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Old 07-08-2002, 05:53 AM   #1
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? on overdriving front wheels on a 4WD

I am reasonably new to this sport and I have noticed some of the faster drivers set their cars up as to over drive the front wheels and then run smaller diameter wheels to stop the drive train from binding up (also running a one-way fron diff). I am just wondering what the performance advantage is of this sort of setup.
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Old 07-08-2002, 07:20 AM   #2
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the overdrive is used to compensate for the faster wear of the rear tires during a main.. you want them equal or similar for the majority of the race..... usually a overdrive ratio is done in 1/8 or 235 were front and rear tires differ in sizze, but on 200mm cars the tires can differ in size at the end of a main, usually the rear wear faster than the front, so the more even the car is the more balanced it stays..........

a car witha front end pullin, ie overdriven will be easyier to drive but the fastest car will be the one with the front and rear pulling equally......... hope that helped..
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Old 07-08-2002, 03:22 PM   #3
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YUP!

Hey dude that was a pretty cool picture edit you did I like it
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Old 07-10-2002, 06:35 AM   #4
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Quote:
Originally posted by ammdrew
the overdrive is used to compensate for the faster wear of the rear tires during a main.. you want them equal or similar for the majority of the race..... usually a overdrive ratio is done in 1/8 or 235 were front and rear tires differ in sizze, but on 200mm cars the tires can differ in size at the end of a main, usually the rear wear faster than the front, so the more even the car is the more balanced it stays..........

a car witha front end pullin, ie overdriven will be easyier to drive but the fastest car will be the one with the front and rear pulling equally......... hope that helped..
So am I correct in saying that overdriving the front and running small diameter to compensate will give slightly faster wear rate on the front as to balance out the faster wear rate on the rear? ie giving a more neutral handling car throughout the whole main.
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Old 08-03-2002, 06:30 AM   #5
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isnt the main raeson why the rear tyres wear down quicker is because theyr ussually a softer compund to the front, so to not have to have over drive, why not use thesame tyre compound F/R???
i know that still have more weight on the rear will still have it wear diff, and having diff shock setups, and type of corners.
Example, fast in but still tight, or long and sweeping
long and sweeping= a lot of rear drift = more rear tyre wear
fast but tight = front slide/lot of body weight roll up in stead of slide = more front tyre wear

OR

More right hand corners = more wear on the left tyres
and Vica Versa

Just my $0.02
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Old 08-31-2002, 06:07 PM   #6
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Overdrive is used to make the front of the car drive faster than the rear. It has nothing to do with tire wear other than teh diameter of the tires effects the amount of over drive you get.

Overdriving the front end is only neccessary when you are using either a one-way front diff or front solid axle with a rear solid axle.
The reason for this is that the solid axle in the rear makes the rear break loose in the corner because both wheels are turning at the same speed. You therefore overdrive the front end to make it pull the rear around in the straightest possible line.

Note: you must use either the front one-way diff or the front solid axle when using a rear solid axle. You make the fronts smaller because as the rears wear down the overdrive is reduced and can become underdrive (the rear pushing) which is almost impossible to control at high speed. The bigger the diameter difference the more the rears have to wear down to reach this stage.

Also, you would normally run softer tires on the rear to give more grip and harder tires on the front to create a bit of push to allow the rear to grip more. If you run the tires the same shore all round you need to run the suspension really soft in the rear and then the car doesn;t work properly. This is the price you have to apy to run in the fast lane. I know. I have been doing it for 15 yrs.
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Old 08-31-2002, 06:10 PM   #7
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Quote:
a car witha front end pullin, ie overdriven will be easyier to drive but the fastest car will be the one with the front and rear pulling equally
It is actually the other way around. The overdriven car will be faster because the overdrive allows you to apply the power a lot earlier on the exit of a corner. That is the main principle of overdrive.

The overdriven car will want to whip around the corner so less steering is required when leaving the corner making it more difficult to control.
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Old 09-01-2002, 08:27 AM   #8
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the fastest car will be the car that pulls equally from all four tires... if a tire slips, or looses traction, it will be slower .. over drive can be used to make a car easyier to drive, ie the front wheels pull the car out of the corner, but that will only make the car feel easyier to drive... not faster.... on some extremely tight tracks you may benifit on stop and go type of cornering by over driving a end of the car and intentionally sliding the car type of turns.. but the reality is you want all four tires to pull equally for the majority of the race so useing a overdrive would be for compensating for tire wear during a long main......

1/8 and 235 run different diameter front and rear tires so they must run a overdrive on the car and the overdrive is a tunning tool depending upon tire wear during the race...... if you find you need it to make your car more neutral i would do a suspension change, you are faster if you can pull with all four tires..... sometimes the fastest setup is not so easy to drive....

thanks dennis.. i am a commercial photographer so i just took two pics and used a bit of photoshop..
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Old 09-01-2002, 09:57 AM   #9
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Quote:
Originally posted by Motorman
YUP!

Hey dude that was a pretty cool picture edit you did I like it
What picture edit,how come i can't see it???
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Old 09-01-2002, 10:57 AM   #10
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I know the theory of overdrive. I have raced 1:8th on-road for 15 years at International level.

It is faster to use a solid axle in the rear with one-way or solid in the front and overdrive the front end regardless of the track layout.

I take it you have only read a few books explaining the theory of it?
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Old 09-01-2002, 11:57 AM   #11
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Hey, modellor!

Good to see you here too.
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Old 09-01-2002, 12:50 PM   #12
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Always got to keep moving. Find some interesting stuff in different forums and nice ideas for new bodies.
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Old 09-02-2002, 09:32 AM   #13
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you must overdrive the 1/8 scale because your tire sizes are different... i have been doing this competitivly for over 12 years and have a pretty good grasp of overdrive underdrive ..... so take it for what it is worth but i have yet to see a major competitiion winner.. runnig a intentional mismatch on front rear pulling.. as in the tire size difference matches the overdrive ratio to facilitate a car that equally pulls with all four wheels.... for the majority of the race, so not nessicarrly the same at the beggining and end but the majority....

but hey if it works for you use it that way ... because all reall 4 wd cars have a very slight front overdrive to keep the vehicle tracking straight....... but ever so slight.......
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Old 09-02-2002, 12:21 PM   #14
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The truth is, most TC are overdriven slightly anyway as soon as the rear tires wear. Unless you have the car setup to get exactly the same wear front & rear, the car will have overdrive. The trick (for the average racer) is not to let the tire split get too large. Personally, I run my MTX-2 with about a 1mm tire split.

My 1/8 scale car is another story. I recently got into 1/8 and the learning curve for it's overdive/tire split/ rollout has been a little overwhelming (it's a totally different set of numbers & driving characteristics to keep up with), but I'm getting it together.
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Old 09-02-2002, 09:15 PM   #15
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I have my serpent impulse overdriven and after reading this forum i checked out how much my rears had worn down after racing last sunday (i race at Sydney Australia Moorebank track thats where last years 1/8th world titles was held)

After running 3= 5 minute heats and a 30 minute final i had worn just over 2 mm from my rear working foam
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