea]

I'm sure with the correct offset 17x9 with 255 will fit under standard arches. I'm pretty sure mattperformance was running a set on his track car at one point.
I would stick with 245 you don't need any bigger on a 2.

[m1tch]

I'm sure with the correct offset 17x9 with 255 will fit under standard arches. I'm pretty sure mattperformance was running a set on his track car at one point.
I would stick with 245 you don't need any bigger on a 2.

I am still looking at options, basically needing a wider rear tyre owing to the large increase in power the car will have - a 255 width seems a fairly common size to be able to get a decent performance tyre in.

[m1tch]

Fitting a longer bracket won't really do anything unless you modify the lower & rear fixing points also. Then you're going to have some funky panel gaps.

Best to do away with the bracket completely & just simply roll the arches to the desired flare.

The panels are secured at the front edge, rear edge as well as top and bottom, the car that I have seen that has this mod still looks fairly standard - I guess its also less of an issue if I need to fit on wider arches as there isn't a panel behind that would need welding!

[1979scotte]

What where you thinking of for the front?
I honestly feel the wider you go the less right these cars feel.
I understand the need for wider tyres with large power but ChrisGB seems to do ok with well over 300 on stock FL admittedly with R888.

Pretty sure the widest I would go on the V6 would be 205 F 225 R.
Currently 185 205 and that is simply silly in the wet.

[Call the midlife!]

Wider the wheels and tyres, the heavier the unsprung weight and increase in drag/friction. You'll be counteracting the increase in power and all your other weight reducing efforts. But obviously you already know this.


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[m1tch]

Wider the wheels and tyres, the heavier the unsprung weight and increase in drag/friction. You'll be counteracting the increase in power and all your other weight reducing efforts. But obviously you already know this.


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I do want to keep the unsprung weight down, the issue being is that there aren't any wide 15" tyres out there that are wider than the stock FL rears - more of a case of finding an easier to source tyre and work on fitting that to the car.

[m1tch]

What where you thinking of for the front?
I honestly feel the wider you go the less right these cars feel.
I understand the need for wider tyres with large power but ChrisGB seems to do ok with well over 300 on stock FL admittedly with R888.

Pretty sure the widest I would go on the V6 would be 205 F 225 R.
Currently 185 205 and that is simply silly in the wet.

I will look to run a staggered setup so the balance is the same, eg 185 front and 215 rear will go to probably a 225 front and 255 rear (increasing the front the same amount as the rear).

I am still going through options for the car, I might still be ok running on FL wheels as the car will have traction control as well as boost by gear so the car won't be making full power in the power gears.

I might look to run your suggested setup of 205 fronts and 225 rears but might drop to a 15" wheels all round to reduce weight - looks like a 205/50/15 and 225/50/15 might work as a combo.

[jonbill]

The tyre sizes you're talking about are enormous for a 1000kg car. Even with serious duration on track I'd doubt you're going to overheat 225 or even 215 tyres. I wouldn't look to change from stock until you've identified a problem (unless you want to cosmetically)

If you're worried about traction, it's worth remembering that contact patch size is largely a function of vehicle weight and inflation pressure. Tyre width doesn't figure significantly.

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[1979scotte]

The tyre sizes you're talking about are enormous for a 1000kg car. Even with serious duration on track I'd doubt you're going to overheat 225 or even 215 tyres. I wouldn't look to change from stock until you've identified a problem (unless you want to cosmetically)

If you're worried about traction, it's worth remembering that contact patch size is largely a function of vehicle weight and inflation pressure. Tyre width doesn't figure significantly.

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You could be right but the Elise cup 260 weighs under 900kg and only has 250hp yet runs 235 rear tyres
The OP is looking at running up to 400bhp and weighing under a ton.
I wouldn't want to go too wide nor to narrow.
With 260ftlb of torque my tyres arent really up to the task especially in the wet.

[BahnStormer]

The tyre sizes you're talking about are enormous for a 1000kg car. Even with serious duration on track I'd doubt you're going to overheat 225 or even 215 tyres. I wouldn't look to change from stock until you've identified a problem (unless you want to cosmetically)

If you're worried about traction, it's worth remembering that contact patch size is largely a function of vehicle weight and inflation pressure. Tyre width doesn't figure significantly.

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You could be right but the Elise cup 260 weighs under 900kg and only has 250hp yet runs 235 rear tyres
The OP is looking at running up to 400bhp and weighing under a ton.
I wouldn't want to go too wide nor to narrow.
With 260ftlb of torque my tyres arent really up to the task especially in the wet.

@1979scotte  remember that the contact patch is a function of length (i.e. tyre height!), width and weight... with stock 15's on the back, the length of your contact patch is already fairly low, even compared  to FL's... I think 8J wheels and 235 width rubber would probably be the limit before you completely compromise the handling....

I guess if it's for show'n'shine only then it might still be okay, but is anybody running wider than 235 rubber for performance reasons?

[jonbill]

That last bit is my point really. Your contact patch will be basically the same however narrow or wide your tyre is. Pretty much any car with more than a couple of hundred bhp/tonne is going to be able to break traction in the wet in multiple gears.

The advantage a wider tyre has is that it has to distort less to achieve the contact patch, so on track where tyre temp can be important a wider tyre has an advantage (although in my case at least, getting some tuition would make a much bigger difference).

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[m1tch]

The tyre sizes you're talking about are enormous for a 1000kg car. Even with serious duration on track I'd doubt you're going to overheat 225 or even 215 tyres. I wouldn't look to change from stock until you've identified a problem (unless you want to cosmetically)

If you're worried about traction, it's worth remembering that contact patch size is largely a function of vehicle weight and inflation pressure. Tyre width doesn't figure significantly.

Sent from my G8441 using Tapatalk

You could be right but the Elise cup 260 weighs under 900kg and only has 250hp yet runs 235 rear tyres
The OP is looking at running up to 400bhp and weighing under a ton.
I wouldn't want to go too wide nor to narrow.
With 260ftlb of torque my tyres arent really up to the task especially in the wet.

@1979scotte  remember that the contact patch is a function of length (i.e. tyre height!), width and weight... with stock 15's on the back, the length of your contact patch is already fairly low, even compared  to FL's... I think 8J wheels and 235 width rubber would probably be the limit before you completely compromise the handling....

I guess if it's for show'n'shine only then it might still be okay, but is anybody running wider than 235 rubber for performance reasons?

I am basing my tyre choice of increasing the width on other cars that have around 400bhp - example being the E90 BMW M3, its running 414bhp and has 265 width rears - although the car is much heavier.

I am trying to strike a balance between wheel and tyre weight vs traction, I know that a wider rear tyre has a different shape contact patch than a narrower tyre, the narrower tyre would also heat up quicker.

My issues is that I am looking for a a tyre combo that can:

Cope with up to 400bhp
Can fit on an easy to get hold of tyre in terms of compound <--- this is the hard part
Doesn't need a huge amount of work to fit

Basically I am trying to match the tyre size for the purpose - issue being is that there aren't really any wide 15s past a 225 out there, would need to step up to a 17 to unlock other options with the 255 being quite a common width for a performance tyre.

I won't be running full power in the wet and will have traction control, would only be running full power in the dry - I will be trying to limit my torque to under 300 ft/lbs to save the gearbox.

The wider tyre isn't for cosmetics, nothing on my car is, its all functional which is why I am trying to find a 15" tyre to run to keep the overall wheel and tyre weight down.

[BahnStormer]

its all functional which is why I am trying to find a 15" tyre to run to keep the overall wheel and tyre weight down.

It sounds like you've pencilled in flared / rolled arches, etc, but if you wanted to keep it looking fairly stock, maybe  17x7J front and 17x8J rear, then you should be fine with 205/45R17 on the front and 235/40R17 on the rear. The front diameter would be the tighter, but only 5.5% up on stock sizes) and the rear diameter would be 3.5% larger and you'd have nearly 10% more width.

There's loads of wheels in those sizes and I'm not sure about the 8J, but the 17x7J OZ Ultraleggera's are lighter than the OEM wheels.

Not sure if you were after proper track tyres for that setup, but the Yoko AD08R's are available in both those sizes mentioned above.

I know you're comparing to other cars in the same power category, but surely they'd need more traction as there's more weight pushing them towards the outside of the corner - comparable aero and you'd be a long way ahead of those cars even on narrower tyres.... plus part of the fun of an MR2 is the "adjustability" on the throttle

*not that I think I'd ever aim for that in a '2 - that's what I've got in my A6 and I I get myself in silly places with that, despite Quattro and 1700kg to haul around!

[m1tch]

its all functional which is why I am trying to find a 15" tyre to run to keep the overall wheel and tyre weight down.

It sounds like you've pencilled in flared / rolled arches, etc, but if you wanted to keep it looking fairly stock, maybe  17x7J front and 17x8J rear, then you should be fine with 205/45R17 on the front and 235/40R17 on the rear. The front diameter would be the tighter, but only 5.5% up on stock sizes) and the rear diameter would be 3.5% larger and you'd have nearly 10% more width.

There's loads of wheels in those sizes and I'm not sure about the 8J, but the 17x7J OZ Ultraleggera's are lighter than the OEM wheels.

Not sure if you were after proper track tyres for that setup, but the Yoko AD08R's are available in both those sizes mentioned above.

I know you're comparing to other cars in the same power category, but surely they'd need more traction as there's more weight pushing them towards the outside of the corner - comparable aero and you'd be a long way ahead of those cars even on narrower tyres.... plus part of the fun of an MR2 is the "adjustability" on the throttle

*not that I think I'd ever aim for that in a '2 - that's what I've got in my A6 and I I get myself in silly places with that, despite Quattro and 1700kg to haul around!

This is true, I am still looking into options on this, if I can get by with basically standard sizes that would be ideal - even going with the 15" wheel option of a 205 front and 225 rear as that's only 1% out.

The good news is that I can look to run any tyre size I want as I can adjust the speedo via the ECU I have which is why I was looking at those 255 rears which I think are 6% out - just trying to find a tyre that is easily available in both a standard road tyre as well as a higher performance tyre - seems that the R888 tyres come in basically any size you want though! I am ideally looking to run a high performance street tyre as the car will be driven on the road for most of the time - and not at full power.

Your point with regards to less weight is a good one, the car will also be rear weight bias anyway which will help with traction with weight over the rear wheels.

Might be able to get away with a simple roll of the stock arches if I need a bit of extra clearance - especially if running fairly low on coilovers.