Frame Rail Bracing

[Red_Bullet]

This carries on from the group buy regarding frame rail reinforcing.

Ruffian147 wrote:

? Just adds more weight to the car. Lightness is speed.

Yep, it is a concern and is certainly verifiable hard truth. Increase mass and decrease acceleration. But hey the supercharger and semi-slicks should compensate to some extent. What if it grips better because of less flex, maintaining the tyre contact patch better...swings and round-abouts maybe.

I do know this much, I have an NB8B and an NA8, the NB8B has all the factory bracing and feels more confidence inspiring and predictable than the NA8. Just sayin....I do know this much, there are people at the track who are faster than me through the corners, which will be a)better driver, or b) better handling car or a combination thereof.

Anyway my NA8 has fairly ugly frame rails which have been a concern and I've often wondered how much these compromise the cars handling. I guess there is only one way to find out. Some say that that so called frame rails only reinforce the floor pan and do nothing for overall chassis rigidity, others swear by braces adding rigidity to overall chassis and car feel. Flip a coin?

[ManiacLachy]

What's the added weight of the rails? Can't be much, and I'm sure my gut is more of a detriment to performance than the rails would be! 2 months of serious diet would more than negate the addition of the rails. The weight is way down low too, so should lower centre of gravity a touch, if the weight is even noticeable.

[Red_Bullet]

Around 8 kg with mounting hardware. I too could do with loosing a bit of weight. Actually at track days I enjoy driving in a group of similarly paced cars more so than just chasing times. Seems more fun to me, than chasing outright times.

[beavis]

It's hard to find an NA nowadays that doesn't have deformed rails. The NB's have certainly fared better, and are apparently more robust, so perhaps that adds to your perception of the NB feeling more solid.

I know many people have gone fast in MX-5's without frame rail upgrades or bracing, so it really is a point of conjecture.

[Magpie]

Making a few assumptions....

If you had 190Nm at 5,500 RPM, your MX5 weighted in at 1,100kg with a 6 speed gear box and a 4.3 final drive, your acceleration would be 1.22m/sec² in 3rd gear. Add 10kg of extra weight and in 3rd at 5,500 you would have 1.21m/sec².

So yes if on a track coming out of a corner in 3rd the extra 10kg will make you slower, after 5 laps you would be over a car length in front!

[Red_Bullet]

Making a few assumptions....

If you had 190Nm at 5,500 RPM, your MX5 weighted in at 1,100kg with a 6 speed gear box and a 4.3 final drive, your acceleration would be 1.22m/sec² in 3rd gear. Add 10kg of extra weight and in 3rd at 5,500 you would have 1.21m/sec².

So yes if on a track coming out of a corner in 3rd the extra 10kg will make you slower, after 5 laps you would be over a car length in front!

Have you been reading the full works of Sir Isaac Newton, Magpie? You must have a spreadsheet for everything! A car length over 5 laps...hmmmm, the difference between winning and loosing at Monaco!

But point taken about how small a difference 8 kg makes to acceleration, deceleration and cornering.

[KevGoat]

Making a few assumptions....

... after 5 laps you would be over a car length in front!

... such assumptions being some bravery and skill ....

[lucmor444]

Can you offset what you lose in acceleration by gains you could possibly get due to increased cornering speeds due to potential handling gains of the braces?

I think ruffian's point is valid however as braces all add weight and take you in a direction contrary to the original light weight philosophy of the MX5.

However I am adding bracing for the possible benefits available and then expect will shed weight by the likely removal of 'luxuries' such as PS and air conditioning (not to mention personal weight loss options, figment of lighter seats, removal of spare wheel etc).

Interesting I recently chatted with a chap from the US that had a swag of different braces. He subsequently changed track and removed them all (sway bars included) bar a ppf brace. He is now faster than ever on the track and better on the road as he believes his suspension is now back to being fully independent!

[Magpie]

But point taken about how small a difference 8 kg makes to acceleration, deceleration and cornering.

Do not get me started However, if you are cornering at 1.5g then that 10kg becomes 15kg of extra load on the tyres...

He subsequently changed track and removed them all (sway bars included) bar a ppf brace. He is now faster than ever on the track and better on the road as he believes his suspension is now back to being fully independent!

I think almost all of us have gone through the 'fit bigger sway bars' and converted back to stock route. The desire to have the car corner flat is eventually replaced with the desire to corner fast and fast is not always 'flat' or 'without body roll'.

[KevGoat]

I seem to recall Automotive+ doing some tests some years ago on the effects on rigidity before/after fitting frame rails. Been unable to find it though.

[lucmor444]

FM tested their rails and measured a 30% reduction in the twisting of an '93 NA's chassis. The car already had a roll bar, strut brace bling and a 'diff' brace fitted.

[JINBA ITTAI]

Interesting I recently chatted with a chap from the US that had a swag of different braces. He subsequently changed track and removed them all (sway bars included) bar a ppf brace. He is now faster than ever on the track and better on the road as he believes his suspension is now back to being fully independent!

^^a newbie question re the above -- what's a ppf brace? .....also, what shocks/springs coilover set up did run on that barless braceless set up?

[NitroDann]

We all know that additional material in the frame rails increases the cars nvh performance but it doesn't improve the cars roadholding performance if it did then Mazda would have sacrificed the weight and put stronger heavier frame rails on the MX5 starting with the na6 but they only increased the frame rails as time went on to compete with other cars which now had very good NVH.

Tldr. Heavy rails improve NVH, that much we know. If they improved performance also it would be a no brainer to add them to NA6 but mazda chose not to.

Dann

[lucmor444]

While no expert on this matter, based on FM info the braces do more than improve NVH.

I also think the premise that the manufacturer would have done it if if works may not always be valid. A manufacturer needs to balance a lot of factors including such things as cost, weight etc etc and everything is a compromise. Even Bugatti has to make choices between what they would like to do and what they can do/can afford to do and still sell cars.

Manufacturers also learn along the way as demonstrated by the additional bracing on NA8s to NA6s and change in chassis design from NA/NB to NC.

And then marketing has its say, such as the need for power steering, power windows, power mirrors etc which have all compromised the fundamental design philosophy of the MX5.

So I do not necessarily accept the premise that if It was needed MAzda would have, particularly in the first series of a car.

[NitroDann]

While no expert on this matter, based on FM info the braces do more than improve NVH.

It also improves rigidity, which is not directly related to performance on its own.

I also think the premise that the manufacturer would have done it if if works may not always be valid.

I completely agree, I use this argument here because most people like it.

Manufacturers also learn along the way as demonstrated by the additional bracing on NA8s to NA6s and change in chassis design from NA/NB to NC.

Again I dont know if this is learning as much as just making the car more luxurious in line with the entire rest of the auto market.

And then marketing has its say, such as the need for power steering, power windows, power mirrors etc which have all compromised the fundamental design philosophy of the MX5.

Exactly.

So I do not necessarily accept the premise that if It was needed MAzda would have, particularly in the first series of a car.

Its no0t a full argument, but it certainly is true that adding mass to the rails doesnt make the car quicker, if that were true than every successfull racecar would have to have them to keep up with the opposition, and they do not.


Dann