Official TAMON Wheel Size Calculator

[Brayden]

With special thanks to forum guru and all-round nice guy Ike, I am proud to unleash the official TAMON wheel calculator.

You'll need to upgrade to the latest version of Java to use this fancy bit of whizz-bangery, but trust me, the effort will be worth it.

Snazzy kick-ass wheel calculator.

If you're a lazy bugger and don't want to upgrade your Java install, or you're stuck using some old stone age computer then you can try the less snazzy (but equally impressive) oldschool compatible version.

Kind of not-so-snazzy but still works wheel calculator.

Not only does the calculator work out all kinds of neat stuff to do with tyre sizes and speedo correction, it also has a groovy bit that lets you mess with gear ratios too! How cool is that?!  8)
(Listed ratios are for a stock F8B)

Anyway, hope you enjoy it... and remember, all praise to Ike!

[ike849]

As brayden has already found somethings might not work as expected....the more people use/test it and tell me about it (just PM me) the faster i can fix it/make it better.

The main reason i developed this was to solve the endless questions on what wheels fit xxxx car. It allows you to input offsets of the rims you want to use to calculate clearances in the wheel arch. Note: Gary from Miata forums has Ok'd me using the same wheel pic design to show the differences between the original and proposed tyres.

I would like to mention that the old version has all the formula i have used in the program at the bottom of the page for those that are interested...

ALSO the Suggested Rim Width & Rim Width Ranges are approximate values only, based on industry "norms" but some tyre manufacturers operate outside thses norms especially low profile tyres!!!! Contact the manufacturer of your tyre NOT the tyre dealer for exact rim width fitments.
Again don't take these values as gospel though they will be correct for the majority of cases.

Enjoy.

[Brokenshire]

I can't get the calculator anymore, can anyone upgrade the link?

[Brayden]

The link is right, it is more likely an incompatibility with the latest version of Java. The "not-so-snazzy" version still works for me though.

[CHooKMaN]

They both work for me and I have updated Java. The snazzy one does take a fair while to load though.

[Brokenshire]

Damn Computers and their constant need to be upgraded!

[ike849]

both the snazzy(requires java 6 or better) and non-snazzy(requires java 1 or better) applets shouldn't take that long to load....

the first time a java applet loads takes a long time (loading up all the java libraries). if you load the snazzy one in a new tab and then close the tab you should still see the java coffee mug next to the clock on the tray bar. if you then load up the snazzy-one again it should take no time at all as java itself is already loaded.

ps. i was working on a new version that calculates the shift point for each gear based on your peak power, peak torque and max rpm, but I haven't had much time in the last 6 months to do anything MB really

[ike849]

have been working on the next version of wheelcalc....

but i need some help..... if you have a dyno graph of your car could you scan it in and email it to me ike849@hotmail.com

In the next version of wheelcalc it estimates your torque curve (based on your pear torque and pear power values) using parabola and linear functions to get the correct shift points for each gear.

I just want to check how close the estimate is to real world examples so the more dyno graphs i have the better!!!!!




2nd point of help needed for those that are maths/physics orientated (or just know the answer).

basically i want to take into account the wheel size when calculating 'road torque' (at the moment it doesn't account to wheel size), as the wheel size is actually part of the gearing.

using this forumla;
road torque = engine torque x diff ratio x gear ratio x wheel size

A dyno graph is typically taken in 4th gear as that has a ratio of 1:1 (or close to it), say my diff ratio was 4.35:1 you end up with;

RT = ET x 4.35 x 1 x wheel size

now to my understanding a dyno graph should show you 'road torque' as it is measured at the wheels WITHOUT the diff ratio accounted for (gear ratio ignored as it is 1:1). so in my example dyno 68nM @ 4500rpm would make the forumla look like this;

68 = ET x 1 x 4.35 x wheel size
68/4.35 = ET x 1 x wheelsize
15.6 = ET x wheelsize

now if you believe dyno guys that say manual cars have a 15% loss of POWER through the transmission (gears + diff + friction on tyre), you can then convert that percentage loss of power at 4500rpm to a torque loss. (I by the way don't like this as the weight of the transmission internals, speed at which they are turning and actual design of the gears needs to be taken into account for an accurate power loss figure, but since the whole shift point is an estimate 15% is easy and will 'probably' put us in the right area)

so 68nM @ 4500rpm = 32kW @ 4500rpm
15% loss equals 27.2kW @ 4500rpm = 57.7nM @ 4500rpm

so i have (57.7 / 4.35 to bring the diff ratio back in)
15.6 = 13.27 x wheelsize
wheelsize = 1.175

now this actually (well quite dodgy really) gives me a ratio for the wheel size for the car when dyno'd (145/70/R12).

How would i get this ratio without being dodgy, ie. is there a way of having a wheel circumference and converting that into a ratio so that it can be factored into the 'road torque'????


once i have these things sorted i will email brayden the new wheelcalc....

[ike849]

a dyno shop has this as their forumla for powertrain losses (it atleast takes rotational speed into account)

BHP loss = ((4.874 x 10^-2) x MPH) + ((3.517x10^-4) x (MPH^2))

for us in aus;
BHP loss = ((4.874x10^-2) x (KMH/1.609)) + ((3.517x10^-4) x (KMH/1.609)^2)


also i must mention the only way to accurately measure drivetrain losses is to engine dyno and then chassis dyno your car back-to-back. As the 'coast' down test they do at dyno shops only accounts for the losses under those load conditions (ie not under full acceleration)


on the wheel size front i forgot to mention that effectively the torque acts through the radius of the wheel. So their must be a way to take it into account which i'm not seeing....

[ike849]

Just realised what I was doing wrong......

road force = wheel torque / tyre radius (force is a linear measurement)

wheel torque = engine torque x gear ratio x diff ratio x losses (torque is a rotational measurement)


so effectively the wheels don't act as a torque multiplier but instead act upon the linear force of the car. This makes everything simple again as when calculating when to shift I can just compare the road force between shift changes and then it is easy to make the comparison between tyre size changes.....

I still need scanned copies of dyno graphs so see how accurate my estimated curves are.... (non-turbo would be good as predicting a turbo cars torque curve is very difficult without knowing boost levels at different rpm)

[Brayden]

I will be able to supply a turbo dyno graph in the future, and will get the boost curve overlayed to make it a bit easier.

If I still have the red ute then I will take it for a run too.

[ike849]

cheers!!! I probably won't get time to work on the new wheel calc until late november... I'm to committed to my job

[Brayden]

Last month ike sent me a new version of the calculator which I have now uploaded. Sorry for the delay! Links remain as per the first post.

I'll let the man do any necessary explaining on the changes.

[ike849]

cheers brayden..... my OCD'ness can now subside.....

major change in this version is the inclusion of 'accurate' shift points based on your road force curve....read the formulas and conversion html at the bottom of the page on how I calculate it.

From the many dyno plots I have looked at (went to my local dyno shop) it predicts 'pretty' much all of the torque curves except when you are talking about big bhp turbo cars (ie. turbo spools up late in rpm range which greatly effects the shape of the torque curve) or nitrious cars....

a quick way to test if your car's shift points are working is to change the engine redline to something silly like 10,000rpm. Most 'normal' cars will have shift points beyond std. redline as designed by the manufacture for easy(lazy) driving.
The exception is for the final shift change as 5th or 6th is usually taller for quieter highway driving and fuel economy (look at the corvette...massive final gear!!!!)