Rear end ratio not only for race

[Felipe]

Hi

I´m new here, and i hope you can help me in my hayabusa project

My differential ratio now is a 3,9 to 1 it is ok for a hayabusa engine ? with a 1050 pounds car ?

and wich overall diameter of tires are better

Thanks in advance

Felipe

[BusaLoco]

Mine is 3.08.

Hope this helps!

Cheers!

BusaLoco

[Felipe]

Hi Busaloco

I don´t have experience with matching bike transmission ratio gears with

car differential ratio. That means i need more help to run the car with

a correct matching to avoid 60 mph at 10.000 rpm

the above include tire overall diameter

Thanks in advance , and sorry about my poor english

Felipe

[Birkin42]

I think there are 2 ways to approach this.

You could find out the engines primary gear reduction (from the engine to the clutch and transmission) and the ratio in top gear. Knowing this as well as determine what the revolutions per mile that your chosen tire and wheel combo will have, you can determine the preferred gear ratio based on max rpm at max anticipated speed or preferred rpm when traveling at say 60 mph. If all this math is daunting, you can let us know what engine you are using, what tire size you plan to use and what you want to traget for speed vs rpm and I'm sure someone could to the math and get you going in the right direction.

 

Another approach to get you in the ball park, consider that likely your rear tire diameter isn't going to be too far off the bikes tire diameter that the engine came from. Most bikes run 17" wheels and will have a taller profile tire then what you will likely run on your 7. Depending on wheels and tire combo you want to run, you can likely figure out the ratio of diameters but I'd guess that yours will be about 80% the size of the bikes rear tire. You can then look at what final drive ratio the motorcycle used (the chain and sprockets driving the rear wheel). The final variable again is the relationship of rpm vs speed you want compared to the bike. I would guess that you would be looking at about 25% higher engine speed for a given road speed. Conveniently, the 80% and 25% cancel each other out and you end up needing a final drive ratio similar to what the bikes final drive was. Most bikes run close to 3:1 reduction so like BusaLoco commented, 3.08 is likely very close to what you want. I know this is what Deman Motorsport put in their BEC cars.

 

If you are running an engine smaller then the typical litre class + sport bike engines, you may want more reduction like your 3.9:1 to get good performance. The other combination where your 3.9:1 ratio might be OK is if you are planning to run larger then normal tires for a 7. This would be an awfully big wheel and tire package though. Something you might see at SEMA but not typical for a performance car.

 

Do you have the engine as well as the tires and wheels picked?

[BusaLoco]

What He Said!

[Felipe]

I think there are 2 ways to approach this.

You could find out the engines primary gear reduction (from the engine to the clutch and transmission) and the ratio in top gear. Knowing this as well as determine what the revolutions per mile that your chosen tire and wheel combo will have, you can determine the preferred gear ratio based on max rpm at max anticipated speed or preferred rpm when traveling at say 60 mph. If all this math is daunting, you can let us know what engine you are using, what tire size you plan to use and what you want to traget for speed vs rpm and I'm sure someone could to the math and get you going in the right direction.

 

Another approach to get you in the ball park, consider that likely your rear tire diameter isn't going to be too far off the bikes tire diameter that the engine came from. Most bikes run 17" wheels and will have a taller profile tire then what you will likely run on your 7. Depending on wheels and tire combo you want to run, you can likely figure out the ratio of diameters but I'd guess that yours will be about 80% the size of the bikes rear tire. You can then look at what final drive ratio the motorcycle used (the chain and sprockets driving the rear wheel). The final variable again is the relationship of rpm vs speed you want compared to the bike. I would guess that you would be looking at about 25% higher engine speed for a given road speed. Conveniently, the 80% and 25% cancel each other out and you end up needing a final drive ratio similar to what the bikes final drive was. Most bikes run close to 3:1 reduction so like BusaLoco commented, 3.08 is likely very close to what you want. I know this is what Deman Motorsport put in their BEC cars.

 

If you are running an engine smaller then the typical litre class + sport bike engines, you may want more reduction like your 3.9:1 to get good performance. The other combination where your 3.9:1 ratio might be OK is if you are planning to run larger then normal tires for a 7. This would be an awfully big wheel and tire package though. Something you might see at SEMA but not typical for a performance car.

 

Do you have the engine as well as the tires and wheels picked?

[Felipe]

Thanks Birkin 42

With that cain of info now i can start

thanks a lot

Felipe

[Felipe]

Who knows where can i get a 3.08 ratio and a Lsd for a Toyota gts differential

Felipe

[Felipe]

I think there are 2 ways to approach this.

You could find out the engines primary gear reduction (from the engine to the clutch and transmission) and the ratio in top gear. Knowing this as well as determine what the revolutions per mile that your chosen tire and wheel combo will have, you can determine the preferred gear ratio based on max rpm at max anticipated speed or preferred rpm when traveling at say 60 mph. If all this math is daunting, you can let us know what engine you are using, what tire size you plan to use and what you want to traget for speed vs rpm and I'm sure someone could to the math and get you going in the right direction.

 

Another approach to get you in the ball park, consider that likely your rear tire diameter isn't going to be too far off the bikes tire diameter that the engine came from. Most bikes run 17" wheels and will have a taller profile tire then what you will likely run on your 7. Depending on wheels and tire combo you want to run, you can likely figure out the ratio of diameters but I'd guess that yours will be about 80% the size of the bikes rear tire. You can then look at what final drive ratio the motorcycle used (the chain and sprockets driving the rear wheel). The final variable again is the relationship of rpm vs speed you want compared to the bike. I would guess that you would be looking at about 25% higher engine speed for a given road speed. Conveniently, the 80% and 25% cancel each other out and you end up needing a final drive ratio similar to what the bikes final drive was. Most bikes run close to 3:1 reduction so like BusaLoco commented, 3.08 is likely very close to what you want. I know this is what Deman Motorsport put in their BEC cars.

 

If you are running an engine smaller then the typical litre class + sport bike engines, you may want more reduction like your 3.9:1 to get good performance. The other combination where your 3.9:1 ratio might be OK is if you are planning to run larger then normal tires for a 7. This would be an awfully big wheel and tire package though. Something you might see at SEMA but not typical for a performance car.

 

Do you have the engine as well as the tires and wheels picked?

I need a complete hayausa with wires loom, ecu etc to be intalled in a Suzuki Forza (Geo Mtro) witn a quaife chain driven differential

[ottocycle]

Hello all,

I will be dealing with this issue too, I want to run 13" rims on my car and would like to know what live rear axle has a 3.08 diff or taller. At the moment I have a 3.54 and 14" rims and I need taller gears.

I had a conversation with Jeff a few months ago on the Toyota V's Mazda rear end options , and I think the Toyota came out on top but I cannot remember which model had what. It is hard to find tall gears for a lightweight rear end.

To you mathematecians, what rear ratios would I need to hit 140 mph at 11,000 rpm using a Hayabusa engine with 22" dia. tires. I do not know what the primary reduction and final drive gears are in a stock Suzuki? Any takers?

Thanks,

 

Dermot.

[BusaLoco]

Don't really know if this helps but here are the Specs for the Caterham Busa Diff

[Birkin42]

Sorry for the slow reply Dermot.

 

In searching the web I found the primary reduction for a Hayabusa is 83/52 and 6th gear is 24/23. I found this for both 1999 and 2008 so it looks likely that they never juggled the ratios.

For reference, the bikes final drive ratio was 40/17 in 1999 and is now 43/18. All the model years seemed to have used a 190/50-17 rear tire. Top speed at red line in 1999 was 199 mph.

 

Based on this and your requested 140 mph at 11000 rpm with 22" OD tires, the required diff ratio would be 3.087:1, not taking into account tire slip. Funny how that worked out perfect with the 3.08 ratio that is typically run, though I believe Demon's typically run tires that are a bit larger then 22" I believe.

 

Hope this helps.

[ottocycle]

Birkin 42,

Thanks for the advice, it is good food for thought. I do not know if I will have the power to move the car that fast, but the ratio could be achieved with a Toyota rear and an after market ring and pinion. It could also make the ratios feel a little wider than they do right now. Bike transmissions are very closely spaced and I am finding I am climbing through the box quite quickly. If I could accelerate as fast as I am right now and take a little longer to wind out each gear it would be a good thing. It could also help with the power oversteer I am experiencing.

Food for thought.

Thanks again,

 

Dermot.

 

PS. Instead of changing rear ratios or axles has anyone ever come accross a "gear increaser" box (the opposite of a gear reduction box) that will handle 150+ HP?

[Birkin42]

Bike transmission, particularly for litre class and larger have very close ratio gearboxes with a very tall first gear. My last street bike, a Honda RC30, had an 81 mph first gear. Bikes with a high CoG and a high power to weight ratio really can't use a low or normal first gear so the ratio make sense for bikes but are not really suited to BEC's. I doubt anyone makes different ratio's, and if they did, I don't know if the trany could take the extra torque that it would general. Would be nice though.

 

I'm surprised that you can get a 3.08 gearset for Toyota rear end. I figured they be higher ratios based on a small high reving engine and a relatively low top speed.

 

I've heard of overdrive gearboxes that can be added on to domestic rwd cars. They speed up the output for more relaxed cruising. Don't know what ratios are available and I don't know how big and heavy they are. You could do a chain or belt drive which might be lighter, more compact and could be placed in the offset from the engine output to the car centerline and then straighten out the drive shaft. The company out in BC Canada that puts Hayabusa's in Caterhams uses a chain drive in this manner. http://www.super7cars.com/Gallery/?album=Our_unique_drive_system_and_reverse

 

Jack

[ottocycle]

Jack,

I agree with you. I think the tallest Toyota rear is about 3.30. The Toyota rear axle is used in the Legend and Dwarf race cars (also bike powered). I think the ring and pinion that give the taller rear is made by an after market company. I have seen 2.5's advertised!

I am looking into adapting an overdrive from an old Jaguar Moss box. I do not know if it will work but before I commit to fabricating my own overdrive or changing to a completely different rear I would like to see if there is an easier path. I have no interest in reinventing the wheel.

Thanks,

 

Dermot.