Drag Radial and Rims?!?!?

[budoboy]

Cause you don't want to be shifting into 4th a hundred feet short of the line?

In my experience the gains from the gearing advantage of small diameter rims/tires outweighs the losses from an early shift (big time).

I've run taller tires and have run much slower in the 1/4 mile even though the 3-4 shift happens after the 1320 mark.

 

[Quick]

There should be some "inflection" point. Smaller tires/gearing will give you better acceleration.

If we assume shifts take zero time with zero torque management then optimum acceleration would be crossing the line just before the engine red lines in your top gear (5th in our case).

Now lets assume shifts take some fixed amount of time and involve some fixed amount of torque management. Think of it as WOT-lift-shift-WOT. During the lift you're losing some amount of ET.

We're talking street cars so they need to be driveable off the track and on the freeway, etc so things kind of work out to where we're talking about crossing the line before the 3-4 shift or after the 3-4 shift.

The extra shift costs you some amount of ET.
The smaller tires give you faster acceleration and gain you some amount of ET.

The gain from the smaller tires is pretty much spread through the whole run(except during the shifts where there is essentially zero gain/loss due to tire size).

The question is how much ET is gained for each unit of drive ratio and how much ET is lost to the extra shift.

The edge case would be where you are currently initiating the 3-4 shift a couple of feet AFTER the line. Then you decrease your tire height/gear ratio a tiny bit and you end up initiating the 3-4 shift BEFORE the line and complete it at or just after the line. I suspect this would cost you ET since I believe the cost of a shift is not insignificant.

Surely youwould probably gain ET if you currently have plenty of room left in 3rd (3-4 shift happens a good ways after the line) and you make a significant reduction in tire size and move the shift to just before the line. The amount gained from the gearing would be more than the cost of the shift.

So if you're moving your shift across the line (from after the line to before the line) you have to move it far enough (total feet) to make up for the cost of the shift.

somebody should be able to calculate that pretty easily...

 

[StevoSRT]

so your saying it has to be close enough to the line to not matter....or far enough in front of the line for you to make up for it....

 

[Quick]

so your saying it has to be close enough to the line to not matter....or far enough in front of the line for you to make up for it....

No (but almost).

*IF* it moves in front of the line, then it has to move far enough from where it was before (not the line).

It doesn't matter if it ends up just in front of the line or not. If you're adding a shift before the line then you have to decrease your tire size enough to make up more than the cost of the shift.

If you don't add a shift in front of the line then any tire size decrease will gain you ET.

For example, lets say that you decrease tire size just a little bit and your shift happens 100' sooner.

If your shift was happening 200' past the line and now it's happening 100' past the line you WILL better your ET.
If you shift was happening 50' past the line and now it's happening 50' before the line ... you might lose ET.

IF you decrease tire size enough and let's say your shift happens 300' sooner you WILL better your ET and it doesn't matter where the shift happens -- before or after the line (better if it happens past the line but you still improve no matter what)>

 

[StevoSRT]

No (but almost).

*IF* it moves in front of the line, then it has to move far enough from where it was before.

It doesn't matter if it ends up just in front of the line or not. If you're adding a shift before the line then you have to decrease your tire size enough to make up more than the cost of the shift.

If you don't add a shift in front of the line then any tire size decrease will gain you ET.

For example, lets say that you decrease tire size just a little bit and your shift happens 100' sooner.

If your shift was happening 200' past the line and now it's happening 100' past the line you WILL better your ET.
If you shift was happening 50' past the line and now it's happening 50' before the line ... you might lose ET.

IF you decrease tire size enough and let's say your shift happens 300' sooner you WILL better your ET and it doesn't matter where the shift happens -- before or after the line (better if it happens past the line but you still improve no matter what)>

:hmm: interesting

 

[Quick]

:hmm: interesting

Executive summary:
If you move your shift from past the line to in front of the line the smaller tire size has to at least make up the cost of the shift.

All you have to do is put some numbers to that :grin:

 

[Inferal]

I have had pretty good luck with the MT 295 at 27.2 in high

 

[Quick]

:hmm: interesting

Hahaha, ...but there's more!

Thats just the overall tire height/gearing part. Like Erik and those guys were saying, you want the optimum sidewall height for the best traction for the particular width and make of DR's you choose.

(I think I would have spent the money on the Harley)

 

[StevoSRT]

I have had pretty good luck with the MT 295 at 27.2 in high

id say so buddy! lol

Hahaha, ...but there's more!

Thats just the overall tire height/gearing part. Like Erik and those guys were saying, you want the optimum sidewall height for the best traction for the particular width and make of DR's you choose.

(I think I would have spent the money on the Harley)

yeah i am gonna say i could use all the help i can get in the 60' department LOL

 

[NYCSRTATE]

So all I gotta do, is get this wheel??
http://www.wheelhq.com/17x105-mustang-1995-cobrar-black.html

And that 325/45/17 M&H Drag Radial??? And call it done??

Can ANYONE confirm that this rim will fit and clear our rear Brembos? Because thats the rim I want powercoated black and all to match the rest of my car

Go 17" rim....the more sidewall the better you will hook......SteveO with the Poweradder you want a 28" tall tire.
Tony for your car I would go with the 26" tall tire and use the extra gearing you will effectively get.You will still cross the traps in third.

Great stuff Erik, Thanks!!

 

[StevoSRT]

Can ANYONE confirm that this rim will fit and clear our rear Brembos? Because thats the rim I want powercoated black and all to match the rest of my car



Great stuff Erik, Thanks!!

If anyone needs more info on the wheels that Tony is talking about....here it is...

Wheel Style: 1995 Cobra-R Wheel Size: 17x10.5" Wheel Backspacing: 6.85" (174mm) Wheel Offset: +28mm (1.10") Tire Size: 315/35-17 Bolt Pattern: 5 x 4.5 inch (5x114.3mm)

 

[Hemi31]

Tony look at the wheel in my sig.......the thing is mine is a 17x9.5......I don't think that 10.5 will fit.

 

[NYCSRTATE]

Tony look at the wheel in my sig.......the thing is mine is a 17x9.5......I don't think that 10.5 will fit.

Oh damn I missed that it is a 10.5 hells no I dont want that.

NEXT, thanks Erik.

 

[Hemi31]

Tony Factory Reproductions(same place I got the Challenger Wheels) is where my Cobra R's came from.......I think they were less than $100 each.

 

[NYCSRTATE]

Tony Factory Reproductions(same place I got the Challenger Wheels) is where my Cobra R's came from.......I think they were less than $100 each.

Erik do you have a link to them?

I might as well get them and just powdercoat them.

Erik is it these guys? I think im narrowing down pattern 5 x 4.25 or 5 x 4.5? The offset is +15mm on the 17 x 9's

http://www.factoryreproductions.com/index.html

 

[Hemi31]

thats them....1999 Cobra R....5x4.5........ask them about hubcentric rings to help center the wheel.

 

[NYCSRTATE]

thats them....1999 Cobra R....5x4.5........ask them about hubcentric rings to help center the wheel.

Awesome thanks Erik!!

See if I can get these before next week.

 

[StevoSRT]

Tony Factory Reproductions(same place I got the Challenger Wheels) is where my Cobra R's came from.......I think they were less than $100 each.

damn thats a good price!!!

thats them....1999 Cobra R....5x4.5........ask them about hubcentric rings to help center the wheel.

Awesome thanks Erik!!

See if I can get these before next week.

when you get the info...let me know dood

 

[NYCSRTATE]

damn thats a good price!!!

when you get the info...let me know dood

Ok here is the update Factory Reproductions does not sell that Cobra-R rim anymore so were screwed there.

Anyone else have any suggestions, I know Jeff (Budoboy) has 5Zigen that I liked but cant seem to find the exact ones on there website, hopefully i can get Jeff to chime in here also.

 

[StevoSRT]

Tony look at the wheel in my sig.......the thing is mine is a 17x9.5......I don't think that 10.5 will fit.

What about these tony?

if your only running 275's....

http://www.wheelhq.com/17x9-mustang-1995-cobrar-black.html


Wheel Style: Ford Mustang Cobra R, 1995 style Wheel Size: 17x9" Wheel Backspacing: 5.95" Wheel Offset: +24mm
(Fits Best 94-04 all) Wheel Weight: N/A lbs. Bolt Pattern: 5 x 4.5 inch

These are like $139 i think tony with free shipping...

which really isnt that bad