26 replies to this topic

[Guess-Works.com]

Been meaning to sort this out and a question has lead me to finish it off.

This is a link to a page which privides you with a selectable list of tyre sizes, Drop gear ratios, gearbox ratios ( by source ) and Final drives ( by source ) and the product of which is a table of the theoretical speed at certain RPM's

Clicky link

Had to drop it there for the mo, but would be one of those things for the new TMF website ?

and looks sommit like this...

Edited by GuessWorks, 15 February 2007 - 02:45 PM.

[Brawlyrox]

GW ur a ledgend that is really really cool!!!!!

as for on the new site, if somebody knows how that could be programmed into it please let me know!!

what a handy bit of kit!

[MiniMoi]

Too bad mine won't go over 5500 rpm in 4th or I would haul a$$ at 7000 rpm. :grin: Definitly time for a 6spd larger wheels and a 2.760 dif.

Great site doesn't take up all the time figuring it out anymore.

MiniMoi

[Jammy]

Shame it doesn't give figures for 8500rpm really.....

[Guess-Works.com]

Now goes to 8k, sorry JB, but I think 8.5k is a little excessive :grin:

also added some of the available Straight cut close ration gearset into the selection.

[Madmax]

lol! aparently it thinks at 8500rpm with 12inch wheels and a 3.44 FD that my mini will top 137mph....i dont think that it takes wind resistance into consideration

[Guess-Works.com]

These are theoretical, if you can get your car upto 8000 rpm in 4th, then that's the speed you'll be doing.

[Madmax]

do you think it takes into account all the variables like av weight, drag co-eficient, rolling resistance etc? If it does then theres some good programming calculations in there.

[Guess-Works.com]

Basic mechanics....

At a certain engine rpm the wheel will go round at a certain rate. this is set by the ratios, and cannot change.

The only thing which will affect your actual velocity is the contact patch between tyre and road. Wind resistance will slow the car down, agreed, but if the contact between tyre and road is maintained as a constant, then then engine rpm will reduce in proportion to the wind resistance.

Yes I appreciate that there are probably co-efficient values which adjust the velocity, in connection the contact patch, otherwise tyres would not wear out, but in the scale of things, probably not worth considering.

[TimS]

he he doubt u cud wheel spin in 4th at 5500rpm. as guessworks said if the velocity changes then so does the rpm uless there is a loss in friction between the trye and road

[MiniMoi]

Yes I appreciate that there are probably co-efficient values which adjust the velocity, in connection the contact patch, otherwise tyres would not wear out, but in the scale of things, probably not worth considering.

The tires wear out because of the friction between the road and the tire. When normally driven without a wheel spin. This can not be a co-efficient value as the wheel will not be spinning faster as opposed to the road. Just look I normally can do about 95-100mph at like 5500-6000rpm. It won't go faster. But in a storm a couple of weeks ago and the wind hitting me head on. I tried out the top speed. I only got it up to 80mph which was at just under 5000rpm. So when ever you have co-efficient values like a hard wind. Your engine will just not be able to push it faster than that max rpm. If you however have a tuned engine which goes easy up to it's max rpm while not in a storm, and could go faster but it would damage the engine. It will do the same speed at max rpm in a storm. The only thing that could be off a little is the tire height as due to wear of the tire. But that should not make much of a difference. Theoratical you will go a little faster when there is a lot of thread left on the tire.

MiniMoi

[Guess-Works.com]

I've been having a play, and for those using IE, the ratios are now also displayed on a graph, sorry ain't got it working for Mozilla...

The graph looks like this and moves as you alter the parameters...

If you float your mouse over the lines, it also gives you the MPH / RPM for the point.

 Graph_pic.JPG   34.04K   83 downloads

New link.... ( I've changed the one at the top too )

Clicky

[Guess-Works.com]

Ok... I've now built in a 'save for reference' button onto the graph, this saves the current graph and changing the selection now shows both the new selection and the saved one ( in green ) for reference... If you're actually thinking about changing ratios and/or final drives it's quite an eye opener.

The below comparison is between a std A+ helical gearbox, and ONLY replacing the gears with a SCCR set, you can see how 1st gear has moved nearer to the original 2nd gear speed, obviously you only see one line for 4th as both ratio's are the same 1:1. Green = A+ Helical, White = SCCR

 Graph_pic.JPG   39.03K   67 downloads

[Chewy]

Hey
Guessworks

My mini has a 1275 mg engine with standard diff and i am running on 10inch minlites and when i am doin 50 the engine is at about 4000 rpm

So what diff is in it many thanks


Chewy

[Guess-Works.com]

are you sure you're doing 50, and you're in 4th ??

cause if you are it's not a std diff, as it would need to be 4.3 or above...